| 摘要 |
In a feedback loop level control circuit for an RF source, the RF output is sensed and compared to a reference level which determines the desired output power level. The difference between the output sample and the reference level constitutes an error signal which is applied to an integrator. The reference level is summed with the output of the integrator and the resulting sum is used to control a modulator which variably attenuates the RF output. When the system is operating in a pulse amplitude modulation mode, the reference level signal is modulated and compared to a threshold signal that determines the lowest output level that can be accurately sensed. If the modulated reference level is above the threshold, the feedback loop is closed, otherwise when the modulation signal reduces the output power level to a level which is too low to detect accurately, the feedback loop is opened.
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