application of op amp

APPLICATIONS OF OPERATIONAL AMPLIFIERS ECE-210

ANALOG CKT’s & LINEAR IC

SUBMITTED TO-

SUBMITTEDBY-

NARENDRA GARG

ABHISHEK CHAUDHARY 10809431 E6802A27

OPERATIONAL AMPLIFIERS The term Operational Amplifier or op amp in short, was coined by John R.Ragazzini in 1947. It denoted a special type of amplifier that could perform a variety of functions like amplification, addition, subtraction, differentiation and integration if the external components

Semiconductor

Corporation.

In

1968

Fairchild developed one of the most famous and regularly used op amp µA741. Since, it was developed it has undergone a lot of changes but still is one the most frequently used op amp. Some of other types of amplifiers are

µA324, µA082,

µA339, etc.

were properly selected. It can perform these mathematical operations due to the combination of high gain and negative feedback.

History: The Operational amplifiers have undergone a lot of development since it was first made. When it was first made,

Fig.1 Fig.2

vacuum tubes were used. The problem was

Figure 1. shows the first type of op amp

that it was too bulky, expensive and used

µA741. Figure 2. shows the new type of

large

op amp µA741 that we use today.

amounts

of

power.

The

first

miniaturization of op amp was made through bipolar junction transistor (BJT).

Ideal Operation Amplifier:

A major break through occurred with the

An Ideal Op Amp has a gain that is equal

development of Integrated Circuit(IC) op

to 1. It is achieved as a→∞ and the

amp. They are made by fabricating

following conditions are achieved.

elements in monolithic form of silicon chip having a size of a pinhead. The first of such a device was developed by Robert J.

Widlar

in

1960s

at

Fairchild

1. rd = ∞. 2. ro = 0. 3. iP = iN = 0.

It is also known as Voltage follower if the external input resistance Ri = ∞ and output

Fig.4 shows the circuit amplifier.

for non-inverting

resistance Ro = 0. It is used to act as a resistance transformer since looking into Fig.4

the input we see an open circuit and into the output we see the short circuit, due to

Inverting Amplifier:

which we get V0 = VI.

Non- Inverting Amplifier: In the non inverting amplifier the voltage

The inverting amplifier has the voltage connected to the negative terminal input through the resistance Rin . By applying Kirchhoff’s Voltage law. We get,

source is connected to the positive terminal. VP = Vin The

output

resistance

R2

is

connected in series with input resistance R1 and the input voltage of the negative

The negative sign indicates that the output will have 180o of phase shift. Hence such a type of amplifier is called inverting amplifier. It is shown in fig.5.

terminal is a fraction of out voltage Vout . Fig.5

VN = (R1 / R1 + R2) Vout By definition of amplifiers, Vout = a VD = a(VP - VN) = a (Vin -(R1 / R1 + R2) Vout thus,

Uses of operational amplifiers:

Gain= A= (Vout / Vin) = (1+ R2/ R1). As a→∞,

Operational Amplifiers are used in radios and music system to enhance the volume

Since the gain A obtained is positive that mean the output and input are in phase and thus such a type of amplifier is called non-inverting amplifier.

without

increase

in

the

consumption of power. In cars the movement of the wiper blades is controlled by the op-amps. In computers op-amps are used in sound control and to increase the

flow of memory in order to make it run

These pictures show the various

faster. In airplanes and jets the op-amps

application of operational amplifiers used

are used to attain high speeds by

in our daily life.

consuming less of power.

APPLICATIONS OF OP-AMPS NEGATIVE CLIPPER:

The above figures show the circuit diagram & waveforms for a clipper circuit. Here the diode is reversed compared to +ve clipper. The negative half cycle of the input gets clipped partially or fully depending on the magnitude of the Vref

CLAMPERS USING OP-AMP: A clamper is a circuit used to shift dc level of the input signal. It adds a desired dc level to the ac input voltage. If the added dc level is positive, it is called as a +ve clamper. Otherwise negative clamping if the added dc level is negative

. The

above figures show the circuit diagram & waveforms for a clamper circuit. The potentiometer ‘p’ is used to vary the reference voltage applied to the noninverting terminal of the OPAMP.The waveforms to be clamped is applied to the inverting terminal & the dc reference

When Vin is +ve, the OPAMP output will be negative. The diode will be reverse biased and the capacitor can’t discharge, as there is no discharge path for it. Output becomes

voltage is applied to the non-inverting terminal of the OPAMP.As both the inputs are non-zero; the circuit can be analyzed

V0’’=Vm +Vin Total output is ,

using superposition theorem.

