CN117318753A - Estimating and correcting transmitter local oscillator leakage in a loop-back path - Google Patents

Abstract

In an example, a system includes a receiver configured to receive a differential input signal from a Quadrature Amplitude Modulation (QAM) transmitter at a differential interface including a first input (426) and a second input (428). The system further includes a first switch (312) coupled to the first input (426) and a second switch (314) coupled to the second input (428), wherein the first switch (312) and the second switch (314) are configured to couple the first input (426) and the second input (428) to the complex mixer (138) in a non-inverting configuration. The system includes a third switch (318) coupled to the first input (426) and a fourth switch (316) coupled to the second input (428), wherein the third switch (318) and the fourth switch (316) are configured to couple the first input (426) and the second input (428) to the complex mixer (138) in an inverted configuration. The complex mixer (138) is configured to generate an output signal based on the non-inverted configuration and the inverted configuration.

Description

Estimating and correcting transmitter local oscillator leakage in a loop-back path

Cross Reference to Related Applications

The present application claims priority from indian provisional patent application No. 202241036648, filed on 27, 6, 2022, entitled "A NOVEL METHOD OF ESTIMATING/CORRECTING TRANSMITTER LO LEAKAGE BY FLIPPING THE DIFFERENTIAL NATURE [ new method of estimating/correcting transmitter LO leakage by flipping differential properties ]", which is incorporated herein by reference in its entirety.

Background

The radio architecture may use a carrier signal generated by a Local Oscillator (LO) to transmit an input signal carrying information. The carrier signal may be much higher in frequency than the input signal. The carrier signal may leak into the final transmitted signal, which is referred to as LO leakage. LO leakage may result in efficiency loss. The wireless standard specifies the maximum allowable amount of LO leakage. A correction signal may be added to the transmit signal to cancel the LO leakage.

Disclosure of Invention

According to at least one example herein, a system includes a receiver configured to receive a differential input signal from a Quadrature Amplitude Modulation (QAM) transmitter at a differential interface including a first input and a second input. The system also includes a first switch coupled to the first input and a second switch coupled to the second input, wherein the first switch and the second switch are configured to couple the first input and the second input to the complex mixer in a non-inverting configuration. The system includes a third switch coupled to the first input and a fourth switch coupled to the second input, wherein the third switch and the fourth switch are configured to couple the first input and the second input to the complex mixer in an inverted configuration. The complex mixer is configured to generate an output signal based on the non-inverted configuration and the inverted configuration.

According to at least one example herein, a method includes receiving a differential QAM input signal from a transmitter. The method further includes causing the first switch and the second switch to provide the differential QAM input signal to the complex mixer in a non-inverting configuration. The method includes causing the third switch and the fourth switch to provide the differential QAM input signal to the complex mixer in an inverted configuration. The method also includes mixing the differential QAM input signal with a complex mixer to produce an output signal. The method includes determining, with a controller, a local oscillator leakage associated with a transmitter based at least in part on an output signal. The method includes correcting local oscillator leakage.

According to at least one example herein, a system includes a transmitter configured to transmit a QAM signal. The system also includes a receiver configured to receive a differential QAM input signal from the transmitter at a differential interface including a first input and a second input. The system includes a first switch coupled to the first input and a second switch coupled to the second input, wherein the first switch and the second switch are configured to couple the first input and the second input to the complex mixer in a non-inverting configuration to generate a non-inverting signal provided to the complex mixer. The system also includes a third switch coupled to the first input and a fourth switch coupled to the second input, wherein the third switch and the fourth switch are configured to couple the first input and the second input to the complex mixer in an inverted configuration to generate an inverted signal input to the complex mixer. The system includes a controller configured to correct for transmitter local oscillator leakage using an inverted signal and a non-inverted signal.

Drawings

Fig. 1 is a block diagram of a transmitter and an auxiliary receiver according to various examples.

Fig. 2 is a block diagram of a transmit/auxiliary receiver (TX/AuxRX) chain according to various examples.

Fig. 3 is a diagram of an auxiliary receiver according to various examples.

Fig. 4 is a circuit diagram of a switching network and complex mixer according to various examples.

Fig. 5 is a flow chart of a method for estimating and correcting transmitter LO leakage according to various examples.

The same reference numbers may be used throughout the drawings to refer to the same or like features (functionally and/or structurally).

Detailed Description

Quadrature Amplitude Modulation (QAM) is a modulation method for transmitting information. QAM transmits two message signals by modulating the amplitudes of two carriers. The two carriers are identical in frequency but out of phase with each other by 90 °, which is called orthogonality or quadrature. One of these waves is called an in-phase (I) signal (I-chain) and the other is called a quadrature (Q) signal (Q-chain). The transmit signal is made up of the addition of the two carriers. At the receiver, these two waves may be separated (e.g., demodulated) due to their orthogonality. The modulated signal is typically a low frequency and low bandwidth waveform compared to the carrier frequency.

