The operation of wireless power transfer systems with multiple transmitters (TXs) or receivers (RXs) is investigated. With multiple TXs or RXs in a limited space, couplings occur between TXs or between RXs. The frequency conditions for maximum efficiency and power transfer under such couplings are proposed. Effective resonant frequency of the TXs or the RXs is changed due to such couplings, and driving and/or resonant frequencies should therefore be adjusted accordingly. The amount and type of the required adjustments are provided. The efficiencies in these conditions are discussed. These concepts are supported by experiments with couplings between TXs or between RXs. Using the proposed frequency adjustments, 51-65-W power is transferred with 45%-57% efficiency, even with very low coupling coefficients of 0.025-0.063 from TX to RX. This improvement is significant compared to the unadjusted cases where less than 4 W is transferred with only 5%-33% efficiency.

Effect of Coupling Between Multiple Transmitters or Multiple Receivers on Wireless Power Transfer

This paper presents a wireless power transfer (WPT) system for powering implantable biomedical devices; the system is configured to achieve high efficiency even with CMOS switches and printed-circuit-board pattern coils and to maintain constant output voltage against coupling and loading variations without any additional blocks. It is shown that the parallel-resonant transmitter (TX) and receiver (RX) topology is advantageous for high efficiency even with lossy but compact components. In addition, the output voltage of the topology is insensitive to coupling and/or loading variations if the operating frequency is automatically adjusted according to coupling variations. A parallel-resonant class-D oscillator TX is developed to track the optimum operating frequency for the constant output voltage. The operating distance for the constant output voltage is also extended using a novel resonator structure, which contains two resonating coils. These proposed schemes allow a compact, efficient, and robust wireless power system. Maximum power of 174 mW can be transmitted with 63% overall efficiency.

Wireless Power Transmission With Self-Regulated Output Voltage for Biomedical Implant

The present invention is directed to perform fine low-voltage control without largely increasing the circuit layout area in a low-power consumption structure. In the case of shifting a region to a low-speed mode, a system controller outputs a request signal and an enable signal to a power switch controller and a low-power drive circuit, respectively, to turn off a power switch and to perform a control so that the voltage level of a virtual reference potential becomes about 0.2 V to about 0.3V. The region operates on voltages between a power supply voltage and a virtual reference potential, so that it is controlled in the low-speed mode.

Semiconductor Integrated Circuit Device

Many critical design trade-offs of the class-E power amplifier (e.g power efficiency) are influenced by the switch on-resistance and the value of dc-feed drain inductance. In literature, the time-domain mathematical analyses of the class-E power amplifier with finite dc-feed inductance assume zero switch on-resistance in order to alleviate the mathematical difficulties; resulting in non-optimum designs. We present analytical design equations in this paper for class-E power amplifier taking into account both finite drain inductance and switch on-resistance. The analysis indicates the existence of infinitely many design equations; conclusions include: 1) class-E conditions (e.g. zero voltage and zero slope) can be satisfied in the presence of switch-on resistance. 2) The drain-efficiency (eta) of the class-E power amplifier is upper limited for a certain operation frequency and transistor technology. 3) Using a finite dc-feed inductance instead of an RF-choke in a class-E power amplifier can increase eta by ap 30%.

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Analytical Design Equations for Class-E Power Amplifiers with Finite DC-Feed Inductance and Switch On-Resistance

A semiconductor memory device comprises memory cells, a bitline connected to the memory cells, a read circuit including a precharge circuit, and a first transistor connected between the bitline and the read circuit, wherein a first voltage is applied to a gate of the first transistor when the precharge circuit precharges the bitline, and a second voltage which is different from the first voltage is applied to the gate of the first transistor when the read circuit senses a change in a voltage of the bitline.

Semiconductor memory device.

This paper reports new RF microelectromechanical systems (MEMS) switches actuated by the combination of electromagnetic and electrostatic forces for low-voltage and low-power operation. The proposed RF MEMS switches have utilized the proper combination of two actuation mechanisms: taking advantage of the large actuation force from electromagnetic actuation for initial movement and the low-power feature from electrostatic actuation for holding the actuator position. Both series- and shunt-type switches have been implemented using the proposed actuation mechanism. From the fabricated switches, feasibility of operation has been successfully demonstrated. The fabricated switches can be operated within several hundred microseconds. In the series-type switch, the isolation has been measured as -34dB and insertion loss as -0.37dB at 20 GHz. In the shunt type switch, the isolation is -20.7dB and insertion loss is -0.85dB at 19.5 GHz. The proposed RF MEMS switches are mechanically robust and the combination of electromagnetic and electrostatic actuations makes it possible to achieve excellent switching characteristics at low power and low voltage below 5 V.

