Field effect tetrode

The field effect tetrode is a solid-state device, constructed by creating two field effect channels back-to-back, with a junction between. It is a four terminal device with interesting properties. It does not have specific gate terminals since each channel is a gate for the other,[1] the voltage conditions modulating the current carried by the other channel.[2]

Current voltage relationship

Where the current in the first channel is ${\displaystyle I_{1}}$, the current in the second channel is ${\displaystyle I_{2}}$, the voltage of the first channel is ${\displaystyle V_{1}}$ - ${\displaystyle V_{2}}$ and in the second channel ${\displaystyle V_{3}}$ - ${\displaystyle V_{4}}$ we have:

${\displaystyle I_{1}=G_{1}(V_{1}-V_{2})\left[1-{\frac {2}{3V_{p}^{1/2}}}{\frac {(V_{1}-V_{3})^{(3/2)}-(V_{2}-V_{4})^{(3/2)}}{(V_{1}-V_{3})-(V_{2}-V_{4})}}\right]}$

and

${\displaystyle I_{2}=G_{2}(V_{3}-V_{4})\left[1-{\frac {2}{3V_{p}^{1/2}}}{\frac {(V_{3}-V_{1})^{(3/2)}-(V_{4}-V_{2})^{(3/2)}}{(V_{3}-V_{1})-(V_{4}-V_{2})}}\right]}$

Where the ${\displaystyle G_{i}}$ are the low-voltage conductance of the channels and ${\displaystyle V_{p}}$ 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 - resistance is not modulated by signal voltage. Signal voltage can exceed bias voltage, pinch-off voltage and junction breakdown voltage. The limit is dependent on dissipation. Signal current flows in inverse proportion to the channel resistances - signal does not modulate the depletion layer, meaning the tetrode can perform at high frequencies. The tuning ratio can be very large - the high resistance limit in the megohms range for symmetrical pinch off conditions.[1]

See also

• Field effect transistor

References

1. Integrated circuits: Design Principles and Fabrication. Raymond M. Warner, Jr. and James N. Fordemwalt (editors). McGraw Hill. 1965. pp. 220–223.CS1 maint: others (link)
2. Academic Press Dictionary of Science and Technology. Christopher G. Morris (editor). Academic Press. 15 September 1992. p. 824. ISBN 9780122004001.CS1 maint: others (link)

External links

• Jedec definition.