METHOD AND APPARATUS FOR MEASURING COMMUNICATIONS LINK QUALITY
First Claim
1. A communications link receiver, comprising:
- a data receiver for receiving a communications signal from a communications link;
a first circuit for producing a high frequency jitter measurement output proportional to an amount of high frequency jitter of said communications signal, said high frequency jitter measurement output having a component that varies with an amount of low frequency jitter present in said communications signal;
a second circuit for producing a low frequency jitter measurement output proportional to an amount of low frequency jitter of said communications signal; and
a correction circuit coupled to said high frequency jitter measurement output and said low frequency jitter measurement output for correcting said high frequency jitter measurement output in conformity with said low frequency jitter measurement output to produce a corrected high frequency jitter measurement output.
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Accused Products
Abstract
A method and apparatus for measuring communications link quality provides accurate on-chip estimation of the difficulty of achieving a particular bit error rate (BER) for a communications link. A low cost/complexity accumulator circuit connected to internal signals from a clock/data recovery (CDR) circuit provides a measure of high frequency and low frequency jitter in a received signal. The low frequency jitter measurement is used to correct the high frequency jitter measurement which may otherwise contain error. The corrected output may be used to adjust operational characteristics of the link or otherwise evaluate the link for operating margin. The correction may be performed by subtracting a portion of the low frequency jitter measurement from the measured high frequency jitter, or the value of the low frequency jitter measurement may be used to select between two or more correction factors that are then applied to the high frequency jitter measurement.
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Citations
4 Claims
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1. A communications link receiver, comprising:
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a data receiver for receiving a communications signal from a communications link;
a first circuit for producing a high frequency jitter measurement output proportional to an amount of high frequency jitter of said communications signal, said high frequency jitter measurement output having a component that varies with an amount of low frequency jitter present in said communications signal;
a second circuit for producing a low frequency jitter measurement output proportional to an amount of low frequency jitter of said communications signal; and
a correction circuit coupled to said high frequency jitter measurement output and said low frequency jitter measurement output for correcting said high frequency jitter measurement output in conformity with said low frequency jitter measurement output to produce a corrected high frequency jitter measurement output. - View Dependent Claims (2)
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3. A method of operating a communications link, said method comprising:
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receiving a communications signal;
determining a measure of high frequency jitter of said communications signal, said measure of high frequency jitter having a dependence on a low frequency jitter of said communications signal;
second determining a measure of low frequency jitter of said communications signal; and
correcting said measure of high frequency jitter in conformity with a value of said measure of low frequency jitter to produce an indication of channel quality in said communications link. - View Dependent Claims (4)
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Specification