Electronic – Finding ground in a battery powered circuit

analogbatteriesground

I don't know if this is an obvious question. I'm powering my circuit (that's used to amplify an EKG signal) by a ±5V battery supply, the amplifier I'm using the ina129 needs a voltage reference that's midway between my voltage supplies.

I considered using a simple voltage divider circuit but found that it becomes unbalanced. Could I use something like the Texas Instruments virtual ground splitter (tle2426) or does it only work for positive voltage supplies?

Best Answer

If you have +5V and -5V then half way between supply voltages is 0V i.e. the common connection of the two batteries - this should be regarded as your "ground" (or 0V) for your circuit. If you read what TI say about the TLE2426 you'll possibly agree: -

In signal-conditioning applications utilizing a single power source, a reference voltage equal to one-half the supply voltage is required for termination of all analog signal grounds. Texas Instruments presents a precision virtual ground whose output voltage is always equal to one-half the input voltage, the TLE2426 “rail splitter.”

You have two power sources namely +5V and -5V and these are likely to have a third wire which you have available that does exactly what the TI chip sets out to do.

Why did the INA129 become unbalanced: -

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Using a resistor divider to feed the REF input means that you are altering the 40k resistance at pin 5 and this will unbalance the ratios of resistors and lead to common-mode signal problems.

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