Best way to get AGND?

[Anonymous]

        Since PSoC analog circuitry uses a virtual ground (AGND), what are some of the ways to bring out the "ground reference" for external circuitry, and to interface voltages referenced to system GND to the analog circuitry on the PSoC?   
   
One way is to connect the AGND reference via a Refmux through a CT block and out an output buffer, but that uses up a resource.   
   
I've brought AGND out on Port2_4 and buffered it externally.   
   
For example, I would like to measure current out of a photodiode, but wanted a 'stiff' reference for making the measurement.   
   
I'm also interested in sensing the drive current to a motor to detect stalls -- here, the current can be quite high, so I'll need a current-sensing resistor interfaced to the PSoC that would allow measurements to fall within the REFHI/REFLO range.   

[MR_41]

Using P2[4] to bring out AGND is not a good solution. There is an internal 8K resistance between the internal AGND and P2[4]. This will increase the source resistance of this AGND and any current sourced or sunk from P2[4] from an external signal will result in the shifting of AGND. The best method is to use the Analog output buffer and bring out the AGND using the RefMux.

You can also bring out AGND using the testmux by writing to the ACBxxCR2 register. In this method, you can bring out AGND from a CT block which already used by another resource like a PGA, INSAMP etc. Following articles describe this method.

http://www.cypress.com/?id=4&rID=33794

http://planetpsoc.com/index.ph...tid=1:analog&Itemid=18

[Anonymous]

        Thanks Ganesh. That's a good technique to know!   
BTW, the first of the two links didn't work (the one to cypress.com).