ABSTRACT
This chapter develops a simple high-level analog design methodology based on an abstract model of a transistor to help designers cope with the system-level design. Integrated systems are getting more complicated, and the analog design no longer stays at the transistor level. The voltage-to-current conversion is made possible only by active devices such as transistors or vacuum tubes. In order to define the driving-point resistances for larger circuits made with many transistors, we need to understand how the driving-point resistances are affected if the other terminals are not grounded. Using low-frequency small-signal driving-point resistances, the low-frequency voltage gain and small-signal input and output driving-point resistances of these three amplifiers can be easily estimated. Small-signal resistances have been commonly derived from small-signal equivalent circuits, and solving small-signal simultaneous equations obtained by applying Kirchoff’s law. At low frequencies, the small-signal input resistance looking into the gate is infinite.
