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Activity Results Report:“Design & Development of Energy Harvesting solution forEnvironment Sensor”
Ultra-low voltage start-up clock generators for micro-scale energy
harvesting: New variants of body-biased stacked inverter based
ring oscillators
In recent years, sensor network systems called Machine to Machine (M2M) and Internet of Things(IoT) have attracted a lot of attention. In such a sensor network system, communication is performed
between a terminal that collects sensor data called an individual sensor node terminal and a serverthat collects the data. To realize an autonomous sensor network by using a power source that uses
energy harvesting has attracted attention. As commercialization of energy-harvesting technology isprogressing, the demand for ultra-low-voltage circuits has become higher.
This work aims to discuss the challenges of implementing an integrated ultra-low voltage start-up
clock/oscillator, the state of the art and propose four new variants of a body-biased stacked inverterbased ring oscillator and analyze the same. The proposed delay cells designed in 180-nm BCD
CMOS process are connected to form a 13-staged ring oscillator (RO) with regular 𝑉𝑡 transistors.
All four proposed variants’ performance is compared against the former works (implemented in thesame process) with respect to the lowest supply voltage required for sustained oscillations,oscillation frequency and peak-to-peak voltage swing (𝑉pp). For a supply voltage of 50 mV, over90% 𝑉DD is obtained from post layout simulations for all four proposed architectures consuming
around 24 pW of average power, out of which the variant that has the maximum swing of 92% (animprovement of 9.2% compared to that of stacked inverter-based RO), can start and sustain anoscillation at 32.5 mV supply voltage. The fastest architecture proposed has a frequency (postlayout) of 131.5 Hz at 50 mV 𝑉DD, which is 62% more than that of the stacked inverter-based ROwith body bias. Monte Carlo analysis reveals that the proposed RO variants’ 𝑉pp have lesser
interquartile range (IQR) and relatively higher median values.

High-Efficiency CMOS Charge Pump for Ultra-Low Power RF
Energy Harvesting Application
One critical component of RF energy harvesting systems responsible for converting the DC voltage
generated by the rectifier into a higher voltage suitable for powering the IoT device is the charge
pump. The efficiency of the charge pump is critical to the overall performance of the energy
harvesting system. A high-Power Conversion Efficiency (PCE) ensures that the maximum amountof energy is transferred from the RF signal to the energy-storage element, minimizing power losses
and increasing the lifespan of the battery-free system. Optimizing the conduction and switchinglosses can improve the PCE of the charge pumpThis paper explains the design and implementation of a switch capacitor DC-DC converter system
for Radio Frequency (RF) energy harvesting applications for an input voltage in the sub-150mV
range, using 180-nm CMOS triple- well BCD technology. The proposed system incorporates acharge pump architecture that employs an improvised Dynamic Gate Biasing (DGB), Forward andReverse Body Bias technique (FRBB), along with a time axis symmetrical clocking scheme
implemented using an advanced bootstrapped CMOS driver to enhance the overall drive capabilityof the system at low input voltages. Post-layout extracted simulations demonstrate that the proposedsystem achieves higher overall efficiency, delivering a peak Power Conversion Efficiency (PCE)of 85.8% at 125mV input voltage, outperforming other state-of-the-art architectures in similar
voltage ranges. Moreover, the proposed system exhibits reliable operation even at input voltages as
low as 85mV, while maintaining good overall efficiency.
The high efficiency obtained from the time-axis symmetric clocking scheme suggests the possible
extension of the proposed architecture to AC inputs, representing a potential avenue for future
research. We believe that the insights gained from this study can contribute to the development of
more efficient and reliable power management systems for low-power applications.

Analysis of L-Matching Networks for Efficient Radio Frequency
Energy Harvesting
An analytical design framework for a lumped (Inductor and Capacitor) L matching network for a
Schottky diode series rectifier is presented in this study, which also demonstrates that a high pass
network is more effective than a low pass network due to greater harmonic suppression. Passivecomponent(L&C) values are derived in a close form equation and utilized to analyze component
quality factor effects on rectifier performance. The theoretical predictions are verified by simulation
for a multiple diode rectifier (SMS7630, HSMS2850, HSMS2862), which results in an
improvement in HP network efficiency of 3 to 5 percent on average throughout a power range of 26 dBm to 12 dBm at a 915MHz frequency. This study confirms the suggested approach using
measurement data developed on FR4 substrate and achieves 78% peak efficiency at 6dBm input
power along with 38dB of dynamic range for > 20% efficiency from -26 dBm to +12dBm in anarea of 1.8 X 2 cm2.
A wide input power range rectifier for harvesting ambient radio frequency energy from 915MHz
ultra-high frequency has been proposed. This brief also demonstrates that a high pass network ismore effective than a low pass network due to greater harmonic suppression. The presentedprototype has only fabricated for SMS7630 to target low power range. The research can be further
improved by fabricating multi diode approach to show wide input power range.

Problem/constraints:• Due to the pandemic effect on the semiconductor supply chain, we have had difficulty in procuring
the components for the experiments effecting the timelines but nevertheless we have exhaustively
worked towards the results for the research carried out.

Research Output:• Mukherjee, Ankur, Ashik C. Jayamon, and Ashudeb Dutta. "Ultra-low voltage start-up clock
generators for micro-scale energy harvesting: New variants of body-biased stacked inverter-based ringoscillators." Microelectronics Journal (2023): 105883. (https://doi.org/10.1016/j.mejo.2023.105883) 2.2
Impact Factor• Mukherjee, Ankur, Ashik C. Jayamon, and Ashudeb Dutta. " High-Efficiency CMOS Charge Pump
for Ultra-Low Power RF Energy Harvesting Application." Under Review Integration VLSI Journal
1.9 Impact Factor• Deepali Pathak, Harshavardhan, and Ashudeb Dutta. " Analysis of L-Matching Networks forEfficient Radio Frequency Energy Harvesting." Under Review IEEE TCAS-II Express briefs Journal
4.4 Impact Factor

Human Capital Development:• Two PhD Students• Two Design Engineers• Two Layout Engineers