Electrotechnics self study notes 1.20

Non exam preparation materials
1.20

Chapter 15 Basic amplifier circuit

Language and music signals of broadcasting , The image and sound signal of TV and the signal of non electric quantity transformed by the sensor contain fundamental wave and harmonic components of various frequencies . Various capacitors have different capacitive reactance to signals of different frequencies => The effect of amplification circuit on the amplitude and phase of signals with different frequencies is not exactly the same , The output signal cannot reproduce the waveform of the input signal , This produces amplitude distortion and phase distortion , Collectively, frequency distortion .
Emitter output , Common collector circuit , Output from emitter .
The output voltage is in phase with the input voltage , And has the function of following （ The magnification is close to 1）, So it is also called emitter follower .
Current amplification , High input resistance , Low output resistance .
application ： Input stage and output stage of multistage amplification circuit , Sometimes it is also connected between two-stage common emitter amplifier circuits , As buffer stage or intermediate isolation stage .
The resistance capacitance coupling amplifier circuit can only be used to amplify AC signals . But other signals are often encountered in industrial control , For example, use thermocouples （ see 1.14 Expand knowledge ） Measure furnace temperature , Because the furnace temperature changes very slowly , So what the thermocouple gives is a slowly changing voltage signal , Resistance capacitance coupling cannot be used , Only direct coupling .
The biggest problem of direct coupled amplifier circuit is zero drift （ When the input signal is zero , The output signal is not constant ）.
The most effective circuit structure to suppress zero drift is differential amplifier . The comparison input of differential amplifier circuit is commonly used in automatic control system .

Expand knowledge ：

1. Fundamental wave refers to the sine wave component equal to the longest period of the complex periodic oscillation , The frequency corresponding to this period is called the fundamental frequency .
2. harmonic ： Strictly speaking , Harmonic refers to the electric quantity whose frequency is an integral multiple of the fundamental wave contained in the current . Twice that 2 Subharmonic , Three times is 3 Subharmonic .
3. Compare input ： The size and relative polarity of the two input signals are arbitrary .