I need a -300mV Voltage Reference for a Potentiostat circuit (http://www.sgxsensortech.com/site/wp-content/uploads/2012/10/AN2-Design-of-Electronics-for-Electrochemical-Cells1.pdf @ page 3). What is the best solution? If I can find a 300mV voltage reference I can use an inverting Operational Amplifier, but it seems that there are no 300mV voltage reference. Thanks all.
If you have a negative power rail then use a shunt voltage reference - basically it's a precision zener diode so it can work on either supply rail. On the negative rail the cathode connects to ground and a resistor feeds the anode from the rail.
Here is one from LT - it's the LT1389 and the first one I found. It's a 1.25V reference and you can use two resistors to divide this down to 300mV. You need to feed it with a minimum of 0.6 uA but because you'll have a potential divider in parallel you'll need to feed the reference and potential divider with a slightly bigger current. You might as well use 1 mA (the device is rated up to 20 mA anyway).