# Op Amp

An operational amplifier (op-amp) is a DC-coupled high-gain electronic voltage amplifier with a differential input and typically a single-ended output. The output voltage an op-amp produces is typically hundreds of thousands of times larger than the voltage difference between its input terminals.

Characteristics of a circuit using an op-amp are set by external components with little dependence on temperature changes or manufacturing variations in the op-amp itself, which makes op-amps popular building blocks for circuit design.

The operational amplifier is one of the most useful and important components of analog electronics. Op-amps are widely used in consumer, industrial, and scientific devices.

## Op Amp Symbol The circuit symbol for an op-amp is shown to the right, where:

• V+: non-inverting input
• V−: inverting input
• Vout: output
• VS+: positive power supply
• VS−: negative power supply

The amplifier's differential inputs consist of a V+ input and a V− input, and the op-amp amplifies only the difference in voltage between the two, which is called the differential input voltage. The output voltage of the op-amp is given by the equation: \begin{equation} V_{out} = {A_{OL} \, (V_{\!+} - V_{\!-})} \end{equation} where

• V+ is the voltage at the non-inverting terminal, V− is the voltage at the inverting terminal and AOL is the open-loop gain of the amplifier.
• The Vout voltage range is limited by the power supply voltages to VS+ and VS-.

## Ideal Op Amp Characteristics

To simplify our calculation of the various practical op-amp configurations, we assume an ideal op-amp which have the following properties:

• Infinite open-loop gain (AOL = ∞)
• voltage range at the output is limited by the power supply voltages to maximum VS+ and minimum VS-. If VS+ and VS- are not specified, then the output voltage range is assumed to be infinite.
• Infinite bandwidth with zero phase shift and infinite slew rate
• Infinite input impedance and so zero input current (I- = I+ = 0)
• Zero input offset voltage
• Zero output impedance
• Zero noise
• Infinite Common-mode rejection ratio (CMRR)
• Infinite Power supply rejection ratio.

## Feedback Configurations

Op amps circuits have the following 3 feedback configurations

• Open Loop - there is no feedback. An opamp used in this configuration is also called a comparator. • Negative Feedback - a fraction of the output signal is connected back to the inverting input (V-). Circuits using this configuration are considered linear op-amp circuits and includes For negative feedback circuits only, we can assume the following (why?) \begin{equation} V_+ = V_- \end{equation}
• Positive Feedback - a fraction of the output signal is connected back to the non-inverting input (V+). Circuits using this configuration includes
• Schmitt Trigger
• Schmitt Trigger Oscillator With advertising revenues falling despite increasing numbers of visitors, we need your help to maintain and improve this site, which takes time, money and hard work. Thanks to the generosity of our visitors who gave earlier, you are able to use this site at no charge.

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