the noise of AD7492

from the figure of the bellow,we use the samping frequency 100khz  to samp the signals,when the time is 40ms,the vibration sigals is coming ,but the analog sinals is no noise(by observating the oscilloscope),and the frequency of analog sinals is about 10khz,but after the conversion of ad7492,we find there are some glitches,when the excitation is starting from the time 40ms.

  • 0
    •  Analog Employees 
    on Jan 30, 2018 2:10 AM

    Hi liufeng.

    I just want to clarify and correct me if i'm wrong, the 10kHz signal starts to sample at 40ms but based on the waveform that you gave, you said that their is noise or glitches on the output of the ADC. First, i assume that x-axis of the waveform is time but may i know if the y-axis is in voltage (V). Second, can you post here the schematic since you are using SAR ADC which needs buffer or ADC driver. There are many possible sources of the noise and distortion in  signal chain. It can the ADC buffer, filter, voltage reference or power supply. For me to give you right answer, let me evaluate your schematic.

    Regards,

    Daryl

  • thank your seriously reply,

    the schematic of ad7492 is shown as follows:and the  x-axis of the waveform is time ,the y-axis is voltage (V),first,the analog signals  are converted to digital signals which would be saved to the RAM IDT71V416L,the write and read programs of IDT71V416L are all be proved to right,before the time 40ms,the data are no noise ,when the time is after the 40ms,the excited signals is coming,the voltage represents the amplitude of the vibration signals.

  • first , the signal before the time 40ms and the signlas after 40ms are also samping and stored,but before the time 40ms ,the noise of signal is so small ,but after the 40ms (the vibration signal is coming )the signal with so many noise,but the analog sinals are no noise(by observating the oscilloscope).

  • the 10kHz signal starts to sample from the begining,their is almost no noise or glitches on the output of the ADC.

    but when the time is after the 40ms,  the excitation signals (vibration signals and the frequency is 10kHz ) is coming ,there are more noise or glitches on the output of the ADC.

  • the analog signals are observed by the oscilloscope,and is shown as follows: