Radio transceiver device and method

Abstract

Apparatus and methods for a transceiver are provided herein. In a first aspect, an observation receiver is implemented to detect common-mode local oscillator (LO) leakage while the observation receiver performs other functions. In a second aspect, the transceiver is implemented with LO leakage compensation circuitry that uses a digital filter (e.g., a Kalman filter) to compensate for transmitter LO leakage. The digital filter combines differential LO leakage observations with common-mode LO leakage observations. In a third aspect, the transmitter includes multiple local loopback paths, including a first loopback path after a variable gain amplifier (VGA) and a second loopback path before the VGA.

Description

Technical Field

[0001] Embodiments of the present invention relate to electronic systems and, more particularly, to transceivers for radio frequency (RF) communication systems. Background Art

[0002] Radio transceivers can be used in various radio frequency (RF) communication systems. For example, a transceiver can be included in a base station or mobile device to transmit and receive signals associated with various communication standards, including, for example, cellular and / or wireless local area network (WLAN) standards. Transceivers can also be used in radar systems, instrumentation, industrial electronics, military electronics, laptop computers, digital radios, and / or other electronic devices. Summary of the Invention

[0003] In one aspect, a transceiver integrated circuit (IC) is provided. The transceiver IC includes a first transmitter, the first transmitter including at least one mixer and a local oscillator (LO), wherein the first transmitter is configured to control the at least one mixer based on the LO to provide upconversion to generate a first radio frequency (RF) transmit signal. The transceiver IC also includes an observation receiver configured to receive an observation signal for observing at least the first transmitter, wherein the observation receiver includes an observation data path configured to process the observation signal to detect the transmit power of the first RF transmit signal, and an LO leakage observation circuit configured to generate leakage observation data based on processed data captured from the observation data path. The first transmitter is configured to process the leakage observation data to compensate for leakage of the LO.

[0004] In some embodiments, the LO leakage observation circuit detects the transmit power without interrupting the observation data path.

[0005] In various embodiments, the observation data path is further configured to process the observation signal to perform digital predistortion (DPD), wherein the LO leakage observation circuit performs DPD without interrupting the observation signal path.

[0006] In certain embodiments, the first transmitter is further configured to compensate for leakage of the LO based on local transmission observation data from one or more local observation paths of the transceiver IC. According to some embodiments, the first transmitter is configured to detect differential LO leakage from the local leakage observation data and to detect common-mode LO leakage from leakage observation data from the observation receiver. According to some embodiments, the first transmitter further includes a variable gain amplifier (VGA) configured to amplify the first RF transmit signal, wherein the one or more local observation paths include a first local observation path after the VGA and a second local observation path before the VGA. According to some embodiments, the first transmitter includes a digital filter configured to process the local leakage observation data and the leakage observation data from the observation receiver. According to some embodiments, the digital filter is a Kalman filter. According to some embodiments, the first transmitter is configured to collect the local leakage observation data and the leakage observation data from the observation receiver in multiple batches. According to various embodiments, the first transmitter is configured to update a value of an LO leakage compensation signal used to compensate for leakage of the LO after receiving the local leakage observation data and a given number of samples of the leakage observation data from the observation receiver.

[0007] In some embodiments, the LO leakage observation circuit includes a digital mixer and a digital accumulator, wherein the digital mixer is configured to generate frequency-shifted data based on mixing data captured from the observation data path, and the digital accumulator is configured to generate the leakage observation data based on accumulation of the frequency-shifted data. According to some embodiments, the LO leakage observation circuit further includes a digital oscillator configured to provide a digital clock signal to the digital mixer. According to some embodiments, the digital oscillator is a numerically controlled oscillator (NCO).

[0008] In various embodiments, the transceiver IC further includes a plurality of transmitters including the first transmitter, wherein the observation signal is configured to observe one of the plurality of transmitters at a given time. According to some embodiments, the LO leakage observation circuit is configured to individually track leakage observation data for each of the plurality of transmitters. According to some embodiments, the selected transmitter for observing the plurality of transmitters is changeable without interrupting operation of the LO leakage observation circuit.

[0009] In certain embodiments, the observation data path includes an analog-to-digital converter (ADC) configured to generate a digital observation signal based on the observation signal and a digital circuit configured to process the digital observation signal.

[0010] In another aspect, a method for compensating for local oscillator (LO) leakage in a transceiver is provided. The method includes generating a first radio frequency (RF) transmit signal using a first transmitter including at least one mixer and a local oscillator (LO) for controlling the at least one mixer, generating an observation signal based on a loopback path from the first transmitter through an RF front end to an observation receiver, processing the observation signal to detect a transmit power of the first RF transmit signal using an observation data path of the observation receiver, generating leakage observation data based on processed data captured from the observation data path, and processing the leakage observation data to compensate for LO leakage.

[0011] In various implementations, leakage observation data is generated without interrupting detection of the transmit power.

[0012] In some embodiments, processing the observation signal includes performing digital predistortion (DPD) on the first RF transmit signal, wherein the leakage observation data is generated without interrupting DPD.

[0013] In certain embodiments, the method further includes compensating for leakage of the LO based on local transmit observation data from one or more local observation paths that do not pass through the RF front end. According to some embodiments, the method further includes detecting differential LO leakage from the local leakage observation data and detecting common-mode LO leakage from leakage observation data from the observation receiver. According to some embodiments, the method further includes amplifying the first RF transmit signal using a variable gain amplifier (VGA) of the first transmitter and generating the local leakage observation data using a first local observation path after the VGA and a second local observation path before the VGA. According to some embodiments, the method further includes combining the local leakage observation data with the leakage observation data from the observation receiver using a digital filter. According to some embodiments, the digital filter is a Kalman filter. According to some embodiments, the method further includes collecting the local leakage observation data and the leakage observation data from the observation receiver in multiple batches. According to various embodiments, the method further includes updating a value of an LO leakage compensation signal used to compensate for leakage of the LO after receiving a given number of samples of the local leakage observation data and the leakage observation data from the observation receiver.

[0014] In some embodiments, generating leakage observation data includes mixing data captured from the observation data path using a digital mixer and accumulating the mixed data to generate leakage observation data. According to some embodiments, generating leakage observation data also includes controlling the digital mixer using a digital oscillator. According to some embodiments, the digital oscillator is a numerically controlled oscillator (NCO).

[0015] In various embodiments, the method further comprises generating a plurality of RF transmit signals using a plurality of transmitters, and observing one of the plurality of transmitters at a given time using the observation receiver. According to various embodiments, the method further comprises individually tracking leakage observation data for each of the plurality of transmitters. According to some embodiments, generating the observation signal comprises amplifying the plurality of RF transmit signals using a plurality of power amplifiers, sensing a plurality of output powers of the plurality of power amplifiers using a plurality of directional couplers, and multiplexing the plurality of directional couplers to obtain the observation signal.

[0016] In certain embodiments, processing the observation signal includes generating a digital observation signal from the observation signal using an analog-to-digital converter (ADC), and processing the digital observation signal using a digital circuit.

[0017] In some embodiments, generating the observation signal includes amplifying the first RF transmit signal using a power amplifier, and sensing output power of the power amplifier using a directional coupler.

[0018] In another aspect, a radio frequency (RF) communication system is provided. The RF communication system includes an RF front end and a transceiver, including a first transmitter configured to provide a first RF transmit signal to the RF front end and an observation receiver configured to receive an observation signal via a loopback path from the first transmitter through the RF front end to the observation receiver. The observation receiver includes an observation data path for processing the observation signal to detect the transmit power of the first RF transmit signal, and a local oscillator (LO) leakage observation circuit configured to generate leakage observation data based on processed data captured from the observation data path. The first transmitter processes the leakage observation data to compensate for LO leakage of the first receiver.

[0019] In some embodiments, the LO leakage observation circuit detects the transmit power without interrupting the observation data path.

[0020] In various embodiments, the observation data path processes the observation signal to perform digital predistortion (DPD), wherein the LO leakage observation circuit does not interrupt the observation data path to perform DPD.

[0021] In certain embodiments, the first transmitter is further configured to compensate for LO leakage based on local transmission observation data from one or more local observation paths of the transceiver. According to some embodiments, the first transmitter is configured to detect differential LO leakage from the local leakage observation data and to detect common-mode LO leakage from leakage observation data from the observation receiver. According to some embodiments, the first transmitter further includes a variable gain amplifier (VGA) configured to amplify the first RF transmit signal, wherein the one or more local observation paths include a first local observation path after the VGA and a second local observation path before the VGA. According to some embodiments, the first transmitter includes a digital filter configured to process the local leakage observation data and the leakage observation data from the observation receiver. According to some embodiments, the digital filter is a Kalman filter. According to some embodiments, the first transmitter is configured to collect the local leakage observation data and the leakage observation data from the observation receiver in multiple batches. According to various embodiments, the first transmitter is configured to update a value of an LO leakage compensation signal used to compensate for LO leakage after receiving a given number of samples of the local leakage observation data and the leakage observation data from the observation receiver.

[0022] In some embodiments, the LO leakage observation circuit includes a digital mixer and a digital accumulator, wherein the digital mixer is configured to generate frequency-shifted data based on mixing data captured from the observation data path, and the digital accumulator is configured to generate the leakage observation data based on accumulation of the frequency-shifted data. In some embodiments, the LO leakage observation circuit further includes a digital oscillator configured to provide a digital clock signal to the digital mixer. According to some embodiments, the digital oscillator is a numerically controlled oscillator (NCO).

[0023] In various embodiments, a transceiver includes: a plurality of transmitters including a first transmitter, wherein the observation signal is configured to observe one of the plurality of transmitters at a given time. According to some embodiments, the LO leakage observation circuit is configured to individually track leakage observation data for each of the plurality of transmitters. According to some embodiments, the selected transmitter for observing the plurality of transmitters is changeable without interrupting operation of the LO leakage observation circuit. According to some embodiments, an RF front end includes a plurality of power amplifiers configured to amplify a plurality of RF transmit signals, a plurality of directional couplers configured to sense a plurality of output powers of the plurality of power amplifiers, and a multiplexer coupled to the plurality of directional couplers and configured to output the observation signal.

[0024] In certain embodiments, the observation data path includes an analog-to-digital converter (ADC) configured to generate a digital observation signal based on the observation signal and a digital circuit configured to process the digital observation signal.

[0025] In various embodiments, the RF front end includes a power amplifier configured to amplify a first RF transmit signal and a directional coupler configured to generate an observation signal based on sensing an output power of the power amplifier.

