| 摘要 |
1,257,520. Automatic gain control; sonar systems. THOMSON C.S.F. 4 Dec., 1969 [11 Dec., 1968], No. 59370/69. Headings H3Q, H4D and H4R. An automatic gain control for signal supplied by a sonar system comprises an attenuator 1 whose loss is controlled by signals derived from the output of the amplifier 2 via two control circuits. One control circuit includes a lowpass filter 5 following a rectifier 3, to provide a rising gain to compensate for the approximately exponential fall in signal level with distance along the reflecting surface, and hence with time, while the other control circuit includes a voltage selector 11 to pass only control signals exceeding a predetermined amplitude and thus provide a fast-acting compression of signal spikes likely to saturate the amplifier. The signals from the two control circuits are fed to control the impedance of a f.e.t. S in the attenuator 1 via a maximum voltage selector formed by the diodes D 3 and D 4 . Instead of controlling the loss in the attenuator the control signal may control the gain of amplifier 2. |
