U.S. patent application number 14/078462 was filed with the patent office on 2014-03-13 for high dynamic range receiver front-end with q-enhancement.
This patent application is currently assigned to QUALCOMM Incorporated. The applicant listed for this patent is QUALCOMM Incorporated. Invention is credited to Bruce A. Judson, Cong T. Nguyen.
Application Number | 20140073281 14/078462 |
Document ID | / |
Family ID | 42813455 |
Filed Date | 2014-03-13 |
United States Patent
Application |
20140073281 |
Kind Code |
A1 |
Judson; Bruce A. ; et
al. |
March 13, 2014 |
HIGH DYNAMIC RANGE RECEIVER FRONT-END WITH Q-ENHANCEMENT
Abstract
A preselect circuit maintains the dynamic range of a received RF
input signal during bandpass filtering of the received RF input
signal. The preselect circuit includes a Q-deficient passive
bandpass filter for coupling to an antenna to receive a received RF
input signal. The preselect circuit further includes a
Q-enhancement circuit coupled to the Q-deficient passive bandpass
filter, wherein the Q-enhancement circuit increases a Q-value of
the Q-deficient passive bandpass filter by compensating for
resistive inductive losses in the bandpass filter.
Inventors: |
Judson; Bruce A.; (San Luis
Obispo, CA) ; Nguyen; Cong T.; (San Diego,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
QUALCOMM Incorporated |
San Diego |
CA |
US |
|
|
Assignee: |
QUALCOMM Incorporated
San Diego
CA
|
Family ID: |
42813455 |
Appl. No.: |
14/078462 |
Filed: |
November 12, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12490268 |
Jun 23, 2009 |
8606211 |
|
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14078462 |
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Current U.S.
Class: |
455/307 |
Current CPC
Class: |
H03H 11/52 20130101;
H03F 2200/241 20130101; H03H 7/1775 20130101; H04B 1/109 20130101;
H04B 1/1036 20130101; H03F 3/195 20130101; H03H 7/03 20130101 |
Class at
Publication: |
455/307 |
International
Class: |
H04B 1/10 20060101
H04B001/10 |
Claims
1. A method, comprising: receiving an RF input signal from an
antenna; passively bandpass filtering the RF input signal in a
Q-deficient passive bandpass filter prior to the RF input signal
being subjected to any active circuit elements; and enhancing a
deficient Q-value of the Q-deficient passive bandpass filter.
2. The method of claim 1, wherein the passively bandpass filtering
the RF input signal further comprises maintaining a dynamic range
of the RF input signal during the passively bandpass filtering.
3. The method of claim 1, further comprising impedance transforming
the RF input signal prior to passively filtering the RF input
signal.
4. A circuit, comprising: means for receiving an RF input signal
from an antenna; means for passively bandpass filtering the RF
input signal in a Q-deficient passive bandpass filter prior to the
RF input signal being subjected to any active circuit elements; and
means for enhancing a deficient Q-value of the Q-deficient passive
bandpass filter.
5. The method of claim 4, further comprising means for impedance
transforming the RF input signal prior to passively filtering the
RF input signal.
Description
BACKGROUND
[0001] 1. Field
[0002] This disclosure relates generally to wireless communication
devices, and more specifically to improving the dynamic range on
the input of a receiver.
[0003] 2. Background
[0004] Communication receivers receive both desirable and
undesirable signals on their inputs. Signal selection filters for a
receiver's "front-end", such as preselect filters, have been
designed for passing the desired signals relatively unfiltered and
attenuating the undesired signals. The effectiveness of signal
selection by a preselector is determined by the Q-value of a
preselector's passband filter. Generally larger components in a
passband filter may provide an adequate Q-value for providing the
desired passband filtering. Conventionally, if the Q-value was
inadequate, then larger, higher Q-value components were substituted
until the preselector's passband filter provided adequate signal
rejection.
[0005] As communication receivers became portable and mobile,
various components in the receiver, including the receiver's
front-end, have been integrated. Design tradeoffs exist between
integration of receiver front-end components, such as passband
filters, and the reduction in the effectiveness or quality of
signal selection and rejection based upon the reduction of the
Q-value of the filter components.
