On Tue, 21 Sep 2004 20:56:00 +0200, "Helmut Sennewald"
wrote:
"Paul Burridge" schrieb im Newsbeitrag
.. .
Hi guys,
I saw in Malvino's Electronic Principles that it is stated that Idss
and gfs (the transconductance/gain) are easy to measure, whereas
Vgs(off) is not and that manufacturers calculate it from this formula
(hope I've remembered it right)
Vgs(off) = -2*Idss/gfs
I've just checked out this assertion by measuring Vgs - v - Id for a
bunch of assorted FETs and found that I could easily establish the
pinch off voltage to within about 0.1V either way. Contrary to what
the book says, I personally have found it a simple matter to measure
Vgs(off). So why do they make out it's a big deal?
Hello Paul,
Vgs_off seems to be often specified at Id=1nA. The measurement
at such low current levels takes a lot of time and it requires a
very clean test fixture.
How have you measured at exactly Id = 1nA +/-0.1nA ?
Best Regards,
Helmut
A typical datasheet:
http://www.fairchildsemi.com/ds/J3/J310.pdf
So, with not too much fault you may use a VTVM as load and see which
voltage it reads....
---
J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/c.htm