| 摘要 |
An RF modulator comprises an RF carrier oscillator 17 having a resonance circuit including a variable capacity diode capable of varying the frequency of oscillation, the RF carrier oscillator outputting a carrier to a mixer 15; a frequency synthesiser circuit 18 for receiving the output signal of the RF carrier oscillator and for outputting phase comparison information formed by phase comparing the carrier oscillator signal and a signal generated by a reference frequency oscillator; a control circuit 19 for receiving the phase comparison information and detecting the deviation from a desired phase for controlling the frequency of oscillation of the RF carrier oscillator 17 to a predetermined frequency; and a voltage varying circuit 20 for applying a predetermined voltage on the basis of the output signal of the control circuit 19 to vary the junction capacity of the variable capacity diode in the RF carrier oscillator 17 by means of an inverse bias voltage to thereby vary the frequency of oscillation of the RF carrier oscillator. The controller 19 may include a microcomputer or other suitable hardware. The control loop arrangement enables uniform performance of the oscillator 17 to be maintained over a wide variable frequency range. The modulator may form part of VCRs, VCPs or satellite receivers. <IMAGE> |
