Crosstalk Decomposition

I found that my 2010 DesignCon paper on crosstalk decomposition was finally referenced in the below paper.  It is nice to see that the topic has interest.  I'd need to critically review the paper for any updates I do to my methods.

Y. Wu and X. Zhang, "Analysis of Channel Crosstalk Decomposition Methods," 2019 IEEE International Symposium on Electromagnetic Compatibility, Signal & Power Integrity (EMC+SIPI), New Orleans, LA, USA, 2019, pp. 575-579.


This paper from 1995 needs to be reviewed if I ever renew my crosstalk decomposition work.

A. H. Zemanian and Yaw-Fu Jan, "Transmission decomposition and crosstalk evaluation in lumped-distributed networks," in IEEE Transactions on Circuits and Systems I: Fundamental Theory and Applications, vol. 42, no. 7, pp. 346-353, July 1995.

Design of 56 Gb/s NRZ and PAM4 SerDes Transceivers in CMOS Technologies

J. Lee, P. Chiang, P. Peng, L. Chen and C. Weng, "Design of 56 Gb/s NRZ and PAM4 SerDes Transceivers in CMOS Technologies," in IEEE Journal of Solid-State Circuits, vol. 50, no. 9, pp. 2061-2073, Sept. 2015.

Disclaimer: I've only read up to and including section III but that includes the PAM4 design, which I am interested in at the time.

Great, well written paper.  This is written by a university group so I felt like they shared a lot of useful information and were not trying to hide details like it feel like if the group was industry based.

• They have a great (first order) explanation as to when you want to choose PAM4 over NRZ.  
• The concept is, the PAM4 eye is 1/3 smaller than the NRZ eye. db(1/3)  = -9.5.  For 56 Gbps, the Nyquist for NRZ is 28 GHz and 14 GHz for PAM4.  Therefore, if the difference in Insertion loss between 28 and 14 G is less than 9.5 dB, you should do NRZ, but if it is larger then PAM4 is a viable option.

• PAM4 Transmitter
• "the number of FFE taps is usually limited to 4 in order to minimize the parasitics".
• May need DLLs to neutralize skews between the multiple data stream, due to the use of clock multiplexing (a half rate clock, quarter rate clock, etc).  
• skew may be an interesting impairment to model.  This would be a form of DCD
• Summer with tuneable weighting combiner to adjust the level spacing.
• These are needed to compensate for a non-linear optical impairment.
• We could model this behavior in a MATLAB function block but would only be useful if we also had a EML (electroabsortion-modulated) laser block that would create the impairment that the tunable weights would be compensating for.  
• Unless an AMI model injected this EML laser impairment, I see little point in including a summer with tunable weights in an AMI model.
• Transmitter includes peaking inductor to increase the edge rate of the transitions.

• PAM4 Receiver
• A pure linear CDR.  They say that it naturally handles multiple levels and is some ways easier to implement than a bang-bang CDR.
• Preamp/Equalizer
• They do slightly equalize the signal differently depending on if it goes to the middle (0 Volt threshold) slicer or the upper/lower slicers..
• PAM4 slicers, linear CDR and DFE
• 3 slicers at the 3 PAM4 threshold values
• Linear CDR
• Apply DFE separately to the three slicers
• Question.  Why is the DFE after the slicer?  I guess I usually combine the slicer with symbol decoder.  Here these functions are separated.  This allows for a soft decision (slicers, or a 2 bit ADC), followed by some DSP (through the DFE) and finally the PAM4 decoder and retimers make the bit decisions.
• This type of circuit is possible since they have a high precision linear CDR.  Then they can operate on the data samples with high confidence.