| 摘要 |
PURPOSE:To detect securely the + or -90 deg. discontinuity in phase of a reproduced color burst signal by detecting the phase discontinuity by phase-detecting the reproduced color burst signal and the output of a reference oscillator shifted in phase by -90 deg.. CONSTITUTION:The output signal of burst gate circuit 51 is inputted to phase detecting circuits 52 and 55 and also inputted to envelope detecting circuit 105 generates a signal that is held at a high level for a period equal to the period of a color burst signal. The output of reference oscillator 56, on the other hand, is shifted by -90 deg. and inputted to circuit 52. The detection output of circut 52 is supplied to 0 deg. detecting circuit 101 and 180 deg. detecting circuit 102, which compare the color burst signal with a reference phase and, when the phase shift is within the range between + or -60 deg. and 180 deg.+ or -60 deg., output high-level signals respectively. Output signals of circuits 101 and 102 are inputted to AND circuit 106 together with the output of circuit 105 by way of OR circuit 103 and inverter circuit 104. Therefore, circuit 106 outputs a signal that shows the + or -90 deg. discontinuity detection of the phase of the reproduced color burst signal. |
