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CDCLVD1208: Question about differential input and output specs

Gregory Duperon
Expert 6710 points
Part Number: CDCLVD1208
Other Parts Discussed in Thread: LMK04808

The input specs of the buffer show a differential input range of 0.3V – 1.6V. But the output specs of the buffer show the differential output magnitude to be from 250mV to 450mV. Does this mean that the differential output of this buffer could potentially not be within the input specs of itself?

I have a customer that plans to daisy chain these buffers together.  Is this possible given the specs?

Thanks.

  • 0
    TI__Mastermind 28550 points
    Hello Gregory,

    The input buffer is specified as differential voltage, pp with units Vpp. (0.3 Vpp to 1.6 Vpp)
    The output is specified as Vod, with units V. The differential Vpp output swing is actually 2x Vod. So Vod = 0.25 to 0.45 V becomes Vdiff,pp = 0.5 Vpp to 0.9 Vpp. Therefore this will work with itself.
    - This is something to be aware of when looking at datasheets as different devices may spec differently, and even in the same datasheet as you have experienced. Actually, I think it's best if a datasheet includes both numbers right next to each other to help with this understanding.

    I personally prefer the Vod spec (V) as you can better describe the differential output signal. However differential output voltage Vpp is good for rise/fall time measurements of a differential signal. Note that differential voltage, Vpp is an mathematical construct that doesn't actually exist anywhere in the device. Note: the Vpp measurement of a single output of a differential signal is 'effectively' the Vod.

    Please refer to the LMK04808 datasheet section 7.2 Differential Voltage Measurement Terminology on page 16 for a more in depth description of this topic with pictures.

    73,
    Timothy