LO leakage occurs if the carrier signal leaks into the final transmission. LO leakage should be below a certain level to meet various standards, such as the IEEE 802.11 (Wi-Fi) standard. To meet these criteria, the carrier signal should not appear at the final output of the transmitter. Some systems have a power detector at the output of the transmitter to measure various LO leakage values and then perform calculations to iteratively find correction values that cancel the LO leakage. However, these iterative processes are time consuming and consume a large amount of power, which makes it difficult to meet the LO leakage criteria.

In the examples herein, a loop-back path (or feedback path) is implemented to measure and then correct for LO leakage. An auxiliary receiver in the loop-back path receives the transmitted QAM signals and uses these signals to estimate LO leakage that appears to be a constant value. The auxiliary receiver itself may also have a leakage that appears to be a constant value. These two constant values (of the transmitter and the auxiliary receiver) are decoupled to find the LO leakage of the transmitter. Examples herein also contemplate other transmitter impairments such as IQ mismatch (IQMM), phase noise, radio Frequency (RF) nonlinearity, etc. IQMM is caused by non-ideal characteristics of the I and Q paths.

In the loopback path described herein, the hardware switch compensates for impairments in the auxiliary receiver path. The loop path includes a complex mixer having differential inputs. The hardware switches coupled to the differential inputs have two configurations. In a first configuration, the sum of the transmit signal and the signal added through the auxiliary path (e.g., leakage) is provided to the complex mixer in a non-inverted configuration. In a second configuration, the switches are switched and the complex mixer is provided with the difference between the transmit signal and the signal added through the auxiliary path in an inverted configuration (e.g., the inverted signal is 180 ° out of phase with the non-inverted signal). The controller analyzes the outputs of the complex mixer for both the non-inverted configuration and the inverted configuration and then cancels the constant leakage signal added through the auxiliary path. The controller then performs other calculations described herein to estimate and correct the transmitter LO leakage. The process is performed by the controller for both the I and Q chains. In the examples herein, the process is performed for a shorter time than other systems. As long as the original IQMM or LO leakage of the loop-back path is the same in both configurations (non-inverting and inverting), the leakage can be high, as the IQMM and LO leakage will be eliminated by switching the non-inverting/inverting configuration of the inputs of the complex mixer. This feature relaxes the analog design requirements on the system. Moreover, the solution is applicable to all QAM-based architectures.

Fig. 1 is a block diagram of a transmitter and an auxiliary receiver according to various examples herein. The system 100 includes some components of the transmitter and auxiliary receiver, but other systems may include components or circuitry that are not shown here for simplicity. The system 100 includes Low Dropout (LDO) voltage regulators 102, 104, and 106. Analog LDO 102 provides supply voltages to transmit analog components 108, 110, 112, and 114, which will be described below. The RF LDO 104 provides a supply voltage to a front end power amplifier (PPA) 116. PA LDO 106 provides a supply voltage to a Power Amplifier (PA) 118.

The transmitter portion of system 100 includes a digital-to-analog converter (DAC) 108 (i_dac) for the I chain and a DAC 110 (q_dac) for the Q chain. DAC 108 is coupled to I-chain FILTER 112 (tx_i_filter) and DAC 110 is coupled to Q-chain FILTER 114 (tx_q_filter). The I-chain filter 112 and the Q-chain filter 114 are coupled to a TX mixer 120.TX mixer 120 is also coupled to a TX local oscillator (TX LO) 122. The output of the TX mixer 120 is coupled to the PPA 116. The output of the PPA 116 is coupled to the PA 118. The output of PA 118 is coupled to antenna 124. Antenna 124 is shown with a load 126 coupled to a ground 128. Antenna 124 may also be coupled to variable capacitors 130 and 132, each coupled to ground 128. In one example, antenna 124 may also be coupled to capacitors 160 and 162. Capacitors 130, 132, 160, and 162 form an attenuator network 164 (e.g., capacitor attenuator 164) for auxiliary receiver 134. Capacitors 130, 132, 160, and 162 attenuate the output power of PA 118 before providing an output to the complex mixer in auxiliary receiver 134. In another example, other circuitry may attenuate the output of PA 118.

The components of the system 100 described above are part of the transmitter path of the system 100. The loop circuit in this example includes a transmitter path and an auxiliary receiver 134. The auxiliary receiver 134 may include many other components not shown in fig. 1, such as LOs, LDOs, and other circuits. The auxiliary receiver 134 may be coupled to a controller 136 configured to perform the operations described herein. The auxiliary receiver 134 includes complex mixers 138 and 140. The complex mixer 138 is a complex mixer for the I chain and the complex mixer 140 is a complex mixer for the Q chain. The complex mixer 138 is coupled to an I-chain FILTER (rx_i_filter) 142, and the complex mixer 140 is coupled to a Q-chain FILTER (rx_q_filter) 144. A receive local oscillator (RX LO) 141 provides LO signals for mixing signals to complex mixers 138 and 140. In one example, the RX LO 141 signal may be the same LO signal as the LO signal from TX LO 122. The I-chain filter 142 is coupled to an I-chain analog-to-digital converter (ADC) 146 (I_ADC). The Q-chain filter 144 is coupled to a Q-chain ADC 148 (q_adc).

