Chulsoon Hwang

A Novel Shielding Effectiveness Matrix of Small Shield Cans Based on Equivalent Dipole Moments for Radio-Frequency Interference Analysis

A definition of a shielding effectiveness (SE) matrix for small shield cans used to suppress intra-system noise coupling in mobile devices is proposed. Assuming shield cans enclosing a noise source can be modeled as equivalent dipole moments along with integrated circuits (ICs), a new SE matrix for radio-frequency interference analysis is defined as a ratio of equivalent dipole moments with and without a shield can. The equivalent dipole moments are experimentally extracted using a GTEM cell and two types of probes (monopole and loop), which mimic well the radiations of ICs. Furthermore, the estimation of suppression of noise coupling to an antenna using the proposed SE matrix is successfully validated through numerical simulations.

Noise coupling path analysis for RF interference caused by LCD noise modulation

RF interference caused by liquid crystal display (LCD) noise modulation in a mobile phone was investigated and its noise coupling path was demonstrated. In the frequency division duplex communications, mobile phones can send (uplink) and receive (downlink) at the same time. When an antenna transmits high power signal, the baseband noise from an LCD panel is modulated into an RF band and causes interference in a receiving antenna. A noise coupling path between an antenna and a display driver IC, which drives the LCD panel, was experimentally demonstrate. In addition, a simple noise source model was proposed to represent modulation mechanism. A network analysis with the modulation model showed good correlation with the measured spectra of the modulated noise in a receiving antenna.

Radiation Noise Source Modeling and Application in Near-Field Coupling Estimation

Near-field coupling in mixed digital/RF circuit design is critical to system sensitivity for modern high speed electronic systems. This paper presents radiation noise source modeling methods and applies equivalent noise source models to near-field coupling estimations. The noise source can be either modeled by physics-based dipole moment model or Huygenss equivalent model with data obtained from near-field scanning. The fundamental principles of both methods are first studied by simulation. A clock buffer integrated circuit is first modeled as a dipole moment model. The tangential fields on Huygenss box can be calculated by a dipole moment model with negligible multiple scattering effect assumption. The noise coupling then can be obtained by surface integration of Poynting vector at the RF antenna receiving port by full-wave simulation.

MoM based current reconstruction using near-field scanning

Multiple digital ICs sharing ground plane have potential problems of ground noise interference to each other. Current distribution on the ground plane can introduce intra-system EMC issues, which can possibly result in receiver desensitization issue in wireless devices. In this paper, a method of moment (MoM) based current reconstruction method is proposed to estimate the current on the ground plane. This method requires phased resolved near field data for accurate current reconstruction. The proposed method is validated by a numerical example. The current reconstructed from the proposed method is compared with the current from the simulation tool. The difference is within 3.5 dB which is acceptable for most engineering practice.

LCD baseband noise modulation estimation for radio frequency interference in mobile phones

A method to predict the modulated noise coupling to an antenna is proposed and experimentally validated using a practical mobile phone. The baseband noise of a liquid crystal display (LCD) is modulated with the Tx carrier signal of cellular communication, resulting in a radio frequency desensitization problem. The modulation mechanism is understood and its circuit representation is proposed to estimate the modulated noise coupling to an antenna. The modulation coefficient, which represents a relationship between the coupled voltage and modulated current, is experimentally extracted from a stand-alone LCD panel. The proposed modulation model is successfully validated through comparison with measurements using a practical mobile phone.

Capacitance-Enhanced Through-Silicon Via for Power Distribution Networks in 3D ICs

The through-silicon via (TSV) structure with enhanced capacitance is proposed for the power distribution network in 3D ICs, where an n+ contact on the top surface surrounding the oxide-silicon interface of the power TSV is used, instead of a p-substrate. The n+ contact supplies the majority carrier to the channel, so the inversion layer can be formed at high frequencies. Since power TSVs are always biased to a voltage higher than the threshold voltage, changing the depletion layer to an inversion layer enables the larger capacitance in the proposed TSV. The voltage and frequency characteristics of the proposed TSV structure are simulated and compared with the conventional structure. In addition, a model based on RC transmission line is proposed to estimate the capacitance degeneration at high frequencies. The model showed a good match with simulated results over a wide frequency range.

IC placement optimization for RF interference based on dipole moment sources and reciprocity

A method to optimize the IC placement in mobile devices from RF interference perspective is proposed. The coupling from the IC to an antenna is estimated by combining the equivalent dipole moment source and reciprocity, which facilitates understanding of coupling physics and design insight for the mobile devices. Based on the proposed method, optimal place for the noisy ICs can be quantitatively determined for each frequency of interest.

Physics-Based Dipole Moment Source Reconstruction for RFI on a Practical Cellphone

A physics-based dipole moment source reconstruction is proposed to estimate the near-field coupling between a liquid crystal display panel to a cellphones cellular antenna. Based on the understanding of the current distribution on the source, a magnetic dipole moment source is reconstructed to replace the real radiation source that is located at the edge of the flexible printed circuit board. To characterize the coupling from the equivalent dipole moment source to the victim antenna, the noise transfer coefficient is proposed. The noise transfer coefficient can be calculated from the near-field scanning and the direct coupling measurements using a wideband source. The proposed physics-based dipole moment source reconstruction and noise transfer coefficient are successfully validated through the measured near-field coupling in a practical cellphone.

Modeling and Estimation of LCD Noise Modulation for Radio Frequency Interference

A liquid crystal display baseband noise, whose spectrum is much lower than RF bands, is modulated with the carrier signal of cellular communication and interferes with an Rx receiver resulting in a desensitization problem. The modulation phenomenon is modeled with impedance parameters and a modulation coefficient. The coupled noise on the embedded cellular antenna is experimentally validated in both small- and large-frequency offset cases. In addition, to estimate the modulated noise coupling to the antenna earlier in the development process, a numerical simulation method considering the impedance of display drive IC is proposed successfully validated.

Modeling optimization of test patterns used in de-embedding method for through silicon via (TSV) measurement in silicon interposer

In this paper, the electrical performance of the test patterns used in the de-embedding method for TSV characterization was studied thoroughly. For all test patterns, full wave models were built and then analyzed based on simulated electrical performances. Equivalent circuit model analysis and parametric study results of the test patterns further demonstrate the accuracy of the full wave models. Furthermore, Scanning Electron Microscopy (SEM) measurements were taken for all the test patterns, and full wave models were optimized based on the measured dimensions. Finally, the response of the TSV pair was obtained by de-embedding the pads and traces from the TSV pair simulation with the test fixtures. Good agreement between the de-embedded results with analytical characterization and the full-wave simulation for a single TSV pair was achieved.