| 摘要 |
A radio frequency (r.f.) amplifier power control system comprises an r.f. power amplifier for supplying r.f. transmission power to an antenna, a current sensing resistor via which operating current is fed to the power amplifier, a differential amplifier having a first input terminal to which a feed-back voltage derived from the sensing resistor indicative of r.f. transmission power is fed and a second input terminal to which a reference voltage is fed thereby to produce, in the presence of a voltage difference between the feed-back voltage and the reference voltage, a control voltage for the power amplifier, whereby the transmission power is controllable in dependence upon the reference voltage, and a shunt which is fed with current from the sensing resistor. The impedance of the shunt is arranged to vary responsively to the control voltage.
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