This application is a divisional application of chinese application 03809045.7 entitled multiple input multiple output radio transceiver, filed on 21/4/2003.
This application claims priority from the following U.S. provisional patent applications (each of which is incorporated herein by reference in its entirety):
US60/319,434, filed on 7/30/2002.
Detailed Description
Fig. 1 shows a block diagram of a radio transceiver 10. The radio transceiver 10 is adapted to process radio frequency signals detected by at least two antennas. The foregoing description has focused on an embodiment with two antennas 12 and 14, and associated transmit and receive channels for each antenna, but the same architecture can be generalized to support N processing channels for N antennas. The radio transceiver is useful for supporting the aforementioned CBF technique. CBF systems and methods are described in detail in the following patent applications: us patent application 10/164,728 entitled "system and method for antenna diversity scheme using joint maximum ratio combining" filed on 6/19/2002; us patent application 10/174,689 entitled "system and method for antenna diversity using equal power connection maximum ratio combining" filed on 2002, 6/19/2002; and U.S. patent application No. 10/064,482 entitled "system and method for joint maximum ratio combining using time domain signal processing", filed on 7/18/2002. All of these pending, commonly assigned patent applications are directed to optimizing the received SNR at a communication base station when communicating with another communication device, thereby increasing the range between the two devices and the data rate of that range.
One advantage of the techniques described in the above-referenced patent application entitled "system and method for antenna diversity using equal power connection maximum ratio combining" is that the output power required from each antenna channel is reduced. Thus, the size of the power amplifier may be reduced, which reduces the overall semiconductor chip area of the IC and more easily isolates other RF circuitry on the IC from the power amplifier.
The radio transceiver 10 includes a receiver and a transmitter. The receiver comprises receiver circuits 20 and 30. Receiver circuitry or portion 20 is for antenna 12 and receiver circuitry or portion 30 is for antenna 14. Similarly, the transmitter includes a transmission circuit 40 for the antenna 12 and a transmission circuit 60 for the antenna 14. Each receiver circuit 20 and 30 includes a downconverter 24, a variable low pass filter 26 and a sample-and-hold circuit 28. Each transmission circuit 40 and 60 includes a sample-and-hold circuit 42, a low-pass filter 44, an upconverter 46, a band-pass filter 48, and a power amplifier 50. Downconverter 24 may include circuitry to perform single-stage (direct) conversion to baseband or two-stage conversion to an intermediate frequency to baseband. Likewise, the upconverter 46 may be upconverted directly to RF or first to intermediate frequency, then to RF. More specific embodiments are described below in conjunction with figures 2-4. The low pass filter 44 may be a variable filter to accommodate a narrowband transmission operating state or one of several wideband transmission operating states.
A front-end section 90 connects the radio transceiver 10 to the antennas 12 and 14. Switches 62 and 64 are connected to antennas 12 and 14, respectively. The switch 62 selects whether the output of the transmission circuit 60 or the input of the receiver circuit 20 is connected to the antenna 12. The switch 64 selects whether the output of the transmit circuit 40 or the input of the receiver channel 30 is connected to the antenna 14. Bandpass filter 22 is connected to one switch terminal of switches 62 and 64. In addition, low pass filters 52 and 54 are connected between the outputs of the power amplifiers 50 in each of the transmission circuits 40 and 60, with the other switch terminals of the switches 62 and 64 being associated with the antennas 12 and 14, respectively.
The outputs of the sample-and-hold circuits 28 of the receiver circuits 20 and 30 are connected to analog-to-digital converters (ADCs) 70 and 72, respectively. The inputs of the sample and hold circuits 42 in the transmission circuits 40 and 60 are connected to digital-to-analog converters (DACs) 80 and 82, respectively. DACs 80 and 82 may receive as inputs first and second digital baseband transmission signals representing complex-weighted transmission signal components of a single baseband signal to be simultaneously transmitted from antennas 12 and 14. The first and second transmitter circuits 40 and 60 process the first and second analog baseband signals for substantially simultaneous transmission. Similarly, antennas 12 and 14 may detect first and second received signals, respectively, which are components of a single signal transmitted to transceiver 10. The first receiver circuit 20 and the second receiver circuit 30 process the first and second received signals substantially simultaneously to allow weighted combining of the resulting digital baseband received signals.
An interface and control module 92 is provided to interface the radio transceiver 10 with other components, such as baseband processing components. For example, the interface and control module 92 receives filter bandwidth control signals, center frequency control signals, and switch control signals, all of which are used to control the operation of specific components in the radio transceiver. In addition, the aforementioned signals may be obtained for controlling a processor or baseband component and connected directly to pins of the appropriate components of the transceiver 10.
The center frequency control signal controls the center frequency of the local oscillator signal used by the down converter 24 in each receiver circuit 20 and 30 and the local oscillator signal used by the up converter 46 in each transmit circuit 40 and 60. In addition, the filter bandwidth control signal controls the cutoff frequency of the variable low-pass filter 26. The switch control signal controls the position of switches 62 and 64 depending on whether transceiver 10 is receiving or transmitting.
A distinctive function of the radio transceiver 10 is to simultaneously receive and process the signals detected by each antenna 12 and 14 to output appropriately combined first and second baseband receive signals, which are obtained (in a baseband processor) using the CBF technique described previously. Conversely, the radio transceiver 10 processes the first and second baseband analog transmission signals (representing weighted components of a single transmission signal) simultaneously and outputs them for transmission via antennas 12 and 14, respectively. The radio transceiver 10 shown in fig. 1 may operate in a half-duplex mode, and if desired, may also operate in a full-duplex mode.
