Circuit and method of digital carrier detection for burst mode communication systems
AssigneeAT&T Bell Laboratories
InventorWilliam B. Wilson
Life of this patent
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Abstract
A digital squelch circuit for detecting valid data signals in a burst mode communication system, such as a packet-based local area network. Transitions in the input signal to the squelch circuit start a counter which asserts at least one signal a predetermined time from the transition. The absence or presence of the signal when the next transition in the input signal occurs determines if the frequency of the input signal is less than or greater than a frequency related to the predetermined time interval. When a predetermined number of transitions meeting the desired frequency requirement are received, the input signal is judged valid.
Claims14
A circuit disposed in an integrated circuit, for comparing an input signal to a first predetermined frequency, characterized by:
- a first timing means for generating a first signal at a first predetermined time after a first polarity transition in an input signal;
- and,
- first comparing means, responsive to the first and input signals, for determining if a second polarity transition in the input signal occurs before or after the first signal is asserted, the second polarity being opposite the first polarity;
- wherein the first predetermined time is substantially one-half the inverse of the first predetermined frequency and the first comparing means indicates to a first output that the frequency of the input signal is greater than or less than the first predetermined frequency.
A method of determining if an input signal has a frequency which is greater than or less than a first predetermined frequency, characterized by the steps of:
- asserting a first signal at a predetermined time after a first polarity transition in the input signal, the predetermined time being substantially one-half the inverse of the first predetermined frequency;
- and,
- determining if a second polarity transition in the input signal occurred before or after the assertion of the first signal, the second polarity being opposite the first polarity;
- wherein if the second polarity transition occurs before the assertion of the first signal, the frequency of the input signal is greater than the first predetermined frequency, and if the second polarity transition occurs after the assertion of the first signal, the frequency of the input signal is less than the first predetermined frequency.
Dependencies are inferred from the claim text.