In an example operation, signals are transmitted in system 100 via the I and Q chains. The message signal on the I-chain passes through DAC 108 where the digital signal is converted to an analog signal. The analog signal on the I-chain is received by the I-chain filter 112 and filtered. Likewise, the message signal on the Q-chain passes through DAC 110 where the digital signal is converted to an analog signal. The analog signal on the Q-chain is received by Q-chain filter 114. Both message signals (I-chain and Q-chain) are sent to TX mixer 120. The signal is mixed by TX mixer 120 with a carrier signal from TX LO 122. As described above, among the signals provided by the TX mixer 120, the I message signal and the Q message signal are out of phase with each other by 90 °. The TX mixer 120 output signal, including the I and Q message signals, is then received by the PPA 116 and the PA 118, where the mixer 120 output signal is amplified and then transmitted via the antenna 124.

The auxiliary receiver 134 receives copies of the transmit signals and uses the message signals in these copies of the transmit signals in the loop-back path to compensate for LO leakage as described herein. Transmitter LO leakage and other impairments of the transmitter and auxiliary receiver 134 are estimated and corrected using the techniques herein. The auxiliary receiver 134 includes two complex mixers 138 and 140. One complex mixer 138 receives and mixes the I chain and the other complex mixer 140 receives and mixes the Q chain. The complex mixer 138 provides the I-chain signal to the I-chain filter 142 and then provides the filtered I-chain signal to the I-chain ADC 146. The I-chain ADC 146 provides an I-chain signal to the controller 136. The complex mixer 140 provides the Q-chain signal to the Q-chain filter 144 and then provides the filtered Q-chain signal to the Q-chain ADC 148. The Q-chain ADC 148 provides a Q-chain signal to the controller 136.

As described below, complex mixers 138 and 140 each generate a non-inverted signal and an inverted signal. Thus, four signals (I-and Q-chain non-inverted signals and inverted signals) are provided to the controller 136. With these four signals, four equations can be created and solved by the controller 136 to compensate for the transmitter LO leakage. Using the compensation, constant leakage in the auxiliary receiver 134 may also be eliminated. The controller 136 may generate correction signals to the transmitter to correct for LO leakage and other impairments. The correction signal may be supplied at an LO correction block 166 that provides the LO correction signal to the inputs of DACs 108 and 110. LO correction block 166 may include any suitable hardware to receive the correction signal and provide the correction signal to the transmit chain. In other examples, the LO correction signal may be provided to other components in the transmit chain.

Hardware switches for creating the non-inverted signal and the inverted signal may be included in complex mixers 138 and 140. Fig. 3-4, described below, provide one example configuration of hardware switches within complex mixers 138 and 140.

In one example, the controller 136 may include a processor 150 and a memory 152. Memory 152 may include any suitable data, code, logic, or instructions. The processor 150 is configured to read and execute computer readable instructions. For example, the processor 150 is configured to invoke and execute instructions, including instructions, in a program stored in the memory 152. The instructions may perform actions described herein, such as estimating and providing correction for LO leakage and other impairments.

In an example, the memory 152 may be integrated with the processor 150. The memory 152 is configured to store various software programs and/or sets of instructions. In some examples, the memory 152 is configured to store instructions for implementing some or all of the various methods and processes provided in accordance with the various examples herein.

In another example, elements of the controller 136 disclosed herein may use any combination of dedicated hardware and instructions stored in a non-transitory medium such as the memory 152. Non-transitory media include all electronic media or storage media except signals. Processor 150 may include one or more microcontrollers, application Specific Integrated Circuits (ASICs), central Processing Units (CPUs), graphics Processing Units (GPUs), and/or other processing resources configured to execute instructions stored on a medium. Examples of suitable non-transitory computer readable media include one or more flash memory devices, battery-powered Random Access Memory (RAM), solid State Drives (SSD), hard Disk Drives (HDD), optical media, and/or other memory devices suitable for storing instructions for processor 150.

Fig. 2 is a block diagram of a transmit/auxiliary receiver (TX/AuxRX) chain in accordance with various examples herein. Some of the components in system 200 represent functions and may be embodied in hardware, software, or may be executed by any suitable component, such as controller 136.

