| 摘要 |
<p>A levelling control arrangement for an RF transmitter circuit which additionally compensates for filter ripple, i.e. frequency dependant power variations caused by the filter (7) disposed between a transmitter amplifier (3) and an antenna (8). The forward and reflected power is sampled by a dual directional coupler (5) between the amplifier (3) and the filter (7). Signals Vfwd and Vrev are thus obtained indicative of the forward and reflected power levels respectively. The reflected signal Vrev is subtracted from the forward signal Vfwd at comparator (22) and the difference signal Vdiff is compared with a reference signal Vref at comparator (25) to produce a signal Vc which is used to control the gain of the amplifier (3) in such manner that the power developed by the amplifier increases as the signal Vrev increases and vice versa. To protect against excessive reflected power levels a limiter (23) may be included which causes the power developed by the amplifier to be reduced only if Vrev exceeds a pre-set threshold.</p> |