[0026] In another aspect, a transceiver includes a transmitter configured to generate a radio frequency (RF) transmit signal, wherein the transmitter is configured to generate first observation data based on observing the RF transmit signal on one or more local observation paths within the transmitter. The transceiver also includes an observation receiver configured to generate second observation data based on processing the observation signal. The transceiver also includes a local oscillator (LO) leakage compensation circuit configured to compensate for transmitter LO leakage of the transmitter, wherein the LO leakage compensation circuit includes a digital filter configured to process the first observation data and the second observation data.

[0027] In various embodiments, the digital filter is a Kalman filter. In some embodiments, the Kalman filter is configured to estimate a correction value for the LO leakage using a plurality of nonlinear equations. In some embodiments, the Kalman filter is further configured to modify the correction value based on a linear update of the Kalman filter using an observation matrix. In some embodiments, the observation matrix corresponds to a Jacobian matrix. In various embodiments, a first portion of the plurality of nonlinear equations is a function of the first observation data, and a second portion of the nonlinear equations is a function of the second observation data. In some embodiments, the LO leakage compensation circuit includes a processor, and the Kalman filter is implemented as software running on the processor.

[0028] In certain embodiments, a transmitter includes a digital transmitter circuit configured to process a digital in-phase (I) signal and a digital quadrature-phase (Q) signal, wherein the digital filter is configured to compensate for LO leakage of the transmitter based at least in part on controlling the digital transmitter circuit. According to some embodiments, the digital filter is configured to control a first DC offset of the digital I signal and a second DC offset of the digital Q signal. According to various embodiments, the digital transmitter circuit includes a programmable finite impulse response (PFIR) filter, wherein the digital filter is configured to control the PFIR. According to some embodiments, the transmitter includes an I-path digital-to-analog converter (DAC) coupled to the digital transmitter circuit and configured to generate an analog I signal, a controllable I-path filter configured to generate a filtered I signal based on filtering the analog I signal, a Q-path DAC coupled to the digital transmitter circuit and configured to generate an analog Q signal, and a controllable Q-path filter configured to generate a filtered Q signal based on filtering the analog Q signal. According to some embodiments, the digital filter controls settings of the controllable I-path filter and the controllable Q-path filter. In some embodiments, the transceiver further includes an I path mixer and a Q path mixer, wherein the I path mixer is configured to receive a filtered I signal and is controlled by an LO, and the Q path mixer is configured to receive a filtered Q signal and is controlled by the LO, wherein the RF transmit signal is generated based on combining an output of the I path mixer and an output of the Q path mixer.

[0029] In some embodiments, the first observation data indicates differential LO leakage of the LO, and the second observation data indicates common-mode LO leakage of the LO.

[0030] In various embodiments, the transmitter includes a variable gain amplifier (VGA) configured to amplify the first RF transmit signal, wherein the one or more local observation paths include a first local observation path after the VGA and a second local observation path before the VGA.

[0031] In another aspect, a method for compensating for local oscillator (LO) leakage in a transceiver is provided. The method includes generating a radio frequency (RF) transmit signal using a transmitter, generating first observation data based on observing the RF transmit signal on one or more local observation paths within the transmitter, generating second observation data using an external loopback path from the transmitter to an observation receiver through a front-end system, and compensating for transmitter LO leakage of the transmitter based on processing the first observation data and the second observation data using a digital filter.

[0032] In certain embodiments, the digital filter is a Kalman filter. According to some embodiments, the method further comprises estimating a correction value for LO leakage using a plurality of nonlinear equations. According to various embodiments, the method further comprises revising the correction value using a measurement matrix based on a linear update of the Kalman filter. According to some embodiments, the measurement matrix corresponds to a Jacobian matrix. According to various embodiments, a first portion of the plurality of nonlinear equations is a function of the first observation data, and a second portion of the nonlinear equations is a function of the second observation data.

[0033] In some embodiments, the method further includes processing a digital in-phase (I) signal and a digital quadrature-phase (Q) signal using digital transmitter circuitry of the transmitter, and compensating for transmitter LO leakage based at least in part on controlling the digital transmitter circuitry using the digital filter. According to some embodiments, controlling the digital transmitter circuitry includes adjusting a first DC offset of the digital I signal and adjusting a second DC offset of the digital Q signal. According to some embodiments, the digital transmitter circuitry includes a programmable finite impulse response (PFIR) filter, wherein controlling the digital receiver circuitry includes adjusting the PFIR.

[0034] In various implementations, the first observation data indicates differential LO leakage of the LO, and the second observation data indicates common-mode LO leakage of the LO.

[0035] In some embodiments, the method further includes amplifying the RF transmit signal using a variable gain amplifier (VGA), wherein the one or more local observation paths include a first local observation path after the VGA and a second local observation path before the VGA.

[0036] In another aspect, a radio frequency (RF) communication system is provided. The RF communication system includes an RF front end and a transceiver. The transceiver includes a transmitter configured to provide an RF transmit signal to the RF front end, wherein the transmitter is configured to generate first observation data based on observing the RF transmit signal on one or more local observation paths within the transmitter. The transceiver also includes an observation receiver configured to generate second observation data based on processing an observation signal received through an external loopback path from the transmitter to the observation receiver via the RF front end. The transceiver also includes a local oscillator (LO) leakage compensation circuit configured to compensate for transmitter LO leakage of the transmitter. The LO leakage compensation circuit includes a digital filter configured to process the first observation data and the second observation data.

[0037] In some embodiments, the digital filter is a Kalman filter. According to some embodiments, the Kalman filter is configured to estimate a correction value for the LO leakage using a plurality of nonlinear equations. According to various embodiments, the Kalman filter is configured to modify the correction value based on a linear update of the Kalman filter using an observation matrix. According to some embodiments, the observation matrix corresponds to a Jacobian matrix. According to some embodiments, a first portion of the plurality of nonlinear equations is a function of the first observation data, and a second portion of the nonlinear equations is a function of the second observation data. According to some embodiments, the LO leakage compensation circuit includes a processor, and the Kalman filter is implemented as software running on the processor.

[0038] In certain embodiments, the transmitter includes a digital transmitter circuit configured to process a digital in-phase (I) signal and a digital quadrature-phase (Q) signal, and the digital filter is configured to compensate for LO leakage of the transmitter based at least in part on controlling the digital transmitter circuit. According to some embodiments, the digital filter is configured to control a first DC offset of the digital I signal and a second DC offset of the digital Q signal. According to various embodiments, the digital transmitter circuit includes a programmable finite impulse response (PFIR) filter, wherein the digital filter is configured to control the PFIR. According to some embodiments, the transmitter includes an I-path digital-to-analog converter (DAC) coupled to the digital transmitter circuit and configured to generate an analog I signal, a controllable I-path filter configured to generate a filtered I signal based on filtering the analog I signal, a Q-path DAC coupled to the digital transmitter circuit and configured to generate an analog Q signal, and a controllable Q-path filter configured to generate a filtered Q signal based on filtering the analog Q signal. According to some embodiments, the digital filter controls settings of the controllable I-path filter and the controllable Q-path filter. According to some embodiments, the RF communication system further includes an I path mixer and a Q path mixer, wherein the I path mixer is configured to receive a filtered I signal and is controlled by an LO, and the Q path mixer is configured to receive a filtered Q signal and is controlled by the LO, wherein the RF transmit signal is generated based on combining an output of the I path mixer and an output of the Q path mixer.

[0039] In various embodiments, the first observation data indicates differential LO leakage of the LO, and the second observation data indicates common-mode LO leakage of the LO.

[0040] In some embodiments, the transmitter includes a variable gain amplifier (VGA) configured to amplify the first RF transmit signal, wherein the one or more local observation paths include a first local observation path after the VGA and a second local observation path before the VGA.

[0041] In various embodiments, the RF front end includes a power amplifier configured to amplify an RF transmit signal and a directional coupler configured to generate an observation signal based on sensing an output power of the power amplifier.

[0042] In another aspect, a transceiver integrated circuit (IC) includes a plurality of mixers, including a first mixer configured to upconvert an analog in-phase (I) signal and a second mixer configured to downconvert an analog quadrature-phase (Q) signal, wherein an output of the first mixer and an output of the second mixer are configured to combine to generate a radio frequency (RF) transmit signal. The transceiver also includes a variable gain amplifier (VGA) configured to amplify the RF transmit signal to generate an amplified RF transmit signal, and a plurality of local loopback circuits, including a first local loopback circuit coupled to an output of the VGA and a second local loopback circuit coupled to an input of the VGA.

[0043] In various embodiments, the transceiver IC further includes at least one subsampling analog-to-digital converter (ADC) configured to process at least one output of the plurality of local loopback circuits. In some embodiments, the at least one subsampling ADC includes a shared subsampling ADC configured to digitize the output of a selected local loopback circuit selected from the first local loopback circuit or the second local loopback circuit. In some embodiments, the first mixer and the second mixer are implemented as harmonic rejection mixers. In some embodiments, the first mixer and the second mixer are configured to reject at least third-order harmonics and fifth-order harmonics.

[0044] In certain embodiments, at least one of the first local loopback circuit or the second local loopback circuit includes an RF harmonic rejection filter. In some embodiments, the RF harmonic rejection filter is configured to reject at least seventh-order harmonics. In some embodiments, the transceiver IC further includes digital transmitter circuitry configured to process a plurality of digital transmit samples captured by the at least one subsampling ADC. In some embodiments, the digital transmitter circuitry is configured to predict the effects of attenuation of the at least one subsampling ADC. In some embodiments, the digital transmitter circuitry includes frequency selection circuitry configured to generate a plurality of frequency-shifted digital transmit samples based on a frequency shift of the plurality of digital transmit samples. In some embodiments, the digital transmitter circuitry further includes accumulator circuitry configured to separately accumulate the plurality of frequency-shifted digital transmit samples and the plurality of non-frequency-shifted digital transmit samples. In some embodiments, the transceiver IC further includes a local oscillator configured to control the first mixer and the second mixer, wherein the frequency shifting circuitry is configured to shift the plurality of digital transmit samples based on a frequency difference between the sampling rate of the local oscillator and the sampling rate of the at least one subsampling ADC. In some embodiments, the transceiver IC further comprises an observation receiver configured to provide a plurality of digital observation samples to the digital transmitter circuit, wherein the accumulation circuit is further configured to accumulate the plurality of digital observation samples after frequency shifting by the frequency shifting circuit. In various embodiments, the transceiver IC further comprises a local oscillator configured to control the first mixer and the second mixer, wherein the frequency shifting circuit is configured to shift the plurality of digital observation samples based on a frequency of the local oscillator. In some embodiments, the at least one subsampling ADC is configured to sample the outputs of the plurality of loopback circuits at a sampling rate less than a carrier frequency of the RF transmit signal.

