| 摘要 |
<p>A frequency translation phase-locked loop (PLL) is provided for detecting the audio information from a television signal. A voltage controllable oscillator (VCO) having a nominal oscillation frequency equal to the frequency difference between the intermediate frequency (IF) picture and sound carriers provides one input to a mixer and a substantially unmodulated picture carrier is supplied as the other input to the mixer. A phase detector has as its first input the output signal from the mixer and as its second input the sound carrier. A lowpass filter coupled between the output of the phase detector and a control input to the VCO completes the PLL. The detected audio information is provided at the output of the lowpass filter. Furthermore, the PLL can provide a defect control signal which, when applied to compensation circuitry, reduces impulse noise effects in the video information.</p> |
