US 7,945,009 B1 · Jitter measurement

Abstract

A specialized structure measures clock-to-data jitter in an optical memory interface by averaging the result of two second-order estimates of zero crossing using measured signal values on either side of the zero crossing. In one embodiment, a first estimate uses two sample points before the zero crossing and one sample point after while the second estimate uses one sample point before the zero crossing and sample two points after. An existing clock associated with an internal analog-to-digital converter is used to evenly space the samples in time. To simplify the second-order estimate calculations, the three samples of the exemplary embodiment are give x values of −1, 0, and +1 respectively. Which of the two roots of the second-order estimates is used is based on the slope of the signal at the zero crossing.

Claims19

Dependent claims

A method of determining in a jitter measurement hardware circuit of an analog-to-digital converter based timing loop a zero crossing time of a signal having an approximately sinusoidal shape with respect to time and in the presence of noise, the method comprising:

receiving the signal at the analog-to-digital converter based timing loop;
determining in the jitter measurement hardware circuit at least a first and second point on the signal before crossing a critical level;
determining in the jitter measurement hardware circuit at least a third and fourth point on the signal following crossing the critical level;
calculating a first approximate critical level crossing time using at least the first, second, and third points;
calculating a second approximate critical level crossing time using at least the second, third, and fourth points;
and
averaging the first and second approximate critical level crossing times to determine the zero crossing time.

4 more elements

A circuit for implementing a calculation of a zero crossing of an output signal in an optical disk interface, the circuit comprising:

an analog-to-digital converter providing a digital output corresponding to the output signal;
a series of delay sample units for collecting signal samples at intervals over time, the series of delay sample units coupled to the analog-to-digital converter;
a zero crossing detector coupled to the series of delay sample units, the zero crossing detector for determining a zero crossing of the output signal;
a first hardware circuit implementing a quadratic function, the first circuit coupled to a first set of the series of delay sample units, wherein the first set of the series of delay sample units provides a first set of signal samples and the first circuit provides a first output corresponding to the result of the quadratic function applied to the first set of signal samples;
a second hardware circuit implementing an other quadratic function, the second circuit coupled to a second set of the series of delay sample units, wherein the second set of the series of delay sample units provides a second set of signal samples such that the first set and second sets of signal samples have at least two common signal samples, the second circuit providing a second output corresponding to the result of the other quadratic function applied to the second set of signal samples;
and
a third circuit for providing an average of the first and second outputs.

4 more elements

An optical disk interface comprising:

an analog-to-digital converter (ADC) with an output;
a finite impulse response (FIR) filter coupled to the output of the ADC;
a detector coupled to an output of the FIR filter;
a phase detector with an input coupled to the output of the ADC;
a limit equalizer with an input coupled to the input of the phase detector;
and
a jitter measurement hardware circuit coupled to an application specific output of the optical disk interface being one of the input of the limit equalizer or an output of the limit equalizer comprising:
a series of delay sample units for collecting signal samples at intervals over time, the series of delay sample units coupled to the application-specific output in the optical disk interface;
a zero crossing detector coupled to the series of delay sample units, the zero crossing detector for determining a zero crossing of the application-specific output;
a first circuit implementing a quadratic function, the first circuit coupled to a first set of the series of delay sample units, wherein the first set of the series of delay sample units provides a first set of signal samples and the first circuit provides a first output corresponding to the result of the quadratic function applied to the first set of signal samples;
a second circuit implementing an other quadratic function, the second circuit coupled to a second set of the series of delay sample units, wherein the second set of the series of delay sample units provides a second set of signal samples such that the first set and second sets of signal samples have at least two common signal samples, the second circuit providing a second output corresponding to the result of the other quadratic function applied to the second set of signal samples;
and
a third circuit for providing an average of the first and second outputs.

10 more elements

Dependencies are inferred from the claim text.

Jitter measurement

Life of this patent

Jitter measurement

Life of this patent

Abstract

Claims19