Inputs at LTC2368-24 got spikes every time CNV goes high

Hi Guys,

I'm having a problem with my ADC LTC2368-24 that every time the CNV signal goes high, some spikes were induced on the inputs. Thus when no signals present at the input, in which the ADC's output should be close to 0, the ADC converts the spike signals and offset my data.

This is my schematic. I have tried different RC filters combinations, different caps values and materials,but nothing seemed to resolve the issue

This is what it looks like on the scope. The purple line is the CNV signal and the yellow line is the analog inputs to the ADC. Please help, I would really appreciate any feedback.

  • 0
    •  Analog Employees 
    on Aug 19, 2020 7:44 PM 6 months ago

    The spikes are expected. If you look at Figure 3 of the LTC2368-24 data sheet you will see the input structure of the ADC. The spikes should be occurring tconv ns after the rising edge of CNV. What you are seeing is the switches closing and the capacitors dumping charge onto the analog inputs. This is the beginning of the acquisition cycle. As long as the glitches settle before the start of the next conversion, there is no problem.