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AD9644 - driving DC-coupled signle ended analong signal

Question asked by topirinkinen on Mar 4, 2013
Latest reply on Mar 8, 2013 by topirinkinen



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:

removing T302/T307

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.


BR, -Topi