U.S. patent application number 11/952482 was filed with the patent office on 2009-06-11 for rf attenuation circuit.
This patent application is currently assigned to SYRACUSE RESEARCH CORPORATION. Invention is credited to John Dougherty, Greg Kliss, John Wiley.
Application Number | 20090146868 11/952482 |
Document ID | / |
Family ID | 40672437 |
Filed Date | 2009-06-11 |
United States Patent
Application |
20090146868 |
Kind Code |
A1 |
Dougherty; John ; et
al. |
June 11, 2009 |
RF ATTENUATION CIRCUIT
Abstract
An RF receiving circuit that selectively attenuates a received
RF signal before it reaches sensitive modifying devices, such as a
low noise amplifier or an analog to digital converter. The
receiving circuit includes a delay element upstream of its
attenuator so that high energy pulses of a short duration (for
example, less than 10 nanoseconds) can be effectively attenuated
despite coupler, detector, threshold and/or switch delays of the
attenuation related circuitry.
Inventors: |
Dougherty; John; (Liverpool,
NY) ; Wiley; John; (Marietta, NY) ; Kliss;
Greg; (Syracuse, NY) |
Correspondence
Address: |
BOND, SCHOENECK & KING, PLLC
ONE LINCOLN CENTER
SYRACUSE
NY
13202-1355
US
|
Assignee: |
SYRACUSE RESEARCH
CORPORATION
North Syracuse
NY
|
Family ID: |
40672437 |
Appl. No.: |
11/952482 |
Filed: |
December 7, 2007 |
Current U.S.
Class: |
342/175 |
Current CPC
Class: |
G01S 7/34 20130101; H03G
3/3036 20130101 |
Class at
Publication: |
342/175 |
International
Class: |
G01S 13/00 20060101
G01S013/00 |
Claims
1. An RF receiver circuit comprising: an antenna adapted to produce
an RF signal in response to electromagnetic waves; a delay element
directly electrically connected to said antenna so that said delay
element receives and delays the RF signal from said antenna; a PRD
electrically connected to said delay element so that said PRD
receives the delayed RF signal from said delay element and
selectively reduces the power of the RF signal; and a modifying
device electrically connected to said PRD so that said modifying
device receives the RF signal from said PRD.
2. The circuit of claim 1 further comprising a PRD controller
electrically connected to said antenna and adapted to control the
power reduction operation of said PRD based on the power of the RF
signal received from said antenna.
3. The circuit of claim 2 wherein: said PRD is characterized by a
PRD delay; said PRD controller is characterized by a PRD controller
delay; and the delay caused by said delay element is approximately
equal to the sum of the PRD delay and the PRD controller delay.
4. The circuit of claim 2 wherein said PRD comprises RF
switches.
5. The circuit of claim 4 wherein said PRD controller comprises a
tunnel diode detector and an RF switch controller amplifier.
6. The circuit of claim 2 wherein said PRD controller comprises a
coupler and is electrically connected to the antenna through the
coupler.
7. The circuit of claim 1 wherein said modifying device is an
LNA.
8. The circuit of claim 1 wherein said modifying device is an
analog to digital converter.
9. An RF receiver circuit comprising: an antenna adapted to produce
an RF signal in response to electromagnetic waves; a delay element
directly electrically connected to said antenna so that said delay
element receives and delays the RF signal from said antenna; at
least one RF switch(es) electrically connected to said delay
element so that said RF switch(es) receive the delayed RF signal
from said delay element and selectively attenuate the RF signal; an
RF switch controller electrically connected to said antenna and
adapted to control the attenuation operation of said RF switch(es)
based on the power of the RF signal received from said antenna,
with said RF switch controller comprising a tunnel diode detector
and a resistor, with said tunnel diode detector and said resistor
being electrically connected in parallel; a coupler adapted and
connected to electrically connect said RF switch controller to the
antenna so that said RF switch controller receives the RF signal
from said antenna; and a modifying device electrically connected to
said RF switches so that said modifying device receives the
attenuated RF signal from said RF switches.
