AnsweredAssumed Answered

AD9959 Evaluation Board Voltage Stability

Question asked by Tal on Jul 6, 2015
Latest reply on Aug 16, 2015 by LouijieC




I need to generate sine waves at different amplitudes and phases in order to balance a bridge circuit.  The bridge is supposed to resolve fractional changes as small as 1/10^-5.  I understand that the 10 bit resolution of the AD9959 channels will not allow me to achieve such precision in the amplitude.  But, my main concern is generating several sine waves with very good phase and amplitude stability over time since I plan to use higher resolution MDAC's to further modify the amplitude.


The reason I ask is that right now, I am using an analogue circuit which provides sine waves with relative phases of 0, 90, 180, and 270. I run these signals through LTC1650's to modify their amplitudes, then sum the signals together with op amps, and supply them to the bridge.  The problem is that the bridge measurement drifts over several hours time (fractional changes up to 1E-3) even if I put the MDAC's and bridge components in a temperature controlled environment. 


Finally, I found that the amplitudes of the sine waves supplied by the analogue circuit (actually, I am using the reference signals from the back of an SR124 lock-in) to the LTC1650's drift over time.  So, I am looking for a better way to produce stable sine waves.


I included some diagrams of the circuit I am trying to emulate. I did not make these myself.  They are from a PhD thesis.


I hope my question is clear.  I will appreciate your help!


Thank you,