| 摘要 |
PURPOSE:To obtain the control signal of the PAL mode without increasing the number of IC pins, in the mode switching circuit of the chrominance signal processing circuit of the NTSC VTR. CONSTITUTION:A set/reset FF is provided, which inputs a set or a reset signal based on a rectangular wave pulse synchronized with the rotation of a drum and inputted from the outside of an IC. A control signal for mode switching is obtained from an output of an SR FF only at the PAL signal without providing IC pins for mode switching. That is, since a signal inputted from an input terminal 1 is as (a) having a higher minimum potential than V1 at the PAL mode, an output waveform of the 1st SW2 is as (b) and at low at all times. An output of the 2nd SW3 goes high when an input signal potential is higher than V2 and an output waveform is as (c). Thus, an output waveform at an output terminal 9 is as (e) and a high control signal is outputted. Thus, the control signal representing the PAL mode is obtained only at the PAL mode by adding four gates through the output of the SW circuit at the input terminal of the vertical synchronizing pulse synchronized with the rotation of the drum. |