In one example operation, a signal x to be transmitted _in 202 receives IQ correction at IQMM correction 204 (from a loop-back loop as described below). iQMM correction 204 produces corrected output signal y _corr 206.TX IQMM 208 is represented by the slave loopY of diameter _corr 206 corrected transmit IQMM. Providing signal y to complex mixer 212 _BB 210 (e.g., baseband signals). Complex mixer 212 mixes the I-chain signal and the Q-chain signal and transmits a signal, where the transmit signal is y _Tx 214。

Other components in system 200 provide a loop-back path for LO leakage estimation and correction. Providing a transmit signal y to an auxiliary receiver 134 _Tx 214 for correction. When the signal passes through the loop of the auxiliary receiver 134, a signal y is transmitted _Tx 214 undergo gain and rotation 216. The signal generated after gain and rotation is represented by y _rot 218. Providing y to complex mixer 220 _rot 218. The operation of complex mixer 220 is described below. Complex mixer 220 includes hardware switches that generate a non-inverted signal and an inverted signal for each of the I and Q chains. After the non-inverted signal and the inverted signal are generated by complex mixer 220, auxRx IQMM 222 is applied to these signals to generate y _RX 224 signal. Providing y to the IQMM estimate 226 _RX 224, wherein the controller or processor performs IQMM estimation so that IQMM may be corrected. The procedure for performing IQMM estimation and correction is described below. After performing the IQMM estimation, a signal v is provided to the IQMM correction 204 _i 228 to correct for LO leakage and other impairments in the transmitted signal.

In the example described herein, the switches in complex mixer 220 are activated to create a non-inverted signal and an inverted signal to correctly determine a constant leakage value. Complex mixer 220 has differential inputs. The switches in the complex mixer 220 invert the connection at the input of the complex mixer 220 to cancel transmit local oscillator leakage (TX LOL) as described below.

Fig. 3 is a diagram of selected components of auxiliary receiver 134 according to various examples herein. The auxiliary receiver 134 may include other circuitry not shown in fig. 3. In this example, a capacitor attenuator 164, hardware switches, and complex mixer 138 of the auxiliary receiver 134 are shown.

In operation, the auxiliary receiver 134 is present in the loop-back path and receives a signal, shown here as y _Tx 214.y _rot 218 is the transmit signal y that has undergone some gain and rotation in the loop-back path _TX 214. Signal y _Tx 214 by attenuating the signal and generating y _rot 218 is received by the capacitor attenuator 164. Capacitor attenuator 164 provides an attenuated signal y to inputs 304 and 306 of complex mixer 138 via switches 312, 314, 316, and 318 _rot 218. Complex mixer 138 produces a differential output signal at output 308 (positive output P) and output 310 (negative output M).

Switches 312, 314, 316, and 318 provide either a non-inverted signal or an inverted signal to complex mixer 138. In the first phase of operation, the switches in the "a" path (switches 312 and 314) are closed, and the switches in the "B" path (switches 316 and 318) are open. At this stage, the signal from the capacitor attenuator 164 is provided to the complex mixer 138 in a non-inverting configuration via the "a" path.

In a second phase of operation, the switch is switched. In the second phase, the switches in the "a" path (switches 312 and 314) are open, while the switches in the "B" path (switches 316 and 318) are closed. At this stage, the signal from the capacitor attenuator 164 is provided to the complex mixer 138 in an inverted configuration via the "B" path. In one example, a controller or processor provides signals to switches 312, 314, 316, and 318 to open or close the switches at the appropriate times.

After both phases are completed, two readings are collected from the output of complex mixer 138. The first "a" path produces a signal X at the output of complex mixer 138 and signal Y is added to X by the auxiliary receiver 134 path. The second "B" path produces a signal negative X at the output of complex mixer 138 and signal Y is added to X via the auxiliary receiver 134 path. The controller or processor can then solve for signal X using an equation representing these two readings from the output of complex mixer 138. An example estimation and correction process is described below.

The complex mixer 140 for the Q-chain may be implemented similarly to the complex mixer 138 and may include a set of differential inputs coupled to a set of switches similar to switches 312-318, which are similarly coupled to the electricalVessel attenuator 164 to receive signal y _rot 218。

Fig. 4 is a circuit diagram of a switch and complex mixer according to various examples herein. In one example, the system 400 may be located within the auxiliary receiver 134. The system 400 includes a bias voltage circuit 402, a switching network 404, and a complex mixer 138. In one example, the voltage VSSA may be a ground voltage. VBIAS is the intermediate voltage (between the supply voltage and ground) around which the input signal swings.

Bias voltage circuit 402 includes terminal 406, which provides VBIAS, and terminals 408 and 410. Terminals 408 and 410 provide carrier signals lo_p and lo_m, e.g., switching signals that mix the higher frequencies of complex mixer 138. Bias voltage circuit 402 includes capacitors 412 and 414, transistor 416, and resistors 418 and 420. Transistor 416 may be one or more transistors that provide a control terminal to turn on or off a transmission gate configuration of the circuit. Bias voltage circuit 402 is configured to provide signal lop_int at terminal 422 and signal lom_int at terminal 424. These signals are voltages that the complex mixer 138 uses to control the operation of the complex mixer 138 by opening and closing the switches of the complex mixer 138.

The switching network 404 includes switches 312, 314, 316, and 318 as described above with respect to fig. 3. These switches are configured to generate an "a" path and a "B" path to provide an input signal to complex mixer 138. The "A" path is in a non-inverted configuration, while the "B" path is in an inverted configuration. The switching network 404 also includes input terminals 426 and 428, capacitors 430 and 432, and resistors 434 and 436.

