Engineering: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 [math]\displaystyle{ I_{1} }[/math], the current in the second channel is [math]\displaystyle{ I_{2} }[/math], the voltage of the first channel is [math]\displaystyle{ V_{1} }[/math] - [math]\displaystyle{ V_{2} }[/math] and in the second channel [math]\displaystyle{ V_{3} }[/math] - [math]\displaystyle{ V_{4} }[/math] we have:
[math]\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] }[/math]
and
[math]\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] }[/math]
Where the [math]\displaystyle{ G_{i} }[/math] are the low-voltage conductance of the channels and [math]\displaystyle{ V_p }[/math] 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
- ↑ 1.0 1.1 Integrated circuits: Design Principles and Fabrication. Raymond M. Warner, Jr. and James N. Fordemwalt (editors). McGraw Hill. 1965. pp. 220–223.
- ↑ Academic Press Dictionary of Science and Technology. Christopher G. Morris (editor). Academic Press. 15 September 1992. p. 824. ISBN 9780122004001. https://archive.org/details/academicpressdic00morr.
External links
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