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THS4551: Simple fully-differential amplifier config

Part Number: THS4551

Dear experts,

I'm trying to amplify a 4.2 mVDC differential signal coming from a load cell into something 30 times greater before entering the resulting voltage into a differential ADC stage. This is my first fully-differential amplifying design but I thought this should be quite straightforward. The following is my circuit design based on the THS4551 with 16-Pin VQFN package:

Real voltages measured from the circuit are marked in blue. As you can see, R127/R17 and R128/R18 are both 30k/1k, resulting in a theoretical gain of 30. However, real measurements done between AIN2 and AIN1 (differential output voltage) are -14.2mVDC so I'm barely getting a gain of 3.38.

I think I'm missing something about the THS4551 or I'm probably using the wrong design. Could anyone help me please solve this puzzle?

Thanks so much for your time.