Analog MOS Integrated Circuits for Signal Processing

Chapter Four

MOS OPERATIONAL AMPLIFIERS

The MOS operational amplifier is the most intricate, and in many ways the most important, building block of switched-capacitor circuits. Its performance usually limits the high-frequency application and the dynamic range of the overall circuit. Without a thorough understanding of the operation and the basic limitations of these amplifiers, the circuit designer cannot determine or even predict the actual response of the overall system. Hence, this chapter gives a fairly detailed explanation of the usual configurations and performance limitations of operational amplifiers. A design example is also worked out to acquaint the reader with the problems and tradeoffs involved in amplifier design.

The technology, and hence the design techniques used for MOS amplifiers change rapidly. Therefore, the main purpose of the discussions is to illustrate the most important principles underlying the specific circuits and design procedures. Nevertheless, the treatment is detailed enough to enable the reader to design high-performance MOS operational amplifiers suitable for most switched-capacitor circuit applications.

4.1. OPERATIONAL AMPLIFIERS¹, ²

In switched-capacitor filters—in fact, in all active filters—the most commonly used active component is the operational amplifier, usually simply called op-amp. Ideally, the op-amp is a voltage-controlled voltage ...