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- Discrete complementary JFETs are N-channel and P-channel JFETs that are built with a similar process technology and are designed to have similar or matching electrical characteristics. Discrete complementary JFETs come in separate P and N-channel packages. Dual discrete complementary JFETS house two N-channel JFETs in one monolithic unit and two P-channel units in another monolithic unit. Because they are built on the same die, dual N-Channel JFETs have nearly equivalent or matched electrical characteristics. The same can be said for the dual P-Channel JFETs. Although, complementary P and N-Channels are built with the same process technology, because of basic differences between the construction of P and N channel devices, electrical specifications such as mobility and transconductance are slightly different for the P and N-Channel JFETs. The complementary and matched nature of the dual N-channel and dual P-channel JFETs is fundamental to the building of many analog circuits, most notably amplifiers. Specifically, topologies are based on a number of complementary matched JFET pairs. As one example, a fully complementary amplifier will use matched N and P-channel JFETs for the differential amplifier front end. Other complementary and matched JFET blocks within complementary amplifiers include stacked and and level translators (level shifters). Source followers (buffers) are another complementary structure found in amplifiers. The complementary source follower, often used in the of an amplifier, can be designed such that it can adjust the output offset voltage to zero, effectively, eliminating the need for an AC coupling capacitor. A complementary source follower can also be paralleled to create power amplifiers. Nelson Pass built such a design based on Toshiba's 2SK170 and 2SJ74 single complementary JFETs with over 1000 parallel JFETs. Today though, since Toshiba discontinued these parts, you would have to build such an amplifier with LSK170 and LSJ74 single complementary pairs or with LSK489 and LSJ689 JFETs. Because the LSK489 and LSJ689 have lower input capacitance than Toshiba parts and are duals the same kind of amplifier design would have lower noise levels and a smaller footprint. Amplifier bias networks will also incorporate JFETs current sources, although not necessarily in matched arrangements. JFET current mirror designs, for use in amplifiers, have been patented using matched JFETs, such as the LSK389 and GaAs JFETs. Besides amplifiers, discrete JFET matched pairs are also used in the design of voltage controlled resistors, voltage controlled current sources, , , voltmeters, phasers and a wide range of analog computational circuits like These blocks often are designed with matched N-channel pairs, matched P-channel pairs, or complementary matched pairs. (en)
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