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The junction field-effect transistor (JFET) is one of the simplest types of field-effect transistor. [1] JFETs are three-terminal semiconductor devices that can be used as electronically controlled switches or resistors , or to build amplifiers .
The JFET (junction field-effect transistor) uses a reverse biased p–n junction to separate the gate from the body. The static induction transistor (SIT) is a type of JFET with a short channel. The DEPFET is a FET formed in a fully depleted substrate and acts as a sensor, amplifier and memory node at the same time.
When referring to a junction field-effect transistor (JFET), the threshold voltage is often called pinch-off voltage instead. [ 1 ] [ 2 ] This is somewhat confusing since pinch off applied to insulated-gate field-effect transistor (IGFET) refers to the channel pinching that leads to current saturation behavior under high source–drain bias ...
Top: source, bottom: drain, left: gate, right: bulk. Voltages that lead to channel formation are not shown. In field-effect transistors (FETs), depletion mode and enhancement mode are two major transistor types, corresponding to whether the transistor is in an on state or an off state at zero gate–source voltage.
Figure 1: Basic N-channel JFET common-source circuit (neglecting biasing details). Figure 2: Basic N-channel JFET common-source circuit with source degeneration. In electronics, a common-source amplifier is one of three basic single-stage field-effect transistor (FET) amplifier topologies, typically used as a voltage or transconductance amplifier.
So much so, that JFET devices are packaged and sold as voltage-controlled resistors. [21] Typically, JFETs when they are packaged as VCRs often have high pinch-off voltages, which result in a greater dynamic resistance range. JFETs for VCRs are often packaged in pairs, which allows VCR designs that require matched transistor parameters.
A JFET can be made to act as a current source by tying its gate to its source. The current then flowing is the I DSS of the FET. These can be purchased with this connection already made and in this case the devices are called current regulator diodes or constant current diodes or current limiting diodes (CLD).
The JFET is externally-powered by the DC voltage V + through a resistor which sets the gain and output impedance. The output audio signal is received though a DC blocking capacitor . An electret microphone is a microphone whose diaphragm forms a capacitor (historically-termed a condenser ) that incorporates an electret .