1. Define an operational amplifier.
An operational amplifier is a direct-coupled, high gain amplifier consisting of one or more differential amplifier. By properly selecting the external components, it can be used to perform a variety of mathematical operations.
2. Mention the characteristics of an ideal op-amp.
Characteristics of an ideal op-amp :
1. Open loop voltage gain is infinity.
2. Input impedance is infinity.
3. Output impedance is zero.
4. Bandwidth is infinity.
5. Zero offset.
3. What happens when the common terminal of V+ and V- sources is not grounded ?
If the common point of the two supplies is not grounded, twice the supply voltage will get applied and it may damage the op-amp.
4. Define input offset voltage.
A small voltage applied to the input terminals to make the output voltage as zero when the two input terminals are grounded is called input offset voltage.
5. Define input offset current. State the reasons for the offset currents at the input of the op-amp.
The difference between the bias currents at the input terminals ofthe op-amp is called as input offset current. The input terminals conduct a small value of dc current to bias the input transistors .Since the input transistors cannot be made identical, there exists a difference in bias currents.
6. Define CMRR of an op-amp.
The relative sensitivity of an op-amp to a difference signal as compared to a common – mode signal is called the common –mode rejection ratio. It is expressed in decibels.
7. Define slew rate.
The slew rate is defined as the maximum rate of change of output voltage caused by a step input voltage. An ideal slew rate is infinite which means that op-amp’s output voltage should change instantaneously in response to input step voltage
8. What causes slew rate ?
There is a capacitor with-in or outside of an op-amp to prevent oscillation. It is this capacitor which prevents the output voltage from responding immediately to a fast changing input.
9. In practical op-amps, what is the effect of high frequency on its performance ?
The open-loop gain of op-amp decreases at higher frequencies due to the presence of parasitic capacitance. The closed-loop gain increases at higher frequencies and leads to instability
10. Why IC 741 is not used for high frequency applications ?
IC 741 has a low slew rate because of the predominance of capacitance present in the circuit at higher frequencies. As frequency increases the output gets distorted due to limited slew rate.
11. Mention some of the linear applications of op – amp.
Adder, subtractor, voltage –to- current converter, current –to- voltage converters, instrumentation amplifier, analog computation, power amplifier, etc are some of the linear op-amp circuits.
12. Mention some of the non – linear applications of op-amp.
Rectifier, peak detector, clipper, clamper, sample and hold circuit, log amplifier, anti –log amplifier, multiplier are some of the non – linear op-amp circuits.
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