Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE) PDF Download

OPERATIONAL AMPLIFIER

1st Stage : Difference amplifier.
2nd Stage : High gain linear amplifier.
3rd Stage : Emitter follower.
4th Stage : DC level shifter and output amplifier.

Ideal Op–amp Characteristics 
1. Input resistance is infinite, Zin = ¥ , so no current enters the input terminal.
2. A zero output resistance, Zout = 0.
3. Infinite voltage gain, A= ¥ .
4. Characteristics do not drift with temperature.

Inverting Amplifier

 Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)
Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

Input Impedance The input resistance is equal to resistance Z.
Unity Follower

 Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

The output signal is in phase with the input signal and of same magnitude.
Input impedance is very high, so it provides very good isolation between stages.

Summing amplifier

 Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)
Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

Differential amplifier

 Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)
Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

differentiator

 Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)
Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

Integrator

 Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

Precision Rectifier Main defect with Si rectifier is its cut in voltage of 0.7 V and so, voltages less than this value cannot be rectified. This defect is over come in op-amp rectifiers and voltages in the mill volt range can be obtained.

 Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

when Vs is + ve diode is ON and feedback loop is established and Vo follows Vs.
When Vs is – ve, diode is OFF and feedback loop is open and V=0

 Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

All Pass filter

 Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)
Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

Band Pass Filter

 Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)
Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

Check what type of filter is given circuit by just inspection putting w = 0 (capacitor open–circuit) and w = ¥ (capacitor short–circuit) In above circuit when w = 0 , C1 = open circuit and Vo = 0 V, similar for w = ¥ (C1 = C2) so it does not passes high as well as low frequency so it is band pass.
Non - Inverting Integration

 Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)
Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

Double Integration

 Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)
Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

Clamper : In some situation it may be necessary to raise or lower reference voltage, which is done by adding or subtracting a dc voltage to the original reference voltage of 0.
Two Type of Clamper Circuit:
(a) If the d.c. level  added is positive, it is positive, it is positive clamper.
(b) If the d.c. level is lowered and negative, its negative clamper.

 Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

Positive Clamper sm V =Vsin wt, for negative swing D conducts and capacitor charge to peak value Vm and cathode end to capacitor is positive

 Vo =Vs + Vc (or Vm) = 2 Vfor positive swing and 0 for negative swing

 Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE) 

Logarithmic Amplifiers

 Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

  • When Vin < 0; diode is off, Op-amp behaves as comparator . At this time Vo = + Vsat
  • WhenVin > 0 diode is ON Vo =– 0.7 V  For small range of Vin. It behaves as logarithmic amplifier.

 Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

Antilogarithmic Amplifier

 Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)
Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

Comparator In a comparator, the level of the applied input voltage is compared with a known reference voltage:

1. As a comparator, the level of the applied input voltage is compared with a known reference voltage.
2. As a comparator, the Op-amp are operated in the open  condition without feedback resistor.
3. Since it is operated in open loop condition, the assumption (V+ =V– = Vd = o) is not applicable.
4. Open loop  gain is very high, so output goes to saturation levels ( ± Vcc) even for very low inputs.
5. If 1 or 2V drops in Rc’s of the transistor of the differential stage, the saturation voltage will be ( ± 13V) for a supply voltage of ( ± 15V) .

 Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

If (V2–V1) = Vin > 0, V= + Vsat
If (V– V1) = Vin < 0, Vo = – Vsat

Zero Crossing Comparator and Detector

 Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)
Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

With sinusoidal, we obtain rectangular pulse waveform at the output.  Output remains at + Vsat or –Vsat till the input voltage is above or below Vref.
Vin > Vref : Vout = – Vsat Vin < Vref : Vout = Vsat 
Output remains at ± Vsat ( ± 13) is not suitable for TTL operation. We can clamp the output voltage to lowest value by connecting at the output zener diodes back to back.

 Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

Vin > Vref : Vo = (VD + VZI) Vin < Vref: Vo = – (VD + VZI) With VD = 0.7, 

For positive Vo, Dz2 act as a diode and for negative V0, DzI acts as a simple diode. 
R restricts the current to the operating point of zener.

This circuit is known as by - phase amplifier:

Slew Rate It is defined as the maximum time rate of change of the output voltage (dvo/dt)max.
Describes the large signal limitation of the opamp.
For faithful reproduction of this sinusoid requires wVm £ slew rate where,Vm = peak amplitude of applied signal w = frequency of input signal.

Timing Circuit Digital systems require some kind of a timing waveform for example, a source of trigger pulses, for clocked sequential systems. Rectangular waveform is most desirable. The generators of rectangular waveforms are referred to as multivibrators.

Three Types of Multivibrator 
1. Astable (or free running) multivibrator.
2. Monostable multivibrator (one-shot), and
3. Bistable multivibrator (or flip-flop).

1. Astable multivibrator is nothing but an oscillator, which generates rectangular waveform. It has two quasi-stable states, and doesnot require any triggering; hence it is referred to as a free running multivibrator.
2. Monostable Multivibrator: has one stable state i.e. under steady state condition, its output is fixed it is either in the low or the high state. When the circuit is triggered with an externally applied pulse it goes into the other state, i.e. if it was in low state, it will go to high and vice-versa. The circuit remains in this state for the elements used in the circuit.
3. Bistable Multivibrator: A multivibrator circuit in which both the states are stable is referred to as a bistable multivibrator or FF. This circuit makes transition pulse is applied.

The document Operational Amplifier | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE) is a part of the Electrical Engineering (EE) Course Electrical Engineering SSC JE (Technical).
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FAQs on Operational Amplifier - Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

1. What is an operational amplifier (op-amp) in electrical engineering?
Ans. An operational amplifier, also known as an op-amp, is an electronic component commonly used in electrical engineering. It is a high-gain differential amplifier with a very high input impedance and a low output impedance. Op-amps are used for various signal processing applications, such as amplification, filtering, and mathematical operations.
2. How does an operational amplifier work?
Ans. An operational amplifier typically consists of a differential input stage, a gain stage, and an output stage. The differential input stage amplifies the voltage difference between its two input terminals. The gain stage amplifies this voltage further, and the output stage provides a low output impedance. The op-amp is designed to have a high open-loop gain and a high common-mode rejection ratio (CMRR), making it an ideal building block for various circuit applications.
3. What are the characteristics of an ideal operational amplifier?
Ans. An ideal operational amplifier is assumed to have the following characteristics: - Infinite open-loop gain. - Infinite input impedance. - Zero output impedance. - Infinite bandwidth. - Infinite common-mode rejection ratio (CMRR). - Zero input offset voltage. - Zero input bias current.
4. How can an operational amplifier be used as an inverting amplifier?
Ans. An operational amplifier can be configured as an inverting amplifier by connecting the input signal to the inverting terminal of the op-amp and providing feedback through a resistor connected between the output and the inverting terminal. The gain of the inverting amplifier is determined by the ratio of the feedback resistor to the input resistor. The output signal is an inverted and amplified version of the input signal.
5. What are some common applications of operational amplifiers?
Ans. Operational amplifiers find extensive use in various electrical engineering applications, including: - Signal amplification: Op-amps can be used to amplify weak signals from sensors or other input sources. - Filters: They can be used to implement low-pass, high-pass, band-pass, and band-stop filters. - Comparators: Op-amps can compare two input voltages and provide a digital output based on their relative magnitudes. - Voltage regulators: They are used in voltage regulators to maintain a stable output voltage. - Analog-to-digital converters (ADCs): Op-amps play a crucial role in the input stage of ADCs, converting analog signals to digital form.
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