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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.

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  • \$\begingroup\$ What about an inverter charge pump and a TL431? \$\endgroup\$ Commented Nov 18, 2013 at 11:56
  • \$\begingroup\$ You could probably get away with using a common reference and scaling as well as inverting with the same opamp. \$\endgroup\$
    – s3c
    Commented Nov 18, 2013 at 12:01

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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).

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  • \$\begingroup\$ It seems a good solution. Can you tell where I can find a schematics of a circuit description? That might help me with the resistors calculation. \$\endgroup\$
    – Maicol
    Commented Nov 18, 2013 at 14:43
  • \$\begingroup\$ What negative supply voltage do you have? \$\endgroup\$
    – Andy aka
    Commented Nov 18, 2013 at 14:45
  • \$\begingroup\$ I haven't yet a negative power supply. For other sensors on the board I can find a 5V power supply. So I thought to choose a -5V power supply and obtain also a +/- 5V double supply voltage for operational amplifiers. \$\endgroup\$
    – Maicol
    Commented Nov 18, 2013 at 14:54
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    \$\begingroup\$ OK then connect the cathode to 0V and feed the -5V via a 1k ohm resistor to the anode - that will produce -1.25V on the anode and there will be 3.75mA through the resistor to the anode. You then need to choose two more resistors that will wire in series but together across the reference chip, anode to cathode. Choose values that in series combine to greater than 1k ohm. I'm thinking a 3k16 from the anode joined to a 1k to the cathode. This divides the -1.25v down to approximately -300mV. \$\endgroup\$
    – Andy aka
    Commented Nov 18, 2013 at 15:01

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