Wei-Shan Soh

Filter design for suppression of noise coupling from PCB to DC power supply

Based on an in-circuit measurement approach, a systematic EMI filter design procedure is developed to suppress the noise from a digital board to the power supply. The two-probe technique adopted for the in-circuit measurement allows the impedances of the power supply and the PCB to be determined under its actual operating condition. With the measured impedance information, a suitable filter topology can be selected and component value computed without any guessing.

Near-field to far-field prediction for high-speed board using an empirical approach

This paper describes a methodology to predict far-field (FF) emissions from a high-speed board based on the fields measured in the near-field (NF) region. The NF to FF transformation is based upon an empirical relationship between the measured fields in both the NF and FF regions. Initial results show that the predicted FF emissions from a high-speed board provide the designer a good confidence on the compliance of regulatory emission limits.

Comprehensive analysis of serpentine line design

Serpentine lines have been widely used in digital circuits to provide the required timing delays. Based on a full-wave simulation tool, some critical parameters that affect the delay characteristic of a serpentine line are carefully studied and analyzed. With the comprehensive study and analysis, a set of practical and useful design guides are concluded for designing a serpentine line to meet the delay specification.

Development of near-field emission limit from radiated-emission limit based on statistical approach

This paper discusses a novel approach to transforming a radiated-emission limit (e.g., CISPR 22 and FCC) from the far-field to the near-field region. The proposed approach combines data from a near-field scanner and a gigahertz transverse electromagnetic cell with statistics to establish a simple relationship between a near-field magnetic field and a far-field electric field. It is shown that the proposed approach has the potential to be a simple, quick, and fairly inexpensive tool for electromagnetic compatibility pre-compliance purposes.

Study of signal integrity and radiated emission of single ended and differential high speed digital signals crossing a slot

With increasing board complexity and operating frequencies, signal integrity (SI) and radiated emission (RE) compliance for high speed digital board is becoming a challenge to printed circuit board (PCB) designers. Together with higher routing density and multiple on-board power supplies, routing traces across split planes are unavoidable. In this paper, SI performance and RE of single ended (SE) and differential signals propagating across slots are studied. Using both experimental and numerical simulation approaches, the impacts of single ended and differential high speed digital signals across a split plane are investigated and analysed.

Impacts of EMI filter on high speed interconnects for digital circuits design

Todays digital data lines are clocking at very high speed, in excess of 100MHz with rise time in the sub-nano second range. The effects of EMI radiation even from short traces are becoming significant and cannot be ignored. The use of resistive termination versus the EMI filter has long been a compromise in terms of cost and necessity. EMI compliance is now becoming a major design challenge for product development rather than a mere good-to-have specification of low emission. This paper carries out a comprehensive study on filter selection, application, impact on receiver waveform signal integrity and far-field emission suppression using a full-wave electromagnetic simulator (CST Microwave Studio). This study will provide high-speed digital designers an in-depth assessment of the use of EMI filter for radiation suppression in high-speed digital layout.

Experimental study of radiated emission from high speed power plane

Power plane has been used commonly for high-speed PCB design to delivery stable power for the circuits as well as to provide low impedance paths for the power delivery currents. Using an experimental approach, the impacts of placement of decoupling capacitors and plane separation on radiated emission from high-speed board are carefully investigated and studied.

EMI filter design to improve electromagnetic immunity of hearing aid devices

Electromagnetic interference (EMI) from mobile phones on hearing aids are investigated. Different operating modes of the hearing aid have different impact on the immunity of the device. An experimental study will be carried out to understand the impact of EMI filter on the compliance of the hearing aid under the operating modes.

Extraction of Clock Driver Output Impedance for Signal Integrity Design

With increasing clock speed in high-speed digital design, proper impedance matching between the printed circuit board trace and the clock driver output is crucial for signal integrity design. Adding a series output resistor is a common technique to match a clock driver output to a high-speed signal trace for its simplicity and ease of implementation. The selection of the value of the series output resistor requires known output impedance of the clock driver, which is not always readily available. Based on an in-circuit measurement approach, a method to extract the output impedance of any clock driver under its actual operating condition has been developed. With the known output impedance of the clock driver, precise selection of the series resistor value for impedance matching purpose has become a relatively simple task without the usual trial-and-error process.

Study of power/ground plane separation on radiated emission suppression

In todays high-speed board design, decoupling using on-board capacitors are necessary to provide stable DC power and to suppress radiated emission from the board. At the higher frequency beyond 300 MHz, one has to rely on the capacitance offered by the power-ground plane pair in multi-layer stackup to provide effective decoupling. This paper provides an in-depth analysis on the suppression of board emission with the reduction of plane separation.