Sync separator apparatus
View Patent ↗An input video signal is inputted into a first clamp circuit, and then inputted into a second clamp circuit as a clamped video signal so as to be inputted into a switch circuit. The second clamp circuit uses a clamp pulse for clamping a video signal within the period of the sync signal that has been created by a clamp timing generator in the rear stage, and outputs a clamped video signal. The video signal has been clamped so as to be pulled into a constant DC voltage, and absorbs the waviness of a sag that superimposes the video signal. This video signal makes it possible to gain a sync output signal which has been sync separated from a sync separator circuit and has no jitter in the output.
1. A sync separator apparatus, comprising:
a first clamp circuit for sync tip clamping a video signal which is inputted;
a second clamp circuit for clamping the output from said first clamp circuit according to predetermined timing;
a switch circuit for selecting and outputting either the output from said first clamp circuit or the output from said second clamp circuit; and
a sync separator circuit for separating and extracting a sync timing signal that is included in said video signal from the output from said switch circuit.
2. The sync separator apparatus according to claim 1 , further comprising a clamp timing generator for generating a timing pulse, which defines said predetermined timing according to which said second clamp circuit clamps, from a sync timing signal that has been extracted by means of said sync separator circuit.
3. The sync separator apparatus according to claim 2 , further comprising a format detection circuit for determining the format of said video signal on the basis of a sync timing signal that has been extracted by means of said sync separator circuit, and generating format information which corresponds to each of the formats of the video signal.
4. The sync separator apparatus according to claim 3 , further comprising an AFC (Automatic Frequency Control) circuit for carrying out a phase locked loop operation using a sync timing signal that has been extracted by means of said sync separator circuit as a reference input signal.
5. The sync separator apparatus according to claim 4 , wherein said switch circuit uses the timing according to which the phase locked loop in said AFC circuit is converted from the locked state to the unlocked state as the timing according to which the output from said second clamp circuit is switched to the output from said first clamp circuit.
6. The sync separator apparatus according to claim 3 , wherein
said clamp timing generator changes the period of said timing pulse in accordance with the width of the sync signal that differs depending on the format of said video signal on the basis of said format information that has been generated by said format detection circuit, and
said second clamp circuit operates in response to said timing pulse.
7. The sync separator apparatus according to claim 3 , wherein said second clamp circuit changes the gain of the clamping in accordance with the period characteristics of the sync signal that differ depending on the format of said video signal by using said format information, and pulls said video signal into a clamp voltage.
8. The sync separator apparatus according to claim 3 , wherein
said format detection circuit detects the vertical sync timing of the field timing or the frame timing of the video signal, and
said switch circuit uses the vertical sync timing of the field timing or the frame timing of the video signal which have been detected by said format detection circuit as the timing according to which the output from said first clamp circuit is switched to the output from said second clamp circuit.
9. The sync separator apparatus according to claim 2 , wherein
said timing pulse that is generated by said clamp timing generator has a predetermined delay from the edge of said sync timing signal that has been extracted by means of said sync separator circuit, and
said second clamp circuit operates in response to said timing pulse.
10. The sync separator apparatus according to claim 1 , wherein said second clamp circuit operates within the sync signal period and carries out a clamp operation where the front edge portion is pulled into a constant DC voltage.
11. The sync separator apparatus according to claim 1 , wherein said second clamp circuit carries out a clamp operation where the gain of the clamping is increased during the period of the vertical sync signal, and the gain of the clamping is decreased during the period of the horizontal sync signal on the effective display.
12. The sync separator apparatus according to claim 1 , wherein said switch circuit selects and outputs the output from said first clamp circuit in the case where said format information is not confirmed, and selects and outputs the output from said second clamp circuit in the case where said format information is confirmed.