Low-power wireless diversity receiver with multiple receive paths

The present application for patent claims priority to Provisional Application No. 60/531,241, entitled “Low-Power Wireless Diversity Receiver with Multiple Receive Paths” filed Dec. 18, 2003, and assigned to the assignee hereof and hereby expressly incorporated by reference herein.

I. Field

The present invention relates generally to electronics, and more specifically to a diversity receiver for wireless communication.

II. Background

In a wireless communication system, a transmitter modulates data onto a radio frequency (RF) carrier signal to generate an RF modulated signal that is more suitable for transmission. The transmitter then transmits the RF modulated signal via a wireless channel to a receiver. The transmitted signal may reach the receiver via one or more propagation paths (e.g., a line-of-sight path and/or reflected paths). The characteristics of the propagation paths may vary over time due to various phenomena such as fading and multipath. Consequently, the transmitted signal may experience different channel conditions and may be received with different amplitudes and/or phases over time.

To provide diversity against deleterious path effects, multiple antennas may be used to receive the RF modulated signal. At least one propagation path typically exists between the transmit antenna and each of the receive antennas. If the propagation paths for different receive antennas are independent, which is generally true to at least an extent, then diversity increases and the received signal quality improves when multiple antennas are used to receive the RF modulated signal.

A multi-antenna receiver conventionally has one RF receiver processing path (or simply, “receive path”) for each receive antenna. Each receive path includes various circuit blocks (e.g., amplifiers, filters, mixers, and so on) used to condition and process a received signal from an associated antenna. The circuit blocks are designed to meet various system requirements such as linearity, dynamic range, sensitivity, out-of-band rejection, and so on, as is known in the art. In conventional diversity receiver designs, the receive path is typically replicated for each receive antenna. The replication of the receive paths with identical circuitry results in higher power consumption, larger area, and higher cost for the multi-antenna receiver, all of which are undesirable. For a portable wireless device, the higher power consumption adversely impacts standby time and reduces talk time between battery recharges.

There is therefore a need in the art for a low-power diversity receiver.

A low-power diversity receiver having good performance is described herein. The diversity receiver includes two or more receive paths, each of which is designated as a primary or secondary receive path. A primary receive path is compliant with applicable system requirements (e.g., IS-98D, cdma2000, GSM and/or W-CDMA requirements). A secondary receive path is designed for low power but is not fully compliant with the system requirements. For example, the secondary receive path may be designed to meet requirements for dynamic range and sensitivity but not for certain out-of-band rejection of large amplitude “jammers”, which are undesired signals outside of the RF channel of interest. The relaxed requirements allow the secondary receive path to be implemented with lower power consumption, less area, and lower cost. The second receive path can provide good performance under most operating conditions. For a multi-antenna receiver, the primary and secondary receive paths may be used to simultaneously process two received signals from two antennas. For a single-antenna receiver, either the primary or secondary receive path may be selected, e.g., depending on whether or not jammers are detected, to process a single received signal from one antenna.

In an exemplary embodiment, a wireless device with two receive paths for one frequency band is described. The first (primary) receive path includes (1) a first amplifier that amplifies a first input signal and provides a first amplified signal and (2) a first downconverter that translates the first amplified signal in frequency (e.g., from RF down to baseband) and provides a first baseband signal. The second (secondary) receive path includes (1) a second amplifier that amplifies a second input signal and provides a second amplified signal and (2) a second downconverter that translates the second amplified signal in frequency and provides a second baseband signal. The first receive path is compliant with system requirements, and the second receive path is non-compliant with some or all of the system requirements. A jammer detector detects for the presence of large amplitude jammers in the first and/or second input signal. If only one receive path is needed, then the first receive path is selected if jammers are detected and the second receive path is selected for use if jammers are not detected. The wireless device may include additional receive paths for additional frequency bands and/or GPS.

Various aspects and embodiments of the invention are described in further detail below.

The features and nature of the present 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:

FIG. 1 shows a wireless communication system;

FIG. 2 shows a single-antenna terminal with two receive paths;

FIG. 3 shows a dual-antenna terminal with two receive paths;

FIG. 4 shows a dual-antenna terminal with five receive paths for two frequency bands and GPS;

FIG. 5 shows a dual-path receiver with a direct-to-baseband architecture;

FIG. 6 shows a dual-path receiver with a super-heterodyne architecture;

FIGS. 7 and 8 show two dual-path receivers that may also be used for the dual-antenna terminal in FIG. 3 ;

FIG. 9 shows a lowpass filter;

FIG. 10 shows a jammer detector; and

FIG. 11 shows a process for operating two receive paths in a wireless terminal.

The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or designs.

FIG. 1 shows a wireless communication system 100 in which a number of wireless terminals communicate with a number of base stations. For simplicity, only two terminals 110 a and 110 b and two base stations 120 a and 120 b are shown in FIG. 1 . Each terminal 110 may receive signals from any number of transmitting sources at any given moment via line-of-sight paths and/or reflected paths. A reflected path is created when a transmitted signal reflects off a reflection source (e.g., a building, tree, or some other obstruction) and arrives at the terminal via a different path than the line-of-sight path. A terminal may also be referred to as a remote station, a mobile station, an access terminal, a user equipment (UE), a wireless communication device, a cellular phone, or some other terminology. Terminal 110 a is equipped with a single antenna, and terminal 110 b is equipped with two antennas. A base station is a fixed station and may also be referred to as an access point, a Node B, or some other terminology. A mobile switching center (MSC) 140 couples to the base stations and provides coordination and control for these base stations.