V0 = V0’+V0’’=Vref + Vm +Vin

With only +Vref given to the non-inverting

In this expression Vref +Vm is the fixed dc

terminal (assuming Vin =0), the OPAMP

level added to the input signal.

output is positive, the diode ‘D’ is forward biased and the output is, V0 ‘=Vref

Note: In the above circuit, a battery Vref can also be used instead of the pot. For negative clamping, the is to be reverse biased. ABSOLUTE

VALUE

OUTPUT

CIRCUIT: This circuit is used for wave shaping of the input signals. Output of this circuit will be always positive, irrespective of the polarity of the input signal.

The above figure shows the minimum circuitry required for a sample & hold circuit. The circuit operation in either of the modes (sampling & holding) depending on the position of the switch.

Sampling mode: In this mode, the switch is in the closed position and the capacitor charges to the instantaneous input voltage.

Hold mode: SAMPLE & HOLD CIRCUIT USING OPAMP:

In this mode, the switch is in the open position. The capacitor is now disconnected

The sample & hold circuit is used to

from the input. As there is no path for the

hold the sampled value of the input

capacitor to discharge, it will hold the voltage

signal for a specified period of time.

on it just before opening the switch. The

Thus S/H operation has two different

capacitor will hold this voltage till the next

processes: sampling the input signal

sampling instant.

and holding the latest sample value. BASIC SAMPLE & HOLD CIRCUIT:

ACTIVE FILTERS USING OPAMP: Filters are frequency selective circuits.They are required to pass a specific band of frequencies and attenuate frequencies outside the band. Filters using an active device like OPAMP are called active filters.Other way to design filters is using passive components like resistor, capacitor and inductor.

the operational amplifier will cease to behave ideally.

Merits of op-amps over other amplifiers. The idea of fully-differential op-amps is not new. The first commercial opamp, the K2-W,

CONCLUSION: Limitations of real amplifier: Real op-amps differ from the ideal model in various respects. IC op-amps as implemented in practice are moderately complex integrated circuits; see the internal circuitry for the relatively simple 741 op-amp.

DC imperfections Real operational amplifiers suffer from several non-ideal effects: Finite gain Open-loop gain is infinite in the ideal operational amplifier but finite in real operational amplifiers. Typical devices exhibit open-loop DC gain ranging from 100,000 to over 1 million. So long as the loop gain (i.e., the product of open-loop and feedback gains) is very large,

the

circuit

gain

will

be

determined entirely by the amount of negative feedback (i.e., it will be independent of open-loop gain). In cases where closed-loop gain must be very high, the feedback gain will be very low, and the low feedback gain causes low loop gain; in these cases,

utilized two dual section tubes (4 active circuit elements) to implement an op-amp with differential inputs and outputs. It required a ±300 Vdc power supply, dissipating 4.5 W of power, had a corner frequency of 1 Hz, and a gain bandwidth product of 1 MHz(1). In an era of discrete tube or transistor op-amp modules, any potential advantage to be gained from fully-differential circuitry was masked by primitive op-amp module performance. Fullydifferential output op-amps were abandoned in favor of single ended op-amps. Fullydifferential op-amps were all but forgotten, even when IC technology was developed. The main reason appears to be the simplicity of using single ended op-amps. The number of passive components required to support a fullydifferential circuit is approximately double that of a single-ended

circuit. The thinking may have been “Why double the number of passive components whe.An op-amp with differential outputs,however, has far more uses than one application.

REFRENCES: Books Reffered: 1.EDC,by J.B Gupta 2.Analog CKT’s,by J.B Gupta Websites: 1.Encyclopeadia.com