THEORY EXAMINATION (SEM–VI) 2016-17 ANALOG SIGNAL PROCESSING

ANALOG SIGNAL PROCESSING (NEC023)

B.Tech Semester VI – Section-Wise Solved Answers

SECTION – A (Short Answer Questions)

(10 × 2 = 20 Marks)

(a) Voltage Feedback Amplifier

A voltage feedback amplifier is an amplifier in which a fraction of the output voltage is fed back to the input. It offers high input impedance, low output impedance, and stable gain.

(b) Transconductance Amplifier

A transconductance amplifier converts input voltage into output current. Its output current is proportional to the input voltage and is widely used in analog signal processing.

(c) Current Conveyor

A current conveyor is an analog building block used for current-mode signal processing. It has three terminals (X, Y, Z) and provides high bandwidth and linearity.

(d) Filter Realization

Filter realization is the process of implementing a desired transfer function using active or passive components such as resistors, capacitors, inductors, op-amps, or OTAs.

(e) General Impedance Converter (GIC) circuit

A GIC is an active circuit that converts one type of impedance into another. It is commonly used to simulate inductors using resistors and capacitors.

(f) Properties of lossless ladders

Lossless ladder networks:                                       Have no resistive losses

Contain only inductors and capacitors                   Provide stable and predictable frequency response

(g) GIC

GIC (General Impedance Converter) allows realization of inductance, capacitance, or resistance using op-amps and passive components.

(h) Realization of simple ladders

Simple ladder networks are realized using series and shunt combinations of L and C elements to achieve desired filter characteristics.

(i) Filter design parameters

Important filter design parameters include:          Cut-off frequency

Passband gain                                                        Stopband attenuation

Quality factor (Q)

(j) Analog signal filtering

Analog signal filtering removes unwanted frequency components from signals using circuits such as low-pass, high-pass, band-pass, and band-stop filters.

SECTION – B (Long Answer Questions)

(Attempt any FIVE – 5 × 10 = 50 Marks)

2(a) Op-amp as amplitude demodulator and peak detector

An op-amp amplitude demodulator extracts the envelope of an AM signal using precision rectification followed by filtering. It overcomes diode threshold limitations.

A peak detector stores the maximum value of the input signal using a diode-capacitor combination with op-amp buffering for accuracy.

2(b) Capacitance multiplier

A capacitance multiplier uses an op-amp and resistor-capacitor network to simulate a large effective capacitance.

Equivalent capacitance:                          Ceq=C(1+A)C_{eq} = C (1 + A)Ceq​=C(1+A)

where A is amplifier gain.                       It is used in power supplies for ripple reduction.

2(c) Compensation of input error sources in op-amp & OTA voltage amplifier

Input errors include:                               Input offset voltage

Bias current                                            Drift

Compensation methods include trimming, bias current compensation resistors, and auto-zero techniques.

For an OTA-based voltage amplifier, output voltage is proportional to transconductance × input voltage × load resistance.

2(d) Full-wave precision rectifier

A full-wave precision rectifier uses op-amps and diodes to rectify both halves of the input signal accurately, even for low-level signals.

Its V-I characteristic shows linear response without diode drop errors.

2(e) KHN-biquad filter

KHN-biquad is a state-variable filter that simultaneously provides:

Band-pass                                              Band-reject

All-pass outputs                                     Transfer functions are derived using integrator stages.

All-pass filter has constant magnitude and varying phase.

2(f) Butterworth and Chebyshev magnitude response

Butterworth filter: Maximally flat passband, smooth response

Chebyshev filter: Ripple in passband but sharper roll-off

Chebyshev provides better selectivity than Butterworth.

2(g) Gorski-Popiel’s embedding & Bruton’s FDNR technique

Gorski-Popiel technique: Used to embed resistors into ladder networks

Bruton’s FDNR technique: Replaces inductors with Frequency Dependent Negative Resistance for IC realization

2(h) Bode sensitivity and delay equalization

Bode sensitivity measures effect of component variation on transfer function.
Delay equalization reduces phase distortion using all-pass networks.

SECTION – C (Very Long Answer Questions)

(Attempt any TWO – 2 × 15 = 30 Marks)

3. Grounded & floating inductors using OTAs and voltage limiter

Using OTAs and capacitors, grounded and floating inductors are simulated.

Equivalent inductance:                                  L=CgmgmL = \frac{C}{g_m g_m}L=gm​gm​C​

A voltage limiter circuit restricts output voltage using diodes or op-amps to protect circuits.

4. Effect of finite gain of op-amp & numerical

Finite gain causes gain error and bandwidth limitation.

Given:

Passband gain = 2                                        Cut-off frequency = 1 kHz

Input capacitor = 10 nF

Cut-off resistor:

R=12πfcC≈15.9 kΩR = \frac{1}{2\pi f_c C} \approx 15.9\,k\OmegaR=2πfc​C1​≈15.9kΩ

Feedback resistors are chosen to achieve gain of 2.

Frequency response shows rising gain after cut-off.

5(a) First-order and second-order filter realization

First-order filter: Single pole, simple roll-off   Second-order filter: Higher selectivity, sharper attenuation

Realized using op-amps, RC networks, and integrators.

5(b) Strategies for equalization design

Equalization strategies include:                     Amplitude equalization

Phase equalization                                        Delay equalization

All-pass networks are commonly used.