A terminal may or may not be capable of receiving signals from satellites 130 . Satellites 130 may belong to a satellite positioning system such as the well-known Global Positioning System (GPS). Each GPS satellite transmits a GPS signal encoded with information that allows GPS receivers on earth to measure the time of arrival of the GPS signal. Measurements for a sufficient number of GPS satellites can be used to accurately estimate a three-dimensional position of a GPS receiver. A terminal may also be capable of receiving signals from other types of transmitting sources such as a Bluetooth transmitter, a wireless local area network (WLAN) transmitter, an IEEE 802.11 (Wi-Fi) transmitter, and so on.

In FIG. 1 , each terminal 110 is shown as receiving signals from multiple transmitting sources simultaneously, where a transmitting source may be a base station or a satellite. In general, a terminal may receive signals from zero, one, or multiple transmitting sources at any given moment. For multi-antenna terminal 110 b , the signal from each transmitting source is received by each of the multiple antennas at the terminal, albeit at different amplitudes and/or phases.

System 100 may be a Code Division Multiple Access (CDMA) system, a Time Division Multiple Access (TDMA) system, or some other wireless communication system. A CDMA system may implement one or more CDMA standards such as IS-95, IS-2000 (also commonly known as “1x”), IS-856 (also commonly known as “1xEV-DO”), Wideband-CDMA (W-CDMA), and so on. A TDMA system may implement one or more TDMA standards such as Global System for Mobile Communications (GSM). The W-CDMA standard is defined by a consortium known as 3GPP, and the IS-2000 and IS-856 standards are defined by a consortium known as 3GPP2. These standards are known in the art.

Low-power diversity receivers that can provide good performance are described herein. A diversity receiver is a receiver with at least two receive paths, with each receive path being capable of conditioning (e.g., amplifying and/or filtering) an RF signal and frequency downconverting the signal to baseband. The low-power diversity receivers may be used for terminals with a single antenna as well as terminals with multiple antennas. Some exemplary low-power diversity receivers are described below.

FIG. 2 shows a block diagram of an embodiment of single-antenna terminal 110 a . In this embodiment, terminal 110 a includes a single antenna 212 and two receive paths 220 a and 220 b . Antenna 212 receives RF modulated signals from base stations 120 and provides a received signal (Prx) that includes versions of the RF modulated signals transmitted by these base stations. A low noise amplifier (LNA) 216 performs low noise amplification on the received signal and provides an input signal (Pin) to both receive paths 220 a and 220 b . Receive path 220 a is designated as the primary receive path, and receive path 220 b is designated as the secondary receive path.

Each receive path 220 processes the input signal from LNA 216 and provides a respective output baseband signal. Receive path 220 a is designed to meet applicable system requirements (e.g., for sensitivity, dynamic range, linearity, out-of-band rejection, and so on) and may be used for all operating conditions. Receive path 220 b is designed for low power and with less stringent requirements and may be used for most operating conditions. Exemplary designs for receive paths 220 a and 220 b are described below.

An analog-to-digital converter (ADC) 230 a receives and digitizes the first output baseband signal (Pout1) from receive path 220 a and provides a first stream of data samples to a data processor 240 for further processing. Similarly, an ADC 230 b receives and digitizes the second output baseband signal (Pout2) from receive path 220 b and provides a second stream of data samples to data processor 240 . Although not shown in FIG. 2 for simplicity, each output baseband signal and each data sample stream may be a complex signal/stream having an inphase (I) component and a quadrature (Q) component.

For the embodiment shown in FIG. 2 , a signal detector 242 detects for the signal level of the desired signal, which is the signal within an RF channel of interest. The desired signal detection may be performed in various manners known in the art. For example, an automatic gain control (AGC) loop is typically used to adjust the gains of variable gain amplifiers (VGAs) located within the receive paths so that output baseband signals at the proper amplitude are provided to the ADCs. The gain control signals for these VGAs are indicative of, and may be mapped to, the desired signal level. A jammer detector 250 receives a first detector input signal (D1) from receive path 220 a and a second detector input signal (D2) from receive path 220 b , detects for the presence of large amplitude jammers in the received signal, and provides a jammer status signal indicating whether or not large amplitude jammers are present in the received signal. A control unit 252 receives the jammer status signal from jammer detector 250 and a Mode control signal from data processor 240 and provides the Enb1 and Enb2 signals used to enable receive paths 220 a and 220 b , respectively. For example, control unit 252 may select (1) receive path 220 a if large amplitude jammers are detected in the received signal and (2) receive path 220 b otherwise.

In one configuration, either receive path 220 a or 220 b is selected for use at any given moment, depending on the operating conditions. In another configuration, both receive paths 220 a and 220 b may be active at the same time to simultaneously process signals from two different systems. ADC 230 b may be omitted, and a switch may be used to provide the output baseband signal from either receive path 220 a or 220 b to ADC 230 a.

