Exam Question
Q1
List the factors that cause deterioration of the frequency response of a transistor amplifier. Explain how each factor affects the performance of the amplifier and the portion of the frequency range where it is effective.
(16)
ETO
ETO Exam papers
📅 Jan 2026
Reference Answer
### Introduction
The frequency response of a transistor amplifier describes how its gain varies with the frequency of the input signal. An ideal amplifier would have a constant gain across all frequencies, but in practice, the gain is constant only over a limited range known as the mid-band. The gain decreases at both low and high frequencies. This deterioration is caused by various capacitive elements in the circuit, some of which are intentionally added (coupling and bypass capacitors) and some of which are inherent to the transistor and circuit layout (parasitic and stray capacitances).
The performance is typically characterized by the lower cut-off frequency (f_L) and the upper cut-off frequency (f_H), which are the points where the voltage gain drops to 70.7% (or -3dB) of its mid-band value. The range between f_L and f_H is the amplifier's bandwidth.
### Mid-Frequency Range Analysis
The frequency response of a transistor amplifier describes how its gain varies with the frequency of the input signal. An ideal amplifier would have a constant gain across all frequencies, but in practice, the gain is constant only over a limited range known as the mid-band. The gain decreases at both low and high frequencies. This deterioration is caused by various capacitive elements in the circuit, some of which are intentionally added (coupling and bypass capacitors) and some of which are inherent to the transistor and circuit layout (parasitic and stray capacitances).
The performance is typically characterized by the lower cut-off frequency (f_L) and the upper cut-off frequency (f_H), which are the points where the voltage gain drops to 70.7% (or -3dB) of its mid-band value. The range between f_L and f_H is the amplifier's bandwidth.
### Mid-Frequency Range Analysis
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