U.S. patent application number 14/882937 was filed with the patent office on 2016-03-10 for signal distribution system cascadable agc device and method.
The applicant listed for this patent is Entropic Communications, LLC. Invention is credited to Keith BARGROFF, Dale HANCOCK.
Application Number | 20160072534 14/882937 |
Document ID | / |
Family ID | 32512584 |
Filed Date | 2016-03-10 |
United States Patent
Application |
20160072534 |
Kind Code |
A1 |
BARGROFF; Keith ; et
al. |
March 10, 2016 |
Signal Distribution System Cascadable AGC Device and Method
Abstract
A cascadable AGC amplifier in a signal distribution system
includes a low noise cascadable amplifier having a through path and
a cascadable output. The cascadable amplifier is also configured to
provide AGC over a predetermined input power range. The cascadable
AGC amplifier can be configured to provide gain or attenuation.
When the cascadable AGC amplifier is implemented in a signal
distribution system, typically as part of a signal distribution
device, an input signal can be gain controlled and supplied to
multiple signal paths without distortion due to degradation of
signal to noise ratio or distortion due to higher order amplifier
products. The distributed signal is not significantly degraded by
distortion regardless of the number of cascadable AGC amplifiers
connected in series or the position of the cascadable AGC amplifier
in the signal distribution system.
Inventors: |
BARGROFF; Keith; (San Diego,
CA) ; HANCOCK; Dale; (San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Entropic Communications, LLC |
Carlsbad |
CA |
US |
|
|
Family ID: |
32512584 |
Appl. No.: |
14/882937 |
Filed: |
October 14, 2015 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12477399 |
Jun 3, 2009 |
7804409 |
|
|
14882937 |
|
|
|
|
11538627 |
Oct 4, 2006 |
7558551 |
|
|
12477399 |
|
|
|
|
10734603 |
Dec 11, 2003 |
|
|
|
11538627 |
|
|
|
|
60433067 |
Dec 11, 2002 |
|
|
|
60433063 |
Dec 11, 2002 |
|
|
|
60433061 |
Dec 11, 2002 |
|
|
|
60433066 |
Dec 11, 2002 |
|
|
|
Current U.S.
Class: |
455/266 ;
330/295 |
Current CPC
Class: |
H03D 7/1458 20130101;
H03F 2200/171 20130101; H03D 7/1425 20130101; H03D 7/1433 20130101;
H03G 3/3036 20130101; H03F 2200/451 20130101; H04Q 2213/13322
20130101; H03D 7/00 20130101; H04Q 2213/1304 20130101; H04H 40/90
20130101; H04B 1/126 20130101; H03F 3/19 20130101; H04Q 2213/1319
20130101; H04Q 3/521 20130101; H04Q 2213/13034 20130101; H04Q
2213/1302 20130101; H03D 2200/0043 20130101; H04N 7/102 20130101;
H03D 2200/0025 20130101; H04N 7/20 20130101; H03F 2200/294
20130101 |
International
Class: |
H04B 1/12 20060101
H04B001/12; H03F 3/19 20060101 H03F003/19 |
Claims
1. An apparatus comprising: switch having a plurality of switch
inputs and a plurality of switch outputs, switch being operable to
switchably couple any of the plurality of switch inputs to any one
or more of the plurality of switch outputs; a plurality of
frequency translation devices, two or more frequency translation
devices of the plurality of frequency translation devices being
operably coupled to a respective switch output, the two or more
frequency translation devices being operable to output two or more
frequency translated switch outputs; and a signal combiner operably
coupled to the plurality of frequency translation devices, the
signal combiner being operable to stack the two or more frequency
translated switch outputs.
2-10. (canceled)
11. The apparatus of claim 1, the apparatus comprising a plurality
of amplifiers, each amplifier having an amplifier input and an
amplifier output, the amplifier output of each amplifier of the
plurality of amplifiers being operably coupled to a respective
switch input.
12. The apparatus of claim 11, wherein the amplifier input of each
amplifier of the plurality of amplifiers is operably coupled to a
low noise block converter.
13. The apparatus of claim 11, wherein each amplifier of the
plurality of amplifiers is a low noise amplifier.
14. The apparatus of claim 11, wherein each of the two or more
frequency translation devices comprises an amplifier and a
mixer.
15. The apparatus of claim 14, wherein an input of the amplifier in
each of the two or more frequency translation devices is coupled to
a respective switch output.
16. The apparatus of claim 14, wherein an input of the amplifier in
each of the two or more frequency translation devices is coupled to
an output of the respective mixer in each of the two or more
frequency translation.
17. The apparatus of claim 14, wherein the mixer in each of the two
or more frequency translation devices is a downconverter.
18. The apparatus of claim 1, wherein each of the two or more
frequency translation devices comprises a filter device.
19. The apparatus of claim 18, wherein the filter device comprises
a bandpass filter.
20. The apparatus of claim 1, wherein the plurality of frequency
translation devices comprises two or more additional frequency
translation devices, each of the two or more frequency translation
devices being connected to another frequency translation device of
the two or more additional frequency translation devices, the two
or more additional frequency translation devices being operable to
further process the two or more frequency translated switch
outputs.
21. The apparatus of claim 1, wherein the apparatus comprises a
digital signal processor (DSP), the DSP comprising the switch, the
plurality of frequency translation devices and the signal
combiner.
22. An apparatus comprising: a multiple-input/multiple-output
switch coupled to receive and switch at least one satellite
intermediate frequency (IF) signal of a plurality of satellite IF
signals, wherein the plurality of satellite IF signals are received
from a satellite front end device comprising a low noise block
downconverter (LNB); a plurality of channelizer devices coupled to
the multiple-input/multiple-output switch and operable to
channelize the at least one satellite IF signal to produce a
plurality of channelized signals; and a channel stacker coupled to
the plurality of channelizer devices and operable to stack the
plurality of channelized signals to produce a stacked channel
signal.
23. The apparatus of claim 22, the apparatus comprising a plurality
of amplifiers, each amplifier having an amplifier input and an
amplifier output, the amplifier output of each amplifier of the
plurality of amplifiers being operably coupled to an input of the
multiple-input/multiple-output switch.
24. The apparatus of claim 23, wherein the amplifier input of each
amplifier of the plurality of amplifiers is operably coupled to a
low noise block converter.
25. The apparatus of claim 23, wherein each amplifier of the
plurality of amplifiers is a low noise amplifier.
26. The apparatus of claim 23, wherein each channelizer device of
the plurality of channelizer devices comprises an amplifier and a
mixer.
27. The apparatus of claim 26, wherein an input of the amplifier in
each channelizer device is coupled to a respective output of the
multiple-input/multiple-output switch.
28. The apparatus of claim 26, wherein an input of the amplifier in
each channelizer device is coupled to an output of the respective
mixer in each channelizer device.
29. The apparatus of claim 26, wherein the mixer in each
channelizer device is a downconverter.
30. The apparatus of claim 22, wherein each channelizer device
comprises a filter device.
31. The apparatus of claim 30, wherein the filter device comprises
a bandpass filter.
32. The apparatus of claim 22, wherein each channelizer device
comprises two or more frequency translation devices.
33. The apparatus of claim 22, wherein the apparatus comprises a
digital signal processor (DSP), the DSP comprising the
multiple-input/multiple-output switch, the plurality of channelizer
devices, and the channel stacker.
34. A method comprising: switching at least one satellite
intermediate frequency (IF) signal of a plurality of satellite IF
signals, wherein the plurality of satellite IF signals are received
from a satellite front end device comprising a low noise block
downconverter (LNB); channelizing the at least one satellite IF
signal to produce a plurality of channelized signals; and stacking
the plurality of channelized signals to produce a stacked channel
signal.
35. The method of claim 34, the method comprising amplifying an
input of the multiple-input/multiple-output switch.
36. The method of claim 34, the method comprising amplifying an
output of the multiple-input/multiple-output switch.
37. The method of claim 34, wherein channelizing comprises
downconverting a band of frequencies.
38. The method of claim 34, wherein channelizing comprises
filtering a band of frequencies.
39. The method of claim 34, wherein the method comprises digital
signal processing, the digital signal processing comprising the
switching, the channelizing, and the stacking.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/538,627, filed Oct. 4, 2006, which, in
turn, is a continuation of Ser. No. 10/734,603, filed Dec. 11,
2003, herein incorporated by reference in their entirety, the
following patent applications:
[0002] U.S. Provisional Patent Application No. 60/433,066, filed on
Dec. 11, 2002, entitled INTEGRATED CROSSPOINT SWITCH WITH BAND
TRANSLATION;
[0003] U.S. Provisional Patent Application No. 60/433,061, filed on
Dec. 11, 2002, entitled IN-LINE CASCADABLE DEVICE IN SIGNAL
DISTRIBUTION SYSTEM WITH AGC FUNCTION;
[0004] U.S. Provisional Patent Application No. 60/433,067, filed on
Dec. 11, 2002, entitled N.times.M CROSSPOINT SWITCH WITH BAND
TRANSLATION;
[0005] U.S. Provisional Patent Application No. 60/433,063, filed on
Dec. 11, 2002, entitled MIXER WITH PASS-THROUGH MODE WITH CONSTANT
EVEN ORDER GENERATION.
