An Energy-Efficient UWB Transmitter with Wireless Injection Locking for RF Energy-Harvesting Sensors

Abstract

An ultralow-power ultrawideband (UWB) transmitter with an energy-efficient injection-locked radio frequency (RF) clock harvester that generates a carrier from an RF signal is proposed for RF energy-harvesting Internet-of-Things (IoT) sensor applications. The energy-efficient RF clock harvester based on the injection-locked ring oscillator (ILRO) is proposed to achieve optimal locking range and minimum input sensitivity to obtain an injection-locked 450 MHz clock in ultralow-power operation. A current-starved inverter-based delay stage is adopted that allows delay adjustment by bias voltage to minimize dynamic current consumption while maintaining a constant delay regardless of changes in process, supply voltage, and temperature (PVT). To minimize static current consumption, a UWB transmitter based on a digital-based UWB pulse generator and a pulse-driven switching drive amplifier is proposed. The proposed injection-locked RF clock harvester achieves the best RF input sensitivity of −34 dBm at a power consumption of 2.03 μW, enabling energy-efficient clock harvesting from low RF input power. In ultralow-power operation, a 23.8% locking range is achieved at the RF injection power of –15 dBm to cope with frequency changes due to PVT variations. The proposed UWB transmitter with RF clock harvester achieves the lowest energy consumption per pulse with an average power consumption of 97.03 μW and an energy consumption of 19.41 pJ/pulse, enabling operation with the energy available in RF energy-harvesting applications.

Estimation of Harvested RF Energy Based on Survey of Ambient RF Power for Optimized Rectifier Design

“…where P IN is the input power which fluctuates over time according to the distribution in Figure 5, the DC output power P DC can be calculated for each rectifier design based on expected value of P IN . By substituting the channel power P CHest from equation (7) as the input power of equation ( 8) and with the simulated PCE of each rectifier design from Figure 13, the DC output power over time can be plotted in Figure 14. To compare the performance of each rectifier based on estimated input power with an isotropic antenna, the total energy within the testing period was calculated by integrating the graph in Figure 14 overtime.…”

“…With additional wireless energy sources, the read range can be increased or additional functionalities e.g., temperature or moisture sensing can be added to the tags [4,5]. In wireless sensor networks, battery time of the sensor nodes e.g., wearable sensors can be prolonged by reducing their power consumption or by including the RFEH capability in the devices [6][7][8]. In general, the power consumption of a wireless sensor node ranges from 1 to 12 mW depending on their applications [9,10].…”

A 1.8–65 fJ/Conv.-Step 64-dB SNDR Continuous- Time Level Crossing ADC Exploiting Dynamic Self-Biasing Comparators

“…To preserve energy efficiency in the complete system, the LC-ADC should be interfaced to an asynchronous processor, such as the SNN described in [6], or send data using a communication protocol which does not require time discretization, such as e.g. the body channel communication used in [10] or a UWB transmitter [26].…”

Dual Piezoelectric Energy Investing and Harvesting Interface for High-Voltage Input

“…In case 2 , where C STOR is already fully charged, the V STOR >= V REF condition is detected by the HIC. Therefore, in this case, all of the energy on the inductor needs to be transferred to the battery.…”

“…These devices are usually powered with lightweight batteries having low capacity that require frequent battery re-charging or replacement, which is undesirable and sometimes difficult in the case of implantable devices. To achieve energy autonomy, widely investigated energy harvesting sources include RF [1][2][3][4], light [5], heat [6], and vibrations [7][8][9]. Among these sources, vibration energy has been extensively investigated due to the abundance of vibrations in the ambient environment.…”