[0006] While it is desirable to further integrate the components of
a receiver, attempts to further integrate bandpass filters results
in inferior performance of the system. System requirements of
narrow bandwidths, low distortion and the need for low-power
consumption run counter to conventional integration approaches.
[0007] Further integration attempts have placed buffer components
at the beginning of the receiver front-end resulting in a reduction
of the dynamic range of the receiver front-end since buffer
components include active devices which operate linearly only over
a defined input signal dynamic range. Accordingly, when an RF input
signal received at the receiver front-end includes undesired
signals (jammer signals) of unpredictable magnitudes, then the
active devices on a receiver's front-end may saturate, generate
intermodulation signals and other non-linearities which may distort
the desired input signal.
[0008] Larger off-chip circuit elements have allowed system
requirements to be attained. However, larger-dimensioned circuit
elements inhibit reductions in the overall dimensions of the device
as well as contributes to increased device costs. Integration
attempts may reduce the overall circuit component dimensions,
however, such designs include shortcomings including difficulties
achieving high operating frequencies with narrow bandwidths (i.e.,
high Q values) and a fundamental limitation on the dynamic range at
high Q values.
[0009] Different receiver architectures (e.g., direct conversion or
low IF designs) have attempted to overcome further integration
shortcomings of passive components, however, the limitations on the
dynamic range is prohibitive. For example, moving the channel
select filtering to baseband results in amplifiers (e.g., Low Noise
Amplifiers (LNAs)) and mixer circuits processing the entire RF
spectrum including jamming (blocking) signals, resulting in the
generation of further spurious responses and further desensitizing
the receiver.
[0010] Improvements to poor dynamic range are possible by
undesirably increasing the current consumption of circuit elements.
For portable or mobile receivers, improving the dynamic range by
increasing power consumption is undesirable and impractical. As
stated, a bandpass filter includes passive elements (e.g., L/C,
transmission lines, acoustic resonators) which in a bulk
manufacturing quantities and integrated implementations results in
very low Q-values for the bandpass filter. Accordingly, there is a
need in the art for a receiver having a receiver front-end that
exhibits high dynamic range on its inputs.
SUMMARY
[0011] Embodiments disclosed herein address the above stated needs
by providing a preselect circuit exhibiting a high dynamic range
during bandpass filtering. In one aspect of the disclosed
embodiments, a preselect circuit includes a Q-deficient passive
bandpass filter for coupling to an antenna to receive a received RF
input signal. The preselect circuit further includes a
Q-enhancement circuit coupled to the Q-deficient passive bandpass
filter, wherein the Q-enhancement circuit increases a Q-value of
the Q-deficient passive bandpass filter by compensating for
resistive inductive losses in the bandpass filter.
[0012] In another aspect of the disclosed embodiments, a receiver
includes a preselector and mixer coupled to the preselect to
down-convert a preselect filtered RF input signal. The preselector
includes a Q-deficient passive bandpass filter for coupling to an
antenna to receive a received RF input signal and a Q-enhancement
circuit coupled to the Q-deficient passive bandpass filter. The
Q-enhancement circuit is configured to increase a Q-value of the
Q-deficient passive bandpass filter by compensating for resistive
inductive losses in the bandpass filter.
[0013] In another aspect of the disclosed embodiments, a wireless
communication device includes an antenna and a receiver coupled to
the antenna. The receiver includes a Q-deficient passive bandpass
filter for coupling to the antenna to receive a received RF input
signal and a Q-enhancement circuit coupled to the Q-deficient
passive bandpass filter. The Q-enhancement circuit is configured to
increase a Q-value of the Q-deficient passive bandpass filter by
compensating for resistive inductive losses in the bandpass
filter.
[0014] In another aspect of the disclosed embodiments, a method for
preselecting a received input signal includes receiving an RF input
signal from an antenna and passively bandpass filtering the RF
input signal in a Q-deficient passive bandpass filter prior to the
RF input signal being subjected to any active circuit elements. The
method further includes enhancing a deficient Q-value of the
Q-deficient passive bandpass filter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 illustrates an example of a communications system
that supports a number of users and is capable of implementing at
least some aspects of the embodiments discussed herein.