Furthermore, the radio transceiver 10 may perform MIMO operations in different bandwidths. For example, radio transceiver 10 may transmit or receive signals in a single RF channel in a radio frequency band, such as a 20MHz 802.11 channel in the 2.4GHz band. However, it may also perform MIMO operation to transmit or receive signals in a wider bandwidth, such as higher data rate signals or signals occupying substantially the entire frequency band, such as 80MHz of the 2.4GHz band. The filter bandwidth control signal sets the cutoff frequency of the low pass filter 26 in each receiver circuit 20 and 30 to low pass filter the desired portion of the RF bandwidth. The radio transceiver 10 also has receive-only, non-MIMO operation in which the output of each receive channel can be obtained to sample any portion or the entire RF band, which is achieved by adjusting the low pass filter 26. The latter function is useful for obtaining samples of the RF band to perform spectral analysis of the RF band. As will be explained in further detail in connection with fig. 13 and 14, the low pass filter 44 in the transmitter may be eliminated and the variable low pass filter 26 used for both received and transmitted signals.
The large dashed box surrounding receiver circuits 20 and 30 and transmission circuits 40 and 60 is intended to indicate that all of these components, including power amplifier 50, may be implemented on one semiconductor Integrated Circuit (IC). Other components may also be implemented on the IC as semiconductor and filter design techniques allow this. The performance advantages achieved by integrating multiple transmit channels and multiple receive channels on the same semiconductor are described above.
Fig. 2-4 show more specific examples of the MIMO radio transceiver shown in fig. 1. Fig. 2 shows a dual-band radio transceiver employing a superheterodyne (dual stage) conversion architecture. Fig. 3 shows a dual band radio transceiver employing a stepped Intermediate Frequency (IF) conversion architecture, which uses only one frequency synthesizer. Fig. 4 shows a dual band radio transceiver employing a direct conversion (single stage) architecture. Fig. 5 illustrates a radio front-end section that may be used with any of the radio transceivers shown in fig. 2-4.
Referring to fig. 2 and 5, a radio transceiver 100 will be described. The radio transceiver 100 shown in fig. 2 is a superheterodyne receiver capable of operating in two different frequency bands, such as one of a 2.4GHz unlicensed band and a 5GHz unlicensed band.
As shown in fig. 5, the radio transceiver 100 is designed to be connected to first and second antennas 102 and 104 via an RF front-end section 105, the RF front-end section 105 comprising transmit/receive (T/R) switches 106 and 108, which are connected to the antennas 102 and 104, respectively. Each T/R switch 106 and 108 has an antenna terminal connected to its associated antenna, a receive output, and a transmit input, and selects either the receive output or the transmit input depending on whether the transceiver is transmitting or receiving in response to a T/R switch control signal. Also in the RF front-end section 105 are band selection switches 110, 112, 114 and 116 which select the output of the antenna from the switches 106 and 108 according to the frequency band of the signal being transmitted or received. The band selection switches 110 and 112 are receive band selection switches each having an input terminal connected to the receive output terminals of the first and second T/R switches 106 and 108, respectively, and a first output terminal connected to the BPFs 120 and 124, respectively, and a second output terminal connected to the BPFs 122 and 126, respectively. The band selection switches 114 and 116 are transmission band selection switches each having first and second inputs and an output. First input terminals of the band selection switches 114 and 116 are connected to the LPFs 128 and 132, respectively, and second input terminals of the switches 115 and 116 are connected to the LPFs 130 and 134, respectively. The outputs of switches 114 and 116 are connected to the transmit inputs of the first and second T/R switches 106 and 108, respectively.
Referring back to fig. 2, on the receive side of the radio transceiver 100, there is a receiver that includes a receiver path or circuit 140 associated with the signal detected by the antenna 102 and a receiver path or circuit 170 associated with the signal detected by the antenna 104. On the transmit side, there is a transmitter that includes a transmit channel or circuit 210 associated with antenna 102 and a transmit channel or circuit 230 associated with antenna 104. Each of the receiver circuits 140 and 170 has two branches: the first branch processes signals from a first radio frequency band and the second branch processes signals from a second radio frequency band.
More specifically, each branch of the receiver circuits 140 and 170 is connected to a respective one of the band pass filters 120, 122, 124 and 126 in the RF front end section 105 shown in fig. 5. In a first branch of the receiver circuit 140, there is a Low Noise Amplifier (LNA)142 and an RF mixer 144 that down-converts the RF signal from a first radio frequency band (RFB1) to an Intermediate Frequency (IF). In a second branch of the receiver circuit 140 there is an LNA152 and an RF mixer 154 which down-converts the RF signal from the second radio frequency band to IF. The IF filter (IFF)145 is connected to the mixer 144 and the mixer 154, and on the output side of the IFF145 are a variable amplifier 146, quad mixers (quad mixers) 148 and 156, and variable low pass filters 150 and 158. The sample-and-hold circuit 160 is connected to the variable low-pass filter 150, and the sample-and-hold circuit 162 is connected to the variable low-pass filter 158. As will be described in greater detail below, a first branch of receiver circuitry 140 (consisting of LNA142 and mixer 144) processes signals from a first RF band (RFB1) detected by antenna 102. A second branch of receiver circuitry 140, consisting of amplifier 152 and mixer 154, processes signals from a second RF band (RFB2) detected by antenna 102. Only one branch of receiver circuitry 140 is active at any given time. Thus, if the output impedance of mixers 144 and 154 is high, IFF145 and variable power amplifier 146 may be shared by the branches (no additional switches are required). Quad mixers 148 and 156 generate in-phase (I) and quadrature (Q) signals of the signal provided to the input of variable amplifier 146. Thus, in summary, receiver circuit 140 has a first downconverter consisting of an RF mixer (144 or 154, depending on which band branch is being used) that downconverts a first received signal detected by antenna 102 (fig. 5) to an intermediate frequency signal, and quad mixers 148 and 156 further downconvert the intermediate frequency signal to I and Q baseband analog signals.
