CMOS Voltage References: An Analytical and Practical Perspective

1

Warm Up

The voltage reference circuits discussed in this book require you to work on electron devices by connecting together transistors, resistors, and capacitors. Therefore you need to understand the properties and limitations of each device in some detail. The easiest way to learn about electron devices is to study their physical models, although they are usually very complex. For example, the Gummel and Poon model of a bipolar transistor lists 45 parameters (Gummel and Poon, 1970) and yet still is not accurate enough to simulate the saturation or junction breakdown behaviors. The BSIM 3.3 model of a MOS transistor has more than 50 coefficients (Liu, 2001) not counting noise and gate leakage parameters. Although all of these variables are useful for the design of voltage reference circuits, only very few numbers and equations have to be remembered for creative work, and the shapes of a few dependencies and some qualitative relationships (not how much, but more or less, increasing or decreasing) of these parameters are much more important.

The following sections will present, from the authors’ point of view, the most important electron device parameters necessary for voltage reference circuit design. Detailed descriptions of the operations of individual electron device can be found in textbooks on analog circuit design or device modeling (Hu, 2010; Sze, 1969). In particular, a large part of this book presents the design and analysis of a special kind of voltage reference circuit, ...