| 摘要 |
PURPOSE:To simplify the constitution in an SECAM color TV system etc. by controlling the oscillation frequency of an oscillator so that the frequency becomes the frequency of the first and the second carriers line sequentially, and obtaining modulated waves obtained by modulating each carrier line sequentially. CONSTITUTION:An FM modulated R-Y signal and a B-Y signal of the SECAM color TV system are supplied to DC shifters 20, 23 respectively. Switches 21, 28 32 are switched from a terminal 24 by a control signal Sc to be a high and a low level at every one horizontal period. One of DC shifters is shifted according to the output value of a sample hold circuit 30, and supplied as the control voltage of a voltage control type variable frequency oscillator 25. The output is compared with one of terminals 27, 29 to which the reference oscillation signals of two carriers are supplied by a phase comparator 26 and the signal corresponding to a phase difference is supplied to the sample hold circuit 32. Thus, the two cariers frequencies are generated line sequentially by changing a PLL loop at each horizontal period. |
