SN55LVCP22-SP: LVDS receiver specifications - Vth and Vtl versus VID(HYS) hysteresis

Hi,

Please see this for the VTH and VTL definition.

With a differential input voltage within the transition regions, a small amount of positive feedback from the output stage of a receiver can cause the positive-going input threshold to be greater than the negative-going threshold creating hysteresis in the response. This feature prevents oscillation of the receiver output from differential noise below the hysteresis value. This failsafe feature does not force the output to a predetermined state but keeps in the last one before entering the transition region.

Thanks

David

Does this mean that if my measured VTH is 80mV, and my measured VTL = -80mV, the part is failing the VID(HYS) spec of 150mV?  Or are you saying that the thresholds supersede the hysteresis, and the MAX hysteresis is only applicable outside of the transition region, if applicable at all?

I understand the voltage thresholds, and I understand hysteresis, as independent concepts.  What I don't understand is how the two specifications work together to define expected/required behavior.

Hi,

Please take a look at this app note, https://www.ti.com/lit/ug/slld009/slld009.pdf, in particular the section on the Differential Input Voltage Threshold, does this help answering your question?

Thanks

David

Unfortunately, no.  This document includes this definition:

"Hysteresis—The difference between the positive and negative going receiver input voltage thresholds. Incorporated into receivers to reduce output oscillations in response to input signal noise."

If the hysteresis is really defined as the difference between positive and negative going thresholds, than your part is failing it's specification... but I don't believe this is correct.

I have one of these parts, and I have measured it's positive going and negative going thresholds at +85mV and -80mV.  Per the definition provided here, that is a hysteresis of 165mV.  But the datasheet for the part defines a MAXIMUM hysteresis of 150mV.

This is where the hysteresis being less than the specified transition region (-100mV to +100mV) does not make sense to me, and this document does not resolve the issue.

So is my part out of specification, since the difference between the positive going and negative going thresholds is 165mV, but the hysteresis is defined as a MAXIMUM of 150mV?