Don Pearce wrote:
Eeyore wrote:
Don Pearce wrote:
Eeyore wrote:
Don't know laterals - haven't kept up. Gimme some numbers and I'll go
have a look.
You're a bit late now they've almost come and gone. Arrived ~ 1980 courtesy of
Hitachi. 2SJ56 and 2SK176 were a classic complementary pair but no longer
manufactured. Equivalent types now sourced by Semelab and Exicon.
http://www.profusionplc.com/pro/gex/...teral%20mosfet
Oh, I thought there was something new going on. They have exactly the Gm
characteristic I was talking about. Here's the thing. Bipolar Gm is
enormously bigger than mosfet, and you can use that in an output stage.
Oh sure. But look at the Hitachi data I posted a few mins later. Look how linear that
curve is especially beyond the typical 100mA quiescent operating current.. Id vs Vgs The
Exicon data sheet doesn't have the equivalent plot for some reason.
The high gm of bipolars is great until you get to a few mA or tens of mA of Ic when it's
crap and that's where crossover distortion comes from. You just can't get rid of it.
Yup, looking now. The transfer characteristic is the alomst-square-law
curve I was expecting; I don't think you can get anything else from a
mosfet. As for Gm, the 0.4V change in Vgs from -1.2 to -1.6 yields a
drain current change of 0.24A (-0.35 to -0.59A) at 75C. That is a Gm of
0.6!
It averages out including higher currents at about 1S.
You can cross over a bipolar output stage long before you hit that
kind of number.
And you'll still get crossover distortion.
Graham