I have AD9644 evaluation board, which I need to use with DC-coupled analog signal.
At this moment I am not interested in ADC performance, so e.g. increased noise floor is not a problem.
The evaluation board is built with transformers/capacitors, blocking any DC component in analog signal.
I'd like to connect my analog DC-coupled signal straight to the ADC analog input , as single ended signal. There are two options:
a) Utilizing the AD8376 (U401) of the evaluation board. This requires changing C402/C403/C404/C406 => 0R, and activating active path (R303 => DNI, R309 => 0R etc; C305 => DNI, R311 => 0R etc), and populating anti-alias filters (between AD8376 and AD9644 (with DC capable topology).
And then feeding the single-ended signal to J301 & J303, and grounding J302/J304.
b) Feeding the single-ended signal straight to AD9644 VIN_POS_A/B and fixing the voltage of VIN_NEG_A/B.
This can be done by:
C305/C306/C311/C312 => 0R
The datasheet of AD8376 isn't precise enough in input => output transfer function. E.g. it doesn't tell how single-ended input to differential output transformation output common mode voltage is generated. A realistic functional SPICE model would be nice too.
Please provide some help so that I can decide which path to take, and what problems I might face.