Radio-frequency Transformers Research Articles

Modular Electromagnetic Transducer for Optimized Energy Transfer via Electric and/or Magnetic Fields.

In this paper, a modular electromagnetic transducer that achieves the optimal transfer of energy from the electric and/or magnetic fields is proposed. Both the magnetic field resonance coupling and the influence of the electric field near the copper transducers of the printed circuit board and inside the FR4-type epoxy material are considered. In our printed arrays of flat transducers, we consider face-to-face capacitances for the study of resonance coupling. Because the space between coil turns is almost double the plate thickness, the coplanar capacitance can be ignored for frequencies under 2 MHz. A radio frequency (RF) transmitter and transducer were built to demonstrate the increased energy transfer efficiency when using both electric and magnetic fields in the near-field region. The transversal leakage flux coupling of a long RF coil was more efficient than a simple axial magnetic field coupling when using pancake transceiver coils. The optimal configuration having one long coil at the base and two or more flat coils as capacitor plates near coil ends generated the highest tandem of magnetic and electrical fields. A power regression tool was used to convert and simplify the transducer current and voltage variation with distance. In this regard, the current change corresponded to magnetic field variation and the voltage change to the electric field variation. New formulas for estimating the near-field region and the self-capacitance of the RF transformer coil are proposed; the optimal function in the frequency domain for a given transducer distance was defined by simulation.

A Methodology Improving Off-Chip, Lumped RF Impedance Matching Network Response Accuracy

Impedance matching is concurrent with any radio frequency (RF) circuit design and is essential for maximizing the gain and efficiency while minimizing the noise of high-frequency amplifiers as well as some mixer topologies. The main impedance matching network components are capacitors, inductors, and RF transformers all of which contain parasitic parameters that influence the matching response S11 curve. After calculating matching network component values using classical matching techniques, the measured and simulated response curves differ depending on the target frequency. This results in multiple calculations and measurement cycles in order to precisely match the source and load at the desired frequency. This article proposes an algorithm and methodology of estimating component parasitic parameters and taking them into account when calculating the main component parameters (capacitance and inductance). The proposed algorithm has been implemented as a toolbox in Cadence Virtuoso and verified through simulation and measurements. Measurement results show, that at 500 MHz 10% tolerance components with parasitics included and values based on classical theory provide a 3.2–9.8% offset from the target frequency. In the same conditions, matching networks with compensated (according to the proposed algorithm) values provide 0.1–8.8% target frequency offset. At 1500 MHz 10% components provided 4–12.3% (non-compensated) and 1–8.7% (compensated) target frequency offset ranges. At 3000 MHz. The frequency offset range of using compensated matching network component values is reduced from 5.5–15.1% to 1.3–8.1%.

Three-dimensional radio-frequency transformers based on a self-rolled-up membrane platform

Radio-frequency (RF) integrated circuits are used for wireless communications and require transformers capable of transferring electrical energy at RF/microwave frequencies. Traditional on-chip RF transformer designs have complex fabrication schemes and offer limited performance scalability. Here we report on-chip RF/microwave transformers that are based on a self-rolled-up membrane platform. The monolithic nature and versatility of this platform allows us to create high-performance transformers while maintaining an ultra-compact device footprint and by using only planar processing. We also show that the performance of the three-dimensional RF transformers improves with scaling, which is in contrast to conventional planar designs. In particular, we observe a continuous rate of increase in the index of performance of our RF transformers as we scale up the turns ratio. This behaviour is attributed to the almost ideal mutual magnetic coupling inherent to the self-rolled-up membrane three-dimensional architecture.

Kinetics of electrons and neutral particles in radio-frequency transformer coupled plasma H− ion source at Seoul National University

In volume production H− ion sources, control of electron temperature is essential due to its close correlation with the generation of vibrationally-excited hydrogen molecules in the driver region as well as the generation of H− ions by dissociative attachment in the extraction region. In the ion source group at Seoul National University (SNU) in Korea, a lot of research effort has been made to the development of a volume production H− ion source based on radio-frequency (RF) transformer-coupled plasma (TCP) for long lifetime continuous wave (CW) operation. It has a spiral RF antenna located outside the discharge chamber to generate a plasma with high electron temperature in the driver region and employs a magnetic filter field to prevent high energy electrons from being transported to the extraction region. In this paper, we present the recent progress on understanding of the underlying physics of the RF TCP H− ion source at SNU. Special attention is paid to the characterization of electron kinetics regime for controlling electron energy distribution and the influence of relaxation of neutral particles during the transport across the magnetic filter region. Effect of the degree of dissociation on the production of H− ions is also discussed.

