John Thomas Fessler

Spread spectrum clock generation for the reduction of radiated emissions

A method is presented for reducing the radiated emissions of an electronic device by frequency modulating (FM) the system clock. This method, referred to as spread spectrum clock generation, or SSCG, is applicable to most microprocessor based systems. A unique waveform used to frequency modulate a digital clock signal results in a spectrum with sideband harmonics that are nearly uniform in amplitude when measured with an EMI receiver. This has the effect of spreading the energy of a discrete frequency harmonic over a wider bandwidth, thereby reducing the amplitudes of the harmonics. Attenuation as high as 13 dB is presented using an experimental setup, an actual SSCG integrated circuit, and theoretically computed results.<<ETX>>

Design considerations of phase-locked loop systems for spread spectrum clock generation compatibility

A technique was proposed which reduces the radiated emissions of a digital clock signal and its associated harmonics by as much as 10-20 dB, depending on frequency. This technique, referred to as spread spectrum clock generation (SSCG), reduces the radiated emissions associated with a clock signal by modulating the signal with a unique waveform. This technique can be used with minimal consideration when used in a system that does not utilize frequency dependent devices such as a phase-locked loop (PLL). For those designs which incorporate a PLL, attention must be given to the design of the PLL in order to minimize clock skew while at the same time maintain maximum attenuation of emissions. This paper presents design considerations and modeling techniques that an EMC engineer should consider when implementing SSCG in PLL based systems.

The effectiveness of an image plane in reducing radiated emissions

A study of the effectiveness of a finite-sized image plane in reducing the amplitude of the radiated emissions due to electric currents flowing near the plane is presented. The method of moments is utilized to examine how well a finite-sized image plane approximates an infinite plane and to analyze the effects of the dimensions of the image plane on the radiated emissions. A 2-D and 3-D analysis is included with similar conclusions drawn in both cases. In addition, measured data are presented which confirm the results of the numerical study.

A study of the interference potential of spread spectrum clock generation techniques

A technique to reduce the radiated emissions of digital clock signals and associated harmonics has previously been presented (Hardin et al. 1994). This technique, referred to as spread spectrum clock generation, or SSCG, intentionally broadbands a normally narrowband signal by frequency modulating the trapezoidal clock signal with a unique modulating waveform. As a result of this modulation, the amplitudes of the harmonics of the clock signal can be reduced by as much as 2-22 dB, depending on the frequency of measurement and the frequency deviation. Since the decrease in the amplitudes of the clock harmonics is accomplished by increasing the bandwidth occupied by the harmonics, a number of SSCG clock harmonics may correspond in frequency to an intentionally transmitted signal, such as radio or television. This raises the question of whether SSCG clock generation techniques result in an increase in the interference potential to wideband broadcast receivers as compared to existing clock generation techniques. An additional question which arises is whether existing electromagnetic interference (EMI) measurement procedures are appropriate for products utilizing this technology. The paper presents experimental studies of the interference characteristics of SSCG to broadcast receivers, in particular to television receivers. The results indicate that SSCG presents no greater interference potential to television receivers and in the case of the television audio quality, creates significantly less interference than standard clock generation techniques and that existing EMI measurement procedures are appropriate.

Effect Of Image Plane Dimensions On Radiated Emissions

The effect of finite dimensions of an image plane on the reduction of radiated emissions is investigated numerically. The applications are important in the reduction of the radiated fields from common-mode currents on Printed Circuit Board (PCB) conductors (lands). Earlier experimental results showed that common-mode currents tend to be the dominant contributors to the emissions from PCB lands [1,2]. Additional experimental results showed that placement of a metallic plane beneath the PCB could dramatically reduce the emissions [3]. The numerical results presented in this paper are intended to confirm these observations and are obtained for a ground plane of infinite length but finite width (2D) and for a ground plane (and current) of finite width and length (3D). These results show that reductions of radiated emissions of the isolated current of around lOdB are obtained when a finite ground plane is placed beneath it. It is also shown that as long as the ground plane dimensions are larger than approximately one wavelength, the height of the current above the ground plane is electrically small and the current is not too close to the edges of the ground plane, image theory provides an adequate characterization of the problem even though the ground plane dimensions are finite.

Received signal strength indication signature for passive UHF tags

Received signal strength indication (RSSI) has commonly been used for estimating the distance between a radio frequency identification (RFID) tag and its reader. However a plot of RSSI vs. frequency reveals a signature specific to the physical surrounding environment. In an attempt to understand how the environment impacts the RSSI signature, an experiment was performed in a “real world” environment where the test setup was shifted incrementally though an open room to see how the RSSI signature changes. In another experiment, the RSSI signature was measured in an anechoic chamber with and without absorbers on the floor so the effect of the ground plane reflection on the RSSI signature could be isolated and examined. The RSSI signature was found to be too complex to pinpoint a single feature as being caused by the ground plane reflection; however it can be concluded that not only is the RSSI signature repeatable within an unchanged physical environment (and therefore not merely random noise), small changes in the environment result in small changes in the RSSI signature. These experiments demonstrate a potential improvement in fingerprinting and distance estimation, if frequency hopping is used to measure RSSI, by averaging RSSI over a frequency range.

A novel z-directed embedded component for the reduction of voltage ripple on the power distribution network for PCBs

A new capacitor package and PCB embedding technique is introduced to significantly reduce the system power distribution network impedance at the pads of surface mounted integrated circuits. The capacitor is multi-layer ceramic capacitor (MLCC) that is a right cylindrical shape with via channels in the outer wall along the axis of the part. The capacitor called a Z-Directed component (ZDC) is then pressed into a hole in the PCB. The connections to the component are then made by the copper plating process similar to via hole construction. This new configuration dramatically improves the PDN performance of PCBs with fewer components than the conventional solution with SMD decoupling capacitors.

A novel Z-directed embedded component for the reduction of voltage ripple on the power distribution network for PCBs

A new capacitor package and PCB embedding technique is introduced to significantly reduce the system power distribution network impedance at the pads of surface mounted integrated circuits. The capacitor is multi-layer ceramic capacitor (MLCC) that is a right cylindrical shape with via channels in the outer wall along the axis of the part. The capacitor called a Z-Directed component (ZDC) is then pressed into a hole in the PCB. The connections to the component are then made by the copper plating process similar to via hole construction. This new configuration dramatically improves the PDN performance of PCBs with fewer components than the conventional solution with SMD decoupling capacitors.

RSSI informed phase method for distance calculations

In an attempt to find an accurate, environmentally robust, and fast process for RFID distance estimations, a method was developed called RSSI Informed Phase. This method uses both phase and RSSI measurements to estimate the distance, and potentially location, of a moving RFID tag. RSSI is initially used to find an approximate reader to tag separation distance. This distance value is applied to find an approximate slope of the phase angle vs. frequency curve. The estimated slope can inform the phase distance calculation, meaning fewer reads are required to find the actual phase angle vs. frequency slope. The reduction in the number of necessary reads accelerates the localization process and makes this method more robust for dynamic environments.