Sunday, April 27, 2014
Operational Amplifier
What is operational amplifier ?
An operational amplifier (or an op-amp) is an integrated circuit (IC) that operates as a voltage amplifier. An op-amp has a differential input. That is, it has two inputs of opposite polarity. An op-amp has a single output and a very high gain, which means that the output signal is much higher than input signal. An op-amp is often represented in a circuit diagram with the following symbol:
These amplifiers are called "operation" amplifiers because they were initially designed as an effective device for performing arithmetic operations in an analog circuit. The op-amp has many other applications in signal processing, measurement, and instrumentation.
Feed back
An ideal opamp has infinite gain. It amplifies the difference in voltage between the + and - pins. Of course in reality this gain is not infinite, but still quite large.
Why feed back is needed ?
The output of the opamp (at to some extents the input also) is constrained by the power supply, we can't get out more than the supply puts in.If we simply put signals into the opamp without feedback it would multiply them by infinity and get a binary output (it would saturate at the supply rails)So, we need some way of controlling the gain. That is what the feedback does.
Pros:
- Can increase or decrease input impedance (depending on type of feedback)
- Can increase or decrease output impedance (depending on type of feedback)
- Reduces distortion (increases linearity)
- Increases the bandwidth
- Desensitizes gain to component variations
- Can control step response of amplifier
Cons:
- May lead to instability if not designed carefully
- Amplifier gain decreases
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| LM741 The opamp that the group is using |
