Hewlett-packard Company

Donald M Lee

Benny W Lai

An out of lock condition is sensed on a data transition by transition basis in clock recovery apparatus. When an out of lock condition is sensed, a range sweeping signal is generated and summed with the correction signal to sweep the frequency of the clock signal over the frequency range of the VCO. When an out of lock condition is absent, i.e., when the VCO is phase locked, simulated data transitions are generated in the frequency/phase detector. An out of lock condition is sensed by a D flip-flop. Data is coupled to the clock input of the flip-flop, the clock signal is delayed by a fraction of its nominal period and coupled to the D input of the flip-flop. The state of the Q output of the flip-flop indicates an out of lock condition.

Clock recovery apparatus with means for sensing an out of lock condition

A variable gain wideband bipolar monolithic amplifier has first and second bipolar transistors connected together in a Darlington configuration. A resistive shunt feedback loop connected between the output and the input of the amplifier controls the gain of the amplifier. The feedback loop includes a field effect transistor, formed on the same chip substantially by the same bipolar process as the bipolar transistors, for varying the impedance of the shunt feedback loop thereby varying the gain of the amplifier. The gain of the amplifier is controlled in response to the application of a control voltage to the gate of the FET. Further, the FET is dc biased for inhibiting the FET from drawing dc current.

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San Jose, CA, United States of America

Donald M Lee