FIG. 3 shows a block diagram of an embodiment of multi-antenna terminal 110 b . In this embodiment, terminal 110 b includes two antennas 312 a and 312 b and two receive paths 320 a and 320 b . The two antennas 312 a and 312 b may be formed in various manners at terminal 110 b (e.g., with printed traces on a circuit board, wire conductors, and so on), as is known in the art. An LNA 316 a amplifies a first received signal (Prx) from antenna 312 a and provides a first input signal (Pin) to receive path 320 a . Similarly, an LNA 316 b amplifies a second received signal (Srx) from antenna 312 b and provides a second input signal (Sin) to receive path 320 b . Receive path 320 a is designated as the primary receive path, and receive path 320 b is designated as the secondary/diversity receive path. LNAs 316 a and 316 b may also be considered as part of receive paths 320 a and 320 b , respectively.

Each receive path 320 processes the input signal from one LNA 316 and provides a respective output baseband signal. Receive path 320 a is designed to meet applicable system requirements and may be used for all operating conditions. Receive path 320 b is designed for low power and with less stringent requirements and may be used for most operating conditions. In one configuration, either receive path 320 a or 320 b is selected for use at any given moment, depending on the operating conditions. In another configuration, both receive paths 320 a and 320 b are active at the same time to simultaneously process two received signals for the same wireless system in order to achieve diversity. In yet another configuration, both receive paths 320 a and 320 b simultaneously process signals for two different systems. Exemplary designs for receive paths 320 a and 320 b are described below.

ADC 330 a receives and digitizes the first output baseband signal (Pout) from receive path 320 a and provides a first data sample stream to a data processor 340 . Similarly, an ADC 330 b receives and digitizes the second output baseband signal (Sout) from receive path 320 b and provides a second data sample stream to data processor 340 . A signal detector 342 detects for the desired signal level. A jammer detector 350 detects for the presence of large amplitude jammers in the first and/or second received signal and provides a jammer status signal. A control unit 352 enables one or both receive paths 320 a and 320 b based on the jammer status signal from jammer detector 350 and the Mode control signal from data processor 340 .

A wireless terminal may be a single-band terminal or a multi-band terminal. A single-band terminal supports operation on one specific frequency band. A multi-band terminal supports operation on multiple frequency bands and typically operates on one of the supported bands at any given moment. A multi-band terminal can communicate with different wireless communication systems operating on different frequency bands. Table 1 lists various frequency bands commonly used for wireless communication as well as the frequency band for GPS.

The PCS band is also known as GSM1900, the DCS band is also known as GSM1800, and the cellular band is also known as an Advanced Mobile Phone System (AMPS) band. A wireless communication system may also operate on a frequency band that is not listed in Table 1.

For each of the frequency bands listed in Table 1 except for GPS, one frequency range is used for the forward link (i.e., downlink) from the base stations to the terminals, and another frequency range is used for the reverse link (i.e., uplink) from the terminals to the base stations. As an example, for the cellular band, the 824 to 849 MHz range is used for the reverse link, and the 869 to 894 MHz range is used for the forward link.

FIG. 4 shows a block diagram of an embodiment of dual-band plus GPS, multi-antenna terminal 110 c (not shown in FIG. 1 ). Terminal 110 c supports operation on two frequency bands, which for clarity are the cellular and PCS bands in the following description. In the embodiment shown in FIG. 4 , terminal 110 c includes two antennas 412 a and 412 b and five receive paths 420 a through 420 e . The received signal (Prx) from antenna 412 a is provided to a diplexer 414 a , which provides a first cellular signal to an LNA 416 a and a first PCS signal to an LNA 416 b . LNAs 416 a and 416 b perform low noise amplification on their signals and provide Pin1 and Pin2 input signals to receive paths 420 a and 420 b , respectively. Similarly, the received signal (Srx) from antenna 412 b is provided to a diplexer 414 b , which provides a second cellular signal to an LNA 416 c and a second PCS signal to an LNA 416 d . LNAs 416 c and 416 d perform low noise amplification on their signals and provide Sin1 and Sin2 input signals to receive paths 420 c and 420 d , respectively. An LNA 416 e performs low noise amplification on a received GPS signal (Grx) and provides a Gin input signal to receive path 420 e . LNAs 416 a through 416 e may also be considered as part of receive paths 420 a through 420 e , respectively.

Each receive path 420 conditions and frequency downconverts its input signal and provides a respective baseband signal. Receive paths 420 a and 420 b are designated as primary receive paths and are designed to meet applicable system requirements. Receive paths 420 c and 420 d are designated as secondary receive paths and are designed for low power and with less stringent requirements. Receive paths 420 c and 420 d may be implemented with circuit blocks that consume less power, occupy smaller area, and cost less than those of receive paths 420 a and 420 b.

For the embodiment shown in FIG. 4 , receive paths 420 a and 420 b share baseband circuit blocks, and receive paths 420 c , 420 d , and 420 e share baseband circuit blocks. A lowpass filter 440 a filters the baseband signal from either receive path 420 a or 420 b and provides a first filtered baseband signal and the D1 detector input signal. A lowpass filter 440 b filters the baseband signal from receive path 420 c , 420 d , or 420 e and provides a second filtered baseband signal and the D2 detector input signal. Amplifiers 442 a and 442 b amplify and buffer the first and second filtered baseband signals and provide the first and second output baseband signals, Pout and Sout, respectively.

