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Why input resistance of a transistor is low?
Due to it, a small change in emitter current. This means that a small signal voltage variation at the input of the transistor produces a large emitter current variation. This shown that the input resistance of a transistor is low. This shows that the output resistance of the transistor is high.
Why is resistance low in output?
Low impedance in a voltage source is usually preferred because it helps to keep out the noise out of the circuit and maintain a stable output voltage. A typical power supply acts as an ideal power supply with a series resistor connected in series with its output.
How is input resistance related to output resistance?
The closed-loop input resistance is effectively ( Ri ‖ Rf )/ (1 + GH ). The effect of negative feedback on output resistance can be analyzed by representing the output as a Thévenin equivalent voltage source with internal voltage of v and open-loop output resistance of Ro. An output voltage of vo is produced by a current io applied to the output.
How to calculate the input resistance of a microphone?
By writing the circuit equations for Fig. 6.2 a, show that υo ≈ υi and show that the input impedance Zi = (1 + A) Ri. Give numerical values. 7. Repeat the calculations in Example 6.2 when the input device is a microphone with υs = 10 mV (rms) and source impedance Rs = 50 kΩ.
Why is input resistance larger in noninverting circuit?
For the noninverting op-amp circuit of Fig. 3.6a, the effective op-amp differential input resistance is made larger by feedback. Since v− tracks v+ as feedback, the differential voltage across the input terminals is the error voltage.
Which is the ideal input resistance for an amplifier?
If the voltage source resistance rs is variable or unknown, the attenuation of the divider and the overall voltage gain will be too. To avoid this, the ideal amplifier input resistance is infinite, so vin = vi independent of rs. FIG. 2.4. Amplifier input and output loading for (a) voltage and (b) current amplifiers.