Linear Integrated Circuits and Applications Short Question and Answers

LINEAR  INTEGRATED CIRCUITS

What is an integrated circuit?

An integrated circuit (IC) is a combination of interconnected circuit elements inseparably associated or with in continuous substrate.

Define monolithic IC.

A monolithic IC is an IC whose elements are formed in place upon or within a semiconductor substrate with at least one of the elements formed within the substrate.

What is a hybrid IC?

A hybrid IC consists of a combination of two or more IC types.

What are the advantages of ICs over discrete circuits?

There are many advantages of ICs over discrete circuits. They are:

•   Low cost.

•   Small size.

•   Improved performance.

•   Low power consumption.

•   High reliability.

•   Mass production capability.

•   Increased operating speed.

•   Less weight.

•   Easy replacement.

What are the applications of ICs?

Integrated circuits have become part and parcel of human life. Computers cellular

phones and other digital appliances are now inextricable parts of the structure of modern societies. That is, modern computing, communications, instrumentation, manufacturing and transport systems, including the internet, all depend on the existence of integrated circuits. Among the most advanced integrated circuits are the microprocessors and microcontrollers which control everything from computers, cellular phones to household appliances.

What is the classification of ICs based on complexity level?

Based on the complexity level (number of gates on a chip) ICs are classified as

•   Small scale integration (SSI).

•   Medium scale integration (MSI).

•   Large scale integration (LSI).

•   Very  large scale integration (VLSI).

What are the different Ie packages?

There are three different IC packages. They are

•   To- glass metal.

•   Ceramic flat package.

•   Dual-in-line (ceramic or plastic type).

What is a differential amplifier? What is the ideal value of its gain?

A differential amplifier is one which amplifies the difference between its two

input signals. The gain with which it amplifies the difference is called its differential gain

and ideally it should be infinite.

What is common mode gain of a differential amplifier?

If the two input signals to a differential amplifier are same, then its output should

be zero. But practically it produces a small output which is proportional to the average common level of the two input signals. The factor by which the differential amplifier amplifies the common mode signal is called its common mode gain.

What is CMRR?  State its ideal value.

The ability of the differential amplifier to reject common mode signal is expressed by the ratio of differential gain to the common mode gain which is called its common mode rejection ratio CMRR. The ideal value of CMRR is infinite.

List out various configurations of a differential amplifier.

•   Dual input, balanced output.

•   Dual input, unbalanced output.

•   Single input, balanced output.

•   Single input, unbalanced output.

What is current mirror?

The circuit in which the output current is forced to equal the input current is called current mirror.

List the advantages of current mirror.

•   Provides very large emitter resistance RE.

•   Requires lesser components than constant current bias.

•   Simple to design.

•   Easy to fabricate.

•     With properly matched transistors, collector current thermal stability is achieved.

Why current mirror circuit is often used?

The constant current bias can be easily replaced by constant current mirror circuit

to improve CMRR. Due to these advantages, current mirror circuit is most commonly used in the integrated circuit op-amps.

What is active load? Why it is used in the differential amplifier?

The current mirror circuit is used as a collector load resistance is called an active load. This circuit provides high value of a.c. collector resistance which is required to achieve high differential gain but it does not disturb d.c. conditions of the circuit. The quiescent voltage required across the current mirror is a fraction of the supply stage. This eliminates the need for high biasing supply voltages. Due to all these advantages, active load is used in the differential amplifier circuit.

What is a voltage reference circuit?

A voltage reference circuit is a constant d.c. voltage source which acts as a reference or standard for other circuits and is independent of changes in parameters like temperature, line voltage, load current etc.

List the performance parameters of a voltage reference circuit.

•   Line regulation.

•   Load regulation.

•   Long term stability.

•   Ripple rejection ratio.

Define slew rate.

Slew rate can be defined as the maximum rate of change of output voltage of op-

amp with respect to time.

Give the different types of IC packages.

ICs are available in three popular packages. They are:

•   Metal can package.

•   Dual-in line package.

•   Flat package or flat pack.

OP-AMP 2nd UNIT

What is an op-amp?

The operational amplifier is a multi-terminal device which is quite complex internally. An operational amplifier is a direct coupled high gain amplifier usually

consisting of one or more differential amplifiers and usually followed by a level translator and an output stage. An operational amplifier is available as a single integrated circuit package. It is a versatile device that can be used to amplify dc as well as ac input signals and was originally designed for computing such mathematical operations.

Mention some applications of op-amp?

With the addition of suitable external feedback components, the modern day op- amp can be used for a variety of applications such as ac and dc signal amplification,

active filters, comparators, oscillators, regulators and other applications.

What are the characteristics of ideal op-amp?

•   Open loop voltage gain, (Aol) = ∞.

•   Input impedance (Ri) = ∞.

•   Output impedance (Ro) = O.

•   Bandwidth (BW) = ∞.

•   Zero offset VO = O,when VI = V2  = O.

 Define input offset voltage.

It is defined as the voltage that must be applied between the input terminals of an op-amp to nullify the output.

Define input bias current.

It is defined as the average of the current entering into the input terminals of op-

amp.

Define input bias current.

It is defined as the average of the current entering into the input terminals of an op-amp.

What are the modes in which op-amp is operated with? Give the gain of the op-amp in each mode.

Open-loop mode: infinite gain. Example: comparator. Closed-loop mode: finite gain. Example: amplifier.

What is an compensated op-amp?

Op-amp, such uses a capacitor internally for compensation is called a

compensated op-amp. This op-amp has a high gain stability and low bandwidth.

What are the methods used in external compensation technique?

•   Dominant-pole compensation.

•   Pole-zero compensation.

What are the methods to improve slew rate?

•     The slew rate can be improved with a higher closed-loop gain and dc supply voltage. But the slew rate also varies with temperature i.e. slow rate decreases with increase in temperature.

What are the AC characteristics of an op-amp?

•   Frequency response.

•   Slew rate.

What are the DC characteristics of an op-amp? Give typical values for an

IC741.

•   Input bias current: 500nA.

•   Input offset current: 200nA.

•   Input offset voltage: 6mV

•   Thermal drift.

 What produces more offset voltage at the output? Input offset current or input bias current?

Input bias current produces more offset voltage at the output.

In what way is 741S a better grade op-amp with a higher slew rate?

741  S is a military grade op-amp with a higher slew rate.

OP-AMP APPLICATIONS UNIT-3

What is a practical Op-amp? Draw its equivalent circuit.

  A practical Op-amp has voltage gain to be less than that of ideal one. Its input impedance is very high, bandwidth is very high ,offset voltage is near to zero , slew rate is very high, and output impedance is near zero.

What is linear op-amp circuit?

 An op-amp circuit which has the output signal with the same shape as that of the input signal is called linear op-amp circuit. The op-amp does not go to saturation during its cycle.

What do you meant by linear circuits?

Linear circuits are the circuits in which the output signal varies with the input signal in a linear manner.

What is non linear op-amp circuit?

 An op-amp circuit which has the output signal with a different shape from the input signal is called non linear op-amp circuit. The op-amp saturates during part of its input cycle.

List out some of the linear op-amp circuits.

Linear op-amp circuits are :

1.  Inverting amplifiers,

2.   Non inverting amplifiers

3.   Differential amplifiers,

4.   Instrumentation amplifiers,

5.   Current boosters ,

6.   Adder, Subtractors,

7.   Power amplifiers,

8.   V-I and I-V converters.

List out some non linear op-amp circuits.

Non linear op-amp circuits are:

1. Comparators

2. Wave shapers

3. Active diode circuits

4. Rectifier circuits

5. Log and antilog amplifiers.