US 4,908,530 AGranted

Non-linear squelch circuit for IEEE-802. 3 protocol

AssigneeHewlett-Packard Company

InventorFred G. Huang

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Abstract

Method and apparatus for non-linearly filtering impulse and low frequency noise received over a network so as to avoid false activation of equipment is disclosed. A squelch circuit assures that only multiple transitions of at least three half-cycles in the received waveform of a proper frequency and amplitude will activate the receive while a single half-cycle, although of a proper frequency and exceeding the threshold, will not falsely activate the receiver. RC circuits provide a variable delay in the squelch portion of the filter to suppress impulses. In an alternative embodiment, double half-cycles will not falsely activate the receiver. Emitter-coupled logic (ECL) circuitry is preferably employed to provide speed adequate for ten-million bit per second transmissions.

Claims15

Dependent claims

A non-linear filter receiving a differential signal comprising:

means for generating a first reference-voltage;
filter means responsive to said received differential signal for generating differential signals representing said received signals having a frequency between a first and a second predetermined frequency;
squelch means responsive to said filtered signals for generating a signal at a first level upon reception of no more than a predetermined number of consecutive half-cycles of said filtered signal and at a second level upon reception of more than said predetermined number of consecutive half-cycles of said filtered signal, said squelch means comprising:
first comparator means responsive to a first of said filtered differential signals and said first reference voltage for generating at an output a binary-valued signal indicative of whether said first filtered differential signal exceeds said first reference voltage;
second comparator means responsive to a second of said filtered differential signals and said first reference voltage for generating at an output a binary-valued signal indicative of whether said first reference voltage exceeds said second filtered differential signal;
first and second passive means coupled to said first and second comparator means output, respectively, for delaying by a first selected amount the time said signal generated at said first and second comparator means, respectively, changes from a first said binary value to a second said binary value;
and
peak-detection means receiving said signals generated at said first and second comparator means outputs for generating at an output said two-level squelch signal when both said received signals exceed in absolute value a second predetermined reference voltage within said first selected delay time, indicating said reception of no more than said predetermined number of consecutive half-cycles of said filtered signal, and
logic means responsive to said filtered signals and said squelch signal for suppressing said filtered signals upon reception of said first level of said squelch signal and for not suppressing said filtered signals upon reception of said second level of said squelch signal.

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Abstract

A non-linear filter receiving a differential signal comprising:

means for generating a first reference-voltage;
filter means responsive to said received differential signal for generating differential signals representing said received signals having a frequency between a first and a second predetermined frequency;
squelch means responsive to said filtered signals for generating a signal at a first level upon reception of no more than a predetermined number of consecutive half-cycles of said filtered signal and at a second level upon reception of more than said predetermined number of consecutive half-cycles of said filtered signal, said squelch means comprising:
first comparator means responsive to a first of said filtered differential signals and said first reference voltage for generating at an output a binary-valued signal indicative of whether said first filtered differential signal exceeds said first reference voltage;
second comparator means responsive to a second of said filtered differential signals and said first reference voltage for generating at an output a binary-valued signal indicative of whether said first reference voltage exceeds said second filtered differential signal;
first and second passive means coupled to said first and second comparator means output, respectively, for delaying by a first selected amount the time said signal generated at said first and second comparator means, respectively, changes from a first said binary value to a second said binary value;
and
peak-detection means receiving said signals generated at said first and second comparator means outputs for generating at an output said two-level squelch signal when both said received signals exceed in absolute value a second predetermined reference voltage within said first selected delay time, indicating said reception of no more than said predetermined number of consecutive half-cycles of said filtered signal, and
logic means responsive to said filtered signals and said squelch signal for suppressing said filtered signals upon reception of said first level of said squelch signal and for not suppressing said filtered signals upon reception of said second level of said squelch signal.

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