Chord™ Signaling Modulation for 100G and 200G Backplane ... · •Mission: Developing IP for...

11OIF 100G Serial and Beyond Workshop © Copyright 2016 Kandou Bus S.A.

Chord™ Signaling Modulation for100G and 200G Backplane Applications

David R StaufferAli Hormati

Margaret Wang JohnstonAmin Shokrollahi

Kandou Bus SAMarch 24, 2016


About Kandou Bus

• Mission: Developing IP for lowest power, highest speed chip-to-chip communication and SerDes based on a new theory of signaling (Chord™ signaling).

• Active in OIF and JEDEC standards committees.

• Paper on Glasswing™ IP was presented at ISSCC 2016:“A Pin-Efficient 20.83Gb/s/wire 0.94 pJ/bit Forwarded Clock CNRZ-5-Coded SerDes up to 12mm for MCM Packages in 28nm CMOS”, Shokrollahi, et al., ISSCC 2016 Session 10.


Current Applications

Networking• Backplane

links• Servers• HPC• etc

Memory links• (LP)DDRx• GDDR• HBM• HMC• And more

Inside Packages• 2.5D

integration• SoC design• FPGAs• etc

Display links• Hand-held

devices• 8K TV• And more

The topic of this presentation is Backplane Links used in Networking and HPC applications.


Agenda

• Description and analysis of ENRZ signaling for CEI-56G-LR (112 Gb/s over 4 wires = 56 Gb/s per pair of wires).

• Description and analysis of ENRZ and ENRZ+ signaling for CEI-112G (225 Gb/s over 4 wires = 112 Gb/s per pair of wires).

• Description and analysis of ENRZ-KMT signaling for CEI-224G (450 Gb/s over 4 wires = 225 Gb/s per pair of wires).


Ensemble NRZ (“ENRZ”) Code Description

ENRZ‒ 3 bits on 4 wires‒ 3 comparators:

o Each compares average of one pair of wires against the other pair‒ If necessary Gearboxes may be used to adapt data path width.

(Also needed for CEI-112G alternative approaches such as PAM-8).

Digital encoder (logic depth 2)

Quaternary values on wires (Higher throughput)

Binary values at input to slicers (low ISI,

DFE)

[1, -1/3, -1/3, -1/3][-1/3, 1, -1/3, -1/3][-1/3, -1/3, 1, -1/3][-1/3, -1/3, -1/3, 1]

[-1, 1/3, 1/3, 1/3][1/3, -1, 1/3, 1/3][1/3, 1/3, -1, 1/3][1/3, 1/3, 1/3, -1]

Codebook

Advantages:• Balanced values on wires

reduce SSO Noise and EMI.• Tolerates common mode noise

similar to differential signals.• Values at slicers are binary, (ISI

Ratio = 1) similar to NRZ signaling.

• Comparators are self-referencing.


ENRZ Backplane Channel Analysis Using COM

• In order to run COM on ENRZ channels, 4-port s-parameter models for each sub-channel need to be extracted from the 8-port ENRZ s-parameter model. Below is the method used for running COM code on ENRZ channels --‒ Start with the 8 port ENRZ s-parameter model‒ Extract binary ENRZ sub-channels

o Example: [1 1 -1 -1] sub-channel

‒ Each sub-channel includes a Thru 4-port s-parameter model and 2 FEXT 4-port s-parameter models for the 2 other sub-channels

‒ Add alien crosstalk channels. Each 8-port alien crosstalk channel will result in 3 4-port alien crosstalk s-parameter models

‒ Compute COM values for each sub-channel


CEI-56G ENRZ Backplane Channel Description

• ENRZ baud rate = 37.5 GBd to provide 112 Gb/s of throughput over 4 wires (= 56Gb/s per pair of wires – same data density as differential pair modulation options).

• Channel was constructed for IL = ~33.6 dB at Nyquist.

• TE Strada Whisper connectors used with pins assigned to provide 50 ohm single-ended signals.

• Analysis included 4 FEXT and 1 or 2 NEXT crosstalk sources on adjacent connector pins.

• PCB Geometry: Trace width = 5mil; intra-pair spacing = 10mil; inter-pair spacing = 20mil.

5 inch daughter card traces

TE Strada Whisper connectors

FR4 trace (er = 3.7, tanD = 0.014) adjusted to meet target IL.

~ 6 mil

~ 6 mil

5 mil

10 mil 20 mil


CEI-56G ENRZ Backplane Channel Results

• COM analysis demonstrates that ENRZ can work over this backplane channel without requiring FEC.

• COM passes for 10-12 BER with 1 or 2 NEXT sources.‒ This BER is sufficient for many HPC applications.

