Digital Circuits to Compensate for
Energy Harvester Supply Variation
Hao-Yen Tang
David Burnett
Energy-harvesting system
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Battery
Solar cell
TEG(Thermoelectric)
RF coupling
Problem:
voltage ripple
Voltage ripple
precharged
Energy
Harvester
~1nF
VLSI block
On-chip
Storage cap
Energy harvester-powered integrated system
Y. Ramadass and A. Chandrakasan, “A battery-less thermoelectric energy
harvesting interface circuit with 35 mv startup voltage,” Solid-State Circuits,
IEEE Journal of, vol. 46, no. 1, pp. 333–341, Jan.
Possible solution
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Work with minimum voltage
Supply regulation (with LDO)
Modified basic cells (Razor)
Dynamic clock period adjusting
Proposed solution
HW2 decoder circuit
(4x cascaded)
Using a Delay-Lock Loop(DLL) to lock the clock period to critical path delay
Clock Generator
(Voltage-Control Oscillator)
Clock Generator
(Voltage-Control Oscillator)
• No crystal
• Ring oscillator
• Supply
Sensitivity
Clock Generator
(Voltage-Control Oscillator)
Critical Path duplica
• Extra delay result
from simultaneous
incoming signal
• Need to be reset
every cycle
• 1 clock cycle measure
1 clock cycle reset
Clock Generator
(Voltage-Control Oscillator)
PFD and loop filter
• Traditional PFD
• Charge pump with
constant gm bias
• Second order loop
filter for stability
Simulation result
Supply Voltage
VCO control signal
Extra power overhead: 40.2uW (12.7% of the reference VLSI block)
Comparison table
Technique
This work
Supply
Modified Basic
Dynamic VDD
regulation[2]
Cell[3]
adjusting[7]
Topology
Dynamically
adjust clock
period
Fix the supply
voltage with LDO
Modify basic cells
to detect errors
Dynamically adjust
clock period by
adjusting analog
supply voltage
Hardware
overhead
1 extra DLL
1 critical path
duplica
1 LDO
Peripheral circuits in
each cell
(proportional to
VLSI block size)
1 LDO
Main issue
Response
time
Large percentage
Need to modify
of power wasted in original VLSI block,
LDO
hardware overhead
proportional to
VLSI block size
Extra power line,
power loss in LDO,
need crystal to
provide a reference
clock
Acknowledgement
• Prof. Bora <3
• EE241 classmates
• Dear teammate