| 摘要 |
PURPOSE:To adjust contrast of a video signal without deteriorating high frequency characteristics of the video signal by giving the video signal to a resistance voltage division circuit consisting of a first resistor and plural second resistors, and by decoding codes from a switch means, switching any one of plural switching elements which are provided in response to second resistors respectively, and by attenuating the video signal. CONSTITUTION:When No.1 switch is selected by a binary rotary switch 70, an output of a switch 70 turns into a 4-bit signal of ''L, L, L, L'', this binary code is given to a decoder 60, a transistor 202 is energized, and the R video signal is potentially divided by a first resistor 12 and a second resistor 102 to be given to the R video amplifier 5R at the post stage. The R video signal is attenuated only by the voltage division ratio which is determined by resistors 12 and 102. Therefore, by properly selecting the resistance values of resistors 12 and 101 or 115, attenuation ratio of the 16 types desired can be obtained. For example, by properly selecting the resistor 101 or 115, the attenuation ratio of the total of 16dB can be obtained at an interval of 1dB. |
