Mechanisms for the correction of I/Q impairments
View Patent ↗Various embodiments of communication devices and associated methods for reducing I/Q impairments in signals used by the communication devices are described. A transmitter device 206 may perform filtering (or matrix multiplication) on digital I and Q signals to pre-correct them before converting them into analog I and Q signals. The pre-correction may pre-compensate for I/Q impairments which have not been introduced yet, but which will subsequently be introduced during digital to analog conversion, I/Q modulation, or other processing that occurs to produce a transmission signal from the original digital I and Q signals. A receiver device may receive a transmission signal, produce digital I and Q signals from it, and perform filtering on the digital I and Q signals to correct I/Q impairments at a plurality of frequency offsets.
1. A method for compensating for I/Q impairments of a receiver, the method comprising:
receiving an analog input signal;
performing I/Q demodulation on the analog input signal to produce an analog inphase (I) signal and an analog quadrature (Q) signal;
digitizing the analog I signal and the analog Q signal to produce respectively a digital I signal and a digital Q signal;
filtering the digital I signal and the digital Q signal in accordance with a 2×2 matrix of digital filters to produce a filtered digital I signal and a filtered digital Q signal, wherein the 2×2 matrix of digital filters at least partially compensates for I/Q impairments of the receiver over a range of frequencies, wherein a frequency response of at least one diagonal component of the 2×2 matrix is computed based on measurements of the I/Q impairments as a function of frequency and the measurements of the I/Q impairments as a function of a negative of frequency, wherein a frequency response of at least one non-diagonal component of the 2×2 matrix is computed based on the measurements of the I/Q impairments as a function of frequency and measurements of the I/Q impairments as a function of the negative of frequency.
2. The method of claim 1 , wherein the filtered digital I signal and the filtered digital Q signal are usable to recover a stream of information bits.
3. The method of claim 2 , further comprising recovering the stream of information bits by performing symbol demodulation on the filtered digital I signal and the filtered digital Q signal.
4. The method of claim 1 , wherein the receiver includes a digitizer, wherein the digitizer performs said digitizing and said filtering, wherein a relationship between amplitude of the analog I signal and amplitude of the filtered digital I signal is calibrated to a known standard, wherein a relationship between amplitude of the analog Q signal and amplitude of the filtered digital Q signal is calibrated to the known standard.
5. The method of claim 1 , wherein the receiver is a test instrument, wherein the analog input signal is generated in response to a transmission of a transmit signal onto the communication medium by a transmitter, wherein the measurements of the I/Q impairments of the receiver do not include I/Q impairments of the transmitter.
6. The method of claim 1 , wherein said filtering is performed in a programmable hardware element or an application specific integrated circuit (ASIC).
7. The method of claim 1 , wherein said filtering is performed by a processor in response to execution of program instructions.
8. The method of claim 1 , wherein one of the diagonal components of the 2×2 matrix is a discrete-time unit impulse function.
9. The method of claim 1 , wherein a second one of the non-diagonal components of the 2×2 matrix is identically equal to zero.
10. A method for compensating for I/Q impairments of a receiver, the method comprising:
receiving an analog input signal;
performing I/Q demodulation on the analog input signal to produce an analog inphase (I) signal and an analog quadrature (Q) signal;
digitizing the analog I signal and the analog Q signal to produce respectively a digital I signal and a digital Q signal;
filtering the digital I signal and the digital Q signal in accordance with a 2×2 matrix of digital filters to produce a filtered digital I signal and a filtered digital Q signal, wherein the 2×2 matrix of digital filters at least partially compensates for I/Q impairments of the receiver over a range of frequencies, wherein a frequency response of one diagonal component of the 2×2 matrix at an arbitrary frequency f in the frequency range is computed based only on a measurement of the I/Q impairments at the frequency for only on a measurement of the I/Q impairments at the frequency −f, wherein a frequency response of one non-diagonal component of the 2×2 matrix at the frequency f is computed based only on the measurement of the I/Q impairments at the frequency f or only the measurement of the I/Q impairments at the frequency −f.
