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## The principle of high efficiency of class C power amplifier is its small through angle , The reason why it is not distorted is ：

Because the load is a resonant loop , Even if the conduction angle is less than 180, But the resonance circuit LC Will store energy . Give the resonant circuit a fixed frequency signal , The output terminal outputs a complete AC sinusoidal signal .

## Why should class C power amplifier use resonant circuit as load ?

1. The distorted collector current pulse can be transformed into an undistorted output cosine voltage .

2. By adjusting the of the resonant circuit LC Resonant resistance R Equal to the collector load required by the amplification tube , Achieve impedance matching .

3. Frequency selection , Select the frequency signal that the amplifier needs to amplify .

## Class C power amplifier works in overvoltage state , Why are there pits in the current waveform ？

iC When reaching the saturation zone , Will follow uBE It decreases with the increase of .

## LC Relationship between oscillator stability and quality factor

Affect the oscillation frequency w Parameters of

Q The bigger it is , same △φ Caused by the △ω The smaller .

As shown in the figure ：Qe’>Qe,△ω’osc1<△ωosc1.

Therefore, increasing the quality factor will increase LC Stability of resonant circuit .

summary ：Q The higher the value , The smaller the frequency change caused by parameter change , The smaller the frequency stability .

## Why does the output of high frequency power amplifier have higher harmonics

Because the high frequency power amplifier works in class c , Both the base current and the collector current are cosine periodic pulses （ Not a complete cosine periodic signal ）, It can be expressed by Fourier series , Its Fourier expansion is ：

Therefore, the output will have high-order harmonics . The voltage transmission coefficient of the quality index of the envelope detector Located in vo(t) Given a specific value Vo Under the circumstances ,id The conduction angle is θc： 1

The voltage transfer coefficient is defined as ：

The first figure shows （Vo>>VD）： 1

because id The output is a cosine pulse signal , Fourier expansion decomposition is performed to obtain ：

To get Vo：

however vo(t) It changes over time , So the conduction angle changes at first , Finally, because the circuit is stable , The conduction angle is stable . In the end ：

summary ： According to the Fourier series analysis and broken line analysis of cosine pulse signal , The voltage coefficient obtained is approximately equal to cosθc, And when R>>Rd when ： The voltage transfer coefficient is approximately equal to 1.