[0045] In various embodiments, the transceiver IC further includes a digital transmitter circuit configured to generate a digital I signal and a digital Q signal, a first DAC configured to generate an analog I signal based on the digital I signal, and a second DAC configured to generate an analog Q signal based on the digital Q signal. In some embodiments, the transceiver IC further includes a local oscillator configured to control the first mixer and the second mixer, wherein the digital transmitter circuit is configured to provide compensation for leakage of the local oscillator based on a plurality of digital transmit samples captured by at least one of the plurality of local loopback circuits. In some embodiments, the transceiver IC further includes an observation receiver configured to generate a plurality of digital observation samples, wherein the digital transmitter circuit is further configured to compensate for leakage of the local oscillator based on the plurality of digital observation samples. In some embodiments, the digital transmitter circuit is configured to provide quadrature error correction (QEC) based on the plurality of digital transmit samples.

[0046] According to various embodiments, the first local loopback circuit includes a controllable attenuator.

[0047] In some embodiments, at least one of the first local loopback circuit or the second local loopback circuit includes a controllable gain circuit.

[0048] In another aspect, a method for performing loopback in a transceiver is provided. The method includes generating a radio frequency (RF) signal based on upconverting an analog in-phase (I) signal using a first mixer, downconverting an analog quadrature-phase (Q) signal using a second mixer, and combining an output of the first mixer and an output of the second mixer. The method also includes amplifying the RF transmit signal using a variable gain amplifier (VGA) to generate an amplified RF transmit signal, and providing loopback using multiple local loopback paths, the multiple local loopback paths including a first local loopback circuit coupled to an output of the VGA and a second local loopback circuit coupled to an input of the VGA.

[0049] In some embodiments, the method further comprises processing at least one output of the plurality of local loopback circuits using at least one subsampling analog-to-digital converter (ADC). According to some embodiments, the method further comprises digitizing the output of a selected local loopback circuit selected from the first local loopback circuit or the second local loopback circuit using a shared subsampling ADC. According to some embodiments, the first mixer and the second mixer are implemented as harmonic rejection mixers. According to some embodiments, the first mixer and the second mixer are configured to reject at least third-order harmonics and fifth-order harmonics.

[0050] In certain embodiments, at least one of the first local loopback circuit or the second local loopback circuit includes an RF harmonic rejection filter. In some embodiments, the RF harmonic rejection filter is configured to reject at least seventh-order harmonics. In some embodiments, the method further includes processing a plurality of digital transmit samples captured by the at least one subsampling ADC using a digital transmitter circuit. In some embodiments, the method further includes predicting the effects of variation of the at least one subsampling ADC using the digital transmitter circuit. In various embodiments, the method further includes generating a plurality of frequency-shifted digital transmit samples based on a frequency shift of the plurality of digital transmit samples. In some embodiments, the method further includes separately accumulating the plurality of frequency-shifted digital transmit samples and the plurality of non-frequency-shifted digital transmit samples. In some embodiments, the method further includes controlling the first mixer and the second mixer using a local oscillator, wherein the plurality of frequency-shifted digital transmit samples are generated based on a frequency difference between the sampling rate of the local oscillator and the sampling rate of the at least one subsampling ADC. In some embodiments, the method further includes frequency shifting a plurality of digital observation samples from an observation receiver and accumulating the plurality of digital observation samples after the frequency shifting. According to some embodiments, the method further comprises controlling the first mixer and the second mixer using a local oscillator, wherein the plurality of digital observation samples are frequency shifted based on a frequency of the local oscillator. According to some embodiments, the method further comprises operating the at least one subsampling ADC at a sampling rate less than a carrier frequency of the RF transmit signal.

[0051] In some embodiments, the method further comprises controlling the first mixer and the second mixer using a local oscillator and compensating for leakage of the local oscillator based on a plurality of digital transmit samples captured by at least one of the plurality of local loopback circuits. In some embodiments, the method further comprises compensating for leakage of the local oscillator based on a plurality of digital observation samples from an observation receiver.

[0052] In various embodiments, the method further includes correcting a quadrature error between the analog I signal and the analog Q signal based on a plurality of digital transmit samples captured by at least one of the plurality of local loopback circuits.

[0053] In another aspect, a radio frequency (RF) communication system is provided. The RF communication system includes an RF front end and a transceiver configured to receive an amplified RF transmit signal. The transceiver includes a plurality of mixers, the plurality of mixers including a first mixer configured to upconvert an analog in-phase (I) signal and a second mixer configured to upconvert an analog quadrature-phase (Q) signal, wherein an output of the first mixer and an output of the second mixer are configured to combine to generate an RF transmit signal. The transceiver also includes a variable gain amplifier (VGA) configured to amplify the RF transmit signal to generate an amplified RF transmit signal. The transceiver also includes a plurality of local loopback circuits, including a first local loopback circuit coupled to an output of the VGA and a second local loopback circuit coupled to an input of the VGA.

[0054] In various embodiments, the transceiver further includes at least one sub-sampling analog-to-digital converter (ADC) configured to process at least one output of the plurality of local loopback circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 is a schematic diagram of a radio frequency (RF) communication system according to one embodiment.

[0056] Figure 2A is a schematic diagram of a portion of an RF communication system according to another embodiment.

[0057] Figure 2B is a schematic diagram of a portion of an RF communication system according to another embodiment.

[0058] Figure 3 is a schematic diagram of an observation receiver according to another embodiment.

[0059] Figure 4 is a schematic diagram of a local oscillator (LO) leakage compensation circuit according to another embodiment.

[0060] Figure 5A is a schematic diagram of a first example of LO leakage.

[0061] Figure 5B is a schematic diagram of a second example of LO leakage.

[0062] Figure 5C is a schematic diagram of a third example of LO leakage.

[0063] Figure 5D is a schematic diagram of a fourth example of LO leakage.

[0064] Figure 5E is a schematic diagram of a fifth example of LO leakage.

[0065] Figure 5Fis a schematic diagram of a sixth example of LO leakage.

[0066] Figure 5G is a schematic diagram of a seventh example of LO leakage.

[0067] Figure 6A is a schematic diagram of one embodiment of a digital transmitter circuit for processing transmit signal samples and observing receiver samples.

[0068] Figure 6B yes Figure 6A Schematic diagram of one embodiment of a digital transmitter circuit illustrating a data flow of transmitted signal samples and observed receiver samples.

[0069] Figure 7 is a schematic diagram of a transmitter according to another embodiment.

[0070] Figure 8 is a schematic diagram of one embodiment of a digital transmitter circuit.

[0071] Figure 9 is a schematic diagram of a transmitter according to another embodiment.

[0072] Figure 10A is a schematic diagram of a circuit including a controllable oscillator, a variable gain amplifier, and a harmonic rejection mixer according to one embodiment.

[0073] Figure 10B yes Figure 10A Diagram of the circuit operating in divide-by-2 mode.

[0074] Figure 10C yes Figure 10A Diagram of the circuit operating in divide-by-4 mode. DETAILED DESCRIPTION

[0075] The detailed description of the following embodiments presents various descriptions of specific embodiments of the present invention. However, the present invention can be implemented in many different ways. In this specification, reference is made to the accompanying drawings in which similar reference numerals may indicate identical or functionally similar elements. It should be understood that the elements shown in the drawings are not necessarily drawn to scale. In addition, it should be understood that certain embodiments may include more elements than shown in the drawings and / or a subset of the elements illustrated in the drawings. In addition, some embodiments may combine any appropriate combination of features from two or more drawings.

[0076] Transceivers are used in radio frequency (RF) communication systems to transmit and receive signals associated with various communication technologies, such as cellular and / or wireless local area network (WLAN) technologies.

[0077] Examples of RF communication systems having one or more transceivers include, but are not limited to, base stations, mobile devices (such as smartphones or cell phones), laptops, tablets, and wearable electronic devices.

[0078] A transceiver includes a transmitter for transmitting RF signals and a receiver for receiving RF signals. To improve transceiver performance, the transceiver can be calibrated to compensate for impairments. Calibrating the transceiver in this manner can reduce error vector magnitude (EVM), reduce out-of-band emissions, and / or otherwise enhance transceiver performance.

[0079] Without calibration, damage to the transceiver may result in degraded performance.

[0080] In one example, a direct-conversion quadrature radio includes a zero intermediate frequency (ZeroIF) transmitter for transmitting RF signals. A ZeroIF transmitter uses a local oscillator (LO) frequency at or near the carrier frequency to upconvert the baseband signal. While ZeroIF transmitters offer significant power and cost advantages over IF and superheterodyne transmitters, they suffer from the limitation of undesirable transmission performance within a limited band.

[0081] One such transmitter impairment is LO leakage, in which a portion of the LO signal used for mixing appears at the transmitter output. LO leakage can be caused by limited isolation between the mixer's LO port and the mixer's signal port. If not corrected or calibrated, LO leakage can cause test failures and the inability to monitor for unwanted transmit emissions.

[0082] For example, undesirable DC offsets in the transmitter baseband can mix with the LO signal, generating LO power at the transmitter output. LO leakage can occur at frequencies with specific restrictions on unwanted transmitter emissions. Consequently, LO leakage can limit transmitter performance in applications with relatively stringent emission regulations. For example, some zero-IF transmitters support non-contiguous carrier aggregation, where the LO frequency may not fall within the desired frequency channel. In such implementations, emission limits can be relatively stringent.

[0083] To reduce or limit such undesirable emissions, the transmitter can be calibrated to reduce the LO leakage level.

[0084] The transmitter may include a non-inverting voltage output V for providing a transmitter output signal tx_p and the inverting voltage output V tx_n In addition, the transmitter output signal has a value approximately equal to (V tx_p -V tx_n ) and the differential components are approximately equal to (V tx_p +V tx_n) / 2. Differential LO leakage affects the differential component of the transmitter output signal, and common-mode LO leakage impacts the common-mode component in the transmitter output signal.

[0085] While differential LO leakage may be observed locally at the transceiver, the common-mode LO leakage component may not be observed locally.Differential LO leakage is also referred to herein as internal LO leakage, and common-mode LO leakage is also referred to herein as external LO leakage.

