Bill Stewart
Absolutely. I mean, has anybody actually used JFETs in recent years? :-)
Well played, sir. :) By the way, the answer is in most cases no, sadly. Most vanilla CMOS processes don't have high quality JFETs available. On older nodes maybe you can get away with turning an N-well and a P+ diffusion into a JFET, but that doesn't work very well in more modern processes because the N-wells have strongly retrograde doping, which makes it hard to pinch off the "bottom" of the channel. Of course, even at older nodes where it might be possible, the fabs don't bother characterizing it for you. Sure, you can characterize it yourself, but if the fab isn't supporting the device that implicitly means they're not monitoring the quality of that device with their PCM structures, so good luck with manufacturability long-term. JFETs are pretty easy to make in high quality bipolar processes because the base diffusion makes a decent JFET body. Doesn't add much/any cost to have them in this case. Of course, if you have a BiCMOS process, then you already have devices with high impedance gates, but for high performance analog design a JFET beats the hell out of a MOSFET, since the latter brings along with it a shitload of 1/f noise. One place I've recently seen JFETs is in really high voltage processes. Think like a mostly normal 0.18u CMOS process with a 600V (Vds) JFET available. Haven't actually worked in such a beast, but you can imagine that compared to MOSFETs, JFETs don't make such great power devices--- who ever heard of a depletion-mode power switch? -=rsw