Timing Models for MOS Circuits

Performance is an important aspect of integrated circuit design, and depends in part on the speed of the underlying circuits. This thesis presents a new method of analyzing MOS circuit delay, based on a single-time-constant approximation. The timing models characterize the circuit by a single parameter, which depends on the resistance and capacitance of the circuit elements. To ensure the single- time-constant approximation is valid for a particular circuit, the timing models provide both an estimate and bounds for the output waveform. For circuits where the bounds are poor, an improved timing model is derived. These simple models provide insight about circuit performance issues, as well as determining the circuit delay. The timing models are first developed for linear networks and then are extended to model MOS circuits driven by a step input. By using the single-time-constant approximation, the output waveform of a complex MOS circuit can be modelled by the output of a circuit consisting of a single MOS transistor and a single capacitor. Finally, a new circuit model of a gate is used to derive the output waveform of a circuit driven by an arbitrary input. The resulting timing model does not depend strongly on the shape of the input: the output waveform only depends on the input''s slope at the gate''s switching voltage.