In this example, switches 312, 314, 316, and 318 are all embodied as transistors. Other examples may use different circuit components to create switches that provide the non-inverted signal and the inverted signal to complex mixer 138. Complex mixer 138 includes transistors 442, 444, 446, and 448. Complex mixer 138 also includes input terminals 450 and 452, and output terminals 454 and 456.

In an example operation, the switching network 404 receives a differential input signal (such as y _rot 218). INP denotes the positive input signal and,INM represents a negative input signal. Capacitors 430 and 432 eliminate a constant portion of the input signal so that only the high frequency component of the signal is coupled from the input to the output. In one example, the resistors 434 and 436 are sized larger than the resistance of the switch. In one example, the "on" resistance of the switch may be less than 5% of the size of resistors 434 and 436. Thus, if the "on" resistance of the switch is slightly non-linear, the overall system will not become non-linear.

Switches 312, 314, 316, and 318 allow switching network 404 to achieve a non-inverted configuration or an inverted configuration. These switches are controlled by the ENZ_FLIP (FLIP-enable) signal and the EN_FLIP (FLIP-enable) signal, which are complementary signals. The ENZ_FLIP signal is provided at the gates or control terminals of the transistors making up switches 312 and 314. If the ENZ_FLIP signal is high, the EN_FLIP signal is low and the transistors of switches 312 and 314 are on, thus operating as closed switches. The input signal travels along an "a" path (represented by the arrow) to input terminals 450 and 452 of complex mixer 138. This is a non-inverting configuration. If the ENZ_FLIP signal is high, the EN_FLIP signal is low. The low EN FLIP signal turns "off" switches 316 and 318 by turning off the associated transistors. A controller or processor (not shown in fig. 4) controls the operation of switches 312, 314, 316, and 318 via the ENZ FLIP signal and the EN FLIP signal.

For an inverted configuration, the controller or processor provides a high en_flip signal and a low enz_flip signal. The high EN FLIP signal turns on the transistors of switches 316 and 318. The low ENZ_FLIP signal turns off the transistors of switches 312 and 314. In this configuration, the input signal travels along a "B" path (represented by the arrow) to input terminals 450 and 452 of complex mixer 138.

Complex mixer 138 receives either a non-inverted signal or an inverted signal at input terminals 450 and 452 depending on the configuration of switches 312, 314, 316, and 318. Transistors 442, 444, 446, and 448 are mixer switches that control the operation of complex mixer 138 to generate differential output signals at output terminals 454 and 456. These transistors turn on or off a complex mixer 138 at the carrier frequency, which mixes the input signals and produces a differential output signal. The differential output signal is represented by a positive Output (OUTP) and a negative Output (OUTM). Transistors 442 and 444 are biased at the gate or control terminal with a lomint signal provided by bias voltage circuit 402 at terminal 424. Transistors 446 and 448 are biased at the gate or control terminal with a lop_int signal, which is provided by bias voltage circuit 402 at terminal 422. The LOM_INT signal and the LOP_INT signal turn on or off transistors 442, 444, 446, and 448 at the carrier frequency to mix the signals and generate a differential output signal. A controller or processor (e.g., controller 136) receives the differential output signals from output terminals 454 and 456 in both the non-inverted and inverted configurations and then provides estimates and corrections for LO leakage and other impairments as described below.

In an example, the "a" path and the "B" path, as well as other circuits in the switching network 404, should not add any distortion to the signal, and both paths should have similar LO leakage. Moreover, the size of the switch should be appropriate so as not to be too large or too small. Too small a switch may reduce the gain of the auxiliary receiver 134 and cause signal distortion. A switch that is too large may have a large switched capacitance in the off state, which may couple the signal through the inactive path ("a" path or "B" path) and cause signal distortion.

The complex mixer 140 of the Q-chain may be implemented in a manner similar to the complex mixer 138, and in an example, a circuit in the system 400 is duplicated in fig. 1, with a first copy of the circuit being associated with the complex mixer 138 and a second copy of the circuit being associated with the complex mixer 140. One complex mixer receives the I-chain signal and the other complex mixer receives the Q-chain signal. A controller or processor (e.g., controller 136) receives the I-chain signal (inverted signal and non-inverted signal) and the Q-chain signal (inverted signal and non-inverted signal) and then provides an estimate and correction.