A jammer detector 450 receives the first and second detector input signals (D1 and D2) from lowpass filters 440 a and 440 b , respectively, detects for the presence of large amplitude jammers in the received signal, and provides the jammer status signal. A control unit 452 receives the jammer status signal and the Mode control signal and provides enable signals used to enable receive paths 420 a through 420 e . For example, control unit 452 may select (1) primary receive path 420 a or 420 b if large amplitude jammers are present, (2) secondary receive path 420 c or 420 d if large amplitude jammers are not present, (3) both receive paths 420 a and 420 c for the cellular band or both receive paths 420 b and 420 d for the PCS band, for the diversity mode, (4) receive path 420 a or 420 b for wireless communication and receive path 420 e for GPS, and so on.

Receive paths 420 a and 420 c are designed for the cellular band, receive paths 420 b and 420 d are designed for the PCS band, and receive path 420 e is designed for GPS frequency. Receive paths 420 a and 420 b may be implemented with narrowband circuit blocks that are tuned to the cellular and PCS bands, respectively. Receive paths 420 c and 420 d may be implemented with narrowband and/or wideband circuit blocks to achieve the desired performance. For example, the circuit blocks in receive paths 420 c and 420 d may be implemented with resistors or low quality inductors, whereas the circuit blocks for receive paths 420 a and 420 b may be implemented with high quality inductors.

The primary receive paths (receive path 220 a in FIG. 2 , receive path 320 a in FIG. 3 , and receive paths 420 a and 420 b in FIG. 4 ) are designed to meet applicable system requirements. For CDMA, IS-98D and cdma2000 specify a two-tone test and a single-tone test. For the two-tone test, two tones (or jammers) are located at +900 KHz and +1700 KHz (or at −900 KHz and −1700 KHz) from the center frequency of a CDMA waveform and are 58 dB higher in amplitude than the CDMA signal level. For the single-tone test, a single tone is located at +900 KHz from the center frequency of the CDMA waveform and is 72 dB higher in amplitude than the CDMA signal level. These tests define the linearity and dynamic range requirements for the receive path. In most systems, jammers are present for only a small fraction of the time and rarely reach the +58 or +72 dB level as specified by IS-98D and cdma2000. Nevertheless, the primary receive paths may be designed to be IS-98D and cdma2000 compliant so that they can provide the specified performance for all operating conditions.

The secondary receive paths (receive path 220 b in FIG. 2 , receive path 320 b in FIG. 3 , and receive paths 420 c and 420 d in FIG. 4 ) are designed to be low-power and with less stringent requirements. For example, the secondary receive paths may be designed to meet dynamic range and sensitivity requirements, albeit assuming that large amplitude jammers are not present in the received signal. With the relaxed requirements, the secondary receive paths may be designed to consume only a fraction (e.g., 50% or 25%) of the power consumed by the corresponding primary receive paths. The secondary receive paths can still provide good performance most of the time since large amplitude jammers are present intermittently. The secondary receive paths can provide substantial power savings if they are used in place of the primary receive paths.

When not operating in the diversity mode, either the primary or secondary receive path is selected for use depending on one or more criteria. These criteria may include (1) presence or absence of large amplitude jammers in the received signal and (2) the desired signal level. Table 2 shows an embodiment for selecting receive path based solely on jammer detection.

Table 3 shows an embodiment for selecting receive path based on jammer detection and desired signal level.

Large amplitude jammers may be deemed to be present in the received signal if their signal level exceeds a particular threshold, as described below. The desired signal may be deemed to be strong if it exceeds a particular signal level. This signal level may be dependent on the actual performance of the secondary path and may be circuit and implementation dependent. The selection of receive path may also be based on other criteria (e.g., received signal quality or signal-to-noise ratio (SNR), pilot received signal strength, power control bits, and so on), and this is within the scope of the invention.

A receive path may be implemented with a super-heterodyne architecture or a direct-to-baseband architecture. In the super-heterodyne architecture, the received signal is frequency downconverted in multiple stages, e.g., from RF to an intermediate frequency (IF) in one stage, and then from IF to baseband in another stage. In the direct-to-baseband architecture, the received signal is frequency downconverted from RF directly to baseband in one stage. The super-heterodyne and direct-to-baseband architectures may use different circuit blocks and/or have different circuit requirements.

FIG. 5 shows a block diagram of a dual-path receiver 500 , which implements the direct-to-baseband architecture and may be used for both single-antenna terminal 110 a and multi-antenna terminal 110 b in FIG. 1 . Receiver 500 includes two receive paths 520 a and 520 b that may be used for receive paths 220 a and 220 b , respectively, in FIG. 2 . In this case, both receive paths 520 a and 520 b are provided with the same input signal, Pin (not shown in FIG. 5 ). Receive paths 520 a and 520 b may also be used for receive paths 320 a and 320 b , respectively, in FIG. 3 . In this case, receive paths 520 a and 520 b are provided with different input signals, Pin and Sin, respectively, as shown in FIG. 5 . The RF portion of receive paths 520 a and 520 b may be used for receive paths 420 a and 420 c , respectively, and for receive paths 420 b and 420 d , respectively, in FIG. 4 , as described below. Receive path 520 a is the primary receive path, and receive path 520 b is the secondary/diversity receive path.

