ANALYSIS AND DESIGN OF LOW VOLTAGE AND LOW POWER ANALOG CIRCUIT BLOCKS

Abstract

This thesis addresses two different areas of analog circuit design. Chapters 1 and 2 are on design of low-pass gm-C ladder filters and analysis of some of the related non-ideal effects respectively. Chapters 3 and 4 are dedicated to the theory and design, respectively, of Low Voltage Low Power (LVLP - 1.5V battery operation with less that 5?W power consumption) Operational Amplifiers using MOS transistors biased in the weak inversion region. The design procedure in Chapter-1 starts with a standard low-pass gm-C synthesis from a normalized double terminated LC ladder. Later, a new method for scaling of the filter for maximization of dynamic range is described. Finally, two filter design examples are worked out using the equations derived in the previous sections. Chapter-2 begins with the description of a new tool for the analysis of gm-C filter networks. Next, exact formulae predicting the effect of finite transconductor DC gain on the DC or passband gain of the overall filter is obtained. Finally, approximate formulae predicting the lowest value of the parasitic pole associated with the transconductor for minimum effect on the pass-band response of the overall filter is obtained. All the works in Chapters 1 and 2 have been successfully verified with Spice simulation in the thesis. In Chapter-3, the theory of MOS transistors in weak inversion is revisited. The theory is extended to obtain a set of useful formulae in order that analog circuits using such region of operation can be analyzed and designed. This chapter also describes a new biasing and sizing technique to be followed in such analog designs. Finally, the chapter concludes with a discussion on the viability and shortcomings of such an approach. Chapter-4 starts with calculation of device sizes as described in Chapter-3. Finally it describes in detail the design and analysis of three types of LVLP operational amplifiers and a Proportional To Absolute Temperature (PTAT) current reference for the biasing of the amplifiers using the device sizes calculated. All the designs in Chapter-4 have been verified with success, with Spice simulation results and measurement results of a test silicon device incorporating the three types of operational amplifiers and the PTAT bias current reference generator, in this thesis. In summary, attempt has been made, in this thesis, to lay down a reasonably good foundation to the two above-mentioned areas where extensive design efforts are still lacking. Seemingly unrelated, both arc promising areas for portable single l.5V battery operated applications. This is because the popular switched-capacitor filters and other analog building blocks are difficult to design for such low-voltage power supplies using a standard 5V or 3V CMOS process. Therefore the need to study deeply the characteristics of alternate filter realizations, suitable for such low- voltage applications, such as the gm-C is felt.