Department of CNET Electronic Circuit II Chapter 1 Mohammed Abdul Gaffar

Amplifier strengthens the weak signal. I/p Signal o/p Signal Amplifier Definition Amplifier strengthens the weak signal. I/p Signal o/p Signal Amplifier

OPERATIONAL AMPLIFIER An operational amplifier  (often op-amp or op amp) is a DC coupled high-gain electronic voltage amplifier. Op-Amp primarily used to perform mathematical operations such as addition, subtraction, integration and differentiation.   Symbol The OP-AMP always has two inputs and one output. +Vcc & -Vee are the biasing voltages.

Operational Amplifers Operational amplifiers (op-amps) are very high gain dc coupled amplifiers. One of the inputs is called the inverting input (-); The other is called the Noninverting input. (+) Usually there is a single output.

Terminals

Internal Circuit of Op-Amp

Ideal And Practical Op-Amp Ideal Op-Amp Infinite gain. Infinite input resistance. Zero output resistance (order of 10’s of ohms) Infinite bandwidth (practically restricted by slew rate). Practical Op-Amp Practically Gain is of the order of 10^5 and is a function of frequency. Gain decreases linearly with slope of 6db/octave, exhibits the characteristic of low pass filter with gain. Input resistance is of the of mega ohm Order due to differential stage at the front end. Output resistance order of tens of ohms. Practically bandwidth of Op-amp restricted by slew rate. Practical Op-amp exhibits offsets and non linearity.

Characteristics of Ideal op-amps Infinite voltage gain, ∞ The Ideal Op-Amp Characteristics of Ideal op-amps Infinite voltage gain, ∞ Infinite bandwidth, and Infinite input impedance/Resistance. In addition, the ideal op-amp has zero output impedance.

Finite gain or very large gain. Finite bandwidth or very high gain. The Practical Op-Amp Finite gain or very large gain. Finite bandwidth or very high gain. And Finite or very big input impedance, Small output impedance.

Block Diagram Internally, the typical op-amp has a differential input, a voltage amplifier, and a push-pull output. the differential amplifier amplifies the difference in the two inputs.

Points for OP-AMP Block diagram Internally the OP-AMP has three amplifier stages. The first stage is the Differential amplifier, it has two inputs and two outputs. The second stage is Voltage amplifier also called as gain stage. It also has two inputs and two outputs. The third stage is Push-Pull amplifier, which has two inputs and only one output.

Basic Differential Amplifier Input stage. Circuit Diagram

Points about the Basic Differential Amplifier. Basic Differential Amplifier is the first stage of the Operational Amplifier. It has two inputs and two outputs. It has the ability to amplify the difference of inputs. If both the inputs are same the output will be zero.