The receiver circuit 170 has means 172-192 to mirror these in the receiver circuit 140 but to process signals from the antenna 104 (fig. 5) in either the first RF band (RFB1) or the second RF band (RFB 2). Similar to receiver circuit 140, receiver circuit 170 has a second downconverter consisting of an RF mixer (174 or 184, depending on which band branch is being used) that downconverts the second receive signal detected by antenna 104 to a second intermediate frequency signal that is the same as the IF of the first intermediate frequency signal generated in receiver circuit 140, and quad mixers 178 and 186 that further downconvert the second IF signal to I and Q baseband analog signals.
It should be understood that although not shown, other components may be present in the receiver circuit. For example, there may be an image rejection filter between the LNA and the mixer following the LNA.
Switches 200 and 202 are connected to sample-and-hold circuits in receiver circuits 140 and 170, respectively, to switch between the I and Q outputs associated with the first and second analog baseband receive signals output by receiver circuit 140 and receiver circuit 170, respectively, for processing by the ADC. Further, the switches 270 and 280 serve an additional function on the transmit side to receive as inputs the outputs of the DACs providing the first and second analog baseband signals to be transmitted.
On the transmit side of the radio transceiver 100, there are two transmit circuits 210 and 230. In the transmission circuit 210, quad mixers 212 and 214 receive as inputs the I and Q data signals, respectively, which are up-mixed to IF by an intermediate frequency local oscillator signal. The outputs of quad mixers 212 and 214 are summed and connected to a variable amplifier 216, which in turn is connected to an RF mixer 218. The RF mixer 218 upconverts the intermediate frequency signal to RF, either RFB1 or RFB 2. Bandpass filters 222 and 224 are connected to the output of the mixer 218. Bandpass filter 222 is associated with RFB1 and bandpass filter 224 is associated with RFB 2. A power amplifier 226 is connected to the output of bandpass filter 222 and a power amplifier 228 is connected to the output of bandpass filter 224. The output of power amplifier 226 is connected to the input of low pass filter 128 (fig. 5), and the output of power amplifier 228 is connected to the input of low pass filter 130 (fig. 5). In summary, the first transmission circuit 210 has an up-converter consisting of quad mixers 212 and 214 that up-mix baseband I and Q signals representing the first transmission signal, and an RF mixer 218 that further up-mixes the intermediate frequency signal to generate a first RF signal that is to be connected to the first antenna 102 (fig. 5). The output of the RF mixer 218 is connected to a bandpass branch consisting of BPF222 and power amplifier 226 or BPF224 and power amplifier 228.
The transmission circuit 230 associated with the antenna 104 has components 232 and 248 and mirrors the transmission circuit 210 to process the second transmission signal component. Similar to the first transmission circuit 210, the second transmission circuit 230 has an up-converter comprised of quad mixers 232 and 234 that up-mix the I and Q baseband signals representing the second transmission signal, and the RF mixer 238 further up-mixes the intermediate frequency signal to generate a second RF signal that will be coupled to the second antenna 104 (fig. 5) for transmission substantially simultaneously with the first RF signal.
The input signals to the transmitter circuits 210 and 230 are provided from DACs (not shown) to switches 270 and 280, which alternately select between baseband I and Q signals, which are connected to respective sample-and-hold circuits 272 and 274 in the transmitter circuit 210 and respective sample-and-hold circuits 282 and 284 in the transmitter circuit 230. The sample-and-hold circuits 272 and 274 are in turn connected to LPFs 276 and 278, respectively, and the sample-and-hold circuits 282 and 284 are connected to LPFs 286 and 288, respectively. LPFs 276 and 278 filter the baseband I and Q signals of the first transmit signal and provide their outputs to quad mixers 212 and 214, respectively. Similarly, LPFs 282 and 288 filter the baseband I and Q signals of the second transmit signal and provide their outputs to quad mixers 232 and 234, respectively. If variable LPFs in the receiver are shared for receive and transmit processing, the number of LPFs may be reduced. Fig. 13 and 14 illustrate techniques for sharing the variable LPFs for transmit and receive operations.
Since the radio transceiver 100 is a super-heterodyne device, RF local oscillator signals and IF local oscillator signals for radio frequencies associated with RFB1 and RFB2 need to be generated. An IF synthesizer (IF LO synth)250 and a Voltage Controlled Oscillator (VCO)252 (including 90 ° phase components, not shown for simplicity) generate in-phase and quadrature phase shifted IF local oscillator signals, which are connected to mixers 148, 156, 178 and 186 and mixers 212, 214, 232 and 234. An RF local oscillator synthesizer (RF LO synth)260 is connected to VCOs 262, 264 and 266, which provides different RF local oscillator signals to the mixers 144, 154, 174 and 184 on the receive side and the mixers 218 and 238 on the transmit side. There are multiple VCOs providing RF signals for multiple RF bands. For example, VCO262 provides an RF local oscillator signal for the unlicensed band of 2.4GHz (for any RF channel or center frequency), VCO264 provides an RF local oscillator signal for the unlicensed band of low 5GHz (for any RF channel or center frequency), and VCO266 provides an RF local oscillator signal for the unlicensed band of high 5GHz (for any RF channel or center frequency).
