BeginnerTopic 27 of 104Electronics & Embedded
Frequency response of amplifiers
Gain falls at low and high frequencies due to coupling capacitors and parasitics.
In depth
Low-frequency roll-off comes from coupling and bypass capacitors; high-frequency roll-off from parasitic and Miller capacitances. Bandwidth is between -3 dB points. Gain-bandwidth product is constant for single-pole amplifiers. Bode plots predict step response.
Key points
- Dominant pole
- Cascading narrows bandwidth
- Rise time≈0.35/BW
ExampleAn audio amplifier needs flat response from 20 Hz to 20 kHz.
What is Frequency response of amplifiers?
Gain falls at low and high frequencies due to coupling capacitors and parasitics.
Why is it important to understand frequency response of amplifiers?
Amplifiers have a useful frequency range set by capacitors and device capacitances, and knowing it prevents audio roll-off and RF loss.
Why does gain fall at low frequency?
Coupling and bypass capacitors have impedances that rise as frequency falls, so less signal reaches the stage.
Why does gain fall at high frequency?
Device capacitances and stray capacitance shunt the signal to ground as frequency rises, reducing the gain.
How is Frequency response of amplifiers used in practice?
Typical applications include checking the bass response of an audio coupling network, predicting the high-frequency limit of a wideband amplifier and choosing coupling capacitors for a low-frequency sensor amplifier.
What should I learn before Frequency response of amplifiers?
Study "Feedback in amplifiers" first (topic 26 of 104 in Electronics & Embedded). It covers the groundwork this topic builds on.
What are the key points of Frequency response of amplifiers?
Dominant pole. Cascading narrows bandwidth. Rise time≈0.35/BW.
Can you give an example of Frequency response of amplifiers?
An audio amplifier needs flat response from 20 Hz to 20 kHz.
What comes after Frequency response of amplifiers?
The next topic is "Power amplifiers", which builds directly on this one.
How difficult is Frequency response of amplifiers?
It is classed as Beginner in Electronics & Embedded (topic 27 of 104). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.