[0086] Common-mode LO leakage can also degrade the performance of transmitters, such as zero-IF transmitters. For example, a balun may be included to convert the transmitter's differential output signal into a single-ended signal suitable for amplification by a power amplifier (PA) and subsequent transmission via an antenna. Ideally, the balun rejects the common-mode component of LO leakage present in the transmitter's differential output signal. However, the balun's limited common-mode rejection ratio (CMRR) can cause some of the common-mode LO leakage to reach the balun's output.

[0087] In contrast, the CMRR of atypical observation receivers used to observe and calibrate transmitters is relatively high, so the observation receiver will not observe common-mode LO leakage. Even in implementations where the observation receiver's CMRR is finite, the observation receiver's GMRR and the CMRR of the balun may not match. Therefore, such observation receivers are not suitable for estimating and compensating for common-mode LO leakage.

[0088] Apparatus and methods for transceivers are provided herein.

[0089] In a first aspect, an observation receiver is implemented to detect common-mode LO leakage. This detection can occur while the observation receiver is performing other functions, such as observing portions of the RF transmit spectrum for power control and / or digital predistortion (DPD) purposes. Thus, the observation receiver is implemented to observe common-mode LO leakage as a background process (e.g., as a batch collection) without interrupting power control and / or DPD.

[0090] In a second aspect, the LO leakage compensation circuit compensates for transmitter LO leakage based on combining differential LO leakage observations (which can be observed locally in the transceiver) with common-mode LO leakage observations (which can be observed via an off-chip path from the transmitter through the RF front-end system to an observation receiver). Thus, the LO leakage compensation circuit can operate based on observations from both the local (on-chip) loopback path and the external (off-chip) loopback path. The LO leakage compensation circuit can include a digital filter, such as a Kalman filter, that processes the differential and common-mode LO leakage observations to generate a combined LO correction signal for compensating the transmitter.

[0091] In a third aspect, a transmitter includes a pair of mixers for generating an RF transmit signal based on upconverted analog I and Q signals, an LO for providing a clock signal to the pair of mixers, a variable gain amplifier (VGA) for amplifying the RF transmit signal to generate an amplified RF transmit signal, and multiple local loopback paths, including a first loopback path after the VGA and a second loopback path before the VGA. The first loopback path and the second loopback path can be used to compensate for LO leakage and other functions, such as orthogonal error correction (QEC). In certain implementations, observations from the local loopback paths are digitized by at least one subsampling ADC, and the mixers are implemented as harmonic rejection mixers and / or the loopback paths include RF filters for filtering out higher-order harmonics. Thus, the transceiver is implemented to reduce harmonics (e.g., third-order, fifth-order, and / or seventh-order harmonics) that would otherwise cause problems due to variations in the subsampling ADC.

[0092] Example of an RF communication system including a transceiver

[0093] Figure 1 FIG. 4 is a schematic diagram of a radio frequency (RF) communication system 40 according to an embodiment. The RF communication system 40 includes a transceiver 1 , an RF front-end system 2 , and an antenna 3 .

[0094] Although one embodiment of the RF communication system 40 is depicted, the teachings herein are applicable to RF communication systems implemented in various ways. Thus, other implementations are possible.

[0095] In the illustrated embodiment, transceiver 1 includes a receiver 4, a transmitter 5, an observation receiver 6, and a local oscillator (LO) leakage compensation circuit 7. Although an example with one transmit channel, one receive channel, and one observation channel is depicted, the teachings herein are applicable to transceivers with other numbers of transmit channels, receive channels, and / or observation channels. Furthermore, the number of transmit channels, receive channels, and observation channels need not be equal.

[0096] Transceiver 1 from the baseband processor ( Figure 1 ) receives in-phase (I) and quadrature-phase (Q) transmit data and provides I and Q receive data to a baseband processor.

[0097] like Figure 1 As shown, transmitter 5 includes an I-path digital-to-analog converter (DAC) 21 a , an I-path filter 22 a , an I-path mixer 23 a , a Q-path DAC 21 b , a Q-path filter 22 b , a Q-path mixer 23 b , and an LO 24 .

[0098] I-path DAC 21a processes I transmit data to generate an analog I signal. This analog I signal is filtered by I-path filter 22a to generate a filtered I signal. The filtered I signal is up-converted to radio frequency by I-path mixer 23a. Specifically, I-path mixer 23a mixes the filtered I signal with a first LO clock signal from LO 24 to generate an up-converted I signal.

[0099] Similarly, Q-path DAC 21b processes the Q transmission data to generate an analog Q signal, which is filtered by Q-path filter 22b to generate a filtered Q signal. Furthermore, Q-path mixer 23b mixes the filtered Q signal with a second LO clock signal from LO 24 to generate an upconverted Q signal.

[0100] LO 24 can be implemented in a variety of ways, including but not limited to using a frequency synthesizer, such as a fractional-N phase-locked loop (PLL). The first LO clock signal and the second LO clock signal can have a phase difference suitable for upconverting the filtered I signal and the filtered Q signal. For example, quadrature or a 90-degree phase difference can be used.

[0101] The up-converted I signal and the up-converted Q signal are combined to generate a differential transmit signal TX. The transmit signal TX is provided to the RF front-end system 2.

[0102] In the illustrated embodiment, the RF front-end system 2 includes a balun 11, a power amplifier (PA) 12, a low-noise amplifier (LNA) 13, an antenna access circuit 14, and a directional coupler 15. Although one example of a front-end circuit is depicted, other implementations are possible. For example, the RF front-end system 2 may include additional structures such as filters, amplifiers, attenuators, duplexers, duplexers, and / or control circuitry. Furthermore, the components may be arranged in other ways, including but not limited to using separate antennas for transmit and receive.

[0103] The balun 11 receives a differential transmit signal TX, which is converted by the balun 11 into a single-ended transmit signal for amplification by the PA 12. The PA 12 outputs an amplified RF transmit signal, which is provided to the antenna 3 via the antenna access circuit 14. The antenna access circuit 14 may include switches, duplexers, duplexers, and / or other structures suitable for controlling access to the transmit and receive paths of the antenna 3.

[0104] like Figure 1 As shown, the directional coupler 15 is included between the output of the PA 12 and the antenna access circuit 14, and is used to sense the amplified RF transmission signal to generate an observation signal OBS. Figure 1 As shown in , the observation signal OBS is supplied to the observation receiver 6 of the transceiver 1 .

[0105] The LNA 13 receives the RF receive signal from the antenna 3 via the antenna access circuit 14. The LNA 13 amplifies the RF receive signal to generate an amplified receive signal RX, which may be single-ended or differential. The receiver 4 processes the amplified receive signal RX to generate I and Q receive data.

[0106] like Figure 1 As shown, the transceiver 1 includes an LO leakage compensation circuit 7 that compensates for the LO leakage of the transmitter 5 based on observations of differential LO leakage and common mode leakage.

[0107] For example, in the illustrated embodiment, the LO leakage compensation circuit 7 includes a differential LO leakage observation circuit 31 for observing the amount of differential LO leakage present in the differential transmit signal TX. Since the transceiver 1 is typically formed on a semiconductor die (separate from the semiconductor die) used to form the RF front-end system 2, the observation of the differential LO leakage can be based on a local observation path of the transceiver 1.

[0108] Continue to refer Figure 1 , LO leakage compensation circuit 7 further includes common-mode LO leakage observation circuit 32 that observes common-mode LO leakage based on data flowing through observation receiver 6. In some implementations, observation receiver 6 is implemented to allow observation of common-mode LO leakage without interrupting other operations of observation receiver 6, such as observing portions of the spectrum of the amplified RF transmit signal for purposes of transmit power control and / or DPD.

[0109] In the illustrated embodiment, LO leakage compensation circuit 7 also includes a digital filter 33 that combines observation signals from differential LO leakage observation circuit 31 and common-mode LO leakage observation signal 32 to generate an LO leakage compensation signal for transmitter 5. In some implementations, digital filter 33 includes a Kalman filter.

[0110] LO leakage compensation circuit 7 can compensate for LO leakage of transmitter 5 in a variety of ways. In one example, digital compensation can be used. For example, a digital adder can be used to add appropriate DC offsets to the I and Q paths. In a second example, analog compensation can be used. For example, a controllable oscillator signal (having controllable differential and / or common-mode components) can be combined with the differential transmit signal TX to provide compensation for LO leakage. Furthermore, a combination of digital and analog techniques can be used.

[0111] Example observation receiver for observing common-mode LO leakage

[0112] Figure 2AFIG. 1 is a schematic diagram of a portion of an RF communication system 110 according to another embodiment. The RF communication system 110 includes an observation receiver 101 and an RF front-end system 102. The observation receiver 101 is a portion of a transceiver ( Figure 2A not shown in the figure).

[0113] The RF front-end system 102 includes a power amplifier 108 and a directional coupler 109. The power amplifier 108 outputs and amplifies the RF transmit signal, which is sensed by the directional coupler 109 to generate an RF observation signal OBS. For clarity of the figure, only the power amplifier 108 and the directional coupler 109 of the RF front-end system 102 are shown. However, the RF front-end system 102 may include other components.

[0114] In the illustrated embodiment, the observation receiver 101 includes an RF analog-to-digital converter (RF ADC) 103 for generating a digital observation signal based on an RF observation signal OBS from the RF front-end system 102. Although an example with the RF ADC 103 is shown, other implementations are possible, such as a configuration using a cascade of an observation mixer and an ADC.

[0115] Continue to refer Figure 2A Observation receiver 101 also includes a digital observation path 104, which includes various digital circuits for processing digital observation signals. Digital observation path 104 is also referred to herein as a digital observation circuit. Digital observation path 104 can be used to perform observations for the purposes of transmit power control, DPD, and / or other functions.

[0116] like Figure 2A As shown, the digital observation path 104 further includes a digital mixer 105, a digital oscillator 106, and a digital accumulator 107 for observing common-mode LO leakage. The digital mixer 105 taps off a portion (or multiple portions) of the digital observation path 104, thereby observing the digital data stream of the observation receiver 101 without interrupting the operation of the observation receiver 101 (e.g., transmit power control and / or DPD).

[0117] The digital mixer 105 is used to frequency shift the tap observation data based on the digital oscillator signal from the digital oscillator 106. Therefore, the frequency content of the common-mode LO leakage observation can be shifted in frequency relative to the data flowing through the digital observation path 104. The digital accumulator 107 accumulates the observation data, which can be used by the LO leakage compensation circuit (now as shown in FIG. Figure 2A In some implementations, the digital oscillator 106 corresponds to a numerically controlled oscillator (NCO).

