🚀 go-pugleaf

In article <1991Jan10.061457.2817538@locus.com> dana@locus.com (Dana H. Myers) writes:
>In article I (esmith@apple.com) write:

someone else>>> It'll probably run hotter 'en 'ell, though.

ELS>> Not unless the 25 MHz chips run hotter 'en 'ell.
ELS>> The 16 and 25 MHz rated parts have the same circuitry implemented in the
ELS>> same (mostly) CMOS process, so the power dissipation of the two will be
ELS>> nearly identical at the same clock speed.

DHM>   The 25Mhz chips DO run hotter than the the 16Mhz parts. CMOS power
DHM> consumption occurs during transitions. There are two reasons why;(1)
DHM> current must flow through the gate capacitances (standard 1/(2*pi*f*C)
DHM> stuff) and (2) there is a brief instant when both the P and N channel
DHM> FETs are conducting. Resultantly, the power consumption of CMOS parts
DHM> is roughly proportional to frequency of operation. A 25Mhz will consume
DHM> about 25/16 (or 150%) of the power a 16Mhz part consumes.

If you read what I said carefully, so will see that I didn't say that
running a 16 MHz rated part at 25 MHz wouldn't increase the generated
heat (i.e., power dissipation).

What I said is that there since 16 MHz and 25 MHz parts are implemented in
the same process, a 16 MHz rated part running at 25 MHz should have
approximately the same power dissipation as a 25 MHz rated part running at
25 MHz.

Similarly, a 25 MHz rated part running at 16 MHz should have approximately
the same power dissipation as a 16 MHz part running at 16 MHz.

So, as I said, a 16 MHz rated part running at 25 MHz is not going to run
"hotter 'en 'ell" unless a 25 MHz rated part running at 25 MHz runs
"hotter 'en 'ell".  Of course, "hotter 'en 'ell" is somewhat subjective.

Of course, depending on the design of a part, it is possible that pushing
the part too far beyond its speed rating may actually damage the part by
allowing the P and N channel FETs to conduct simultaneously for extend
periods of time.  I would not expect this to happen unless you try to push
the part not just beyond its own speed rating, but somewhat beyond the
maximum speed rating offered by the vendor.

In summary, I think we both are in agreement about the characteristics
of CMOS parts.

I repeat that I do not reccomend running parts in excess of their ratings
(speed or otherwise) in any type of production system.

DHM> Good advice, even if I wouldn't hire you to design CMOS computers
DHM> for me :-) :-).

Maybe you'll reconsider?  :-) :-)



--
Eric L. Smith      Opinions expressed herein do not necessarily reflect those
esmith@apple.com   of my employer, friends, family, computer, or even me!  :-)