BACKGROUND OF THE INVENTION
[0006] 1. Field of the Invention
[0007] The invention relates to the field of electronic
communications. More particularly, the invention related to the
field of Radio Frequency (RF) signal distribution.
[0008] 2. Description of the Related Art
[0009] Signal distribution systems, such as RF signal distribution
systems, typically are arranged in branched configurations. In a
branched configuration, the signal typically originates at the
center, or trunk, and the signal is distributed from the point of
origin to the multiple end points of the branches. Each
distribution branch from the trunk can be split into one or more
smaller branches. Additionally, the smaller branches themselves may
divide into even smaller branches one or more times prior to
reaching a destination.
[0010] An RF communications signal distributed along a system is
typically amplified several times along the various signal
distribution paths prior to reaching a device at a destination.
However, various factors operate to degrade the quality of the
original signal prior to its reaching a device at a
destination.
[0011] The quality of a signal is often measured as a ratio of the
signal power to the noise power, referred to as signal-to-noise
ratio (SNR). The signal power can be defined as the power of the
portion of the signal that contains the desired information. The
noise power can be defined as the combination of the random
fluctuations that are uncorrelated to the information power and the
undesired distortion products. The undesired distortion products
can be defined to be those signal components that do not replicate
the original information. Although the noise power is here used to
mean the combination of the uncorrelated signals with the
distortion products, other noise definitions can be used to gauge
the signal quality. For example, the noise power can be represented
by only the uncorrelated signals, or the noise can be represented
by the uncorrelated signals and some of the distortion
products.
[0012] The signal to noise ratio (SNR) typically measures the ratio
of the signal to the noise and distortion experienced by the
signal. Thermal noise is often a large contributor to the noise
power in systems that use received radio waves as the signal
source. The thermal noise level often represents the noise floor
that cannot be further reduced through the use of active or passive
devices. Passive losses, through passive signal division or
attenuation, reduce the signal power but typically do not reduce
the level of thermal noise. As such, signal attenuation can result
in degradation of SNR.
[0013] Signal amplification can be used to offset some of the
effects of attenuation in a signal distribution system. However,
active devices, such as amplifiers, do not provide signal gain
without affecting the noise and distortion that degrade the signal
quality. For example, amplifiers typically introduce uncorrelated
noise into the signal that further degrades the SNR. Some of the
amplifier noise contribution is quantified as an amplifier noise
figure, which may also be expressed as a noise factor. An
amplifier's noise figure may directly contribute to signal
degradation and degradation of SNR when the system operates in low
power conditions close to the noise floor as is typical in a system
using received RF signals.
[0014] Additionally, an amplifier may contribute distortion
products that degrade the SNR. One prevalent amplifier distortion
product that often contributes to in-band noise in wideband or
multi-channel distribution systems is a third order intermodulation
distortion product. The level of third order intermodulation
distortion contributed by a particular amplifier is typically
predicted based on an amplifier characteristic known as the third
order intercept (IP3). The third order intercept represents a
fictional operating point at which the amplifier third order
distortion products would be equal in amplitude to the desired
signal component. A higher amplifier IP3 is desirable. However,
amplifier IP3 often correlates with amplifier power consumption.
Thus, an amplifier with a high IP3 typically consumes more power
than an amplifier having a lower IP3. Amplifier power consumption
is of great concern because of constraints on power dissipation as
well as constraints on the ability to dissipate the heat that is
associated with higher power devices. Additionally, amplifiers that
have low noise figures often have correspondingly low IP3.
[0015] A device, whether passive or active, can typically be
designated to operate within one particular set of signal
parameters at a particular location within a signal distribution
system. However, signal parameters within particular location in a
signal distribution system often change radically based on the
number of branches before or after the device and the number of
passive and active devices placed before or after a device. Thus, a
device that is optimized for one set of operating parameters may be
a dominant noise source in another set of signal parameters.
[0016] What is desirable is a device and method of signal
distribution that is invariant to changes in signal powers and
distribution system configurations. Additionally, it is typically
desirable for the device to minimize its degradation of SNR under
many operating conditions. The device should also allow for the
creation of numerous branches in the signal distribution path, with
the inclusion or deletion of signal branches having minimal affect
on other branches of the signal distribution system.
SUMMARY OF THE INVENTION
[0017] An AGC amplifier and a method of distributing signals in a
signal distribution system are disclosed. The AGC amplifier uses a
power detector and feedback to a control input of a variable gain
amplifier to maintain the output power of the variable gain
amplifier at a predetermined AGC setpoint. The detector can be
connected to the output of the variable gain amplifier to provide
an output referred AGC function. The AGC setpoint can be chosen to
be a signal power within an optimal operation range of the signal
distribution system.
[0018] The output of the AGC amplifier can be connected to an
in-line signal path and can also be connected to a cascade output.
The cascade output allows a single AGC amplifier to provide the AGC
function for two signal paths. The noise contribution is minimized
for devices connected in cascade with the AGC amplifier. Another
AGC amplifier having an in-line path and a cascade output can be
connected in series with the cascade output of a first AGC
amplifier to generate additional signal paths.
[0019] The AGC amplifier can be implemented within an integrated
circuit, which may include additional elements. The integrated
circuit can include a crosspoint switch in series with the in-line
signal path output of the AGC amplifier. The integrated circuit can
also include a band translation device in series with the in-line
signal path output of the AGC amplifier.
[0020] The AGC amplifier and signal distribution method can be
implemented in a satellite television distribution system where the
signals are received as satellite downlink signals and are
distributed to multiple locations within a building, such as a
residence. Alternatively, the AGC amplifier and signal distribution
method can be implemented in a cable television, cable radio,
terrestrial television, terrestrial radio, telephone, or data
distribution system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The features, objects, and advantages of the invention will
become more apparent from the detailed description set forth below
when taken in conjunction with the drawings in which like reference
characters identify correspondingly throughout and wherein:
[0022] FIG. 1 is a functional block diagram of a signal
distribution system configured to receive signals from satellites
and distribute them to multiple user devices.
[0023] FIGS. 2A to 2D are functional block diagrams of AGC
amplifiers.
[0024] FIGS. 3A-3B are functional block diagrams of cascaded
amplifier configurations.
[0025] FIG. 4 is a functional block diagram of an integrated band
translation switch interfacing with additional components to
provide two signal outputs.
[0026] FIG. 5 is a functional block diagram of cascaded integrated
band translation switches.
[0027] FIG. 6 is a flowchart of a method of distributing signals
using cascadable AGC amplifiers.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0028] Signal distribution systems are typically used to link
together geographically remote parts of a communication system.
Often, a centralized point exists from which the signals originate,
or branch. The signal distribution system can be used to provide a
signal of interest to one or more devices at one or more geographic
locations.
[0029] FIG. 1 is a functional block diagram of a signal
distribution system 100 that is typical of a satellite television
system that can be implemented at a residence or other building.
The signal distribution system 100 includes an antenna 120 having
antenna feeds 122, 124 coupled to two inputs of a low noise block
126. The outputs of the low noise block 126 are coupled to two
inputs of a distribution switch 130. The distribution switch
outputs are connected to first, second, and third set top boxes
152, 154, 156, using first and second transmission lines 142, 144.
The output of the first set top box 152 is connected to a first
output device 162. A signal splitter 170 splits into two signals
the signal coupled from the distribution switch 130 by the second
transmission line 144. A first signal splitter 170 output is
coupled to the second set top box 154 and the second signal
splitter 170 output is coupled to the third set top box 156. The
output of the second set top box 154 is connected to a second
output device 164 and the output of the third set top box 156 is
connected to a third output device 166.
[0030] The antenna 120 includes two antenna feeds 122, 124.
However, multiple antennae can be used. Additionally, each antenna
120 can have one or more antenna feeds 122, 124, and each antenna
120 is not limited to having only two feeds 122, 124.
Alternatively, the antenna 120 can be a configuration that does not
utilize an antenna feed, such as a whip or horn.
[0031] The antenna 120 receives one or more signals from a
satellite 110. Additionally, the satellite 110 can provide a signal
of a particular polarization and modulation type. Again, there may
be more than one satellite 110 providing signals to the antenna
120. The signals from a particular satellite 110 can be in the same
frequency band as signals from another satellite (not shown) or can
be in distinct frequency bands. The signals from multiple
satellites can each have the same polarity and modulation type or
can be different from each other.
