Analog Devices and Passive Components

Abstract

Analog devices allow the design of circuits whose inputs and outputs are continuously varying quantities, such as resistance, capacitance, current, and voltage. The measured analog signal has an infinite number of possible values. The information is conveyed by the instantaneous value of the signal. Initially, analog circuits were designed primarily with bipolar transistors (Chap. 3). Analog {MOSFETs}, however, have become increasingly important because of their higher packing density, lower cost, high input impedance, and performance that has gradually approached that of bipolar transistors While several component parameters can be simultaneously optimized for digital and analog applications, there are specific analog requirements that are different from digital. In particular, the trend in high-performance, high-density digital {MOSFETs} is to reduce the size to deep submicron and nanoscale dimensions and operate at supply voltages as low as about 0.8 V, while analog devices typically require higher voltages and hence larger dimensions, particularly to ensure a sufficiently large signal-to-noise ratio. Other parameters, such as high transistor cut-off frequency, high maximum oscillation frequency, and high Early voltage, low bipolar base resistance, low component mismatch, and low noise, are of particular importance to analog applications. The relative importance of these parameters depends on application. When mixed analog and digital components are designed on the same die, such as in system on a chip ({SoC}), there is a trade-off between simultaneously optimizing the two sets of components and manufacturing cost