SIGNAL GENERATION AND PROCESSING APPLICATIONS USING CURRENT MODE BUILDING BLOCKS

Abstract

This thesis presents a comprehensive study on signal generation and processing using current-mode active building blocks (ABBs), specifically focusing on the Universal Voltage Conveyor (UVC) and the Voltage Differencing Buffered Amplifier (VDBA). These elements represent a significant advancement in analog signal processing, offering improved performance in speed, linearity, power efficiency, and CMOS compatibility over traditional voltage-mode circuits. The work addresses key bottlenecks in existing oscillator and filter designs by developing novel circuit architectures that are compact, low-power, and capable of robust and tunable operation under practical non-idealities. The research is structured in four parts. The first part introduces the foundational principles of analog signal processing and the advantages of current-mode operation. It also presents a literature review on the evolution and applications of UVC and VDBA, identifying gaps in tuning flexibility, harmonic distortion, and sensitivity to component variations. Particular attention is given to the third-order quadrature sinusoidal oscillator (TOQSO) and multiple-input single-output (MISO) universal filter designs. The second part of the thesis proposes two innovative circuits: an improved TOQSO using UVC and a compact, electronically tunable MISO universal filter using VDBA. The proposed TOQSO achieves independent control over the frequency of oscillation (FO) and condition of oscillation (CO), reducing total harmonic distortion (THD) to below 1.5%, a marked improvement over existing OTA- and CCII-based designs. The MISO filter, designed using a single VDBA, two grounded capacitors, and one resistor, realizes all five second-order filter responses (low-pass, high-pass, band-pass, band-reject, and all- vii pass) without the need for reconfiguration. Both circuits exploit the strengths of their respective ABBs to address the shortcomings of earlier designs. In the third part, rigorous mathematical modeling is presented for both circuits, followed by detailed sensitivity analysis that confirms the low dependence of key parameters (ω₀ and Q) on passive component variations. SPICE simulations using 0.18 μm CMOS technology validate the theoretical predictions. For the TOQSO, output waveforms, frequency spectra, and Lissajous patterns confirm sinusoidal oscillation with quadrature phase accuracy and spectral purity. For the MISO filter, frequency response plots for each mode demonstrate accurate cutoff and center frequencies. Simulation results align closely with analytical derivations. To bridge the gap between simulation and real-world applicability, experimental prototypes of both designs were implemented using commercially available ICs. The TOQSO exhibited stable sinusoidal outputs with precise 90° phase difference, and the filter achieved consistent performance across a frequency range from 10.5 kHz to 500.5 kHz. These results confirm the feasibility and robustness of the proposed circuits under practical conditions, including non-idealities such as voltage tracking errors and finite transconductance mismatches. A comparative performance analysis against conventional designs—OTA-, CCII-, and CDBA-based—demonstrates the superiority of the proposed solutions in terms of spectral purity, power efficiency, component count, and CMOS integration readiness. The VDBA- based filter exhibits lower power consumption and higher Q-factor than its counterparts, while the UVC-based oscillator outperforms in frequency stability and THD. The thesis concludes by outlining the broader implications of these findings. The proposed designs contribute to the advancement of low-voltage, low-power analog front-end systems, particularly in wearable biomedical devices, adaptive communication systems, sensor interfaces, and energy-constrained IoT nodes. Their compactness and simplicity make them ideal candidates for integration into modern VLSI systems. viii Future directions for research include extending these architectures for fully electronically tunable operation, deploying them in multi-band or reconfigurable systems, and implementing them in deep-submicron or emerging device technologies such as FinFETs and CNTFETs. Furthermore, integrating these circuits into system-on-chip (SoC) solutions for biomedical and communication applications could significantly enhance performance and miniaturization. Through its dual focus on theoretical rigor and practical validation, this thesis contributes to the evolving landscape of analog signal processing, establishing reliable and efficient building blocks for next-generation analog integrated circuits.