Johan H. Huijsing

Design of low-voltage, low-power operational amplifier cells

Preface. List of Symbols. 1. Introduction. 2. Low-Voltage Analog Design Considerations. 3. Input Stages. 4. Output Stages. 5. Overall Topologies. 6. Realizations. Index.

Compact low-voltage and high-speed CMOS, BiCMOS, and bipolar operational amplifiers

Preface. List of symbols. 1. Introduction. 2. Input Stages. 3. Output Stages. 4. Overall-Design Techniques. 5. Realizations. Index.

Low-Voltage Analog Design Considerations

In today’s system design the term low-voltage is used for circuits which are able to run on supply voltages somewhere between 1 and 5 Volts. These low supply voltages put an upper limit on the number of gate-source voltages and saturation voltages which can be stacked. However, the supply voltage itself does not relay anything about the required circuit topology. For example, designing a 3-V amplifier in a process with threshold voltages of about 1 V allows about two stacked gate-source voltages, while designing a 3-V amplifier using a process having low threshold voltages of 0.5 V allows about five stacked gate-source voltages. Therefore, in order to be able to categorize the different circuit topologies, a classification of low-voltage in terms of gate-source voltages and saturation voltages will be given in section 2.2. This classification will be used throughout this book.

Capacitively-Coupled Chopper Operational Amplifiers

In Chap. 3, the basic capacitively-coupled chopper topology for operational amplifiers (opamp) has been described. In this chapter, two capacitively-coupled chopper opamps (CCOPA) will be presented. They both achieve wide input common-mode voltage range (CMVR) and high precision. The first opamp employs a single-path architecture and features high power efficiency and simplicity. The second opamp is more complex and employs a multipath architecture. Thus, it is less power efficient, but has a wider bandwidth and a smoother transfer function.

Capacitively Coupled Chopper Instrumentation Amplifiers for High-Side Current Sensing

In Chap. 1, it was mentioned that high-side current sensing is an important application for capacitively coupled chopper amplifiers.

Capacitively Coupled Chopper Instrumentation Amplifiers for Low-Voltage Applications

Chapter 6 has explored the use of a CCIA for high-side current sensing applications, where its wide CMVR and high power efficiency can be optimally leveraged.

Capacitively Coupled Chopper Amplifiers

As discussed in Chap. 1, capacitively coupled chopper amplifiers can potentially handle input common-mode voltages far beyond their own supplies. Furthermore, their inherent use of chopping means that they can also achieve microvolt offset and low 1/f noise.

Choppers for High Input Common-Mode Voltages

As described in Chaps. 1 and 3, capacitively coupled chopper amplifiers can potentially achieve an input CMVR equal to the breakdown voltage of their input capacitors.

The Chopping Technique

As briefly explained in Chap. 1, the chopping technique has been applied to convert DC input signals into AC signals that can then be capacitively coupled to the input stage of a capacitively coupled amplifier. Since chopping up-modulates offset and 1/f noise away from DC, high precision, i.e., microvolt offset and low 1/f noise, can be achieved. These characteristics make such amplifiers ideally suited for the amplification of small low-frequency signals. In this chapter, the basic working principle of chopping and its application in precision amplifiers will be discussed. It will be shown that chopping usually results in AC ripple at the chopping frequency, which must then be suppressed. Thus, the techniques to reduce this ripple will also be described. After this, the non-idealities of chopping will be discussed, followed by a summary of its pros and cons. Finally, conclusions will be drawn at the end of the chapter.

Overall Topologies and Frequency Compensation

An operational amplifier intended for use in VLSI mixed-mode systems should be able to operate under conditions which differ from application to application. One can think of different types of passive feedback, varying load impedances, process variations, temperature variations, and many more. Under all these varying conditions an operational amplifier has to be stable. To achieve this stability, it has to act like a one-pole system up to its unity-gain frequency under all circumstances.