11. The method of claim 10 , wherein the I/Q impairments at the frequency f and the I/Q impairments at frequency −f are constrained such that the I/Q impairments at f are determined by the I/Q impairments at −f, or such that the I/Q impairments at frequency −f are determined by the I/Q impairments at f.
12. The method of claim 11 , wherein the I/Q impairments include a gain imbalance and a phase skew, wherein the gain imbalance at the frequency f and the gain imbalance at frequency −f are constrained to be equal, wherein the phase skew at the frequency f and the phase skew at the frequency −f are constrained to be negatives of each other.
13. The method of claim 11 , wherein the I/Q impairments include a gain imbalance and a phase skew, wherein the gain imbalance at the frequency f and the gain imbalance at frequency −f are constrained to be equal, wherein the phase skew at the frequency f and the phase skew at the frequency −f are constrained to be equal.
14. A receiver comprising:
an I/Q demodulator configured to receive an analog input signal, and perform I/Q demodulation on the analog input signal to produce an analog inphase (I) signal and an analog quadrature (Q) signal;
a digitization unit configured to digitize the analog I signal and the analog Q signal to produce respectively a digital I signal and a digital Q signal;
a digital circuit configured to filter the digital I signal and the digital Q signal in accordance with a 2×2 matrix of digital filters to produce a filtered digital I signal and a filtered digital Q signal, wherein the 2×2 matrix of digital filters is configured to at least partially compensate for I/Q impairments of the receiver over a range of frequencies, wherein a frequency response of at least one diagonal component of the 2×2 matrix is computed based on measurements of the I/Q impairments as a function of frequency and the measurements of the I/Q impairments as a function of a negative of frequency, wherein a frequency response of at least one non-diagonal component of the 2×2 matrix is computed based on the measurements of the I/Q impairments as a function of frequency and the measurements of the I/Q impairments as a function of the negative of frequency.
15. The receiver of claim 14 , wherein the filtered digital I signal and the filtered digital Q signal are usable to recover a stream of information bits.
16. The receiver of claim 15 , further comprising:
means for recovering the stream of information bits by performing symbol demodulation on the filtered digital I signal and the filtered digital Q signal.
17. The receiver of claim 14 , wherein the receiver is a test instrument, wherein the analog input signal is generated in response to a transmission of a transmit signal by a transmitter, wherein the measurements of the I/Q impairments of the receiver do not include I/Q impairments of the transmitter.
18. The receiver of claim 14 , wherein the digital circuit is a programmable hardware element or an application specific integrated circuit (ASIC).
19. The receiver of claim 14 , wherein digital circuit is a processor that is configured to perform said filtering in response to execution of program instructions.
20. A computer-implemented method for configuring a receiver to at least partially compensate for I/Q impairments of the receiver, the method comprising:
receiving measurements of the I/Q impairments of the receiver over a frequency band, wherein the receiver includes an I/Q demodulator, a pair of analog-to-digital converters (ADCs) and a digital circuit, wherein the I/Q demodulator is configured to generate an analog I signal and an analog Q signal from an analog input signal, wherein the ADCs are configured to sample the analog I and Q signals to respectively obtain digital I and Q signals, wherein the digital circuit is configured to filter the digital I and Q signals to respectively obtain filtered digital I and Q signals;
computing a 2×2 matrix of digital filters based on the measurements, wherein the 2×2 matrix of digital filters is computed to achieve at least partial compensation for the I/Q impairments of the receiver over the frequency band, wherein a frequency response of at least one diagonal component of the 2×2 matrix is computed based on the measurements as a function of frequency and the measurements as a function of a negative of frequency, wherein a frequency response of at least one non-diagonal component of the 2×2 matrix is computed based on the measurements as a function of frequency and the measurements as a function of the negative of frequency;
programming the digital circuit to implement the 2×2 matrix of digital filters, wherein the digital circuit, when so programmed, is configured to at least partially compensate for the I/Q impairments of the receiver over the frequency band.
21. The method of claim 20 , wherein the digital circuit is a programmable hardware element or an application specific integrated circuit (ASIC).