The interface and control module 290 interfaces to/from external devices such as clock signals, data signals, and enable signals of the baseband processor and/or the control processor. Transceiver control signals originating from an external device may be connected to the appropriate transceiver components or to pins of the appropriate components through interface control module 290. The transceiver control signals include, for example, RF center frequency control signals, filter bandwidth control signals, transmission gain adjustment signals, reception gain adjustment signals, and switch control signals. The RF center frequency control signal controls which RF band and particular RF channel in that band is used for the RF LO synthesizer 260 and associated VCO262, 264 or 267 to output the local oscillator signal. An example of a frequency synthesizer suitable for use with the radio transceiver described herein is described in U.S. provisional application No. 60/319,518 entitled frequency synthesizer for multiband superheterodyne transceiver application, filed on 9/4 2002. The filter bandwidth control signal controls the variable bandwidth low pass filters 150, 158, 180 and 188 to operate in either a wide band mode (passing the entire band or substantial portion thereof) or a narrow band mode (passing a portion such as a single RF channel). The transmission gain control signal controls the gains of the variable amplifiers 216 and 236 on the transmission side, and the reception gain control signal controls the gains of the variable amplifiers 146 and 176 on the reception side. The switch control signal controls the position of the switches 106, 108, 110, 112, 114, 116, 200 and 202 in accordance with the operating state and operating frequency band of the radio transceiver 100.
Most of the components of the radio transceiver 100 are implemented in a semiconductor IC. The large dashed portions indicate those components that may be included in the IC. However, additional components may also be implemented in the IC.
With reference to fig. 2-5, the operation of the transceiver 100 will be described. For example, RFB1 is a 2.4GHz unlicensed band and RFB2 is one of the 5GHz unlicensed bands. It should be understood that the same architecture shown in fig. 2 may be used for other applications, and that a 2.4/5GHz dual band application is only one example. For this example, the IF is 902.5MHz, the frequency output of the IF LO synth250 is 1805MHz, and the RF local oscillator signal output by the RF LO synthesizer ranges from 3319.5 MHz to 4277.5 MHz. The variable low pass filters 150, 158, 180 and 188 are each controllable to filter multiple bandwidths in the RF band, for example, so that MIMO receive processing of signals detected by the antennas 102 and 104 ranges from 20MHz bandwidth up to 80MHz or 100MHz bandwidth. Similarly, the variable low pass filters 276, 278, 286, and 288 are each controllable to filter multiple bandwidths in the RF band, for example, to enable MIMO transmission processing of baseband signals to be transmitted from a 20MHz bandwidth up to an 80MHz or 100MHz bandwidth. In addition, as described below in connection with fig. 13 and 14, the variable low pass filters 150, 158, 180, and 188 may be shared variably for receive and transmit processing. In summary, the radio transceiver 100 operates in half-duplex mode when it is not simultaneously transmitting and receiving either RFB1 or RFB 2.
The radio transceiver 100 may also operate in a non-MIMO configuration. For example, the output of only one receive channel may be used with an appropriate variable low pass filter bank to sample any portion or the entire desired RF band to obtain data to analyze portions or all of the spectrum of the RF band.
Depending on whether the radio transceiver is transmitting or receiving and where the RF band is operating, both the T/R switch and the band select switch in the RF front-end section 105 (fig. 5) are controlled.
For example, when radio transceiver 100 is receiving at RFB1, switches 106 and 108 are both moved to their upper positions to select the receive side of transceiver 100. The RF LO synthesizer 260 is controlled to output an RF local oscillator signal that will down-convert a particular (sub-band) from the RFB 1. Switches 110 and 112 are both moved to their upper positions to select the corresponding branches of bandpass filters 120 and 124 (associated with RFB1) and receiver circuits 140 and 170. Filter 120 band-pass filters the signal detected by antenna 102 and filter 124 band-pass filters the signal detected by antenna 104. Low pass filters 150,158, 180 and 188 are all controlled to operate in the required bandwidth. The two signals detected by antennas 102 and 104 may be spatially distinct signals of the same transmission signal. The signal from antenna 102 is downconverted to IF by mixer 144, filtered by IF filter 145, then downconverted to baseband I and Q signals by quad mixers 148 and 156 and filtered by lowpass filters 150 and 158. Each I and Q signal derived from this signal is sample-and-hold or selected by switch 200 for output to the ADC. Receiver circuitry 170 performs similar operations on signals detected by antenna 104.
