Picture signal detecting apparatus

A picture signal detecting apparatus comprising:

• a phase locked loop configured to generate a carrier wave reproduced on the basis of a picture modulated signal in which an original carrier wave has been amplitude-modulated in accordance with a picture signal;
• a detecting circuit configured to synchronously detect the picture signal from the picture modulated signal using the reproduced carrier wave;
• a sample-and-hold circuit configured to sample and hold a control voltage of a voltage controlled oscillator in the phase locked loop in a locked state of the phase locked loop when the picture modulated signal is in a state of normal modulation that is less than or equal to a predetermined degree of modulation threshold value, and output the control voltage as a hold voltage;
• an overmodulation detecting circuit configured to detect a state of overmodulation in which the degree of modulation threshold value has been exceeded;
• and
• a control voltage switching circuit configured to input the hold voltage to the voltage controlled oscillator instead of the control voltage in the state of overmodulation;
• wherein the sample-and-hold circuit includes:
• (1) a synch separator configured to generate a sampling gate pulse corresponding to a specified signal period within a horizontal scanning period from the picture signal,
• (2) a comparator configured to generate a comparator output based on a comparison of the control voltage and the hold voltage, and
• (3) a shift register configured to successively approximate the control voltage based on the comparator output and the sampling gate pulse.