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100kHz - 3.5MHz
Output maintains a constant 1.5V peak-to-peak
Simulates terribly on here as transients take forever, works amazing in real life. The main amplifying transistor the BF199, the FET is a 2N7000, the dc amplifying transistor is the BC548, and the diode is a 1N5711 Schottky diode.
The purpose of this circuit is to maintain a constant amplitude sine-wave for the entire frequency range. This is not possible without AGC action as the Miller effect of common-emitter amplifiers attenuates higher frequencies, simulated as a 33pF capacitor between the collector and base.
The idea is to open up a bypass channel in parallel with the 2.2k resistor to allow more current to flow which increases the gain of the amplifier. The half-wave rectifier on the output monitors the signals amplitude. If the amplitude increases too much, the FET’s gate is turned more off which decreases current and reduces the gain and amplitude of the output signal. If the signal is too low in amplitude, the FET’s gate is turned more on which increases current and increases the gain. A negative feedback loop that keeps the amplitude steady at 1.5V.
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