19 - Talking Electronics

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506 Principles of ElectronicsIn the previous chapters, we have discussed the cir-cuit applications of an ordinary transistor. In thistype of transistor, both holes and electrons play partin the conduction process. For this reason, it is some-times called a bipolar transistor. The ordinary or bipo-lar transistor has two principal disadvantages. First, ithas a low input impedance because of forward biasedemitter junction. Secondly, it has considerable noiselevel. Although low input impedance problem may beimproved by careful design and use of more than onetransistor, yet it is difficult to achieve input impedancemore than a few megaohms.

508 Principles of Electronics JFET polarities. Fig. 19.2 (i) shows n-channel JFET polarities whereas Fig. 19.2 (ii) shows thep-channel JFET polarities. Note that in each case, the voltage between the gate and source is such that the gate is reverse biased. This is the normal way of JFET connection. The drain and source

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