Stephen O'Reilly

Impedance formulas for planar magnetic structures with spiral windings

It is well established that magnetic components may be reduced in size by operating at high frequency. Miniaturization of magnetic components is ideally suited to microelectronics technologies such as thick films, which lend them to planar geometries. This paper describes new analytical models, which predict inductance- and frequency-dependent eddy-current losses in magnetic substrates. Prototype devices were fabricated by a thick-film process with four layers of conductors on a single ferrite substrate and in a sandwich configuration, consisting of conductors between ferrite slabs. The prototype devices were tested in the frequency range 10 kHz-100 MHz. The measurements confirm the validity of the analytical models. Simulation with finite-element analysis was employed to identify different sources of losses: eddy current losses in ferrite substrates; proximity effect losses in conductors; and dielectric losses.

Current sensor in PCB technology

A novel DC/AC current sensor works on the fluxgate principle. The core in the form of a 7/10-mm ring made of electrodeposited permalloy is sandwiched in the middle of a printed circuit board (PCB), whereas the sensor excitation winding is also integrated in the copper layers of the PCB. To lower the sensor power consumption, the excitation winding was tuned by a parallel capacitor. The peak-peak/rms ratio of 5.2 was achieved for the excitation frequency of 25 kHz. The open-loop sensor has 100-mV/A sensitivity; the characteristics have a linearity error of 10% and hysteresis below 0.1% in the 1-A range.

MCM-L integrated transformers for low power applications

Designs for planar magnetic core structures fabricated in printed circuit board (PCB) technology have been developed by the authors. The technology is applied to producing integrated transformers for low power conversion in this paper. It involves using processes and materials which are compatible with existing PCB techniques, and structures are designed to be integrated with other circuitry in a typical PCB layer count. Structures are designed to support voltage levels of up to 18 V at 3 W power.

Characterisation of embedded filters in advanced printed wiring boards

Abstract This paper describes the design, fabrication and test of a range of third order LC low pass Butterworth filters in MCM-L technology. There are seven filters in the range, each consisting of two inductors and one capacitor with cut-off frequencies ranging from 10 to 540 MHz. Inductance values range from 9.9 to 530 nH, and capacitance values vary from 14 to 723 pF. Air-core (by which we mean no magnetic material) spiral winding structures are designed to provide the inductive functions. A new FR4 type laminate material, which was developed by ISOLA, is used to form integrated parallel plate capacitor structures. The range of filters was successfully manufactured and electrically characterised using a HP4195A impedance analyser. Some environmental testing was also carried out on the embedded filters. These included thermal shock and humidity testing. There were no obvious changes in device performance after the environmental tests.

Analysis of the performance of integrated inductors (fabricated in MCM-L technology) in RF amplifier applications

Research in integrated passive components is becoming more widespread, as the advantages of increased reliability, reduced cost and improved performance are recognised. The subject of this paper is the integration of inductor components in MCM-L technology for RF applications. A detailed analysis of the sensitivity of an RF amplifier to components of parasitic impedance associated with MCM-L integrated inductors is presented. SPICE circuit models are used for this purpose. The performance of a range of integrated test devices is compared with specifications for equivalent commercial devices. Inductance values ranging from 4.5-27.4 nH are produced, with Q-values of up to 100. Such performance is shown to be perfectly suited for the application of integrated inductors in RF amplifier circuits.