# Operational Amplifier

## Presentation on theme: "Operational Amplifier"— Presentation transcript:

Operational Amplifier

Ideal OP Amp Circuit model Two golden rules to perform calculations on op amps with negative feedback: iin=0, no current flow into op amp. V+=V- Typically one end of op amp is connected to ground, therefore, V+=V-= 0V, virtual ground. Often V+ is connected to ground to avoid stability problem.

Applications: building block for analog systems
Amplifiers Adders and Substractors Integrators & Differentiators Clock generators Filters Digital-to-analog converters

Using op-amps No flexibility

Let’s build a circuit……noninverting amplifier

When A is very large Suppose A=106, R1=9R, R2=R Gain:
determined by resistance ratio insensitive to A, temperature, fab variation

Why did this happen? Negative feedback
e.g. vIN=5V Suppose I perturb the circuit (e.g. force v0 momentarily to 12V somehow Stable point is when v+v- Key: negative feedback  portion of output fed to –ve input. e.g. Car antilock brakes  small corrections

How to control a high-strung device
Antilock brakes

More op amp insights: Observe, under negative feedback, We also know
 Yield an easier analysis method (under negative feedback)

Insightful analysis method: under negative feedback

Voltage follower Why is this circuit useful?
has minimum effects on previous and next circuit.

Inverting Amplifier Feedback resistor, always to negative input

If RS1=RS2=…=RSN=RS

Non-innverting Amplifier
Feedback resistor, always to negative input

Differential Amplifier: Substractor
Very useful if both signals are corrupted with noise: Electrocardiogram (EKG)