Within receive path 520 a , a VGA 524 a amplifies the input signal (Pin) with a first variable gain (Gp1). A filter 526 a filters the signal from VGA 524 a to pass signal components in the band of interest and remove out-of-band noise and undesired signals. For two-way communication, signals are transmitted simultaneously on the forward link and reverse link. The transmitted signal sent by the terminal on the reverse link is typically much larger in amplitude than the received signal for the forward link. Filter 526 a may pass the RF components for the receive frequency range (e.g., from 869 to 894 MHz for cellular band) and filter out and suppress the RF components for the transmit frequency range (e.g., from 824 to 849 MHz for the cellular band). Filter 526 a may thus have a passband that corresponds to an entire frequency range/band of interest (e.g., cellular). Because of the potentially large difference in the transmit and receive signal levels, filter 526 a needs to provide a large amount of out-of-band rejection in order to meet system requirements. Filter 526 a may be implemented with a surface acoustic wave (SAW) filter (which has a sharp roll-off and is often used for applications requiring large attenuation of out-of-band signals), a ceramic filter, or some other type of filter.

A VGA 528 a amplifies the signal from filter 526 a with a second variable gain (Gp2) and provides a first conditioned signal having the desired signal level. VGAs 524 a and 528 a provide the required amplification for the Pin signal, which may vary by 90 dB or more. Additional gain may be provided by other circuit blocks in the receive path. A downconverter 530 a receives and frequency downconverts the first conditioned signal with a first LO signal and provides a first baseband signal. The frequency of the first LO signal is selected such that the signal component in the RF channel of interest is downconverted to baseband or near-baseband. For CDMA, each frequency band covers many RF channels, and each RF channel has a bandwidth of 1.23 MHz. A wireless terminal typically receives signal on one RF channel at any given moment.

A lowpass filter 540 a filters the first baseband signal to pass the signal components in the RF channel of interest and to remove noise and undesired signals that may be generated by the downconversion process. For the direct-to-baseband architecture, filter 526 a may pass the entire frequency band of interest, and lowpass filter 540 a would then pass the RF channel of interest. Lowpass filter 540 a may be implemented with various filter types (e.g., Butterworth, elliptical, Chebychev, and so on), with the proper filter order and bandwidth, and with sufficient bias current to meet linearity and dynamic range requirements. Lowpass filter 540 a provides a first filtered baseband signal and the D1 signal for the jammer detector. An amplifier 542 a amplifies and buffers the first filtered baseband signal and provides the first output baseband signal (Pout).

An LO generator 546 a provides the first LO signal used to downconvert the Pin signal from RF to baseband. LO generator 546 a may be implemented with a voltage controlled oscillator (VCO) or some other type of oscillator. The frequency of the LO signal is selected such that the signal component in the RF channel of interest is downconverted to baseband or near-baseband. A phase locked loop (PLL) 548 a receives the first LO signal and generates a control signal for LO generator 546 a such that the frequency and/or phase of the first LO signal is locked to a reference signal (not shown in FIG. 5 ).

Receive path 520 b processes the Sin signal and provides the second output baseband signal (Sout), in similar manner as receive path 520 a . For each receive path, the frequency downconversion may be performed in various manners. For example, frequency downconversion may be performed by mixing the RF input signal down to baseband, as shown in FIG. 5 . The frequency downconversion may also be performed by sampling or digitizing the RF input signal and using the aliasing property of data sampling to generate samples at baseband. Frequency downconverters 530 a and 530 b may be implemented with mixers, ADCs, mixer (e.g., for downconverter 530 a ) and ADC (e.g., for downconverter 530 b ), and so on. RF sampling may be more readily implemented on the secondary receive path 520 b since the specifications are simpler.

FIG. 5 shows a specific design for receive paths 520 a and 520 b . In general, a receive path may perform signal conditioning using one or more stages of amplifier, filter, mixer, and so on, which may be arranged in a different manner from that shown in FIG. 5 . Moreover, a receive path may employ other circuit blocks not shown in FIG. 5 for signal conditioning.

FIG. 5 shows receive paths 520 a and 520 b having the same circuit blocks. However, different circuit designs may be used for the circuit blocks in receive paths 520 a and 520 b because of the different requirements and objectives for the primary and secondary receive paths.

Receive path 520 a is designed to meet applicable system requirements, e.g., linearity, dynamic range, and sensitivity requirements. To achieve this, the RF circuit blocks in receive path 520 a are typically narrowband circuits tuned to a specific frequency band (e.g., cellular or PCS band). For example, VGAs 524 a and 528 a and downconverter 530 a may be implemented with narrowband circuits to achieve the desired linearity over a wide dynamic range. The narrowband circuit blocks may use matching and tuned circuits, inductive degeneration, and other circuit techniques known in the art to achieve the desired performance. Lowpass filter 540 a may be designed with a relatively sharp roll-off (e.g., as a 5-th order elliptical filter) in order to attenuate large amplitude jammers in the input signal. These jammers can take up a large portion of the dynamic range of the subsequent ADC if they are not sufficiently filtered. LO generator 546 a is designed to have good phase noise performance. In general, good performance for the circuit blocks within receive path 520 a typically requires the use of larger-size circuit components (e.g., larger capacitors, inductors and/or transistors) and large amounts of bias current.

