Time-interleaved analog-to-digital converter for signals in any Nyquist zone
Processing a signal by receiving an analog input signal located outside of a first Nyquist zone that is between 0 and fs/2; passing the analog input signal through an M-channel time-interleaved analog-to-digital converter (TI-ADC) to generate a TI-ADC output signal; and estimating and correcting a timing skew error in the TI-ADC output signal. Alternatively, an electronic circuit that includes an input for an analog input signal, an M-channel time-interleaved analog-to-digital converter (TI-ADC) and a timing skew error estimating and correcting circuitry. The analog input signal is located outside of a first Nyquist zone that is between 0 and fs/2. The TI-ADC receives the analog input signal and generates a TI-ADC output signal. The timing skew error estimating and correcting circuitry estimates and corrects a timing skew error in the TI-ADC output signal.
1. A method for processing a signal, the method comprising the steps of:
receiving an analog input signal located outside of a first Nyquist zone that is between 0 and f S /2;
passing the analog input signal through an M-channel time-interleaved analog-to-digital converter (TI-ADC) to generate a TI-ADC output signal; and
estimating and correcting a timing skew error in the TI-ADC output signal by creating a 90-degrees phase shifted version of the TI-ADC output signal, and multiplying the phase shifted version of the TI-ADC output signal by an estimate of the timing skew and a constant that depends on the Nyquist zone of the analog input signal.
2. The method of claim 1 , further comprising the steps of:
up-sampling the TI-ADC output signal to form multiple spectral copies of the TI-ADC output signal;
selecting one of the spectral copies that has a same frequency location as the analog input signal; and
estimating and correcting the timing skew error in the selected spectral copy.
3. The method of claim 1 , wherein:
a Hilbert transform filter creates the 90 degrees phase shifted version of the TI-ADC output signal.
4. The method of claim 1 , wherein:
a value of the constant is: (−1) k └k/2┘π, where k represents the Nyquist zone of the analog input signal and brackets (└ ┘) denote rounding towards zero.
5. The method of claim 1 , wherein the estimating and correcting further comprises:
generating a first estimated error component that is proportional to a derivative of the analog input signal at carrier frequency of 0;
generating a second estimated error component that is proportional to the analog input signal phase shifted by 90-degrees and multiplied by a constant which is proportional to an original carrier frequency of the analog input signal; and
subtracting the first and second estimated error components from the TI-ADC output signal.
6. The method of claim 1 , wherein each of the M channels has a unique correction coefficient.
7. The method of claim 1 , wherein M>2.
8. The method of claim 1 , further comprising the step of:
inserting a pilot tone in the analog input signal;
and wherein the estimating and correcting utilizes the pilot tone.
9. The method of claim 8 , wherein the pilot tone is in a different Nyquist zone than that of the analog input signal.
10. An electronic circuit comprising:
an input for an analog input signal located outside of a first Nyquist zone that is between 0 and f S /2;
an M-channel time-interleaved analog-to-digital converter (TI-ADC) that receives the analog input signal and generates a TI-ADC output signal; and
a timing skew error estimating and correcting circuitry that estimates and corrects a timing skew error in the TI-ADC output signal by creating a 90-degrees phase shifted version of the TI-ADC output signal and multiplying the phase shifted version of the TI-ADC output signal by an estimate of the timing skew and a constant that depends on the Nyquist zone of the analog input signal.
11. The electronic circuit of claim 10 , further comprising:
a pilot tone that is inserted in the analog input signal;
and wherein the timing skew error estimating and correcting circuitry utilizes the pilot tone.
12. The electronic circuit of claim 11 , wherein the pilot tone is in a different Nyquist zone than that of the analog input signal.
13. The electronic circuit of claim 10 , further comprising:
a Hilbert transform filter that creates the 90 degrees phase shifted version of the TI-ADC output signal.
14. The electronic circuit of claim 10 , wherein:
a value of the constant is: (−1) k └k/2┘π, where k represents the Nyquist zone of the analog input signal and brackets (└ ┘) denote rounding towards zero.
15. The electronic circuit of claim 10 , wherein the timing skew error estimating and correcting circuitry:
generates a first estimated error component that is proportional to a derivative of the analog input signal at carrier frequency of 0;
generates a second estimated error component that is proportional to the analog input signal phase shifted by 90-degrees and multiplied by a constant which is proportional to an original carrier frequency of the analog input signal; and
subtracts the first and second estimated error components from the TI-ADC output signal.
16. The electronic circuit of claim 10 , wherein each of the M channels has a unique correction coefficient.
17. The electronic circuit of claim 10 , wherein M>2.
18. An electronic circuit for processing a signal comprising:
a means for receiving an analog input signal located outside of a first Nyquist zone that is between 0 and f S /2;
an M-channel time-interleaved analog-to-digital converter (TI-ADC) means for receiving the analog input signal and generating a TI-ADC output signal;
a means for up-sampling the TI-ADC output signal to form multiple spectral copies of the TI-ADC output signal;
a means for selecting one of the spectral copies that has a same frequency location as the analog input signal; and
a means for estimating and correcting the timing skew error in the selected spectral copy.