CMOS logic with ground for Vdd

[Pimpom]

I'm designing an analog circuit with a regulated +/-12V supply. I
want to include a 4000 series CMOS logic device to switch a
sub-circuit at sub-Hz frequency.

I haven't worked out all the details but, at this stage, using
ground as Vdd and -12V as Vss looks like a convenient way to go.
Is there any reason why this is inadvisable? Any caveats? (Proper
care will be taken to ensure that no pin will be pulled outside
Vdd and Vss).

 

[Clive Arthur]

On 17/04/2020 12:12, Pimpom wrote:

I'm designing an analog circuit with a regulated +/-12V supply. I want
to include a 4000 series CMOS logic device to switch a sub-circuit at
sub-Hz frequency.

I haven't worked out all the details but, at this stage, using ground as
Vdd and -12V as Vss looks like a convenient way to go. Is there any
reason why this is inadvisable? Any caveats? (Proper care will be taken
to ensure that no pin will be pulled outside Vdd and Vss).

I've done this, no problems at all except make sure it's *very* clearly
marked on the circuit diagram for the repair technician.

--
Cheers
Clive

 

On Fri, 17 Apr 2020 16:42:17 +0530, Pimpom <nobody@nowhere.com> wrote:

I'm designing an analog circuit with a regulated +/-12V supply. I
want to include a 4000 series CMOS logic device to switch a
sub-circuit at sub-Hz frequency.

I haven't worked out all the details but, at this stage, using
ground as Vdd and -12V as Vss looks like a convenient way to go.
Is there any reason why this is inadvisable? Any caveats? (Proper
care will be taken to ensure that no pin will be pulled outside
Vdd and Vss).

No problem. Older 4k cmos would latch up and short the supply if you
transiently forward-bias an ESD diode, which gets worse at high supply
voltages. Maybe watch out for that, with the unusual supplies.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Pimpom]

On 4/17/2020 6:14 PM, Clive Arthur wrote:

On 17/04/2020 12:12, Pimpom wrote:
I'm designing an analog circuit with a regulated +/-12V supply. I want
to include a 4000 series CMOS logic device to switch a sub-circuit at
sub-Hz frequency.

I haven't worked out all the details but, at this stage, using ground as
Vdd and -12V as Vss looks like a convenient way to go. Is there any
reason why this is inadvisable? Any caveats? (Proper care will be taken
to ensure that no pin will be pulled outside Vdd and Vss).

I've done this, no problems at all except make sure it's *very* clearly
marked on the circuit diagram for the repair technician.

Noted, and thanks. I'm not sure yet if this will go into production.

 

[Pimpom]

On 4/17/2020 8:26 PM, jlarkin@highlandsniptechnology.com wrote:

On Fri, 17 Apr 2020 16:42:17 +0530, Pimpom <nobody@nowhere.com> wrote:

I'm designing an analog circuit with a regulated +/-12V supply. I
want to include a 4000 series CMOS logic device to switch a
sub-circuit at sub-Hz frequency.

I haven't worked out all the details but, at this stage, using
ground as Vdd and -12V as Vss looks like a convenient way to go.
Is there any reason why this is inadvisable? Any caveats? (Proper
care will be taken to ensure that no pin will be pulled outside
Vdd and Vss).

No problem. Older 4k cmos would latch up and short the supply if you
transiently forward-bias an ESD diode, which gets worse at high supply
voltages. Maybe watch out for that, with the unusual supplies.


Thanks.

 

[piglet]

On 17/04/2020 12:12 pm, Pimpom wrote:

I'm designing an analog circuit with a regulated +/-12V supply. I want
to include a 4000 series CMOS logic device to switch a sub-circuit at
sub-Hz frequency.

I haven't worked out all the details but, at this stage, using ground as
Vdd and -12V as Vss looks like a convenient way to go. Is there any
reason why this is inadvisable? Any caveats? (Proper care will be taken
to ensure that no pin will be pulled outside Vdd and Vss).

The idea of "Ground" is a ghastly human simplification that mostly
serves just to make schematics not look messy but hides the real truth!

piglet