Phase-locked loop timing recovery circuit
First Claim
1. A timing recovery circuit, comprising:
- sampling means for sampling an incoming line code signal according to a selectable sample rate;
a feed forward equalizer, coupled to the sampling means, comprises a transversal filter for receiving and filtering the sampled incoming line code signal, the transversal filter comprising N taps, each of the N taps providing an output, N-1 multipliers for multiplying each of the outputs of N-1 of the N taps by a respective coefficient factor, each of the N-1 multipliers providing an output, and an adder for adding the respective outputs of the N-1 multipliers and the output of the Nth tap to produce a filtered signal that is adapted to the sampled incoming line code signal;
a decision feedback equalizer, coupled to the feed forward equalizer, for cancelling an intersymbol interference in the filtered signal, for adjusting the filtering in the feed forward equalizer, and for recovering timing information from the filtered signal;
phase determining means, coupled to a multiplier in the feed forward equalizer, the phase determining means receiving a coefficient factor from the multiplier and creating a phase correction signal in response thereto;
sample control means, coupled to the phase determining means and the sampling means, for creating a sample control signal for selecting the sample rate of the sampling means in response to the phase correction signal generated by the phase determining means.
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Accused Products
Abstract
A timing recovery apparatus for recovering the timing from sparse timing information in multi-level or partial response codes. The timing recovery apparatus includes a switch for sampling an incoming line code signal according to a selectable sample rate, a feed forward equalizer for filtering the sampled signal, a decision feedback equalizer for cancelling intersymbol interference in the filtered signal and for recovering the timing in the sampled signal. The timing recovery circuit creates a phase correction signal in response to a signal received from the feed forward equalizer and thereby control the sample rate of the sample switch so that the signal-to-noise ratio at the node before the decision is maximized. The voltage controlled crystal oscillator may be controlled within a certain frequency range by using a second phase detector which compares the phase of the signal controlling the sampling of the incoming line code with a reference clock.
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Citations
15 Claims
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1. A timing recovery circuit, comprising:
- sampling means for sampling an incoming line code signal according to a selectable sample rate;
a feed forward equalizer, coupled to the sampling means, comprises a transversal filter for receiving and filtering the sampled incoming line code signal, the transversal filter comprising N taps, each of the N taps providing an output, N-1 multipliers for multiplying each of the outputs of N-1 of the N taps by a respective coefficient factor, each of the N-1 multipliers providing an output, and an adder for adding the respective outputs of the N-1 multipliers and the output of the Nth tap to produce a filtered signal that is adapted to the sampled incoming line code signal; a decision feedback equalizer, coupled to the feed forward equalizer, for cancelling an intersymbol interference in the filtered signal, for adjusting the filtering in the feed forward equalizer, and for recovering timing information from the filtered signal; phase determining means, coupled to a multiplier in the feed forward equalizer, the phase determining means receiving a coefficient factor from the multiplier and creating a phase correction signal in response thereto; sample control means, coupled to the phase determining means and the sampling means, for creating a sample control signal for selecting the sample rate of the sampling means in response to the phase correction signal generated by the phase determining means. - View Dependent Claims (2, 3, 4, 5, 6)
- sampling means for sampling an incoming line code signal according to a selectable sample rate;
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7. A timing recovery circuit, comprising:
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sampling means for sampling an incoming line code signal according to a selectable sample rate; a transversal filter means, coupled to the sampling means, for filtering the sampled signal, said transversal filter means having N delay taps, each of the taps providing an output, the transversal filter means further comprising N-1 coefficient means, each coupled to one of N-1 of the N taps, for multiplying the respective output of the N-1 taps by a respective coefficient factor, and an adder for adding the outputs of the N-1 coefficient means to the output of the Nth tap; decision feedback equalizer means, coupled to the transversal filter means, for estimating intersymbol interference in the output of the transversal filter means and for generating an error signal fed back to the transversal filter means; accumulating means for receiving the output of the transversal filter means and the estimated intersymbol interference from the decision feedback equalizer means, for accumulating the estimated symbol interference and the output of the transversal filter means, and for generating an output in response thereto; decision means, coupled to the accumulating means, for receiving the output of the accumulating means and for recovering timing information from the sampled signal; phase determining means, coupled to the transversal filter means, for comparing a coefficient value for the (N-1)th tap to a threshold level and for generating a phase correction signal in response thereto; and sample control means, coupled to the phase determining means and the sampling means, for creating a sample control signal for selecting the sample rate of the sample means in response to the phase correction signal. - View Dependent Claims (8, 9, 10)
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11. A timing recovery circuit, comprising:
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first sampling means for sampling an incoming line code signal according to a first sample rate; a feed forward equalizer, coupled to the first sampling means, the feed forward equalizer further comprising a transversal filter means for receiving and filtering the sampled incoming line code signal, the transversal filter means having N taps, each of the N taps providing an output, N-1 coefficient means for multiplying the outputs of N-1 of the N taps by a respective coefficient factor, and an adder for adding the outputs of the N-1 coefficient means and the output of the Nth tap to produce a filtered signal that is adapted to the sampled incoming line code signal; a decision feedback equalizer, coupled to the feed forward equalizer, for cancelling intersymbol interference in the filtered signal, for recovering timing information from the sampled signal, and for generating an error signal in response thereto for adjusting the filtered signal in the feed forward equalizer; phase determining means, coupled to the decision feedback equalizer, for creating a phase correction signal in response to the recovered timing information and the error signal; and sample control means, coupled to the phase determining means and the first sampling means, for creating a sample control signal for selecting a new sample rate for the sample means in response to the phase correction signal generated by the phase determining means. - View Dependent Claims (12, 13, 14, 15)
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Specification