[0032] In the signal distribution system 100 of FIG. 1, each of the
antenna feeds 122, 124 is connected to an independent input of a
low noise block 126 that outputs signals to the distribution switch
130. Of course, the distribution switch 130 is not limited to a
2.times.2 switch but can have any number of input ports and output
ports, for example, the distribution switch 130 can be, for
example, a 2.times.4 switch, a 4.times.4 switch, or some other
switch arrangement.
[0033] The distribution switch 130 is configured to process the
received satellite signals. The distribution switch 130 can, for
example, amplify, filter, and frequency downconvert the received
satellite signals. The distribution switch 130 can be configured as
a pair of low noise block converters (LNB's) that each block
convert the signals from one of the distribution switch 130 inputs
to an intermediate frequency. The distribution switch 130 can also
be configured to allow each of the input signals provided from the
first antenna feed 122 can be block converted in the distribution
switch 130 and routed to any of the switch outputs. Similarly, the
signal provided from the second antenna feed 124 can be block
converted in the distribution switch 130 and routed to any of the
switch outputs. Typically, the distribution switch 130 is
configured such that the signals from only one signal source are
routed to a particular switch output. Alternatively, one or more of
the block converted signals can be routed to the same distribution
switch 130 output.
[0034] The outputs of the distribution switch 130 can be connected
to remote locations using cabling when the antenna 120 and
distribution switch 130 are installed in a geographically remote
location from the desired signal destinations. The outputs of the
distribution switch 130 are typically routed to remote destinations
with transmission lines, which can be coaxial cables. The
distribution switch 130 can be positioned local to the low noise
block 126 and antenna feeds 122 and 124, or may be positioned
remote from the low noise block 126 and antenna feeds 122 and
124.
[0035] In one embodiment, the distribution switch 130 is co-located
with the antenna 120, low noise block 126, and antenna feeds 122
and 124. In another embodiment, the distribution switch 130 can be
located remote from the antenna 120. For example, cables or
transmission lines can couple the signals from the low noise block
126 to a distribution switch 130 positioned inside a structure near
one or more set top boxes 152 and 154. Similarly, in other
embodiments, the distribution switch 130 can be positioned in an
intermediate location between the antenna 120 and the set top boxes
152 and 154. In some embodiments, the low noise block 126 is
omitted and signals from the antenna feeds 122 and 124 can be
coupled to the distribution switch 130 using cables. Similarly,
output signals from the distribution switch 130 can be coupled to
set top boxes or other destination devices using cables or some
other distribution system.
[0036] In a first embodiment, the distribution switch is positioned
local to the low noise block 126 and antenna 120. A first
transmission line 142 distributes the signal from the first output
port of the distribution switch 130 to a remote location within the
signal distribution system 100. The end of the first transmission
line 142 is connected to a first set top box 152 located remote
from the distribution switch 130.
[0037] A second transmission line 144 distributes the signal from
the second output port of the distribution switch 130 to a signal
splitter 170. A first output of the signal splitter 170 is coupled
to the second set top box 154. The second set top box 154 can be
located at a location remote from the distribution switch 130 and
signal splitter 170 and can also be at a location remote from the
first set top box 152. A second output of the signal splitter 170
is coupled to a third act top box 156. The output of the third set
top box 156 is coupled to a third output device 166.
[0038] The first and second transmission lines, 142 and 144, can be
parallel lines, twisted pairs, coaxial line, waveguide, and like,
or any other means for distributing the signal. Additionally,
although transmission lines are typically used to minimize signal
loss and signal reflections, the system can use other means for
distributing the signal that are not transmission lines. For
example, wires, wire bundles, and the like, can be used for
distributing the signals from the distribution switch 130 to the
set top boxes 152, 154. However, for signals that can be considered
Radio Frequency (RF) signals, the signals are typically distributed
using transmission lines. The RF information signals can, for
example, be in the range of KHz up to several GHz. Of course, the
signal distribution system 100 is not limited to distributing RF
signals, but can distribute other signals, such as baseband signals
or optical signals.
[0039] The transmission lines 142, 144, are typically non-ideal
passive devices. Thus, the transmission lines attenuate the signal
power. However, the attenuation contributed by the transmission
lines 143, 144 typically do not attenuate the noise power to the
same degree as the signal power. For example, a passively
attenuator, such as a length of transmission line may not
significantly degrade the thermal noise. Additionally, the
transmission lines 143, 144 can contribute other types of cable
related signal degradation. For example, the transmission lines can
affect flatness, tilt, phase distortion, group delay distortion,
reflection, interference, noise pick-up and microphonic noise of
the distributed signals. Thus, the losses contributed by the
transmission lines 143, 144 typically degrade the SNR of the signal
distributed to set top boxes 152, 154.
[0040] The first and second transmission lines 142 and 144 are
couples to corresponding inputs of set top boxes 152, 154 and 156.
The second transmission line 144 couples to the second and third
set top boxes, 154 and 156, via the signal splitter 170. In one
embodiment, the frequency bands for the signals output from the
distribution switch 130 do not correspond to frequency bands used
by the output devices 162 and 164. Thus, the set top boxes 152, 154
can further frequency translate the signals to operating bands
compatible with the output devices 162, 164, and 166. Additionally,
the output signals from the distribution switch 130 cab be in a
format that is not compatible with the format used by the output
devices 162, 164, and 166. The set top boxes 152, 154, and 156 can
then function as signal processing stages. For example, the
satellite downlink signals can be digitally modulated in a format
that is not compatible with the output devices 162, 164, and 166
which can be typical television receivers. The set boxes 152, 154;
and 156 can be configured to demodulate the distally modulated
signals, process the demodulated signals, and then modulate
television channel carrier frequencies with the signals for
delivery to the television output devices 162, 164, and 166.
[0041] Alternatively, if the signals output from the distribution
switch 130 are in a format and are at a frequency band that is
compatible with the output devices 162, 164, and 166 the set top
boxes 152, 154, and 156 may not be required. In still another
alternative, one or more of the functions performed by the set top
boxes 152, 154, and 156 can be integrated into the output devices
162, 164, and 166. In still another embodiment, the signal 170 can
be configured to perform signal processing, such as frequency
conversion or demodulation.
[0042] In the embodiment described in FIG. 1, each of the set top
boxes 152, 154, and 156 is connected to a single device 162, 164,
and 166. However, more than one output device e.g. 162, 164 can be
connected to the output from a single set top box, for example 152.
Alternately, outputs from more than one set top boxes 152, 154, and
156 can be combined or otherwise connected to a single output
device, for example 162, although such a configuration is not
typical.
[0043] An output device, for example 162, can be configured to tune
to a particular channel within the one or more frequency bands
provided by the set top box, such as 152. The output device 162 can
process the signal from the selected channel to present some media
content, such as video or audio, to a user.
[0044] For example, the output devices, 162, 164, and 166 can be
television receivers and can display a television signal
corresponding to a signal transmitted by the satellite 110. The
output devices 162, 164, and 166 can be other types of devices in
other signal distribution systems. For example the output devices
162, 164, and 166 can be telephones, radio receivers, computers,
network devices, and the like, or other means for outputting a
signal.
[0045] The output devices 162, 164, and 166 can have a range of
signal quality over which the output is considered acceptable. For
example, the output devices 162, 164, and 166 can provide
acceptable outputs for input SNR above a predetermined level, which
may represent a desired minimum SNR. However, the SNR at the input
to the output devices, 162, 164, and 166 is typically determined by
the signal processing performed in the set top boxes 152, 154 and
156. Thus, the signal quality is typically related to the signal
quality at the input of the set top boxes 152, 154, and 156. Thus,
the signal distribution system 100 is typically configured to
provide a signal at the input to the set top boxes 152, 154, and
156 having a SNR greater than the desired minimum.
[0046] Although FIG. 1 is a functional block diagram of a satellite
signal distribution system, Other signal distribution systems have
similar structures. For example, cable distribution systems, which
may distribute television, radio, data, and/or telephony signals,
typically provide a single access point to a geographic area, such
as a residence. The signal from the one access point is then
typically split, amplified, distributed, and can be combined with
other signals, such as, for example the satellite television
signals. Communication systems having wireless communication links
can also have similar structures. For example, a terrestrial
television or radio system can include a single antenna and
distribute the signals received at the single antenna to multiple
output devices using a signal distribution system 100 that can
amplify, split, distribute, and/or combine the received
signals.
[0047] The signal distribution system is not limited to a
residence, but can span many residences, businesses, or locations
not associated with dwellings or buildings. The signal distribution
system is characterized by its features and is not limited to any
particular application.