[0118] Figure 2BFIG. 1 is a schematic diagram of a portion of an RF communication system 120 according to another embodiment. The RF communication system 120 includes an observation receiver 111 and an RF front-end system 112. The observation receiver 111 is a portion of a transceiver ( Figure 2B not shown in the figure).

[0119] The RF front-end system 112 includes power amplifiers 108a, 108b, ...108n, directional couplers 109a, 109b, ...109n, and a multiplexer 115. Any number of power amplifiers and directional couplers may be included, as indicated by the ellipsis. Furthermore, the power amplifiers 108a, 108b, ...108n may transmit at the same or different frequencies. The multiplexer 115 is used to select a specific sensed signal from the directional couplers 109a, 109b, ...109n to provide as the RF observation signal (OBS).

[0120] By multiplexing the directional couplers 108a, 108b, ... 108n, a common observation receiver may be used to observe multiple transmit paths through the RF front-end system 120. However, other implementations are possible.

[0121] In the illustrated embodiment, the observation receiver 111 includes the RF ADC 103 and the digital observation path 104, as described above with respect to Figure 2A The observation receiver 111 further includes digital mixers 105a, 105b, ... 105n, digital oscillators 106a, 106b, ... 106n (any or all of which may be NCOs), and digital accumulators 107a, 107b, ... 107n.

[0122] Digital mixers 10Sa, 10Sb, ... 10Sn tap data from digital observation path 104 to observe the digital data stream of observation receiver 111 without interrupting the operation of observation receiver 111 (eg, transmit power control and / or DPD).

[0123] In addition, multiple instances of mixers, oscillators, and accumulators are provided to separately track common-mode LO leakage associated with multiple transmission paths. For example, each of the PAs 108a, 108b, ... 108n can amplify an RF transmit signal generated using a different LO, so the common-mode LO leakage can vary across transmit channels.

[0124] Thus, based on which directional coupler 109a, 109b, ... 109n is selected by the multiplexer 115, the corresponding accumulator 107a, 107b, ... 107n of the observation receiver 111 may be activated.

[0125] By accumulating frequency shift samples indicative of common-mode LO leakage in the background, the user can change the observed path and / or perform any other desired operations in the RF front-end system 112 without stopping for common-mode LO leakage observation. Thus, the common-mode LO leakage compensation process can be transparent to the user.

[0126] Figure 3 FIG2 is a schematic diagram of an observation receiver 270 according to another embodiment. The observation receiver 270 includes an RF ADC 201, an ADC interface with a first-in-first-out (FIFO) 202, an input multiplexer 203, a digital down-conversion mixer 204, a fine NCO, and a CMOS controller. 205, I path decimator 206a, first I path finite impulse response (FIR) filter 207a, second I path FIR filter 208a, first I path interpolator 211a, second I path interpolator 212a, third I path interpolator 213a, first I path multiplexer 221a, second I path multiplexer 222a, third I path multiplexer 223a, fourth I path multiplexer 224a, fifth I path multiplexer 225a, sixth I path multiplexer 226a, first I path half-band (HB) filter 231a, second I path HB filter 232a, I path mixer 235a, Q path decimator 206b, first Q path FIR filter 207b, second Q path FIR filter 208b, first Q path interpolator 211b, second Q path interpolator 212b, third Q path interpolator 213b, first Q path multiplexer 221b, second Q path multiplexer 222b, third Q path multiplexer 223b, fourth Q path multiplexer 224b, fifth Q path multiplexer 225b, sixth Q path multiplexer 226b, first Q path HB filter 231b, second Q path HB filter 232b, Q path mixer 235b, peak detection and power measurement circuit 241, detection multiplexer 242, NCO 245 , formatter 246 , cross-link 248 , framer 249 , observation capture random access memory (RAM) 251 , observation capture multiplexer 252 , leakage observation multiplexer 254 , leakage observation NCO 255 ​​, leakage observation mixer 256 , and leakage observation accumulator 257 .

[0127] Although one embodiment of an observation receiver is shown, the teachings herein are applicable to observation receivers implemented in other ways.

[0128] Example Kalman filter for processing local and external LO leakage observations

[0129] Figure 4FIG. 3 is a schematic diagram of an LO leakage compensation circuit 310 according to another embodiment. The LO leakage compensation circuit 310 includes a differential LO leakage observation circuit 301 , a common-mode LO leakage observation circuit 302 , and a Kalman filter 303 .

[0130] In the illustrated embodiment, Kalman filter 303 processes the differential and common-mode LO leakage observations to generate a combined LO correction signal for compensating the transmitter of the transceiver.

[0131] Figures 5A-5G Various transmitter LO leakage conditions that may occur during transceiver operation are described. Figures 5A-5G Describes the sampling frequency f s , but for all graphs, f s You can use f s / 2, where f s is the sampling rate of the ADC. Additionally, data collection can be performed around a single alias point if desired.

[0132] Figure 5A Figure 1 is a diagram of the first example of LO leakage. In this example, there is no transmit signal, but there is internal transmitter LO leakage.

[0133] In some implementations, perturbations are introduced in this case (e.g., to discover the channel for correction purposes) because no signal is present. In addition, when the transmitter LO leakage correction loop is run (e.g., in Figure 1 At the end of each pass, an adjustment is made to the transmitter DC (e.g., a digital adjustment is made to the I and Q transmit signals input to the transmitter) to attempt to correct for LOL. This adjustment can be used along with the before and after measurements as a perturbation.

[0134] When starting from an initial correction point, channel information can be inherited from a previously run calibration or other valid channel. If such information is not available, an initial guess can be used as the transmitter LO leakage correction loop iteratively adjusts and learns from the results. For example, in the absence of channel information, the digital filter of the LO leakage compensation circuit (e.g., a Kalman filter) can be initialized to a general guess with a high uncertainty range. At the end of the first data acquisition process, the Kalman filter can estimate the correction.

[0135] In some implementations, the correction is limited to a reasonable amount, such as 128 least significant bits (LSBs). Although the estimated correction may be wrong, it can be used as a perturbation in the next pass to help adjust to the actual correction value. For example, this situation may correspond to an algorithmic edge case and rarely occurs in practice because there is usually a transmitted signal or inherited channel information available.

[0136] Continue to refer Figure 5A In certain implementations, the correction is implemented using Equation 1 below, where LB' corresponds to the frequency-shifted loopback samples, as discussed further below.

[0137] Equation 1

[0138]

[0139] Figure 5B 1 is a diagram illustrating a second example of LO leakage. The second case corresponds to a case where the LO leakage is below the carrier frequency.

[0140] In this case, a very accurate channel measurement is required because we will observe a large intentional TX signal at the LO, which needs to be measured at LPBCK and removed from the correction. In order to input the loopback measurement (observation receiver) to the transit signal, the measurement can be divided by the channel, so an accurate channel is required for accurate cancellation. In digital transmitter electronics, an accumulator can provide this information.

[0141] Figure 5C is a diagram of a third example of LO leakage. In this case, the carrier image is at the LO frequency. In the third case, the loopback ADC is at frequency f s is run, so the transmit spectrum at 2f0-LO is shown in the loopback spectrum at the same location as the LO frequency.

[0142] Figure 5D Figure 1 is a diagram of the fourth example of LO leakage. In this fourth example, the carrier is at the LO frequency and the carrier image is at the –LO frequency.

[0143] refer to Figures 5B-5D , the TX can be measured at LO and –LO, and the observation receiver can be measured at the LO frequency. Therefore, a Kalman filter operating on three variables can be used: g0 (gain at LO frequency), g1 (gain at LO frequency), and u (correction).

[0144] for Figure 5B In the second case shown, g0 can be calculated by cross-correlation. Figure 5C In the third case shown, both g0 and g1 can be calculated by cross-correlation. In this third case, the Kalman filter learns g1 separately from g0. Therefore, in this case, g1 will be learned with a large signal, while g0 will be learned by correction.

[0145] When no signal is present, the Kalman filter knows the corrections previously made and the corresponding impact on the current measurement. Therefore, the Kalman filter can automatically use the corrections as perturbations to generate channel information.

[0146] Figure 5E Figure 1 is a fifth example of LO leakage. In this example, there is internal transmitter LO leakage, and the carrier is off at both the LO and –LO frequencies.

[0147] Figure 5F Figure 1 is a diagram of the sixth example of LO leakage. In this example, there is external transmitter LO leakage and the carrier is at the LO frequency.

[0148] Figure 5G Figure 1 is a diagram of the seventh example of LO leakage. In this example, there is external transmitter LO leakage and the carrier is offset from the LO frequency.

[0149] Although seven examples of LO leakage are described, other LO leakage situations are possible. For example, in another example, when there is no transmit signal, there is external LO leakage.

[0150] Figure 6A is a schematic diagram of one embodiment of a digital transmitter circuit 410 for processing transmit signal samples (TX) and observing receiver samples (LPBCK). Figure 6B yes Figure 6A Schematic diagram of one embodiment of a data stream 420 of transmitted signal samples and observed receiver samples from a digital transmitter circuit 410.

[0151] The digital transmitter circuit 410 receives digital samples of the RF transmit signal TX indicative of the differential LO leakage signal.The digital transmitter circuit 410 also receives digital samples of the observation signal LPBCK received from the observation receiver via loopback.

[0152] In the illustrated embodiment, the digital transmitter circuit 410 includes a frequency selection circuit (FSC) 401 for observing samples at different frequencies. The FSC 401 shifts the TX and LPBCK samples to generate TX samples with no shift, TX samples with a shift of 2*(f s The FSC 401 comprises a TX sample of the TX signal (-LO) and a LPBCK sample of the LPO shifted LO (thus reducing the LO content to DC). The shifting can be implemented in any suitable manner, for example, using digital mixers 403 and 404 controlled by NCOs 405 and 406. In some implementations, the FSC 401 includes a digital accumulator 407 for accumulating each of the three shifted samples.

[0153] For internal LO leakage observation, the TX / LPBCK signal can come from FSC 401. However, for external LO leakage observation, the TX signal does not need to be routed through FSC 401, but can be independently routed to a separate LOL accumulator.

[0154] External LOL observation depends on the mapping of the transmitter to the observation receiver, which can be controlled by the user. Since internal (quadrature error correction (QEC) and LO leakage) observations do not depend on the mapping of the transmitter to the observation receiver, internal observations are sometimes possible even when external observations are not possible. If external observations depend on FSC, external observations may block internal observations until the mapping of the transmitter to the observation receiver is changed.

