Using LM98725

Hello experts,

we are designing a prototype for our small xray system using cmos sensor M118-232C3. I want to know can we use LM98725 with this CIS module and how?

77 Replies

  • In reply to Hooman Hashemi:

    Hi Hooman,

    I have tried to replace .01uF capacitor with 1uF as you told but I have noticed that when the sensor is in dark the output from the sensor is constant around 0.6 volts but as I connect the output to the LM98725 input the dark output voltage becomes 3.3V (as shown in image).

    Blue = sensor output ac coupled.

    Red = sensor output after 1uF cap. but not connected to LM98725

    So I have decided to coupled the sensor directly with the LM98725.

    INCLK (yellow), Sensor output (blue), and sensor clock (red)

    how can I read the 16 bit output data, is it 8 bits data on rising and falling edge of the CMOS clock?

  • In reply to Martin Wolf11:

    for dc coupling should i used autoCLPIN?
  • In reply to Martin Wolf11:

    Hi Martin,
    Please contact me directly via email so that we can find out the best support avenue:
    hooman.hashemi@ti.com

    Regards,
    Hooman
  • In reply to Hooman Hashemi:

    Hello Hooman,

    I would like to thank for your support in configuring the LM98725 chip for our experimental project. Finally I have got some result but its not that good in the attachment you can see it. I have tried to put a specific pattern on the sensor and it gives us following output. It seems that the sensor follows the given light pattern but I think I have to adjust the offset values. How can I adjust the offset in SH mode?
     

    Pattern placed on the sensor:

    Sensor output:

    sensor output in ambient light without any pattern:

    How can I set the offset to get a white pixel on the gaps between the lines. 
    My second question is when I coupled the sensor with the scintillator to get output from the sensor on X-ray exposure it gives output but don't get any digital data from the LM98725 chip. All values are zero from the three channels. Do you have any idea what's wrong with the chip configuration.

    Regards,

    Martin 

  • In reply to Martin Wolf11:

    Hi Martin,

    Glad to hear that things have improved!

    The DAC and PGA register settings for each channel (Red, Green, Blue) should be adjusted for the following goals.

    Adjust DAC values until the average values for the black lines are at approximately 5% of the full scale value. For a CIS sensor the Even/Odd feature doesn’t need to be enabled, so the Even DAC values are the only ones that need to be adjusted.

    Adjust PGA values until the average values for a bright white signal (the brightest expected) is near 90 to 95% of the full scale value.

     The settings above can be done manually or the Automatic Black and White Level Calibration Loops can be used to do it automatically.

    See Section 7.4.12 of the datasheet for more information.

    Here are the basics:

    • If the sensor has reference dark pixels, the Black level calibration features may be used to automatically adjust the DAC values until the target dark level values are met.
    • If the instrument has a calibration step where a bright white calibration image is available the White level calibration features can be used to set the PGA values until the target brightness value is met.

    Hope this helps.

    Regards,

    Hooman

  • In reply to Hooman Hashemi:

    Hello Hooman,

    By full scale value you mean the max. value at 16 bit data i.e. 65535 or the max. amplitude value from the sensor (3.3V). Right now I get zero values on black line but if set offset 5%of the full scale value then it would be 3276 and the 95% of the full value is 62258. So these two values are the range of my digital signals? 

    In my sensor the first 38 pixels are inactive pixels but its not mention in the datasheet that they are black pixels but they give an output around 1V as you can see in the scope image where I marked 1. I have set this as a VCLP reference. (0.35Vin). Is it correct or should I set the VCLP at position 2. Because you told me to set the minimum output value as a VCLP value. 

  • In reply to Martin Wolf11:

    Hello Hooman,

    I have tried to calibrate but results are still not so good. I'm confused to understand the settings for Black Target and White Target because I want to set black target value around 3200 and white target value around 63000 but in the register settings we only have 8 bits. How I can configure these 8 bits to set my desired value. Please explain. Second thing I wanna know is to recall the calibration process we have to apply High logic on cal pin, so do I need to hold this high logic during the complete cal. process end or just at beginning like a short pulse to start calibration.  

    For white calibration loop my sensor was half covered with the scintillator that produces the blue light during calibration. Should I cover the whole sensor with the light or its okay?