| 摘要 |
A nonlinear signal transducer U, such as a light-emitting diode or a semiconductive laser, is maintained at a suitable operating point by a constant biasing current and receives an electrical input signal by way of a series resistor R from a main amplifier AM of variable gain. The output voltage of the main amplifier is detected and integrated to provide a first reference voltage which is compared with the load voltage of the transducer U in a differential amplifier AE1, forming part of a first feedback loop, to adjust a voltage generator GT controlling the output voltage of the main amplifier AM so as to eliminate any voltage drop across the series resistor R as long as the input signal is absent or has an instantaneous magnitude equal to its mean value. A second feedback loop includes a peak-to-peak detector DP which emits a voltage proportional to the signal amplitude, that voltage being compared with a second reference voltage in a differential amplifier AE2 serving to adjust a current generator GC1 which controls the gain of the main amplifier AM. The second reference voltage may be varied manually or in response to changes in the output of the transducer U. |