[0155] To avoid external LO leakage observations blocking internal QEC observations, the TX accumulator used for external LOL observations can look directly at the TX signal (instead of going through the FSC) so that the TX QEC can access the FSC simultaneously.

[0156] In some embodiments, a separate I / Q accumulator is built into the digital transmission path, unconnected and independent of the FSC 401. A similar I / Q accumulator can be built into the observation path of each transmitter channel. The I / Q accumulator can perform accumulation based on control from the transmitter LO leakage block. This loopback data can also be frequency-shifted using an NCO so that the LO is at baseband DC, as discussed previously.

[0157] In some implementations, batch acquisition is used to acquire TX and LPBCK samples, and they are not allowed to update to the accumulator until both samples are acquired. To achieve this, the active accumulator, holding registers, and final accumulator can be used for TX sampling. For LPBCK samples, the active accumulator and final accumulator can be used. During data collection, the active accumulator sums the samples of the TX stream. Once the batch size is reached, the active accumulator can be transferred to the holding register, and the active accumulator is cleared to start the next batch of samples. There is no need to use the ORX holding register, because once the active accumulator completes a batch, the contents can be directly added to the final accumulator.

[0158] One embodiment of a model of a Kalman filter for processing transmitter leakage observation data is now described.

[0159] The transmitter (T X ) LO leakage (e.g., differential LO leakage). Equation 2 is provided below, where y int[n] is the internal loopback output after rotating the Tx LO frequency to DC, x0[n] is the user Tx signal near DC, x1[n] is the interfering user Tx aliased onto the Tx LO at the loopback output, go is the complex channel from Tx to the loopback at the LO frequency (DC), g1 is the complex channel from Tx to the loopback at the interfering frequency, and μ c is the current Tx LO leakage correction value, μ int is the Tx LO leakage observable at the loopback output but returned to the Tx input, and μ[n] is uncorrelated zero-mean white noise from the Tx, the loopback, or both.

[0160] Equation 2

[0161] y int [n] = g0(x0[n] + μ c +μ int )+g1x1[n]+u[n]

[0162] Tx LO leakage (e.g., common mode LO leakage) is also observed through an external path looped back to the observation receiver (ORx). Equation 3 is provided below, where y ext [n] is the external ORx output after rotating the Tx LO frequency to DC, x0[n] is the user Tx signal near DC, h0 is the complex channel from Tx to ORx at the LO frequency (DC), μ c is the current Tx LO leakage correction value, μ int is the Tx LO leakage observable at the loopback output, but returned to the Tx input, μ ext is the additional Tx LO leakage observable at the ORx output, returned to the Tx input, and v[n] is the uncorrelated zero-mean white noise from Tx, ORx, or both.

[0163] Equation 3

[0164] y ext [n]=h0(x0[n]+μ c +μ int +μ ext )+v[n]

[0165] In some implementations, the Kalman filter is implemented to learn μc to eliminate the combined μ at the Tx / ORx output by making frequent internal observations but infrequent external observations. int +μ ext It can be assumed that the internal leakage μ int captures the time-varying component of LO leakage, while μ ext A static bias can be assumed, which varies much less frequently over time.

[0166] Equations 4 and 5 below define the correlation and summation operations.

[0167] Equation 4

[0168]

[0169] Equation 5

[0170]

[0171] Regarding the observed internal LO leakage, when using FSC, the Tx input can be cross-correlated with the internal loopback output to quickly learn the unknown channel, as shown in Equations 6 and 7.

[0172] Equation 6

[0173]

[0174] Equation 7

[0175]

[0176] Since the user Tx signal may have a mean value close to zero, cross-correlation is not suitable for directly estimating the unknown leakage μ int The following equation 8 involves calculating the sum (similar to the known constant reference signal μ) c X cross-correlation).

[0177] Equation 8

[0178] S(y int )=g0(S(x0)+μ c )+g0μ int +g1S(x1)+S(u)

[0179] Therefore, based on the internal path observation, we have 3 complex observation equations with 3 unknowns (g0, g1, μ int ) and 3 noise contributors (C(u, x0 * ), C(u, x1 * ), S(u)). Since g0μ int The observation equation is nonlinear in the unknown case.

[0180] For observed external LO leakage, using an external LOL accumulator block, time-synchronized summation of the Tx input and ORx output can be performed as shown in Equation 9 below.

[0181] Equation 9

[0182] S(y ext )=h0(S(x0)+μ c )+h0μ int +h0μ ext +S(u)

[0183] For the observed external LO leakage, there is a problem with 3 unknowns (h0, μ int , μ ext ) and a single complex observation equation for the noise contributor (S(v)). Since h0μ int and h0μ ext The observation equation is nonlinear in the unknown case.

[0184] The above observation equation can be linearized by grouping the channel and LOL unknowns together (e.g., estimating LOL at the loopback / ORx output instead of referenced to the Tx input), but the nonlinear form allows for the use of μ int Connecting internal and external unknowns, μ int Refers to the same common Tx input. Because the observation equation is nonlinear, a nonlinear estimation algorithm (such as a Kalman filter) can be used.

[0185] Combining the above internal and external observation equations, there are a total of 5 unknown state variables, as shown in Equation 10.

[0186] Equation 10

[0187] x≡[g0, g1, μ int ,h0,μ ext ] T

[0188] The same state transition matrix can be used to allow for time variations introduced by process noise. The prediction step of the Kalman filter can be given by equations 11 and 12 listed below.

[0189] Equation 11

[0190] x t|t-1 =x t-1|t-1

[0191] Equation 12

[0192] P t|t-1 =P t-1|t-1 +Q

[0193] The update step of the Kalman filter can include two steps: (i) using the full nonlinear observation equation, estimating the observation value that should be given the current value of the unknown quantity; and (ii) performing a linear Kalman filter update by defining the Jacobian matrix as the observation matrix.

[0194] Regarding the first step, the following equations 13, 14, 15, 16, and 17 can be used to estimate the observed values ​​that should be given and the current estimates of the unknown quantities.

[0195] Equation 13

[0196]

[0197] Equation 14

[0198]

[0199] Equation 15

[0200]

[0201] Equation 16

[0202] S(y int )=g0(S(x0)+μ c )+g0μ int +g1S(x1)

[0203] Equation 17

[0204] S(y ext )=h0(S(x0)+μ c )+h0μ int +h0μ ext

[0205] Regarding the second step, a linear Kalman filter update may be performed using the Jacobian of the observation system as the observation matrix, as shown in Equation 18 below.

[0206] Equation 18

[0207]

[0208] For the case where some observations are missing, the corresponding columns can be removed from the Jacobian matrix and the Kalman update is performed with the reduced observation dimension. For example, if external observation data is not available at the current time step, the observation dimension is reduced from 4 to 3.

[0209] Example of a transmitter implemented using multiple local loopbacks

[0210] Figure 7FIG2 is a schematic diagram of a transmitter 540 according to another embodiment. The transmitter 540 includes a digital transmitter circuit 520, an I-path DAC 521a, an I-path controllable filter 522a, an I-path mixer 523a, a Q-path DAC 521b, a Q-path controllable filter 522b, a Q-path mixer 523b, a variable gain amplifier (VGA) 525, a first local loopback circuit 531, a second local loopback circuit 532, and a subsampling ADC 533.

[0211] like Figure 7 As shown, the digital transmitter circuit 520 receives I transmit data and Q transmit data, which are provided to an I path DAC 521 a and a Q path DAC 521 b after digital processing, respectively.

[0212] I-path DAC 521a converts I transmission data into an analog I signal. This analog I signal is filtered by I-path controllable filter 522a to generate a filtered I signal. The filtered I signal is up-converted to radio frequency by I-path mixer 523a. Specifically, I-path mixer 523a mixes the filtered I signal with a first LO clock signal from LO 524 to generate an up-converted I signal.

[0213] Similarly, Q-path DAC 521b processes the Q transmission data to generate an analog Q signal, which is then filtered by Q-path controllable filter 522b to generate a filtered Q signal. Furthermore, Q-path mixer 523b mixes the filtered Q signal with a second LO clock signal from LO 524 to generate an upconverted Q signal.

[0214] LO 524 can be implemented in a variety of ways, including but not limited to using a frequency synthesizer, such as a fractional-N PLL. The first LO clock signal and the second LO clock signal can have a phase difference suitable for upconverting the filtered I signal and the filtered Q signal. For example, a quadrature phase difference can be used.

[0215] The upconverted I signal and the upconverted Q signal are combined to produce a differential transmit signal, which is amplified by the VGA525 to produce an amplified differential transmit signal provided between pins TX+ and TX-. The amplified differential transmit signal is provided to the RF front-end system (e.g., Figure 1 RF front-end system 2).

[0216] like Figure 7 As shown, the digital transmitter circuit 520 further includes an LO leakage compensation circuit 534 for adjusting the I transmit signal and the Q transmit signal to compensate for LO leakage caused by the LO 524. Such LO leakage may include differential LO leakage and common-mode LO leakage.

[0217] LO leakage compensation is based on transmit samples TX of the RF transmit signal generated by the transmitter 540 and the ... Figure 1 The observation receiver 6) captures the observation samples OBS.

[0218] In the illustrated embodiment, in addition to the external loopback path through the observation receiver, the transmitter 540 also operates using multiple (two in this example) local loopback paths. Specifically, a first local loopback circuit 531 is included for observing the RF transmission signal after amplification by the VGA 525, and a second local loopback circuit 532 is included for observing the RF transmission before amplification by the VGA 525.

[0219] Including multiple local loopback paths provides a number of advantages. For example, the first local loopback path 531 includes the effects of the VGA 525 as well as any noise coupled through the RF transmit signal output pin. However, when the VGA 525 is operating at a low gain setting, the amplified RF transmit signal may have a low signal-to-noise ratio (SNR), which results in delays due to the large number of samples taken for averaging. Furthermore, any calibration of LO leakage using the first local loopback path 531 also exposes downstream circuitry (e.g., a power amplifier) ​​to the RF transmit signal generated by the transmitter 540.

[0220] In contrast, the second local loopback path 532 can be used even when the VGA 525 is turned off to prevent the RF transmit signal from propagating to (and potentially damaging) downstream circuitry. Furthermore, the second local loopback path 532 is shielded from the effects of output impedance matching and exhibits good SNR even when the VGA 525 gain setting is low. However, the second local loopback path 532 may miss the effects of LO leakage occurring after the VGA 525.

