Isolated channel mosfets? - Page 1
Forum section: electronics / beginners

author: Deactivated-1
author_rank: Frequent Contributor
timestamp: December 13, 2021, 03:54:45 pm
content: I found a mention of Isolated channel from gate mosfets in a russian magazine, and can't find any info on them in english, doesn anyone know what they're for and what's the isolated gate meant for? (Might sound stupid, but could it be like the supressor grid in a pentode, but instead just being able to drive a signal into that as well as the gate?)schematic symbols in the attached image:[ Attachment Invalid Or Does Not Exist ]

author: TimFox
author_rank: Super Contributor
timestamp: December 13, 2021, 04:08:15 pm
content: There aredual-gateMOSFETs, which were popular in 100 MHz applications (TV and FM), where the second gate was analogous to the screen grid, and could be used to inject the LO signal for heterodyne mixing.

author: wraper
author_rank: Unknown
timestamp: December 13, 2021, 05:00:20 pm
content: They are literally usual MOSFETs (field-effect transistors with insulated gate).https://en.wikipedia.org/wiki/MOSFETQuoteThose 4 examples are depletion/enhancement mode MOSFETs with p/n channel type.

author: NorthernWing
author_rank: Contributor
timestamp: December 13, 2021, 05:09:16 pm
content: That's not the gate, those 4-pin FETs just have a separate body terminal. The body is usually tied to the source in most MOSFETs because there are only a few situations for things like using a FET as an analog pass transistor where you might want to tie the body to some other voltage. They're otherwise the same as any other 3-pin MOSFET.

author: wraper
author_rank: Unknown
timestamp: December 13, 2021, 05:14:43 pm
content: Those П pins mean Подложка (Substrate).http://hightolow.ru/transistor4.php

author: TimFox
author_rank: Super Contributor
timestamp: December 13, 2021, 06:56:50 pm
content: Quote from: ELS122 on December 13, 2021, 04:52:12 pmNo they aren't. I was referring to your question about analogous screen grids.

author: David Hess
author_rank: Super Contributor
timestamp: December 14, 2021, 05:32:50 am
content: NorthernWing has it right; MOSFETs are inherently 4 terminal devices but conventionally the body is tied to the source. An example of a classic 4 terminal MOSFET is the 3N170. Micrel makes the MIC94030 for high side power switching.

author: rpiloverbd
author_rank: Regular Contributor
timestamp: December 14, 2021, 12:11:19 pm
content: Not sure. Is there any chance that the article was talking aboutIGBT(Insulated gate bipolar transistor)?

author: tooki
author_rank: Super Contributor
timestamp: December 14, 2021, 05:15:50 pm
content: Quote from: ELS122 on December 13, 2021, 03:54:45 pmThe MOSFET is the best known type of IGFET, the insulated-gate field effect transistor, to the point that they’re basically synonyms, though nobody says IGFET any more. So for all intents and purposes, all it means is MOSFET.

author: TimFox
author_rank: Super Contributor
timestamp: December 14, 2021, 09:54:07 pm
content: Quote from: ELS122 on December 14, 2021, 04:22:36 pmThe second gate is like unto the supressor grid (G3) in a 6AS6, or G3 of a 6L7. Special pentodes such as the 6AS6 were designed for supressor control. It was rare to inject a signal into the screen (G2) of a pentode, but gate 2 of the dual-gate MOSFET was not forward-biased as in a screen grid.Otherwise, gate 2 acted like the screen grid, or the upper grid in a cascode of two triodes.Anyway, I was making statements of fact, not refutation of your premises.