| 摘要 |
A first order phase-locked loop includes a tuning circuit which allows phase lock to be quickly reached, and to be maintained during transient situations such as loss of the data signal. Such an improved circuit has a tuning circuit for the voltage controlled oscillator which utilizes two capacitors. Two signals are used to drive a first, larger, capacitor, and have the same duty cycle when the capacitor voltage is proper and the voltage controlled oscillator is operating at the correct frequency. A second, smaller, capacitor is used to quickly achieve phase lock with the incoming data signal. The use of two oppositional signals to drive the capacitors allows them to more quickly be charged or discharged to the proper voltage level to obtain both frequency and phase lock with the incoming data signal. Thus, the circuit is able to quickly acquire lock during power-up, or reacquire lock under circumstances where the operating condition of the circuit changes suddenly. The circuit always locks to the correct frequency, as opposed to a harmonic thereof.
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