Synchronization techniques using an interpolation filter
First Claim
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1. A modem comprising:
- a transmit engine that transmits samples to a host; and
a receive engine to receive samples from a host, the receive engine including;
an equalizer; and
a synchronization recovery circuit, coupled to the equalizer, to estimate a frequency difference between a local sample clock and a remote sample clock, the synchronization recovery circuit including;
a discrete Fourier transform (DFT) circuit, coupled to the equalizer, that transforms input signals received from one or more taps of the equalizer to generate the +B/4 and −
B/4 spectral components of the DFT, where B equals the baud rate; and
a comparator, coupled to the DFT, that measures the phase difference between the +B/4 and −
B/4 components to produce a first signal indicative of the frequency difference between the local sample clock and the remote sample clock.
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Abstract
The taps of an equalizer are used as inputs to a discrete Fourier transform (DFT). Certain spectral components are extracted from the DFT and used to estimate the frequency difference. The frequency difference estimate is filtered using a phase locked loop and used to adjust one clock to synchronize the transmit and receive clocks.
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Citations
13 Claims
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1. A modem comprising:
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a transmit engine that transmits samples to a host; and
a receive engine to receive samples from a host, the receive engine including;
an equalizer; and
a synchronization recovery circuit, coupled to the equalizer, to estimate a frequency difference between a local sample clock and a remote sample clock, the synchronization recovery circuit including;
a discrete Fourier transform (DFT) circuit, coupled to the equalizer, that transforms input signals received from one or more taps of the equalizer to generate the +B/4 and −
B/4 spectral components of the DFT, where B equals the baud rate; and
a comparator, coupled to the DFT, that measures the phase difference between the +B/4 and −
B/4 components to produce a first signal indicative of the frequency difference between the local sample clock and the remote sample clock.- View Dependent Claims (2, 3, 4)
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5. A method comprising:
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receiving a frequency offset from a plurality of equalizer taps;
transforming input signals corresponding to the frequency offset to generate the +B/4 and −
B/4 spectral components of a discrete Fourier transform (DFT), where B equals the baud rate;
measuring the phase difference between the +B/4 and −
B/4 components; and
producing a first signal that is indicative of the frequency difference between a local sample clock and a remote sample clock. - View Dependent Claims (6, 7)
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8. A receive engine comprising:
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an equalizer; and
a synchronization recovery circuit, coupled to the equalizer, to estimate a frequency difference between a local sample clock and a remote sample clock, the synchronization recovery circuit including;
a discrete Fourier transform (DFT) circuit, coupled to the equalizer, that transforms input signals received from one or more taps of the equalizer to generate the +B/4 and −
B/4 spectral components of the DFT, where B equals the baud rate; and
a comparator, coupled to the DFT, that measures the phase difference between the +B/4 and −
B/4 components to produce a first signal indicative of the frequency difference between the local sample clock and the remote sample clock.- View Dependent Claims (9, 10, 11)
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12. A synchronization recovery circuit comprising:
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a discrete Fourier transform (DFT) circuit that transforms input signals received from one or more taps of an equalizer to generate the +B/4 and −
B/4 spectral components of the DFT, where B equals the baud rate; and
a comparator, coupled to the DFT, that measures the phase difference between the +B/4 and −
B/4 components to produce a first signal indicative of a frequency difference between a local sample clock and a remote sample clock.- View Dependent Claims (13)
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Specification