2π Low Drift Phase Detector for High-Precision Measurements

In modern particle accelerators, radio frequency (RF) phase detectors have to fulfill high demands on stability and accuracy to meet the goals of state-of-the-art synchronization systems. Especially challenging are those cases where the RF signal phase shift accuracy must be measured with fs accuracy for several hours over the full $2 {\pi }$ phase detection range. In these cases special measures on the component’s nonlinearities and RF channel isolation have to be taken. The long-term stability of the phase detector is mostly affected by temperature and humidity variations. To meet the synchronization goals, we have built a phase detector that incorporates a high-speed dual analog-to-digital converter (ADC) with a special circuit for continuous phase drift calibration. In the calibration circuit we successfully combined the RF signal with an RF calibration signal (second tone) to compensate common phase drift that occurs in the microstrip lines, the RF transformers, and the ADC. The second-tone RF signals are directly converted to the digital domain by the fast ADC and, based on signal processing in the field-programmable gate array, are used to calculate the RF signal phase shift correction caused by detector drifts. In this paper, potential error sources of the analog and the digital part of the so-called two-tone calibration technique that limit the phase detector precision are discussed. Finally, the experimental results are presented showing a long-term phase measurement stability better than 0.01 ^\circ \hbox {pk}-\hbox {pk} $ evaluated at an RF frequency of 1.3 GHz over a few days.

The Matching Unit for the RF Ion Source at HUST

A revised L mode matching unit is used for the radio-frequency (RF) ion source test facility at Huazhong University of Science and Technology (HUST). The revised matching unit is composed of a series capacitance, a parallel capacitance and a RF transformer. The electrical parameters of the two capacitances are estimated when the RF transformer is approximated to be ideal. Without plasma, impedance matching for a nine turn RF coil and a six turn RF coil indicates that the approximation could work well. However, after plasma ignition, the matching condition becomes bad when impedance matching without plasma. Then impedance matching by frequency variation as well as the parallel capacitance tuning together is discussed to keep good matching condition in the running of the ion source.

Imbalance-Based Self-Test for High-Speed Mixed-Signal Embedded Systems

Precisely measuring specifications of differential analog and mixed-signal circuits is a difficult problem for self-test development because the imbalance introduced by the design-for-test circuitry on the differential signaling causes nonlinearity on the test stimulus, resulting in degrading device-under-test (DUT) performance. This problem triggers low test accuracy and serious yield loss. This brief proposes a novel test methodology to accurately predict individual DUT specifications by overcoming the imbalance problem with the imbalance generator, a radio-frequency transformer, and a programmable capacitor array based on a loopback test configuration. The imbalance generator produces spectral loopback responses of different weight. Nonlinear equations are then derived to characterize DUT specifications. Hardware measurement results show that this approach can be used to predict the specifications of a DUT in a production test.

Modeling and simulation of high voltage and radio-frequency transformer

This work presents a methodology for designing a 50 kW RF transformer operating at a frequency of 400 kHz with a view to operation with minimal magnetic losses used in the project experimental treatment of industrial wastes and effluents of petrochemical thermal plasma. This innovator model of a RF transformer offers many advantages over traditional transformers, the main ones being their small size for this power level, high power density, low electromagnetic radiation level, and easy and economic manufacturing. The equivalent circuit was obtained practically and theoretically at the university lab. From the project, simulations are made to evaluate the performance of different parameters as a function of magnetic induction, current density, and temperature.

Transformer-Coupled Loopback Test for Differential Mixed-Signal Dynamic Specifications

Loopback tests for a differential mixed-signal device under test (DUT) have rarely been attempted since any imbalance introduced by design-for-test (DfT) circuitry on differential signaling delivers an imperfect sinusoidal wave to the DUT input or output, thereby degrading the DUT performance. In addition, this methodology inherently suffers from fault masking. These problems trigger low test accuracy and serious yield loss. This paper presents a novel methodology for the efficient prediction of individual DUT dynamic performance parameters with a radio-frequency (RF) transformer in loopback mode to overcome the imbalance of DfT circuitry and the fault masking. Cascaded RF transformers with different multiplicative weights are selected in three combinations by a multiplexer to create three separate loopback responses. These responses are used to characterize the DUT dynamic performance. Hardware measurement results show that this approach can be effectively used to predict the specifications of a DUT.