[0221] Continue to refer Figure 7 For cellular communications using frequency range 1 (FR1) of fifth generation (SG) technology, the RF transmit signal may have a relatively high frequency, for example, up to approximately 7.125 GHz. In this embodiment, the subsampling ADC 533 operates at a sampling rate less than the carrier frequency of the RF transmit signal. Using a subsampling ADC provides many advantages, such as reducing area, power consumption, and / or cost.

[0222] To help prevent degradation effects (e.g., image problems) from hindering the operation of LO leakage correction, I-path mixer 523a and Q-path mixer 523b can be implemented as harmonic rejection mixers. In some implementations, I-path mixer 523a and Q-path mixer 523b are at least third-order harmonic rejection mixers, or more preferably third-order and fifth-order harmonic rejection mixers.

[0223] By implementing the mixer in this manner, the problems caused by reducing the third and fifth order harmonic components are alleviated.

[0224] In some implementations, higher order harmonics, such as the seventh order harmonic, are accounted for using RF filters included in the first local loopback circuit 531 and the second local loopback circuit 532. Thus, a combination of a harmonic rejection mixer and an RF filter can be used to reduce issues caused by downconversion.

[0225] To further illustrate the frequency reduction, an LO leakage compensation circuit can be implemented to model and predict the effect of frequency reduction. For example, FSC (see Figure 6A and 6B ) can be included in the digital transmitter circuitry to help implement such functions. Thus, digital processing can serve as another layer of compensation for degradation.

[0226] Figure 8 is a schematic diagram of one embodiment of a digital transmitter circuit 570. For example, the digital transmitter circuit 570 may be used to Figure 7 In the digital transmitter circuit 520. Figure 8 As shown, the digital transmitter circuit 570 includes a QEC / LO leakage compensation circuit 561, a programmable finite impulse response filter (PFIR) 562, an interpolation / filtering circuit 563, a frequency selection and accumulation circuit 564, and a processor 565, which includes software stored in a memory and is operable to implement a Kalman filter 566.

[0227] The digital transmitter circuit 570 processes the digital I and Q transmit signals and provides the processed digital I and Q transmit signals to a pair of DACs ( Figure 8 The digital I and Q transmit signals are sent from the baseband processor ( Figure 8 (not shown) received.

[0228] In the illustrated embodiment, the frequency selection and accumulation circuit 564 receives transmit samples TX of the locally acquired RF transmit signal (via one or more on-chip local loopback paths) and observation samples OBS captured from the observation receiver via one or more external loopback paths (via the RF front end). The frequency selection and accumulation circuit 564 can shift the frequency of the samples (e.g., using a digital mixer and NCO) and accumulate the frequency-shifted samples, for example, as previously described with respect to Figure 6A and 6B As stated.

[0229] Processor 565 receives the accumulated samples, and Kalman filter 566 operates to process the accumulated samples to control at least the settings of LO leakage compensation in QEC / LO leakage compensation circuit 561. Although shown as controlling only QEC / LO leakage compensation circuit 561 (e.g., the DC offset added to each of the digital I and Q transmit signals), Kalman filter 566 may control other circuits.

[0230] For example, the Kalman filter 566 can control the PFIR 562 to add controllable filters (e.g., Figure 7 Equalization can be provided by controlling the I-path controllable filter 522a and the Q-path controllable filter 522b of the transmitter and / or the settings of the controllable filters themselves (e.g., the inductor and / or capacitor values ​​used for filtering). Additionally or alternatively, the Kalman filter 566 can control the frequency, amplitude, and / or phase settings used to calibrate the transmitter's LO leakage. For example, in some cases, a calibration cycle is run using a test tone that can be injected when the transmit signal is not present or added to the transmit signal when present. Thus, the Kalman filter 566 can provide dither or other perturbations to aid calibration.

[0231] Although one example of a digital transmitter circuit is described, other implementations are possible.

[0232] Figure 9 FIG2 is a schematic diagram of a transmitter 620 according to another embodiment. The transmitter 620 includes various components, including a pair of DACs 601, a pair of controllable filters 602, a pair of mixers 603, a VGA 604, a first local loopback path LB1, a second local loopback path LB2, and a sub-sampling ADC 614.

[0233] like Figure 9 As shown, the first loop-back path LB1 is located after the VGA 604 and includes a controllable attenuator 609, a first gain control and harmonic filtering circuit 611. In addition, the second loop-back path LB2 is located before the VGA 604 and includes an input switch 610 (with the ability to flip the polarity of the differential RF transmit signal) and a second gain control and harmonic filtering circuit 612.

[0234] Continue to refer Figure 9 , the first loopback path LB1 is coupled to the third gain control and harmonic filtering circuit 613 through the first pair of switches 616a, and the second loopback path LB2 is coupled to the third gain control and harmonic filtering circuit 613. The output of the third gain control and harmonic filter circuit 613 is provided to the sub-sampling ADC 614. The sub-sampling ADC 614 outputs samples of the RF transmit signal and / or the amplified RF transmit signal.

[0235] To help prevent attenuation effects from hindering the operation of LO leakage correction, the pair of mixers 603 can be implemented as harmonic rejection mixers, for example, mixers that reject third- and fifth-order harmonics. By implementing the mixers in this manner, the problems caused by the reduction of third- and fifth-order harmonic components are alleviated. This attenuation can occur because the subsampling ADC 614 has a sampling rate that is less than the carrier frequency of the RF transmit signal.

[0236] In some embodiments, the described gain control and RF filters of harmonic filtering circuits 611-613 are used to account for higher order harmonics, such as the seventh order harmonic.Thus, the combination of a harmonic correction mixer and an RF harmonic filter can be used to reduce problems caused by frequency reduction.

[0237] To further illustrate attenuation, a digital transmitter circuit can be implemented that processes transmit samples from a sub-sampled ADC to model and predict the effects of attenuation. For example, FSC (see Figure 6A and 6B ) can be included in digital transmitter circuits to help implement such functions. Thus, digital processing can serve as another layer of compensation for attenuation.

[0238] Figure 10A is a schematic diagram of a circuit 720 including a controllable oscillator 701 , a VGA 707 , and a harmonic rejection mixer 700 according to one embodiment. Figure 10B yes Figure 10A FIG. 7 is a diagram of circuit 720 operating in divide-by-2 mode. Figure 10C yes Figure 10A Diagram of circuit 720 when operating in divide-by-4 mode.

[0239] like Figure 10A As shown, a controllable oscillator 701 (eg, a fractional-N PLL) outputs a pair of clock signals CKP and CKN. Circuit 720 also includes a controllable frequency divider 702 that can divide the pair of clock signals CLKP and CKN by a controllable division ratio (eg, 1, 2, or 4).

[0240] Control circuit 720 also includes a divide-by-2 mode circuit 703 and a divide-by-4 circuit 704 for processing the output of controllable divider 702 to generate multiple LO clock signal phases that are mixed with the I and Q signals by mixer 705. In this example, six LO clock signal phases (I0, I1, I2, Q0, Q1, Q2) are used for harmonic suppression of third-order and fifth-order harmonics. The outputs of mixer 705 are combined by combiner 706 to generate the RF transmit signal provided to VGA 707.

[0241] By using multiple mixers 705 combined in this manner, third and fifth order harmonic suppression is provided.

[0242] When the controllable oscillator 701 operates at a relatively low frequency (eg, 3.5 GHz or lower), the divide-by-4 circuit 704 may be used to generate multiple clock signal phases, such as Figure 10B shown.

[0243] However, when the desired LO frequency is relatively high (e.g., greater than 3.5 GHz), it may not be feasible to operate the controllable oscillator 701 at four times the LO frequency and use the divide-by-4 circuit 704. Therefore, a divide-by-2 circuit 703 is included that provides division by 2 and uses interpolation to generate other LO clock signal phases to provide harmonic suppression of the third and fifth order harmonics. Example results of the divide-by-2 mode are shown in FIG. Figure 10C shown.

[0244] in conclusion

[0245] The transceivers here can handle signals of various frequencies, including not only RF signals between 100 MHz and 7 GHz, but also higher frequency signals such as X-band (approximately 7 GHz to 12 GHz), K-band, and RF-band. u frequency band (approximately 12GHz to 18GHz), K band (approximately 18GHz to 27GHz), K a Band (approximately 27 GHz to 40 GHz), V-Band (approximately 40 GHz to 75 GHz), and / or W-Band (approximately 75 GHz to 110 GHz). Thus, the teachings herein are applicable to various RF communication systems, including microwave systems.

[0246] The above description may refer to elements or features as being "connected" or "coupled" together. As used herein, unless expressly stated otherwise, "connected" means that one element / feature is directly or indirectly connected to another element / feature, and is not necessarily mechanically connected. Similarly, unless expressly stated otherwise, "coupled" means that one element / feature is directly or indirectly coupled to another element or feature, and is not necessarily mechanically coupled. Therefore, although the various schematic diagrams shown in the figures depict exemplary arrangements of elements and components, in actual embodiments, additional intervening elements, devices, features, or components may be present (assuming that the functionality of the depicted circuits is not adversely affected).

[0247] Although certain embodiments have been described, these embodiments are presented by way of example only and are not intended to limit the scope of the present disclosure. In fact, the novel devices, methods, and systems described herein can be embodied in a variety of other forms; in addition, various omissions, substitutions, and changes in the form of the methods and systems described herein can be made without departing from the spirit of the present disclosure. For example, although the disclosed embodiments are presented in a given arrangement, alternative embodiments may use different components and / or circuit topologies to perform similar functions, and some elements may be deleted, shifted, added, subdivided, combined, and / or modified. Each of these elements can be implemented in a variety of different ways. Any appropriate combination of the elements and actions of the various embodiments described above can be combined to provide further embodiments. Therefore, the scope of the present invention is limited only by reference to the appended claims.

[0248] It should be understood that any claim may rely on any prior claim of the same type, unless this is obviously technically infeasible.

