-=> Roy J. Tellason said to Greg Mayman
 -=> about "BAG OF CHIPS" on 01-31-04  12:05.....

 RJT> Much went on with numbers back when.

Sure did. And there were some great confusions. I remember seeing
one diode number that had FIVE different types, depending on
which manufacturer it came from.

 RJT> I have one of those too,  they used one in the C64,  the MC4044.  The

IIRC the MC4040 and 4044 were paired up for a phase locked loop,
as mentioned in a Motorola Application Data sheet.
 
 GM> And you could use level translator chips - the 4049 and 4050 will
 GM> do that for you. Or a two transistor buffer will also do it.

 RJT> If I'm remembering right they'll take a higher-range logic level swing
 RJT> and translate it down to somewhat lower a range,  but that's not what I

Yes you're right. The input can go more positive than the + rail.
I was thinking of some other chip, but I can't find it in my data
book.

 RJT> need here, I'd need something that would take a zero-based logic swing
 RJT> and translate it to a bipolar one.  There's probably some simple way to
 RJT> do this but it's not apparent to me at the moment.

.  +5v rail------------+-----------
.                      |           |
.                 ------------    4700
.  +2.5v ref ----| -          |    |
.                |  1/4 LM339 |----+---- out
.    in ---------| +          |
.                 ------------
.                      |
.  -5v rail------------

That's the simplest way to do it with the least number of
components. The ref source can be a voltage divider (2 x 10k)
between +5v and 0v, and the same ref can feed all four
comparators.

The only problem with this is that the 339 isn't very fast, I
think it's about 1.5uS to swing the output.

This is a much faster level converter but with more components...

+5v rail-------------+----------------------
.                    |                      |
.                   22k                     |
.                    |                      e
.                    +-----100k-----------b   TR2-PNP
.                    |                      c
.                    c                      |
in -------100k-----b   TR1-NPN              +----- out
.                    e                      |
.                    |                    4700
.                   gnd                     |
.                                        -5v rail

Both transistors are GP types. This circuit is very fast, and I
have tested it to frequencies above 10MHz. With RF transistors it
should go even higher.

In theory, if you use MOS-FETs you can leave out the 2x100k
resistors for an even lower parts count and higher speed, but I
haven't tried it myself.

   ,-./\
  /     \ From Greg Mayman, in beautiful Adelaide, South Australia
  \_,-*_/    "Queen City of The South"    34:55 S  138:36 E
       v

... The important thing is not to stop questioning -- A. Einstein
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