ch2 low freqy response

Frequency response

The analysis of integrated-circuit behavior which studied in the second stage of electrical department was concerned with low frequency performance, and the effects of parasitic capacitance in transistors were not considered. However, as the frequency of the signal being processed by a circuit increases, the capacitive elements in the circuit eventually become important. In this chapter, the small signal behavior of integrated circuits at high frequencies is considered. The frequency response of single-stage amplifiers is treated first, followed by an analysis of multistage amplifiers, and those parts of the circuit that limit its frequency response are identified.
The basic topology of the small-signal equivalent circuits of bipolar and MOS single-stage amplifiers are similar. Therefore the frequency-response analysis for each type of single-stage circuit is initially carried out using a general small-signal model that applies to both types of transistors, and the general results are then applied to each type of transistor. For example in the general model becomes C" in the bipolar model and Cgs in the MOS model. However, some devices specific small-signal elements are not included in the general model. for example, the gm generator and capacitors in the MOS models arc not incorporated in the general model. The effect of such device-specific elements will be handled separately in the bipolar and MOS sections.