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

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

and

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

Where the $G_{i}$ 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 - 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.
2. Academic Press Dictionary of Science and Technology. Christopher G. Morris (editor). Academic Press. 15 September 1992. p. 824. ISBN 9780122004001.

External links

• Jedec definition.