摘要 |
<p>The output level of a power amplifier (1) for amplifying an input signal (9) is controlled by a control signal (8). A signal responsive to the power amplifier output level (10) is generated by a detector (11) and input to a variable gain amplifier (3), whose gain is controlled by a control signal (4). The variable gain amplifer output (5) is compared with a reference voltage (6) by an arithmetic unit (7) to produce a difference signal which forms the control signal (8) for the power amplifier. The control signal (8) thus provides a negative feedback signal to control the power amplifier output level. The output level can be varied without varying the reference voltage (6) by varying the gain of the variable gain amplifer using the gain control signal (4). The gain is increased in order to decrease the power amplifer output level and vice versa. <IMAGE></p> |