10. The circuit of claim 9 wherein said RF switch controller
further comprises a capacitor connected in parallel with both said
resistor and said tunnel diode detector.
11. The circuit of claim 9 wherein said RF switch controller
further comprises a capacitor connected in series with said
resistor and in parallel with said tunnel diode detector.
12. The circuit of claim 9 wherein said RF switch controller
further comprises an RF switch controller amplifier.
13. The circuit of claim 9 wherein: said RF switches are
characterized by an RF switch delay; said RF switch controller and
said coupler are characterized by an RF switch controller delay;
and the delay caused by the delay element is approximately equal to
a sum of the RF switch delay and the RF switch controller
delay.
14. The circuit of claim 9 wherein the delay element comprises a
transmission line.
15. The circuit of claim 9 wherein said delay element comprises a
delay filter.
16. The circuit of claim 9 wherein said delay element is adapted to
cause a delay of less than 10 nanoseconds.
17. The circuit according to claim 9 further comprising an RF
radiation source located and adapted to generate the
electromagnetic waves received by the antenna.
18. The circuit of claim 17 wherein said RF radiation source
generates the RF radiation in the form of pulses of less than 10
nanoseconds in duration.
19. The circuit of claim 9 wherein the RF signal has a frequency of
greater than 300 MHz.
20. A radar device comprising: an RF radiation source adapted to
generate electromagnetic radar waves having a pulse time of less
than 10 nanoseconds and a frequency of greater than 300 MHz; an
antenna adapted and located to receive the radar waves and to
produce an RF signal in response to the electromagnetic waves; a
delay element directly electrically connected to said antenna so
that said delay element receives and delays the RF signal from said
antenna; at least one RF switch(es) electrically connected to said
delay element so that said RF switch(es) receive the delayed RF
signal from said delay element and selectively attenuate the RF
signal; an RF switch controller electrically connected to said
antenna and adapted to control the attenuation operation of said RF
switch(es) based on the power of the RF signal received from said
antenna, with said RF switch controller comprising: a tunnel diode
detector, a resistor, with said tunnel diode detector and said
resistor being electrically connected in parallel, a first
capacitor connected in parallel with both said resistor and said
tunnel diode detector, a second capacitor connected in series with
said resistor and in parallel with said tunnel diode detector, and
an RF switch controller amplifier; a coupler adapted and connected
to electrically connect said RF switch controller to the antenna so
that said RF switch controller receives the RF signal from said
antenna; and an LNA electrically connected to said RF switches so
that said LNA device receives the attenuated RF signal from said RF
switches.
Description
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0001] Not applicable.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to circuits for converting
received radio frequency signals ("RF signal", see definitions
section) signal into modified signals (see Definitions section) and
more particularly to radar receiver circuitry for converting
received radar RF signals into modified signals useful in
generating radar information.
[0004] 2. Description of the Related Art
[0005] It is conventional to convert radio waves into electrical RF
signals. Radios, radar, cell phones and other wireless
communication systems all do this. It is conventional to convert RF
signals into modified RF signals by the use of modifying devices.
One example of this is when a received RF signal is processed by a
low noise amplifier modifying device. Another example of this is
when an RF signal is processed by a modifying device into an
intermediate frequency ("IF") electrical signal. A couple of
conventional circuits for processing RF signals will now be
discussed.
[0006] U.S. Pat. No. 6,191,725 ("Lavoie") at FIG. 1 ("FIG. 1
Lavoie") discloses an automatic gain control circuit for
electromagnetic wave receiving systems, such as radar warning
receivers. In FIG. 1 Lavoie, a radar pulse is received, presumably
as an RF signal (Lavoie does not disclose this part of the FIG. 1
Lavoie system in detail). The RF signal is converted to an IF
signal, presumably by modifying it with a low noise amplifier
("LNA") and/or other appropriate modifying device(s) (again, Lavoie
does not disclose this part of the FIG. 1 Lavoie system in detail).
