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

ANALOG SIGNAL PROCESSING (EEC011)

Time: 3 Hours  Max Marks: 100

SECTION – A (Short Answer Questions)

(10 × 2 = 20 Marks)

(a) Impedance

Impedance is the total opposition offered by a circuit to alternating current (AC). It is a combination of resistance and reactance and is expressed as

Z=R+jXZ = R + jXZ=R+jX 

(b) Difference between digital and analog signal

An analog signal varies continuously with time, while a digital signal has discrete levels, usually represented by binary values 0 and 1.

(c) Filter with example

A filter is a circuit that allows certain frequencies to pass and blocks others.
Example: A low-pass filter allows low-frequency signals and attenuates high-frequency signals.

(d) Biquads

Biquads are second-order filter sections used in analog and digital filter design. They consist of two reactive elements and provide stable filter characteristics.

(e) Signal rectification

Signal rectification is the process of converting an AC signal into a unidirectional (DC) signal using diodes.

(f) Peak and valley

A peak is the maximum value of a signal, while a valley is the minimum value of a signal.

(g) Transconductance

Transconductance is the ratio of change in output current to change in input voltage, expressed as

gm=dIdVg_m = \frac{dI}{dV}gm​=dVdI​ 

(h) Grounded inductor

A grounded inductor is an inductor whose one terminal is connected to ground, commonly used in active filter design.

(i) Voltage limiter circuit

A voltage limiter circuit restricts the output voltage to a predetermined level, protecting circuits from over-voltage.

(j) Gyrator with example

A gyrator is an active circuit that simulates an inductor using resistors and capacitors.
Example: Op-amp-based gyrator circuit.

SECTION – B (Long Answer Questions)

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

2(a) Differentiation and addition linear analog functions

Differentiation:
An op-amp differentiator produces an output proportional to the rate of change of input signal:

Vo=−RCdVidtV_o = -RC \frac{dV_i}{dt}Vo​=−RCdtdVi​​

Addition:
An adder circuit sums multiple input signals using an op-amp, commonly used in signal mixing.

2(b) Impedance transformation and conversion

Impedance transformation converts one impedance value to another using active or passive circuits.
Op-amps can be used to transform low impedance to high impedance and vice versa.

2(c) Signal rectification with example

Rectification is done using half-wave or full-wave rectifiers.
A full-wave rectifier converts both halves of AC input into DC, improving efficiency.

2(d) Logarithmic amplifier

A logarithmic amplifier produces an output proportional to the logarithm of input signal.
Applications include:

Signal compression

Measurement of wide dynamic range signals

2(e) Notch and All-Pass (AP) transfer functions

Notch filter: Rejects a narrow band of frequencies.

All-Pass filter: Passes all frequencies but changes phase.

Example:

H(s)=s2+ω02s2+ω0Qs+ω02H(s) = \frac{s^2 + \omega_0^2}{s^2 + \frac{\omega_0}{Q}s + \omega_0^2}H(s)=s2+Qω0​​s+ω02​s2+ω02​​ 

2(f) Op-amp as amplitude demodulator

An op-amp demodulator extracts the envelope of AM signals using rectification followed by filtering.

2(g) Amplitude demodulation

Amplitude demodulation recovers the original message signal from a modulated carrier.
Methods include:                         Envelope detector                          Synchronous detector

2(h) Ladder design

Ladder design uses LC or RC ladder networks to design filters with improved stability and frequency response.

SECTION – C (Very Long Answer Questions)

(Attempt any TWO – 2 × 15 = 30 Marks)

3. Generalized converter

A generalized converter is a circuit that converts one electrical quantity into another, such as voltage-to-current or current-to-voltage conversion.

Types:                                             V-I converter

I-V converter

Block diagram:
Input → Converter → Output        These are widely used in instrumentation and signal processing systems.

4. Peak and valley detection methods

Peak and valley detection identifies maximum and minimum signal levels.

Methods:

Diode-based detector

Op-amp-based detector

Op-amp circuits provide higher accuracy and faster response.

5. Detailed notes

(a) C-filters

C-filters use capacitors and op-amps to perform filtering operations. They are compact and suitable for integrated circuits.

(b) Voltage limiting

Voltage limiting circuits protect components by restricting output voltage.
They use diodes, Zener diodes, or op-amps.