Continuous time very low frequency analog signal processors

Abstract

In this work, basic analog integrated circuits such as integrators, multipliers, comparators, summers and impedance scaling networks which serve as the basic building blocks for designing complicated continuous time analog signal processing systems are analyzed and designed. These circuits are designed to operate at low supply voltages and consume low power. Special emphasis is laid on very low frequencies of operation (of the order of a few Hertz). For an Operational Transconductance Amplifier- Capacitor (OTA-C) integrated circuit implementation, this directly translates to a very small transconductance (of the order of a few nA/V) and a very large on-chip capacitance (of the order of several hundred pF). Both the above mentioned aspects of low frequency IC design are addressed in this thesis. Specifically, a family of OTA'S with very small transconductances has been designed using several design schemes such as current division, use of floating gate Metal Oxide Semiconductor Field Effect Transistors (MOSFET'S) and bulk driven transistors. A detailed comparison has been made among these schemes in terms of performance characteristics such as power consumption, active silicon area and signal to noise ratio. A multiplier based OTA with very small transconductance has also been designed with a view to obtain a wide transconductance tuning range. Moreover, an impedance scaling circuit has also been designed in order to realize very large capacitors on-chip. As sample applications for these circuits, a low pass filter, relaxation oscillator, band pass filter and a band pass based oscillator have also been designed. A11 circuit design has been done through a novel approach by the use of an all-region MOSFET model. A11 the above mentioned circuits have been designed, simulated and eventually fabricated in a 1.2[] NWELL CMOS process available through MOSIS. The fabricated circuits have all been tested for functionality and performance in the lab and measurement results are tabulated.