Technique for the measurement of I/Q impairments associated with a sampled complex signal
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 estimating I/Q impairment information associated with a sampled complex signal produced by a receiver, the method comprising:
(a) directing a device to stimulate the receiver with a stimulus signal having an isolated tone at displacement frequency f and a void interval at displacement frequency −f, wherein displacement frequencies f and −f are displacements with respect to a local oscillator frequency of the receiver, wherein the sampled complex signal is a baseband signal produced by the receiver;
(b) computing a Discrete-Time Fourier transform value C I at frequency f of an I component of the sampled complex signal;
(c) computing a Discrete-Time Fourier transform value C Q at frequency f of a Q component of the sampled complex signal;
(d) computing a gain imbalance g of the sampled complex signal at frequency f based on magnitudes of the values C I and C Q , wherein the gain imbalance g includes a gain imbalance of the receiver.
2. The method of claim 1 , further comprising:
(e) computing a phase skew φ of the sampled complex signal at frequency f based on phases of the values C I and C Q , wherein the phase skew φ includes a phase skew of the receiver.
3. The method of claim 2 , wherein the device is a transmitter whose local oscillator frequency is offset from the receiver's local oscillator frequency by a non-zero amount, wherein the gain imbalance g and phase skew φ include an effect of I/Q impairments of the transmitter.
4. The method of claim 1 , wherein the device is a calibration tone generator.
5. The method of claim 1 , further comprising:
applying a time-domain window to the sampled complex signal prior to said computing the value C I and said computing the value C Q .
6. The method of claim 1 , wherein the receiver is a vector signal analyzer.
7. The method of claim 1 , wherein one or more of (b), (c) and (d) are performed by a programmable hardware element.
8. The method of claim 1 , wherein one or more of (b), (c) and (d) are performed in dedicated digital circuitry.
9. The method of claim 1 , wherein one or more of (a), (b), (c) and (d) are performed by a processor in response to execution of program instructions.
10. A computer system for estimating I/Q impairment information associated with a sampled complex signal produced by 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 a device to stimulate the receiver with a stimulus signal having an isolated tone at displacement frequency f and a void interval at displacement frequency −f, wherein displacement frequencies f and −f are displacements with respect to a local oscillator frequency of the receiver, wherein the sampled complex signal is a baseband signal produced by the receiver;
compute a Discrete-Time Fourier transform value C I at frequency f of an I component of the sampled complex signal;
compute a Discrete-Time Fourier transform value C Q at frequency f of a Q component of the sampled complex signal;
compute a gain imbalance g of the sampled complex signal at frequency f based on magnitudes of the values C I and C Q , wherein the gain imbalance g includes a gain imbalance of the receiver.
11. The computer system of claim 10 , wherein the program instructions, when executed by the processor, further cause the processor to:
compute a phase skew φ of the sampled complex signal at frequency f based on phases of the values C I and C Q , wherein the phase skew φ includes a phase skew of the receiver.
12. The computer system of claim 11 , wherein the device is a transmitter whose local oscillator frequency is offset from the receiver's local oscillator frequency by a non-zero amount, wherein the gain imbalance g and phase skew φ include an effect of I/Q impairments of the transmitter.
13. The computer system of claim 10 , wherein the device is a calibration tone generator.
14. The computer system of claim 10 , 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 the value C I and said computing the value C Q .
15. The computer system of claim 10 , wherein the receiver is a vector signal analyzer.
16. A non-transitory computer-accessible memory medium for estimating I/Q impairments associated with a sampled complex signal produced by a receiver, wherein the memory medium stores program instructions, wherein the program instructions, when executed by a computer system, cause the computer system to:
(a) direct a device to stimulate the receiver with a stimulus signal having an isolated tone at displacement frequency f and a void interval at displacement frequency −f, wherein displacement frequencies f and −f are displacements with respect to a local oscillator frequency of the receiver, wherein the sampled complex signal is a baseband signal produced by the receiver;
(b) compute a Discrete-Time Fourier transform value C I at frequency f of an I component of the sampled complex signal;
(c) compute a Discrete-Time Fourier transform value C Q at frequency f of a Q component of the sampled complex signal;
(d) compute a gain imbalance g of the sampled complex signal at frequency f based on magnitudes of the values C I and C Q , wherein the gain imbalance g includes a gain imbalance of the receiver.
17. The memory medium of claim 16 , wherein the program instructions, when executed by the computer system, further cause the computer system to:
(e) compute a phase skew φ of the sampled complex signal at frequency f based on phases of the values C I and C Q , wherein the phase skew φ includes a phase skew of the receiver.
18. The memory medium of claim 17 , wherein the device is a transmitter whose local oscillator frequency is offset from the receiver's local oscillator frequency by a non-zero amount, wherein the gain imbalance g and phase skew φ include an effect of I/Q impairments of the transmitter.
19. The memory medium of claim 16 , wherein the device is a calibration tone generator.
20. The memory medium of claim 16 , 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 the value C I and said computing the value C Q .