The converted IF signal of Lavoie then passes through an analog
delay line to a fast programmable attenuator, and then to an
amplifier. The fast programmable attenuator of FIG. 1 Lavoie is
controlled by control circuitry based on a comparison of amplitude
of the received IF signal to an appropriate reference level. The
analog delay line provides the programmable attenuator with time to
settle. It is noted that the programmable attenuator of FIG. 1
Lavoie does not provide protection to circuit components upstream
of the programmable attenuator, such as the modifying device(s)
that would be required for FIG. 1 Lavoie to convert a received RF
pulse into a corresponding IF pulse. Also, the programmable
attenuator of FIG. 1 Lavoie attenuates solely on the basis of the
amplitude of the IF signal, and does not account for the frequency
or duration of a pulse present in the IF signal.
[0007] U.S. Pat. No. 7,088,794 ("Nichols") discloses an automatic
gain control RF signal processor for receiver systems, such as
radar intercept receivers. As shown at FIGS. 1 and 2 of Nichols, in
the Nichols circuitry, an electrical signal passes through the
following devices in the following order: (i) any modifying
device(s) necessary to convert the received RF signal into an
analog IF input signal (see left hand side of FIG. 1 of Nichols);
(ii) an attenuator; (iii) a fixed amplifier; (iv) a bandpass
filter; (v) an analog to digital converter; and (vi) a digital
delay. The digital delay is used so that the front edge of the
signal is not missed due to latency in the decision-making process
within the threshold and control logic. It is noted that the
delayed portion of the signal that passes through the digital delay
is not attenuated after it has been delayed because the attenuator
is upstream of the delay in the Nichols circuitry. It is further
noted that the modifying device(s) needed to converted the RF
signal presumably received in Nichols into the analog input signal
shown at the left side of FIG. 1 in Nichols are not protected by
the attenuator of Nichols because these devices would be upstream
of the attenuator and therefore not subject to the signal
attenuation it provides.
[0008] Description Of the Related Art Section Disclaimer: To the
extent that specific publications are discussed above in this
Description of the Related Art Section, these discussions should
not be taken as an admission that the discussed publications (for
example, published patents) are prior art for patent law purposes.
For example, some or all of the discussed publications may not be
sufficiently early in time, may not reflect subject matter
developed early enough in time and/or may not be sufficiently
enabling so as to amount to prior art for patent law purposes. To
the extent that specific publications are discussed above in this
Description of the Related Art Section, they are all hereby
incorporated by reference into this document in their respective
entirety(ies).
BRIEF SUMMARY OF THE INVENTION
[0009] The present invention is directed to a circuit where an RF
signal first passes through a delay circuit and then passes through
a power reducing device ("PRD", see Definitions section) before it
passes through any modifying devices. Some embodiments of the
present invention are more specifically directed to a circuit where
an RF signal first passes through a delay circuit and then passes
through a power reducing device before it passes through an RF
signal to IF signal conversion device (see definitions section).
Some embodiments of the present invention are more specifically
directed to a circuit where an RF signal first passes through a
delay circuit and then passes through a power reducing device
before it passes through a low noise amplifier (see definitions
section). Some embodiments of the present invention are adapted for
RF signals at frequencies above several hundred MHz. Some
embodiments of the present invention are adapted for RF signals
with short pulse widths of less than 10 nanoseconds.
[0010] In some embodiments of the present invention, the power
reducing circuitry is characterized by a response time and the
delay of the delay circuit is approximately equal to the response
time of the power reducing circuitry. In some embodiments of the
present invention, the power reducing circuitry includes RF
switches, an RC network, a tunnel diode detector and a coupler.
[0011] Various embodiments of the present invention may exhibit one
or more of the following objects, features and/or advantages:
[0012] (i) useful in a radar receiver that uses very large pulses
of energy, such as through the wall radar;
[0013] (ii) useful in a radar receiver that uses very short pulses
of energy;
[0014] (iii) prevents damage to radar receiver circuitry, such as
low noise amplifiers;
[0015] (iv) improves performance of radar receiver circuitry;
[0016] (v) dramatically attenuates powerful, unwanted signals;
[0017] (vi) prevents analog to digital converter saturation;
[0018] (vi) prevents damage to the front end of a wideband or ultra
wideband radar or communication system receiver;
[0019] (vii) circuitry potentially has other uses in the fields of
medical imaging, optics, diagnostic electronics and/or measurement
electronics;
[0020] (viii) reduces the magnitude of very short duration (for
example, less than 10 nanosecond), high energy received pulses;
[0021] (ix) performs a high speed limiting function at high
frequency above several hundred Mhz; and
[0022] (x) limits amplitude of an RF signal so that it is within
the designed amplitude range of relatively inexpensive RF signal
processing components (for example, amplifiers and analog to
digital converters).
