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THS1206M: THS1206M calibration in test mode.

Mark Khusid
Prodigy 50 points
Part Number: THS1206M
Other Parts Discussed in Thread: THS1206

The THS1206 has a Test Input Enable that is controlled by bits 8 and 9 of Control Register 0.  It appears that it is possible to enter this mode and obtain a conversion of the extremes of the ADC input voltage range, as well as the midpoint.  With appropriate firmware / software, it is conceivable to enter this mode on power - up, and perform a sort of self - calibration, where the results of these readings are stored within an external memory and are later used for all subsequent calculations within the processor.

My questions is, what are the drawbacks to doing so?  For example, does it take a very long time to enter and leave this mode?  Does it require cycling power to leave the test mode?  Are there any side effects to entering test mode?

Thank you very much.

Mark Khusid

Design Development Engineer

Moog, Inc.

  • 0
    TI__Guru**** 180961 points

    Hi Mark,

    Entering test mode after power up (assuming the references are settled) is no problem, and you could certainly use this as a calibration scheme.  After exiting test mode, you can write the desired values to the configuration registers and proceed as normal.  No side effects, no need to power cycle the device. 

    Running test mode during normal operation would cause you to lose sync with the DATA_AV signal, so at a minimum you should reset the FIFO or simply re-write both configuration registers and go back into normal operation.

  • 0 in reply to Tom Hendrick
    Prodigy 50 points

    Tom,

      So on sheet 4 of the datasheet, when it states offset error and gain error after calibration, this is after calibration using the ADC's test mode?  What is the uncalibrated offset and gain error?  What is the difference between calibration in single - ended mode and calibration in differential mode?  Are there any documented instructions as to how to perform the calibration?  On page 27 of the datasheet, it talks about Control Register 1, bit 8.  What is the proper way to control this bit?  Is there a way to set the offset register?

    Thank you very much.

    Mark Khusid

    Development Design Engineer

    Moog, Inc.

  • 0 in reply to Mark Khusid
    TI__Guru**** 180961 points

    Hi Mark,

    Bit 8 in CR1 is a little different.  Offset CAL essentially shorts the inputs to ground and does a conversion so its not quite the same thing as the internal test modes.  In either single ended or differential mode, the result ideally would be zero for this conversion.  Whatever the result is, it can be stored internally to the THS1206 and added/subtracted form future conversion results.  There is no access to the internal offset CAL register and unfortunately, I do not have ready access to data that says what the offset might be before calibration. 

    Once you set bit8 in CR1 you would need to clear it.  The easiest thing is to write to the two configuration registers with the desired values for the end application.