Harry G. Skinner

A Wideband Frequency-Shift Keying Modulation Technique Using Transient State of a Small Antenna (Invited Paper)

The rate of wireless data transmission is limited by the antenna bandwidth. We present an e-cient technique to realize a high-rate direct binary FSK modulation by using the transient properties of high-Q antennas. We show that if the natural resonance of a narrowband resonant-type antenna is switched at a high rate, the radiating signal follows the variation of resonant frequency and provides a high-rate data-transmission regardless of the narrowband characteristics of the antenna. The bit-rate in this method is dictated by the switching speed rather than the impedance bandwidth. Since the proposed technique employs the antenna in a time-varying arrangement, carrier frequencies are not required to be simultaneously within the antenna bandwidth. When demanded, the antenna is tuned to required carrier frequency according to a sequence of digital data. Moreover, if the switching frequency is properly chosen such that the stored energy in the near-zone is not dramatically disturbed, any variation in the antenna resonance will instantaneously appear in the far-fleld radiation due to the previously accumulated energy in the near fleld. Therefore, depending on the Q factor and switching speed, radiation bandwidth of the antenna can be improved independently from the impedance bandwidth. Furthermore, we show that a single RF source is su-cient to excite both carrier frequencies and the need for a VCO is obviated. Experimental results are presented to validate the feasibility of the proposed technique.

Mitigation techniques for RFI due to broadband noise

Mobile computing devices such as Laptops, tablets, smartphones and the like mostly have GPS, WLAN, and cellular capabilities whose performance could be degraded in the presence of broadband noise in the receiver antennas vicinity due to integrated high speed buses and digital circuitry. Shielding, as a passive technique, has become a convention in the mobile wireless industry and we present here a study of its effectiveness particularly in the near-field (as inside a smartphone for instance). We also present some novel active techniques such as bus activity control and RFI data encoding. In the former one, the correlation that exists between the activity level of the bus and its noise coupled to the radio is used in an adaptive algorithm that indirectly estimates the noise affecting the data transmission and controls the bus activity level to meet some require SNR. In the latter one, line encoding is used to reduce the spectral contribution to RFI of a data bus at some specific frequency band. Using K to N (K <; N) codes, simulations show a reduction of the noise of more than 10dB.

Statistical Modeling of the Interference Noise Generated by Computing Platforms

The trend of electronic systems toward higher integration and higher performance has also brought new challenges to the design of radio transceivers. The decrease of switching times accompanied by the increase of clock speeds, data rates, and interconnection speeds contribute to improve the overall system performance. At the same time, they also affect wireless communications due to an increment of the emissions of electromagnetic radiation. In this paper, we show that the statistics of the baseband components of the noise follow the K-distribution. The one-sided version of this distribution has been derived before as a model for the envelope of sea echo in radar and sonar, however, we show here that its two-sided version can also be used to model the interference noise that affects a transceiver located inside a computer platform. The model shows good agreement with experimental measurements. Also, a closed-form expression of the bit error rate (BER) and some bounds are computed.

Correlation of EMI measurements and simulations for simple package geometries

This paper presents three measurement- and one simulation-approaches to quantify radiation from IC-package geometries. Two test boards were built and measured by using a semi-anechoic chamber, GTEM cell and near-field scan. Good correlations were achieved between measurements and simulations. Advantages and limits of each approach were addressed.

New Spread Spectrum Clocking Techniques for Improved Compatibility with Cellular and Wireless Subsystems

Spread spectrum clocking is an established technique for reducing electromagnetic interference arising from clocking signals. Though effective for reducing interference with other devices, SSC can increase the interference with radio receivers inside the device itself. New SSC techniques have been developed to reduce this internal interference while retaining the external interference benefits. Laboratory measurements and test chip results show significant reduction in radio interference. The techniques are applicable to switching voltage regulators and high-speed digital computing and communications systems.

Radio frequency interference

The article consists of a Powerpoint presentation on radio frequency interference. The areas discussed include: radio frequency interference; electromagnetic interference; mobile Internet device and wireless sensitivity requirement.

Evaluating impact of RFI on WLAN / WWAN performance

A collection of slides from the authorpsilas conference presentation is given.

Connectors, Cables, and Power Planes

This chapter explores the methods for experimenting with PCB construction, connectors, power planes, and silicon and packages. There are many knobs to turn in order to impact interference. Some knobs provide large changes and some not so many, but they are all usually additive. Power delivery in silicon is different from that in packages or motherboards. Due to fabrication constraints, full metal planes cannot be processed. Instead, power is delivered through a complex multilayer mesh of orthogonal nets. A major source of emissions can originate from connectors, cables, and power planes. It is well known that cables can be significant sources for radiated emissions. The power topologies that combine planar loops and grids or planes in power distribution show significant differences over any of the simple loop structures. These complex structures are more indicative of actual power distributions. The test boards were designed to be used with both the GTEM cell and the Intel NFS system. The test boards come in two parts: the first is 10-cm square and is uniform in topology and provides a platform for the second part; the second part is a pseudo-BGA meant to simulate the package and the silicon structure. One can start by analyzing resonance structures in the PCB and determining which wireless frequencies may have problems due to board construction.

The Structure of Signals

This chapter explains the different aspects of the structure of signals and how each element of this complex structure can be addressed to develop a strategy toward minimizing the interference impact of the signals that are used in the platforms. The edge rate asymmetry will produce even harmonics, where a symmetric signal does not. The two key measurement techniques used widely are narrowband near-field scanning, where a fine-scale electric or magnetic field probe is stepped across the surface of the package or the silicon, and the energy distribution of the DUT is mapped; and broadband measurement using the VLSI GTEM, where a test board with a single IC is measured for broadband emissions from 100 MHz to 6 GHz. These measurements can be used as guides to develop analytical methods to allow a designer to investigate possible functional floor planning early in the silicon and package design cycle. The duty cycle can impact amplitude and variation in harmonic components of signals. The effect of the time differentiation of the signal is to decrease the amplitude of the lower-order harmonics with little impact on the higher harmonics. This chapter also examines repetitive signals, non-repetitive signals, clocks that have been scrambled, and clocks that have been spread out in time in order to lower their associated harmonic amplitudes.

Analysis of Symbols

This chapter elaborates the impact of signal structure in the platform and the variation in RFI as a result of that variation and suggests many possible approaches to interference mitigation that may be pursued through application of signal structure techniques. Digital display frames and their associated symbols present a problem to the EMI engineer and their spectra fall somewhere between a purely repetitive symbol sequence such as a clock, and a purely random sequence of a finite set of symbols such as a pseudorandom bit stream (PRBS). The best approach to producing the lowest emissions profile is to scramble both the data stream and the clock, thereby producing spectra similar to the PRBS, which has the lowest set of spectral peaks. This chapter compares the inner product of a symmetric clock and two symbols chosen from opposite ends of the ranking table. The results indicate that the inner product method allows the designer an opportunity early in the design cycle to choose from a given symbol set which symbols should be used for highly repetitive symbol streams.