[0048] Additionally, although FIG. 1 shows only the signal 170
interposed between the distribution switch 130 and set top boxes
154 and 156, elements other than the transmission lines 142, 144,
and signal splitter 170 can be interposed between the distribution
switch 130 and the set top boxes 152, 154, and 156. The additional
distribution devices can include active or passive power dividers,
active or passive power combiners, amplifiers, attenuators,
filters, switches, crosspoint switches, multiplexers,
de-multiplexers, frequency translation devices, encoders, decoders,
and the like or any other means for distributing a signal. Each of
these additional signal distribution devices can contribute to the
noise experienced by the distributed signal.
[0049] For example, a two-way passive power divider allows a signal
at one input to be split equally into two output signals, each
having half the original signal power, while maintaining an
impedance match at all ports. An ideal two-way passive divider
reduces the SNR by 3dB However, in practice, the degradation is
often higher.
[0050] Active signal distribution devices can contribute to signal
degradation, for example by generating distortion products that
degrade SNR. The distortion contributed by an active device
typically increases as the input signal power to the device
increases. Additionally, the location of an active device within
the signal distribution system 100 can affect the impact that the
device has on SNR. An active device located at an input to the
signal distribution system can experience a larger signal power,
and thus degrade the SNR more than an identical device located at a
the end of a transmission line, e.g. 142, where the signal power
can be significantly attenuated.
[0051] Because the distortion typically increases at a rate greater
than the rate of increase in signal power, the SNR degrades for
input signals that are large in relation to the device
capabilities. A large input signal can be defined as a signal that
generates a predetermined level of distortion in an active device.
For example, a signal can be large when measured in relation to the
input signal level required to generate a 1 dB amplifier output
compression. Alternatively, a signal can be large when measured in
relation to an input signal level required to generate a particular
third order product. That is, a signal can be defined to be large
if a two-tone intermodulation test produces a third order
intermodulation distortion product that is a predetermined level
below the output signal, for example 40 dB. The definition of a
large signal is relative to the signal distribution system in which
a device is used and the previous definitions are not
exhaustive.
[0052] Conversely, when the signal is small, the uncorrelated noise
level may dominate the determination of SNR. Because an attenuator
typically degrades signal power and may not degrade the
uncorrelated noise power by an equivalent amount, the SNR following
the attenuator can degrade. The placement of a passive device can
also affect the amount of SNR degradation contributed by the
device. Attenuators placed where the signal is large may not affect
the SNR while identical attenuators placed where the signal is
small may significantly degrade the SNR.
[0053] Thus, there exists an optimum signal range that maximizes
SNR in the system. The optimum depends on the precise signal
distribution system and the nature of the information signal
distributed. The Automatic Gain Control (AGC) amplifier that is
detailed below can help the system maintain the optimal operating
range and thus help to maintain an optimum SNR in the system. The
AGC amplifier can diminish the effects that subsequent distribution
devices have on the SNR at the set top boxes 152, 154, and 156.
Additionally, the AGC amplifier can minimize adverse effects of
adding or removing distribution paths in the signal distribution
system 100. The AGC amplifier can, for example, be integrated into
the distribution switch 130 or signal splitter 170.
[0054] FIGS. 2A and 2D are functional block diagrams of AGC
amplifiers that can be, for example, integrated into the
distribution switch 130 and/or signal splitter 170 of FIG. 1. The
AGC amplifier can also be implemented in an intermediate signal
processing device, such as the signal splitter 170 or some other
signal distribution device, alternatively referred to as a
distribution device or signal processing device. Typically, the AGC
amplifiers are not added as stand alone devices, but are
implemented in conjunction with other distribution devices.
[0055] In some embodiments, intermediate signal distribution
devices may not include AGC amplifiers. Such intermediate signal
processing devices lacking an AGC amplifier may be configured for
use in particular locations within the signal distribution system.
In other embodiments, the intermediate signal distribution devices
can, for example, include an AGC amplifier as the initial signal
processing element.
[0056] Implementing an AGC amplifier with a signal distribution
device allows the performance of the signal distribution system 100
to be substantially unaffected by the physical location of the
signal distribution device. That is, the performance of the signal
distribution system 100 is substantially indifferent to the
placement of a signal distribution device at the front end of a
cable run or at the back end of the cable run.
[0057] Implementing the AGC amplifier in the distribution device
130 immediately following the low noise block 126 can compensate
for gain variations in the low noise block 126. Thus, embodiments
implementing the distribution device 130 and low noise block 126
locally or in a single housing may advantageously eliminate a
production adjustment of the low noise block 126 gain. Thus, the
AGC function implemented in the distribution block 130 can provide
a lowered production cost by eliminating a production tuning
step.
[0058] Each of the AGC amplifier embodiments shown in FIGS. 2A and
2D can be implemented with a signal distribution device as an
integrated circuit, as discrete devices, or as a combination of
integrated circuits and discrete devices. An integrated circuit
can, for example, incorporate multiple independent AGC amplifiers
in parallel, with each AGC amplifier controlling the power of a
signal received from a satellite downlink. The integrated circuit
can be manufactured on a variety of substrate materials such as
silicon, germanium, gallium arsenide, indium phosphide, sapphire,
diamond, and the like, or any other suitable substrate material.
Additionally, the AGC amplifier embodiments can be manufactured
using a variety of manufacturing techniques including bipolar, FET,
BiCMOS, CMOS, SiGe, and the like.
[0059] FIG. 2A is a functional block diagram of a first AGC
amplifier embodiment. The AGC amplifier includes a variable gain
amplifier (VGA) 210 and a detector 220 connected to the output of
the VGA 210. An output of the detector 220 is connected to a gain
control input of the VGA 210 to control the gain of the
amplifier.
[0060] The AGC amplifier implements an output referred AGC function
to attempt to maintain the output power of the power amplifier at a
predetermined optimal level, also referred to as the AGC set point.
The AGC function is a process that attempts to maintain a signal
power at the AGC set point. The AGC function increases the gain of
the amplifier 210 when the output signal is below the AGC set
point. The AGC function can continue to increase the gain of the
VGA 210 as required, up to a maximum gain value. The VGA 210
continues to provide the maximum gain value as long as the output
signal power remains below the AGC set point.
[0061] Conversely, the AGC function decreases the gain of the VGA
210 when the output signal power is above the AGC set point. The
AGC function can continue to decrease the gain of the VGA 210 as
required, down to a minimum value. The AGC function continues to
provide the minimum gain value as long as the output signal power
remains greater that the AGC set point.
[0062] Within a system such as the signal distribution system 100
of FIG. 1, there is typically a limit of input signal range. That
is, the input to the signal distribution system 100 typically falls
within a predetermined range. In such a system, it is possible to
configure the AGC range such that one or more of the AGC limits is
not ever reached. For example, the input signal from the satellite
110 may vary over a predetermined range. If the AGC amplifier in
the distribution switch 130 or signal splitter 170 has an AGC range
that is greater than the input signal range, the AGC function may
never reach its limits.
[0063] Initially, an input signal having an input signal power,
Pin, is provided to the input 215 of the VGA 210. The control
signal provided to the VGA 210 can initially be set to control the
VGA 210 to provide the maximum available gain, Gmax. The VGA 210
than provides an output signal having an output power, Pout,
substantially equal to Pin+Gmax, for example, measured in terms of
decibels relative to a milliwatt (dBm).
[0064] The output from the VGA 210 is connected to an input of a
power detector 220. The power detector 220 measures the output
signal power and generates a control signal that can correlate with
the output signal power. For example, the power detector 220 can be
configured to provide an output voltage that correlates with a
given power level. Alternatively, the power detector 220 can be
configured to provide an output current that correlates with a
given power level.
[0065] The power detector 220 can be configured to measure the
power of the composite amplifier output, signal, including desired
signals, noise, and distortion. Such a power detector 220 can be a
broadband detector and can detect a power level over a broad
frequency band. Alternatively, the power detector 220 can measure
the power of only a portion of the output power for the VGA 210.
For example, power detector 220 can measure the power in a
predetermined bandwidth, where the predetermined bandwidth
represents only a portion of the bandwidth of the signal output
from the VGA 210. The predetermined bandwidth can, for example, be
entirely within a desired signal bandwidth of the output from the
VGA 210. Alternatively, the predetermined bandwidth can partially
overlap or be exclusive of a desired signal bandwidth of the VGA
210 output.
[0066] The output of the power detector 220 is connected to a
control input of the VGA 210. The AGC amplifier can be configured
to provide an output referred AGC function. For example, the power
detector 220 can detect an output power of the VGA 210. The power
detector 220 can also include a comparator having an AGC set point
coupled to one comparator input. The detected output power can be
provided to the second input of the comparator and compared to a
AGC set point. The output of the comparator can be filtered, for
example using an integrator. The output of the integrator can be
the detector output control signal that controls the gain of the
amplifier.
[0067] For example, a high power signal, one that is greater than
the AGC set point, at the input to the power detector 220 produces
a control voltage. The control voltage value corresponds with an
amplifier gain value that is smaller than the original gain value.
