ALL DIGITAL TRANSMITTER NOISE CORRECTION

• US 20140269970A1
• Filed: 03/12/2013
• Published: 09/18/2014
• Est. Priority Date: 03/12/2013
• Status: Active Grant

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Analog Devices, Inc.
• Inventors: PRATT, Patrick, FORBES, Peadar Antony
• Granted Patent: US 9,048,900 B2
• Time in Patent Office: Days
• US Class Current: 375/285
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence
• CPC Class Codes: H04B 1/10 Means associated with receiver for limiting or suppressing noise or interference
• CPC Class Codes: H04B 1/123 using adaptive balancing or compensation means adaptive filter circuits and algorithms H03H
• CPC Class Codes: H04B 1/525 with means for reducing leakage of transmitter signal into the receiver
• CPC Class Codes: H04L 5/14 Two-way operation using the same type of signal, i.e. duplex
• CPC Class Codes: H04L 5/1423 for simultaneous baseband signals
• CPC Class Codes: H04L 5/1461 Suppression of signals in the return path, i.e. bidirectional control circuits

Abstract

An all digital model of nonlinear transmitter signal distortion in signals received at a receiver of a transmitter-receiver may be used to estimate distortion. The estimated distortion may then be cancelled from the received signals to improve signal quality of the received signal. The digital nonlinear model may be part of an estimator circuit that estimates nonlinear distortion terms by applying a formula or transformation to a digitized version of the signals transmitter at a transmitter of the transmitter-receiver. A mixer may be used to shift a frequency of the estimated nonlinear terms away from a transmitter frequency so that the nonlinear terms can later be subtracted from the incoming signal received at the receiver at a receiver frequency. Circuits and methods are provided.

Claims

1. A circuit comprising:

an estimator circuit modeling nonlinear signal distortion from a transmitter at a receiver based on an analysis of an outgoing digital signal converted to an analog signal and transmitted at the transmitter;

a mixer mixing an output of the estimator circuit with a frequency offset signal and shifting the estimator circuit output to an intermediate frequency offset representing a difference between frequencies of the transmitter and the receiver; and

a subtractor coupled to the mixer and subtracting the frequency shifted estimator circuit output from a digitized incoming signal received at the receiver.

2. The circuit of claim 1, further comprising:

an interpolator coupled to the estimator and interpolating a portion of the outgoing digital signal falling into a band of the incoming signal;

a delay unit coupled to the mixer and delaying the estimator circuit output until the estimator circuit output is synchronized with a corresponding portion of the incoming signal at the subtractor; and

a decimator coupled between the mixer and the subtractor and downsampling the mixed estimator circuit output to a frequency of the incoming signal before the subtractor subtracts the downsampled estimator output from the incoming signal.

3. The circuit of claim 1, wherein the estimator circuit models a transmitter baseband nonlinearity before modeling nonlinearity between the transmitter and the receiver of the full duplex radio, the output of the transmitter baseband nonlinearity model used as an input for the modeling of nonlinearity between the transmitter and the receiver.

4. The circuit of claim 3, wherein the estimator circuit:

(i) models transmitter baseband nonlinearity at least in part as;

5. The circuit of claim 1, further comprising an adaptive engine coupled to the estimator circuit and the subtractor, the adaptive engine configured to:

compare an output of the subtractor after subtracting the mixed estimator circuit output from the digitized incoming signal to the digitized incoming signal and the outgoing digital signal;

identify an error in the modeled nonlinearity at the estimator circuit based on the comparing; and

modify at least one nonlinearity model coefficient in the estimator circuit to reduce the identified error.

6. The circuit of claim 5, wherein the adaptive engine is further configured to iteratively compare the output of the subtractor to the digitized incoming signal and the outgoing digital signal and modify at least one nonlinearity model coefficient in the estimator circuit until the identified error is minimized.

7. The circuit of claim 3, further comprising an adaptive engine coupled to the estimator circuit and the subtractor, the adaptive engine configured to:

compare an output of the subtractor after subtracting the mixed estimator circuit output from the digitized incoming signal to the digitized incoming signal and the outgoing digital signal;

identify an error in each of the modeled nonlinearities at the estimator circuit based on the comparing; and

modify at least one nonlinearity model coefficient of each model in the estimator circuit to reduce the identified error.

8. The circuit of claim 1, further comprising:

the transmitter;

the receiver;

a power amplifier coupled to the transmitter;

a first analog to digital converter (ADC) coupled to the power amplifier and converting the outgoing digital signal to the analog signal;

a second ADC coupled between the receiver and the subtractor, the second ADC digitizing the incoming signal received at the receiver;

a mixer coupled between the receiver and the second ADC, the mixer mixing the incoming signal with an oscillating signal;

a radio frequency amplifier coupled between the receiver and the mixer; and

a low pass filter coupled between the mixer and the second ADC.

9. The circuit of claim 1, further comprising:

a channelization circuit splitting the outgoing digital signal and the digitized incoming signal on a channel by channel basis and separately outputting each channel; and

a plurality of estimator circuits, mixers, and subtractors, with an estimator circuit, a mixer, and a subtractor for each channel, wherein;

each estimator circuit models nonlinear signal distortion between the transmitter and the receiver for each respective channel,

each mixer mixes an output of the estimator circuit for the respective channel with a frequency offset signal for the respective channel, and

each subtractor is coupled to a mixer for the respective channel and subtracts the mixed estimator circuit output for the respective channel from the channelized digitized incoming signal for the respective channel outputted by the channelization circuit.