One example process for estimating and correcting TX LO leakage is described herein. In other examples, other processes may be useful. In this example process, the LO leakage of the signal of the I chain and the LO leakage of the signal of the Q chain may be represented by equation (1) and equation (2):

y _DC-Tx ＝I _Tx ；Q _Tx (1)

as the signal passes through the loop of the auxiliary receiver 134, the signal is affected by gain (a) and rotation (θ), as shown in equation (3) for both the I and Q chains:

G _Dw ＝A _I .cos(θ _I )；A _Q .cos(θ _Q ) (3)

the mixer of the auxiliary receiver connected to the input of the ADC (e.g., ADC 146 and 148) provides additional gain as shown in equation (4):

G _Rx ＝B _I ；B _Q (4)

the auxiliary receiver 134 adds its own constant leakage as shown in equation (5):

y _DC-Rx ＝I _Rx ；Q _Rx

in a non-inverting configuration, the constant leakage of the I chain may be represented by equation (6), and the constant leakage of the Q chain may be represented by equation (7):

y _DC-ADC-I ＝I _Tx A _I B _I cos(θ _I +Φ)+Q _Tx A _Q B _Q sin(θQ)+I _Rx B _I (6)

y _DC-ADC-Q ＝I _Tx A _I B _I sin(θ _I +Φ)+Q _Tx A _Q B _Q cos(θ _Q )+Q _Rx B _Q (7) In the inverted configuration, the constant leakage of the I chain may be represented by equation (8), and the constant leakage of the Q chain may be represented by equation (9):

y _DC-ADC-I ＝-I _Tx A _I B _I cos(θ _I +Φ)+Q _Tx A _Q B _Q sin(θ _Q )+I _Rx B _I (8)

y _DC-ADC-Q ＝-I _Tx A _I B _I sin(θ _I +Φ)-Q _Tx A _Q B _Q cos(θ _Q )+Q _Rx B _Q (9)

four equations (6, 7, 8, and 9) can be solved to determine the Transmitter (TX) LO leakage I _TX And Q _TX . For simplicity, the replacement may be performed as follows:

x＝I _Tx

y＝Q _Tx

a＝A _I B _I cos(θ _I +Φ)

b＝A _Q B _Q sin(θ _Q )

c＝A _I B _I sin(θ _I +Φ)

d＝A _Q B _Q cos(θ _Q )

p＝I _Rx B _I

s＝Q _Rx B _Q

y _I ＝y _DC-ADC-I

y _Q ＝y _DC-IDC-Q

with these alternatives, the variables of the solution are required to be a, b, c and d. Thus, four linear equations can be used to solve for these variables. The overall constant leakage from the ADC is shown in equation (10):

I _Tx and Q _Tx The I and Q chain signals in the transmitter, respectively. I _Rx And Q _Rx The I-chain signal and the Q-chain signal, respectively, are received by the auxiliary receiver 134. For simplicity, more alternatives may be performed:

in this solution, two constant leakage inserts are used for each chain, these two constant leakage inserts being defined by I _Tx-1 、I _TX-2 、Q _Tx-1 And Q _Tx-2 Given. Transmitting signal I _Tx-1 、I _TX-2 、Q _Tx-1 And Q _Tx-2 And some LO leakage occurs. These insertions are shown in equations (11) and (12):

after transmitting these signals, three acquisitions S are determined ₁ 、S ₂ And S is ₃ . Equations (13), (14) and (15) show these three captures. Y, Y ₁ And Y ₂ Is the result signal at the output:

S ₁ →AT+BR＝Y (13)

S ₂ →A(T+T ₁ )+BR＝Y ₁ (14)

S ₃ →A(T+T ₂ )+BR＝Y ₂ (15)

with these captures, T ₁ 、T ₂ 、Y、Y ₁ And Y ₂ Are known. T (T) ₁ 、T ₂ To transmit signals Y, Y ₁ 、Y ₂ For receiving signals. Thus, can be foundThe remaining variables in equations (13), (14) and (15) are solved. If S ₂ Subtracting S ₁ ，S ₃ Also subtract S ₁ BR and T may be eliminated. These subtractions eliminate the BR portion (which is a constant leakage from the auxiliary receiver 134). These operations are shown in equations (16) and (17):

S ₂ -S ₁ →AT ₁ ＝Y ₁ -Y (16)

S ₃ -S ₁ →AT ₂ ＝Y ₂ -Y (17)

the above matrix can be rewritten as equations (18) and (19):

the only remaining unknown variable is a, which can be estimated by rewriting the matrix of T1 and T2, as shown in equations (11) and (12) above. Equation (20) can be used to estimate a:

the transmit characteristics are denoted by a and equation (20) provides this estimate, so transmit characteristics such as TX LO leakage can be eliminated. However, the auxiliary receiver 134 component is still present. Auxiliary receiver 134 components (e.g., constant leakage and other impairments) may be eliminated by switching the switching network 404 as described above and providing a non-inverted signal and an inverted signal. From equation (20), A is known, and then T (from I) can be estimated using equations (21) and (22) _Tx And Q _Tx Constant leakage represented):

AT+BR＝Y ₁ (21)

-AT+BR＝Y ₂ (22)

equation (21) represents the non-inverting path (Y1), and equation (22) represents the inverting path (Y2). By subtracting these two equations, T can be determined as shown in equations (23) and (24) below:

thus, two processes are performed to estimate the leakage measurement T and provide a correction signal to the transmitter. The first procedure is to estimate A, which requires three captures S ₁ 、S ₂ And S is ₃ . The second procedure is to estimate T, which reuses one more acquisition. After estimating T using the loop circuit, a negative T may be generated in the transmit path to correct T. In the examples herein, four signals (non-inverted I signal, non-inverted Q signal, and inverted Q signal) provide information for estimating and correcting T. The circuits and hardware described herein generate these four signals and the method performs computations to estimate and correct for TX LO leakage and other impairments.

