Atsushi Shirane

13.8 A 5.8GHz RF-powered transceiver with a 113μW 32-QAM transmitter employing the IF-based quadrature backscattering technique

Although it is obvious that using a trillion sensor nodes for wireless sensor network (WSN) application would deeply exacerbate the spectral congestion issue, RF-powered sensor nodes [1,2] still support only low spectral-efficiency modulation such as OOK. State-of-the-art standard-compliant RF transceivers for low-power applications have been achieving multilevel modulation such as n/8 D8PSK [3], but their power consumption is as large as 1mW without PA even in the 400MHz band because of the large power consumption of the RF synthesizer, which is required to provide high-frequency accuracy and low phase noise for multilevel modulation. This work presents an IF-based quadrature backscattering technique, enabling n-PSK and n-QAM without an RF PLL. The presented technique exploits the passive RFID technologies, but can realize both amplitude and phase modulation concurrently. Our TX in 65nm Si CMOS achieves spectral efficiency of 3.3b/s/Hz with 32QAM while consuming 113uW with a 0.6V power supply in our measurements, which has 6.6 times better spectral efficiency than previous RF-powered wireless transceivers [1,2]. The prototype RF-powered sensor node with our transceiver including the TX, RX, and an RF energy harvester (RF-EH), succeeds in a wireless temperature-sensing application.

RF-Powered Transceiver With an Energy- and Spectral-Efficient IF-Based Quadrature Backscattering Transmitter

This study introduces a 5.8 GHz RF-powered transceiver that includes a transmitter using an IF-based quadrature backscattering (IFQB) technique. The IFQB transmitter can produce a quadrature modulated signal without active RF circuits, such as PLL, local generation, and local distribution circuits. Thus, the IFQB technique can significantly reduce the power consumption while achieving denser constellations by the quadrature modulation. The RF-powered transceiver consists of the IFQB transmitter, an OOK receiver, and a power management unit (PMU) for RF powering. The transmitter and receiver operate under a 0.6 V power supply provided by the PMU to further reduce the power consumption. We fabricated a prototype RF-powered transceiver using a 65 nm Si CMOS process to confirm the validity of the proposed technique. During the measurements, the transmitter achieved 2.5 Mb/s with a 32-QAM modulation while consuming 113 μW. In addition, a wireless temperature sensing demonstration was conducted using the prototype sensor node with the presented RF-powered transceiver.

A 2.3 pJ/bit frequency-stable impulse OOK transmitter powered directly by an RF energy harvesting circuit with −19.5 dBm sensitivity

The proposed 2.5-GHz-band impulse transmitter technology realizes frequency-stable impulse generation against PVT variation and superior energy-per-bit operation, and it can be powered directly from a - 19.5-dBm-sensitivity RF energy harvesting circuit without any regulators that are generally essential to power RF circuits. The transmitter occupies 0.38 mm2 in a 65nm CMOS technology. The maximum frequency difference among measured output return-loss peak of 9 chips with 3 different process corners under 0.5 V supply is about 50 MHz without any frequency calibration. Our prototype achieves 1 Mb/s signal transmission under 2.3 μW power consumption from 0.5 V supply thanks to pulse-level duty cycling operation of maximally digital architecture.

A Multi-Band Quadrature Clock Generator With High-Pass-Filtered Pulse Injection Technique

A high-pass-filtered (HPF) pulse injection technique is proposed to reduce spurs near the carrier signal due to injection locking. By using this technique, a multi-band quadrature clock generator consisting of a wide-frequency range injection-locked PLL and a frequency-selectable local buffer is demonstrated. The proposed clock generator was fabricated in a 65 nm CMOS. For a 100 MHz reference, the circuit can output 1.0, 2.0, and 4.0 GHz quadrature outputs with an eight-phase VCO and the buffer. It shows an 1 MHz-offset phase noise -105 dBc/Hz and a reference spur level of -50 dBc at 2.0 GHz, with enabling HPF pulse injection. The total power consumption is lower than 32 mW at 4 GHz.

