OTRA BASED SIGNAL GENERATORS AND THEIR PERFORMANCE ANALYSIS

Abstract

The reduction of the minimum feature size of MOS transistor for digital very-large-scale integration (VLSI) circuits has been ongoing for the past few decades. As the channel length is scaled down into deep sub-micrometer dimensions, the lower power supply voltage is required to ensure the device reliability. To be compatible with digital VLSI technologies, analog integrated circuits, which can operate at low supply voltages, also, received significant attention. The current mode signal processing emerged as low voltage design technique for analog circuits which was manifested in proposition of numerous current mode analog building blocks for the realization of various signal processing and generation circuits. The Operational transresistance amplifier (OTRA), a current-controlled voltage source, is one among those. Due to its inherent pros like bandwidth independent of closed loop gain, high slew rate and simplicity in assimilating the effect of parasitic capacitances at the input ports OTRA is being used widely for signal processing and generating applications. Sinusoidal oscillators are extensively used in the field of communication, instrumentation, testing and measurements. Versatility of oscillators in electronic applications coupled with advantages of OTRA and availability of limited literature has led the author of the thesis to explore the area of OTRA based signal generation. In this work several OTRA based sinusoidal oscillators that provide additional features not available in previously known OTRA oscillators have been presented. It is useful to minimize the number of active blocks and passive elements in the oscillator topologies from power consumption optimization, reduction in parasitic ix

effects and area efficient design viewpoint. Therefore, sinusoidal oscillator design with single OTRA is given due consideration and three second order oscillators are presented. Additionally, the viability of oscillators providing low frequencies oscillations is also examined. Another significant contribution is development of single OTRA based third order SO having smaller component spread in condition of oscillation compared to available topologies, which is a desirable feature from IC fabrication viewpoint. Quadrature oscillators find widespread applications in the field of communication. In this work, five new structures (one second order and four third order designs) are presented. Out of these five circuits, three third order topologies are derived from a generic structure. The second order design also qualifies for low frequency operations. Further, four new oscillators are presented that are capable of generating a wide range of frequencies from very low to high. All the topologies provide electronic tuning, independent control of frequency of oscillations without disturbing the condition of oscillation. One of the configurations provides linear tuning, which is suitable for measurement and instrument applications. Finally, a new OTRA based Wein bridge oscillator with wider tuning range is proposed in this work. A detailed mathematical formulation of harmonic distortion analysis is also presented to ascertain the linearity of the proposed design. The non-ideal behavior of all proposed configurations is studied by considering nonidealities of OTRA and various performance analyses such as sensitivity, frequency stability, harmonic and phase noise analysis as applicable are carried out. Functionality of all propositions is verified through simulations using SPICE/Cadence Virtuoso spectre ADE tool using 0.18 µm CMOS process parameters. Further, few circuits are verified experimentally also and post layout simulation results are included for rest.