The high power detector 220 output reduces the gain of the VGA 210
such that the power detected at the output of the VGA 210 is
substantially equal to the AGC set point.
[0068] Although the VGA 210 is shown as an amplifier, the AGC
function can be implemented with gain only, a combination of gain
and attenuation, or attenuation only. Additionally, the VGA 210 can
be implemented with multiple stages and multiple devices. For
example, the VGA 210 can be configured as multiple cascaded
variable gain amplifiers, or as amplifiers cascaded with variable
attenuators, or as multiple variable gain amplifiers in parallel,
and the like.
[0069] Additionally, power detector 220 can be a diode detector, a
crystal detector, and the like. The power detector 220 can be
configured to sample mean power, peak power, RMS voltage, mean
voltage, peak voltage, mean current, RMS current, peak current, or
some other value correlated to signal level. The power detector can
be a single device or can be constructed of multiple devices. As
discussed above, the power detector 220 can include, for example, a
detector, a comparator, and integrator, or some other signal
conditioning block.
[0070] Although the power detector 220 is shown to provide an
output referred AGC function, the power detector 220 can be
configured detect the signal power at other locations, such as at
the input of the VGA 210. The power detector 220 can be configured
to detect the signal power at some other location that is remote
from the VGA 210, such as at the input to a set top box of FIG.
1.
[0071] The actual AGC function can be implemented using a variety
of techniques, including feedback and feed-forward. Regardless of
whether the AGC function is configured as output referred using
feedback, or output referred using feed-forward techniques, the AGC
function can operate to provide a substantially stable output level
over an predetermined AGC range.
[0072] FIG. 2B is a functional block diagram of an embodiment of an
AGC amplifier. The AGC amplifier includes a constant gain amplifier
232 at the input to the AGC amplifier. The output of the constant
gain amplifier 232 is connected to the input of a VGA 234. The
output of the VGA 234 is connected to a power detector 240. The
output signal from the power detector 240 is connected to the
control input of the VGA 234 to control the gain of the VGA
234.
[0073] The AGC amplifier embodiment in FIG. 2B is similar to the
embodiment of FIG. 2A except that a constant gain amplifier 232 is
implemented before the VGA 234. The AGC amplifier of FIG. 2B
operates effectively the same as the AGC amplifier of FIG. 2A. The
gain of the constant gain amplifier 232 can set a lower limit on
the gain of the AGC amplifier. However, the gain of the constant
gain amplifier 232 can be negated by attenuation in the VGA 234 if
the VGA is configured to provide attenuation. The constant gain
amplifier 232 can be included in an AGC amplifier, for example, in
order to provide a front end amplifier in the AGC amplifier having
a low noise figure.
[0074] FIG. 2C is a functional block diagram of another AGC
amplifier embodiment. The AGC amplifier includes a VGA 252 at the
input of the AGC amplifier. The output of VGA 252 is connected to a
constant gain amplifier 254. The output of the constant gain
amplifier 254 is the output of the AGC amplifier. The output of VGA
252 is also connected to the input of the power detector 260. The
detected output is provided to the control input of VGA 252. Thus,
in the embodiment of FIG. 2C, the power detector 260 detects the
power of an intermediate stage, rather than the input or output of
the AGC amplifier. Of course, the embodiment of FIG. 2A can be
modified to correspond to the embodiment of FIG. 2C by cascading
the AGC amplifier with a constant gain amplifier. Although a
constant gain amplifier 254 is implemented after the VGA 252, the
composite AGC amplifier can be interpreted as being output
referred.
[0075] FIG. 2D is another embodiment of an AGC amplifier. The AGC
amplifier is an embodiment of a VGA coupled with a signal
distribution device. The AGC amplifier includes a VGA 270 at the
input of the AGC amplifier. The output of the VGA 270 is connected
to the input of a mixer 280. A LO 284 drives an LO port of the
mixer 280. The output of the mixer 280 is the output of the AGC
amplifier. The output of the mixer 280 is also connected to the
input of the power detector 290. The detected output is provided to
the control input of the VGA 270.
[0076] In this AGC amplifier configuration, the AGC function is
combined with band translation. The AGC amplifier power controls
the output to track the AGC set point and can also frequency
convert the signal from an input frequency band to an output
frequency band. As noted earlier, a VGA such as 270 can be combined
with a variety of signal distribution devices. The signal splitter
170 of FIG. 1 can represent another embodiment of a VGA coupled
with a signal distribution device.
[0077] The VGA 270 operated in a manner as described above in
relation to the other AGC amplifier embodiments. The output of the
VGA 270 is connected to an input port of the mixer 280. The mixer
280 operates to frequency convert the signal from a first frequency
band to a second frequency band. An LO 284, which can be a fixed
frequency LO or a variable frequency LO, drives the LO port of the
mixer 280. The mixer 280 provides an output signal that includes a
frequency component that is at the sum of the input signal
frequencies and LO frequency a frequency component that is at the
difference of the input signal frequencies and the LO
frequency.
[0078] The power detector 290 can be configured to detect signals
within a predetermined frequency band. Thus, the power detector 290
can detect the signals in the desired frequency band while ignoring
signals outside the frequency band of interest. The AGC amplifier
can thus be configured to provide a controlled signal amplitude
combined with a frequency conversion.
[0079] The benefits of including an AGC stage in the signal
distribution system, such as within the distribution switch 130 or
signal splitter 170 in the system of FIG. 1, can be illustrated
with a comparison of an AGC signal distribution implementation with
a fixed gain signal distribution implementation. FIGS. 3A and 3B
show embodiments of cascaded amplifier configurations. the
configuration in FIG. 3A includes fixed gain amplifiers while the
configuration of FIG. 3B includes the AGC amplifiers. Such cascaded
amplifier configurations can be included in the signal distribution
switch of FIG. 1, for example, to provide three independent copies
of a single input signal destined for three different geographic
locations within the signal distribution system.
[0080] FIG. 3A is an embodiment of a fixed gain signal distribution
section 300, such as a distribution section that can be implemented
in the distribution switch of FIG. 1. For example, the devices in
the distribution section 300 can be distributed at front end,
intermediate location, or near a termination of a signal
distribution system. The fixed gain distribution section 300
includes three gain devices 310, 320, and 330 connected in series.
Each of the gain devices, for example 310, can be configured as an
active power divider having a fixed gain of 0 dB, a noise figure
(NF) of 3 dB, and an input third order intercept point (IIP3) of
+30 dBm. Alternatively, each of the gain devices can include an
amplifier in conjunction with some other type of signal
distribution device.
[0081] A first fixed gain device 310 includes a fixed gain
amplifier 312 followed by a passive power divider 314 having a
first output 318a and a second output 318b. The composite gain
through the fixed gain amplifier 312 and passive power divider 314
to one of the outputs, for example 318b, can be configured to be 0
dB. The second output 318a of the first fixed gain device 310 is
connected to the input of a second fixed gain device 320. The
second fixed gain device 320 also contains a fixed gain amplifier
322 and a passive power divider 324 having a first output 328a and
a second output 328b. The second output 328b of the second fixed
gain device 320 is connected to the input of a third fixed gain
device 330. The third fixed gain device 330 is similarly configured
with a fixed gain amplifier 332 followed by a passive power divider
334 having two outputs 338a, 338b.
[0082] An alternative signal distribution section 350 including AGC
amplifiers is shown in FIG 3B. The embodiments of the signal
distribution section 350, including the AGC amplifiers, can be
implemented in the distribution switch of FIG. 1.
[0083] Three gain devices, 360, 370, and 380 are cascaded in the
signal distribution section. Each of the gain devices 360, 370, and
380 includes an AGC amplifier followed by a passive power divider.
Each of the gain devices, 360, 370, and 380 may also include an AGC
amplifier in conjunction with one or more other signal distribution
devices.
[0084] Each of the gain devices, for example 360, can have an
output referred AGC function with an AGC set point of 0 dBm, an
IIP3 of +30 dBm, and a NF of 3 dB at 0 dB of gain. The gain device,
for example 360, can have a gain range of from -20 dB to +20 dB.
Each of the AGC amplifiers can be, for example, one of the AGC
amplifier configurations shown in FIGS. 2A-2C.
[0085] An input signal is provided to an input of the first gain
device 360. The input signal is coupled to the input of an AGC
amplifier 362. The output of the AGC amplifier 362 is connected to
the input of a power detector 364. The output of the power detector
364 is connected in a control input of the AGC amplifier. The
output of the AGC amplifier 362 is also connected to the input of a
power divider 360 that has first and second outputs, 368a and 368b
respectively.
