SuperRange: Wide Operational Range Power Delivery Design for both STV and NTV
Computing
Xin He, Guihai Yan, Yinhe Han, Xiaowei Li
Institute of Computing Technology, Chinese Academy of Sciences
• Microprocessor’s supply voltage range has been gradually increasing in these year– Intel Pentium Processor has a supply voltage range
from 0.9V to 1.5V to support DVFS– Intel Sandy Bridge Processor requires a higher than
nominal voltage to boost performance
The need of wide operation range
20.9VIntel Pentium Processor
1.5VTurbo Boost in Intel Sandy Bridge
(66.7%)
DVFS
Turbo
– Near Threshold Computing: set supply voltage to a value near to transistor’s threshold voltage (0.4V-0.6V)
The need of wide operation range
3
Intel ISSCC20120.28V-1.2V
Future Microprocessor has wide supply voltage range. Brings challenges to power delivery design
DVFS
Turbo
NTC
• Voltage regulator is key to deliver power at a specified voltage level– Linear regulator-LDO– Switching regulator
• Buck regulator(Off-VR)• Switch capacitor regulator(On-VR)
Background of Power Delivery Design
Buck Regulator Switch Capacitor Regulator
• VRs are delivering power to wide operational range cores
Power Conversion Efficiency Characteristics
High PCE High PCE
Low PCE Low PCE
• Off-VR:– High switching loss
• On-VR:– Narrow optimal region
• LDO-VR:– Limited efficiency
Conventional design can’t meet the need of wide voltage range
• Explore the design space of wide operational range power delivery design
• Propose SuperRange, a wide operation range power delivery scheme
• Present a VR aware power management algorithm to maximize performance under given power budget
Contribution
• Explore three optional design 1. Off-VRs
• Two Off-VR evenly located2. Off-VR + LDO-VR
• An Off-VR serves as an frontend3. Off-VR + On-VR
• Off-VR delivers to STV and On-VR to NTV
Design space exploration
• Loss in Off-VRs
Option 1： Off-VRs scheme
20% Cross 10%
dominants!
𝑃𝑐𝑎𝑝=𝐶𝑜𝑉❑2 𝑓
𝑃𝑐𝑎𝑝 𝑖𝑚𝑝𝑙𝑦𝑠𝑓
• In LDO-VR
– PCE is limited by the ratio of output voltage to input voltage
• PCE is lower than 30% when delivering to NTV region
Option 2： LDO-VR scheme
• Using Off-VR to deliver to STV region• Two step voltage conversion
• How to decide intermediate voltage
Option 3： Off-VR + On-VR scheme
1) Fixed intermediate voltage – Off-VR delivers fixed output voltage 2V– Tuning On-VR params to achieve further
conversion• PCE of Off-VRs is high• On-VR couldn’t deliver to all NTV levels at high
PCE
𝑉 𝑥=𝐷∗𝑉 𝑖𝑛
2) Using varied intermediate voltage – Off-VR delivers to varied voltage levels
• Duty cycle tuning– On-VR further step these intermediate values
to 0.4V-0.6V
– Pros:• On-VR has high PCE(around 80%)
– Cons:• The PCE of Off-VR remains low because of
small load current
Off-VR + On-VR scheme
• Multi-phase Off-VR provides an opportunity to improve load current, thus PCE get improved– Modern Off-VR can dynamically change number of working
phases
• Decreasing the number of working phases would increase output ripple– 1.5uH inductor is big enough to reduce the ripple with acceptable area overhead
Proposed SuperRange Design
• Supporting STV– Voltage conversion to STV is performed by Off-VR
• Supporting NTV– Two step conversion.
• Off-VR sets to single working phase• On-VR achieves further conversion(e.g. 3:1)
SuperRange Overview
• Maximize performance under given power budget– Find optimal core counts and VF
setting
VR aware power management algorithm
• PCE with varying load current– Although low voltage improve app power efficiency, it degrades
the PCE
More cores, Low voltage Few cores, High voltage
• Determine voltage setting candidates– Computes the total powers when all cores are active at
each voltage level– Selects the lowest voltage () and the highest voltage ()
• Determine active core count– Calculate max active core count at voltage and get
corresponding performance– Compare the performance with and make decisions
Algorithm
• Target processor characteristics – Multicore processor consists 16 ALPHA cores which has 9
power state• (1.2v, 1.9GHz), (1.1v, 1.7GHz), (1.0v, 1.5GHz)… (0.4v, 0.3GHz)
– 32MB LLC, distribute directory-based MESI– On chip interconnection: mesh + router
• Voltage regulator model– Single topology (3 to 1) Switch capacitor voltage regulator – Buck voltage regulator like TI TPS 54912
Experimental Setup
Power Conversion Efficiency
SuperRange combines the advantages of Off-VR and On-VR andexhibits high PCE over the entire voltage range
• Performance comparison in power-constrait system
Comparison
SuperRange outperforms LDO scheme by 50% and Off-VR scheme by 30%
• Maximum achievable performance comparison under shrinking power budget
Comparison
On average, SuperRange achieve 52% and 170% higher PCEthan Off-VR and LDO-VR scheme.
• Power delivery design for wide operational range is an important issue
• Explore the optional power delivery design scheme
• The proposed SuperRange scheme achieves high PCE over the entire operational range
• Propose a VR aware power management algorithm
Conclusion
• Thank You for Your Attention
• Question?
