Northern Telecom Limited

Quantum Corporation

Edward Lloyd Henderson

Russell W Brown

Toai A Doan

A phase locked loop has an average zero phase start circuit to detect and correct for the average phase difference between a data signal and a VCO clock signal over a short interval at the beginning of phase-lock acquisition. The average zero phase start circuit has a data comparator to split the data stream into odd and even portions; odd and even pulse position detectors to detect the phase difference between pulses of the odd and even data signals and corresponding pulses of the VCO clock; and a ramp generator to generate a voltage corresponding to the sum of the detected phase differences. The ramp generator employs a capacitor and switched current sources that discharge the capacitor at a fixed rate to generate the voltage. After 4 phase difference measurements are taken, the VCO is stopped, and another current source discharges the capacitor at 4 times the fixed rate. A ramp comparator indicates when the capacitor voltage converges with a reference voltage to restart the VCO in the desired phase alignment with the data signal.

Averaging zero phase start for phase locked loops

A circuit for controlling the on-off ringing of a line powered electronic tone ringer in a telephone set. The circuit, which includes a variable rate charge-discharge suppression circuit, effectively prevents up to 300 volt peak, 12 Hz transient spikes on the line from actuating the tone ringer, yet still responds to a 35 volt RMS, 18 Hz ringing signal.

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Kanata, Canada

Edward Lloyd Henderson