Methods and devices for handling channel mismatches of an I/Q down-converted signal and a two-channel TI-ADC
A method and device for handling an in-phase and quadrature (“I/Q”) channel mismatch of an I/Q down-converted signal, and a use of the device. A discrete-time complex valued signal r(n) based on an analog-to-digital conversion of the I/Q down-converted signal is obtained. The obtained discrete-time complex valued signal r(n) is oversampled by a factor of two or more. An intermediate signal v(n) is formed from the discrete-time complex valued signal r(n). The intermediate signal v(n) corresponds to the real part of a π/2 frequency shifted version of the obtained discrete-time complex valued signal r(n). A procedure for obtaining an estimate of a frequency dependent mismatch of a two-channel time-interleaved analog-to-digital converter (“TI-ADC”) is applied on the formed intermediate signal v(n). Thereby a TI-ADC mismatch estimate is obtained. The I/Q channel mismatch is estimated and/or compensated based on the obtained TI-ADC mismatch estimate.
1. A method for handling an in-phase and quadrature (“I/Q”) channel mismatch of an I/Q down-converted signal, wherein the method comprises:
obtaining a discrete-time complex valued signal r(n) that is based on an analog-to-digital conversion of the I/Q down-converted signal, wherein the obtained discrete-time complex valued signal r(n) is oversampled by a factor of two or more;
forming an intermediate signal v(n) that corresponds to the real part of a π/2 frequency shifted version of the obtained discrete-time complex valued signal r(n);
applying, on the formed intermediate signal v(n), a procedure for obtaining an estimate of a frequency dependent mismatch of a two-channel time-interleaved analog-to-digital converter (“TI-ADC”) thereby obtaining a TI-ADC mismatch estimate; and
estimating and/or compensating the I/Q channel mismatch based on the obtained TI-ADC mismatch estimate.
2. The method as claimed in claim 1 , wherein the intermediate signal v(n) corresponds to 2Re{r(n)j n }, where Re indicates the real part and j is the imaginary unit.
3. The method as claimed in claim 1 , wherein the I/Q channel mismatch is being compensated by applying, on the intermediate signal v(n) and based on the obtained TI-ADC mismatch estimate, a procedure for compensating a frequency dependent mismatch of a two-channel TI-ADC, thereby obtaining a compensated version v c (n) of the intermediate signal v(n).
4. The method as claimed in claim 3 , wherein a compensated version r c (n) of the discrete-time complex valued signal r(n) is formed, which compensated version r c (n) corresponds to a π/2 frequency shift of an analytic representation of said compensated version v c (n), which π/2 frequency shift is in the opposite direction compared to said π/2 frequency shifted version of the obtained discrete-time complex valued signal r(n).
5. The method as claimed in claim 1 , wherein the I/Q channel mismatch is being compensated by first estimating, based on the obtained TI-ADC mismatch estimate, the I/Q channel mismatch and then compensating the I/Q channel mismatch by applying, on the discrete-time complex valued signal r(n) and based on the estimated I/Q channel mismatch, a procedure for compensating an I/Q channel mismatch of an I/Q down-converted signal, thereby obtaining a compensated version r c (n) of the discrete-time complex valued signal r(n).
6. The method as claimed in claim 1 , wherein the forming of the intermediate signal v(n) comprises alternatingly taking every second sample from respective real and imaginary parts of the obtained discrete-time complex valued signal r(n).
7. The method as claimed in claim 1 , wherein the obtaining of the discrete-time complex valued signal r(n) comprises:
obtaining a wideband discrete-time complex valued signal r w (m) based on the analog-to-digital conversion of the I/Q down-converted signal, wherein wideband indicates that r w (m) has an angular cut-off frequency such that ω c T≧π/2, where ω c is the angular cut-off frequency and T corresponds to the sample period used in the analog-to-digital conversion; and
interpolating the wideband discrete-time complex valued signal r w (m) to obtain the discrete-time complex valued signal r(n) that is oversampled by a factor of two or more.
