Synchronous detector
View Patent ↗A synchronization signal detector includes a horizontal synchronization level detector, a synchronization signal extractor, a first filter circuit, and a synchronous separator. The horizontal synchronization level detector detects a horizontal synchronization detection level HL for detecting a horizontal synchronization signal from a video signal Din. The synchronization signal extractor outputs a limited signal D 1 obtained by extracting only a signal within a limit range (HL−n) to (HL+m) that is set based on the horizontal synchronization detection level HL from the video signal Din. The first filter circuit removes a high frequency component of the limited signal D 1 and outputs it. The synchronous separator detects a horizontal synchronization signal HS from the output signal of the first filter circuit.
1. A synchronous detector for detecting a synchronization signal from an input signal, the synchronous detector comprising:
a limiting circuit outputting a signal obtained by extracting a portion in a predetermined level range from an input signal, as a limited signal;
a synchronization detection section detecting a synchronization signal from the limited signal; and
a level detector detecting a slice level,
wherein the limiting circuit sets an arbitrary width including the slice level as the predetermined level range, and the synchronization detection section detects the synchronization signal based on the slice level.
2. The synchronous detector according to claim 1 , wherein the predetermined level ranges is set based on a level range of the synchronization signal.
3. The synchronous detector according to claim 2 , wherein the predetermined level range is equal to or higher than a first level and equal to or lower than a second level, and the limiting circuit outputs the limited signal that sets a signal with a lower level than the first level in the input signal to the first level and sets a signal with a higher level than the second level in the input signal to the second level.
4. The synchronous detector according to claim 2 , wherein the predetermined level range is equal to or higher than approximately a bottom level of the synchronization signal and equal to or lower than approximately a pedestal level.
5. The synchronous detector according to claim 1 , wherein the synchronization detection section includes a first filter circuit removing a high frequency component of the limited signal and outputting the signal, and a synchronous separator detecting a synchronization signal from an output signal of the first filter circuit.
6. The synchronous detector according to claim 5 , further comprising: a second filter circuit outputting a filtered signal after removing a high frequency component from an input signal, wherein the limiting circuit receives the filtered signal as the input signal and generates the limited signal from the filtered signal.
7. The synchronous detector according to claim 6 , wherein the second filter circuit is a low pass filter with a higher cutoff frequency than the first filter circuit or a band pass filter used to remove a predetermined signal.
8. A synchronous detector for detecting a synchronization signal from an input signal, the synchronous detector comprising:
a limiting circuit outputting a signal obtained by extracting a portion in a predetermined level range from an input signal, as a limited signal;
a synchronization detection section detecting a synchronization signal from the limited signal; and
a level detector detecting a slice level and a pedestal level;
wherein the limiting circuit sets an arbitrary width to the pedestal level as the predetermined level range, and the synchronization detection section detects the synchronization signal based on the slice level.
9. The synchronous detector according to claim 8 , wherein the synchronization detection section includes a first filter circuit removing a high frequency component of the limited signal and outputting the signal, and a synchronous separator detecting a synchronization signal from an output signal of the first filter circuit.
10. The synchronous detector according to claim 9 , further comprising: a second filter circuit outputting a filtered signal after removing a high frequency component from an input signal, wherein the limiting circuit receives the filtered signal as the input signal and generates the limited signal from the filtered signal.
11. The synchronous detector according to claim 10 , wherein the second filter circuit comprises a low pass filter with a higher cutoff frequency than the first filter circuit or a band pass filter used to remove a predetermined signal.
12. The synchronous detector according to claim 8 , wherein the predetermined level ranges is set based on a level range of the synchronization signal as a limited signal.
13. The synchronous detector according to claim 12 , wherein the predetermined level range is equal to or higher than a first level and equal to or lower than a second level, and the limiting circuit outputs the limited signal that sets a signal with a lower level than the first level in the input signal to the first level and sets a signal with a higher level than the second level in the input signal to the second level.
14. The synchronous detector according to claim 12 , wherein the predetermined level range is equal to or higher than approximately a bottom level of the synchronization signal and equal to or lower than approximately a pedestal level.
15. A synchronous detector for detecting a synchronization signal from an input signal, the synchronous detector comprising:
a limiting circuit outputting a signal obtained by extracting a portion in a predetermined level range from an input signal, as a limited signal; and
a synchronization detection section detecting a synchronization signal from the limited signal;
wherein the synchronization detection section includes a first filter circuit removing a high frequency component of the limited signal and outputting the signal, and a synchronous separator detecting a synchronization signal from an output signal of the first filter circuit.
16. The synchronous detector according to claim 15 , further comprising: a second filter circuit outputting a filtered signal after removing a high frequency component from the input signal, wherein the limiting circuit receives the filtered signal as the input signal and generates the limited signal from the filtered signal.
17. The synchronous detector according to claim 16 , wherein the second filter circuit comprises a low pass filter with a higher cutoff frequency than the first filter circuit or a band pass filter used to remove a predetermined signal.
18. The synchronous detector according to claim 15 , wherein the predetermined level ranges is set based on a level range of the synchronization signal as a limited signal.
19. The synchronous detector according to claim 18 , wherein the predetermined level range is equal to or higher than a first level and equal to or lower than a second level, and the limiting circuit outputs the limited signal that sets a signal with a lower level than the first level in the input signal to the first level and sets a signal with a higher level than the second level in the input signal to the second level.
20. The synchronous detector according to claim 18 , wherein the predetermined level range is equal to or higher than approximately a bottom level of the synchronization signal and equal to or lower than approximately a pedestal level.