[0016] FIG. 2 is a block diagram of a transmitter system and a
receiver system in a wireless communication system capable of
implementing at least some aspects of the embodiments discussed
herein.
[0017] FIG. 3 is a block diagram illustrating an RF section of a
wireless communication device including a preselector capable of
implementing at least some aspects of the embodiments discussed
herein.
[0018] FIG. 4 is a circuit diagram illustrating a preselector
including an active element at the input.
[0019] FIG. 5 is a circuit diagram illustrating a preselector
including passive elements at an input capable of implementing at
least some aspects of the embodiments discussed herein.
[0020] FIG. 6 is a flow diagram illustrating a method for receiving
an input signal capable of implementing at least some aspects of
the embodiments discussed herein.
DETAILED DESCRIPTION
[0021] Various embodiments are now described with reference to the
drawings, wherein like reference numerals are used to refer to like
elements throughout. In the following description, for purposes of
explanation, numerous specific details are set forth in order to
provide a thorough understanding of one or more embodiments. It may
be evident, however, that such embodiment(s) may be practiced
without these specific details. In other instances, well-known
structures and devices are shown in block diagram form in order to
facilitate describing one or more embodiments.
[0022] The word "exemplary" is used herein to mean "serving as an
example, instance, or illustration." Any embodiment described
herein as "exemplary" is not necessarily to be construed as
preferred or advantageous over other embodiments.
[0023] Note that the exemplary embodiment is provided as an
exemplar throughout this discussion, however, alternate embodiments
may incorporate various aspects without departing from the scope of
the present embodiments. Specifically, one embodiment is applicable
to a data processing system, a wireless communication system, a
mobile IP network and any other system desiring to receive and
process a wireless signal.
[0024] Circuits and devices described herein may operate in
wireless communication systems. Wireless communication systems are
widely deployed to provide various types of communication such as
voice, data, and so on. These systems may be based on Code
Division-Multiple Access (CDMA), Time Division-Multiple Access
(TDMA), or some other modulation techniques. A CDMA system provides
certain advantages over other types of systems, including increased
system capacity.
[0025] A wireless communication system, including the circuits and
devices described herein, may be designed to support one or more
standards such as the "TIA/EIA/IS-95-B Mobile Station-Base Station
Compatibility Standard for Dual-Mode Wideband Spread Spectrum
Cellular System" referred to herein as the IS-95 standard, the
standard offered by a consortium named "3rd Generation Partnership
Project" referred to herein as 3GPP, and embodied in a set of
documents including Document Nos. 3GPP TS 25.211, 3GPP TS 25.212,
3GPP TS 25.213, and 3GPP TS 25.214, 3GPP TS 25.302, referred to
herein as the W-CDMA standard, the standard offered by a consortium
named "3rd Generation Partnership Project 2" referred to herein as
3GPP2, and TR-45.5 referred to herein as the cdma2000 standard,
formerly called IS-2000 MC.
[0026] The circuits, devices, systems and methods described herein
may be used with High Data Rate (HDR) communication systems. An HDR
communication system may be designed to conform to one or more
standards such as the "cdma2000 High Rate Packet Data Air Interface
Specification," 3GPP2 C.S0024-A, Version 1, March 2004, promulgated
by the consortium "3rd Generation Partnership Project 2." The
contents of the aforementioned standard are incorporated by
reference herein.
[0027] An HDR subscriber station, which may be referred to herein
as an Access Terminal (AT), may be mobile or stationary, and may
communicate with one or more HDR base stations, which may be
referred to herein as Modem Pool Transceivers (MPTs). An access
terminal transmits and receives data packets through one or more
modem pool transceivers to an HDR base station controller, which
may be referred to herein as a Modem Pool Controller (MPC). Modem
pool transceivers and modem pool controllers are parts of a network
called an access network. An access network transports data packets
between multiple access terminals. The access network may be
further connected to additional networks outside the access
network, such as a corporate intranet or the Internet, and may
transport data packets between each access terminal and such
outside networks. An access terminal may be any data device that
communicates through a wireless channel or through a wired channel,
for example using fiber optic or coaxial cables. An access terminal
may further be any of a number of types of devices including but
not limited to PC card, compact flash, external or internal modem,
or wireless or landline phone. The communication channel through
which the access terminal sends signals to the modem pool
transceiver is called a reverse channel. The communication channel
through which a modem pool transceiver sends signals to an access
terminal is called a forward channel.
