On Sat, 23 Feb 2002, Konrad Burylo wrote: > To make it clear: NMOS technology use two kinds of N-channel transistors: > enhancement mode (normally off) and depletion mode ones (normally on). CMOS > technology use enhancement mode N-channel and P-channel (instead of > depletion mode N-channel). Depletion mode transistors are what I'd call normally "half on". It is possible to turn them off with a negative Vgs and to turn them on more with a postive Vgs, but they are typically used with Vgs=0V as resistive elements. > I haven't heard of PMOS logic chips - but the hole mobility is about 2.5 > times less than electron mobility and P-channel transistor should have ~2.5 > times wider channel to have the same transconductance as N-channel one. So > PMOS gates would simply be bigger... Or slower. In fact, generally not as good. Does anyone know of any PMOS logic ICs? I was surprised to find out recently that the SN76489 DCSG used in a number of old systems is in fact bipolar - current injection logic if I'm not mistaken. > Marko - have you tried to exchange the crystal with a different one ? I'm > curious if it's not just an accident, that oscillator runs without > capacitors. Once I was doing something with AT-mega, and it didn't work > without capacitors. Also didn't work with 100nF one (a guy put one 33pF and > one 100nF by a mistake) ;-) If those capacitors are doing what I think they are doing, they are there to improve the start-up time. If this isn't important in your circuit, then by all means leave them out. Richard Message was sent through the cbm-hackers mailing list
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