Op amps make JFET circuits repeatable

摘要

Recause they use practically no bias current (a useful feature in itself), JFETs also have practically no current noise. This feature means that you can use JFETs in very-high-resistance circuits and obtain good noise performance. JFETs are also fast devices, with garden-variety types specified in the hundreds of megahertz. On the flip side, JFETs are difficult to exploit in a manufacturing environment because they have widely varying dc specifications. With a simple resistor-based bias network, the same part number can give results that differ by several volts from device to device.