[0028] FIG. 1 illustrates an example of a communications system 100
that supports a number of users and is capable of implementing at
least some aspects of the embodiments discussed herein. Any of a
variety of algorithms and methods may be used to schedule
transmissions in system 100. System 100 provides communication for
a number of cells 102A-102G, each of which is serviced by a
corresponding base station 104A-104G, respectively.
[0029] Wireless communication devices 106 in the coverage area may
be fixed (i.e., stationary) or mobile. As shown in FIG. 1, various
wireless communication devices 106 are dispersed throughout the
system. Each wireless communication device 106 communicates with at
least one and possibly more base stations 104 on a forward link and
a reverse link at any given moment depending on, for example,
whether soft handoff is employed or whether the terminal is
designed and operated to (concurrently or sequentially) receive
multiple transmissions from multiple base stations.
[0030] The forward link refers to transmission from a base station
104 to a wireless communication device 106, and the reverse link
refers to transmission from a wireless communication device 106 to
a base station 104. In FIG. 1, base station 104A transmits data to
wireless communication devices 106A and 106J on a forward link;
similarly base station 104B transmits data to wireless
communication devices 106B and 106J, base station 104C transmits
data to wireless communication device 106C, and so on.
[0031] FIG. 2 is a block diagram of a transmitter system 210 and a
receiver system 250 in a wireless communication system 200. At
transmitter system 210, traffic data is sent (typically in packets
that may be of variable lengths) from a data source 212 to a
Transmit (TX) data processor 214. TX data processor 214 then
formats and codes the traffic data to provide coded data. The coded
data is then modulated (i.e., symbol mapped) based on one or more
modulation schemes (e.g., BPSK, QSPK, M-PSK, or M-QAM) to provide
modulation symbols (i.e., modulated data).
[0032] A Transmitter (TMTR) unit 216 then converts the modulated
data into one or more analog signals and further amplifies,
filters, quadrature modulates, and upconverts the analog signals to
generate a modulated signal. The modulated signal is then
transmitted via an antenna 218 and over a wireless communication
link to one or more receiver systems.
[0033] At receiver system 250, the transmitted modulated signal is
received by an antenna 252 and provided to a receiver (RCVR) 254.
Within receiver 254, the received signal is conditioned (e.g.,
filter, amplified, frequency downconverted, and quadrature
downconverted) and the conditioned signal is further digitized to
provide ADC samples. The Analog-to-Digital Converter (ADC) samples
may further be digitally pre-processed within receiver 254 to
provide data samples. Receiver 254 includes a preselector,
described below, in accordance with various aspects of the
embodiments described herein.
[0034] A Receive (RX) data processor 256 then receives and
processes the data samples to provide decoded data, which is an
estimate of the transmitted data. The processing by RX data
processor 256 may include, for example, equalization, demodulation,
deinterleaving, and decoding. The processing at RX data processor
256 is performed in a manner that is complementary to the
processing performed at TX data processor 214. The decoded data is
then provided to a data sink 258.
[0035] A controller 260 directs the operation at the receiver
system. A memory unit 262 provides storage for program codes and
data used by controller 260 and possibly other units within the
receiver system.
[0036] The signal processing described above supports transmissions
of various types of traffic data (e.g., voice, video, packet data,
and so on) in one direction from the transmitter system to the
receiver system. A bi-directional communication system supports
two-way data transmission. The processing shown in FIG. 2 can
represent the forward link (i.e., downlink) processing in a CDMA
system, in which case, transmitter system 210 can represent a base
station and receiver system 254 can represent a terminal. The
signal processing for the reverse link (i.e., uplink) is not shown
in FIG. 2 for simplicity.
