IEE5011 –Autumn 2013 Memory Systems Duty Cycle Correctors (DCC) In GDDR5 SDRAM

Kuang-Yu,Li 2013

IEE5011 –Autumn 2013Memory Systems

Duty Cycle Correctors (DCC) In GDDR5 SDRAM

Kuang-Yu, LiDepartment of Electronics Engineering

National Chiao Tung [email protected]

NCTU IEE5011 Memory Systems 2013Kuang-Yu,Li

Outline IntroductionBasics

DCC and GDDR5

Comparison Analog and Digital DCC

All-Digital DCCDCC in GDDR5 Conclusion

2


IntroductionGDDR5

AMD first shipped in 2008Sony used in 2013

3


Basic GDDR5 (1/4)

4


Basic GDDR5 (2/4)Pre-fetch of 8Array Bank GroupingNew training and trackingNew Clocking

5


Basic GDDR5 (3/4)Data strobe signal (DQS)~>Write data clock(WCK)CK x 1, WCK x2 , Data x4

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Basic GDDR5 (4/4)

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[1]


Basics DCC (1/3)Why do we need Duty-Cycle-Correctors ?

Improve valid data windowReduce duty cycle error

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Basic DCC (2/3)Corrects input to 50% duty-cycleTwo functions:

Detect define 50% boundary

Correct adjust edge until correct

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Basic DCC (3/3)Design :

Location –on/off pathIntegration -embedded or notLocking timeOperating frequency rangeOffset -comes from detectorImplementation -analog or digitalOther (power, area…)

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Analog DCCSimple negative feedback

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Analog DCC :Detector Integrating Error

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Analog DCC :CorrectorCross-coupled differential pair

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,m

Max cn pO cyc

g RCCorrect V

I t


Digital DCCSimple negative feedback

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Digital DCC :DetectorDetection Loop

Time-mutiplexing between clocksIntegrated error and amplified

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Digital DCC :CorrectorChargepump :offset adjusting

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Analog and Digital ComparisonDigital DCC is preferred!

Power ,range ,function ,supply, mismatch

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Analog Digital

DCC sharing X V

Common mode Variation

Insensitive Sensitive

Correction range Narrow Wide

Power Efficient X V

Manual override X V

[2]


All-Digital DCC(ADDCC)Wide-range, high resolutionCombined with DLL

Low jitter and fast lock timeOpen loop scheme

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DLL_out

[3]


ADDCC: TimingRising of DLL_out and Hclk

Phase error ε,WSG delay α

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ADDCC: Cycle Detector

Dual delay line with WSGOvercoming trade-offsSmall Overhead

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Measured Result

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Process 0.18um CMOS

Operating frequency 440MHz~1.5GHz

Supply 1.8V

Duty cycle ratio 50±2%

Peak-to Peak jitter [email protected]

Maximum lock-in time ADDCC:5 cycles

Area 0.053mm2

Power [email protected]% --> 50.6% @440MHz


GDDR5 Clock DistributionP:PLL ,G:Global DriverDQ Pad

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DCC in GDDR5 Wide-range, fast-lock, offset tolerant [5]

Anti-harmonic binary search(ABS)

CML and PLL in clock distribution

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DCC in GDDR5 :AdjusterBetween Rx and Driver

Off clock-path –jitter free4 phase clock

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Step: 6psRange: ±100ps


DCC in GDDR5 :DetectorSwitch ,ABS circuit, 2 latches, comparatorTo adder based counter -> Adjuster

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DCC in GDDR5 :Detection Methodology iclk vs. qclk and qclk vs. iclkb

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DCC in GDDR5 :ABS CircuitWeighted Delay Cell and range adjuster

Anti-harmonic and wide frequency range

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Measured Result Operating frequency and correction range

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Measured Result :Locking TimeFive input clock ranges

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Measured Result :Locking process

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Chip Microphotograph0.0017mm2

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DCC in GDDR5 Summary

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Process 54m CMOS triple-metal

Operating frequency 800MHz~3.5GHz(1.6 GHz~7 GHz)

Supply 1.5V

Correction range -100ps ~ +100ps

Step resolution 6ps

Lock-in time Min:64 cycles

Max:256 cycles

Area 0.017mm2

Power [email protected]


ConclusionDigital DCC in state of the art DRAM design is

necessary and importantDCC in GDDR5 with wide-range fast-lock duty-

cycle corrector with offset-tolerant capabilityWCK is up to 3.5GHz to sustain 7Gbps/pin

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Reference [1] Kho, R ,et.al, “A 75 nm 7 Gb/s/pin 1 Gb GDDR5 Graphics Memory Device With Bandwidth Improvement

Techniques”, IEEE Journal of Solid-State Circuits, vol.45,no.1 ,pp120 - 133, Jan. 2010 [2] L. Raghavan et.al, “Architectural Comparison of Analog and Digital Duty Cycle Corrector for High Speed I/O Link,”

VLSI Design, pp 270-275,Jan.2010 [3] Dongsuk Shin et.al, “A 7ps-Jitter 0.053mm2 Fast-Lock ADDLL with Wide-Range and High-Resolution All-Digital

DCC”, ISSCC,pp184-185, Feb. 2007 [4] Shao-Ku Kao et.al, “All-Digital Fast-Locked Synchronous Duty-Cycle Corrector” IEEE Transactions on Circuits and

Systems ,vol.53,pp 1363 - 1367, Dec. 2006 [5] Dongsuk Shin , Kwang-Jin Na et.al, “Wide-Range Fast-Lock Duty-Cycle Corrector with Offset-Tolerant Duty-Cycle

Detection Scheme for 54nm 7Gb/s GDDR5 DRAM Interface,” Symposium on VLSI Circuits Digest of Technical Papers,pp 138-139, June 2009

[6] Kyung Hoon Kim et.al, “A 5.2Gb/p/s GDDR5 SDRAM with CML Clock Distribution Network”, ESSCIRC ,pp194 - 197, Sept. 2008

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IEE5011 –Autumn 2013 Memory Systems Duty Cycle Correctors (DCC) In GDDR5 SDRAM

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