Measuring the I/Q impairments of a receiver
View Patent ↗Systems and methods for measuring transmitter and/or receiver I/Q impairments are disclosed, including iterative methods for measuring transmitter I/Q impairments using shared local oscillators, iterative methods for measuring transmitter I/Q impairments using intentionally-offset local oscillators, and methods for measuring receiver I/Q impairments. Also disclosed are methods for computing I/Q impairments from a sampled complex signal, methods for computing DC properties of a signal path between the transmitter and receiver, and methods for transforming I/Q impairments through a linear system.
1. A computer-implemented method for determining I/Q impairments of a receiver, the method comprising:
directing that an input signal be supplied to the receiver, wherein the input signal includes an isolated tone at displacement frequency f and includes a void interval around displacement frequency −f, wherein the receiver is configured to demodulate the input signal in order to obtain a sampled complex signal, wherein displacement frequencies f and −f are displacements relative to a local oscillator frequency of the receiver;
computing the I/Q impairments of the receiver at frequency f based on the sampled complex signal;
repeating said directing and said computing for values of the frequency f spanning a specified frequency band;
storing the I/Q impairments of the receiver for said values of the frequency f in a memory.
2. The method of claim 1 , wherein the input signal is supplied by a transmitter whose local oscillator frequency is offset by a non-zero value from the local oscillator frequency of the receiver.
3. The method of claim 1 , wherein the input signal is supplied by a calibration tone synthesizer.
4. The method the claim 1 , wherein said computing the I/Q impairments of the receiver at frequency f includes:
computing a Discrete-Time Fourier transform value C I at frequency f of an I component of the sampled complex signal;
computing a Discrete-Time Fourier transform value C Q at frequency f of a Q component of the sampled complex signal;
computing a gain imbalance of the receiver at frequency f based on magnitudes of the values C I and C Q ; and
computing a phase skew of the receiver at frequency f based on phases of the values C I and C Q .
5. The method of claim 4 , further comprising:
applying a time-domain window to the sampled complex signal prior to said computing of the values C I and C Q .
6. The method of claim 4 , wherein the sampled complex signal is not windowed prior to said computing of the values C I and C Q .
7. The method of claim 1 , wherein said computing the I/Q impairments of the receiver at frequency f is performed by a programmable hardware element of the receiver.
8. A computer system for determining I/Q impairments of a receiver, the computer system comprising:
a processor; and
memory storing program instructions, wherein the program instructions, when executed by the processor, cause the processor to:
direct that an input signal be supplied to the receiver, wherein the input signal includes an isolated tone at displacement frequency f and includes a void interval around displacement frequency −f, wherein the receiver is configured to demodulate the input signal in order to obtain a sampled complex signal, wherein displacement frequencies f and −f are displacements relative to a local oscillator frequency of the receiver;
compute the I/Q impairments of the receiver at frequency f based on the sampled complex signal;
repeat said directing and said computing for values of the frequency f spanning a specified frequency band; and
store the I/Q impairments of the receiver for said values of the frequency f in a memory.
9. The computer system of claim 8 , wherein the input signal is supplied by a transmitter whose local oscillator frequency is offset by a non-zero value from the local oscillator frequency of the receiver.
10. The computer system of claim 8 , wherein the input signal is supplied by a calibration tone synthesizer.
11. The computer system the claim 8 , wherein said computing the I/Q impairments of the receiver at frequency f includes:
computing a Discrete-Time Fourier transform value C I at frequency f of an I component of the sampled complex signal;
computing a Discrete-Time Fourier transform value C Q at frequency f of a Q component of the sampled complex signal;
computing a gain imbalance of the receiver at frequency f based on magnitudes of the values C I and C Q .
12. The computer system the claim 11 , wherein said computing the I/Q impairments of the receiver at frequency f also includes:
computing a phase skew of the receiver at frequency f based on phases of the values C I and C Q .
13. The computer system of claim 11 , wherein the program instructions, when executed by the processor, further cause the processor to:
apply a time-domain window to the sampled complex signal prior to said computing of the values C I and C Q .
14. A non-transitory computer-accessible memory medium for determining I/Q impairments of a receiver, wherein the memory medium stores program instructions, wherein the program instructions, when executed by a computer system, cause the computer system to:
direct that an input signal be supplied to the receiver, wherein the input signal includes an isolated tone at displacement frequency f and includes a void interval around displacement frequency −f, wherein the receiver is configured to demodulate the input signal in order to obtain a sampled complex signal, wherein displacement frequencies f and −f are displacements relative to a local oscillator frequency of the receiver;
compute the I/Q impairments of the receiver at frequency f based on the sampled complex signal;
repeat said directing and said computing for values of the frequency f spanning a specified frequency band;
store the I/Q impairments of the receiver for said values of the frequency f in a memory.
15. The memory medium of claim 14 , wherein the input signal is supplied by a transmitter whose local oscillator frequency is offset by a non-zero value from the local oscillator frequency of the receiver.
16. The memory medium of claim 14 , wherein the input signal is supplied by a calibration tone synthesizer.
17. The memory medium the claim 14 , wherein said computing the I/Q impairments of the receiver at frequency f includes:
computing a Discrete-Time Fourier transform value C I at frequency f of an I component of the sampled complex signal;
computing a Discrete-Time Fourier transform value C Q at frequency f of a Q component of the sampled complex signal;
computing a gain imbalance of the receiver at frequency f based on magnitudes of the values C I and C Q ; and
computing a phase skew of the receiver at frequency f based on phases of the values C I and C Q .
18. The memory medium of claim 17 , wherein the program instructions, when executed by the computer system, further cause the computer system to:
apply a time-domain window to the sampled complex signal prior to said computing of the values C I and C Q .
19. The memory medium of claim 17 , wherein the sampled complex signal is not windowed prior to said computing of the values C I and C Q .
20. The memory medium of claim 14 , wherein said computing the I/Q impairments of the receiver at frequency f is performed by a programmable hardware element of the receiver.