image sensor line problem

Question

I have an image sensor problem and I am looking everywhere to identify the problem but couldn't. Attached is the problem I observe. As you can see there are several horizontal lines in the image.

So far, I have checked power, clocks and all seems in order. Appreciate any ideas you may have. (If I get a test image from sensor-diagonal tiles etc-, all seems to be good. So, I am assuming it is not communication with the sensor. Sensor datasheet is here)

I am not looking for a specific answer but more of a direction and/or ideas. Somebody with the right experience could know where to look.

Apparently this type of problems can be observed in other sensors. See the link.

I have realized, I missed out one critical information, if I reduce the clock frequency of the sensor the problem disappears. So there is a clock frequency dependency. However I do not suspect read out since if I set the test pattern, regardless of frequency all is good.

Imager Power Supply Noise figures

Analog Supply

Digital Supply

UPDATE

After further testing, I figured the problem is same in every frame. Previously, I was wrong. Here is the 4 images from different times. Images are stiched together, all 480x752

Answer 1

If the pattern of the column is the same whenever they appear, the problem is called fixed-pattern noise. This is just something you need to deal with, especially when dealing with a raw sensor. The sensor vendor should be able to help with characterizing it.

To deal with it, you can either go through a manual calibration procedure that allows you to derive offset and gain correction factors for each column, which you then store in nonvolatile memory, or you can develop an adaptive algorithm that can recognize and compensate for FPN in live images on the fly.

To characterize the FPN, you'll need to take a series of flat-field images (same amount of light on each pixel) at various light levels (including completely dark) and various exposure times. For each combination of light level and exposure, take the average value of the pixels in each column, and average these values over many frames (to eliminate thermal noise).

From this set of data for each sensor column, you will be able to determine what gain and offset values to apply to that column to eliminate the fixed pattern. You will also be able to determine whether the correction values need to be different for different exposure times, or a common set of values will work well enough for all exposure settings.

You'll also want to do this across a number of individual sensors, to make sure that the statistical variations among sensors don't invalidate the solution you come up with.

Answer 2

Can you post the whole image? Looks like bias lines on the CCD. I'm also going to guess it is a high frame rate sensor, because the lines are so noticeable. Are you doing anything else while reading out, or doing anything else with the sensor? I think the timing for each line has to be consistent.

Answer 3

This can arise through several mechanisms which I'll list. But there is asome analysis you can do as well.

1) There looks like a vertical line through the image in which it should be a uniform grey (right hand side) plot that single column on a graph and look for patterns. -> if you see binary count sequences then it's likely the row decoders on chip. --> "solution" would be to increase by-pass capacitors and try to filter/split power supplies more.

2) If the noise looks less like a count sequence but still has some characteristic frequencies. then it could be Power supply noise. Look to your how well you power supplies are filtered, how your ground planes are laid out.

--> as an aside, you can run a FFT over that sampled column to see if there are dominant frequencies.

--> knowing the line rate you should be able to calculate the frequency of the aggressor signal.

Answer 4

I've noticed similar stripes when powering the analog part of the MT9V032 with a switching regulator and a passive LC filter. You could try to generate the analog supply with a linear regulator with low noise and good PSRR (e.g. TPS79333).

Answer 5

Do you have the schematics of the Aptina MT9V032 Camera Board (MT9V032_DEMO_HEAD)? You can see that every supply pin has its 100nF cap with 1uF in parallel, but the PLLVDD pin is erroneously connected to VAA. Check the MT9V034 Board instead. Ferrites are good for high frequency noise suppression, but they do not work on low frequency noise, they may even increase it. You could also try a Ripple Blocker, e.g. MIC94300 from Micrel. There are free samples available. Could you post the camera parts of your schematics and layout?