RF Transmitter and Auxiliary Receiver to Capture Transmit Signal Data to Compensate for Transmit Signal Impairments

Patent metadata

Field	Value
Publication number	US-2020177288-A1
Application number	US-201916697236-A
Country	US
Kind code	A1
Filing date	Nov 27, 2019
Priority date	Nov 30, 2018
Publication date	Jun 4, 2020
Grant date	—

Abstract

A transmitter for an RF communications system, that includes an auxiliary receiver for capturing transmit signal data for use in compensating/correcting transmit signal impairments (such as for DPD, QMC, LOL). The transmitter (such as Zero IF) includes analog chain elements that introduce transmit signal impairments (such as PA nonlinearities). The auxiliary receiver is configured to receive loopback transmit RF signals, and includes an RF direct sampling ADC to convert the loopback transmit RF signals to digital transmit RF signals. Digital down conversion circuitry is configured to downconvert the digital transmit RF signals to captured digital transmit baseband signals, and data capture circuitry is configured to generate the transmit signal data based on the captured digital transmit baseband signals.

First claim

1 . A circuit for use in an RF (radio frequency) communications system, the circuit comprising:
a transmitter including digital and analog signal chains, to output from the analog signal chain transmit RF signals based on digital baseband signals input from the digital signal chain, the transmitter including:
analog signal chain elements that introduce transmit signal impairments, and
impairment compensation circuitry in the digital signal chain to compensate or correct for the transmit signal impairments, based on transmit signal data derived from the transmit RF signals; and
an auxiliary receiver to receive loopback transmit RF signals, the auxiliary receiver including:
an RF direct sampling ADC to convert the loopback transmit RF signals to digital transmit RF signals,
digital down conversion circuitry to downconvert the digital transmit RF signals to captured digital transmit baseband signals, and
data capture circuitry to generate the transmit signal data based on the captured digital transmit baseband signals.

2 . The circuit of claim 1 , wherein the transmit signal impairments include at least one of: power amplifier nonlinearity, I and Q signal mismatch, and local oscillator leakage.

3 . The circuit of claim 1 , wherein the analog signal chain elements introducing transmit signal impairments include a power amplifier, and wherein:
the impairment compensation circuitry including digital pre-distortion circuitry; and the auxiliary receiver to generate transmit signal data for use in estimating power amplifier nonlinearity signal impairment, and adapting the digital pre-distortion circuitry based on the estimated power amplifier nonlinearity.

4 . The circuit of claim 1 , wherein the digital downconversion circuitry includes a numerical controlled oscillator.

5 . The circuit of claim 1 , wherein:
the transmitter analog signal chain includes I and Q upconversion mixers with a fractional local oscillator; and the digital down conversion circuitry includes a fractional digital mixer.

6 . The circuit of claim 1 , wherein:
the transmitter is configured to transmit first band and second band transmit RF signals; and the auxiliary receiver is configured to receive corresponding loopback first band and loopback second band transmit RF signals, and is configured with:
digital down conversion circuitry configured with first and second digital mixers that are time-multiplexed between the first band and the second band digital transmit RF signals.

7 . The circuit of claim 1 , wherein the circuit further comprises a receiver integrated with the transmitter and the auxiliary receiver, as a transceiver.

8 . A transceiver circuit for use in an RF (radio frequency) communications system, the circuit comprising:
a transmitter including digital and analog signal chains, to output from the analog signal chain transmit RF signals based on digital baseband signals input from the digital signal chain, the transmitter including:
analog signal chain elements that introduce transmit signal impairments, and
impairment compensation circuitry in the digital signal chain to compensate or correct for the transmit signal impairments, based on transmit signal data derived from the transmit RF signals;
an auxiliary receiver to receive loopback transmit RF signals, the auxiliary receiver including:
an RF direct sampling ADC to convert the loopback transmit RF signals to digital transmit RF signals,
digital down conversion circuitry to downconvert the digital transmit RF signals to captured digital transmit baseband signals, and
data capture circuitry to generate the transmit signal data based on the captured digital transmit baseband signals; and
a receiver including analog and digital signal chains, to receive through the analog signal chain received RF signals, and to convert the received RF signals to digital baseband signals.

