ANALOG SIGNAL PROCESSING – KEC-064
Section-wise Important Questions & Ready Answers
SECTION A
(Attempt all questions in brief – 2 marks each)
(a) Active Filter and Its Uses
An active filter is an electronic filter that uses active components such as operational amplifiers along with resistors and capacitors. It provides signal amplification along with filtering. Active filters are used in audio processing, communication systems, biomedical instruments, and signal conditioning circuits.
(b) High Pass Filter Using Op-Amp
A high-pass filter using an op-amp consists of a capacitor at the input followed by a resistor, allowing high-frequency signals to pass while attenuating low-frequency components. The op-amp provides gain and buffering.
(In exam, neat circuit diagram is expected)
(c) Chebyshev Co-efficient C₂(ω)
For a Chebyshev filter, the coefficient C2(ω)C_2(\omega)C2(ω) is derived from Chebyshev polynomials and determines the ripple behavior in the passband. It depends on the filter order and ripple factor ε.
(d) Properties of Butterworth Response
Butterworth response is maximally flat in the passband and exhibits a smooth monotonic decrease in magnitude with frequency. It has no ripples in either the passband or stopband.
(e) Constant-Resistance Lattice
A constant-resistance lattice is a filter structure in which the input and output impedances remain constant over the operating frequency range, ensuring impedance matching.
(f) Filter Used for Delay Equalization
All-pass filters are used for delay equalization. They maintain constant magnitude response while adjusting phase response to minimize signal distortion and group delay variations.
(g) FDNR and Its Application
FDNR stands for Frequency Dependent Negative Resistance. It is an active circuit element used in active filter synthesis to simulate inductors and design high-order filters without using physical inductors.
(h) LC Ladder Circuit and Zero Energy Dissipation
An LC ladder circuit consists only of inductors and capacitors. Since these elements store energy without dissipating it as heat, the total energy dissipation in an ideal LC ladder is zero.
(i) Grounded and Floating Resistor Using OTA
Operational Transconductance Amplifiers (OTA) can be configured to realize grounded and floating resistors by controlling transconductance through bias current.
(Circuit diagram expected in exam)
(j) Summer Using Op-Amp
An op-amp summer adds multiple input signals by connecting them through resistors to the inverting terminal. The output voltage is proportional to the weighted sum of input voltages.
(Neat circuit diagram required)
SECTION B
(Attempt any three – 10 marks each)
2(a) Three Op-Amp Based Biquad Filter
A three op-amp biquad filter consists of two integrators and a summing amplifier. By selecting appropriate component values, it can realize low-pass, high-pass, band-pass, band-stop, and all-pass responses. The design offers independent control of gain, quality factor, and center frequency.
2(b) Butterworth vs Chebyshev Magnitude Response
Butterworth filters provide a maximally flat passband with no ripple, ensuring smooth frequency response. Chebyshev filters introduce ripples in the passband but achieve sharper roll-off. Butterworth filters are preferred where phase linearity is important, while Chebyshev filters are used when sharper cutoff is required.
2(c) Equalization of First-Order Filter
Equalization compensates for amplitude and phase distortion. For a first-order filter, an all-pass or compensating network is added to flatten the overall response and improve group delay characteristics.
2(d) Bruton’s FDNR Technique
Bruton’s technique replaces inductors in LC ladder filters with FDNR elements using op-amps. This enables realization of high-order active filters with resistors and capacitors only. It improves stability and reduces size and cost.
(Neat sketch expected)
2(e) Switched Capacitor Cascaded Filter
Switched capacitor filters simulate resistors using capacitors and clock signals. Cascading such filters allows realization of higher-order responses with high accuracy and compatibility with IC fabrication.
SECTION C
3(a) Current Conveyor and Its Advantages
A current conveyor is an analog building block that transfers current and voltage with high bandwidth. Compared to op-amps, it offers higher slew rate, better frequency response, and improved linearity. Integrator and differentiator circuits can be designed using current conveyors for high-speed applications.
3(b) Sallen-Key Biquad Filter
The Sallen-Key filter is a second-order active filter using an op-amp and RC network. It is widely used due to simplicity and ease of tuning. Depending on component selection, it can realize LPF, HPF, BPF, and notch responses. Transfer functions are derived using standard circuit analysis.
