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International Symposium on Low Power Electronics and Design
Switched-Capacitor Boost Converter Design and Modeling for Indoor Optical Energy Harvesting with
Integrated Photodiodes
Stanley W. Hsu, Erin Fong, Vipul Jain, Travis Kleeburg, Rajeevan Amirtharajah
University of California, Davis
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• Introduction/Motivation• Integrated Photodiode• Switched-Capacitor Boost Converter
(SCBC)• Delta-Sigma Modulator (DSM)• Supply Ripple Effects on DSM• Summary
2
Outline
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• Introduction/Motivation• Integrated Photodiode• Switched-Capacitor Boost Converter
(SCBC)• Delta-Sigma Modulator (DSM)• Supply Ripple Effects on DSM• Summary
3
Outline
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Introduction• Ultra-low voltage sensor circuits powered by
free-space optics (Kleeburg, 2010)• Integrated photovoltaics for optical
power, data, and clock delivery• Subcutaneous medical implants
• Ultra-low duty cycle sensor (Ayazian, 2012)• Integrated photovoltaics
(2.5 mm x 2.5 mm)• Off-chip capacitive and resistive
transducers, and electrodes
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– Rectified AC mains at 120 Hz
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Energy Harvesting from Indoor Lighting
– Pulse-width-modulated dimming at > 200 Hz
• Low light intensity limits harvested energy
• Issue: light flickering
Source: ksj.mit.edu Source: www.dlsound.net
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Integrated Photodiode
Power Electronics
Vdd Domain Circuits
Light
Vdd
Indoor Lighting-Powered Sensor
Bypass Capacitor
Supply ripple
Cost, Area/Volume
Circuit performance
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• Introduction/Motivation• Integrated Photodiode• Switched-Capacitor Boost Converter
(SCBC)• Delta-Sigma Modulator (DSM)• Supply Ripple Effects on DSM• Summary
7
Outline
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Integrated Photodiode Designs
P+/NW P+/DNW
Voc 523 mV 508 mV
Isc density 134 A/mm2 52 A/mm2
Power generated/area 557.5 W/mm2 210 W/mm2
P+/NW P+/DNW
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Integrated Photodiode Results
3 P+/DNW photodidoes stacked in series (no bypass capacitor)
Increasing frequency or duty cycle decreases ripple.
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• Introduction/Motivation• Integrated Photodiode• Switched-Capacitor Boost Converter
(SCBC)• Delta-Sigma Modulator (DSM)• Supply Ripple Effects on DSM• Summary
10
Outline
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• Phase 2 – Charge capacitors to VIN• Phase 1 – Boost output to 4x VIN
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Switched-Capacitor Boost Converter
S4
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Buck Converter Model
Fast Switching Limit:
Slow Switching Limit:
(Seeman, 2008)
i
swi
ic
out
outSSL fC
a
i
vR
2, )(
i iriFSL aRR 2
, )(2
22FSLSSLo RRR
Combined Output Impedance:
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Proposed Boost Converter Model
Model accounts for bottom plate parasitic effects and allows cascading of multiple stages
N=4
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SCBC Output vs. Switching Frequency
Model is accurate to within 10%, from 500 Hz to 5 MHz
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SCBC Simulated Ripple to Output Ratio
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• Introduction/Motivation• Integrated Photodiode• Switched-Capacitor Boost Converter
(SCBC)• Delta-Sigma Modulator (DSM)• Supply Ripple Effects on DSM• Summary
16
Outline
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Conventional 1st Order DSM Design
Integrator Pre-Amp
+
1-bit DAC
Analoginput
Digitaloutput
-error
Latch
Comparator
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Proposed 1st Order DSM Design
Low Pass Filter
Pre-Amp
+
1-bit DAC
Analoginput
Digitaloutput
-error
Latch
Removed!
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Proposed 1st Order DSM Schematic
Attenuates input!Gain <1
Switched-capacitorlow pass filter
1b DAC feedback
Dynamic ComparatorNo pre-amplifier
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DSM Die Photo and Measured Results1
Technology 180 nm 180 nm
Supply Voltage 1.4 V 1.8 V
Sampling Rate 50 kHz 1.6 MHz
Nyquist Rate 4 kHz 4 kHz
SNDR @ -7dBFS input
~27 dB ~50dB
SNDR ~27 dB
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• Introduction/Motivation• Integrated Photodiode• Switched-Capacitor Boost Converter
(SCBC)• Delta-Sigma Modulator (DSM)• Supply Ripple Effects on DSM• Summary
21
Outline
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• Sampling switch behaves as passive mixer (Cook, 2006)
• Distortion due to passive mixing– Sampling switch
• Mixing between input and ripple
– 1b DAC feedback switch• Mixing between ripple and itself
22
Supply Ripple Effects on DSM
)(tVin )()()( tVtVtV inclkout
)(tVclk
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Measured DSM Lower Sideband Spectrum
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Measured DSM SNDR vs. Ripple
Vdd = 1.4VSampling Rate = 50 kHzInput Amplitude = -7dBVdd
~4.5 bits
~2 bits
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• Introduction/Motivation• Integrated Photodiode• Switched-Capacitor Boost Converter
(SCBC)• Delta-Sigma Modulator (DSM)• Supply Ripple Effects on DSM• Summary
25
Outline
![Page 26: International Symposium on Low Power Electronics and Design Switched-Capacitor Boost Converter Design and Modeling for Indoor Optical Energy Harvesting](https://reader036.vdocuments.mx/reader036/viewer/2022062516/56649e3a5503460f94b2c72e/html5/thumbnails/26.jpg)
• P+/NW integrated photodiodes achieves
557.5 µW/mm2 with Voc=523 mV• Switched-capacitor boost converter model for
predicting output voltage to within 10% accuracy from 500Hz to 5 MHz
• Supply ripple effects on passive delta-sigma modulator results in IM2 distortion at
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Summary
ripplein Nff
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Integrated Photodiode
Power Electronics
Vdd Domain Circuits
Light
Vdd
Summary
Bypass Capacitor
If DSM can tolerate an increased supply ripple from 10% to 21% of Vdd, bypass capacitor can be reduced from 56.5 nF to 3.86 nF.
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• Texas Instruments for chip fabrication– William McIntyre– Arun Rao– Keith Schoendoerfer– Greg Winter– Bijoy Chatterjee
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Acknowledgements