• COM passes for 10-15 BER with 1 NEXT source.‒ Subchannel #0 fails with 2 NEXT sources, but this could be corrected

with a light FEC or crosstalk cancellation targeted on this subchannel.

COM margin ≥ 2dB is required to “pass”, consistent with CEI-56G-LR project criteria.

Case # # of CrosstalkAggressors

BER COM Margin

FEXT NEXT [1 -1 -1 1]Subchannel #2

[1 -1 1 -1]Subchannel #1

[1 1 -1 -1]Subchannel #0

1 4 2 10-12 3.89 dB 3.41 dB 2.15 dB

2 4 2 10-15 2.88 dB 2.41 dB 1.24 dB

3 4 1 10-15 3.20 dB 2.83 dB 2.28 dB


Path to CEI-112G

Two Chord™ signaling paths to CEI-112G are possible:

• ENRZ supports CEI-56G data rates without FEC.It is reasonable to assume that with some incremental improvements in channel technology, ENRZ can support CEI-112G data rates with a KP4 or equivalent FEC.

• Alternatively, incremental architecture enhancements to the ENRZ SerDes would support CEI-112G data rates over legacyCEI-56G backplanes with a KP4 or equivalent FEC.


CEI-112G ENRZ Backplane Channel Description

• ENRZ baud rate = 75.0 GBd to provide 225 Gb/s of throughput over 4 wires (= 112Gb/s per pair of wires).

• Channel IL @ 37.5 GHz:‒ Case 1: 41.7 dB‒ Case 2: 44.6 dB‒ Case 3: 47.6 dB

• Connector S-Parameters for CEI-56G analysis were scaled to 2x frequency. (100G connector S-Parameters not available.)

• Analysis included 4 FEXT and 2 NEXT crosstalk sources on adjacent connector pins.


Scaled S-Parameters for connectors


Case 1 Channel

Case 3 Channel


CEI-112G ENRZ Backplane Channel Results

• The CEI-56G-LR channel has a loss of 33.6 dB @ 18.75 GHz => ~57 dB at 37.5 GBd. This channel fails COM due to high loss, and therefore some improvement in channel technology must be assumed. Assumptions:‒ Channel technology will get somewhat better for next generation.

3 channels with different levels of Insertion Loss were evaluated.‒ FEC similar to KP4 is assumed as it will likely be ubiquitous at higher speeds.

• COM analysis demonstrates that ENRZ can work over the case #1 channel assuming a FEC similar to KP4.

• Based on COM analysis, channels #2 and #3 would also work with a slightly stronger FEC code.‒ Alternatively, reduction of NEXT crosstalk would allow these channels to pass.


Channel Case #

Insertion Loss COM Margin @ BER = 10-6

@37.5 GHz @18.75 GHz [1 -1 -1 1]Subchannel #2



1 41.7 dB 21.3 dB 4.59 dB 4.26 dB 3.05 dB

2 44.6 dB 22.9 dB 3.32 dB 2.94 dB 1.08 dB

3 47.6 dB 24.6 dB 1.90 dB 1.71 dB -0.10 dB


ENRZ+ Architecture Description

ENRZ+‒ 3 bits on 4 wires‒ LPF limits spectral bandwidth of signal on wires‒ Comparators in conjunction with first DFE tap

recover original data from band limited signal.

Low Pass Filter reduces spectral bandwidth by

factor of 2.Band-limited

Quaternary values on wires

First tap of DFE reverses affect of LPF

and restores binary signal

Advantages:• Band-limiting the ENRZ signal

allows baud rate to double without increasing the spectral bandwidth of the channel.

1+z-1

LPF

1+z-1

LPF

1+z-1

LPF

1+z-1

LPFDFE

DFE

DFE


CEI-112G ENRZ+ Backplane Channel Description

• ENRZ baud rate = 75.0 GBd to provide 225 Gb/s of throughput over 4 wires (= 112Gb/s per pair of wires – same data density as differential pair modulation options).

• Low Pass Filter limits spectral bandwidth to frequencies below 18.75 GHz.‒ Also reduces eye amplitude by a factor of 2.

• Channel is the same as was used for CEI-56G analysis: IL = ~33.6 dB @ 18.75 GHz.• No scaling for TE Strada Whisper connector S-Parameters. • Analysis included 4 FEXT and 2 NEXT crosstalk sources on adjacent connector pins.


TE Strada Whisper connectors

FR4 trace (er = 3.7, tanD = 0.014) of same length/loss as CEI-56G.

~ 6 mil

~ 6 mil

5 mil

10 mil 20 mil


CEI-112G ENRZ+ Backplane Channel Results


Case # # of Crosstalk Aggressors

BER COM Margin




1 4 2 10-6 3.92 dB 3.71 dB 3.06 dB

2 4 2 10-7 3.14 dB 2.93 dB 2.30 dB

1 0

Transient simulations over 10,000 UI – at DFE sample point without VGA stage.


