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ad1938+adau1452 noise

Category: Hardware

Dear ADI staff:
I designed a DSP board using AUAU1452 and AD1938, and controlled it using STM32F103RCT6 with a sampling frequency of 48K, using hardware mode,
During testing, it was found that AD1938 had noise issues after heating up. The noise increased with temperature, and when the temperature reached around 75 degrees Celsius, the noise suddenly decreased. After that, the noise remained stable
If heat dissipation is added to AD1938 when the temperature rises, the noise will decrease
Please help analyze the reason, thank you

Parents
  • To provide some additional information about the issue: I connected a 2.2 MΩ resistor from the ADC IN N port to ground, and this issue occurred. If I do not connect this resistor, the speaker produces high-frequency noise, and the FFT spectrum from the AP test shows a spike at the location indicated by the red arrow.

        

  • Audio inputs should always be connected when testing the circuit for noise, never floating. Even the most expensive and highest quality audio components will pick up horrible noise on inputs that are left unconnected. If you want to test "no input" then short the (+) and (-) pins together and then make the noise measurements.

    You're seeing noise because these inputs are floating. I suspect that adding the 2.2 MΩ resistor is stopping the (-) input from floating, but now you're inviting Johnson-Nyquist noise, and high value resistors have more noise.

Reply
  • Audio inputs should always be connected when testing the circuit for noise, never floating. Even the most expensive and highest quality audio components will pick up horrible noise on inputs that are left unconnected. If you want to test "no input" then short the (+) and (-) pins together and then make the noise measurements.

    You're seeing noise because these inputs are floating. I suspect that adding the 2.2 MΩ resistor is stopping the (-) input from floating, but now you're inviting Johnson-Nyquist noise, and high value resistors have more noise.

Children
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