Broadcast band RF amplifier

Posted on Dec 29, 2012

The circuit has a frequency response ranging from 100 Hz to 3 MHz; gain is about 30 dB. Field-effect transistor Ql is configured in the common-source self-biased mode; optional resistor Rl sets the input impedance to any desired value. Commonly, it will be 50 ohms. The signal is then direct-coupled to Q2, a common-base circuit that isolates the input and output stages and provides the amplifier's exceptional stability. Q3 functions as an emitter follower, to provide low output impedance (about 50 ohms). For higher output impedance, include resistor R8.

Broadcast band RF amplifier
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It will affect impedance according to this formula: R8 - Rout-50. Otherwise, connect output capacitor C4 directly to the emitter of Q3.

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