Field-effect Tetrode
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The tetrode field-effect transistor or field-effect tetrode is a
solid-state Solid state, or solid matter, is one of the four fundamental states of matter. Solid state may also refer to: Electronics * Solid-state electronics, circuits built of solid materials * Solid state ionics, study of ionic conductors and their use ...
semiconductor device A semiconductor device is an electronic component that relies on the electronic properties of a semiconductor material (primarily silicon, germanium, and gallium arsenide, as well as organic semiconductors) for its function. Its conductivity li ...
, constructed by creating two field-effect channels back-to-back, with a junction between. It is a four-terminal device which does not have specific gate terminals because each channel is a gate for the other, the voltage conditions modulating the current carried by the other channel.


Current–voltage relationship

Where the voltage on the first channel is V_ - V_ and the voltage on the second channel is V_ - V_, the current in the first channel, I_, and the current in the second channel, I_, are given by: I_ = G_(V_ - V_) \left - \frac \frac \right/math> and I_ = G_(V_ - V_) \left - \frac \frac \right/math>, where the G_ are the low-voltage conductance of the channels and V_p is the pinch-off voltage (assumed to be the same for each channel).


Applications

The field-effect tetrode can be used as a highly linear electronically
variable resistor A potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat. The measuring instrum ...
– resistance is not modulated by signal voltage. Signal voltage can exceed
bias voltage In electronics, biasing is the setting of DC (direct current) operating conditions (current and voltage) of an active device in an amplifier. Many electronic devices, such as diodes, transistors and vacuum tubes, whose function is processing ...
, pinch-off voltage, and junction breakdown voltage. The limit is dependent on dissipation. Signal current flows in
inverse proportion In mathematics, two sequences of numbers, often experimental data, are proportional or directly proportional if their corresponding elements have a constant ratio, which is called the coefficient of proportionality or proportionality constant ...
to the channel resistances. The signal does not modulate the
depletion layer In semiconductor physics, the depletion region, also called depletion layer, depletion zone, junction region, space charge region or space charge layer, is an insulating region within a conductive, doped semiconductor material where the mobile ...
, so the tetrode can perform at high frequencies. The tuning ratio can be very large – the high resistance limit is in the megohms range for symmetrical pinch-off conditions.


See also

*
Field-effect transistor The field-effect transistor (FET) is a type of transistor that uses an electric field to control the flow of current in a semiconductor. FETs (JFETs or MOSFETs) are devices with three terminals: ''source'', ''gate'', and ''drain''. FETs contro ...
*
Multigate device A multigate device, multi-gate MOSFET or multi-gate field-effect transistor (MuGFET) refers to a metal–oxide–semiconductor field-effect transistor (MOSFET) that has more than one gate on a single transistor. The multiple gates may be control ...
, other multi-gate devices *
Tetrode transistor A tetrode transistor is any transistor having four active terminals. Early tetrode transistors There were two types of tetrode transistor developed in the early 1950s as an improvement over the point-contact transistor and the later grown-junction ...
, any transistor having four active terminals


References

Semiconductor devices {{Electronics-stub