Why? In short, you see a "distortion" because the BJT's is a nonlinear device and the voltage gain is not constant but it changes together with the Ic current exponentially.Why is it distorted?
The distortion is due to the non-linear relation between the base current vs. the base-emitter voltage.there is thd of 8.3%
The distortion is due to the non-linear relation between the base current vs. the base-emitter voltage.
If you add some negative feedback (at the cost of a loss in gain), then the distortion will be smaller.
For example, adding an unbypassed emitter resistor of 100 ohms reduces the THD to <0.5% (below).
It also reduces the gain to about 50.
View attachment 216054
Hi Jony130 - I am afraid that you have mixed Vin with the DC value Vbe.Why? In short, you see a "distortion" because the BJT's is a nonlinear device and the voltage gain is not constant but it changes together with the Ic current exponentially.
Av = Vout/Vin = - (Rc * Is)/Vt * exp^(Vin/Vt) (with CE capacitor across RE ressitor)
Where Vt = 26mV is a Thermal Voltage
But it is the task of C3 to increase the gain......that is its only purpose. If the distortion is to large, the classical method is to shunt only a part of the emitter resistor with a capacitor (the resistor must be split up in two resistors).Crutschow is right. Problem is C3. That capacitor has it reactance impedance is paralleled RE, dramatically increase AC gain and reduce negative feedback which related directly to distortion (actually it is more complicated).
Yes - thats what happens very often in electronics: We have to find a trade-of between two (or more) conflicting requirements.When you split resistor, you increase total impedance (AC gain reduced).
It depends, of course, on the lowest frequency to be amplified. All three capacitors cause a high-pass behaviour.how did the designer compute the three capacitor values?
They are determined by the desired low-frequency rolloff.how did the designer compute the three capacitor values?
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