DDL - faster Nernst cell sensing

[Ludis Langens]

bcroe at juno.com wrote:
> 
> If you came up with a "negative" pulse Ip generator,
> you might be able to dispense with the virtual
> ground.  The negative pulse could be generated
> with capacitive coupling from all positive circuitry
> since it is just a fixed digital pulse.  Not so easy
> to do with a straight analog drive.

There is no need for a virtual ground (ala DIY-WB) or even a negative
supply.  One side of the pump cell doesn't need to be held at a constant
voltage.  Connect both sides to active drivers.  One side gets driven to
a low voltage while the other is driven to a high voltage.  Reverse the
order to get current flowing in the opposite direction.  This is how GM
runs their IACs.  The voltage levels chosen need to be such that the
sense cell voltages stay within the range that the circuit can handle.

This design requires translating the sense voltage to the common ground
environment.  However, that's conceptually the same as converting the
"output" signal in the virtual ground system to the real ground system.

I suspect that Gar's old EGOR design used this approach.  The messages
at the time implied the whole thing (except for the heater) ran off a
single 5 volt supply.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/


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