| 摘要 |
<p>The amplifier receiving an input signal (Ve) applied across input terminals (E1, E2) provides an output across a load (2) via output terminals (S1, S2). The circuit includes an operational amplifier (5) and a junction transistor (10) whose base is connected to the operational amplifier output. The emitter is connected to the second output terminal (S2) via a resistor (RE) and the collector is connected to the first output terminal. A feedback circuit consists of a resistance (Rb) between the collector and the operational amplifier (+) input, and a second resistance (Ra) connecting this input to the input signal. The emitter of the transistor is connected to the (-) input of the op. amplifier. The effective output impedance of the amplifier is determined as a function of the three resistors (Ra, Rb, RE) which may be chosen to give the required value. The impedance of the amplifier may be matched to a load- for example a telephone line if the amplifier is used in the first stage of a telephone link.</p> |
