DC DC converters for energy harvesting - SMDP-C2SD
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DC DC converters for energy harvestingShouri Chatterjee
June 15, 2017
√ L/C Rs
tanh(te/τe/2) tan(ω0tc/2)
tc has to be very small to get voltage boost. Overlapped clocking leads to shoot-through losses.
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DC-DC converter for scavenging
RF or piezo energy converted to DC. This DC power needs to be pushed into a battery. A 300 nW sensitive, DC-DC converter for energy scavenging applications. Not constant frequency, constant duty cycle. Timing is optimized for minimum switching and minimum resistive losses.
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Chip overview
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TS ≈ TW ≈ RST 2
Pres = A TD
Management
Power management, power monitor (Skewed comparator†, ‘detach-OK’ comparator†, 12 Vdd 1-2
band-gap and current reference generator)
Oscillator† and frequency divider 7 Vcore 1
‘OV-comp’† 12 Vcore 0.9-1.3
‘ZCD’ <2 VD 1.5
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Measured efficiency
Available Power [µW]
RS= 5 k
Load current [µA] 10−1 100 101 10210−2
0
10
20
30
40
50
60
70
10
20
30
40
50
60
p ti o n [ n A
]
How good are we?
ISSCC 2010 JSSC 2010 TI ISSCC 2012 This Ramadasa Carlson bq25504 J.-P. Im work
Process 0.35 µm 0.13 µm - 0.13 µm 0.18 µm Output 1.8 V 1 V 1.8-5.5 V 2 V 1-2 V
Power needed - - > 1 µW - > 300 nW Current - - 330 nA - 60 nA
Minimum input 20 mV 20 mV 80 mV 40 mV 70 mV η at 2 µW - - 38% - > 50%
η at 10 µW - - 78% - 75% Peak η 58% 75% 93% 62% 78% Startup Mechanical External Self Noise External
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CB
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N=9, Sample open circuit voltage, enable U1, BC = N-1
Skip 2 cycles of U1, enable SAR, reset oscillator
Set code = max(COSC)/2, span = max(COSC)/4
At U1
Disable U1, enable energize/dump from oscillator, wait for search phase
COSC
Oscillator
output
MSB is set to one
code = code-span
span = span/2
S1, S3
S0, S2 control
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Harvesting efficiency
10 −2
10 −1
10 0
10 1
10 2
Power [µW]
High efficiency over a very wide range of input power levels. Not achieved in our earlier work. Not achieved by any of our competitors.
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Cs
Rext
Data
Designed integrated circuit
1.5 mm×3 mm chip contains three energy harvesters with MPPT, wireless sensor node with memory, wake-up radio, frequency synthesizer, transmitter.
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10
30
50
70
90
2.2 6
62
85
Most of the power is wasted as resistive and switching losses.
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20
40
60
80
100
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0
200
400
600
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Conclusions
Developed state-of-the-art DC-DC converters that can scavenge energy from energy sources as weak as 300 nW. Modified energy harvesting architecture allows us to harvest from powers as low as 10 nW.
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More reading
G. Chowdhary, S. Chatterjee, “A 300-nW sensitive, 50-nA DC-DC converter for energy harvesting applications”, IEEE Transactions on Circuits and Systems - I, vol. 62, no. 11, Nov. 2015, pp. 2674-2684. G. Chowdhary, A. Singh, S. Chatterjee, “An 18-nA, 87% efficient solar, vibration and RF energy-harvesting power management system with a single shared inductor”, IEEE Journal of Solid State Circuits, in press.
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June 15, 2017
√ L/C Rs
tanh(te/τe/2) tan(ω0tc/2)
tc has to be very small to get voltage boost. Overlapped clocking leads to shoot-through losses.
2 / 31
DC-DC converter for scavenging
RF or piezo energy converted to DC. This DC power needs to be pushed into a battery. A 300 nW sensitive, DC-DC converter for energy scavenging applications. Not constant frequency, constant duty cycle. Timing is optimized for minimum switching and minimum resistive losses.
3 / 31
Chip overview
4 / 31
TS ≈ TW ≈ RST 2
Pres = A TD
Management
Power management, power monitor (Skewed comparator†, ‘detach-OK’ comparator†, 12 Vdd 1-2
band-gap and current reference generator)
Oscillator† and frequency divider 7 Vcore 1
‘OV-comp’† 12 Vcore 0.9-1.3
‘ZCD’ <2 VD 1.5
11 / 31
Measured efficiency
Available Power [µW]
RS= 5 k
Load current [µA] 10−1 100 101 10210−2
0
10
20
30
40
50
60
70
10
20
30
40
50
60
p ti o n [ n A
]
How good are we?
ISSCC 2010 JSSC 2010 TI ISSCC 2012 This Ramadasa Carlson bq25504 J.-P. Im work
Process 0.35 µm 0.13 µm - 0.13 µm 0.18 µm Output 1.8 V 1 V 1.8-5.5 V 2 V 1-2 V
Power needed - - > 1 µW - > 300 nW Current - - 330 nA - 60 nA
Minimum input 20 mV 20 mV 80 mV 40 mV 70 mV η at 2 µW - - 38% - > 50%
η at 10 µW - - 78% - 75% Peak η 58% 75% 93% 62% 78% Startup Mechanical External Self Noise External
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CB
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N=9, Sample open circuit voltage, enable U1, BC = N-1
Skip 2 cycles of U1, enable SAR, reset oscillator
Set code = max(COSC)/2, span = max(COSC)/4
At U1
Disable U1, enable energize/dump from oscillator, wait for search phase
COSC
Oscillator
output
MSB is set to one
code = code-span
span = span/2
S1, S3
S0, S2 control
20 / 31
21 / 31
Harvesting efficiency
10 −2
10 −1
10 0
10 1
10 2
Power [µW]
High efficiency over a very wide range of input power levels. Not achieved in our earlier work. Not achieved by any of our competitors.
22 / 31
23 / 31
Cs
Rext
Data
Designed integrated circuit
1.5 mm×3 mm chip contains three energy harvesters with MPPT, wireless sensor node with memory, wake-up radio, frequency synthesizer, transmitter.
26 / 31
10
30
50
70
90
2.2 6
62
85
Most of the power is wasted as resistive and switching losses.
27 / 31
20
40
60
80
100
28 / 31
0
200
400
600
29 / 31
Conclusions
Developed state-of-the-art DC-DC converters that can scavenge energy from energy sources as weak as 300 nW. Modified energy harvesting architecture allows us to harvest from powers as low as 10 nW.
30 / 31
More reading
G. Chowdhary, S. Chatterjee, “A 300-nW sensitive, 50-nA DC-DC converter for energy harvesting applications”, IEEE Transactions on Circuits and Systems - I, vol. 62, no. 11, Nov. 2015, pp. 2674-2684. G. Chowdhary, A. Singh, S. Chatterjee, “An 18-nA, 87% efficient solar, vibration and RF energy-harvesting power management system with a single shared inductor”, IEEE Journal of Solid State Circuits, in press.
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