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AD7171 Pulse Noise

Periodic pulses (128kHz, 60mV peak, 150ns width) are observed at Vin (+).
-Does this affect the conversion result?
-Could you tell me the settling time of AD7171?

Since Analog Input Channel is Unbuffer, an OPAMP buffer is prepared to reducing input impedance.
Refer to Figure14. Signal Conditioning Circuit.

  • Hi,

    The settling time is equal to 24ms. It is the require time for the very first conversion. Subsequent conversions will be available at 125Hz.

    May I know what is your input voltage? Does periodic pulses comes directly from your input source or there is something in your setup that causes this pulses? When you tried to perform a noise test by shorting the analog inputs and bias it to mid supply, are you still seeing this pulses?

    May I know what is your application? and how many samples do you require for your measurements?

    Thanks,

    Jellenie

  • Hi,

    >what is your input voltage?
    0.5 to 2.5V DC.

    >Does periodic pulses comes directly from your input source or there is something in your setup that causes this pulses?
    Disconnecting the op amp output from the AD7171 Vin +, no pulse noise was observed.
    I guess it is not due to the input source.

    >When you tried to perform a noise test by shorting the analog inputs and bias it to mid supply, are you still seeing this pulses?
    No pulse noise was observed at the input ports Vin + and Vin-.
    The measurement system is shown in the attached diagram.

    >what is your application? and how many samples do you require for your measurements?
    The application is DC voltage measurement.
    A minimum of 16 points are required.

    Thank you,

    Tomoya

  • Hi,

    Apologies for the delay.

    Can you also share the scope shot of the pulses as well as the schematic for the AFE? When you disconnect the AFE (op amp) to the ADC. Can you see the pulses at the OP AMP output? I was trying to figure out where the pulses is coming from. From the above scope shot I do not see any pulses, this isolates your ADC from the AFE. So might worth checking if the pulses are coming from the input source or the AFE (OP AMP). Can you also probe the input of your OP AMP and as well as its output when it is disconnected and as well as connected to ADC.

    Thanks,

    Jellenie