Claims

1. A transceiver integrated circuit, comprising: a first transmitter comprising at least one mixer and a local oscillator (LO), wherein the first transmitter is configured to control the at least one mixer based on the LO to provide up-conversion to generate a first radio frequency transmit signal; and an observation receiver configured to receive an observation signal for observing at least the first transmitter via a loopback path from the first transmitter through the RF front end to the observation receiver, wherein the observation receiver includes an observation data path and an LO leakage observation circuit, the observation data path being configured to process the observation signal to detect the transmission power of the first RF transmission signal, and the LO leakage observation circuit being configured to generate leakage observation data based on processing data captured from the observation data path. The first transmitter is configured to process local transmission observation data from one or more local observation paths of the transceiver integrated circuit that do not pass through the RF front end to generate local leakage observation data, and process the local leakage observation data and the leakage observation data from the observation receiver to compensate for leakage of the LO. 2 . The transceiver integrated circuit of claim 1 , wherein the LO leakage observation circuit detects the transmit power without interrupting the observation data path. 3 . The transceiver integrated circuit of claim 1 , wherein the observation data path is further configured to process the observation signal to perform digital predistortion (DPD), wherein the LO leakage observation circuit does not interrupt the observation data path to perform DPD. 4 . The transceiver integrated circuit of claim 1 , wherein the first transmitter is configured to detect differential LO leakage from the local leakage observation data and to detect common-mode LO leakage from the leakage observation data from the observation receiver.

5. The transceiver integrated circuit of claim 1 , wherein the first transmitter further comprises a variable gain amplifier (VGA) configured to amplify the first RF transmit signal, wherein the one or more local observation paths comprise a first local observation path after the VGA and a second local observation path before the VGA.

6. The transceiver integrated circuit according to any one of claims 1 to 5, wherein the first transmitter comprises a digital filter configured to process the local leakage observation data and the leakage observation data from the observation receiver.

7. The transceiver integrated circuit of claim 6, wherein the digital filter is a Kalman filter.

8. The transceiver integrated circuit according to any one of claims 1-5 and 7, wherein the first transmitter is configured to collect the local leakage observation data and the leakage observation data from the observation receiver in multiple batches.

9. The transceiver integrated circuit of claim 8 , wherein the first transmitter is configured to update a value of an LO leakage compensation signal for compensating for leakage of the LO after receiving a given number of samples of the local leakage observation data and the leakage observation data from the observation receiver.

10. The transceiver integrated circuit according to any one of claims 1 to 5, wherein the LO leakage observation circuit comprises a digital mixer and a digital accumulator, the digital mixer being configured to generate frequency-shifted data based on mixing data captured from the observation data path with a digital oscillation signal, and the digital accumulator being configured to generate the leakage observation data based on accumulation of the frequency-shifted data. 11 . The transceiver integrated circuit of claim 10 , wherein the LO leakage observation circuit further comprises a digital oscillator configured to provide a digital clock signal to the digital mixer.

12. The transceiver integrated circuit according to any one of claims 1 to 5, further comprising: A plurality of transmitters including the first transmitter, wherein the observation signal is configured to observe one of the plurality of transmitters at a given time, and wherein the LO leakage observation circuit is configured to individually track leakage observation data for each of the plurality of transmitters.

13. The transceiver integrated circuit of claim 12, wherein the selected transmitter for observing the plurality of transmitters is changeable without interrupting operation of the LO leakage observation circuit.

14. The transceiver integrated circuit according to any one of claims 1 to 5, wherein the observation data path comprises an analog-to-digital converter and a digital circuit, the analog-to-digital converter being configured to generate a digital observation signal based on the observation signal, and the digital circuit being configured to process the digital observation signal.

15. A method for compensating for local oscillator (LO) leakage in a transceiver, the method comprising: generating a first radio frequency transmit signal using a first transmitter comprising at least one mixer and a local oscillator (LO) controlling the at least one mixer; generating an observation signal based on a loopback path from the first transmitter through the RF front end to an observation receiver; processing the observation signal to detect a transmit power of the first radio frequency transmit signal using an observation data path of the observation receiver; generating leakage observation data based on processing data captured from the observation data path; processing local transmission observation data from one or more local observation paths that do not pass through the RF front end to generate local leakage observation data; and The local leakage observation data and the leakage observation data from the observation receiver are processed to compensate for leakage of the LO. The method of claim 15 , wherein the leakage observation data is generated without interrupting the detection of the transmit power. 17 . The method of claim 15 , wherein processing the observation signal comprises performing digital predistortion (DPD) on the first RF transmit signal, wherein the leakage observation data is generated without interrupting DPD.

18. The method of any one of claims 15-17, further comprising using a digital filter to combine the local leakage observation data and the leakage observation data from the observation receiver.

19. A radio frequency communication system comprising: RF front end; and The transceiver includes: a first transmitter configured to provide a first radio frequency transmission signal to the radio frequency front end; and an observation receiver configured to receive an observation signal via a loopback path from the first transmitter through the RF front end to the observation receiver, The observation receiver includes an observation data path and a local oscillator (LO) leakage observation circuit, wherein the observation data path is used to process the observation signal to detect the transmission power of the first RF transmission signal, and the local oscillator (LO) leakage observation circuit is configured to generate leakage observation data based on processing data captured from the observation data path. The first transmitter processes local transmission observation data from one or more local observation paths that do not pass through the RF front end to generate local leakage observation data, and processes the local leakage observation data and the leakage observation data from the observation receiver to compensate for leakage of the LO of the first transmitter.

20. A transceiver comprising: a transmitter comprising at least one mixer and a local oscillator (LO), and configured to control the at least one mixer based on the LO to provide up-conversion to generate a radio frequency transmit signal, wherein the transmitter is configured to generate first observation data regarding leakage of the LO of the transmitter based on observing the radio frequency transmit signal on one or more local observation paths within the transmitter; an observation receiver configured to receive an observation signal from an external loopback path for observing at least the transmitter, and generate second observation data on leakage of the LO of the transmitter based on processing of the observation signal; and A local oscillator (LO) leakage compensation circuit is configured to compensate for leakage of a LO of the transmitter for the transmitter based on the first observation data and the second observation data, wherein the LO leakage compensation circuit includes a digital filter configured to process the first observation data and the second observation data.

21. The transceiver of claim 20, wherein the digital filter is a Kalman filter.

22. The transceiver of claim 21, wherein the Kalman filter is configured to estimate a correction value for leakage of the LO using a plurality of nonlinear equations.

23. The transceiver of claim 22, wherein the Kalman filter is further configured to modify the correction value based on a linear update of the Kalman filter using an observation matrix.

24. The transceiver of claim 23, wherein the observation matrix corresponds to a Jacobian matrix.

25. The transceiver of any one of claims 22-24, wherein a first portion of the plurality of nonlinear equations is a function of the first observation data, and wherein a second portion of the plurality of nonlinear equations is a function of the second observation data.

26. The transceiver of claim 20, wherein the transmitter comprises digital transmitter circuitry configured to process a digital in-phase signal and a digital quadrature-phase signal, wherein the digital filter is configured to compensate for leakage of an LO of the transmitter based at least in part on controlling the digital transmitter circuitry. 27 . The transceiver of claim 26 , wherein the digital filter is configured to control a first DC offset of the digital in-phase signal and a second DC offset of the digital quadrature-phase signal.

28. The transceiver of claim 26, wherein the digital transmitter circuit comprises a programmable finite impulse response (PFIR) filter, wherein the digital filter is configured to control the PFIR.

29. The transceiver of claim 26 , wherein the transmitter comprises an in-phase path digital-to-analog converter (DAC) coupled to the digital transmitter circuit and configured to generate an analog in-phase signal, a controllable in-phase path filter configured to generate a filtered in-phase signal based on filtering the analog in-phase signal, a quadrature-phase path DAC coupled to the digital transmitter circuit and configured to generate an analog quadrature-phase signal, and a controllable quadrature-phase path filter configured to generate a filtered quadrature-phase signal based on filtering the analog quadrature-phase signal.

30. The transceiver of claim 29, wherein the digital filter controls settings of the controllable in-phase path filter and the controllable quadrature-phase path filter.

31. The transceiver of claim 29, further comprising an in-phase path mixer and a quadrature-phase path mixer, the in-phase path mixer being configured to receive a filtered in-phase signal and being controlled by an LO, the quadrature-phase path mixer being configured to receive a filtered quadrature-phase signal and being controlled by the LO, wherein the RF transmit signal is generated based on combining an output of the in-phase path mixer and an output of the quadrature-phase path mixer.

32. The transceiver of any one of claims 20-31, wherein the first observation data indicates differential LO leakage of the LO, and the second observation data indicates common-mode LO leakage of the LO.

33. The transceiver according to any one of claims 20-31, wherein the transmitter comprises a variable gain amplifier (VGA) configured to amplify the RF transmit signal, wherein the one or more local observation paths comprise a first local observation path after the VGA and a second local observation path before the VGA.

34. A method for compensating for local oscillator (LO) leakage in a transceiver, the method comprising: Using a transmitter to control at least one mixer based on the local oscillator LO to provide up-conversion to generate a radio frequency transmission signal; generating first observation data regarding leakage of an LO of the transmitter based on observing the radio frequency transmit signal on one or more local observation paths within the transmitter; generating second observation data regarding leakage of the LO of the transmitter based on processing an observation signal from an external loopback path from the transmitter to an observation receiver through a front-end system; and The transmitter is compensated for leakage of an LO of the transmitter based on processing the first observation data and the second observation data using a digital filter.

35. The method of claim 34, wherein the digital filter is a Kalman filter.

36. The method of claim 35, further comprising estimating a correction value for leakage of the LO using a plurality of nonlinear equations, wherein a first portion of the plurality of nonlinear equations is a function of the first observation data, and wherein a second portion of the plurality of nonlinear equations is a function of the second observation data.

37. The method of any of claims 34-36, further comprising processing a digital in-phase signal and a digital quadrature-phase signal using digital transmitter circuitry of the transmitter, and compensating for leakage of an LO at the transmitter based at least in part on controlling the digital transmitter circuitry using the digital filter.

38. A radio frequency communication system comprising: RF front end; and Transceivers, including: a transmitter comprising at least one mixer and a local oscillator (LO), and configured to control the at least one mixer based on the LO to provide up-conversion to provide a radio frequency transmit signal to the radio frequency front-end, wherein the transmitter is configured to generate first observation data regarding leakage of the LO of the transmitter based on observing the radio frequency transmit signal on one or more local observation paths within the transmitter; an observation receiver configured to generate second observation data regarding leakage of the LO of the transmitter based on processing an observation signal received from an external loopback path from the transmitter to the observation receiver through the RF front end; and A local oscillator (LO) leakage compensation circuit is configured to compensate for leakage of a LO of the transmitter for the transmitter based on the first observation data and the second observation data, wherein the LO leakage compensation circuit includes a digital filter configured to process the first observation data and the second observation data.

39. The radio frequency communication system of claim 38, wherein the digital filter is a Kalman filter.

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