[0023] According to one aspect of the present invention, an RF
receiver circuit includes an antenna, a delay element, a PRD and a
modifying device. The antenna is adapted to produce an RF signal in
response to electromagnetic waves. The delay element is directly
electrically connected (see definitions section) to the antenna so
that the delay element receives and delays the RF signal from the
antenna. The PRD is electrically connected to the delay element so
that the PRD receives the delayed RF signal from the delay element
and selectively reduces the power of the RF signal. The modifying
device is electrically connected to the PRD so that the modifying
device receives the RF signal from the PRD.
[0024] According to a further aspect of the present invention, an
RF receiver circuit includes an antenna, a delay element, an RF
switch, an RF switch controller a coupler and a modifying device.
The antenna is adapted to produce an RF signal in response to
electromagnetic waves. The delay element is directly electrically
connected to the antenna so that the delay element receives and
delays the RF signal from the antenna. The RF switch is
electrically connected to the delay element so that the RF switch
receives the delayed RF signal from the delay element and
selectively attenuates the RF signal. The RF switch controller is
electrically connected to the antenna and is adapted to control the
attenuation operation of the RF switch based on the power of the RF
signal received from the antenna. The RF switch controller includes
a tunnel diode detector and a resistor. The tunnel diode detector
and the resistor are electrically connected in parallel. The
coupler is adapted and connected to electrically connect the RF
switch controller to the antenna so that the RF switch controller
receives the RF signal from the antenna. The modifying device is
electrically connected to the RF switch so that the modifying
device receives the attenuated RF signal from the RF switch.
[0025] According to a further aspect of the present invention,
radar device includes an RF radiation source, an antenna, a delay
element, an RF switch, an RF switch controller, a coupler and an
LNA. The RF radiation source is adapted to generate electromagnetic
radar waves having a pulse time of less than 10 nanoseconds and a
frequency of greater than 300 MHz. The antenna is adapted and
located to receive the radar waves and to produce an RF signal in
response to the electromagnetic waves. The delay element is
directly electrically connected to the antenna so that the delay
element receives and delays the RF signal from the antenna. The RF
switch is electrically connected to the delay element so that the
RF switch receives the delayed RF signal from the delay element and
selectively attenuates the RF signal. The RF switch controller is
electrically connected to said antenna and adapted to control the
attenuation operation of the RF switch based on the power of the RF
signal received from the antenna. The RF switch controller includes
a tunnel diode detector, a resistor, a first capacitor, a second
capacitor and an RF switch controller amplifier. The resistor and
the tunnel diode detector are electrically connected in parallel.
The first capacitor is connected in parallel with both the resistor
and the tunnel diode detector. The second capacitor is connected in
series with the resistor and in parallel with the tunnel diode
detector. The coupler is adapted and connected to electrically
connect the RF switch controller to the antenna so that the RF
switch controller receives the RF signal from the antenna. The LNA
is electrically connected to the RF switch so that the LNA device
receives the attenuated RF signal from the RF switch.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The present invention will be more fully understood and
appreciated by reading the following Detailed Description in
conjunction with the accompanying drawings, in which:
[0027] FIG. 1 is a schematic of a circuit according to a first
embodiment of the present invention; and
[0028] FIG. 2 is a schematic of a circuit according to a second
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0029] FIG. 1 shows an RF receiver circuit 100 including antenna
102; delay element 104; PRD controller 106; PRD 108; and modifying
devices 110. The antenna may be any type of antenna now known or to
be developed in the future for converting RF electromagnetic waves
into an RF signal. The RF signal generated by the antenna is sent
to the delay element and the PRD controller. The delay element may
be any type of circuitry for delaying a signal now known or to be
developed in the future. The PRD controller may be hardware and/or
software based. The PRD controller sends a control signal 107 to
the PRD based on the amount of power in the RF signal. If the RF
signal is sufficiently powerful, then the PRD controller will
control the PRD to reduce the power of the RF signal. The PRD
controller is characterized by a PRD controller delay.
