Consider the following π-Model at high frequency. Where r b is t
Consider the following π-Model at high frequency.
Where rb is the base spreading resistance, Cn is the diffusion capacitance of emitter junction and Cu is the transition capacitance of the collector junction.
Which of the following statements regarding the Miller effect is/are TRUE?
A. It occurs in common Emitter configuration.
B. Miller effect refers to an increase in Input capacitance of common emitter configuration.
C. Due to the Miller effect, input impedance increases at high frequencies.
D. Due to the Miller effect, the Bandwidth of the common emitter configuration decreases
Please scroll down to see the correct answer and solution guide.
Right Answer is:
SOLUTION
Miller Effect:
Miller effect occurs in the common-emitter configuration.
It refers to an increase in input capacitance of CE configuration due to the appearance of Cm ∥ Cn
Cin = Cm + Cn
Where, Cm – Miller capacitance
Cm = Cμ (1 - Av)
1 - Av is a Miller Multiplies
Due to the increase in Input capacitance, it has 2 undesired effects:
(1) Higher 3 dB frequency or Bandwidth of CE amplifier decreases
\({f_H} \propto \frac{1}{{{C_{in}}}}\)
BW ≃ fH
\(BW \propto \frac{1}{{{C_{in}}}}\)
(2) The input impedance of the CE amplifier decreases at high frequencies.
\({Z_{in}} = {r_\pi }\parallel {X_{{C_{in}}}}\)
\({C_{in}} \uparrow \to {X_{{C_{in}}}} \downarrow \)
Hence Zin ↓
When Zi ↓ → Ri’ (Input resistance including biasing resistor)↓
\(\frac{{{V_0}}}{{{V_s}}}\)(Gain) decreases
Miller effect is undesired it will disturb the operation of common emitter amplifies at high frequencies
Option (1), (2), and (4) are correct.
