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Original question:

TDC1000-C2000EVM: Attenuation of weak signal of LNA and PGA of TDC chip in TDC1000-C2000EVM

TDC1000-C2000EVM: About the LNA amplify of TDC1000-C2000

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Intellectual 2145 points
Part Number: TDC1000-C2000EVM
Other Parts Discussed in Thread: TDC1000

Hi Team

Figure 0728 is without LNA，5661 is with LNA，1526 is with LNA and prolong the time of autozero in order to include the echo time in. So my question is whether the LNA amplification effect exists only in the common-mode and AUTOZERO phases and has an inhibitory effect on the waveform after that phase. Hope the engineers give the answer, thank you.

1526

1526

 

 

0728

0728

5661

Best Regards,

William

  • 0
    TI__Mastermind 19640 points

    Hello William,

    Thank you for the scope captures. Just to make sure I understand your question correctly, are you asking if the LNA is only active during the common-mode and Autozero timing sections of a measurement? (Red portions in the figure below). And during the following timing such as the Wait/Echo listen period the LNA instead of amplifying the signal, the signal is being attenuated?

    Was the PGA gain active during these scope captures? and if so what was the gain setting?

    Best,

    Isaac

  • 0 in reply to Isaac Lara
    TI__Intellectual 2145 points

    Hi Isaac

    Thanks for your kindly reply, 

    PGA is always active.  the gain is 21db. When I switch the gain of PGA into 9db, it turned out to be correct.  So I suppose that the gain is too high and the power  supply can't feed it.  Is it correct?

    Best regards,
    William

  • 0 in reply to Links
    TI__Mastermind 19640 points

    Hello William,

    As far as we are aware that is not issue with the TDC1000. How do you know the value you obtained from a PGA at 9dB vs 21dB is correct? Did you enter a known signal?

    Additionally in the measurements with the LNA gain active did you have any input resistance for the LNA. The LNA DC gain is dependent on the input resistance with the internal feedback resistor of the LNA. Rf/Rin gives us the gain of the LNA. In the datasheet a value of Rin = 900 ohm is used, so I recommend sticking to that value in order to avoid other issues that may arise from having the gain too high.

    Best,

    Isaac