An Analysis of Perfect-Magnetic-Coupling Ultra-Low-Loss Micromachined SMIS RF Transformers for RFIC Applications

Selective removal of the silicon underneath a set of single-turn multilayer interlaced stacked (SMIS) radio-frequency (RF) transformers with nearly perfect magnetic-coupling factor (k <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IM</sub> ~1) and high resistive-coupling factor (k <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Re</sub> ) is demonstrated. This process is based on the inductively coupled-plasma (ICP) deep trench technology. Improvement of 20.6 and 15.7 dB in isolation (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> ) were achieved at 5.2 and 8 GHz, respectively, for a dummy open device after the backside ICP etching. Q-factor increases of 102% (from 4.96 to 10.03) and 23.2% (from 2.24 to 2.76), G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Amax</sub> increases of 11.8% (from 0.76 to 0.85) and 4.5% (from 0.88 to 0.92), and NF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min </sub> decreases of 0.49 dB (from 1.22 to 0.73 dB) and 0.19 dB (from 0.55 to 0.36 dB) were achieved at 5.2 and 8 GHz, respectively, for an SMIS transformer with an overall dimension of 170times240 mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2 </sup> after the backside ICP etching. The G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Amax</sub> of 0.85 and 0.92 are both state-of-the-art results among all reported on-chip transformers. Furthermore, the reasons why the SMIS transformer exhibits better performances than the traditional bifilar and the traditional stacked transformer are explained. These results show that the micromachined SMIS transformers are very promising for RF integrated circuit applications

A transformer-coupled double-resonant probe for NMR imaging and spectroscopy.

A new type of double-resonant coil which takes advantage of the properties of a radio-frequency transformer is described. Two concentric loops are wound in close proximity to yield a high mutual inductance. The primary side is tuned to 34 MHz for 31P and the secondary side is tuned to 85 MHz for protons. A single lead allows program control over frequency without the need to rearrange cabling. Proton and phosphorus spectroscopy are made possible over essentially the same volume of interest without the need for repositioning the sample.

Transmission-Line Transformers

The radio-frequency transformers described in this paper consist of matched transmission lines of equal length and characteristic impedance. The lines are connected according to rules given in the text. These transformers exhibit a very broad frequency response which can be readily estimated; two methods of analysis are presented. The computations agree well with the test results.

The use of a radio frequency transformer to increase the sensitivity of a radio frequency admittance bridge

This paper describes a technique by which the sensitivity of a radio-frequency admittance bridge was increased by using an r.f. transformer, in order to measure small changes of admittance. The bridge measured the admittance of the primary circuit with the unknown admittance connected across the secondary, the nominal value of the secondary to primary turns ratio being √2. Using this method, measurements at frequencies between 5 and 30 MHz were made of the admittance of a plane capacitor of about 1 pF capacitance, to an accuracy of about 2%, and of changes in this admittance to less than 4%. The system was calibrated by a least-squares method, which also enabled the standard errors in the calibration to be evaluated. The results of measurements made on the plane capacitor in vacuum are presented, and the advantages and limitations of the method are discussed.

Transformers, Inductors and Filters

Transformers, inductors and filters have continually played important roles throughout the field of electronics. Relatively crude electromagnetic devices were employed in early telephone and radio communication systems and today their vastly improved descendants are still found in most electronic systems. The sizes of electronic power transformers have been reduced through the development of new core materials and suitable hightemperature insulating materials. Design methods for audio and video transformers have been evolved which, in combination with improved core materials, made it possible to provide broad-band transformers having low distortion effects. Pulse transformers were developed for radar systems and made practical the hydrogen thyratron type pulse modulator. The performance characteristics of intermediate-frequency and radio-frequency transformers have been improved and their sizes reduced through the development of pressed-powdered iron and ferrite core materials. The linearity and stability of iron-cored inductors for filters have been improved through core materials development. Nonlinear inductors were made more nonlinear through the development of rectangular hysteresis loop magnetic alloys and ferrites, providing many new types of electromagnetic devices for electronic circuitry. Advances in electronics have made obsolete some applications of transformers and inductors but also have opened up other opportunities for inductive devices of novel or new characteristics.

