| 摘要 |
PURPOSE:To always retain a white noise level constant by a method wherein a level control of an attenuator is always defined within a just previous repeating period. CONSTITUTION:A video signal which is received in a receiving circuit 1 and is sent out of an amplifier 2 is sent to a next stage and along with this, it is lead to an attenuator 6 and a change-over switch 7. A white noise passing through the change-over switch 7 enters a low frequency filter 8 and it is sent out of the low frequency filter 8 as a signal of a DC level having a value equal to a mean value of a white noise, and then, it is retained in a sample hold circuit 9 in the next stage. A sample hold value in the sample hold circuit 9 is amplified through an amplification circuit 10 and is entered into a control terminal of the attenuator 6. The white noise level in the video signal sent out of the attenuator 6 is always limited within a constant value. |