The radio transceiver 100 performs MIMO transmission operations in a similar manner. LPFs 276, 278, 286, and 288 in the transmitter (or shared LPFs of the receiver) are all controlled to filter the required bandwidth. Further, the RF LO synth 260 is controlled to output an RF local oscillator signal according to the frequency band of the signal to be transmitted. Assuming that a signal will be transmitted on a channel in RFB2, switches 106 and 108 are moved to their bottom positions, thereby selecting the transmit side of radio transceiver 100. Switches 114 and 116 are moved to their bottom positions to select the legs of transmission circuits 210 and 230 associated with RFB 2. The analog baseband signal to be transmitted is composed of first and second signal components, which are to be transmitted simultaneously by respective antennas 102 and 104. The appropriate RF local oscillator signal is output to mixers 218 and 238. The I and Q signals of the first transmit signal component are up-converted to IF by quad mixers 212 and 214. Variable amplifier 216 adjusts the gain of the resulting IF signal and mixer 218 upconverts the IF signal to RF. The filter 224 band-pass filters the RF signal output by the mixer 218, and the power amplifier 228 amplifies the output of the band-pass filter 224. The low pass filter 130 filters harmonics of the output of the power amplifier 228 and the resulting output is connected to the antenna 102 via switches 114 and 106. Similar operations are also performed for the I and Q signals of the second transmission signal component. The band pass filter 246 filters the RF signal and the power amplifier 248 amplifies the filtered signal, which is in turn connected to the low pass filter 134. The resulting filtered signal is coupled to the antenna 104 via switches 116 and 108.
Fig. 3 shows a radio transceiver 100' similar to the radio transceiver 100, but employing a variable or stepped IF architecture instead of a superheterodyne architecture. In particular, in the receiver circuitry of the radio transceiver 100', the received RF signal is down-mixed to an intermediate frequency dependent on the RF local oscillator signal, and an IF filter is not required or optional. Similar principles apply to transmission circuits. Thus, the RF local oscillator signal output of the RF L0 synthesizer 260 is connected to divide-by-4 circuitry, which in turn provides IF local oscillator signals to the mixers 148 and 156 in the receiver circuitry 140, the mixers 178 and 186 in the receiver circuitry 170, the mixers 212 and 214 in the transmission circuitry 210, and the mixers 232 and 234 in the transmission circuitry 230. Divide by 4 circuit 265 generates an IF local oscillator signal based on an RF local oscillator signal provided by RF LO synthesizer 260. No IF filter is required and only one synthesizer (for the RF local oscillator signal) is required. In addition, the operation of the radio transceiver 100' is similar to the operation of the radio transceiver 100.
The transceivers of fig. 2 and 3 have certain advantages, making them suitable for highly integrated and low cost implementations. First, the superheterodyne architecture of fig. 2 and the stepped IF architecture of fig. 3 allow for the integration of a power amplifier in the transmitter of a radio transceiver IC. This is because the power amplifier output frequency falls outside the VCO resonant range, thereby avoiding injection-lock of the VCO. This is not possible in other architectures such as the direct conversion architecture shown in fig. 4. Second, the stepped IF transceiver of fig. 3 does not require an IF filter, thereby reducing the material cost of the radio transceiver. Even the super-heterodyne design of fig. 2 may be implemented without an IF filter under certain design parameters. The design of fig. 3 has the dual advantages of easier integration of the power amplifier and no need for an IF filter. Thus, the radio transceiver design of fig. 3 may be desirable where cost, integration, and IC size are important.
Referring now to fig. 4, a direct conversion radio transceiver architecture 300 is depicted. Similar to the radio transceiver 100, the radio transceiver 300 has a plurality of receiver circuits 310 and 340 in the receiver and a plurality of transmission circuits 370 and 400 in the transmitter. The receiver circuits are identical, and the transmission circuits are also identical. In the receiver circuit 310, there are two amplifiers 312 and 314 connected to a switch 316. Amplifier 312 receives the bandpass filtered signal in band RFB1 from the bandpass filter in RF front-end section 105 (fig. 2), and similarly, amplifier 314 receives the bandpass filtered signal in band RFB 2. The output of switch 316 is connected to a variable amplifier 318 to adjust the gain of the signal provided to its input. The output of variable amplifier 318 is connected to mixers 320 and 322, which down-mix the amplified received signal by the IF local oscillator signal to generate I and Q signals. The output of mixer 320 is coupled to a low pass filter 324 and the output of mixer 322 is coupled to a low pass filter 326. For example, low pass filters 324 and 326 are third order low pass filters that may be off-chip for better linearity, away from the rest of the transceiver components. The outputs of low pass filters 324 and 326 are connected to variable low pass filters 328 and 330, respectively. The variable low pass filters 328 and 330 are variably controlled to vary their cutoff frequency to select either a narrow band (e.g., 10MHz) or a wide band (e.g., 40 MHz). Variable low pass filters 328 and 330 are connected to sample and hold circuits 332 and 334, respectively. The outputs of sample and hold circuits 332 and 334 are baseband I and Q signals representing the signal detected by antenna 102. The switch 336 is controlled to alternate between baseband I and Q signals for connection to a single ADC and save the cost of a second ADC.
The receiver circuit 340 has components 342 and 366 that are the same as those in the receiver circuit 310. Receiver circuits 310 and 340 perform direct conversion or zero intermediate frequency down conversion of the detected RF signal to baseband. In summary, the first receiver circuit 310 has a first downconverter comprising quad mixers 320 and 322 that downconvert a first receive signal detected by the antenna 102 directly to baseband I and Q signals. Similarly, second receiver circuit 340 has a second downconverter comprising quad mixers 350 and 350 that downconvert a second receive signal detected by antenna 104 directly to baseband I and Q signals.
