DDL - faster Nernst cell sensing

[Bernd Felsche]

Carter Shore tapped away at the keyboard with:

> On Tue, 27 Nov 2001 18:22:09 Ludis Langens wrote:
> 
> > 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.

> Are you referring to an H-bridge driver arrangement?
> Lot's of IC solutions out there. For low current
> applications, you can use the outputs of two CMOS
> buffers driving each side, one input gate to each side
> of an inverter. 

That's the method used in the DDL. Initially based on a H-bridge
drive, it's gone through a couple of development iterations.

No virtual ground exists. The common between the pump and Nernst
cells bounces up and down. The comparator reference, used to detect a
change in Nernst cell voltage, floats on the common. ADC can still
be used to measure the magnitude and direction of the transition.

-- 
Bernd Felsche - Innovative Reckoning, Perth, Western Australia
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