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AD9644 - driving DC-coupled signle ended analong signal

Hi,

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

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  • Hi,

    The AD9644 is not designed to be driven from a single ended source, so option b is not recommended.  Option a above would require the AD8376 to provide a dc coupled single ended to to differential conversion at the input, and a differential output signal with 1.75Vp-p swing and 0.6V common mode.  I moved this post to the amplifier section of Engineering Zone where someone should be able to help you understand the options. 

    Best Regards,

    David

Reply
  • Hi,

    The AD9644 is not designed to be driven from a single ended source, so option b is not recommended.  Option a above would require the AD8376 to provide a dc coupled single ended to to differential conversion at the input, and a differential output signal with 1.75Vp-p swing and 0.6V common mode.  I moved this post to the amplifier section of Engineering Zone where someone should be able to help you understand the options. 

    Best Regards,

    David

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