Receive path 520 b is designed for low-power and with less stringent requirements, which assumes that large amplitude jammers are not present in the received signal. Because of the less stringent requirements, VGAs 524 b and 528 b , downconverter 530 b , filter 540 b , and amplifier 542 b may be designed with smaller-size circuit components (e.g., smaller capacitors) and smaller amounts of bias current. VGAs 524 b and 528 b and downconverter 530 b may be implemented without using inductors (which typically occupy a large area) or by using inductors of lower quality (which can occupy a smaller area). Filter 526 b may be implemented with on-chip circuit components instead of an external SAW filter (which may be needed for filter 526 a ). Because large amplitude jammers are assumed to be absent for receive path 520 b , the overall gain may be distributed differently for the secondary receive path in a manner to further reduce power consumption, area, and cost. Lowpass filter 540 b may be implemented with a lower order (e.g., as a 3-rd order elliptical filter) than lowpass filter 540 a . Using these various circuit design techniques, receive path 520 b may be designed to consume only a fraction (e.g., 50% or 25%) of the power and occupy only a small fraction of the area required by receive path 520 a.

FIG. 6 shows a block diagram of a dual-path receiver 600 , which implements the super-heterodyne architecture and may also be used for both single-antenna terminal 110 a and multi-antenna terminal 110 b . Receiver 600 includes two receive paths 620 a and 620 b that may be used for receive paths 220 a and 220 b , respectively, in FIG. 2 , and for receive paths 320 a and 320 b , respectively, in FIG. 3 . The RF portion of receive paths 620 a and 620 b may be used for receive paths 420 a and 420 c , respectively, and for receive paths 420 b and 420 d , respectively, in FIG. 4 .

Within receive path 620 a , the input signal (Pin) is amplified by a VGA 614 a , filtered by a filter 616 a , and downconverted from RF to IF by a frequency downconverter 622 a . The IF signal from downconverter 622 a is further amplified by a VGA 624 a , filtered by a bandpass filter 626 a , amplified and buffered by an amplifier 628 a , and downconverted from IF to baseband by a frequency downconverter 630 a . The baseband signal from downconverter 630 a is filtered by a lowpass filter 640 a and amplified and buffered by an amplifier 642 a to obtain the first output baseband signal (Pout).

For the super-heterodyne architecture, bandpass filter 626 a may be implemented with a SAW filter and may perform RF channel selection (i.e., may have a passband corresponding to one RF channel, instead of an entire frequency band). If the RF channel selection is performed by bandpass filter 626 a , then the requirements for lowpass filter 640 a may be relaxed.

An LO generator 646 a provides a first LO signal used for RF to IF downconversion and a second LO signal used for IF to baseband downconversion. Typically, the IF is fixed, the frequency of the first LO signal is selected such that the signal component in the RF channel of interest is downconverted to the fixed IF, and the frequency of the second LO signal is also fixed.

Receive path 620 b processes the Sin signal and provides the second output baseband signal (Sout), in similar manner as receive path 620 a . Receive path 620 b may be implemented with circuit blocks that consume less power, occupy smaller area, and are lower cost than those of receive path 620 a.

Referring back to FIG. 4 , receive paths 420 a through 420 e may be implemented with the direct-to-baseband architecture or the super-heterodyne architecture. For the direct-to-baseband architecture, each of receive paths 420 a through 420 e may be implemented with VGAs 524 and 528 , filter 526 , and frequency downconverter 530 in FIG. 5 . For the super-heterodyne architecture, each of receive paths 420 a through 420 e may be implemented with VGAs 614 and 624 , amplifier 628 , filters 616 and 626 , and frequency downconverters 622 and 630 in FIG. 6 .

Two LO generators operating independently, as shown in FIGS. 5 and 6 , may be used for the primary and secondary receive paths. This design allows the primary and secondary receive paths to operate simultaneously and independently to process two signals on two different RF channels. This capability may be useful for various applications. For example, a terminal with this capability can receive two simultaneous transmissions on two RF channels from one or two systems. As another example, a terminal with this capability can perform mobile-assisted hand-off (MAHO) to select the best base stations to communicate with. The terminal can receive a transmission from a serving base station with the primary receive path and can simultaneously search for signals from other base stations with the secondary receive path. This would then allow the terminal to initiate a hand-off to another base station that is better than the serving base station, if one is found. If independent operation of the primary and secondary receive paths is not needed, then one LO generator may be shared by both receive paths.

Although not indicated in FIGS. 2 through 6 for simplicity, the primary receive paths (receive path 220 a in FIG. 2 , receive path 320 a in FIG. 3 , receive paths 420 a and 420 b in FIG. 4 , receive path 520 a in FIG. 5 , and receive path 620 a in FIG. 6 ) may be designed with multiple power modes, e.g., a high power mode and a low power mode. In the high power mode, the circuit blocks (e.g., amplifiers, mixers, and so on) within the primary receive paths may be biased with high current to meet applicable system requirements under the worst-case operating condition, such as those specified by IS-98D or cdma2000. In the low power mode, the circuit blocks within the primary receive paths may be biased with less current that can still meet applicable system requirements under more moderate operating condition, e.g., with no jammers or low amplitude jammers. The primary receive paths may also be designed with more than two power modes, with more current being used for more severe operating condition.