[0037] FIG. 3 is a block diagram of one aspect illustrating an
exemplary RF section of a wireless communication device 300
including the receive system 250 of FIG. 2. Wireless communication
device 300 may be any of a variety of mobile or stationary devices
with wireless capabilities, such as a cellular radiotelephone,
satellite phone, smart phone, personal digital assistant (PDA),
mobile or desktop computer, digital video or audio device, gaming
console, television console, a set top box, or any other device
equipped for wireless communication.
[0038] As shown in FIG. 3, device 300 includes an antenna 352 that
transmits and receives wireless RF signals. A duplexer 314 couples
RX signals (RX SIGNAL) received by antenna 352 to a receiver 354,
and couples TX output signals (TX SIGNAL) generated by a
transmitter 318 to antenna 352. In the example of FIG. 3, receiver
354 includes preselector 320, low noise amplifier (LNA) 333, mixer
324, local oscillator (LO) 326, and a filter 330. Transmitter 318
includes a power amplifier 328 that amplifies an RF output signal
to produce a TX RF signal for transmission via duplexer 314 and
antenna 352. Transmitter 318 also may include a modem,
digital-to-analog converter, mixer and filter circuitry (not shown)
to modulate and filter the output signal, and up-convert the signal
from a baseband to a transmit band.
[0039] In receiver 354, preselector 320 filters and amplifies the
RX signal and is further described below. In receiver 354, LNA 322
amplifies the RX signal. LNA 322 may be a differential amplifier
producing differential output signals. Mixer 324 may be a wideband
mixer that multiplies the amplified, signal from preselector 320
with the RX LO frequency to down-convert the desired RX signal to
baseband, thereby producing an RX baseband signal. Filter 330
filters the RX baseband signal to reduce the TX leakage signal and
thereby reduce undesirable distortion. Filter 330 may provide
further filtering (i.e., a notch frequency filter) at which the TX
signal is strongly attenuated. Filter 330 may be configured such
that the notch frequency generally corresponds to the offset
frequency of the down-converted TX leakage signal relative to the
center frequency (e.g., 0 Hz) of the baseband. Filter 330 may also
be configured to substantially reject frequencies outside the
desired baseband. Receiver 354 may further include an
analog-to-digital converter and modem (not shown) to demodulate and
decode the desired RX signal.
[0040] Antenna 352 may receive a RX signals (RX SIGNAL) including
both a desired signal and a jammer signal, as shown in FIG. 3.
Hence, preselector 320 may receive an RX signal including the
desired signal and possibly the jammer signal, as well as the TX
leakage signal coupled from the transmit path via duplexer 314.
Preselector 320 filters and amplifies this combined RX signal to
produce an amplified RF signal. The TX leakage signal may produce
second order distortion and cross modulation distortion (XMD). The
jammer signal is an undesired signal that may correspond to a
signal generated from a nearby source such as a wireless
transmission station. In some cases, a jammer signal may have an
amplitude that is much higher than that of the desired signal and
may be located close in frequency to the desired signal. The TX
leakage signal also may have a large amplitude relative to the
desired signal because the transmit signal produced by power
amplifier 328 is often much larger in amplitude than the desired
signal.
[0041] The TX leakage signal is outside the RX band. However, TX
leakage signal still may cause undesirable distortion. For example,
any non-linearity in preselector 320 can cause the modulation of TX
leakage signal to be transferred to the narrow-band jammer,
resulting in a widened spectrum around the jammer. This spectral
widening is referred to as cross modulation distortion (XMD). This
XMD acts as additional noise that degrades the performance of the
wireless communication device. This noise degrades sensitivity so
that the smallest desired signal that can be reliably detected by
receiver 354 needs to have a larger amplitude. XMD can also be
generated in mixer 324.
[0042] In wideband receivers, the received RF signal (RX SIGNAL)
may either be downconverted from a wide frequency range to a lower
intermediate frequency (IF) using, for example, a super heterodyne
receiver or directly downconverted to baseband accoruding to, for
example, a Zero Intermediate Frequency (ZIF) receiver. These
receivers utilize a preselector 320 including a bandpass filter
with a narrow bandwidth for preselection requiring a high-Q filter.
