Conventional wireless power transfer (WPT) receivers use radio frequency (RF) communication blocks for data transmission and communication. These receivers utilize traditional RF components which are quite power-hungry as they use typical RF blocks such as Mixer, low noise amplifier (LNA), and power amplifiers (PA). For low-powered systems especially those for on-chip, this is not an efficient solution. Therefore, a communication technique called passive backscattering, allows a receiver to communicate with a source or any reader without using any active RF components. Backscattering system enables simultaneous power delivery (using magnetic resonance) and communication using the same power transfer link. It utilizes the same power link from which it harvests energy, then modulates and reflects some part of it back to the transmitter/source in a detectable form.
Figure 1 shows a potential application of an on-chip WPT system integrated with a passive backscattering link for continuous temperature monitoring of sensitive biomedical vaccines. it is reported that a significant amount of biomedical vaccines lose their potency if they are not stored in proper temperature from the time of their manufacturing till delivery. Such on-chip receivers can be used in bare die form, submersed into the vaccine vial providing a real-time temperature of the vaccines making the vaccine cold chain cycle smart and secure.
Figure 1 On-chip WPT system with backscattering capability for vaccine health monitoring applications
The magnetically coupled resonance-WPT (MCR-WPT) technique was introduced by a group of researchers at the Massachusetts Institute of Technology (MIT), where they demonstrated a very high power transfer efficiency using magnetically coupled resonating coils [1]. MCR-WPT uses the phenomena of inductive coupling and resonance on a single system. Primary and secondary coils are loaded with capacitors to make the system resonant (Figure 2). Despite low coupling coefficients, MCR-WPT provides high power transfer at a single resonant frequency.
Figure 2. Generic MCR-WPT System.
The efficiency of the overall system is very closely related to quality factors of the transmitting and receiving coils, transmission distance, and the geometry of the coils. For on-chip receivers, the coil area is one of the main concerns as the coil dimensions are bounded by the die area. Moreover, due to lossy silicon substrate, high Q inductive coils are not possible [2]. Due to these reasons, rigorous electromagnetic modeling of on-chip coil along with transmitter coil coupling is required for optimizing all the factors required for a high power transfer efficiency.
On-chip WPT receiver consists of a power receiver, a sensor or a dedicated circuit to be powered up, and a backscattering communication module. A simple backscattering scheme uses a simple switch to shunt the receiver coil. The switch changes the impedance of the coils as seen by the transmitter. This change of impedance is detected at the transmitter side referred as a passive backscattered signal [3].
Figure 3. Magnetically Coupled WPT system with backscattering integration using separate coils
Recent literature focuses on the backscattering implementation using different coils for power transfer and backscattering data receiving as shown in Figure 3, and very few in [4][5][6] have discussed implementation for on-chip systems.
Our solution is to implement an on-chip WPT system, having the capability of passive backscattering using a single power transfer coil. The design goal of this project will be to implement an on-chip resonant WPT system that is capable of harvesting energy from external off-chip coils, then power up the on-chip circuitry (which mainly includes the rectifier and sensor blocks), and reflect the data back to the transmitter/source as a ‘backscattered signal’ using a passive binary modulation scheme as shown in Figure 4. i.e. variation in the receiver impedance seen at transmitter side[3].
Figure 4. Magnetically Coupled WPT system with backscattering integration using same coils
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Specification |
Target |
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WPT Frequency |
200 MHz |
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Backscattering Frequency |
<20 MHz |
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Power |
<1 mW |
|
Area |
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CMOS is stable and mature IC technology that can integrate both analog and digital components in a very cost-effective manner making miniaturized WPT systems.
Engr. Hamza Atiq; hamza.atiq@nu.edu.pk
Prof. Dr Rashad Ramzan; rashad.ramzan@nu.edu.pk
Dr. Hassan Saif; hassan.saif@nu.edu.pk
National University of Computer and Emerging Sciences (FAST-NUCES) introduced the first specialized
MS integrated circuit (IC) design program in Pakistan in Spring 2020. The IC Design Lab at FAST-NUCES
has the licensed Cadence tools and TSMC 65nm pdk. Currently, 25 graduate students are enrolled in the
MS IC design program at FAST-NUCES Pakistan. Further details about the MS ICD program at FAST-
NUCES can be found at the following link.
http://isb.nu.edu.pk/rfcs2/MS.htm
The applied project is the MS thesis work. The schematic level simulation have been completed in TSMC
65 nm pdk. Due to lack of funding, we are unable to tapeout the proposed idea. Thus, the SSCS
assistance is required to tapeout this proposal.
Schematic,GDS and Measurement Results
The project focuses on the implementation of Passive Backscattering for on-chip Wireless Power Transfer (WPT) systems. The design goal of this project is to implement an on-chip resonant WPT system that is capable of harvesting energy from external off-chip coils, then power up the on-chip circuitry , and reflect the data back to the transmitter/source as a ‘backscattered signal’ using a passive binary modulation scheme as shown in Figure 4. i.e. variation in the receiver impedance seen at transmitter side.
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