9 . The circuit of claim 8 , wherein the transmit signal impairments include at least one of: power amplifier nonlinearity, I and Q signal mismatch, and local oscillator leakage.

10 . The circuit of claim 8 , wherein the analog signal chain elements introducing transmit signal impairments include a power amplifier, and wherein:
the impairment compensation circuitry including digital pre-distortion circuitry; and the auxiliary receiver to generate transmit signal data for use in estimating power amplifier nonlinearity signal impairment, and adapting the digital pre-distortion circuitry based on the estimated power amplifier nonlinearity.

11 . The circuit of claim 8 , wherein the digital downconversion circuitry includes a numerical controlled oscillator.

12 . The circuit of claim 8 , wherein:
the transmitter analog signal chain includes I and Q upconversion mixers with a fractional local oscillator; and the digital down conversion circuitry includes a fractional digital mixer.

13 . The circuit of claim 8 , wherein:
the transmitter is configured as a dual band transmitter to transmit first band and second band transmit RF signals; and the auxiliary receiver is configured to receive corresponding loopback first band and loopback second band transmit RF signals, and is configured with:
digital down conversion circuitry configured with first and second digital mixers that are time-multiplexed between the first band and the second band digital transmit RF signals.

14 . A method for use in an RF (radio frequency) communications system, comprising:
generating transmit RF signals based on digital baseband signals, in a transmitter with digital and analog signal chains, the analog signal chain introducing transmit signal impairments; in the digital signal chain, compensating or correcting for the transmit signal impairments based on transmit signal data derived from the transmit RF signals; receiving loopback transmit RF signals in an auxiliary receiver, and: converting the loopback transmit RF signals to digital transmit RF signals in an RF direct sampling ADC, downconverting the digital transmit RF signals (digital down conversion) to captured digital transmit baseband signals, and generating the transmit signal data based on the captured digital transmit baseband signals.

15 . The method of claim 14 , wherein the transmit signal impairments include at least one of: power amplifier nonlinearity, I and Q signal mismatch, and local oscillator leakage.

16 . The method of claim 14 , wherein the transmit signal impairments include power amplifier nonlinearity, and further comprising:
digitally pre-distorting the digital baseband signals; and generating transmit signal data for use in estimating power amplifier nonlinearity signal impairment, and adapting digitally pre-distorting the digital baseband signals based on the estimated power amplifier nonlinearity.

17 . The method of claim 14 , wherein digital downconversion uses a numerical controlled oscillator.

18 . The method of claim 14 , further comprising:
converting the digital baseband signals to analog baseband signals, and using I and Q upconversion mixers with a fractional local oscillator; and digital downconversion is accomplished with a fractional digital mixer.

19 . The method of claim 14 , further comprising:
transmitting first band and second band transmit RF signals; and receiving loopback first band and second band transmit RF signals; and performing digital down conversion using first and second digital mixers that are time-multiplexed between the first band and the second band digital transmit RF s

Assignees

• Texas Instruments Inc

Inventors

• Oswal Sandeep
• Pentakota Visvesvaraya
• Venkataraman Jagannathan
• Balakrishnan Jaiganesh
• Dantoni Francesco

Classifications

• H04B1/04

  Circuits · CPC title

• H04B17/13 Primary

  of power amplifiers, e.g. gain or non-linearity · CPC title

• H04L27/364

  Arrangements for overcoming imperfections in the modulator, e.g. quadrature error or unbalanced I and Q levels · CPC title

• H04B2001/0408

  with power amplifiers · CPC title

• H03F3/24

  of transmitter output stages · CPC title