[sdiy] Muxes at maximum voltage.

[Oren Leavitt]

Hi Karl,

CMOS logic thresholds are usually about half of the voltage between Vdd 
and Vss *relative to Vss*.
In this case, +6V will definitely be a logic '1'. 0V will be iffy since 
it is in the middle of the +/-7.5V supply. You'll need -6V for a 
definite logic '0'.

I've found it easier to run the old CMOS muxes from 0 to +15V and 
level-shift the analog signal to +7.5V.
I think Maxim or Analog Devices has pin-for-pin replacements for the 
405x and 4016 that will handle a full +/-15V.

Oren

Karl Dalen wrote:

>Hi!
>
>Im about to use a 4051 at +/- 7,5V and logic
>to set mux channel driven from +6V, the specs
>dont tell if 0 to +6V logic are enough for
>logic (ViH) to drive the mux switch!
>Anyone with this experience?
>
>Im about to avoid using logic level translators
>such as an transistor array, eg ULN2808 etc.
>Im trying to squeese out as much bipolar
>dynamic range out of old CMOS muxes!
>
>Thanks!
>KD
>
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-- 
Oren Leavitt
oleavitt at ix.netcom.com