22. A computer system for configuring a receiver to at least partially compensate for I/Q impairments of the receiver, the computer system comprising:
a processor; and
memory that stores program instructions, wherein the program instructions, when executed by the processor, cause the processor to:
receive measurements of the I/Q impairments of the receiver over a frequency band, wherein the receiver includes an I/Q demodulator, a pair of analog-to-digital converters (ADCs) and a digital circuit, wherein the I/Q demodulator is configured to generate an analog I signal and an analog Q signal from an analog input signal, wherein the ADCs are configured to sample the analog I and Q signals to respectively obtain digital I and Q signals, wherein the digital circuit is configured to filter the digital I and Q signals to respectively obtain filtered digital I and Q signals;
compute a 2×2 matrix of digital filters based on the measurements, wherein the 2×2 matrix of digital filters is computed to achieve at least partial compensation for the I/Q impairments of the receiver over the frequency band, wherein a frequency response of at least one diagonal component of the 2×2 matrix is computed based on the measurements as a function of frequency and the measurements as a function of a negative of frequency, wherein a frequency response of at least one non-diagonal component of the 2×2 matrix is computed based on the measurements as a function of frequency and the measurements as a function of the negative of frequency; and
program the digital circuit to implement the 2×2 matrix of digital filters, wherein the digital circuit, when so programmed, is configured to at least partially compensate for the I/Q impairments of the receiver over the frequency band.
23. The computer system of claim 22 , wherein the digital circuit is a programmable hardware element or an application specific integrated circuit (ASIC).
24. A method for compensating for I/Q impairments of a transmitter, the method comprising:
receiving a digital inphase (I) signal and a digital quadrature (Q) signal;
filtering the digital I signal and the digital Q signal in accordance with a 2×2 matrix of digital filters to produce a filtered digital I signal and a filtered digital Q signal, wherein the 2×2 matrix of digital filters at least partially pre-compensates for the I/Q impairments of the transmitter over a range of frequencies, wherein a frequency response of at least one diagonal component of the 2×2 matrix is computed based on measurements of the I/Q impairments of the transmitter as a function of frequency and the measurements as a function of a negative of frequency, wherein a frequency response of at least one non-diagonal component of the 2×2 matrix is computed based on the measurements as a function of frequency and the measurements as a function of the negative of frequency;
converting the filtered digital I and Q signals to analog form in order to obtain respective analog I and Q signals;
performing I/Q modulation on the analog I and Q signals to produce a modulated analog signal.
25. The method of claim 24 , wherein the transmitter is a test instrument, wherein the modulated analog signal is transmitted to a receiver through a channel, wherein the measurements of the I/Q impairments of the transmitter do not include I/Q impairments of the receiver.
26. The method of claim 24 , wherein said filtering is performed in a programmable hardware element (PHE) or an application specific integrated circuit (ASIC).
27. The method of claim 24 , wherein said filtering is performed in a processor in response to execution of program instructions.
28. The method of claim 24 , wherein the digital I signal and the digital Q signal carry one or more streams of information bits.
29. A method for compensating for I/Q impairments of a transmitter, the method comprising:
receiving a digital inphase (I) signal and a digital quadrature (Q) signal;
filtering the digital I signal and the digital Q signal in accordance with a 2×2 matrix of digital filters to produce a filtered digital I signal and a filtered digital Q signal, wherein the 2×2 matrix of digital filters at least partially pre-compensates for the I/Q impairments of the transmitter over a range of frequencies, wherein a frequency response of at least one diagonal component of the 2×2 matrix at an arbitrary frequency f in the frequency range is computed based only on a measurement of the I/Q impairments at the frequency for only on a measurement of the I/Q impairments at the frequency −f, wherein a frequency response of at least one non-diagonal component of the 2×2 matrix at the frequency f is computed based only on the measurement of the I/Q impairments at the frequency for only on the measurement of the I/Q impairments at the frequency −f;
converting the filtered digital I and Q signals to analog form in order to obtain respective analog I and Q signals;
performing I/Q modulation on the analog I and Q signals to produce a modulated analog signal.