Many wireless systems have an open loop transmit power specification that dictates the amount of transmit power to use at the start of a transmission based on the received power level. A terminal typically does not know the transmit power level needed for reliable communication when the terminal is first powered on or first starts to transmit. In this case, the forward and reverse links may be assumed to be reciprocal of one another, i.e., the path loss for the reverse link is assumed to be equal to the path loss for the forward link. The terminal can estimate the path loss for the forward link based on a pilot received from a base station and can determine the amount of transmit power to use for the reverse link transmission based on the forward link measurement. However, if the terminal is equipped with multiple antennas, then the received power level may change abruptly when different antennas are selected for use. This open loop power disturbance may result in the wrong transmit power level being used for the reverse link transmission.

FIG. 7 shows a block diagram of a dual-path receiver 700 that may be used for dual-antenna terminal 110 b in FIG. 3 . Receiver 700 includes two receive paths 720 a and 720 b . Receive path 720 a is the primary receive path and couples to a duplexer 714 a , which further couples to a transmitter unit (TMTR) 710 and an antenna 712 a . Duplexer 714 a routes the transmit signal from transmitter unit 710 to antenna 712 a and further routes the received signal from antenna 712 a to receive path 720 a . Receive path 720 b is the secondary receive path and couples to a SAW filter 714 b , which further couples to an antenna 712 b . For this embodiment, the terminal only transmits from antenna 712 a and not antenna 712 b . Antenna 712 a may be a whip/dipole antenna or some other type of antenna. Antenna 712 b may be an internal antenna, a printed antenna, or some other type of antenna.

Receive path 720 a includes an LNA 716 a , a switch 722 a , a filter 726 a , a VGA 728 a , a frequency downconverter 730 a , a lowpass filter 740 a , and an amplifier 742 a , all of which function as described above for FIGS. 2 through 6 . Receive path 720 b includes the same circuit blocks as receive path 720 a . The circuit blocks for receive path 720 a may be designed and biased to be spec-compliant, and the circuit blocks for receive path 720 b may be designed and biased for low power. The circuit blocks for receive path 720 a may also be designed with multiple power modes, as described above.

In a first operating mode, both receive paths 720 a and 720 b are selected for use to achieve diversity. For this mode, switches 722 a and 722 b are both switched to the “A” position and pass the output of LNAs 716 a and 716 b , respectively, to filters 726 a and 726 b , respectively. If diversity is not needed, then either receive path 720 a or 720 b may be selected for use depending on the operating condition. In a second operating mode, receive path 720 a is selected for use if large amplitude jammers are detected. For this mode, switch 722 a is switched to the “A” position, and the entire receive path 720 b may be powered down. In a third operating mode, receive path 720 b is selected for use if no jammers or low amplitude jammers are detected. For this mode, switches 722 a and 722 b are both switched to the “B” position, and the output of LNA 716 a is routed to filter 726 b . LNA 716 b in receive path 720 b and all of the circuit blocks after switch 722 a in receive path 720 a may be powered down. LNA 716 a may also be biased with less current to conserve power. For all three operating modes, the received signal power can be measured from antenna 712 a . The overall gain from switch 722 to amplifier 742 may be determined for each receive path and used to account for the received signal power measurements. Switches 722 a and 722 b can mitigate open loop power disturbance.

FIG. 8 shows a block diagram of a dual-path receiver 702 that may also be used for dual-antenna terminal 110 b in FIG. 3 . Receiver 702 includes two receive paths 721 a and 721 b . Each receive path 721 includes all of the circuit blocks in receive path 720 in FIG. 7 . However, switches 722 a and 722 b are placed after filters 726 a and 726 b , respectively, in receive paths 721 a and 721 b , respectively. If filter 726 a has better electrical characteristics than filter 726 b , then improved performance may be obtained by using filter 726 a instead of filter 726 b . In general, switch 722 a may be located anywhere within receive path 721 a , and switch 722 b may be located anywhere within receive path 721 b.

FIG. 9 shows an embodiment of a lowpass filter 940 , which may be used for each of the lowpass filters shown in FIGS. 4 , 5 and 6 . Lowpass filter 940 includes a single-pole filter section 942 and bi-quad filter sections 944 and 946 . Single-pole filter section 942 implements one real pole. Each of bi-quad filter sections 944 and 946 implements a pair of complex poles. A 5-th order (e.g., elliptical, Butterworth, Bessel, or Chebychev) filter may be implemented with all three filter sections 942 , 944 , and 946 .

The lowpass filters for the receive paths may also be implemented with other filter designs. Furthermore, the lowpass filters for the primary and secondary receive paths may be implemented with the same or different filter designs. For example, a 5-th order lowpass filter may be used for the primary receive path, and a 3-rd order lowpass filter may be used for the secondary receive path.

