Re: 6502 to 8501: new details

From: Richard Atkinson (
Date: 2002-02-27 15:02:34

On Sat, 23 Feb 2002, Richard Atkinson wrote:

> > 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.

Sorry to answer my own post but I learnt some things last night at Tony
Duell's talk on HP calculators. Apparently most calculators from the HP35
until the Saturn processor series used a PMOS process. They made one in
NMOS and another in CMOS, but all the early ones were PMOS.


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