Pilar Molina Gaudó

Exact analysis of a simple class E circuit version for device characterization purposes

The mathematical exact analysis of a simple class E high-efficiency switching mode tuned power amplifier is performed. The simple network only contains one capacitor and one inductor. Switch duty-cycle and Q cannot be chosen independently, and thus this circuit is only of interest for applications in which a high harmonic content in the load is permitted. In this paper, this circuit is used as a test bench for extracting, with no need for optimization, the parameters of a simple FET output port model in high frequency switching conditions. This method is a quick way to predict if a transistor will be useful in a class E application. Experimental measurements showing good agreement with theoretical results are presented.

Dynamic Model of Class-E Inverter With Multifrequency Averaged Analysis

This paper presents a novel dynamic model of a single-switch class-E inverter. Both the transient and steady-state behaviors of main variables are derived using a multifrequency averaged (MFA) modeling method. The analysis of the boundary conditions reveals that, under some approximations, the performance of the generalized averaged model is close to that of the “exact” or topological one. A detailed analysis of the errors and limitations of the model has been derived. Contrary to other class-E inverter models, based on the input-output behavioral black-box approach, the MFA modeling technique leads to a large-signal knowledge-based model. The advantage of this type of model is that it is applicable to a wide set of analysis and control design tools. The proposed model is verified by comparing the MFA, state-space, and experimental results, showing good agreement for the dynamic behavior of the inverter under supply voltage modulation and also for the frequency and phase modulation of the input control signal.

Output power capability of class-E amplifiers with nonlinear shunt capacitance

The nonlinearity of the shunt capacitance in a HF class-E power amplifier produces a switch peak voltage higher than expected, in particular at frequencies where the shunt capacitance is solely provided by the device parasitic. Peak values have to be accurately estimated in order to avoid device breakdown and to be able to choose a convenient and not too overestimated transistor for the application. Furthermore, the nonlinear behavior modifies the output power capability of a device in class-E operation. When dealing with a lossy nonlinear device, reducing the ON duty cycle of a design bellow 0.5 might help achieving higher frequencies in ideal class-E conditions, whereas increasing it results in higher output power and efficiency. For the first time, an analysis of peak voltage values and output power capability of a class-E amplifier is presented for several duty-cycles and nonlinearity parameters. Experimental results show good agreement with numerical analysis.

Silicon carbide JFET resonant inverter for induction heating home appliances

This paper presents a one switch silicon carbide JFET normally-ON resonant inverter applied to induction heating for consumer home cookers. The promising characteristics of silicon carbide (SiC) devices need to be verified in practical applications; therefore, the objective of this work is to compare Si IGBTs and normally-ON commercially available JFET in similar operating conditions, with two similar boards. The paper describes the gate circuit implemented, the design of the basic converter in ideal operation, namely Zero Voltage Switching (ZVS) and Zero Derivative Voltage Switching (ZVDS), as well as some preliminary comparative results for 700W and 2 kW output power delivered to an induction heating coil and load.

Improving Medium Access in Through-The-Earth VLF-LF Communications

In order to improve the communication range of Through-The-Earth (TTE) radio using electrodes, the impedance load seen by power stage load must be minimized. This impedance depends on the wires, the electrode contact and the path between the electrodes (earth). Of the three elements, we cannot influence the earth impedance. The wire impedance can be minimized employing short cables and avoiding coiling them. This paper presents a method for characterizing the electrode contact impedance and provides suggestions to minimize it. Therefore some impedance measurements with several electrodes and a variety of contact conditions have been performed in order to improve our knowledge of medium access. To further prove the results measurements have been made with a voice radio application.

Direct DDFS FM modulator with baseband interpolator

This paper presents a high linearity FM modulator completely based on simple digital blocks. Direct Digital FM modulator (DDFM) has been built using an optimized Direct Digital Frequency Synthesizer (DDFS). High speed linear interpolation has been employed in the DDFS structure allowing to meet the stringent requirements of an analog FM broadcast application. Presented prototype maintains low cost and simplicity. Proper investigation and definition of error sources has been developed to fulfill requirements with the least resource utilization. Experimental results verify high modulation linearity and SINAD performance while maintaining good spectral purity SFDR over all synthesized frequency range.

Phase shift deskew of oscilloscope current and voltage sensing probes by means of energy balance

To model losses of active devices in switching operation, such as for example in class E amplifiers, it is of interest to characterize equivalent switching losses in cut-off and conduction. These losses vary with frequency, drain (or collector) current and voltage, among others. Ideally, losses can be estimated by means of power balance. To be able to perform accurate power balance measurements, instant power has to be known and integrated. Recent advances in oscilloscope and current probes, allow time-domain measurements well in the RF and microwave frequency ranges. To obtain reliable results accurate phase shift between current and voltage sensing probes (skew) has to be known for the particular measurement frequency and test-set. This is particularly important when losses are small compared to overall power delivery which is the case of high efficiency power amplifiers and also because, in switching circuits, losses occur by simultaneous presence of voltage and current during conmutation in very short periods of time. This paper proposes a simple adjustment method, also based in power balance. Practical results obtained are consistent and included herein.