| 摘要 |
<p>An automatic gain control system incorporating a novel amplifier of controllable gain is described. The amplifier is d.c. coupled throughout and capable of wideband operation. It employs a cascoded differential transistor amplifier for producing the principal voltage gain supplemented by input and output emitter followers. Gain control is achieved by the application of gain control potentials to the bases of the upper rank transistors. Gain reduction is produced first in the upper rank by the controlled degeneration produced by a pair of nonlinear impedances in series with the emitter leads of the upper rank transistors, and sequentially in the lower rank transistors by the controlled degeneration produced by two pairs of nonlinear impedances coupled in a degenerative feedback path about the lower rank transistors and in the input circuit to a pair of input emitter followers. In addition, the amplifier produces an indication of gain control action which, when the amplifier is used as an intermediate frequency amplifier of a television system, permits one to derive a second gain control signal, which after thresholding may be used for further gain reduction in the tuner. The amplifier is adapted for integrated circuit fabrication.</p> |
