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Consider the Discrete JFET When You Have a Priority Performance Objective


Though not as well known as the bipolar transistor or op amp, this long-established transistor still excels in where you need to optimize circuit behavior, such as for lowest noise. Many engineers are somewhat familiar with discrete bipolar transistors, such as the venerable 2N2222. They are also comfortable with the MOSFET (metal-oxide semiconductor field-effect transistor) as a discrete device for amplifying analog signals and switching power signals, as well as its role as the key digital structural element in large-scale ICs. But alongside these devices is the JFET (junction field-effect transistor), which was developed soon after the bipolar transistor. To many designers, the JFET is the nearly ideal three-terminal solid-state device, and its operation and parameters are analogous to the vacuum-tube triode. The difference is that the JFET is, of course, a low-voltage, much-more efficient device, although it can't deliver the power that a vacuum tube can. For applications which require extremely low noise, the JFET is often offers superior performance compared to any other discrete device, as well as op amps.

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