Analog IC modules design using trapezoidal association of MOS transistors in 0.35 μm technology

This works addresses how analog modules can be designed in a pre-diffused array of digital - i.e. minimum length - transistors. The mapping of each original single transistor of the circuit into an equivalent trapezoidal association of digital transistors (TAT) is analyzed. Three methodologies for the calculation of the equivalent TAT are presented: a linear resistor, a current model and a small-signal equivalent array approximation. These methods are applied to two IC modules designed with TAT associations in 0.35 μm technology to show the effect of the single-to-TAT conversions and to compare the conventional and the TAT design: a two-stage Miller operational amplifier and a track-and-latch switched analog comparator. The results are compared to the performance of the single-transistor designs, showing that minimum-length digital transistors can be properly arranged to obtain reasonable specifications for middle performance analog circuits. The advantages of the digital array are the reduced prototype time. The layout design of the TAT associations and of the full modules were done with LIT, an interactive layout tool.