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AD698 - Issues With Modifying Gain

Question asked by Jack_Burgess on Jul 24, 2018
Latest reply on Aug 6, 2018 by Jack_Burgess

Hi All,


I'm trying use a AD698APZ in half-bridge configuration with a DVRT and I'm running into some show-stopping problems..


The set-up; includes the AD698 tuned to an excitation frequency of 800 Hz using a 47nF capacitor across the frequency pins and 1.22uF capacitors across all three filter positions. The offset 2 has been set to 8060 Ohms and no phase lead/lag circuit has been used.


With a 20k feedback resistor the gain of the output is stable with a 200mV window between displacement extremes however a slight drift in offset but still readable using a DMM.


When I try to increase the feedback resistor size to 100k Ohms get a larger window (aiming to get closer to 10V rather than 200mV), the offset drift increases so much that the output is unreadable with no major increase in gain.


Any ideas as to what could be the problem?