Crosstalk-Aware Transmitter Pulse-Shaping for Parallel Chip-to-Chip - - PowerPoint PPT Presentation

Crosstalk-Aware Transmitter Pulse-Shaping for Parallel Chip-to-Chip Links

Mike Bichan, Anthony Chan Carusone

Department of Electrical and Computer Engineering University of Toronto

ISCAS 2007

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Board-to-Board Channel

Connectors Chips Daughtercards Board

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Characterize the Channel

Chip2 Chip1 crosstalk

Rx Rx Rx Tx Tx Tx

Z0=50 Ω

1 2 3 4 5 −0.2 0.2 0.4 0.6 0.8 1 through crosstalk1 crosstalk2

Voltage (V) Time (ns)

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Impulse and Frequency Responses

1 2 3 4 5 −0.02 0.02 0.04 0.06 1 2 3 4 5 −0.02 0.02 0.04 0.06 Volts 1 2 3 4 5 −0.02 0.02 0.04 0.06 Time (ns) through crosstalk1 crosstalk2 10

7

10

8

10

9

−50 −40 −30 −20 −10 through crosstalk1 crosstalk2 Frequency (Hz) Channel Gain (dB) Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 4 / 20

System Model

Crosstalk Chip-to-Chip Channel Transmit Filter (many links in parallel) Tx G Rx H C Rx H G Tx H G Tx C Rx

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Conventional Solutions

Tx Chip-to-Chip Channel Transmit Filter (many links in parallel) Tx

• 1
• 1

C C Rx Rx Rx H H H G G G Tx

slew-rate limiting

pro: simple con: not good when ISI is severe

crosstalk cancellation in addition to transmit filter G

pro: good performance con: hardware cost

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Example: Different Pulse Shapes

1 UI 1 UI 1 UI square pulse 1 total tap 1 tap per UI pre-emphasis pulse 2 total taps 1 tap per UI fractionally-spaced 6 total taps 3 taps per UI

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Example: Different Pulse Shapes

1 UI 1 UI 1 UI square pulse 1 total tap 1 tap per UI pre-emphasis pulse 2 total taps 1 tap per UI fractionally-spaced 6 total taps 3 taps per UI

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Example: Different Pulse Shapes

1 UI 1 UI 1 UI square pulse 1 total tap 1 tap per UI pre-emphasis pulse 2 total taps 1 tap per UI fractionally-spaced 6 total taps 3 taps per UI

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Optimize with Respect to a Figure of Merit

Definition E2C = crosstalk-free eye opening maximum possible crosstalk

Crosstalk-Free Eye Opening 1 Unit Interval (UI) Maximum Possible Crosstalk Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 10 / 20

Find E2C for each Pulse Shape

200 400 600 −0.6 −0.4 −0.2 0.2 0.4 0.6

485 mV

1 2 3 4 5 −0.02 −0.01 0.01 0.02 0.03 0.04 0.05 0.06

∗ ∗ =

Time (ps) Voltage (V) Time (ns) Voltage (V)

PRBS7

200 400 600 −0.2 −0.15 −0.1 −0.05 0.05 0.1 0.15 0.2

crosstalk = 157 mV

1 2 3 4 5 −0.02 −0.01 0.01 0.02 0.03 0.04 0.05 0.06

∗ ∗ =

Time (ps) Voltage (V) Time (ns) Voltage (V)

PRBS7 E2C =

485 mV 2×157 mV = 1.54

Repeat calculation for all candidate pulse shapes

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Maximum E2C for Various Filter Types at 2.7 Gb/s

1 2 3 4 5 6 1 2 3 4 5 6

4.5 5 5.5 6 6.5 i n c r e a s i n g E 2 C

Total Taps Taps per UI E2C 1 1/2 1/3 1/4 1/5 1/6 Tap Delay (in UI)

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Increasing Total Taps

1 2 3 4 5 6 1 2 3 4 5 6

4 . 5 5 5 . 5 6 6.5

Total Taps Taps per UI E2C

1 1/2 1/3 1/4 1/5 1/6 Tap Delay (in UI) Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 13 / 20

Increasing Granularity

1 2 3 4 5 6 1 2 3 4 5 6

4 . 5 5 5 . 5 6 6.5

Total Taps Taps per UI E2C

1 1/2 1/3 1/4 1/5 1/6 Tap Delay (in UI) Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 14 / 20

Increasing Taps per UI

1 2 3 4 5 6 1 2 3 4 5 6

4 . 5 5 5 . 5 6 6.5

Total Taps Taps per UI E2C

1 1/2 1/3 1/4 1/5 1/6 Tap Delay (in UI) Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 15 / 20

Hardware Proof-of-Concept

Combiner Power Combiner Power Combiner Power

Oscilloscope ParBERT

Chip-to-Chip Channel

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Channel Introduces ISI and Crosstalk

2.7 Gb/s PRBS: 231–1 input to channel square pulse

• utput from

channel no aggressors

• utput from

channel two aggressors

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Filter Opens the Eye

• utput from channel

two aggressors square pulse input jitterRMS = 53 ps pulse shape chosen to maximize E2C 3 total taps 2 taps per UI jitterRMS = 33 ps

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Filter Improves Bit Error Rate

−1 −0.5 0.5 1 10

−15

10

−10

10

−5

10

Crosstalk Aware Pulse Shape Square Pulse Bit Error Rate Sampling Phase (Unit Intervals) −1 −0.5 0.5 1 10

−10

10

−8

10

−6

10

−4

10

−2

10 Crosstalk−Aware Pulse Shape Pre−emphasis Pulse Shape Bit Error Rate Sampling Phase (Unit Intervals)

square pulse: BER = 10−5 crosstalk-aware pulse: BER < 10−12 pre-emphasis pulse: BER = 10−7 crosstalk-aware pulse: BER = 10−5

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Conclusion

Crosstalk is significant in board-to-board channels Received eye opening can be increased by taking crosstalk into account when equalizing Crosstalk-aware pulse shape decreased BER by 102 at 2.7 Gb/s

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