High speed self-adjusting clock recovery circuit with frequency detection
First Claim
1. A clock recovery circuit for establishing bit synchronization with an NRZ data formatted bit stream comprising:
- a matched filter for receiving said NRZ data formatted bit stream for producing a filtered output signal indicative of edge transitions in said NRZ data formatted bit stream;
first and second sample and hold circuits having inputs coupled to said matched filter, said sample and hold circuits being complementarily clocked by a VCO signal to hold quadrature samples, said first sample and hold circuit for generating an in-phase data output signal;
a third sample and hold circuit having an input coupled to said second sample and hold circuit, said third sample and hold circuit being clocked on positive and negative transitions of said in-phase data output signal and generating a data crossover sample;
a multiplier for multiplying said in-phase data output signal with output from said third sample and hold circuit;
a lowpass filter coupled to said multiplier for filtering output of said multiplier to generate a DC value of a phase error signal proportional to any phase error between said in-phase data output signal and said data crossover sample; and
a variable controlled oscillator (VCO) having its control input coupled to said low ass filter, said variable controlled oscillator generating said VCO signal with a controllable phase according to said DC value provided by said lowpass filter, said VCO being coupled to said first and second sample and hold circuits to complementarily clock said first and second sample and hold circuits,whereby a data transition tracking loop is provided which is high speed, inherently self-adjusting;
is independent of data transition density with significantly reduced ripple in said phase error signal generated by said multiplier.
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Abstract
A clock recovery circuit based upon an early-late gate approach is applied to high speed serial communication links using NRZ data. The circuit has no systematic phase offset and therefore requires no external phase adjustment circuits or mechanisms. The circuit is used in high speed integrated receivers for applications including fiber optics, disk-drive read/write electronics, mobile communications and high rate- twisted pair data transmission in multimedia systems. Quadrature samples are obtained and held which follow the shape of the NRZ data transition as a function of phase offset. The data signal is passed through the limiter giving rise to a sawtooth shaped phase error signal. A derivative of the error function is taken to provide a frequency error signal to provide for frequency detection and assistance in frequency acquisition of the phase lock loop circuit generating the recovered clock signal from a variably controlled oscillator.
143 Citations
20 Claims
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1. A clock recovery circuit for establishing bit synchronization with an NRZ data formatted bit stream comprising:
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a matched filter for receiving said NRZ data formatted bit stream for producing a filtered output signal indicative of edge transitions in said NRZ data formatted bit stream; first and second sample and hold circuits having inputs coupled to said matched filter, said sample and hold circuits being complementarily clocked by a VCO signal to hold quadrature samples, said first sample and hold circuit for generating an in-phase data output signal; a third sample and hold circuit having an input coupled to said second sample and hold circuit, said third sample and hold circuit being clocked on positive and negative transitions of said in-phase data output signal and generating a data crossover sample; a multiplier for multiplying said in-phase data output signal with output from said third sample and hold circuit; a lowpass filter coupled to said multiplier for filtering output of said multiplier to generate a DC value of a phase error signal proportional to any phase error between said in-phase data output signal and said data crossover sample; and a variable controlled oscillator (VCO) having its control input coupled to said low ass filter, said variable controlled oscillator generating said VCO signal with a controllable phase according to said DC value provided by said lowpass filter, said VCO being coupled to said first and second sample and hold circuits to complementarily clock said first and second sample and hold circuits, whereby a data transition tracking loop is provided which is high speed, inherently self-adjusting;
is independent of data transition density with significantly reduced ripple in said phase error signal generated by said multiplier. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method of recovering a clock signal from an NRZ data bit stream comprising the steps of:
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detecting edge transitions of said NRZ data bit stream; generating a quadrature sample signal corresponding to said NRZ data bit stream; selectively passing said quadrature sample signal to a phase detector output, said quadrature sample signal being passed to said phase detector output if said NRZ data makes a low to high transition, a negative of said quadrature sample signal being passed to said phase detector output if said NRZ data signal makes a high to low transition, otherwise if said NRZ data signal makes no transition, holding a previous phase error value in said phase detector output; controlling a variably controlled oscillator (VCO) according to said phase detector output; and generating a recaptured clock signal by said controlled VCO, whereby said clock signal is recovered in a self-adjusting circuit with no steady state phase error, whereby ripple induced phase jitter is substantially eliminated, whereby phase error output is independent of data density and high speed operation is enabled. - View Dependent Claims (16, 17, 18, 19)
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20. A circuit for recapturing a clock signal from an NRZ data bit stream comprising:
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clocked sample and hold circuit means for sampling and holding an in-phase sample signal of said NRZ data bit stream; clocked sample and hold circuit means for sampling and holding-a quadrature sample signal of said NRZ data bit stream; phase detector circuit means for selectively passing said quadrature sample signal to a phase detector output, said quadrature sample signal being passed to said phase detector output if said NRZ data makes a low to high transition, the negative of said quadrature sample signal being passed to said phase detector output if said NRZ data makes a high to low transition, and previously passed quadrature sample signal being held at said phase detector output if said NRZ data makes no transition; and variable controlled oscillator means for receiving said phase detector output and responsively generating an in-phase clock signal, said clocked sample and hold circuit means for sampling and holding an in-phase sample signal of said NRZ data bit stream and said clocked sample and hold circuit means for sampling and holding a quadrature sample signal of said NRZ data bit stream being complementarily clocked by said inphase clock signal.
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Specification