As a transconductance amplifier, the small signal input voltage, v be for a BJT or v gs for a FET, times the device transconductance g m, modulates the amount of current flowing through the transistor, i c or i d.
voltage in, current out) or as a voltage amplifier (voltage in, voltage out). The common emitter or source amplifier may be viewed as a transconductance amplifier ( i.e. When larger multi-stage amplifiers are assembled, both types of transistors are often interspersed with each other.įigure 9.2: Basic n-type inverting voltage amplifier circuit (neglecting biasing details) The same basic amplifier stages can just as easily be implemented using p-type transistors (PNP, PMOS). In this chapter we will primarily be using n-type transistors (NPN, NMOS) in the example circuits. The remaining terminal is what is thus common to both input and output. The easiest way to determine if a device is connected as common emitter/source, common collector/drain, or common base/gate is to examine where the input signal enters and the output signal leaves. This leads to the names common emitter, etc. This means one of the transistor terminals must be common to both the input and output circuits. Representing the basic amplifier as a two port network as in figure 9.1, there would need to be two input and two output terminals for a total of four. The transistor, as we have seen in the previous chapter, is a three-terminal device.
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