MIDI Control (ASM1)

[Batz Goodfortune]

Y-ellow Harry.
	
At 10:09 PM 10/17/99 -0700, Harry Bissell wrote:
>OK if we had it out before we can have it out again...
>
>1) I agree that the DG series of mux are a fine and wonderful product. Good
>stuff...
>and also changes with applied voltage, but not as much as the CMOS...
>
>2) By locating the gates at the summing junction, the voltage drop is
>minimized... it still changes but not so you would notics... It is also
possible
>to put an "on" gate in series with the feedback for a first order pass at
nulling
>that on-resistance change...
>A trick to remember with the DG series too, if you are real serious...
>
>3) The error is from the voltage across the gates, when on... if they are
off it
>doesn't matter. Assume 100K input resistors and 300 ohms for the gate, the
>voltage change across the gate is only 30mV which will NOT even register
on the
>curves for the CMOS mux, and (as you mentioned...) the DG is even better.
>
>4) If I had to allow honest +- 10V signal levels (lets say its a patch bay
for an
>existing modular and no modules can be changed...) The DG are the clear
>winners...
>
>5) But the CMOS is good like I described it... anyone who still doesn't
agree,
>just ship me your worthless Prophet Fives (rev 3). I can live with the CMOS
>switching....

Ok. Yup. I can see your point and I hadn't thought of that. That's very
interesting and probably workable even if matching isn't perfect. However I
feel that by the time you've added all the extra op-amps, "Null gates",
associated passive components and extra board space, would it not be
cheaper to have used a DG family switch in the first place?

I don't know about the prophets but I know that back then, chances are it
would have been cheaper for them to do it with standard CMOS.  I'm not sure
if the DG family was available back then but the nearest equivalent would
have been the NSC LF133xx family. Which were horrendously expensive. These
were almost identical to the DG family but about 5 times the price circa 1980.

But as I see it, the problem here is one of cross point switching
mux/demuxing and there are some very elegant solutions on the market these
days. Some with excellent transfer function and simple control Requiring a
durth of the board space and containing 99% of the glue logic required to
control and latch them. You simply tell them what you want and they do it
until you instruct them differently. Unlike CMOS switches which require
external latches or tie up precious ports on your micro.

I think there are a whole host of reasons not to use CMOS. But I'm indebted
to you in pointing out that method of nullifying them. I've got bucket
loads of CMOS switches I was wondering how I was going to use. :)

Thanks in advance.

be absolutely Icebox.

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