| 摘要 |
PURPOSE:To automatically detect an input frequency in a set by correcting an external input when the output of a waveshape generation circuit is compared with the external input. CONSTITUTION:When the period of a synchronizing pulse VSYNC increases, the charging time of a capacitor 2 is prolonged. A first comparison circuit 3 confirms that a triangular voltage VCR is high and produces an output VCO. A latch circuit 4 inputs the output VCO of the comparison circuit 3 to the input of a first FF4a. When the signal VSYNC is input to the circuit 4, the data of the output VCO of the comparison circuit 3 is input to second FF4b. Then, when next synchronizing pulse VSYNC is input to the circuit 4, the data of the output VCO of the comparison circuit 3 becomes a correction input VISUB to be latched. A correction circuit 5 operates the input VISUB for an external input VSYG and outputs a correction output VOSUB. Thus, each time a synchronizing frequency is input, the frequency change is measured. Accordingly, the frequency can be effectively switched. |
