This design note introduces matched resistor networks for precision amplifier applications and describes how to achieve high-precision matched resistor networks using the LT5400 amplifier.
Design Note 502 analyzes how resistor non-idealities affect circuit parameters such as common mode rejection ratio (CMRR), harmonic distortion, and stability. It highlights that while ideal op amp configurations assume perfect matching, real-world feedback resistors often limit performance.
The document specifically compares the LT5400 matched resistor network with thick film and through-hole surface mount resistors. Results indicate that the LT5400 offers superior accuracy for precision applications, such as driving 18-bit ADCs, by providing better CMRR and lower harmonic distortion compared to standard discrete components.
A 2.5V common mode input results in an offset of 23µV when using the LT5400.
The worst-case CMRR contribution from the resistors is 70dB.
A compensation capacitor of approximately 18pF achieves 8% overshoot.