Interruptable voltage-controlled oscillator and phase-locked loop using same

摘要

The fall-time of an ECL gate is precisely controlled using a fixed capacitor, which is connected between the positive supply voltage and the ECL gate output terminal, and a variable current source connected between ground and the ECL gate output terminal. A time-delay circuit is obtained by controlling the variable current source with an error voltage of a phase-locked loop such that the time-delay precisely tracks the frequency of the reference signal for the phase-locked loop. A signal detector circuit is obtained by combining time-delay circuits. A voltage-controlled oscillator is assembled by connecting 3 ECL gates with controlled fall-times in a ring oscillator configuration. Addition of a non-inverting input to one ECL gate makes the voltage-controlled oscillator interruptible. Combining a voltage-controlled oscillator of the type described with a phase detector fed by a reference signal provides a phase-locked loop with the control voltage thereof providing a frequency-to-voltage conversion function. A system for providing a receiver clock reference signal from a received signal is provided by phase-locking the output signal of a first phase-locked loop to a system reference signal to generate a first-loop control voltage. A second phase-locked loop is phase-locked to the received signal with a second-loop control voltage. In addition, the second phase-locked loop is also frequency-locked to the system reference signal by the first-loop control voltage. This system is particularly useful for recovering a receiver clock reference from a Manchester-encoded signal.