Sizing the Miller Op. Amp.
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Fixing currents and transistors widths of Op. Amps is a multifaceted task owing to the growing number of choices that can be made. Sizing implies hierarchy. Some objectives ought to be satisfied whichever choices. They shape the specifications list. A typical example is the I.G.S gain-bandwidth product. Other objectives are desirable but not mandatory. They determine attributes like power consumption versus area. Specifications determine the dimensions of the g m ∕ I D sizing spacewhile attributes delineate optimization areas within the sizing space. The specificationsof the Miller Op. Amp considered in this chapter are twofold: a prescribed gain-bandwidth product and an assessment regarding stability. The sizing space conforms to a two-dimensional space. Every point represents a distinct Miller Op. Amp that fulfills the same specifications. Low-power consumption demarcates a region within the 2D sizing space. Area minimization relates to another region. Eventually regions intersect easing choices. Whichever combination, specifications must be met anyway.
The axes of the sizing space play the same role as the gate voltage, drain current or normalized drain current in the I.G.S. They represent variables controlling the modes of operation of transistors or ensembles of transistors. In the Miller Op. Amp, we are going to focus on the two stages and control their behavior by means of two distinct vectors. Each vector is supposed to control transistors that have a strong impact on the fulfillment of the specifications.
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