Chapter: Electronic Circuits : Frequency Analysis of BJT and MOSFET Amplifiers
General shape of frequency response of amplifiers
General shape of frequency
response of amplifiers
An audio
frequency amplifier which operates over audio frequency range extending from 20
Hz to 20 kHz. Audio frequency amplifiers are used in radio receivers, large
public meeting and various announcements to be made for the passengers on
railway platforms. Over the range of frequencies at which it is to be used an
amplifier should ideally provide the same amplification for all frequencies.
The degree to which this is done is usually indicated by the curve known as
frequency response curve of the amplifier.
To plot
this curve, input voltage to the amplifier is kept constant and frequency of
input signal is continuously varied. The output voltage at each frequency of
input signal is noted and the gain of the amplifier is calculated. For an audio
frequency amplifier, the frequency range is quite large from 20 Hz to 20 kHz.
In this frequency response, the gain of the amplifier remains constant in
mid-frequency while the gain varies with frequency in low and high frequency
regions of the curve. Only at low and high frequency ends, gain deviates from
ideal characteristics. The decrease in voltage gain with frequency is called
roll-off.
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