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How does bypassing the emitter resistor affect the input resistance?
Emitter Bypass Capacitor When an emitter resistance is added in a CE (Common Emitter) amplifier, its voltage gain is reduced, but the input impedance increases. If the bypass capacitor is removed, an extreme degeneration is produced in the amplifier circuit and the voltage gained will be reduced.
How do you bypass a resistor?
A wire in the left circuit is shorting the 100Ω resistor. All current will bypass the resistor and travel through the short. The voltage across the 100Ω resistor is going to be zero.
How to determine the value of the bypass capacitor?
How we’re able to determine the value of the bypass capacitor that we need is based on the principle that the resistance that the capacitor offers to the AC signal should be 1/10th or less of the resistance in parallel with the capacitor. Remember that current always takes the path of least resistance.
What should be the reactance of an emitter resistor?
The typical value of an emitter resistor is 400-500Ω. The resistance is kept low so that gain on the transistor isn’t lowered too much. So let’s say we choose an emitter resistor of 470Ω. This means that we want the reactance of the capacitor to be one-tenth of 470Ω or less, which is 47Ω or lower.
But as the emitter resistance is a feedback resistor, it will also reduce the amplifiers gain due to fluctuations in the emitter current IE owing to the AC input signal. To overcome this problem a capacitor, called an “Emitter Bypass Capacitor”, CE is connected across the emitter resistance as shown.
How are cathode resistors bypassed in a capacitor?
Cathode Bypass Capacitor. A cathode resistor in a typical triode preamp is bypassed within a large capacitor to eliminate negative form of feedback is called as the cathode degeneration, which significantly increases gain.