| 摘要 |
A circuit for automatically limiting fluctuations in the output power level of a transmitter by providing a feedback control signal which is based on the output power level. An RF signal (100) is input to a terminal of the RF detector (200). When the RF signal (100) is more negative than a bias voltage (209), a capacitor (208) begins charging. When the RF signal (100) becomes more positive than the bias voltage (209), the voltage in the charged capacitor (208) is added to the RF signal (100) and then averaged by the capacitors (214 and 206) to form voltage VE. Voltage VE in conjunction with the current setting circuitry (230) establishes a tail current (235) which is comprised of transistor (216) current (225) and the current from the RF detector (200). The tail current (235) tends to remain constant whereas the transistor current (225) is responsive to power changes in the RF signal (100) and represents the difference between the output power level of the RF power amplifier and the specified reference (110). The current (235) is amplified by current amplifier (220) to provide the feedback control signal (120). Thus, when the power of RF singal (100) increases, transistor current (225) decreases. This causes the feedback control signal to decrease the output of the RF power amplifier. Likewise, when the power of the RF signal (100) decreases, transistor current (225) increases. This causes the feedback control signal to increase the output of the RF power amplifier.
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