Voltage applied to the gate causes the substrate under the gate to “flip polarity”. That allows them to be used as radio “mixers” to multiply one signal by another.Į-MOSFETs In an enhancement-mode MOSFET, the drain is isolated from the source because the substrate is doped opposite the source and drain. Like JFETs, D-MOSFETs are used in the front ends of radio receivers because of their inherently low internal noise.ĭ-MOSFET AGC Amplifiers Since gm depends on the Q-point, MOSFETs are used for Automatic Gain Control in radio receiversĭ-MOSFET Mixers Unlike JFETs, D-MOSFETs can be built with two gates. In addition, a class-A MOSFET amplifier can work with VGS = 0.ĭ-MOSFET Amplifiers The equations for Zin, Zout and Av developed for JFET amplifiers can be used with D-MOSFET amplifiers.
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