10. The circuit of claim 8, further comprising:

a digital downconverter coupled to the second ADC and downconverting and channelizing at separate outputs the digitized incoming signal; and

a plurality of mixers and subtractors, with a mixer and a subtractor for each channel, wherein;

the estimator circuit models nonlinearity between the transmitter and the receiver for each respective channel and outputs the modeled nonlinearity to a respective mixer for the respective channel,

each mixer mixes an output of the estimator circuit for the respective channel with a frequency offset signal for the respective channel, and

each subtractor is coupled to a mixer for the respective channel and subtracts the mixed estimator circuit output for the respective channel from the channelized digitized incoming signal for the respective channel outputted by the digital downconverter.

11. The circuit of claim 10, further comprising an adaptive engine coupled to the estimator circuit and the subtractor for each channel, the adaptive engine configured to:

compare an output of the subtractor of at least one channel after subtracting the mixed estimator circuit output for the at least one channel to the channelized incoming signal and the outgoing signal for the at least one channel;

identify an error in the modeled nonlinearity at the estimator circuit for the at least channel based on the comparing; and

modify at least one nonlinearity model coefficient in the estimator circuit for the at least one channel to reduce the identified error.

12. A multi transmitter-receiver noise cancellation circuit comprising a number n≧

2 of circuits of claim 10, wherein each of the n circuits of claim 10 includes;

n estimator circuits, mixers, and subtractors for each active channel;

each of the n estimator circuits for each active channel is coupled to the respective channel output of the signal splitter for the respective circuit; and

the subtractor for each active channel is coupled to the respective channel output of the digital downconverter for the respective circuit.

13. A noise cancellation circuit comprising:

a plurality of receivers, each coupled to a respective analog-digital converter (ADC);

a plurality of transmitters, each coupled to a respective ADC; and

a plurality of digital noise correcting circuits, each noise correcting circuit including an estimator circuit coupled to a mixer coupled to a subtractor, with at least one noise correcting circuit coupled between each of the transmitters and the receiver ADCs, wherein

each estimator circuit models nonlinear signal distortion between a respective transmitter and a respective receiver based on a digitized version of an outgoing signal transmitted at the respective transmitter,

each mixer mixes an output of the respective estimator circuit with a respective frequency offset signal, and

each subtractor subtracts the mixed estimator circuit output from the respective estimator circuit from an incoming signal digitized at the respective receiver ADC.

14. A method comprising:

digitizing incoming radio frequency (RF) signals received at a receiver and outgoing signals for transmission at a RF transmitter;

channelizing the digitized incoming and outgoing signals;

modeling nonlinear signal distortion between the transmitter and the receiver on at least one channel based on an analysis of at least one of the channelized outgoing signals;

mixing the modeled distortion on at least one channel with an offset signal offsetting the modeled distortion based on a difference in angular frequencies of the at least one channel of the transmitter and the receiver; and

subtracting the offsetted modeled distortion from the at least one channel of the channelized incoming RF signal.

15. The method of claim 14, further comprising:

interpolating the digitized outgoing signals before modeling nonlinear distortion; and

decimating the offsetted modeled nonlinear distortion before the subtracting.

16. The method of claim 15, further comprising delaying offsetted modeled nonlinear distortion until the offsetted modeled nonlinear distortion is time aligned with a corresponding section of the channelized incoming RF signal before decimating the offsetted modeled nonlinear distortion.

17. The method of claim 14, further comprising:

modeling a nonlinear transmitter baseband signal distortion based on an analysis of at least one of the channelized outgoing signals before modeling nonlinear distortion between the transmitter and the receiver; and

modeling the nonlinear distortion between the transmitter and the receiver using a result of the modeled nonlinear transmitter baseband signal distortion.

18. The method of claim 14, further comprising:

interpolating the digitized outgoing signal before modeling nonlinear distortion;

modeling a nonlinear transmitter baseband signal distortion based on an analysis of at least one of the channelized outgoing signals before modeling nonlinear distortion between the transmitter and the receiver;

modeling the nonlinear distortion between the transmitter and the receiver using a result of the modeled nonlinear transmitter baseband signal distortion;

delaying the modeled nonlinear distortion between the transmitter and the receiver until the modeled nonlinear distortion between the transmitter and the receiver is time aligned with a corresponding section of the channelized incoming RF signal; and

decimating the delayed modeled nonlinear distortion between the transmitter and the receiver after an end of the delaying.

19. The method of claim 14, further comprising:

digitizing a plurality of incoming radio frequency (RF) signals received at a plurality of receivers and a plurality of outgoing signals for transmission at a plurality of RF transmitters;

channelizing each of the digitized incoming and outgoing signals;

modeling nonlinear distortion between each of the transmitters and at least one of the receivers on at least one channel based on an analysis of at least one of the channelized outgoing signals at each of the transmitters;

mixing the modeled nonlinear distortion between each of the transmitters and the at least one receiver on at least one channel with an offset signal offsetting the modeled nonlinear distortion based on a difference in angular frequencies of the at least one channel of each respective transmitter and the at least one receiver; and

subtracting the offsetted modeled nonlinear distortion between each of the transmitters and the at least one receiver from the respective channelized incoming RF signal received at the at least one receiver.

20. The method of claim 14, further comprising:

comparing an output of the subtracting to the channelized incoming signal and the channelized outgoing signal for the at least one channel;

identifying a modeling error for the at least channel based on the comparing; and

modifying at least one nonlinearity model coefficient in the modeling for the at least one channel to reduce the identified error.