As noted above, when not operating in the diversity mode, either the primary or secondary receive path for the desired frequency band is selected for use depending on whether or not jammers are detected in the received signal. Jammers are large amplitude, undesired out-of-band signals that can distort the desired in-band signal. The detector input signals used for jammer detection may be obtained from various points along the receive path but should include out-of-band signal components. The detector input signals may be broadband signals with a flat frequency response that gives equal weight to signal components at different frequencies. However, jammers that are closer in-band (i.e., closer to the desired RF channel) tend to be more detrimental to the desired signal than jammers that are farther away in frequency. Thus, the detector input signals may be rolled off (e.g., with a first-order lowpass filter response) to allow for discrimination of the frequency offset of the jammers. This would then give jammers closer in more weight and jammers farther away less weight.

For the embodiments shown in FIGS. 4 , 5 and 6 , the lowpass filters also provide the detector input signals (D1 and D2) used to detect for the presence of jammers in the received signals. In an embodiment, the detector input signals are taken after single-pole filter section 942 in the lowpass filters.

FIG. 10 shows a block diagram of a jammer detector 1050 , which may be used for the jammer detectors in FIGS. 2 , 3 and 4 . The D1 and D2 signals for the primary and secondary receive paths are rectified by rectifiers 1052 a and 1052 b , filtered by lowpass filters 1054 a and 1054 b , and provided to comparators 1056 a and 1056 b , respectively. Each rectifier 1052 converts its detector input signal from a sinusoidal signal (with positive and negative amplitude) to a single-ended signal (with only positive amplitude) and may be implemented with a diode. Each lowpass filter 1054 may be implemented, for example, with a single-order lowpass filter of an appropriate bandwidth (e.g., several hundred Hertz). Each comparator 1056 compares its filtered signal against a threshold level (Vth) and provides an output signal, which is (1) logic high (‘1’) if the filtered signal amplitude is larger than the threshold level, indicating the presence of large amplitude jammers in the received signal, and (2) logic low (‘0’) otherwise. Detector logic 1058 combines the output signals of comparators 1056 a and 1056 b and provides the jammer status signal to control unit 252 , 352 , or 452 .

In general, jammer detection may be performed based on (1) only the D1 signal, (2) only the D2 signal, or (3) both the D1 and D2 signals. The filtered signals from lowpass filters 1054 a and 1054 b may be compared against the threshold level as shown in FIG. 10 to obtain a 1-bit output signal. These filtered signals may also be digitized with an ADC to obtain multiple bits of resolution. The jammer status signal may be used to select either the primary or secondary receive path. The jammer status signal may also be used to adjust (e.g., the gains and/or bias currents of) the circuit blocks in the primary and/or secondary receive paths.

FIG. 11 shows a flow diagram of a process 1100 for operating two receive paths in a wireless terminal. The presence of large amplitude jammers in a first input signal or a second input signal is detected (block 1112 ). The first and second input signals may be from (1) one antenna for a single-antenna terminal or (2) two antennas for a multi-antenna terminal. The primary receive path (which is spec-compliant, e.g., IS-98D compliant) is enabled to process the first input signal if large amplitude jammers are detected (block 1114 ). The secondary receive path (which is not fully spec-compliant) is enabled to process the second input signal if large amplitude jammers are not detected (block 1116 ). The primary and secondary receive paths are both enabled if the multi-antenna terminal is operating in a diversity mode and the received signals from both antennas are to be processed simultaneously. Electrical characteristics (e.g., gains, bias currents, and so on) of the circuit blocks in the enabled receive path(s) may also be adjusted based on the detected jammer signal level and/or the desired signal level (block 1118 ).

The low-power diversity receiver described herein can provide good performance for both single-antenna and multi-antenna terminals under most operating conditions. The worst-case operating condition occurs when (1) the desired signal is near “sensitivity”, which is the lowest detectable received signal level, and (2) the jammers are at maximum signal level and located at a small frequency offset away from the desired signal. This worst-case condition is a low probability event. For the single-antenna terminal, the low-power secondary receive path may be used for most operating conditions. For the multi-antenna terminal, the diversity mode is typically needed for only 20 to 50 percent of the time. For the remaining 50 to 80 percent of the time, a single receive path may be used, and the secondary receive path may be selected if large amplitude jammers are not detected. For both single-antenna and multi-antenna terminals that are portable, the secondary receive path consumes less power and improves both standby time between battery recharges and talk time.

The low-power diversity receiver described herein may be used for a wireless terminal to receive forward link transmissions from base stations. The low-power diversity receiver may also be used for a base station to receive reverse link transmissions from user terminals.

The low-power diversity receiver described herein may be used for various wireless communication systems such as a CDMA system, a TDMA system, a GSM system, an AMPS system, a multiple-input multiple-output (MIMO) system, an orthogonal frequency division multiplexing (OFDM) system, an orthogonal frequency division multiple access (OFDMA) system, a wireless local area network, and so on.

A large portion of a diversity receiver (possibly all circuit blocks except SAW filters, control units 252 , 352 , and 452 , and data processors 240 and 340 ) may be implemented on one or more RF integrated circuits (RFICs). The diversity receiver may also be fabricated with various IC process technologies such as complementary metal oxide semiconductor (CMOS), bipolar junction transistor (BJT), bipolar-CMOS (BiCMOS), silicon germanium (SiGe), gallium arsenide (GaAs), and so on.

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.