T
Tim Williams
- Jan 1, 1970
- 0
In my semiconductor physics class, the prof said a past student project
involved using a FET as an UJT. Now, the physics behind this is basically
injecting carriers into the channel, basically super-enhancing it, in such a
way that incremental resistance (with respect to the gate, which is now the
emitter) goes negative.
Now, it seems to me that your average FET has a fairly conductive channel,
maybe 300 ohms for a 2N3819 (give or take), and that's a weak FET as FETs
go. So you super-enhance that, and it's going to drop to what, 30 ohms? 3
ohms? That's pretty low to make use of, at least without going *Phut*. As
I recall, UJTs were in the 5kohm range, so they'd be lightly doped, and as a
result fairly sensitive (large change in resistance).
Would it work better with source or drain as the common terminal? With
lithographic construction, one end is bound to be longer, which means more
length to make use of the injected carriers. Actually, that'll only be true
if they make vertical FETs... maybe they're all lateral?
Tim
involved using a FET as an UJT. Now, the physics behind this is basically
injecting carriers into the channel, basically super-enhancing it, in such a
way that incremental resistance (with respect to the gate, which is now the
emitter) goes negative.
Now, it seems to me that your average FET has a fairly conductive channel,
maybe 300 ohms for a 2N3819 (give or take), and that's a weak FET as FETs
go. So you super-enhance that, and it's going to drop to what, 30 ohms? 3
ohms? That's pretty low to make use of, at least without going *Phut*. As
I recall, UJTs were in the 5kohm range, so they'd be lightly doped, and as a
result fairly sensitive (large change in resistance).
Would it work better with source or drain as the common terminal? With
lithographic construction, one end is bound to be longer, which means more
length to make use of the injected carriers. Actually, that'll only be true
if they make vertical FETs... maybe they're all lateral?
Tim
