| 摘要 |
A power control circuit comprises a signal input, a controllable attenuator, an amplifier, an output, a power detector, a reference circuit, a comparator, an external control input, an error detector, and a controller. The comparator, error detector, and controller are digital circuits realized by a microprocessor. The attenuator is between the signal input and the input to the amplifier to regulate the amplifier's output. The power detector couples to the amplifier output to generate a measurement signal representing the power at the output. The reference circuit generates a reference signal representing a predetermined minimum output when the signal input is nonzero. The comparator compares the measurement and reference signals and generates a decision signal indicating if the signal input is nonzero. The external control input receives an external control signal. The error detector is coupled to the power detector and the external control input and computes the difference between the external control signal and the measurement signal. When the measurement signal is at or above the minimum power, the controller provides an integral of the computed difference to control the variable attenuator. When the measurement signal is below the minimum power, the controller keeps the attenuator at a prior constant value.
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