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There is an error at the output due to the resistor matching. How can I minimize or eliminate this error?

I am using LTC6363 to convert my single-ended signal to the differential signal that my ADC requires.  I have the amplifier configured in a gain of 1 and have discovered that the gain-setting resistors dominate my CMRR performance.  Because of the way the amplifier’s input common-mode voltage is modulating in my circuit, this is creating an error at the output due to the resistor matching.

  • Fully differential and difference amplifiers usually have very high common-mode rejection (CMRR).  In practice, when resistors are configured around the amplifiers, the matching of those resistors can often dictate the overall CMRR.  What you have observed in your circuit is a less-obvious affect caused by this same resistor mismatch.  Using the fixed-gain version of LTC6363 (LTC6363-1) will help greatly with the issue you are seeing.  These parts have integrated gain-setting resistors which match incredibly well and thus provide excellent rejection of these errors.  Resistor networks like LT5400 and LT5401 can also be used to achieve the same excellent performance with many other amplifiers.  DN502 gives an overview of the benefits of using these matched resistor networks and for those seeking further information DN1023 provides a deep-dive into the supporting calculations.