**Basics of Operational Amplifier**

Operational amplifier is so named as it is
used to perform mathematical operations such as addition, subtraction,
multiplication, differentiation, integration and many more. As op-amp has wide
range of applications, some of its various applications are in industrial,
communication, computer, control, and medical applications in additional with
them in military applications too.

An
integrated circuit manufacturing industries incorporates integrated
transistors, diodes, resistors and capacitors within op-amp ICs. So it is an
extremely versatile device which has countless applications in many more areas.

Since
the op-amp is an integrated device, we don’t find any discrete components like
active components such as transistors and diodes and passive components like R,
L & C. consequently, it offers small size, low cost, high reliability, more
temperature stability and low power consumption.

**Block Diagram of A typical Op-Amplifier**:

1à Non
inverting input terminal

2à Inverting
input terminal

3àDual input
balanced output differential amplifier

4à Dual
input unbalanced output differential amplifier

5à Emitter
follower with constant current source. It is used to shift the DC level to
ground in order to keep Q-point stable and also to limits the output voltage
swing.

6à
Complementary symmetry push-pull amplifier.

**Schematic Symbol of an Op-Amplifier**

Five basic terminals of op-amp :

Pin2àNon inverting terminal

Pin3à Inverting terminal

Pin7&pin4à Power
supplies

Pin6à Output terminal

**Equivalent Circuit of an Op-Amplifier:**

V

_{d}à Differential input voltage
R

_{in}à Input resistance of an op-amp
R

_{out}à Output resistance of an op-amp
A

_{vd}& R_{out}à Thevenin’s voltage source and Thevenin’s resistance respectively looking back into the output terminals of an op-amp**Note:**An electrical equivalent circuit is used to analyze basic operating principles of op-amp and in observing the effects of feedback.

**Ideal Op-Amp**

**Characteristics**

__:___{ a) }R

_{i}=∞

b) R

_{o}=0

c)
A

_{0L}=∞
d) BW=∞

e)
Zero offset voltages

f) CMRR=∞

**R**

_{i}

**=**

**∞:**

Since
input resistance is infinite, Ib1&Ib2 bias currents are ideally zero and
practically very small. Due to R

_{i }is very large loading effect is avoided.**R**

_{0}**=0:**

Since
output resistance is zero the voltage across output terminals is independent of
current flowing through the load. If R

_{o}=0 , it is used to drive infinite number of sources.**A**

_{0L}**=∞:**

It
implies there is a finite amount of output voltage for the zero differential
input voltages.

**BW=∞:**

It
shows, op-amp is used for both DC&AC where the frequency ranges from 0 HZ to high frequency.

**Zero offset :**

It
means for V

_{1}=V_{2}=0 the V_{o}_{ }must be zero.

**CMRR(Common Mode Rejection Ratio):**

For
an ideal op-amp, CMRR=ρ=A

_{d }_{/ }A_{c}=∞
A

_{d}àdifferential mode gain A_{c}àcommon mode gain

**DC Characteristics of Op-Amp:**

**a)**

__V__

_{ios}**The spurious i/p voltage causes to get small mv of output even in the presence of both the inputs are grounded. For an ideal op=amp it should be zero.**

__:__

**b)**

__I__

_{ios}**The algebraic difference between the two bias currents is called input offset currents.**

__:__

I

_{ios}=|I_{b1}-I_{b2}|**c)**

**I/P Bias Current:**The average sum of two bias currents flowing into an op-amp for the two bases of the transistors is called as input bias current.

I

_{b}=(I_{b1}+I_{b2})/2**d)**

**Thermal Drift:**The effect of variation in temperature causes changes in V

_{ios}, I

_{ios }& I

_{b }is referred as thermal drift.

**AC**

**Characteristics :**

**a)**

**Gain Bandwidth Product:**The range of operating frequencies of an op-amp at its unity gain is called gain bandwidth product. It also describes frequency response where variation in magnitude and phase of the gain due to change in frequency.

**b)**

**Slew Rate:**The maximum rate of change of output voltage is known as slew Rate.

SR=dVo

**/**dt**|**_{max}
SR= dVo

**/**dt**|**_{max}=I_{max}**/**C
---------------------------------------------------------------------------------

Article By

--------------

**Mr.K.Pithamber**

Assistant Professor

CSE Department

LAQSHYA Institute of Technology & Sciences

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