[0086] The second output 368b of the first gain device 360 is
connected to the input of a second gain device 370. The output from
the first gain device 360 is coupled to the input of an AGC
amplifier 372. The output of the AGC amplifier 372 is connected to
the input of a power detector 374. The output of the power detector
374 is connected to a control input of the AGC amplifier. The
output of the AGC amplifier 372 is also connected to the input of a
power divider 376 that has first and second outputs, 378a and 378b
respectively.
[0087] The second output 378b of the second gain device 370 is
connected to the input of a third gain device 380. The output from
the second gain device 370 is coupled to the input of an AGC
amplifier 382 in the third gain device 380. The output of the AGC
amplifier 382 is connected to the output of a power detector 384.
The output of the power detector 384 is connected to a control
input of the AGC amplifier. The output of the AGC amplifier 382 is
also connected to the input of a power divider 386 that has first
and second outputs, 388a and 388b respectively.
[0088] The performance of the fixed gain distribution section 300
can be compared against the performance of the variable gain
distribution section 350 for two operating conditions. In the first
operating condition, the input signal is relatively small and
uncorrelated noise is a significant factor limiting the SNR. In the
second operating condition, the input signal is relatively large,
and distortion products are significant factors limiting the
SNR.
[0089] In the first operating condition, the input signal is
relatively small. The configuration of the fixed gain distribution
section 300 does not change. However, the variable gain
distribution section 350 automatically configures itself to provide
gain, up to a maximum gain level.
[0090] An active device, such as an amplifier, typically has
multiple noise sources associated with it. The noise contribution
of cascaded amplifiers can be reduced if the front end device has
significant gain. The noise contribution of subsequent stages can
become insignificant, and thus, the degradation to SNR can be
minimized. Additionally, other noise contributors after the first
gain stage, or front end device, degrade the SNR less than without
the front end gain device. Thus, including the front end gain stage
reduces the overall system SNR degradation. The performance of the
fixed gain distribution section 300 can be compared to the variable
gain distribution section 350 by examining the noise figures. The
noise figure in a cascaded system is given by the following
formula:
nf cascade = nf 1 + i = 2 N nf 1 - 1 j = 1 i - 1 A j ,
##EQU00001##
where N=number of stages, A.sub.j=gain of jth stage
[0091] The noise figure values in the formula are given as ratios,
while noise figure specified for the devices are given in dB. Thus,
the NF for the gain devices, for example 310 or 370, needs to be
converted from decibels to ratios before application of the
formula. Table 1 provides a summary of the cascaded noise figures
for the two gain distribution sections, 300, 350. Psig represents
the signal power, in dBm at either the input or output of the gain
devices. The gain of the elements is provided in dB. The noise
figure, in dB, is provided for each gain device and the
corresponding cascaded noise figure, in dB, is provided at the
output of each gain device.
TABLE-US-00001 TABLE 1 FIXED GAIN DISTRIBUTION SECTION Psig (dBm)
-20 -- -20 -- -20 -- -20 Gain (dB) 0 0 0 NF (dB) 3 3 3 NFtot (dB) 3
4.8 6 VARIABLE GAIN DISTRIBUTION SECTION Psig (dBm) -20 -- 0 -- 0
-- 0 Gain (dB) 20 0 0 NF (dB) 3 3 3 NFtot (dB) 3 3.02 3.04
[0092] Thus, it can be seen that the ability of the variable gain
distribution section 350 to include gain in an initial amplifier
section results in greatly reduced signal degradation due to noise
contributed by subsequent stages when compared to the fixed gain
distribution section 300. Noise contributors after the initial gain
section degrade the SNR less than without the gain section.
Therefore, overall system degradation of SNR can be reduced with
the inclusion of an initial gain section.
[0093] In the second operating condition, the input signal is
relatively large. The configuration of the fixed gain distribution
section 300 does not change. However, the variable gain
distribution section 350 automatically configures itself to provide
attenuation, up to a maximum attenuation level. When input signal
levels are relatively large, distortion components, such as third
order intermodulation distortion products, can be the dominant
factor in degrading SNR. A cascaded IIP3 for the signal
distribution sections, 300, 350 can be calculated and compared to
illustrate the advantages of variable gain distribution over fixed
gain distribution. The cascaded IIP3 of a gain section is given by
the formula:
1 IP tot = 1 IP 3 1 + i = 2 n j = 1 i - 1 A j IP 3 i
##EQU00002##
[0094] The IP3 values in the formula are the linear terms and are
not the values in dBm. Similarly, the gain values are provided as
ratios and are not in dB. Table 2 provides a summary of the
cascaded IIP3 for the two gain distribution sections 300, 350. Psig
represents the signal power, in dBm at either the input or output
of the gain devices. The gain of the elements is provided in dB.
The IIP3, in dBm, is provided for each gain device and the
corresponding cascaded IIP3, in dBm, is provided at the output of
each gain device.
TABLE-US-00002 TABLE 2 FIXED GAIN DISTRIBUTION SECTION Psig (dBm)
+20 +20 +20 +20 Gain (dB) 0 0 0 IIP3 (dBm) +30 +30 +30 IIP3tot
(dBm) +30 +27 +25.2 VARIABLE GAIN DISTRIBUTION SECTION Psig (dBm)
+20 0 0 0 Gain (dB) -20 0 0 IIP3 (dBm) +30 +30 +30 IIP3tot (dBm)
+30 +29.96 +29.91
[0095] Thus, it can be seen that the ability of the variable gain
distribution section 350 to include attenuation in an initial
amplifier section results in greatly reduced signal degradation due
to noise contributed by subsequent stages when compared to the
fixed gain distribution section 300. Distortion contributors after
the initial attenuation stage degrade the SNR less than without the
attenuation stage. The overall system degradation of SNR can be
reduced with the inclusion of an initial attenuation section.
[0096] The inclusion of an AGC function in a signal distribution
section can thus improve the quality of the signal compared to a
fixed gain configuration. The advantages of the variable gain
section over the fixed gain section under the extreme conditions of
low input signal power and high input signal power show that the
variable gain distribution section has flexibility as to its
position within a signal distribution system. The variable gain
distribution section need not be placed at the front end or as a
final stage in a signal distribution system.
[0097] FIG. 4 is a functional block diagram of a specific
embodiment of signal distribution system 400 including an
integrated crosspoint switch with band translation (band
translation switch 410 and external components. The band
translation switch 410 includes four inputs for LNB's, a cascadable
output corresponding to each of the inputs, and two outputs
configured to interface with set top boxes. The band translation
switch 410 is configured to interface with LNB's signals having a
dual band-stacked frequency plan. The dual band-stacked frequency
plan includes an upper band block and a lower band block. The band
translation switch outputs maintain the dual band-stacked frequency
plan, but allow the upper or lower band block from any of the LNB
signals to be configured as an output upper band block. Similarly,
the upper or low band block from any of the LNB signals can be
configured as an output lower band block. A more detailed
description of the band translation switch 410 is provided
below.
[0098] The band translation switch 410 includes four inputs
configured to interface with up to four LNB's. Each LNB provides a
signal conforming to a dual bandstacking frequency plan having an
upper band block and a lower band block. For example, the LNB
signals can be satellite downlink signals from selected transponder
groups. The lower band block can be 950-1450 MHz and the upper band
block can be 1650-2150 MHz.
[0099] Each of the signal inputs is connected to the input of an
amplifier 420a-420d. The amplifiers 420a-420d are configured as Low
Noise Amplifiers (LNA's) that both buffer and amplify the input
signals from the LNB's. The output from each of the amplifiers
420a-420d is connected to a corresponding input on a crosspoint
switch 430. Additionally, the output from each of the amplifiers
420a-420d is connected to a corresponding cascade output of the
band translation switch 410.
[0100] The crosspoint switch 430 is configured as a 4.times.4
switch. Any of the four amplified LNB input signals can be
selectively routed to any of the four outputs of the crosspoint
switch 430 independently and simultaneously. For example, the
crosspoint switch 430 can include a two-bit control for each
output. The value of the two-bit control can be programmed to
selectively route the signal from one of the four points. The band
translation 410 can, for example, receive the two bit control words
from a set top box. Alternatively, the set top box may send one or
more control messages to a microprocessor implemented local to the
crosspoint switch and the microprocessor can generate the one or
more two bit control words. In the embodiment shown in FIG. 4, each
of the four outputs from the crosspoint switch 430 is connected to
a band translation device 440a-440d. One or more outputs from the
crosspoint switch 430 can be couples to the same band translation
device, for example 440a.
[0101] The band translation device 440a-440d are configured to
selectively frequency translate the signals or to pass the signals
without frequency translation. Each of the band translation devices
440a-440d can select frequency translation or pass through
independently of the other devices. Because a dual band-stacked
frequency plan is used in this embodiment, the band translation
devices 440a-440d are configured to swap the positions of the upper
and lower band blocks when frequency translation is selected.
