Trying to find MOSETs with Gm < 0.4millisiemens

[rakeshvadyala]

Hi All:

I was trying to find a company which sells MOSFETs with Transconductance (Gm) < 0.4millisiemens.

If any one knows from where i can get the above devices please post me.

Thanks and Regards,
Ray

 

[Papabravo]

This is a bit like nailing jelly to a tree. The parameter gm, or forward transconductance, is the slope of the Id vs. Vgs characteristic curve. It has a very small slope for Vgs < Vgs(th). For Vgs >> Vgs(th) the slope is increasing linearly given the quadratic nature of that particular curve. So gm will be in a range from 0 to 400 uS(.4 mS) as Vgs goes from 0 to some voltage which may be less than, equal to, or greater than Vgs(th).

It is also worth mentioning that no manufacturer I could find has a parametric search on this parameter for what should by now be altogether obvious reasons.

 

[Hero999]

Use negitive feedback to control the gain in your amplifier. Requesting a transistor with a gain below a certain level isn't very sensible. You realy want as much gain as possible then use negitive feedback to cut it down to a reasonable level.

 

[Analog]

This is a bit like nailing jelly to a tree. The parameter gm, or forward transconductance, is the slope of the Id vs. Vgs characteristic curve. It has a very small slope for Vgs < Vgs(th). For Vgs >> Vgs(th) the slope is increasing linearly given the quadratic nature of that particular curve. So gm will be in a range from 0 to 400 uS(.4 mS) as Vgs goes from 0 to some voltage which may be less than, equal to, or greater than Vgs(th).

It is also worth mentioning that no manufacturer I could find has a parametric search on this parameter for what should by now be altogether obvious reasons.

Exactly! The minimum gm is no big deal, one can bias the gm to be zero, if you're sufficiently close to vgs(off). The max gm is another story, as the max slope occurs just before IDSS on the transconductance curve.