[0030] The PRD may be any type of PRD now known or to be developed
in the future. The PRD is characterized by a PRD delay. A total
delay is the sum of the PRD controller delay and the PRD delay. The
delay element should be designed to delay the RF signal for a time
period approximately equal to the total delay. Because the PRD
receives the RF signal from the delay element on a delayed basis it
can respond in time to reduce the power of the RF signal before it
communicates the RF signal to the modifying devices. In this way,
RF receiver circuit 100 protects the modifying devices from
degraded performance and/or damage.
[0031] FIG. 2 shows a preferred RF receiver circuit 200 including
antenna 202; delay element 204; RF switches 208; LNA 10; coupler
212; resistor 214; capacitor 216; tunnel diode detector ("detector
diode") 218; capacitor 220; and RF switch controller amplifier
("comparator amp") 222.
[0032] The coupler preferably provides adequate isolation from the
input pulse so that the maximum power level seen by the detector
diode is within its input operating range.
[0033] The delay element is preferably a transmission line, delay
filter and/or similar device. The delay element is preferably
chosen so that incoming pulses are delayed long enough to provide
sufficient time for the processing components to react, especially
the comparator amp, the tunnel diode detector, and the RF
switches.
[0034] The capacitors and resistor used in this circuit are
selected to match the characteristic impedance of the upstream
signals. The resistance value for the resistor is preferably the
characteristic impedance of the antenna and transmission line. For
most typical systems, this would be 50 ohms. The preferred
capacitor values depend on the characteristics of the detector
diode selected. These values are preferably selected so that the
total impedance of the network made up by the detector diode and
the two capacitors would be the same as the impedance of the
resistor (normally 50 ohms).
[0035] The RF switches selectively switch on and off to selectively
attenuate portions of the RF signal that are sufficiently high in
power such that they would otherwise damage the LNA and/or other
modifying devices in the radar receiver. The resistor and
capacitors form an RC network. The coupler, RC network, tunnel
diode detector and RF switch controller amplifier work together to
control the RF switches to switch on and off and selectively
attenuate the RF signal by control signal 207.
[0036] The coupler, RC network, tunnel diode detector and
comparator amp characterized by a controller delay. The RF switches
are characterized by an RF switch delay. The total delay is the sum
of the controller delay and the RF switch delay. The delay element
should be designed to delay the RF signal for a time period
approximately equal to the total delay.
[0037] Because the RF switches receive the RF signal from the delay
element on a delayed basis they can respond in time to reduce the
power of the RF signal before it communicates the RF signal to the
modifying devices. For example, in circuit 200 the delay element
delays the RF signal for approximately 5 nanoseconds. This is an
appropriate value for radar receiver systems with short (for
example, less than 10 nanosecond) received pulses having high
energy and operating frequencies of several hundred MHz or more.
The 5 nanosecond delay means that little or none of the high energy
pulse will be passed to the LNA and/or other modifying devices
before the RF switches can responds by attenuating the high power
RF signal down to a level consistent with good performance and
prevention of component damage.
[0038] Now the reasons that preferred circuits according to the
present invention can perform effectively at operating frequencies
of several hundred MHz and above. Conventional limiting circuits
generally rely on a single solid state limiter device (usually a
Schottky or Pin-Diode). These devices passively detect and then
attenuate RF signals above a set power level, but they all take
some time to react. For this reason, very short pulses (less than a
few nanoseconds) are able to pass right through before the device
can begin attenuating. On the other hand, preferred circuits
according to the present invention are able to stop these pulses by
coupling off some of the power at the input, detect the existence
of a high power pulse with a detector diode (which doesn't need to
attenuate the signal but instead has to only trigger the
comparator, so it can operate much faster than a limiter) and
trigger the comparator amplifier which activates a high speed RF
switch that will attenuate the signal path before the high speed
pulse has had a chance to pass through the delay line. If the power
level is beneath the threshold of the detector diode, the RF switch
would not be activated and therefore the signal would come out of
the delay line and pass through the circuit untouched. Simply put,
the input pulse is being delayed while the detector circuit decides
if the switches should be thrown or not.