Unfortunately, active bandpass filters may exhibit limited dynamic
range or excessive current draw and, therefore, result in the
inclusion of both desired RX signals and undesired received signals
(e.g., jammer signals and TX leakage signal) in the RF
amplification process.
[0043] FIG. 4 illustrates a preselector 400 including an initial
active element. Preselector 400 includes in an active input buffer
404 for receiving the RX signal (e.g., desired signal and any
jammer signal) and the TX leakage signal (also collectively
referred to herein as the "RF input signal 402"). The active input
buffer 404 buffers and amplifies the RF input signal 402 to form an
actively buffered RF input signal at node A.
[0044] The actively buffered RF input signal is subjected to a
passive bandpass filter 406 including a capacitor C 408, an
inductor L 410 including a resistive inductive loss illustrated as
resistor Rp 412. In practical implementations of mobile or portable
receivers, passive bandpass filters, such as passive bandpass
filter 406, are implemented according to mass-produced passive
components such as capacitors and inductors of reduced dimensions
and tolerances. Reduced dimensions and tolerances of bandpass
filter components results in a Q-deficient passive bandpass filter.
A Q-deficient bandpass filter exhibits inadequate passband
selection and out-of-band rejection of the RF input signal and high
loss.
[0045] Conventionally, the Q-value of passive bandpass filters
could be adequately increased based upon selection of higher
Q-value capacitors and inductors or large resonate cavities, albeit
of larger dimensions. However, in portable and mobile devices, the
Q-value of a Q-deficient passive bandpass filter 406 may be
augmented by a Q-enhancement circuit 414. In one aspect, the
Q-enhancement circuit 414 is coupled in parallel to the resistive
inductive loss resistor Rp 412 of the Q-deficient passive bandpass
filter 406. The Q-enhancement circuit 414 may be configured as a
negative resistor for compensating for the resistive inductive loss
resistor Rp 412. The Q-enhancement circuit 414 may be implemented
as a transconductance active device as illustrated.
[0046] Preselector 400 may further include an output buffer 416
coupled to the Q-deficient passive bandpass filter 406 and the
Q-enhancement circuit 414. The output buffer 416 may provide
impedance matching with the mixer 324 of FIG. 3.
[0047] One of the shortcomings of preselector 400 includes the
active configuration of active input buffer 404. The active input
buffer 404 includes a transistor 418 which directly receives the
unpredictably fluctuating dynamic range (i.e., signal level
magnitudes) of the RF input signal. For example, a high signal
level of the RF input signal, such as a jamming signal, frequently
exceeds the dynamic range of the transistor 418 resulting in
saturation of transistor 418 causing the generation of distortion
in the form of cross modulation distortion (XMD) discussed above.
Accordingly, the active input buffer 404 restricts the dynamic
range of the preselector 400. While the dynamic range of an active
input buffer may be extended by providing excessive current to the
active transistor, excessive and unnecessary power consumption runs
counter to the prudent power management design goals for portable
and mobile devices. Accordingly, due to the broad dynamic range
requirements for a receiver 354 of FIG. 3, a high dynamic range
preselector is desired.
[0048] FIG. 5 illustrates a preselector in accordance with various
aspects of the disclosed embodiments. Accordingly, a preselector
500 includes passive bandpass filtering with an acceptably narrow
bandwidth attainable without unduly restricting the dynamic range.
The preselector 500 receives an RF input signal 502 which is
initially passed to a Q-deficient passive bandpass filter 504. The
Q-deficient passive bandpass filter 504 is a resonator and may
include different components include discrete inductors/capacitors,
transmission lines, cavity resonators and acoustic resonators. The
Q-deficient passive bandpass filter 504 is illustrated to include a
capacitor C 506, an inductor L 508 including a resistive resonator
loss illustrated as resistor Rp 510
[0049] The Q-deficient passive bandpass filter 504 includes only
passive elements which provide a high dynamic range for filtering
the entire RF input signal. Therefore, before the high dynamic
range RF input signal encounters any active devices, it has already
been filtered by the Q-deficient passive bandpass filter 504 which
has rejected the out-of-band signals which would tend to exhibit
the dynamic range extremes. The dynamic range is bounded by noise
on the lower end of the range and by linearity of the devices on
the upper end of the range. Passive devices such as passive
capacitors and inductors introduce essentially no noise on the
lower end of the dynamic range and do not become non-linear on the
upper end of their dynamic range. In contrast, active devices, such
as transistor 418 of FIG. 4, introduce noise on the lower end of
their dynamic range and then saturates on the upper end of the
dynamic range causing an introduction of non-linearities into the
RF input signals. Accordingly, active devices have a much smaller
dynamic range than passive devices and are therefore undesirable in
receiver front-ends for passing signals that have not been
initially filtered into the dynamic range of the active device.