[0102] Each of the band translation devices 440a-440d includes a
mixer. The band translation switch 410 also includes one or more
local oscillators (LO). In one embodiment with a dual band-stacked
frequency plan, a single LO can be routed to all of the band
translation devices 440a-440d. In another embodiment, the local
oscillator frequency can be fixed when a dual band-stacked
frequency plan is implemented. An LO frequency of 3.1 GHz, or
2.times. (the band center mean), can be used to perform the
frequency translation.
[0103] In another embodiment, a plurality of variable frequency LOs
can be used with the band translation devices 440a-440d. For
example, each of the band translation devices 440a-440d can have a
separate independently controlled LO output frequencies. Thus, each
of the band translation devices 440a-440d can frequency translate
its input signal independently of the frequency translation
performed by any other band translation device.
[0104] LO buffer amplifiers (not shown) distribute the signal from
the LO output to each of the band translation devices 440a-440d.
The output of the band translation devices 440a-440d are connected
to the outputs of the band translation switch 410.
[0105] Each of the outputs of the band translation switch 410 is a
dual bandstacked signal. Each of the outputs of the band
translation switch 410 is connected to filter 450a-450d. The
filters 450a-450d are configured to pass signals in one of the
predetermined frequency bands in the dual band-stacked frequency
plan. The filters 450a-450d reject signals outside of the passband,
including the signals at the undesired frequency band. The filters
450a-450d can be configured with tunable passbands or can be
configured to have fixed passbands.
[0106] In the present embodiment, the filters 450a-450d are
configured as bandpass filters with fixed passbands. The first
filter 450a is configured as a bandpass filter that passes the
upper band block of the frequency plan. A second filter 450b is
configured as a bandpass filter that passes the lower band block.
Similarly, a third filler 450c is configured to pass the upper band
block and a fourth filter 450d is configured to pass the lower band
block. The outputs of the first and second filters 450a-450b are
connected to respective first and second inputs of a first signal
combiner 460a. Similarly, the output of the third and fourth
filters 450c-450d are connected to first and second inputs of a
second signal combiner 460b. The filters 450a-450d are not limited
to bandpass filters, but can be, for example, bandpass filters
(BPF), lowpass filters (LPF) or highpass filters (HPF). In other
embodiments, other frequency selective devices can be used to limit
the frequency response of the outputs. The filters 450a-450d can
have passbands that are narrower than the frequency bandwidth of
the input signals. For example, an input to a filter, for example
450a, can include multiple carriers. However, the filter 450a can
be configured to pass a subset of all of the carriers.
[0107] The signal combiners 460a-460b are configured to sum the
signals provided at their inputs and to provide the summed signal
at an output. The outputs from the signal combiners 460a-460b are
the band translated outputs of the signal distribution system 400.
Each of the outputs is connected to a set top box for further
processing and for distribution to an end user device.
[0108] As discussed above, one or more frequency selective devices
can be used as the filters 450a-450d. For example, a diplexer can
be used to filter and to band-stack signals. The diplexer can be
used as the filters, for example 450a and 450b, and signal combiner
460a.
[0109] Of course, the band translation switch 410 is not limited to
operating with band stacked input signals. For example, each of the
LNB's can provide signals in the same frequency band. The band
translation switch 410 can be configured to frequency translate and
combine portions of the single band input signals. The crosspoint
switch 430 can, for example, route the output of the first
amplifier 420a to a first band translation device 440a. An LO in
the first band translation device 440a can be configured to
frequency translate the signal such that one or more channels from
the input signal are translated to desired output frequencies. The
first filter 450a can be configured to pass only those desired
channels and reject all undesired frequencies an channels.
[0110] Similarly, the crosspoint switch 430 can be configured to
route the output of the second amplifier 420b to a second band
translation device 440b. The second band translation device 440b
can be configured to frequency translate a portion of the input
signal to desired output frequencies. The second filter 450b can be
configured to pass only those desired channels and reject all
undesired frequencies and channels.
[0111] The first and second band translation devices 440a-440b in
conjunction with the first and second filters 450a-450b can be
configured to produce selected channels in mutually exclusive
frequency bands. The combiner 460a can then sum the filtered
outputs to produce a composite output signal from independent
single band input signals, where each filter includes one or more
channels. In one embodiment of the single band input signal
configuration, each band translation device and filter pair, for
example 440a and 450a, is configured to frequency translate one or
more channels from each of one or more input signal bands. The
frequency translated signals can be combined into a single band
signal or a multiple band signal.
[0112] Similarly, some embodiments can have multiple band
translation devices and multiple filters. Each of the multiple band
translation devices can frequency translate one or more channels
from one or more input bands. The outputs of the multiple filters
can be summed to provide a single composite signal having a desired
channel line up.
[0113] One embodiment of the band translation switch 410 can be
used in a signal distribution system designed to provide
distribution of satellite television signals in a residence. The
AGC amplifiers 420a-420d provide variable gain and attenuation
based on the power of the input signal. The measurement point for
the AGC function is at the output of the AGC amplifiers 420a-420d
and the gain of the crosspoint switch 430 and the band translation
devices 440a-440d are fixed.
[0114] Each AGC amplifier 420a-420d followed by a crosspoint switch
430, band translation device 440a-440d, and signal combiner
460a-460b can be configured to provide a total gain that ranged
from a minimum of -7 dB to a maximum of +7 dB. The corresponding NF
of a path through the band translation switch 410 from the AGC
amplifier, for example 420a, through to the output of a band
translation device, for example 440a, can vary from, for example, a
high of 24 dB to a low of 10 dB. The signal path experiences a
higher NF when providing attenuation and has a lower NF when the
gain is unity or greater. Similarly, the IIP3 associated with the
signal path can range from a minimum of -7 dBm to a maximum of +7
dBm. For example, the IIP3 of the signal path can -15, -10, -7, -6,
-5, -4, -3, -2, -1, 0, +1, +2, +3, +4, +5, +6, +7, +10, +15, +20,
+25, or +30 dBm.
[0115] The IIP3 of the AGC amplifier 420a is typically higher when
the amplifier is configured to provide attenuation, which
contributes to the composite IIP3 of the signal path. The IIP3 of
the AGC amplifier 420a can vary in proportion to the gain of the
amplifier.
[0116] Because the AGC amplifier 420a also provides the signal to a
cascade output, the characteristics of the AGC function at the
cascade output are substantially the, same as the characteristics
of the AGC amplifier 420a. Also because the AGC function is
provided before the cascade output, the benefits of the AGC
function are experienced in the main signal path as well as the
signal path through the cascade output.
[0117] This band translation switch 410 configuration can be used
in a signal distribution system where the input to the band
translation switch 410 can be expected to vary over the range of
-50 dBm through -10 dBm. The AGC amplifiers 420a-420d can be
configured to have an input referred AGC setpoint of -17 dBm, where
the output refers to the output signal of the switch 400. The band
translation switch 410 need not actually measure the power at the
output of the switch 400. Because the devices following the band
translation switch 410 have fixed gains, the AGC output can be
interpreted as being output referred to any point past an AGC
amplifier where the gain or attenuation is fixed.
[0118] Using this AGC setpoint, the AGC amplifier, for example
420a, provides a gain of 7 dB when the input signal is -24 dBm or
below. Additionally, the AGC amplifier 420a provides -7 dB of gain,
or 7 dB of attenuation, when the input signal is -10 dBm or
greater. Thus, within the input power range of -24 dBm through -10
dBm the AGC amplifier 420a provides a constant output power of -17
dBm.
[0119] FIG. 5 is a functional block diagram of multiple band
translation switches 510, 520, 530, 540, and 550, connected in a
signal distribution system. The band translation switches 510, 520,
530, 540, and 550, can be configured with LNBs to provide the
distribution switch of FIG. 1. However, as noted earlier, one or
more of the band translation switches 510, 520, 530, 540, and 550
can be positioned at other locations within the signal distribution
systems. For example, one or more of the band translation devices
can be positioned near the signal input, at an intermediate
position within the signal distribution system, or near a
termination or destination device of the signal distribution
system.
[0120] A first band translation switch 510 includes an LNA input
that can be connected to an LNB that block converts a satellite
downlink transmission. The output of the first band translation
switch 510 is connected to an output of a second band translation
switch 520 that, in turn, has an output connected to a third band
translation switch 530. A cascade output of the first band
translation 510 is connected to the input of a fourth band
translation switch 540. The output of the fourth band translation
switch 540 is connected to the input of a fifth band translation
switch 550.
