| 摘要 |
PURPOSE:To operate a de-emphasis circuit in excellent manner, by detecting the DC level of tip a synchronizing signal to be sampled and adjusting the bias level of a variable bias circuit according to this DC level. CONSTITUTION:A variable bias circuit 2 includes a synchronizing signal and stored on a medium through frequency modulation. The output of this circuit is transmitted to a de-emphasis circuit 3. The synchronizing signal in the output signal of the circuit 3 is sampled with the synchronizing signal from a synchronizing generation circuit 5 and the DC component at the tip of this signal is detected at a sample hold circuit 4. A voltage corresponding to the detected DC level is applied to the circuit 2 through the adjustment of a DC amplifying cirucit 6. Thus, the DC level of the tip of the synchronizing signal to be de-emphasized is kept constant to increase dynamic range and lower the operating voltage. |