[0050] Continuing reference to FIG. 5, the Q-deficient passive
bandpass filter 504 is configured at the input of preselector 500
to receive the RF input signal prior to the RF input signal passing
through any active devices. Furthermore, the preselector 500 is
configured at the input of the receiver 354 of FIG. 3 to receive
the received RF input signal (RX signal and TX leakage signal)
prior to the RF input signal passing through any active devices.
According to the various aspects of the embodiments disclosed
herein, the RF input signal received at antenna 352 of FIG. 3 first
passes through the Q-deficient passive bandpass filter 504 of FIG.
5 before passing through any active devices.
[0051] In operation, the received RF input signal (RX signal and TX
leakage signal) first couples to the passive preselect filtering of
Q-deficient passive bandpass filter 504 including the capacitor C
506 and the inductor L 508 before connection to any active device.
Coupling the received RF input signal first to non-active circuitry
results in a lower power configuration since an active circuit
receiving a received RF signal (RX signal) would require high power
in order to exhibit a large dynamic range. The Q-deficient passive
bandpass filter 504 provides filtering of at least a portion of
unwanted signals (e.g., jammer signals and TX leakage signal) thus
reducing the dynamic range requirements of subsequent active
devices in receiver 354 of FIG. 3.
[0052] It is noted that in mobile or portable devices including
receivers, the reduction in physical dimensions of filter circuit
components results in a reduction in the "Q-value" of the filter
resulting from the filter circuit components. Accordingly,
realization of reduced-dimension bandpass filters results in a
reduction in the Q-value of the filters. As stated, one method for
increasing the Q-value of a Q-deficient passive bandpass filter is
to mitigate the resistive losses in the passive components of the
passive bandpass filter by providing a negative resistance.
Accordingly, preselector 500 further includes a Q-enhancement
circuit 512 coupled in parallel to the resistive inductive loss
resistor Rp 510 of the Q-deficient passive bandpass filter 504. The
Q-enhancement circuit 512 may be configured as a negative resistor
for compensating for the resistive inductive loss resistor Rp 510.
The Q-enhancement circuit 512 may be implemented as a
transconductance active device as illustrated in FIG. 5.
Accordingly, the first active device through which the RF input
signal passes is the active device in the Q-enhancement circuit 412
and not an active device associated with an active input buffer
such as active input buffer 404 of FIG. 4 which includes transistor
404.
[0053] The Q-enhancement circuit may be variously configured. In
one aspect, Q-enhancement circuit 512 is configured as a negative
resistance to cancel the effect of losses, such as resistive
inductive loss illustrated as resistor Rp 510. Positive feedback
from Q-enhancement circuit 512 reduces the effect of losses in
inductor loss resistance Rp 510. The amount of positive feedback is
controlled by the ratio of capacitors 526 and 528 with the Q-value
being determined by the feedback provided by the capacitors 526 and
528 as well as the current following through transistor 514. The
losses of inductor 508 and capacitor 506 are modeled by the
inductor loss resistance Rp 510.
[0054] In one aspect, the Q-enhancement circuit 512 is configured
as a negative resistance circuit arranged in a Colpitts
configuration. The Q-enhancement circuit 512 includes a transistor
514 having a collector coupled to a power source 516 via resistor
518. Resistor 518 can be replaced with an inductor. A first bias
resistor 520 is coupled between a power source 522 and the base of
the transistor 514. A current source 524 is coupled between the
emitter of the transistor 514 and a ground potential. A first
feedback capacitor 526 is coupled between the base and emitter of
the transistor 514. A second feedback capacitor 528 is coupled
between the emitter of the transistor 514 and the ground
potential.
