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 Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 1 / 20
Board-to-Board Channel Chips Daughtercards Connectors Board Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 2 / 20
Characterize the Channel Chip1 Z 0 =50 Ω Chip2 Tx Rx Tx Rx Tx Rx crosstalk 1 0.8 through Voltage (V) crosstalk1 0.6 crosstalk2 0.4 0.2 0 −0.2 0 1 2 3 4 5 Time (ns) Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 3 / 20
Impulse and Frequency Responses 0.06 through 0 0.04 0.02 0 −10 Channel Gain (dB) −0.02 0 1 2 3 4 5 0.06 0.04 crosstalk1 −20 Volts 0.02 0 −30 −0.02 0 1 2 3 4 5 0.06 crosstalk2 0.04 −40 through 0.02 crosstalk1 0 crosstalk2 −50 −0.02 7 8 9 0 1 2 3 4 5 10 10 10 Time (ns) Frequency (Hz) Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 4 / 20
System Model Transmit Filter Chip-to-Chip Channel Crosstalk Tx G H Rx C Tx G H Rx C Tx G H Rx (many links in parallel) Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 5 / 20
Conventional Solutions slew-rate limiting pro: simple Transmit Filter con: not good Chip-to-Chip Channel when ISI is severe crosstalk Tx G H Rx -1 cancellation in C Tx G H Rx addition to transmit -1 C filter G Tx G H Rx pro: good (many links in parallel) performance con: hardware cost Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 6 / 20
Example: Different Pulse Shapes 1 UI square pulse 1 total tap 1 tap per UI 1 UI 1 UI fractionally-spaced pre-emphasis pulse 6 total taps 2 total taps 3 taps per UI 1 tap per UI Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 7 / 20
Example: Different Pulse Shapes 1 UI square pulse 1 total tap 1 tap per UI 1 UI 1 UI fractionally-spaced pre-emphasis pulse 6 total taps 2 total taps 3 taps per UI 1 tap per UI Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 8 / 20
Example: Different Pulse Shapes 1 UI square pulse 1 total tap 1 tap per UI 1 UI 1 UI fractionally-spaced pre-emphasis pulse 6 total taps 2 total taps 3 taps per UI 1 tap per UI Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 9 / 20
Optimize with Respect to a Figure of Merit Definition crosstalk-free eye opening E 2 C = maximum possible crosstalk Crosstalk-Free Eye Opening Maximum Possible 1 Unit Interval (UI) Crosstalk Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 10 / 20
Find E2C for each Pulse Shape 0.6 0.06 0.05 0.4 Voltage (V) Voltage (V) 0.04 0.2 0.03 = 485 mV 0.02 0 ∗ ∗ PRBS7 0.01 −0.2 0 −0.4 −0.01 −0.02 −0.6 0 1 2 3 4 5 Time (ns) 0 200 400 600 Time (ps) 0.2 0.06 0.15 0.05 Voltage (V) 0.1 0.04 Voltage (V) 0.03 0.05 = 0.02 0 ∗ ∗ PRBS7 0.01 −0.05 0 −0.1 −0.01 −0.15 −0.02 crosstalk = 157 mV 0 1 2 3 4 5 Time (ns) −0.2 0 200 400 600 Time (ps) 485 mV E 2 C = 2 × 157 mV = 1 . 54 Repeat calculation for all candidate pulse shapes Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 11 / 20
Maximum E2C for Various Filter Types at 2.7 Gb/s E2C 6 1/6 1/5 5 i n c r e a s i n g E 2 C 1/4 4 Tap Delay Taps per UI 6.5 (in UI) 3 1/3 6 2 1/2 5.5 5 4.5 1 1 1 2 3 4 5 6 Total Taps Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 12 / 20
Increasing Total Taps E2C 6 1/6 5 1/5 Taps per UI 4 1/4 Tap Delay 6.5 (in UI) 3 1/3 6 2 1/2 5 . 5 5 4 . 5 1 1 1 2 3 4 5 6 Total Taps Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 13 / 20
Increasing Granularity E2C 6 1/6 5 1/5 Taps per UI 4 1/4 Tap Delay 6.5 (in UI) 3 1/3 6 2 1/2 5 . 5 5 4 . 5 1 1 1 2 3 4 5 6 Total Taps Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 14 / 20
Increasing Taps per UI E2C 6 1/6 5 1/5 Taps per UI 4 1/4 Tap Delay 6.5 (in UI) 3 1/3 6 2 1/2 5 . 5 5 4 . 5 1 1 1 2 3 4 5 6 Total Taps Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 15 / 20
Hardware Proof-of-Concept Power Combiner Power Chip-to-Chip Oscilloscope ParBERT Combiner Channel Power Combiner Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 16 / 20
Channel Introduces ISI and Crosstalk 2.7 Gb/s PRBS: 2 31 –1 input to channel output from output from channel channel square pulse no aggressors two aggressors Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 17 / 20
Filter Opens the Eye output from channel pulse shape chosen to maximize E2C two aggressors 3 total taps square pulse input 2 taps per UI jitter RMS = 53 ps jitter RMS = 33 ps Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 18 / 20
Filter Improves Bit Error Rate 0 0 10 10 −2 10 −5 10 Bit Error Rate Bit Error Rate −4 10 −10 10 −6 10 −8 10 −15 10 Crosstalk−Aware Pulse Shape Crosstalk Aware Pulse Shape Square Pulse Pre−emphasis Pulse Shape −10 10 −1 −0.5 0 0.5 1 −1 −0.5 0 0.5 1 Sampling Phase (Unit Intervals) Sampling Phase (Unit Intervals) square pulse: pre-emphasis pulse: BER = 10 − 5 BER = 10 − 7 crosstalk-aware pulse: crosstalk-aware pulse: BER < 10 − 12 BER = 10 − 5 Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 19 / 20
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 10 2 at 2.7 Gb/s Mike Bichan, Anthony Chan Carusone Crosstalk-Aware Equalization Over Chip-to-Chip Links 20 / 20
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