| 摘要 |
<p>The synchronising circuit synchronises an oscillator to the frequency of the colour sync. signal in a PAL colour t.v. signal, and is effective even at small signal to noise ratios. The PAL switch is synchronised by a signal of half the line frequency. A gating pulse, whose position coincides with that of a colour sync. interval, is added to the half-line-freq. signal in a first AND-gate. The output of the first sync. demodulator is amplified and held. The held voltage level is used to control the frequency of the oscillator.</p> |