[0055] The preselector 500 may further include an impedance
transformer 530 used to decouple the incoming RF input signal from
the antenna 352 of FIG. 3. The impedance transformer 530 may be
adjusted to match the electrical load of the antenna-side of the
preselector 500 in order to maximize the power transfer and
minimize reflections from the RF input signal, thus obtain the
desired overall filter response.
[0056] FIG. 6 is a flow diagram illustrating a method for receiving
an input signal capable of implementing at least some aspects of
the embodiments discussed herein. A process 600 illustrates
maintaining a high-dynamic range for a received RF input signal in
a preselector circuit. In step 602, an RF input signal is received
from the antenna and may pass through a duplexer 314 of FIG. 3 and
an impedance transformer 530 of FIG. 5. As stated, the received RF
input signal may include high-dynamic range signal levels on the RF
input signals which would normally become distorted in a receiver
front-end.
[0057] In a step 604, the received RF input signal is passively
filtered in a Q-deficient bandpass filter. The Q-deficient passive
bandpass filter includes only passive elements which provide a high
dynamic range for filtering the entire RF input signal. Therefore,
before the high dynamic range RF input signal encounters any active
devices, it has already been filtered by the Q-deficient passive
bandpass filter which has rejected the out-of-band signals which
would tend to exhibit the dynamic range extremes. Passive devices
such as passive capacitors and inductors introduce essentially no
noise on the lower end of the dynamic range and do not become
non-linear on the upper end of their dynamic range. In contrast,
active devices, introduce noise on the lower end of their dynamic
range and then saturates on the upper end of the dynamic range
causing an introduction of non-linearities into the RF input
signals.
[0058] In step 606, the Q-value of the Q-deficient bandpass filter
is enhanced using a Q-enhancement circuit. As stated, in mobile or
portable devices including receivers, the reduction in physical
dimensions of filter circuit components results in a reduction in
the narrowness of the bandwidth or Q-value of the filter resulting
from the filter circuit components. Accordingly, realization of
reduced-dimension bandpass filters results in a reduction in the
Q-value of the filters. The Q-value is increased by mitigating the
resistive losses in the passive components of the passive bandpass
filter by providing a negative resistance. Accordingly, a
Q-enhancement circuit is coupled in parallel to the resistive
inductive loss resistor of the Q-deficient passive bandpass filter.
Accordingly, the first active device through which the RF input
signal passes is the active device in the Q-enhancement circuit and
not an active device associated with an active input buffer.
[0059] Those of skill in the art would understand that information
and signals may be represented using any of a variety of different
technologies and techniques. For example, data, instructions,
commands, information, signals, bits, symbols, and chips that may
be referenced throughout the above description may be represented
by voltages, currents, electromagnetic waves, magnetic fields or
particles, optical fields or particles, or any combination
thereof.
[0060] Those of skill would further appreciate that the various
illustrative logical blocks, modules, circuits, and algorithm steps
described in connection with the embodiments disclosed herein may
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 artisans may 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 embodiments.
[0061] The various illustrative logical blocks, modules, and
circuits described in connection with the embodiments disclosed
herein may 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 may be a microprocessor, but in the
alternative, the processor may be any conventional processor,
controller, microcontroller, or state machine. A processor may 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.
[0062] The steps of a method or algorithm described in connection
with the embodiments disclosed herein may be embodied directly in
hardware, in a software module executed by a processor, or in a
combination of the two. A software module may 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 known in the art. An exemplary storage medium is coupled to
the processor such the processor can read information from, and
write information to, the storage medium. In the alternative, the
storage medium may be integral to the processor. The processor and
the storage medium may reside in an ASIC. The ASIC may reside in a
user terminal. In the alternative, the processor and the storage
medium may reside as discrete components in a user terminal
[0063] The previous description of the disclosed embodiments is
provided to enable any person skilled in the art to make or use the
present invention. Various modifications to these embodiments will
be readily apparent to those skilled in the art, and the generic
principles defined herein may be applied to other embodiments
without departing from the spirit or scope of the invention. Thus,
the present 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.
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