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AM26C31: Change in differential output voltage not matching as per datasheet.

Prodigy 110 points

Replies: 5

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Part Number: AM26C31

Currently I am working on project in which I have used this part number to generate one differential signal. As per datasheet the change in the output differential voltage is -400mV to +400mV. But during testing I have found out the differential swing is from +3.6V to -3.6V. I checked the reference board also and I found the total differential swing of around 6.5V. Any suggestion?

  • Hello,

    AM26C31 specifies a typical output differential amplitude of +/- 3.1 V for a 100-Ohm load (see "VOD" specification in Section 6.5 of the datasheet).  So, this result sounds expected to me.  What is the 400 mV specification you are referencing?

    Regards,
    Max

  • In reply to Max Robertson:

    Hi Max, 

    I got your point but 3.1 is typical VOH for differential signal. For output differential voltage swing which I have highlighted in the image it is mentioned as +/- 400mV. In my case this swing is around 7.2V.

    Please correct me if I am getting it wrong.

  • In reply to RAHUL JHA:

    Hi Rahul,

    Sorry for the delay due to the holiday.  The spec that you highlighted is actually not the differential output swing.  That would simply be "VOD" (the line above it).  This spec defines the mismatch between the VOD for the high state versus the VOD for the low state.  Ideally these would be perfectly matched (i.e., same amplitude, opposite polarity) and this spec value would simply be 0.  However, realistically there may be some small mismatch between the two states' amplitudes and so this spec constrains that mismatch to a maximum of 400 mV.  Please let me know if that doesn't make sense.

    Regards,
    Max

  • In reply to Max Robertson:

    Hi Max,

    Thanks a lot for the clarification. Now I got your point and I really appreciate that.

    One last thing, can you tell me what could be the maximum voltage swing for differential signals?

  • In reply to RAHUL JHA:

    The maximum limit would theoretically be the VCC voltage of the device (in both positive and negative directions).  Practically, though, the swing will always be a little less due to some voltage drop through the driver circuitry.

    Regards,
    Max