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Original question:

SN65HVD63: Can this be adapted for a twisted pair operation (not coax)?

SN65HVD63: Error in Figure 20, Measurement of Modem Receiver Propagation Delays

Lauren Mayfield
Expert 7985 points
Part Number: SN65HVD63


Hi team,

Can you please explain Figure 20? 

tPHL and tPLH are specified  from a point on the RXIN where the voltage is 0.5VL.

It doesn't make sense that 0.5VL is half the RXOUT voltage which is going to be ~2.5V for a 5V supply or 1.65V for a 3.3V supply but RXIN VPP can be a lot less than that.

Moreover it cant be a typo for 0.5VPP either because the receiver doesn’t know what VPP is going to be before it happens.

Is VPP supposed to be VL on the figure for the RXIN graph? If not, can you clarify the receiver propagation timing?

Thanks,

Lauren

  • 0
    TI__Guru 62920 points

    Lauren,

    The voltages on the OOK portion of the RX timing waveform should really be referenced to VPP, not VL.  VL would only make sense as a reference for the logic pins (like RXOUT and DIR).  Thanks for pointing that out - we can make sure to correct it in the next revision.

    It's a good point that even correcting for the typo and considering this reference voltage as 0.5*VPP, it still doesn't make perfect sense because the point at which the receiver detects the change in input state is when the voltage exceeds VIT.  The parameter was characterized with a fast transition time on the OOK signal (comparable to what is generated by the transmitter), though, and so the point at which VIT is exceeded, 0.5*VPP is exceeded, and VPP is reached would all be within a few nanoseconds of one another.  Since the propagation delay is on the order of microseconds (dominated by the demodulation delay), the distinction of the exact threshold level on the transition would not materially impact the spec value.

    Please let me know if that doesn't make sense or if there are any further questions.

    Regards,
    Max