CEI-112G ENRZ+ Backplane Channel Results

• COM analysis demonstrates that ENRZ+ works over existing CEI-56G backplane channels with a FEC similar to KP4.

• ENRZ+ architecture in the Chord™ signaling roadmap provides an incremental solution to support CEI-112G in the event channel technology improvements do not materialize.

• ENRZ+ also provides an incremental solution on the road to CEI-224G.



BER COM Margin




1 4 2 10-6 3.92 dB 3.71 dB 3.06 dB

2 4 2 10-7 3.14 dB 2.93 dB 2.30 dB


Path to CEI-224G• Paths forward to 224G will need to rely on more efficiently utilizing the

spectral bandwidth available on the medium.

• Adding additional channels using frequency domain multiplexing is one means of increasing the spectral utilization.‒ ENRZ+ reduced the spectral width needed for the baseband signal.‒ Frequency spectrum above the baseband signal can be utilized to carry

additional channels.

• Kandou Multi Tone (KMT) combines with ENRZ to provide6 subchannels of information over 4 wires.‒ 3 subchannels are sent as an ENRZ+ baseband signal.‒ 3 subchannels are ENRZ+ encoded and amplitude modulated

on a passband signal using a 19.75 GHz subcarrier.‒ Baud rate = 75 GBd => 450 Gb/s of total throughput over 4 wires.


ENRZ-KMT Architecture Description

b0

b1

b2

b3

b4

b5

Enco

der (

x2)

LPF

LPFsin(wt)

+

LPF

LPFsin(wt)

+

LPF

LPFsin(wt)

+

LPF

LPFsin(wt)

+

w0

w1

w2

w3

Rx F

ront

end

LPF

HPFsin(wt)

LPF DFE

DFE b0

b1

LPF

HPFsin(wt)

LPF DFE

DFE b4

b5

LPF

HPFsin(wt)

LPF DFE

DFE b2

b3

Parallel data paths for baseband and passband

ENRZ-encoded data.

Baseband data is transmitted below 18.75 GHz. Passband data is amplitude modulated on a 19.75 GHz subcarrier.

Analog stage filters decompose signal into

baseband and passband components.


CEI-224G ENRZ-KMT Backplane Channel Description

• ENRZ baud rate = 75.0 GBd to provide 450 Gb/s of throughput over 4 wires (= 225 Gb/s per pair of wires – same data density as differential pair modulation options)

• Case #1 Channel (pg 10): Insertion Loss = 41.7 dB @ 37.5 GHz• Connector S-Parameters for CEI-56G analysis were scaled to 2x frequency for 100G

analysis.‒ Approach chosen due to lack of availability of 100G connector data.

• Analysis included 4 FEXT and 1 or 2 NEXT crosstalk sources on adjacent connector pins


Scaled S-Parameters for connectors



CEI-224G ENRZ-KMT Backplane Channel Results

1 0

Transient simulations of Baseband Channels over 10,000 UI – at DFE sample point without VGA stage.

01

Transient simulations of Passband Channels over 10,000 UI – at DFE sample point without VGA stage.


CEI-224G ENRZ-KMT Backplane Channel Results

• For the channel in this analysis: IL = 41.7 dB @ 37.5 GHz.‒ This is a 27% reduction in insertion loss over the current

CEI-56G-LR definition.‒ This is a reasonable goal for the CEI-224G generation.

• COM analysis demonstrates that ENRZ-KMT works over this channel with an appropriate FEC.

• COM passes for 10-5 BER with 1 or 2 NEXT sources.



BER COM Margin




1 4 1 10-6 2.53 dB 2.36 dB 1.82 dB

2 4 2 10-5 3.43 dB 3.16 dB 2.03 dB

3 4 1 10-5 3.50 dB 3.34 dB 2.75 dB


Summary and Conclusions

Kandou Bus can provide Chord™ signaling solutions for backplane applications for at least the next two generations of interface speeds.• ENRZ provides a “No FEC” solution for backplane interfaces over

CEI-56G-LR channels.• ENRZ+ provides a solution for next generation CEI-112G

backplane interfaces over the existing CEI-56G-LR channel.• ENRZ-KMT provides a solution for future CEI-224G backplane

interfaces.


KANDOUreinventing the

BUS

Chord™ Signaling Modulation for 100G and 200G Backplane ... · •Mission: Developing IP for...

Documents

Transcript of Chord™ Signaling Modulation for 100G and 200G Backplane ... · •Mission: Developing IP for...