It will be appreciated by those of ordinary skill in the art that in receiver circuits 310 and 340, quad mixers 320 and 322 and quad mixers 350 and 352 may be wideband mixers capable of covering both RFB1 and RFB2, or separate quad mixers may be provided for each RF band.
On the transmit side, the transmit circuit 370 includes first and second sample-and-hold circuits 372 and 374 that receive the I and Q data signals for the first transmit signal from the switch 371. The outputs of the sample and hold circuits 372 and 374 are connected to low pass filters 376 and 378. The outputs of the low pass filters 376 and 378 are connected to quad mixers 380 and 382, respectively. Quad mixers 380 and 382 up-mix the I and Q signal outputs filtered by lowpass filters 376 and 378 to output I and Q signals, which are combined and connected to a variable amplifier 384. The variable amplifier 384 adjusts the gain of the first RF signal and provides the signal to the band pass filters 386 and 388, which are associated with RFB1 and RFB2, respectively. The outputs of the bandpass filters 386 and 388 are connected to power amplifiers 394 and 396. Power amplifiers 390 and 392 amplify the RF signals for frequency bands RFB1 and RFB2, which are connected to RF front end 105.
The transmission circuit 400 has components 402-422 that are identical to those in the transmission circuit 370. The input of the transmission circuit 400 consists of the I and Q signals of the second transmission signal, which are alternately provided by a switch 401. Thus, in summary, the first transmission circuit 370 includes a frequency upconverter made up of quad mixers 380 and 382 that upconvert baseband I and Q signals directly to RFI and Q signals that are combined to form the first RF signal. The second transmission circuit 400 includes a frequency upconverter made up of quad mixers 410 and 412 that upconvert the baseband I and Q signals directly to RFI and Q signals, which are combined to form a second RF signal.
A dual mode Phase Locked Loop (PLL)430, VCOs 432, 434, and 436, a square pulse module 438, and a 90 ° phase shifter 440 may be provided to provide appropriate in-phase and quadrature RF local oscillator signals to the mixers 320 and 322 in the receiver circuit 310, the mixers 350 and 352 in the receiver circuit 370, the mixers 380 and 382 in the transmission circuit 370, and the mixers 410 and 412 in the transmission circuit 400, respectively. Dual-mode PLL430 is a standard component for generating high frequency signals. Square pulse module 438 acts as a frequency doubling device to reduce the pull of the VCO (pull) caused by the power amplifier. For example, to provide RF mixing signals for the 2.4GHz unlicensed band and the high and low 5GHz unlicensed bands, the VCO432 generates RF signals in the 1200-1240MHz range, the VCO434 generates RF signals in the 2575-2675MHz range, and the VCO436 generates RF signals in the 2862-2912MHz range.
Similar to the radio transceiver 100, there are control signals connected to the appropriate components to control operation. The radio transceiver 300 has the same operation state as the radio transceiver 100. The filter bandwidth control signal controls the variable low pass filters 328, 330, 358, and 360 according to the operating bandwidth of the transceiver 300. The receive gain control signal controls variable amplifiers 318 and 348. The switch control signals control the respective switches in the radio transceiver 300 and the front-end section, which are controlled depending on whether the radio transceiver is in a receive mode or a transmit mode and depending on which frequency band the transceiver is operating in, either RFB1 or RFB 2. The RF center frequency control signal controls dual-mode PLL410 and VCOs 412-416 depending on which RF band and which RF channel in that band the transceiver is operating in. The transmit gain control signal controls the variable amplifiers 384 and 414 in the transmit circuit.
Fig. 6-10 show different front-end components. In fig. 6, the front end 500 component includes many of the same components as the front end component 105, albeit in a slightly different configuration. LPFs 128, 130, 132, and 134 may be integrated on a radio transceiver IC or combined in radio front end 500. In place of switches 106 and 108, duplexers 502 and 504 are used for band selection from antennas 102 and 104. As is well known in the art, a diplexer is a three-port device having one common port and two other ports, one for high frequency signals and one for low frequency signals. Thus, the duplexers 106 and 108 function as band selection switches. In the example of fig. 6, the two frequency bands supported are the 2.4GHz band and the 5.25GHz band. Switches 110, 112, 114 and 116 are transmit/receive switches that select the appropriate signal depending on whether the transceiver is transmitting or receiving. For example, when a radio transceiver is transmitting signals in the 2.4GHz band through antennas 102 and 104, duplexer 502 receives a first 2.4GHz transmit signal from switch 110 and couples it to antenna 102, and duplexer 504 receives a second 2.4GHz transmit signal from switch 114 and couples it to antenna 104. All other switch positions are essentially irrelevant. Similarly, when receiving signals in the 5.25GHz band, duplexer 502 couples a first 5.25GHz receive signal from antenna 102 to switch 112, and duplexer 504 couples a second 5.25GHz receive signal from antenna 104 to switch 116. Switch 112 selects the output of duplexer 502 and switch 116 selects the output of duplexer 504.
As is well known in the art, the radio transceiver is connected to a baseband processor, which may be a separate integrated circuit, as shown By Baseband Integrated Circuit (BBIC)510 in fig. 6 and 7.
