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TDC1000: TDC1000 - External Filter

Part Number: TDC1000
Other Parts Discussed in Thread: TEST,


I have a customer that wants to put a filter before going to the compinpin. See note: 

Separate subject…we are looking at a potential new design with the TDC.  I haven’t used the TDC as much as other engineers here at SSI, and would like to have a little more capability in this new design – at least for development purposes.  The TDC datasheet has a statement about more complex filters and external gain between the PGAOUT and COMPIN.  I know the TDC eval board uses a op amp to buffer the COMPIN signal to hook up with an oscilloscope and there is TIDA00322 test data report that uses an active FET probe to monitor the COMPIN signal.  Is this to not effect the band pass filtering, prevent loading the output of the PGA, or something with the COMPIN?  I was thinking about making an active filter that would give me 3dB-6dB of extra gain before going to the COMPIN.  What should I be more worried about effecting – COMPIN or PGAOUT?  Are there any TI designs that do this or is this a note in the datasheet?

Any thoughts here? 



  • Hi Jason,

    Thank you for relaying the customer question,

    I do not think we have any content/reference designs on instances of integrating other components in the TDC1000 signal path. Section 8.3.5 of the TDC1000 datasheet is the most informative content available for calculating filter component values. As you referenced, it is possible to create more complex filters by inclusion of additional components.

    You are correct, the EVM buffer is to ensure the probe of the scope does not affect the performance of the filter in an unexpected manner. I would be more concerned with influencing PGAOUT over COMPIN.

    The most important characteristic of modifying the filter is in ensuring AC coupling between the amplifier stages

    Thank you,