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We use the AR0521 CMOS image sensor and the iMX8 MPU for video recording.

75% of our PCBs don't have an image at the output, only green and pink vertical lines (see picture), but other PCBs work correctly.

output image

We did not find the difference between working and non-working boards. We already checked and tested:

  • sensor power supply and MPU power supply from PMIC (within the limits allowed in the datasheet)
  • MIPI CSI (send test image from sensor to MPU) and watch the MIPI signal on an oscilloscope (we checked only the presence of the signal itself, but not the signal edges, since the bandwidth of the oscilloscope does not allow this)
  • MPU 24 MHz clock

Test pattern and image taken from a working and non-working board: enter image description here enter image description here

After cooling the boards in the freezer for half an hour, the non-working boards started working, but only until the reboot. We also checked the installation on an x-ray and did not see any problems with the sensor and MPU. Replacing the sensor with a new component did not help.

What could be the reason for the failure of the boards?

Anna Kuznetsova
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    Sounds to me like it could be a layout issue. Slight differences in silicon and PCB set up let some of the boards work but not others. MIPI is pretty fussy; 0.15mm within a diff pair, 1.5mm between diff paris. Check the lenghts of every line first. – Puffafish Feb 28 '23 at 10:01
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    What is the scanning direction? If top-down, it looks like long streams of 1's and 0's coming out, would that explain anything? How does the power consumption compare to the working boards? Maybe there is latch-up if you reboot (powering up too quickly)? Are there on-chip configuration settings you might have missed? – Sven B Feb 28 '23 at 14:55

1 Answers1

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we checked only the presence of the signal itself, but not the signal edges, since the bandwidth of the oscilloscope does not allow this

So, you never verified the signal integrity... I guess that's where the problem is. But you'll need a better scope, and specific probing techniques.

Kuba hasn't forgotten Monica
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