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The book focuses on the design of integrated operational amplifiers that approach the limits of low supply voltage or very high bandwidth. The resulting realizations span the whole field of applications from micro-power CMOS VLSI amplifiers to 1-GHz bipolar amplifiers. The work is especially useful for professional designers who like to improve their amplifier designs to match the state of the art. The book is also of interest to graduate students in the field of analog circuit design. After discussing the fundamentals of low-voltage power-efficient operational amplifier design in the first chapter, chapter 2 discusses input stages. First, basic input stages are discussed, followed by rail-to-rail input stages with constant transconductance for constant bandwidth. New input-stage circuits that result in compact solutions are presented (section 2.4). Finally, new compact PTAT bias-current generators are discussed by which a constant transconductance of CMOS input stages as a function of temperature can be obtained (section 2.5). In chapter 3, output stages are discussed. First, rail-to-rail output stages are treated. A rail-to-rail output-voltage swing can be obtained by using a common-source connected or common-emitter connected output stage. Class-AB biasing assures a compromise between power consumption and distortion. Two types of class-AB biasing principles can be distinguished: feedforward class-AB control and feedback class-AB control. Numerous examples of both principles are given in CMOS as well as in bipolar technology. In addition, the stability of the class-AB control loop of feedback biased output stages is analyzed (section 3.5). Especially interesting is the feedback class-AB biasing with a simple minimum selector which can be applied in CMOS as well as in bipolar technology (section 3.5). Secondly, aii-NPN output stages are presented. Thanks to the excellent performance of NPN transistors, all-NPN output stages are still important for achieving very high bandwidth or very high output-current capability. Finally, an overview of output stages in BiCMOS technology is given (section 3.7). For bipolar output stages in bipolar and BiCMOS amplifiers very important protection circuits are discussed which limit the output current and the saturation of output transistors (section 3.8).
Chapter 4 treats the overall design of operational amplifiers. In order to obtain sufficient gain, an operational amplifier consists of several cascaded gain stages. Since each stage introduces a dominant pole, frequency compensation is required to shape the frequency response. The only frequency compensation techniques suited to general purpose amplifiers are based on Miller compensation. Using Miller compensation the bandwidth reduces when the number of stages increases. The optimization of two-stage Miller compensated amplifiers is discussed. If the supply voltage is equal to one gate-source voltage and one saturation, at least three stages are needed to achieve sufficient gain in bipolar technology, in BiCMOS technology. and in CMOS technology. A three-stage amplifier can be compensated using nested-Miller compensation. Two new active versions of nested-Miller compensation are introduced: cascoded-nested-Miller compensation (section 4.6.2) and mirrored-nested-Miller compensation (section 4.6.3). In the final chapter, chapter 5, many realizations are presented. Two amplifiers have been designed in bipolar technology. The first amplifier is a wideband amplifier with a very high unity-gain frequency of I GHz. The second amplifier has a rail-to-rail class-AB output stage with a high ratio between the maximum output current and the quiescent current. Five amplifiers have been designed in CMOS technology. Three Amplifiers are based on a compact topology that can operate on a supply voltages down to one gatesource voltage and two saturation voltages which amounts to about 1.4 V. The two other CMOS amplifiers are based on an ultimate-low-voltage topology and can operate on supply voltages down to one gate-source voltage and one saturation voltages which amounts to about 1.2 V. In BiCMOS technology, five amplifiers have been designed. The first two amplifiers are based on a compact topology. Two other amplifiers are designed to operate on low supply voltages down to 1.3 V. The final amplifier uses a powerful combination of an aii-NPN output stage driven by a PMOS intermediate stage to obtain a power-efficient wideband amplifier. The amplifier has a unity-gain frequency of 200 MHz and can operate down to 2.5 V