Fig. 7 shows a front-end section 500' similar to the front-end section 500, but with its transmit/receive switch effectively integrated on the radio transceiver IC. Many known technologies can integrate switches like transmit/receive switches on the transceiver IC. When the transmit/receive switch is integrated on the radio transceiver IC, for each antenna, a quarter wave element 515 is provided in the radio front end 500' at each branch of the duplexer for each antenna. Fig. 8 shows this structure for one antenna 102, as an example only, but it is repeated for each antenna. When a signal is being transmitted, the transmit/receive switch is switched to the terminal connected to ground so that the signal output of the corresponding Power Amplifier (PA) of the transmitter is selected and connected to the duplexer, and when a signal is received, it is switched to the other terminal so that the received signal passes through the quarter-wave element 515, the transmit/receive switch, and passes to the LNA in the receiver. The quarter wave element 515 may be any quarter wave transmission line. One embodiment of the quarter wave element 515 is a microstrip structure disposed on a printed circuit board. The quarter wave feature of the quarter wave element 515 produces a phase shift that acts as an impedance transformer, either shorting the connection between the bandpass filter and ground or creating an open circuit depending on the position of the switch.
The radio transceiver IC and front end architecture shown in fig. 6 and 7 are useful for a Network Interface Card (NIC) to function as an 802.11x WLAN station.
Fig. 9 shows a front-end section 600 interfacing with two radio transceiver ICs to provide a 4-channel MIMO radio transceiver arrangement. One example of the use of this type of architecture is in an Access Point (AP) of a WLAN. However, up to here the described radio transceiver architectures were used for 2-channel MIMO operation, 4-channel MIMO operation may even provide greater connection limits with other devices when used with the maximum ratio combining scheme mentioned above.
The front-end section 600 interfaces the two radio transceiver ICs to the 8 antennas 602 and 616. BBIC660 is connected to two radio transceiver ICs that operate in tandem to transmit 4 weighted components of a single signal or receive 4 components of a single received signal. Antennas 602, 606, 610, and 614 are dedicated to one frequency band, such as the 2.4GHz band, while antennas 604, 608, 612, and 616 are dedicated to another frequency band, such as the 5GHz band. In the front-end section 600, there are 8 transmit/receive switches 620 and 634, each associated with one of the antennas 602 and 616, respectively. There are also 8 bandpass filters 640 and 654 each connected to one of the transmit/receive switches 620 and 634. The transmit/receive switch 620 and 634 may be integrated on the respective radio transceiver IC instead of being part of the front-end section 600. Although not shown in detail, the LPF is also integrated on the radio transceiver IC. The operation of the front-end component 600 is similar to what has been described above. The transmit/receive switch 620 and 634 are controlled to select the appropriate signal depending on whether the transceiver IC is operating in a transmit mode or a receive mode.
Fig. 10 shows a front-end component 600' that is similar to front-end component 600, but which does not include a transmit/receive switch. Further, the transceiver 670 is a single IC integrating 4 channels (which are included in the two transceiver ICs shown in fig. 9). The transmit/receive switch is integrated on the transceiver IC 670. The operation of the front-end component 600' is similar to the operation of the front-end component 600. Fig. 10 illustrates the ability to scale the number of MIMO channels to 3, 4 or more separate channels.
Fig. 9 and 10 also show radio transceivers 100, 100', and 300 configured in various instances to support multi-channel capabilities in a communication device, such as an AP. For example, as shown in fig. 9, one radio transceiver, such as an access point, may perform 2-channel MIMO communication with devices on a channel, while other radio transceivers may perform 2-channel MIMO communication with devices on another channel. Instead of interfacing to one baseband IC, each may interface to a separate baseband IC or a single baseband IC capable of dual channel operation simultaneously.
Fig. 11 and 12 show a configuration whereby the number of DACs and ADCs connected to the radio transceiver can be variably reduced. Typically, for each signal that requires processing, a separate DAC or ADC should be required. However, in a half-duplex radio transceiver, there is an opportunity to share the DAC and ADC since the transmit and receive operations do not occur simultaneously. For example, fig. 11 shows a structure that includes two ADCs 710 and 720 and three DACs 730, 740, and 750. The ADC720 and DAC730 are shared. Switch 760 selects the input to ADC720 and switch 770 selects the output of DAC 730. An interleaver (MUX)780 is coupled to the ADC720 to transmit output therefrom and to the DAC730 to condition input thereto. The ADC, DAC and digital MUX780 may be located on a separate integrated circuit than the radio transceiver integrated circuit. For example, these components may be located on a baseband integrated circuit with baseband demodulator 790 and baseband modulator 795 thereon.
The number of ADCs is reduced by using a single ADC720 to digitize the received Q signal and the transmit power level signal. Similarly, the number of DACs may be reduced by sharing a single DAC730 to convert the transmit I signal and the receiver gain control signal. The digital MUX780 is provided as a signal (or transmit I signal or receiver gain control signal) to the input of the shared DAC 730. Similarly, the signal output by the shared ADC720 (either the digital receive Q signal or the digital transmit power level signal) is sent by the digital MUX780 to the appropriate destination.
As described above, one way to facilitate sharing of the ADC and DAC is to provide switches 760 and 770. These switches may be located on the transceiver IC. The output of switch 760 is connected to the shared ADC720, one input is connected to the LPF at the output of the local oscillator, which produces the received Q signal, and the other input is connected to the output of the power detector, which produces the transmit power level signal. Switch 760 is controlled to select one of two positions depending on whether the ADC is to be used for the received Q signal or the transmit power level signal. Similarly, switch 770 has its input connected to shared DAC730, one output connected to the variable power amplifier in the receiver, and the other output connected to the LPF, which provides the transmit I signal to the in-phase local mixer in the transmitter. The switch 770 is controlled to select one of two positions depending on whether the shared DAC is to be used for the receiver gain control signal or the transmit I signal. The structure shown in fig. 11 may be repeated for each receive channel/transmit channel pair in the transceiver.
