Hi,
I connected a self designed sensor board to the EVAL-AD7134FMCZ. Therefore I removed Device 0 from the eval-board and connected serial+data lines from my board to the eval-board.
I can see that communication via the AD7134 Evaluation Software is working well, as i could sample a sinusoidal signal with the correct frequency (but somehow shifted to negative range of the y-axis). My problem seems to be related to the applied common mode voltage.
Below you can see my input circuitry, using the recommendet LTC6363-1 from the datasheet. The VCM signal applies the VCM=VREF/2=2.048V to the LTC6363's output voltage that is directly connected to the AD7134's AIN0+ (connected to AIN1+) and AIN0- (connected to AIN1-) using 2:1 channel averaging.
So, if I apply a fully differential DC voltage of 1V to the input of LTC6363, I can measure a differential voltage of 1V directly of the input of the AD7134. I also measure 2.548V at AIN0+ and 1.548V at AIN0-, both measured against AGND. This all seems to be fine.
But with the AD7134 Evaluation Software do not get the correct result. It somehow measures -1.81V when I apply 1V to the LTC6363-1 input.
When I apply the same DC voltage of 1V to the input of Device 1 (also using channel averaging), I can measure the correct result in the Evaluation Software (without using a fully differential amplifier inbetween). I checked the registers and they are the same for both devices.
Is there the possibility that the wrong measurement is related to the fully differential amplifier? Is there a problem with the AD7134 Evaluation SW when using the fully differential amplifier because of VCM voltage?
As I can see in the schematics for Device 1, the VCOM_2 is not applied to the voltage that is applied to connector P9 (AIN0+_INP_2 and AIN0-_INP_2). This is the only difference that I can see in the two setups (my sensor vs. Device 1 on eval-board)
See result on Device 1 (left, CH4) and result of my sensor (right, CH0)
Best Regards, David