8. The method as claimed in claim 7 , wherein the interpolating is made by a factor of two or more.
9. The method as claimed in claim 8 , wherein the interpolating is being performed by means of a half-band filter.
10. A device for handling an in-phase and quadrature (“I/Q”) channel mismatch of an I/Q down-converted signal, wherein the device comprises:
an obtaining circuitry, configured to obtain a discrete-time complex valued signal r(n) that is based on an analog-to-digital conversion of the I/Q down-converted signal, wherein the obtained discrete-time complex valued signal r(n) is oversampled by a factor of two or more,
a forming circuitry, configured to form an intermediate signal v(n) from the discrete-time complex valued signal r(n), which intermediate signal v(n) corresponds to the real part of a π/2 frequency shifted version of the obtained discrete-time complex valued signal r(n),
an applying circuitry, configured to apply, on the formed intermediate signal v(n), a procedure for obtaining an estimate of a frequency dependent mismatch of a two-channel time-interleaved analog-to-digital converter (“TI-ADC”) to thereby obtain a TI-ADC mismatch estimate, and
an estimating circuitry and/or compensating circuitry, configured to respectively estimate and/or compensate the I/Q channel mismatch based on the obtained TI-ADC mismatch estimate.
11. The device as claimed in claim 10 , wherein the intermediate signal v(n) corresponds to 2Re{r(n)j n }, where Re indicates the real part and j is the imaginary unit.
12. The device as claimed in claim 10 , wherein the compensating circuitry is configured to compensate the I/Q channel mismatch by applying, on the intermediate signal v(n) and based on the obtained TI-ADC mismatch estimate, a procedure for compensating a frequency dependent mismatch of a two-channel TI-ADC, to thereby obtain a compensated version v c (n) of the intermediate signal v(n).
13. The device as claimed in claim 12 , wherein the compensating circuitry is further configured to form a compensated version r c (n) of the discrete-time complex valued signal r(n), which compensated version r c (n) corresponds to a π/2 frequency shift of an analytic representation of said compensated version v c (n), which π/2 frequency shift is in the opposite direction compared to said π/2 frequency shifted version of the obtained discrete-time complex valued signal r(n).
14. The device as claimed in claim 10 , wherein the estimating circuitry and compensating circuitry are configured to compensate the I/Q channel mismatch by first estimating, based on the obtained TI-ADC mismatch estimate, the I/Q channel mismatch and then compensating the I/Q channel mismatch by applying, on the discrete-time complex valued signal r(n) and based on the estimated I/Q channel mismatch, a procedure for compensating an I/Q channel mismatch of an I/Q down-converted signal, to thereby obtain a compensated version r c (n) of the discrete-time complex valued signal r(n).
15. The device as claimed in claim 10 , wherein the forming circuitry is configured to alternatingly taking every second sample from respective real and imaginary parts of the obtained discrete-time complex valued signal r(n).
16. The device as claimed in claim 10 , wherein the obtaining circuitry is configured to obtain a wideband discrete-time complex valued signal r w (m) based on the analog-to-digital conversion of the I/Q down-converted signal, wherein wideband indicates that r w (m) has an angular cut-off frequency such that ω c T≧π/2, where ω c is the angular cut-off frequency and T corresponds to the sample period used in the analog-to-digital conversion, and the obtaining circuitry is configured to interpolate the wideband discrete-time complex valued signal r w (m) to obtain the discrete-time complex valued signal r(n) that is oversampled by a factor of two or more.
17. The device as claimed in claim 16 , wherein the obtaining circuitry is configured to interpolate the wideband discrete-time complex valued signal r w (m) by a factor of two or more.
18. The device as claimed in claim 17 , wherein the obtaining circuitry is configured to perform the interpolation by means of a half-band filter.