It should be understood that switches 760 and 770 are optional. As shown in fig. 12, if the radio transceiver ICs are half-duplex transceivers, they may be replaced by ordinary signal paths, which means that the receiver and transmitter are not operating simultaneously. Thus, for example, the shared DAC730 will convert whichever digital signal (transmit I signal or receiver gain control signal, depending on whether the transceiver is operating in a receive mode or a transmit mode) is provided to it, and the DAC730 will output an analog version of that signal on both channels. If the transmit I signal is selected for processing by the shared DAC730, the receiver will be off, so that connecting the analog version of the transmit I signal to the variable power amplifier in the receive channel will have no effect, but it will also be connected to the in-phase local oscillator in the transmitter, which is desirable. Similar situations remain if the switches for the shared ADC720 are replaced by a common signal path structure.
A single ADC and a single DAC may be shared between signals at the transmitter and receiver (since in a half-duplex transceiver, the transmitter and receiver are typically not operating at the same time). The above identified signals are merely examples of transmitter and receiver signals that may be multiplexed to a single ADC or a single DAC.
Fig. 13 and 14 show structures that allow sharing of LPFs used to filter baseband receive signals and baseband transmit signals in the radio transceivers of fig. 2-4. As an example, a single antenna channel of the direct conversion radio transceiver 300 is selected to illustrate the filter sharing technique. For simplicity, some intermediate components, such as variable amplifiers and sample-and-hold circuits, are not shown. LPFs 328 and 330 are shared to filter received I and Q signals (RXI and RX Q) associated with an antenna, such as antenna 102, and to filter baseband transmit I and Q signals (TXI and TX Q) to be transmitted. Each of the switches 710 and 720 has two inputs and one output connected to the inputs of the LPFs 328 and 330, respectively. Connected to the inputs of switch 710 are the receive I signal output of quad mixer 320 and the baseband transmit I signal. Similarly, connected to the input of switch 720 are the receive Q signal output of quad mixer 322 and the baseband transmit Q signal. The transmit/receive control signal is connected to the switches 710 and 720 so that the switches either select the terminal to which the receive I and Q signals are connected or select the terminal to which the transmit I and Q signals are connected. In fig. 13, it is assumed that the output impedance at each filter is low and each load impedance is high (typical in most analog ICs), so that the outputs of each filter are variably summed. Thus, only one multiplexer is required at the output of the filter. The structure of fig. 14 is similar to that of fig. 15, but additional switches 730 and 740 are provided in case the impedance is not as described above.
In summary, a multiple-input multiple-output (MIMO) radio transceiver is provided that includes a receiver and a transmitter, both of which may be implemented in the same integrated circuit. The receiver includes at least first and second receiver circuits, each receiver circuit processing signals from a corresponding one of the first and second antennas. The first receiver circuit includes a first downconverter coupled to the first antenna that downconverts a first receive signal detected by the first antenna to produce a first baseband signal. The second receiver circuit includes a second downconverter coupled to the second antenna that downconverts a second receive signal detected by the second antenna to produce a second baseband signal. Each receiver circuit may also include a low pass filter. The transmitter includes at least first and second transmitter circuits, each processing a signal to be transmitted by a corresponding one of the first and second antennas. The first transmitter circuit includes a first upconverter that upconverts a first baseband analog signal to generate a first RF frequency signal. Similarly, the second transmitter circuit includes a second upconverter that upconverts the second baseband analog signal to generate a second RF frequency signal. Each of the first and second transmitter circuits further comprises a bandpass filter and a power amplifier, both of which may be integrated on the same integrated circuit as the other transmitter components.
Similarly, a multiple-input multiple-output (MIMO) radio transceiver is provided that includes a receiver including at least first and second receiver circuits, each receiver circuit processing signals from a corresponding one of the first and second antennas, and a transmitter having at least first and second transmitter circuits. The receiver and the transmitter may be implemented on one integrated circuit. The first receiver circuit includes a first downconverter coupled to the first antenna that downconverts a first receive signal detected by the first antenna to produce a first in-phase baseband signal and a first quadrature baseband signal. The second receiver circuit includes a second downconverter coupled to the second antenna that downconverts a second receive signal detected by the second antenna to generate a second in-phase baseband signal and a second quadrature baseband signal. Each receiver circuit may also include a low pass filter to filter their in-phase and quadrature signals. The transmitter includes at least first and second transmitter circuits, each processing a signal to be transmitted by a respective one of the first and second antennas. The first transmitter circuit includes a first upconverter that upconverts the first in-phase baseband analog signal and the first quadrature baseband analog signal to generate a first RF frequency signal. The second transmitter circuit includes a second upconverter that upconverts the second in-phase baseband analog signal and the second quadrature baseband analog signal to generate a second RF frequency. Each transmitter circuit may also include a bandpass filter and a power amplifier, both of which may be implemented on the same integrated circuit as the other components.
Whilst the foregoing description relates to a MIMO radio transceiver having two antennas, and thus two receiver circuits and two transmitter circuits, it will be appreciated that the same concepts described herein may be extended generally to a radio transceiver having N transmitter circuits and N receiver circuits for operation with N antennas.
The above description is merely exemplary.