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Design of on-chip switched capacitor converters
M. Bochenek, W. Dabrowski, F. Faccio, J. Kaplon, S. Michelis
This research project has been supported by a Marie Curie Initial Training Network Fellowship of the European Community’s & Seventh Framework Programme under contract number (PITN-GA-2008-211801-ACEOLE)
Outline
ATLAS–CMS Power Working Group 31 March 2010
● Overview of step-down converters,
● Switched capacitor step-down converter proposed for the serial and the DC-DC powering scheme,
● Results from the Cadence simulations,
● Overview of step-up charge pumps,
● Switched capacitor voltage doubler proposed for the serial powering scheme,
● Results from the Cadence simulations.
Switched capacitor step-down converter
ATLAS–CMS Power Working Group 31 March 2010
Simple switched capacitor DC-DC step-down converter
● Four switches● Two capacitors
The simplest model for the 2:1 converter contains:
ATLAS–CMS Power Working Group 31 March 2010
Phase 1:● Switches S1 and S3 are closed,● Switches S2 and S4 are opened,● CX and CL are connected in series.
Phase 2:● Switches S1 and S3 are opened,● Switches S2 and S4 are closed,● CX and CL are connected in parallel.
Simple step-down converter
ATLAS–CMS Power Working Group 31 March 2010
Practical solution for the DC-DC step-down converter
Power efficiency = 97%
ATLAS–CMS Power Working Group 31 March 2010
● VDD = 1.9 V● VOUT = 926 mV● IOUT = 60 mA● CX = 1000 nF● CL = 200 nF● f = 500 kHz
Schematic diagram of the non-overlapping clock generator used
in the step-down converter
2 x NOR gate3 x inverter2 x current starved
inverter
C1 = C2 = 20fF
ATLAS–CMS Power Working Group 31 March 2010
Schematic diagram of the buffer used in the step-down converter
ATLAS–CMS Power Working Group 31 March 2010
M4 M3 M1M2
570μ570μmm
200μ
200μ
mm
M4 buffer M3 buffer M2 bufferNon-overlappingclock generator M1 buffer
Layout of the step-down DC-DC converter
ATLAS–CMS Power Working Group 31 March 2010
Time response of the converter
ATLAS–CMS Power Working Group 31 March 2010
20 mV20 mV
Power efficiency and output voltage versus output current
ATLAS–CMS Power Working Group 31 March 2010
Results from the corner analysis for the step-down converter
ATLAS–CMS Power Working Group 31 March 2010
Results from the corner analysis for the step-down converter
ATLAS–CMS Power Working Group 31 March 2010
Switched capacitor step-up converter
ATLAS–CMS Power Working Group 31 March 2010
Overview of the simplest voltage doubler
The simplest model contains:
● Three switches● One capacitor
ATLAS–CMS Power Working Group 31 March 2010
Simple voltage doubler
Phase 1:● Switches S1 and S3 are closed,● Switch S2 is opened,● Capacitor is charged to the supply voltage VDD
Phase 2:● Switches S1 and S3 are opened,● Switch S2 is closed,● Bottom plate of the capacitor on VDD, while the capacitor maintains its charge VDDC (from the previous phase).
ATLAS–CMS Power Working Group 31 March 2010
Solution for the voltage doubler pumping on both clock edges
● M1 and M2 use thin (2.2nm) gate oxide,● M3 - M6 use thick (5.2nm) gate oxide,● VIN = 0.9V, CPUMP = 470nF, CHOLD = 470nF, CPOL = 10pF.
● VDD = 0.9 V● VOUT = 1.59 V● IOUT = 30 mA● CPUMP = 470 nF● CHOLD = 470 nF● f = 1 MHz
= 85% Power efficiency
ATLAS–CMS Power Working Group 31 March 2010
Practical solution for the level shifter
ATLAS–CMS Power Working Group 31 March 2010
430μ430μmm
265μ
265μ
mmLayout of the step-up DC-DC converter
ATLAS–CMS Power Working Group 31 March 2010
Time response of the converter
ATLAS–CMS Power Working Group 31 March 2010
15 mV 15 mV
Power efficiency and output voltage versus output current
ATLAS–CMS Power Working Group 31 March 2010
Results from the corner analysis for the step-up converter
ATLAS–CMS Power Working Group 31 March 2010
Conclusions:
ATLAS–CMS Power Working Group 31 March 2010
● The results from the simulations are promising:97 % for the step-down converter,85 % for the step-up converter,
● The core layouts of both designs are (almost) ready,
● The final assembly of the chip still has to be done,
● We are going to submit the chip in the IBM 130nm technology in May 2010.
Thank you for your attention!