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ADS6145: Recommended value for the filter constant of the ADC input part from the fully differential amplifier.

Conor
Guru 11405 points
Part Number: ADS6145
Other Parts Discussed in Thread: THS4509, , LMH5401, THS4151

Hi, 

Figure 98 of the ADS6145 datasheet and Figures 7 and 8 of the EVM user guide provide example circuits using the THS4509.
These are circuits assuming AC coupling, do you have any examples of circuits assuming DC coupling?

Also please let me know if there is a recommended value for the filter constant of the ADC input part from the fully differential amplifier.

Thanks,

Cocor

  • 0
    TI__Mastermind 35350 points

    Hi Conor,

    The LHM3401 or LMH5401 would be a good suitable choice for DC coupled applications.

    On the filter between the output of the amp and input of the ADC, that would depend on the application.

    We can help you with that but we need more information/requirements to go.

    Regards,

    Rob

  • 0 in reply to Rob Reeder
    Guru 11405 points

    Hi, Rob

    Rob Reeder said:
    The LHM3401 or LMH5401 would be a good suitable choice for DC coupled applications.

    Thank you for the information.
    Do you have a recommended circuit for DC coupling?

    Rob Reeder said:
    We can help you with that but we need more information/requirements to go.

    I would appreciate it if you could tell me what kind of information you need.

    Thanks,

    Conor

  • 0 in reply to Conor
    TI__Mastermind 35350 points

    Hi Conor,

    I would review page 26/27 in the LMH5401 datasheet, here these is a good DC coupling reference circuit.

    From there we would need to know what BW you need to setup the anti-aliasing filter. This could be as simple as an RC lowpass filter if you don't plan to pass much else other than DC.

    So, we would need to know, BW, for starters.

    Regards,

    Rob

  • 0 in reply to Rob Reeder
    Guru 11405 points

    Hi, Rob

    If possible, we would like to consider a power supply of ±15V. Isn't THS4151 suitable for DC coupling?

    The circuit assumes an input signal of ±3.3V 1MHz, but DC input is also possible, so I would like to use DC coupling.

    I simulated with PSpice, so please let me know if you have any observations or advice.

    AnalogInput.pdf

    Thanks,

    Conor

  • 0 in reply to Conor
    TI__Mastermind 35350 points

    Hi Conor,

    This should work, I would try to get the output common mode voltage as close as possible to what the ADC requires, which is 1.5V.

    I will forward this post to our HSAmps team to review. I want to make sure I didn't miss anything.

    Thanks,

    Rob

  • +1
    TI__Expert 8650 points

    HI Conor, 

    I took a look at your circuit and it should work fine as you have it. However, you really shouldn't need the input biasing network unless you are using that to try and trim the offset of the amplifier circuit. 

    Best, 

    Jacob