A low-voltage and low-power RF MEMS series and shunt switches actuated by combination of electromagnetic and electrostatic forces

A fully integrated quadrature VCO at 8 GHz is presented. The VCO is implemented using a transformer-based LC tank in 0.18 /spl mu/m CMOS technology, in which two VCOs are coupled to generate I-Q signals. The VCO is realized employing the drain-gate transformer feedback configuration proposed here. This makes use of the quality factor enhancement in the resonator using a transformer and the deep switching-off technique by controlling gate bias. By turning off switching transistors of the differential VCO core deeply, the phase noise performance is improved more than 10 dB. The measured phase noise values are -110 and -117 dBc/HZ at the offset frequencies of 600 kHz and 1 MHz respectively. The tuning range of 250 MHz is achieved with the control voltage from 0 to 1 V. The VCO draws 8 mA in two differential core circuits from 3 V supply. When the bias voltage goes down to 2.5 V, the phase noise decrease only 2 dB compared to that of 3 V bias. The VCO performances are compared with previously reported quadrature Si VCOs in 5/spl sim/12 GHz frequency range.

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8-GHz CMOS quadrature VCO using transformer-based LC tank

In this paper, we present a receiver front-end and a frequency source suitable for wireless sensor network applications, in which power consumption is severely restricted under several milliwatts. For such an extremely low-power receiver, current-reusing and frequency multiplying schemes are proposed for both the RF front-end and frequency source. The proposed front-end achieves a conversion gain of 30.5 dB and a noise figure of 10.2 dB at the 10-MHz intermediate frequency (IF), taking only 500-muA bias current from a 1.0-V supply voltage. The measured phase noise of the fabricated frequency source is -115.83 dBc/Hz at 1 MHz offset from a 2.2-GHz center frequency, taking 840 muA from a 0.7-V supply. The front-end performance is compared with the previously reported low-power front-ends operating in similar frequency ranges

A Low-Power 2.4-GHz Current-Reused Receiver Front-End and Frequency Source for Wireless Sensor Network

A fully integrated 20 GHz frequency source is implemented with a VCO and a doubler in a 0.18 /spl mu/m CMOS process. A 10 GHz quadrature voltage controlled oscillator (QVCO) is implemented using a transformer-coupled resonator. The VCO can be tuned between 10.2 and 11.4 GHz and has low phase noise of -118.67 dBc/Hz at 1 MHz offset frequency with 1.8 V power supply. The figure of merit (FOM) is 188 dB. The 20 GHz differential signal is generated by harmonics of quadrature signals of the VCO with a balanced frequency doubler. To increase the output power of the harmonics, pinch-off clipping is used without any buffers or DC level shifter, since the proposed VCO has RF signals with low DC level. The frequency multiplier, the output of which can be tuned between 19.8 and 22 GHz, has a low noise of - 111.67 dBc/Hz at 1 MHz offset frequency. The phase noise of the multiplier is 7 dB higher than that of the VCO. The output power is -6.83 dBm and the VCO output power is -6 dBm.

/pdf/20-ghz-integrated-cmos-frequency-sources-with-a-quadrature-4w5fmbz5sb.pdf

20 GHz integrated CMOS frequency sources with a quadrature VCO using transformers

Fully integrated 10-, 20-, and 40-GHz frequency sources are presented, which are implemented with a 0.18-/spl mu/m CMOS process. A 10-GHz quadrature voltage-controlled oscillator (QVCO) is designed to have output with a low dc level, which can be effectively followed by a frequency multiplier. The proposed multipliers generate signals of 20 and 40 GHz using the harmonics of the QVCO. To have more harmonic power, a frequency doubler with pinchoff clipping is used without any buffers or dc-level shifters. The QVCO has a low phase noise of -118.67 dBc/Hz at a 1-MHz offset frequency with a 1.8-V power supply. The transistor size effect on phase noise is investigated. The frequency doubler has a low phase noise of -111.67 dBc/Hz at a 1-MHz offset frequency is measured, which is 7 dB higher than a phase noise of the QVCO. The doubler can be tuned between 19.8-22 GHz and the output is -6.83 dBm. A fourth-order frequency multiplier, which is used to obtain 40-GHz outputs, shows a phase noise of -102.0 dBc/Hz at 1-MHz offset frequency with the output power of -18.0 dBm. A large tuning range of 39.3-43.67 GHz (10%) is observed.

Taek-Sang Song

Papers

A low-voltage and low-power RF MEMS series and shunt switches actuated by combination of electromagnetic and electrostatic forces

8-GHz CMOS quadrature VCO using transformer-based LC tank

A Low-Power 2.4-GHz Current-Reused Receiver Front-End and Frequency Source for Wireless Sensor Network

20 GHz integrated CMOS frequency sources with a quadrature VCO using transformers

K- and Q-bands CMOS frequency sources with X-band quadrature VCO