paper 28.7 – isscc2005 a 3gb/s ac coupled chip-to … 3gb/s ac coupled chip-to-chip communication...
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Paper 28.7 – ISSCC2005
A 3Gb/s AC Coupled Chip-to-Chip Communication using a Low Swing Pulse Receiver
Lei Luo, John M. Wilson, Stephen E. Mick, Jian Xu, Liang Zhang and Paul D. Franzon
North Carolina State University, Raleigh, NC
2
High density High density CapacitivelyCapacitively Coupled I/OsCoupled I/Os
3D-IC
Proximity Comm.
Chip1 Chip2
Chip3 Chip4
AC Coupled Interconnect
Circuit View
DensityFlexibilityMore integrationLonger DistanceLossy
3
i
ii
iii
pulse signaling waveformscircuit view
i ii iiiRXTX
AC Coupled Interconnect (ACCI)AC Coupled Interconnect (ACCI)
75um I/O pitch6,000+ I/Os /cm2
Low power
physical structure
Interconnects
AC Connection(Capacitive Coupling)
Trench
DC Connection(Buried Solder Bump)
Chip1 Chip2
Substrate
6
Traditional EqualizationTraditional Equalization
TX RX
Frequency
Channel
Bit-rate/2Frequency
Equalizing Filter
Bit-rate/2Frequency
Equalized Channel
Bit-rate/2
7
ACCI EqualizationACCI Equalization
Frequency
Pulse RX (latch)
Bit-rate/2Frequency
Equalized Channel
Bit-rate/2Frequency
ACCI Channel
Bit-rate/2
RXTX
8
ISI of Pulse SignalISI of Pulse SignalCurrent Bit Next Bit
600 800 1000 Time (ps)
RXTXVpp
(mV)
13% Tail
3% Tail
160
120
80
40
0
9
EYE at RX inputEYE at RX input
Increasing CouplingCapacitance
Vpp
(mV)
Time (ps)
150
100
50
0
-50
-100
-150
-2000 200 400
ISI limit
Swing limit
10
Components of ACCIComponents of ACCI
ACCI Channel
TX outputs NRZ to channel
Pulse RX converts pulses back to NRZ, then goes to clock and data recovery
11
Low power driverLow power driver
Current Mode Vs. Voltage Mode50 ohm TL load Vs. Cap loadStatic current Vs. dynamic current10mA Vs 1.3mA (to get a 0.25VSEPP output swing, for 0.18um CMOS)
10mA 1.3mA
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Power SavingPower SavingPower of 0.18um Driver
0
5
10
1520
25
30
35
40
0.2 0.3 0.4 0.5
Output Swing (V)
Pow
er o
f Driv
er (m
W)
Current Mode DriverVM Driver @ 5GbpsVM Driver @ 4GbpsVM Driver @ 3GbpsVM Driver @ 2Gbps70% less
89% less
ACCI Driver consumes dynamic power, depending on data rate and data activity
13
(All scaled to 0.18um/1.8Vdd).
ACCI need sensitive pulse receiverACCI need sensitive pulse receiver
14
Vb
Vpulse in+
Vnrz out+ Vnrz out-
Vpulse in-
M1
M3
M5
M2
M4
M6
M7 M8
M11 M12
M10
M9Vb
Vpulse in+
Vnrz out+ Vnrz out-
Vpulse in-
M1
M3
M5
M2
M4
M6
M7 M8
M11 M12
M10
M9
A low swing pulse receiverA low swing pulse receiver
latch
Input Stage Input Stage
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Vpulse in+
M1
M3
M5
Vpulse in+
M1
M3
M5
Input stageInput stage
ISI due to limited bandwidthSwing Vs. bandwidth tradeoff INV and feedback ratio
Without ISI
With ISI
16
Latch stageLatch stage
Vb
M7 M8
M11 M12
M10
M9Vb
M7 M8
M11 M12
M10
M9
Latch : M11 and M12; Edge Detector: M7 and M8Swing and bandwidth tradeoff M10
Without or with weak clamp_D: Huge ISI
With proper clamp_D: Minimized ISI
Without M10
With M10
17
Simulated Simulated ShmooShmoo PlotPlot
Works over wide range of Coupling Capacitance, TL Length, up to 3Gb/s
Pass Criteria: 0.8 UI Eye Opening
TL(cm)
CC(fF)
230
180
130
80
300 5 10 15 20 25
18
Test chipTest chip
15 cm50 ohmPCB trace
Multi-Phase DLL
PRBS Generator
MUX TX
RXSampler
Clock Recovery
Multi-Phase DLL
BER TesterScope
Clock Source
Data
BER
Clock Reference
Test Chip
Data
Clock Recovered
Clock
Clock
Control
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TXT
RXT1 RXT2 RXT3 RXT4 RXT5
TX1-7 and Pads
RX1-5 and Pads
Die photoDie photo
TSMC 0.18um CMOS, 2mm by 3.5mm
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Test Setup on PCBTest Setup on PCB
15 cm long 50 ohm differential PCB trace
150fF Coupling Capacitors
21
Chip and Measured dataChip and Measured data
< 10-12BER60um by 60um on-chip (150fF)Coupling Caps
134Total
116.5Clock, testcircuit andbuffers
10Pulse RX5DriverPower
(mW)
7ps RMSJitter of recover data15cm and 50ohm micro-strip lineLink
3Gb/s/channelData Rate1.8VSupply VoltageTSMC 0.18um CMOS 1P 6MProcess
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MCMMCM--D TestD Test
• 0.35 um CMOS Flip-chip• 5.6cm MCM Line• 5Gbps over two channels
(2.5Gb/s/ch)
TSMC 0.35µm Chip Bump Trenches & ACI
Assembled ACCI System
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Substrate / Chip BondingSubstrate / Chip Bonding
Substrate
Chip
ACCI chip and substrate
Buried solder bumps
ACCI coupling capacitor and buried solder bumpsCoupling capacitor
MCM-D fabricated and assembled by MCNC