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Original question:

ADS54J60EVM with an Thorlabs PDB480C-AC

ADS54J60EVM: DC coupling

Maurício Ferreira
Prodigy 150 points
Part Number: ADS54J60EVM


Hello,

I have a question regarding the use of the ADS54J60EVM with a balanced photodetector such as Thorlabs PDB450C (www.thorlabs.com/thorproduct.cfm.
The detector output is DC coupled, but we are only interested in the AC component. Given that the ADS54J60EVM analog inputs are AC coupled, can we introduce a DC block and still use this board without modifying it? Is there any incompatibility with this setup?

Best regards

  • 0
    TI__Mastermind 18095 points

    The  default set-up on the EVM is a single-ended interface through the transformers.  The low frequency response is limited by the frequency response of the transformers.  This interface inherently is AC coupled.

    If you need/want differential interface, then you can bypass the transformers and jumper over the pads as shown in the schematics and outlined in the User's Guide.  This option per the schematic shows a series 0.1 uF coupling cap.  This will also be AC coupled, but the low frequency response is dictated by the value of the cap.

    If you ultimately need a DC coupled interface, this can be done by replacing the cap with a jumper resistor.  Do be mindful that the proper Vcm must be supplied in this configuration.

    --RJH