Sampling method for time-interleaved data converters in frequency-multiplexed communications systems
View Patent ↗A wide band analog-to-digital converter used in a frequency multiplexed communication system. The converter includes a plurality, M, of time-interleaved analog-to-digital converter subunits (ADC subunits). The sampling rate, FS 1 , of the M ADC subunits is selected to locate one or more integer multiples of a Nyquist frequency of a respective subunit ADC in one or more guard bands, and/or such that one or more integer multiples of FS 1 are also located in the guard bands.
1. An apparatus for receiving a signal from a frequency multiplexed communication system comprising:
a plurality, M, of time-interleaved analog-to-digital converter (ADC) subunits, coupled to receive the signal from the frequency multiplexed communication system at an input and provide a digital representation thereof at an output; and
a clock circuit, coupled to provide one or more clock signals to the plurality, M, of time-interleaved ADC subunits, such that at least one of the ADC subunits samples the frequency multiplexed communication signal at a sample clock rate, FS 1 , and such that the M ADC subunits together providing an aggregate sample clock rate, FS, of the frequency multiplexed communication signal, and further such that FS 1 is a predetermined frequency selected to locate a Nyquist frequency of a respective one of the M ADC subunits in one or more guard band regions of the frequency-multiplexed communication system, and such that one or more integer multiples of FS 1 are located in one or more guard band regions of the frequency-multiplexed communication system.
2. The apparatus of claim 1 wherein the clock circuit further calibrates the time-interleaved ADC subunits by generating a sample clock signal, FS 1 , such that spurious content in the digital representation provided at the output is also located in at least one guard band region.
3. An apparatus for receiving a signal from a frequency multiplexed communication system comprising:
a plurality, M, of time-interleaved analog-to-digital converter (ADC) subunits, coupled to receive the signal from the frequency multiplexed communication system at an input and provide a digital representation thereof at an output;
a clock circuit, coupled to provide one or more clock signals to the plurality, M, of time-interleaved ADC subunits, such that at least one of the ADC subunits samples the frequency multiplexed communication signal at a sample clock rate, FS 1 , and such that the M ADC subunits together providing an aggregate sample clock rate, FS, of the frequency multiplexed communication signal, and further such that FS 1 is a predetermined frequency selected to locate a Nyquist frequency of a respective one of the M ADC subunits in one or more guard band regions of the frequency-multiplexed communication system, and such that one or more integer multiples of FS 1 are located in one or more guard band regions of the frequency-multiplexed communication system; and
wherein guard bands for selected channels of the frequency-multiplexed communication system are not located on integer multiples of a channel spacing, and additional constraints are added to the sampling frequency, FS 1 , such that one or more selected integer multiples of the sampling frequency, FS 1 , do not fall within the selected channels.
4. The apparatus of claim 1 wherein
FS=M×FS 1
and
FS is greater than a Nyquist sampling rate of the frequency multiplexed communication signal.
5. The apparatus of claim 1 wherein the communication system is cable system.
6. The apparatus of claim 5 wherein a nominal channel spacing used in the cable system is 6 MHz, and
FS 1 =J× 12 MHz
where J is an integer such that J does not equal 7, 13 or 14.
7. The apparatus of claim 6 wherein a Nyquist sampling rate of the frequency multiplexed communication signal in the cable system is 2004 MHz, so that
FS=M×J× 12 MHz>2004 MHz
where
M×J> 167.
8. The apparatus of claim 1 wherein the frequency multiplexed system is a cable system that provides a stated number of frequency multiplexed cable channels, and at least one additional signal is received having frequency content above the highest cable channel, and wherein FS is selected as a least common multiple of FS 1 and a sample clock used to sample the additional signal.
9. A method for receiving a signal from a frequency multiplexed communication system comprising:
receiving a frequency multiplexed communication signal;
providing a digital representation of the frequency multiplexed communication signal at a plurality, M, of time-interleaved analog-to-digital converter (ADC) subunits; and
calibrating the plurality, M, of time-interleaved ADC subunits by providing one or more clock signals to the at least one of the time-interleaved ADC subunits, such that at least one ADC subunit samples the frequency multiplexed communication signal at a sampling rate, FS 1 , and such that the M ADC subunits together providing an aggregate sample rate, FS, and such that one or more spurious signal due to mismatch in the subunit ADCs fall within a predetermined guard band of the frequency multiplexed communication system.
10. The method of claim 9 wherein the sampling frequency is further selected such that a Nyquist frequency of a respective one of the M ADC subunits is co-located with one or more guard band regions of the frequency-multiplexed communication system, and such that one or more integer multiples of FS 1 are co-located in one or more guard band regions of the frequency-multiplexed communication system.
11. A method for receiving a signal from a frequency multiplexed communication system comprising:
receiving a frequency multiplexed communication signal;
providing a digital representation of the frequency multiplexed communication signal at a plurality, M, of time-interleaved analog-to-digital converter (ADC) subunits;
calibrating the plurality, M, of time-interleaved ADC subunits by providing one or more clock signals to the at least one of the time-interleaved ADC subunits, such that at least one ADC subunit samples the frequency multiplexed communication signal at a sampling rate, FS 1 , and such that the M ADC subunits together providing an aggregate sample rate, FS, and such that one or more spurious signal due to mismatch in the subunit ADCs fall within a predetermined guard band of the frequency multiplexed communication system; and
wherein guard bands for selected channels are not located on integer multiples of a channel spacing, and additional constraints are added to the sampling frequency, FS 1 , such that one or more selected integer multiples of the sampling frequency do not fall within the selected channels.
12. The method of claim 9 wherein
FS=M×FS 1;
and
FS is greater than a Nyquist sampling rate of the frequency multiplexed communication signal.
13. The method of claim 9 wherein the communication system is cable system.
14. The method of claim 13 and further wherein
a nominal channel spacing used in the cable system is 6 MHz, and
FS 1 =J× 12 MHz
where J is an integer such that J does not equal 7, 13 or 14.
15. The method of claim 14 wherein a Nyquist sampling rate of the frequency multiplexed communication signal in the cable system is 2004 MHz, so that
FS=M×J× 12 MHz>2004 MHz
and
M×J> 167.
16. The method of claim 9 wherein the frequency multiplexed system is a cable system that provides a stated number of frequency multiplexed cable channels, and at least one additional signal is received having frequency content above the highest cable channel, and wherein FS is selected as a least common multiple of FS 1 and a sample clock used to sample the additional signal.