Recently, a highly efficient midrange wireless transfer technology using electromagnetic resonance coupling has been proposed and has received much attention due to its practical range and efficiency. The resonance frequency of the resonators changes as the gap between the resonators changes. However, when this technology is applied in the megahertz range, the usable frequency is bounded by the industrial, scientific, and medical (ISM) band. Therefore, to achieve maximum power transmission efficiency, the resonance frequency has to be fixed within the ISM band. In this paper, an automated impedance matching (IM) system is proposed to increase the efficiency by matching the resonance frequency of the resonator pair to that of the power source. The simulations and experiments verify that the IM circuits can change the resonance frequency to 13.56 MHz (in the ISM band) for different air gaps, improving the power transfer efficiency. Experiments also verified that automated IM can be easily achieved just by observing and minimizing the reflected wave at the transmitting side of the system.

Automated Impedance Matching System for Robust Wireless Power Transfer via Magnetic Resonance Coupling

A software-defined radio (SDR) receiver with baseband programmable RF bandpass filter (BPF) and complex impedance match is presented. The passive mixer-first architecture used here allows the impedance characteristics of the receiver's baseband circuits to be translated to the RF port of the receiver. Tuning the resistance at the baseband port allows for a real impedance match to the antenna. The addition of "complex feedback" between I and Q paths allows for matching to the imaginary component of the antenna impedance. By implementing both real and imaginary components with resistors in feedback around low noise baseband amplifiers, noise figure is also kept low. Tunable sampling capacitors on the baseband side of the passive mixer translate to tunable-Q filters on the RF port which allow for very good out-of-band linearity. Furthermore, the concept of in-band and out-of-band must be redefined as the impedance match and BPF center frequency move with the LO frequency, such that matching and filtering track the receive frequency. Additionally, 8-phase mixing is shown to provide significant benefits such as impedance matching range, rejection of blockers at LO harmonics, and lower noise figure (NF). Measurements from the receiver implemented in 65 nm CMOS show 70 dB of gain, NF as low as 3 dB, and 25 dBm out-of-band IIP3. Furthermore, tunable impedance matching shows that S11 <;- 30 dB can be achieved at any receive frequency from 0.1-1.3 GHz.

A Passive Mixer-First Receiver With Digitally Controlled and Widely Tunable RF Interface

RF MEMS technology was initially developed as a replacement for GaAs HEMT switches and p-i-n diodes for low-loss switching networks and X-band to mm-wave phase shifters. However, we have found that its very low loss properties (high device Q), its simple microwave circuit model and zero power consumption, its high power (voltage/current) handling capabilities, and its very low distortion properties, all make it the ideal tuning device for reconfigurable filters, antennas and impedance matching networks. In fact, reconfigurable networks are currently being funded at the same level-if not higher-than RF MEMS phase shifters, and in our opinion, are much more challenging for high-Q designs.

Tuning in to RF MEMS

소형 안테나 ( Small Antennas )

In this paper, a class of passive mixer-first, LNA-less receivers is analyzed in depth. Quadrature passive mixers are shown to present the impedance of their baseband port to the RF port and vice versa. This transparency property, in combination with resistive feedback differential amplifiers, and “complex” feedback between the I and Q paths, can be used to control the impedance at the RF port. This impedance can be tuned using only baseband components (i.e., resistors). The noise limits of such an architecture are analyzed and simulated, and are shown to be comparable to standard RF-LNA-first receivers. Accounting for the higher harmonics of the LO frequency proves critical in accurately analyzing the behavior of these circuits and their ability to provide an impedance match with low noise figure. Additionally, it is shown that expanding quadrature passive mixers to harmonic rejection mixers allows for even better noise performance and wider matching range.