A radio-frequency transformer attenuator for use with a level recorder

A radio-frequency transformer attenuator for use with a level recorder

A radio-frequency transformer attenuator for use with a level recorder

A transformer-type attenuator is described which is designed to operate at 10.7 Mc/s. It can be substituted for the potentiometer of a commercial high-speed level recorder, no modifications to the recorder itself being necessary. A method of recording field strength is described, using the attenuator and level recorder with a receiver having an intermediate frequency of 10.7 Mc/s. The same apparatus could be adapted to control counters indicating the times during which the field strength exceeds specified levels.

A wide band high-power radio-frequency transformer

A push-pull power output transformer which will deliver 10 kVA over a frequency range from 0.2 to 10 Mc/s is described. The transformer is designed for an 8 to 1 voltage step-down and for a duty cycle of 1 sec in every 10. A toroidal core consisting of 0.0006 in. thick Mumetal tape is surrounded by a polythene former upon which two four-turn primaries are wound. The case itself is a single-turn secondary winding. The core and windings are convection-cooled with paraffin oil. The effects of core proximity and conductor shape on the leakage-inductance, shunt-capacitance product of a single-turn secondary construction are examined. It is shown that a strip winding has no advantages over wire for the primary.

An Untuned Radio-Frequency Amplifier

This paper outlines in brief a number of untuned radio-frequency transformers which have been used in the past. It discusses their characteristics and reasons for their limitations. It is pointed out that if the plate-load impedance of a tube can be increased at the high frequencies, the amplification will be increased. A method of doing this by closely coupling a circuit tuned to a high frequency is analyzed, and the equation for amplification is derived. The construction of a transformer embodying this principle is next described and amplification curves throughout the broadcast band are given for several varieties.

Note on Day-to-Day Variations in Sensitivity of a Broadcast Receiver

A series of sensitivity measurements on a highly sensitive broadcast receiver over a period of one month indicates that large variations in sensitivity may occur. The importance of these variations in sensitivity is pointed out with particular reference to intercomparison of receiver measuring equipment and production testing of radio receivers. In this particular study, a high degree of correlation between relative humidity and sensitivity was found; i.e., days of high relative humidity were also days of low sensitivity and vice versa. This effect is probably attributable to increased losses in the radio-frequency transformers during periods of high relative humidity. It is shown that changes in sensitivity may be delayed as much as four days after the corresponding changes in relative humidity.

Note on the development of an electron tube amplifier: Which uses 60-cycle alternating current to supply power for the filaments and plates

Electron tube amplifiers now form an important part of practically all radio receiving sets except the most simple types. Storage cells, which have heretofore usually been required for operating amplifiers, require constant attention, are bulky and heavy, and have other serious disadvantages. The dry cells, which are often used as a source of plate voltage, have a comparatively short life and are expensive and inconvenient. It would be much more convenient to use an amplifier which could be supplied with power from 100-volt, 60-cycle mains. This paper describes a five-stage amplifier which operates satisfactorily on 60-cycle supply for both filaments and plates. This amplifier has three radio-frequency stages and two audio-frequency stages, and uses a crystal detector. A special transformer with five windings is used, the primary being supplied with 110-volts a-c. The 60-cycle current when used in an ordinary amplifier circuit introduces a strong 60-cycle note which offers serious interference. This has been practically eliminated by balancing resistances, grid condensers and special grid leaks of comparatively low resistance, telephone transformer in the output circuit, and crystal detector instead of electron tube detector. In the final form of the amplifier, there is only a slight residual hum which is not objectionable. The amplification obtained with a-c. supply was as good as that obtained with the same amplifier used with d-c. supply. The complete unit is light, compact, and portable. For the reception of damped waves, the amplifier as constructed operated most satisfactorily for wave lengths from 200 to 750 meters. This range was determined by the working range of the radio-frequency transformers used. By using suitable radio-frequency transformers, it is expected that the amplifier will be effective for the reception of damped waves and undamped waves as long as 10,000 meters. For the reception of undamped waves, a separate heterodyne should be employed. The paper gives circuit diagrams, and states the values of the condensers, resistors and inductors used.