Planar Solenoidal Inductor in Radio Frequency Micro-Electro-Mechanical Systems Technology for Variable Inductor with Wide Tunable Range and High Quality Factor

A planar solenoidal inductor for the realization of a variable inductor with a wide tunable range and a high quality factor (Q-factor) is proposed in this work. Prototype inductors are designed and fabricated using a two-metal micro-electro-mechanical systems (MEMS) process to demonstrate the potential use of the tunability of the inductance and the Q-factor. Inductance tuning from 1 to 3.3 nH was achieved and the tunability obtained was as high as 230% at 2 GHz. A Q-factor of more than 20 was observed in the frequency range of 2.5 to 6 GHz.

A 21 V output charge pump circuit with appropriate well-bias supply technique in 0.18 μm Si CMOS

Most of MEMS (Micro Electro Mechanical Systems) actuators require high control voltage such as 20 V. One of the significant challenges for MEMS implementation on Si CMOS is that the control voltage exceeds pn-junction breakdown voltage. The present work proposes a charge pump circuit that can generate higher output voltage than the breakdown voltage by applying appropriate bias voltages to backgate and deep-N-well of N-MOSFETs. Measurements showed that the prototype can generate DC voltage of 21V in 0.18 μm Si CMOS with 11V and 15 V breakdown voltage of pn-junction.

A Study of Digitally Controllable Radio Frequency Micro Electro Mechanical Systems Inductor

This work proposes a micro electro mechanical systems (MEMS)-based digitally controlled solenoid-inductor. The inductor is fabricated by using a MEMS process. 2-bit tuning characteristics are measured, and tuning linearity and Q-factor degradation due to switching loss are discussed. The linear inductance tuning from 1.7 to 2.2 nH was achieved at 2 GHz. A Q-factor of more than ten was observed in the frequency range of 1.2 to 7.4 GHz. The validity of the proposed inductor was confirmed by investigating the effect of switch resistance.

A process-scalable RF transceiver for short range communication in 90 nm Si CMOS

This paper presents the RF CMOS transceiver that potentially has the process scalability in terms of area and supply voltage. The proposed transceiver does not contain any inductor and employs inverter-based topology for attaining scalability and large voltage headroom. The prototype transceiver for short-range communication fabricated in 90nm Si CMOS process has area of 0.2mm2 and achieves 500 Mb/s communication at 1V supply voltage. The transmitter with the new linearity compensation technique provides EVM of less than -28 dB at -5dBm output from 0.5 to 2.5 GHz range. The receiver employs active peaking and cherry-hooper techniques and realizes sensitivity of -60dBm and dynamic range of 50 dB at 1 GHz.

An ultra-low-power 32QAM RF transmitter

This paper introduces a quadrature modulation transmitter featuring the new IF-based quadrature backscattering technique to yield spectral efficient modulation schemes while reducing the power consumption. A 5.8 GHz RF-powered transceiver with the proposed transmitter was fabricated in 65 nm Si CMOS technology. The transmitter achieves 2.5 Mb/s, 32-QAM modulation while consuming 113 μW under 0.6 V power supply.

An RF energy harvesting power management circuit for appropriate duty-cycled operation

In this study, we present an RF energy harvesting power management unit (PMU) for battery-less wireless sensor devices (WSDs). The proposed PMU realizes a duty-cycled operation that is divided into the energy charging time and discharging time. The proposed PMU detects two types of timing, thus, the appropriate timing for the activation can be recognized. The activation of WSDs at the proper timing leads to energy efficient operation and stable wireless communication. The proposed PMU includes a hysteresis comparator (H-CMP) and an RF signal detector (RF-SD) to detect the timings. The proposed RF-SD can operate without the degradation of charge efficiency by reusing the RF energy harvester (RF-EH) and H-CMP. The PMU fabricated in a 180 nm Si CMOS demonstrated the charge operation using the RF signal at 915 MHz and the two types of timing detection with less than 124 nW in the charge phase. Furthermore, in the active phase, the PMU generates a 0.5 V regulated power supply from the charged energy.