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, the voltage conditions modulating the current carried by the other channel.

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.

See also

• Field effect transistor

External links

• Jedec definition.