[0039] If the switches need to be thrown, the delay line affords
the processing circuit a chance to react before the pulse reaches
the output. This circuit will work at all RF frequencies (assuming
the components are selected to handle the frequencies of interest).
Due to the physics of the problem, pulses this short in duration
can not exist at frequencies below several hundred MHz.
DEFINITIONS
[0040] The following definitions are provided to facilitate claim
interpretation and claim construction:
[0041] Present invention: means at least some embodiments of the
present invention; references to various feature(s) of the "present
invention" throughout this document do not mean that all claimed
embodiments or methods include the referenced feature(s).
[0042] First, second, third, etc. ("ordinals"): Unless otherwise
noted, ordinals only serve to distinguish or identify (e.g.,
various members of a group); the mere use of ordinals implies
neither a consecutive numerical limit nor a serial limitation.
[0043] Electrically connected: means either directly electrically
connected, or indirectly electrically connected, such that
intervening elements are present; in an indirect electrical
connection, the intervening elements may include inductors and/or
transformers.
[0044] Directly electrically connected: electrically connected
without any intervening elements that substantially change the
electrical characteristics of the electrical energy and/or signal
passing between the directly electrically connected elements.
[0045] RF signal: any electrical signal having a frequency or rate
of oscillation such that it could produce and or have been
generated by radio waves in an electromagnetic field; the range of
radio frequencies for electromagnetic fields extends through at
least the range of 3 Hz to 300 GHz; some modified signals (see
Definition of "modified signal") may also be considered as RF
signals depending primarily upon whether the frequency of the
modified signal.
[0046] Modified signal: an RF signal that has been modified in some
way by a modifying device to make it more useful.
[0047] Modifying device: any circuitry that makes an RF signal into
a modified signal, including, but not necessarily limited to,
amplifiers, low noise amplifiers, filters, RF signal to IF signal
converters and/or mixers; generally speaking, modifying devices can
suffer degraded performance or even damage if subjected to an RF
input signal having too much power.
[0048] Power reducing device ("PRD"): any device that can decreases
the power of an RF pulse, including, but not necessarily limited to
limiters and/or attenuators.
[0049] To the extent that the definitions provided above are
consistent with ordinary, plain, and accustomed meanings (as
generally shown by documents such as dictionaries and/or technical
lexicons), the above definitions shall be considered supplemental
in nature. To the extent that the definitions provided above are
inconsistent with ordinary, plain, and accustomed meanings (as
generally shown by documents such as dictionaries and/or technical
lexicons), the above definitions shall control. If the definitions
provided above are broader than the ordinary, plain, and accustomed
meanings in some aspect, then the above definitions shall be
considered to broaden the claim accordingly.
[0050] To the extent that a patentee may act as its own
lexicographer under applicable law, it is hereby further directed
that all words appearing in the claims section, except for the
above-defined words, shall take on their ordinary, plain, and
accustomed meanings (as generally shown by documents such as
dictionaries and/or technical lexicons), and shall not be
considered to be specially defined in this specification. In the
situation where a word or term used in the claims has more than one
alternative ordinary, plain and accustomed meaning, the broadest
definition that is consistent with technological feasibility and
not directly inconsistent with the specification shall control.
[0051] Unless otherwise explicitly provided in the claim language,
steps in method steps or process claims need only be performed in
the same time order as the order the steps are recited in the claim
only to the extent that impossibility or extreme feasibility
problems dictate that the recited step order (or portion of the
recited step order) be used. This broad interpretation with respect
to step order is to be used regardless of whether the alternative
time ordering(s) of the claimed steps is particularly mentioned or
discussed in this document.
* * * * *