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Voltage gain in power amplifier

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Member level 5
May 13, 2011
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What should be the minimum voltage gain in a class C power amplifier.Is it ok if the voltage gain is less than 0.5 in PA and still hyave the efficiency greater than 70%:?:

Classification of amplifier is determined by efficiency. That's all.
Your voltage gain at 0.5 less than unity isn't important.

Well more specifically you want your power added efficiency... which will be low if your signal gain is poor.

PA = Powe Amplifier. It turns a voltage swing across a high impedance ( Pin = V^2/R) into a voltage swing across a lower impedance. It was a good term to use in the days of the thermionic valve where Pin was miniscule (very high input impedance) and Pout was perhaps 1000 times greater. With the advent of the junction transistor, with low input imedances, hence significent input power, the overall power gain could easily be as low as 3. MOSFETs with their high imput impedance, have got back to being more like a valve. PA is the term really for the output stage of a HiFi set or a transmitter rather then used for signal manipulation.

True indeed...
In fact today, audio is going either Class A, AB or Class D.
Class C is just a classroom topic.

For power, Class D is current trend.

Although it's not explicitely said in the initial post, I would expect that the question refers to RF PA (the only domain of class C according to my knowledge). If so, the operation frequency, transistor type (MOS or BJT) and circuit topology should be known for a specific answer.

It's obvious however, that a low power gain (e.g. < 15-20 dB) won't be compatible with high overall efficiency.

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