Emitter Follower Voltage Gain

129

01:02:45

The voltage gain comes from the split resistor on the right. It basically reduces the emitter degeneration effect on the transistors. The only problem is that without a transformer, you can't galvanically separate the input source from the output. Basically the input must be referenced to the mid-point of the split resistor, rather than ground. This makes the circuit unsuitable for combining with other stages on the input side. The output is ground referenced, so it's not an issue to be followed by other stages, just not preceded. 

published 2 years ago

jason9

2 years ago

The bode plot seems to indicate that the only voltage amplification greater than unity occurs due to a resonance that peaks at 708Hz (and with zero phase shift at 729Hz, the observed oscillation frequency). All other frequencies significantly above or below the resonance demonstrate no overall gain.

thebugger

2 years ago

Due to the RC filters. It's basically a Wien Bridge Oscillator. If you remove the RC chains and add a normal source at the primary of the transformer, you get gain at significant range.

jason9

2 years ago

I see. The voltage feedback to the transformer secondary provides the gain.

yereon

2 years ago

always appreciate your posts.

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