Analog Electronics – Page 33
Frequency Response of Amplifiers
The frequency response of an amplifier describes how the gain of the amplifier varies with signal frequency.
It shows the relationship between amplifier gain and input signal frequency.
Three Frequency Regions
- Low Frequency Region
- Mid Frequency Region
- High Frequency Region
Low Frequency Region
- Gain decreases at low frequencies
- Due to coupling capacitors and bypass capacitors
- Capacitive reactance becomes large
Mid Frequency Region
- Gain remains constant
- Amplifier operates normally
- This region is called midband gain
High Frequency Region
- Gain decreases at high frequencies
- Due to internal transistor capacitances
- Parasitic capacitances affect performance
Cutoff Frequencies
The frequencies at which the gain drops to 70.7% of maximum gain are called cutoff frequencies.
- Lower cutoff frequency = fL
- Upper cutoff frequency = fH
Gain at cutoff = 0.707 × Maximum Gain
Bandwidth
The bandwidth of an amplifier is the difference between upper and lower cutoff frequencies.
Bandwidth = fH − fL
Example Problem
If an amplifier has:
- Lower cutoff frequency = 100 Hz
- Upper cutoff frequency = 100 kHz
Find bandwidth.
BW = fH − fL
BW = 100000 − 100
BW = 99.9 kHz
Important GATE Points
- Midband gain is constant
- Cutoff occurs at 70.7% gain
- Bandwidth determines amplifier performance
- Higher bandwidth means better amplifier
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