19. A method for handling a frequency dependent mismatch of a two-channel time-interleaved analog-to-digital converter (“TI-ADC”) wherein the method comprises:
obtaining a discrete-time signal v(n) based on an analog-to-digital conversion performed by the two-channel TI-ADC on a continuous-time signal, wherein the discrete-time signal v(n) is bandlimited to a bandpass region,
forming an intermediate signal r(n) that corresponds to (−j) n multiplied by an analytic representation of the obtained discrete-time signal v(n), where j is the imaginary unit,
applying, on the formed intermediate signal r(n), a procedure for obtaining an estimate of an in-phase and quadrature (“I/Q”) channel mismatch of an I/Q down-converted signal, thereby obtaining an I/Q channel mismatch estimate, and
estimating and/or compensating the frequency dependent mismatch of the two-channel TI-ADC based on the obtained I/Q channel mismatch estimate.
20. The method as claimed in claim 19 , wherein the frequency dependent mismatch of the two-channel TI-ADC is being compensated by applying, on the intermediate signal r(n) and based on the obtained I/Q channel mismatch estimate, a procedure for compensating an I/Q channel mismatch of an I/Q down-converted signal, thereby obtaining a compensated version r c (n) of the intermediate signal r(n).
21. The method as claimed in claim 20 , wherein a compensated version v c (n) of the discrete-time signal v(n) is formed, which compensated version v c (n) corresponds to 2Re{r c (n)j n }, where Re refers to the real part and j is the imaginary unit.
22. The method as claimed in claim 19 , wherein the frequency dependent mismatch of the two-channel TI-ADC is being compensated by first estimating, based on the obtained I/Q channel mismatch estimate, the frequency dependent mismatch of the two-channel TI-ADC and then compensating the frequency dependent mismatch of the two-channel TI-ADC by applying, on the discrete-time signal v(n) and based on the estimated frequency dependent mismatch of the two-channel TI-ADC, a procedure for compensating a frequency dependent mismatch of a two-channel TI-ADC, thereby obtaining a compensated version v c (n) of the discrete-time signal v(n).
23. A device for handling a frequency dependent mismatch of a two-channel time-interleaved analog-to-digital converter (“TI-ADC”) wherein the device comprises:
an obtaining circuitry, configured to obtain a discrete-time signal v(n) based on an analog-to-digital conversion performed by the two-channel TI-ADC on a continuous-time signal, wherein the discrete-time signal v(n) is bandlimited to a bandpass region;
a forming circuitry, configured to form an intermediate signal r(n) that corresponds to (−j) n multiplied by an analytic representation of the obtained discrete-time signal v(n), where j is the imaginary unit;
an applying circuitry, configured to apply, on the formed intermediate signal r(n), a procedure for obtaining an estimate of an in-phase and quadrature, “I/Q”, channel mismatch of an I/Q down-converted signal, to thereby obtain an I/Q channel mismatch estimate; and
an estimating circuitry and/or compensating circuitry, configured to respectively estimate and/or compensate the frequency dependent mismatch of the two-channel TI-ADC based on the obtained I/Q channel mismatch estimate.
24. The device as claimed in claim 23 , wherein the compensating circuitry, is configured to compensate the frequency dependent mismatch of the two-channel TI-ADC by applying, on the intermediate signal r(n) and based on the obtained I/Q channel mismatch estimate, a procedure for compensating an I/Q channel mismatch of an I/Q down-converted signal, to thereby obtain a compensated version r c (n) of the intermediate signal r(n).
25. The device as claimed in claim 24 , wherein the compensating circuitry, is further configured to form a compensated version v c (n) of the discrete-time signal v(n), which compensated version v c (n) corresponds to 2Re{r c (n)j n }, where Re refers to the real part and j is the imaginary unit.
26. The device as claimed in claim 23 , wherein the estimating circuitry and compensating circuitry are configured to compensate the frequency dependent mismatch of the two-channel TI-ADC by first estimating, based on the obtained I/Q channel mismatch estimate, the frequency dependent mismatch of the two-channel TI-ADC and then compensating the frequency dependent mismatch of the two-channel TI-ADC by applying, on the discrete-time signal v(n) and based on the estimated frequency dependent mismatch of the two-channel TI-ADC, a procedure for compensating a frequency dependent mismatch of a two-channel TI-ADC, to thereby obtain a compensated version v c (n) of the discrete-time signal v(n).