30. The method of claim 29 , wherein the I/Q impairments at the frequency f and the I/Q impairments at frequency −f are constrained such that the I/Q impairments at f are determined by the I/Q impairments at −f, or such that the I/Q impairments at frequency −f are determined by the I/Q impairments at f.
31. The method of claim 30 , wherein the I/Q impairments include a gain imbalance and a phase skew, wherein the gain imbalance at the frequency f and the gain imbalance at frequency −f are constrained to be equal, wherein the phase skew at the frequency f and the phase skew at the frequency −f are constrained to be negatives of each other.
32. The method of claim 30 , wherein the I/Q impairments include a gain imbalance and a phase skew, wherein the gain imbalance at the frequency f and the gain imbalance at frequency −f are constrained to be equal, wherein the phase skew at the frequency f and the phase skew at the frequency −f are constrained to be equal.
33. A transmitter comprising:
a digital circuit configured to receive a digital inphase (I) signal and a digital quadrature (Q) signal, and filter the digital I signal and the digital Q signal in accordance with a 2×2 matrix of digital filters to produce a filtered digital I signal and a filtered digital Q signal, wherein the 2×2 matrix of digital filters at least partially pre-compensates for I/Q impairments of the transmitter over a range of frequencies, wherein a frequency response of at least one diagonal component of the 2×2 matrix is computed based on measurements of the I/Q impairments of the transmitter as a function of frequency and the measurements as a function of a negative of frequency, wherein a frequency response of at least one non-diagonal component of the 2×2 matrix is computed based on the measurements as a function of frequency and the measurements as a function of the negative of frequency;
a digital-to-analog conversion (DAC) unit configured to convert the filtered digital I and Q signals to analog form in order to obtain respective analog I and Q signals;
an I/Q modulator configured to perform I/Q modulation on the analog I and Q signals to produce a modulated analog signal.
34. The transmitter of claim 33 , wherein the transmitter is a test instrument, wherein the modulated analog signal is transmitted to a receiver through a channel, wherein the measurements of the I/Q impairments of the transmitter do not include I/Q impairments of the receiver.
35. The transmitter of claim 33 , wherein the digital circuit is a programmable hardware element (PHE) or an application specific integrated circuit (ASIC).
36. The transmitter of claim 33 , wherein the digital circuit includes a processor configured to perform said filtering in response to execution of program instructions.
37. The transmitter of claim 33 , wherein the digital I signal and the digital Q signal carry one or more streams of information bits.
38. A method for configuring a transmitter to at least partially compensate for I/Q impairments of the transmitter, the method comprising:
receiving measurements of the I/Q impairments of the transmitter over a frequency range, wherein the transmitter includes a digital circuit, a pair of digital-to-analog converters (DACs) and an I/Q modulator, wherein the digital circuit is configured to filter a digital I signal and a digital Q signal to respectively obtain a filtered digital I signal and a filtered digital Q signal, wherein the pair of DACs is configured to convert the filtered digital I and Q signals to analog form in order to respectively obtain analog I and Q signals, wherein the I/Q modulator is configured to modulate a carrier signal with the analog I and Q signals to obtain a modulated carrier signal;
computing a 2×2 matrix of digital filters for the digital circuit based on the measurements, wherein the 2×2 matrix of digital filters is computed to achieve at least partial pre-compensation for the I/Q impairments of the transmitter, wherein a frequency response of at least one diagonal component of the 2×2 matrix is computed based on the measurements as a function of frequency and the measurements as a function of a negative of frequency, wherein a frequency response of at least one non-diagonal component of the 2×2 matrix is computed based on the measurements as a function of frequency and the measurements as a function of the negative of frequency;
programming the digital circuit to implement the 2×2 matrix of digital filters, wherein the digital circuit, when so programmed, is configured to at least partially pre-compensate for the I/Q impairments of the transmitter.