The procedure for estimating and correcting constant leakage described using equations (1) through (24) is only one example, and other examples may be useful. The process may be performed by a controller, such as controller 136, using software or firmware.

Fig. 5 is a flow chart of a method 500 for estimating and correcting transmitter local oscillator leakage according to various examples herein. The steps of method 500 may be performed in any suitable order. In some examples, the hardware components described above with respect to fig. 1-4 may perform method 500. In some examples, any suitable hardware, software, or digital logic may perform method 500.

Method 500 begins at 510, where secondary receiver 134 receives a differential QAM input signal from a transmitter. The input signals may include an I-chain signal and a Q-chain signal. The auxiliary receiver 134 may include hardware (e.g., a mixer) that is duplicated so that the auxiliary receiver 134 may process both the I-chain signal and the Q-chain signal as described herein.

The method 500 continues at 520, where a controller (e.g., the controller 136) causes the first switch 312 and the second switch 314 to provide differential QAM input signals to the complex mixer 138 in a non-inverting configuration. In one example, the switches may be transistors. In other examples, a different number of switches may be useful.

Method 500 continues at 530, where a controller (e.g., controller 136) causes third switch 316 and fourth switch 318 to provide differential QAM input signals to complex mixer 138 in an inverted configuration. In one example, the switches may be transistors. In other examples, a different number of switches may be useful.

Method 500 continues at 540 where complex mixer 138 mixes the differential QAM input signals as provided in blocks 520 and 530 to produce an output signal. In one example, a complex mixer may mix differential QAM input signals using transistors that are switched at the frequency of the carrier frequency.

The method 500 continues at 550 where the controller 136 estimates or determines local oscillator leakage associated with the transmitter based at least in part on the differential output signal. In one example, a controller receives an inverted differential output signal and a non-inverted differential output signal. The controller also receives inverted differential output signals and non-inverted differential output signals from the I chain and from the Q chain. With these four signals (non-inverted in-phase, non-inverted quadrature, inverted quadrature), the controller 136 can estimate local oscillator leakage from the transmitter and can also correct for some impairments of the auxiliary receiver 134.

The method 500 continues at 560 where the controller 136 corrects for local oscillator leakage. In an example, the controller 136 creates a correction signal that is inverted from the LO leakage. The correction signal may be generated in the transmitter based on the estimate. In one example, the correction signal may be an offset within the data provided to DACs 108 and 110 by LO correction block 166, where the offset corrects for LO leakage.

In the examples herein, a loop-back path is implemented to measure and correct transmitter LO leakage using an auxiliary receiver. Examples herein also contemplate other transmitter impairments such as IQ mismatch (IQMM), phase noise, radio Frequency (RF) nonlinearity, etc. In the loop-back path, the hardware switch compensates for impairments in the auxiliary receiver path using two configurations. In a first configuration, the sum of the transmit signal and the signal added through the auxiliary path (e.g., leakage) is provided to the complex mixer in a non-inverted configuration. In a second configuration, the switch is switched and the difference between the transmit signal and the signal added through the auxiliary path is provided to the complex mixer in an inverted configuration. The controller analyzes the outputs of the complex mixers for both the non-inverted configuration and the inverted configuration and then cancels the constant signal added through the auxiliary path. The process is performed by the controller for both the I and Q chains. In the examples herein, the process is performed for a shorter time than other systems. As long as the original IQMM or LO leakage of the loop-back path is the same in both configurations (non-inverting and inverting), the leakage can be high, which relaxes the analog design requirements of the system. Moreover, the solution is applicable to all QAM-based architectures.

The term "coupled," as used herein, may encompass a connection, communication, or signal path that enables a functional relationship consistent with the disclosure. For example, if device a generates a signal to control device B to perform an action, then: (a) In a first example, device a is coupled to device B through a direct connection; or (B) in a second example, device a is coupled to device B through intermediate component C, provided that intermediate component C does not change the functional relationship between device a and device B, and device B is therefore controlled by device a via the control signals generated by device a.

A device "configured to" perform a task or function may be configured (e.g., programmed and/or hardwired) by a manufacturer at the time of manufacture to perform the function, and/or may be configured (or reconfigurable) by a user after manufacture to perform the function and/or other additional or alternative functions. The configuration may be performed by firmware and/or software programming the device, by constructing and/or laying out hardware components and interconnections of the device, or a combination thereof.

Circuits or devices described herein as including certain components may alternatively be coupled with those components to form the described circuits or devices. For example, structures described as including one or more semiconductor elements (e.g., transistors), one or more passive elements (e.g., resistors, capacitors, and/or inductors), and/or one or more power sources (e.g., voltage and/or current sources) may instead include only semiconductor elements within a single physical device (e.g., a semiconductor die and/or Integrated Circuit (IC) package), and may be coupled with at least some of the passive elements and/or power sources at the time of manufacture or after manufacture (e.g., by an end user and/or a third party) to form the described structures.