Implications of Passive Mixer Transparency for Impedance Matching and Noise Figure in Passive Mixer-First Receivers

To preserve link quality of mobile phones, under fluctuating user conditions, an adaptively controlled series-LC matching circuit is presented for multi-band and multi-mode operation. Following a bottom-up approach, we discuss the design of an RF-MEMS unit cell for the construction of a 5-bit switched capacitor array. To reduce dielectric charging of the RF-MEMS devices their average biasing voltage is minimized by applying a bipolar waveform with a small high/low duty-cycle obtained from a high-voltage driver IC. RF-MEMS capacitive switches are applied because of their high linearity, low loss, large tuning range, and easy control in the discrete domain. Application specific RF-MEMS pull-in and pull-out voltage requirements are derived. An impedance phase detector is used to feed mismatch information to an up-down counter providing robust iterative control. The measured MEMS array capacitance tuning ratio is almost a factor 10. Module insertion loss is 0.5 dB at low-band and high-band. Harmonic distortion is less than -85ndBc at 35 dBm output power and the EVM, measured in EDGE-mode, is less than 1% at 27 dBm . The adaptively controlled module, connected to a planar inverted-F antenna, shows desired impedance correction. For extreme hand-effects the maximum module impedance correction at 900 MHz is -75jOmega.

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A GSM/EDGE/WCDMA Adaptive Series-LC Matching Network Using RF-MEMS Switches

The link quality of mobile phones suffers from antenna mismatch due to fluctuating body effects. Techniques for adaptive control of impedance-matching L networks are presented, which provide automatic compensation of antenna mismatch. To secure reliable convergence, a cascade of two control loops is proposed for independent control of the real and imaginary parts of impedance. A secondary feedback path is used to enforce operation into a stable region when needed. These techniques exploit the basic properties of tunable series and parallel LC networks. A generic quadrature detector that offers a power-independent orthogonal reading of the complex impedance value is presented, which is used for direct control of variable capacitors. This approach renders calibration and elaborate software computation superfluous and allows for autonomous operation of adaptive antenna-matching modules.

Adaptive Impedance-Matching Techniques for Controlling L Networks

A 54.6 GHz divide-by-3 injection locked frequency divider with low power consumption is presented. A resistive feedback is implemented to achieve a stable dc input and higher injection efficiency. Compared with the conventional design, it exhibits a better supply voltage rejection and wider locking range while a small silicon area is maintained. Fabricated in a TSMC 65 nm bulk CMOS process, this divider operates from 48.8 to 54.6 GHz and consumes 3 mW from a 0.9 V supply.

A 3 mW 54.6 GHz Divide-by-3 Injection Locked Frequency Divider With Resistive Harmonic Enhancement

To cope with the problem of instability and imperfect reverse isolation, a millimeter-wave voltage-voltage transformer feedback low noise amplifier has been analyzed, designed, and measured in CMOS 65 nm technology. Analytical formulae are derived for describing the stability, gain, and noise in this circuit topology. An analogy with the classic concept of Masons's invariant is used to illustrate how the transformer feedback provides the required reverse isolation in the LNA. Based on the developed theoretical analysis, the circuit is implemented as a fully integrated 60 GHz two-stage differential low noise amplifier in 65 nm CMOS technology. A flat gain of 10 dB is achieved over the entire 6 GHz bandwidth. The measured noise figure is 3.8 dB.

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Analysis and Design of a 60 GHz Wideband Voltage-Voltage Transformer Feedback LNA

Under antenna mismatch conditions at high output power, voltage clipping (due to collector voltage saturation) is the main cause of power amplifier linearity degradation. To preserve linearity under mismatch three adaptive methods are presented that make use of the detected minimum collector peak voltage. This detected signal controls either the amplifier output power, load-line, or supply voltage. These concepts are generalized analytically, and calculated results compare well to simulations. Measurements demonstrate am error vector magnitude reduction of 5% and an adjacent channel power ratio improvement of 10 dB at a voltage standing wave ratio of 4 for an EDGE amplifier with adaptively controlled output power. These adaptive methods offer a cost and size effective alternative to the use of an isolator.

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Reza Mahmoudi

Papers

A GSM/EDGE/WCDMA Adaptive Series-LC Matching Network Using RF-MEMS Switches

Adaptive Impedance-Matching Techniques for Controlling L Networks

A 3 mW 54.6 GHz Divide-by-3 Injection Locked Frequency Divider With Resistive Harmonic Enhancement

Analysis and Design of a 60 GHz Wideband Voltage-Voltage Transformer Feedback LNA

Adaptive methods to preserve power amplifier linearity under antenna mismatch conditions