[0121] Each of the band translation switches, 510, 520, 530, 540,
and 550, can be the band translation switch of FIG. 4 and can
include on of the AGC amplifiers of FIGS. 2A-2C. Each of the band
translation switches, 510, 520, 530, 540, and 550, can be
configured similarly so the first band translation switch 510. In
the first band translation switch 510, an input VGA 512 receives
the input signal from LNB's. The VGA 512 typically has a low noise
figure, such that the noise figure of the band translation switch
510 from the input to a band translation output is below 3 dB, 4
dB, 5 dB, 6 dB, 8 dB, 10 dB, 12 dB, 14 dB, 15 dB, 20 dB, 25 dB, 30
dB, 35 dB or 40 dB. The noise figure of the band translation switch
510 from an input to the cascade output is typically closer to the
value of noise figure of the VGA 512 and can be, for example less
than 3 dB, 4 dB, 5 dB, 6 dB, 8 dB, 9 dB, 10 dB, 12 dB, 14 dB, 15
dB, 20 dB, 24 dB, 25 dB, 30 dB, 35 dB or 40 dB.
[0122] Additionally, the VGA 512 contributes to the IIP3 of the
band translation switch 510. The band translation switch 510
typically has an IIP3, measured from an input to an output of a
band translation device, of greater than -40, -30, -20, -10, -8,
-7, -6, -5, -4, -3, -2, -1, 0, +1, +2, +3, +4, +5, +6, +7, or +8,
+15, +20, +22, +25, +26, +27, +28, +29, or +30 dBm. Similarly, the
band translation switch 510 typically has an IIP3, measured from an
input to the cascade output of greater -10, -5, +1, +2, +3, +4, +5,
+6, +7, +8, +9, +10, +15, +20, +25, or +30 dBm.
[0123] The output of the VGA 512 is connected to a detector 514 and
N.times.M crosspoint switch 516. The detector 514 detects the power
output by the VGA 512 and provides a detected output that is
connected to the control input of the VGA 512. Additionally, the
output of the VGA 512 drives the cascade output of the first band
translation switch 510. The output of the N.times.M crosspoint
switch 516 is connected to a band translation device 518.
[0124] Although only one VGA 512 and detector 514 are shown in the
first band translation switch 510, more than one VGA 512 and
cascade output can be included in a band translation switch, as
shown in FIG. 4. Thus, the benefits of having an AGC function in
line with a signal distribution path can be provided to two signal
paths originating from a single VGA, for example 512, in a single
band translation switch, 510.
[0125] Each of the subsequent band translation switches 520, 530,
540 and 550, can also be connected to signal paths at their cascade
outputs and can likewise control the signal level and minimize the
subsequent noise contributions by utilizing an input AGC stage. The
fourth band translation switch 540 connected to a cascade output of
the first band translation switch 510 does not contribute noise to
the originating signal path and further controls noise
contributions from subsequent stages.
[0126] FIG. 6 is a flowchart of a signal distribution method 600
for use in a signal communication system, such as the satellite
communication system shown in FIG. 1. The method 600 begins at
block 602 where the distribution signals are received. The signals
can be received from a satellite, as in FIG. 1, or can be received
from an antenna configured to receive terrestrial signals, a cable,
or an optical link. Additionally, the signals can be received from
a combination of sources.
[0127] After receiving the signals to be distributed, the signals
are amplified, typically by a low noise amplifier, as shown in
block 610. Because the gain can be varied from a positive gain
value to a negative value, the amplifier may not be a low noise
amplifier under all operating condition and can be an attenuator
under some operating conditions. In this context, a negative gain
value refers to attenuation.
[0128] After amplification, the output power is measured, block
612. Because output power is measured after the gain stage, the
subsequent AGC function based on the measured output power can be
referred to as output referred AGC. The measured output power is
then used as a factor for varying the gain, block 614. As
previously discussed, the gain can typically be varied over a range
spanning positive gain to attenuation.
[0129] A cascade output is also provided, block 620, and can be
provided after the AGC function. The gain controlled signal can be
provided as a cascade output, as is shown in FIGS. 4 and 5.
[0130] Additionally, the signal is routed to a destination path,
block 630, such as by the N.times.M crosspoint switch shown in FIG.
4. The signal that is routed to the destination by the N.times.M
crosspoint switch is typically independent of the signal provided
to the cascade output. Thus, as is shown in the band translation
switch of FIG. 4, the output of the AGC section is provided as a
cascade output and is also provided to the input of the N.times.M
crosspoint switch to be routed to one of M possible distribution
paths.
[0131] The signal that is routed to a distribution path can then be
band translated, block 640. A band translation block can include a
mixer to selectively translate the signal from a first frequency
block to a second frequency block. Additionally, the band
translation block can be configured to have a pass through path
where the signal is not frequency translated.
[0132] Following band translation, the signal output from the band
translation block can be filtered, block 650, to remove noise and
unwanted frequency components that are outside of a band of
interest. Two or more of the filtered signals can be combined to
produce a composite signal, block 660. The two or more filtered
signals can originate from one or more independent signal
distribution paths. Each of the filtered signals can be in a
distinct frequency band. Alternatively, one or more of the filtered
signals can be in a frequency band that overlaps the frequency band
of another of the filtered signals.
[0133] Although the method 600 is shown with flow from one block to
the next, the order of the method blocks is not limited to the
order shown in FIG. 6.
[0134] The discussions provided above describes an AGC amplifier in
conjunction with a signal distribution device and method of signal
distribution using AGC in conjunction with a signal distribution
device. The AGC amplifier in combination with a signal distribution
device allows for insertion of in-line cascadable devices without
significantly degrading the system SNR. The AGC amplifier can also
include a cascade output to allow for creation of additional signal
distribution paths without the additional path significantly
degrading the performance of the signal path from which it branches
and/or the signal path it feeds. The cascade output can be used to
provide the AGC function without the subsequent signal distribution
function. This may be particularly advantageous, for example, when
the signal distribution function is a band translation
function.
[0135] The AGC amplifier in combination with a signal distribution
device can be inserted as an in-line device that minimizes
degradation of system SNR regardless of its location within the
signal distribution system. An output referred AGC function is used
to keep output power relatively constant over an input operating
range in order to maintain an optimal signal operating range within
the distribution system.
[0136] Electrical connections, couplings, and connections have been
described with respect to various devices or elements. The
connections and couplings can be direct or indirect. A connection
between a first and second device can be a direct connection or can
be an indirect connection. An indirect connection can include
interposed elements that can process the signals from the first
device to the second device.
[0137] Those of skill in the art will understand that information
and signals can be represented using any of a variety of different
technologies and techniques. For example, data, instructions,
commands, information, signals, bits, symbols, and chips that can
be referenced throughout the above description can be represented
by voltages, currents, electromagnetic waves, magnetic fields or
particles, optical fields or particles, or any combination
thereof.
[0138] Those of skill will further appreciate that the various
illustrative logical blocks, modules, circuits, and algorithm steps
described in connection with the embodiments disclosed herein can
be implemented as electronic hardware, computer software, or
combinations of both. To clearly illustrate this interchangeability
of hardware and software, various illustrative components, blocks,
modules, circuits, and steps have been described above generally in
terms of their functionality. Whether such functionality is
implemented as hardware or software depends upon the particular
application and design constraints imposed on the overall system.
Skilled persons can implement the described functionality in
varying ways for each particular application, but such
implementation decisions should not be interpreted as causing a
departure from the scope of the present invention.
[0139] The various illustrative logical blocks, modules, and
circuits described in connection with the embodiments disclosed
herein can be implemented or performed with a general purpose
processor, a digital signal processor (DSP), an application
specific integrated circuit (ASIC), a field programmable gate array
(FPGA) or other programmable logic device, discrete gate or
transistor logic, discrete hardware components, or any combination
thereof designed to perform the functions described herein. A
general-purpose processor can be a microprocessor, but in the
alternative, the processor can be any processor, controller,
microcontroller, or state machine. A processor can also be
implemented as a combination of computing devices, for example, a
combination of a DSP and a microprocessor, a plurality of
microprocessors, one or more microprocessors in conjunction with a
DSP core, or any other such configuration.
[0140] The steps of a method or algorithm described in connection
with the embodiments disclosed herein can be embodied directly in
hardware, in a software module executed by a processor, or in a
combination of the two. A software module can reside in RAM memory,
flash memory, ROM memory, EPROM memory, EEPROM memory, registers,
hard disk, a removable disk, a CD-ROM, or any other form of storage
medium. An exemplary storage medium can be coupled to the processor
such the processor can read information from, and write information
to, the storage medium. In the alternative, the storage medium can
be integral to the processor. The processor and the storage medium
can reside in an ASIC.
[0141] The above description of the disclosed embodiments is
provided to enable any person skilled in the art to make or use the
invention. Various modifications to these embodiments will be
readily apparent to those skilled in the art, and the generic
principles defined herein can be applied to other embodiments
without departing from the spirit or scope of the invention. Thus,
the invention is not intended to be limited to the embodiments
shown herein but is to be accorded the widest scope consistent with
the principles and novel features disclosed herein.
* * * * *