[pdf] Analog Design for Cmos VLSI Systems

 

 

 The purpose of this book is to describe the design techniques of analog integrated circuits and to teach the reader how to properly design CMOS operational amplifiers and comparators for mixed analog-digital integrated systems. Analog circuits have become an increasingly critical factor for the systems design. The huge amount of transistors made available by sub-micron technologies allows us to integrate entire systems on chip (SoC). Therefore, analog sections, digital parts, and possibly sensors must use the same technology, the same supply voltage, the same silicon substrate and so on. Moreover,

the increased speed of operation and the augmented resolution of digital processors require performing analog functions: such as speed, dynamic range, power supply and noise rejection. Without a deep understanding of the operation and the limits of basic analog circuits, the designer can not properly design the analog processing functions required by modern systems. Thus, this book gives a fairly detailed study of CMOS circuit configurations, learning performances and limits.

This book evolved from a set of lecture notes written in 1986 for an inhouse training short course presented in a semiconductor company. Later the material formed the basis of a graduate course on analog CMOS integrated circuit offered since 1998 at the Pavia University, Italy. The initial set of lecture notes progressed in time following the technology evolution. The reference technology migrated from a CMOS to the CMOS used in this book. The circuit techniques moved from design targets like 5 V and tens of MHz bandwidth to the present 1.8 V and hundreds of MHz bandwidth. However, such an amazing change did not modify much of the basic philosophy: to follow a bottom-up approach. The teaching starts from basic physics elements, discusses the features of the MOS transistor, studies the passive components, and considers circuit design of basic blocks, current and voltage reference. In this way the reader acquires all the elements necessary to properly design op-amps and comparators.

 

The book contains six chapters. Chapter 1 provides those physical, technological and device modelling issues necessary to properly comprehend the behaviour of MOS transistors and their modelling. Chapter 1 starts with a resume of the basic principles of solid state physics and discusses the properties of the basic materials used in microelectronics. This enables the modelling of MOS transistors, both at a simple level, and at a more complex level for computer simulation. Finally, the chapter studies noise performances and discusses layout techniques.

Chapter 2 examines the basic properties of integrated resistors, capacitors and analog switches. The features of integrated components are quite different from the ones of discrete elements. Therefore, it is essential that the reader knows limits and performances well.
 

Chapter 3 studies simple gain stages, differential pairs, differential to single ended convertors, output stages, etc. The approach conforms the hierarchical view of the teaching pattern: the reader must become familiar with and understand the features and performances of simple cells before studying more complex cells. 

 

The basic building blocks studied in Chapter 3 and other analog functions require, as essential elements for their operation, current generators and voltage biases. Chapter 4 covers the basic architecture of current and voltage sources. This enables the reader to know how to design these “auxiliary” blocks appropriately, to recognize their functional limits, and to estimate costs and benefits for the best design decision.
 

Chapter 5 deals with operation amplifiers (usually referred to as op-amps). The function and operation of op-amps should be well known to the reader. For this reason, the chapter deals with those circuit implementations that are specifically used in CMOS integrated VLSI systems. Namely, the chapter studies a special category of op-amp: the operational transconductance amplifiers (OTAs). An OTA achieves a large gain exploiting its large output resistance. The reader will learn that when used inside an integrated architecture an op-amp drives capacitive loads. This makes the request of having a low output impedance of little importance.

Chapter 6 studies CMOS comparators. A comparator is together with the op-amp the basic block used in analog signal processors. Ideally, it generates an output logic signal as response to an analog input. Since a real circuit does not achieve the ideal function it is essential to know how the limitations affec