The circuits described herein may be reconfigured to include replaced components to provide functions at least partially similar to those available prior to component replacement. Unless otherwise stated, components shown as resistors generally represent any one or more elements coupled in series and/or parallel to provide the amount of impedance represented by the illustrated resistors. For example, the resistors or capacitors shown and described herein as a single component may alternatively be a plurality of resistors or capacitors, respectively, coupled in parallel between the same nodes. For example, the resistors or capacitors shown and described herein as a single component may alternatively be a plurality of resistors or capacitors, respectively, coupled in series between the same two nodes as the single resistor or capacitor.

The term "ground" as used in the above description includes chassis ground, floating ground, virtual ground, digital ground, common ground, and/or any other form of ground connection that may be suitable or adapted for the teachings herein. Unless otherwise indicated, herein, "about," "approximately," or "substantially" preceding a parameter means within +/-10% of the parameter. Modifications to the described examples are possible within the scope of the claims, and other examples are also possible.

Claims (20)

1. A system, comprising:

a receiver configured to receive a differential input signal from a Quadrature Amplitude Modulation (QAM) transmitter at a differential interface comprising a first input and a second input;

a first switch coupled to the first input and a second switch coupled to the second input, wherein the first switch and the second switch are configured to couple the first input and the second input to a complex mixer in a non-inverting configuration;

a third switch coupled to the first input and a fourth switch coupled to the second input, wherein the third switch and the fourth switch are configured to couple the first input and the second input to the complex mixer in an inverted configuration; and is also provided with

Wherein the complex mixer is configured to generate an output signal based on the non-inverted configuration and the inverted configuration.

2. The system of claim 1, wherein the differential input signal comprises an in-phase (I) chain signal.

3. The system of claim 2, wherein the differential input signal comprises a quadrature (Q) chain signal.

4. A system according to claim 3, wherein the output signal is generated for both the I chain and the Q chain.

5. The system of claim 4, further comprising:

a controller configured to correct transmitter local oscillator leakage using both inverted and non-inverted signals of the I and Q chains.

6. The system of claim 5, wherein the controller is further configured to correct for leakage associated with the receiver.

7. The system of claim 1, further comprising:

a first resistor coupled to the first input, the first switch, and the second switch; and

a second resistor coupled to the second input, the third switch, and the fourth switch.

8. A method, comprising:

receiving a differential Quadrature Amplitude Modulation (QAM) input signal from a transmitter;

causing the first switch and the second switch to provide the differential QAM input signal to a complex mixer in a non-inverting configuration;

causing third and fourth switches to provide the differential QAM input signal to the complex mixer in an inverted configuration;

mixing the differential QAM input signal with the complex mixer to produce an output signal;

determining, with a controller, local oscillator leakage associated with the transmitter based at least in part on the output signal; and

and correcting the local oscillation leakage.

9. The method of claim 8, wherein the complex mixer comprises a first input and a second input.

10. The method of claim 8, wherein the differential QAM input signal comprises an in-phase (I) chain signal.

11. The method of claim 10, wherein the differential QAM input signal comprises a quadrature (Q) chain signal.

12. The method of claim 11, further comprising generating the output signal for both the I chain and the Q chain.

13. The method of claim 12, further comprising correcting the local oscillator leakage with an inverted signal and a non-inverted signal of both the I chain and the Q chain.

14. The method of claim 8, wherein receiving the differential QAM input signal from a transmitter comprises receiving the differential QAM input signal at an auxiliary receiver coupled to the transmitter.

15. The method of claim 8, further comprising providing an inverted output signal and a non-inverted output signal with the complex mixer.

16. The method of claim 15, further comprising cancelling impairments of a receiver based at least in part on the inverted output signal and the non-inverted output signal.

17. The method of claim 8, further comprising providing a correction signal to the transmitter to correct the local oscillator leakage.

18. A system, comprising:

a transmitter configured to transmit a Quadrature Amplitude Modulation (QAM) signal;

a receiver configured to receive a differential QAM input signal from the transmitter at a differential interface including a first input and a second input;

a first switch coupled to the first input and a second switch coupled to the second input, wherein the first switch and the second switch are configured to couple the first input and the second input to a complex mixer in a non-inverting configuration to generate a non-inverted signal provided to the complex mixer;

a third switch coupled to the first input and a fourth switch coupled to the second input, wherein the third switch and the fourth switch are configured to couple the first input and the second input to the complex mixer in an inverted configuration to generate an inverted signal input to the complex mixer; and

a controller configured to correct transmitter local oscillator leakage using the inverted signal and the non-inverted signal.

19. The system of claim 18, wherein the complex mixer is configured to generate a differential output signal for an I-chain of QAM signals.

20. The system of claim 18, wherein the controller is further configured to provide a correction signal to the transmitter to correct for the transmitter local oscillator leakage.