39. A computer system for configuring a transmitter to at least partially compensate for I/Q impairments of the transmitter, the computer system comprising:
a processor; and
memory that stores program instructions, wherein the program instructions, when executed by the processor, cause the processor to:
receive measurements of the I/Q impairments of the transmitter over a frequency range, wherein the transmitter includes a digital circuit, a pair of digital-to-analog converters (DACs) and an I/Q modulator, wherein the digital circuit is configured to filter a digital I signal and a digital Q signal to respectively obtain a filtered digital I signal and a filtered digital Q signal, wherein the pair of DACs is configured to convert the filtered digital I and Q signals to analog form in order to respectively obtain analog I and Q signals, wherein the I/Q modulator is configured to modulate a carrier signal with the analog I and Q signals to obtain a modulated carrier signal;
compute a 2×2 matrix of digital filters for the digital circuit based on the measurements, wherein the 2×2 matrix of digital filters is computed to achieve at least partial pre-compensation for the I/Q impairments of the transmitter, wherein a frequency response of at least one diagonal component of the 2×2 matrix is computed based on the measurements as a function of frequency and the measurements as a function of the negative of frequency, wherein a frequency response of at least one non-diagonal component of the 2×2 matrix is computed based on the measurements as a function of frequency and the measurements as a function of the negative of frequency;
program the digital circuit to implement the 2×2 matrix of digital filters, wherein the digital circuit, when so programmed, is configured to at least partially pre-compensate for the I/Q impairments of the transmitter.
40. The computer system of claim 39 , wherein the digital circuit is a programmable hardware element or an application specific integrated circuit (ASIC).
41. A method for operating a transmitter, the method comprising:
receiving a digital inphase (I) signal and a digital quadrature (Q) signal;
transforming the digital I signal and the digital Q signal in accordance with a 2×2 matrix of constants to produce a resultant digital I signal and a resultant digital Q signal;
converting the resultant digital I and Q signals to analog form in order to obtain respective analog I and Q signals;
performing I/Q modulation on the analog I and Q signals to produce a modulated analog signal;
wherein the 2×2 matrix is configured to at least partially pre-compensate for I/Q impairments of the transmitter at frequency f, wherein a first of the constants, corresponding a first diagonal element of the 2×2 matrix, is computed based on a measurement of the I/Q impairments of the transmitter at frequency f and a measurement of the I/Q impairments of the transmitter at frequency −f, wherein a second of the constants, corresponding to a first non-diagonal element of the 2×2 matrix, is computed based on the measurement at frequency f and the measurement at frequency −f.
42. The method of claim 41 , wherein the digital inphase (I) signal and the digital quadrature (Q) signal represent a complex exponential tone at frequency f.
43. The method of claim 41 , wherein the digital inphase (I) signal and the digital quadrature (Q) signal carry respective streams of binary information.
44. A transmitter comprising:
a digital circuit configured to receive a digital inphase (I) signal and a digital quadrature (Q) signal, and transform the digital I signal and the digital Q signal in accordance with a 2×2 matrix of constants to produce a resultant digital I signal and a resultant digital Q signal;
a digital-to-analog conversion (DAC) unit configured to convert the resultant digital I and Q signals to analog form in order to obtain respective analog I and Q signals;
an I/Q modulator configured to performing I/Q modulation on the analog I and Q signals to produce a modulated analog signal, wherein the 2×2 matrix is configured to at least partially pre-compensate for I/Q impairments of the transmitter at frequency f, wherein a first of the constants, corresponding a first diagonal element of the 2×2 matrix, is computed based on a measurement of the I/Q impairments of the transmitter at frequency f and a measurement of the I/Q impairments of the transmitter at frequency −f, wherein a second of the constants, corresponding to a first non-diagonal element of the 2×2 matrix, is computed based on the measurement at frequency f and the measurement at frequency −f.
45. The transmitter of claim 44 , wherein the digital inphase (I) signal and the digital quadrature (Q) signal represent a complex exponential tone at frequency f.
46. The transmitter of claim 44 , wherein the digital inphase (I) signal and the digital quadrature (Q) signal carry respective streams of binary information.