In radio frequency interference study, equivalent dipole moments are widely used to reconstruct real radiation noise sources. Previous reconstruction methods, such as least square method (LSQ) and optimization method are affected by parameter selections, such as number and locations of dipole moments and choices of initial values. In this paper, a new machine learning based source reconstruction method is developed to extract the equivalent dipole moments more accurately and reliably. Based on the near-field patterns, the proposed method can determine the minimal number of dipole moments and their corresponding locations. Furthermore, the magnitude and phase for each dipole moment can be extracted. The proposed method can extract the dominant dipole moments for the unknown noise sources one by one. The proposed method is applied to a few theoretical examples first. The measurement validation using a test board and a practical cellphone are also given. Compared to the conventional LSQ method, the proposed machine learning based method is believed to have a better accuracy. Also, it is more reliable in handling noise in practical applications.

Machine Learning Based Source Reconstruction for RF Desense

The mechanism of a universal serial bus 3.0 connector caused radio frequency interference (RFI) to a nearby antenna is studied. The connector radiation is modeled by an equivalent stripline-fed slot antenna, based on the analysis of the common mode current path on the connector structure. With the proposed connector model, the original connector radiation source can be replaced by an equivalent magnetic dipole source, which is directly correlated with the physical quantity on the connector. Applying reciprocity theorem, the equivalent dipole source can be applied to predict the coupled noise power to the antenna. The proposed connector radiation mechanism and model are validated through full-wave simulation and measurement. The application of the magnetic dipole source for RFI estimation is demonstrated in a real laptop system.

Mechanism and Validation of USB 3.0 Connector Caused Radio Frequency Interference

Dipole moment model is widely used to represent real noise source to estimate near field coupling between noise source and the victim antenna. However, direct full wave simulation of large number of dipole moment is often very time-consuming. Also, another set of full wave simulation is needed if parameters change. A more scalable approach is needed. In this paper, a transfer function based dipole moment model is proposed to solve this issue. The proposed method only needs one-time full wave simulation. The results obtained from this one-time simulation can be reused for other cases if the same antenna structure is used. The proposed method will use the simulation results to construct transfer functions. The method is implemented in CST where several high performance computing methods are available. The validation of a test board with both simulation and measurement data is also provided.

Radio frequency interference estimation using transfer function based dipole moment model

A high-speed USB3.x IO is analyzed using the System level efficient ESD design methodology [1] using on-board current and voltage measurements for the TX and RX pins. The interactions between external ESD protection device and the on-chip ESD protection circuit is investigated in measurement and simulation.

An Application of System Level Efficient ESD Design for HighSpeed USB3.x Interface

This article proposes a novel radio frequency interference (RFI) mitigation method and applies it to a real consumer electronic device. Through near-field scanning, an equivalent dipole moment of the noise source containing the CPU and DDR memory chip is reconstructed. The near-field components of the victim Wi-Fi antenna are measured to obtain the transfer function. By determining the relationship between the dipole moment and the antenna near field, the noise source is rotated by a certain angle to reduce RFI. Rotating the source to reduce RFI is implemented in such a way that it does not compromise the signal integrity, and it does not require an additional shield can. New boards with the suggested changes are fabricated and the measured results show the RFI reduction up to 8 dB compared with the original board.

A Novel RFI Mitigation Method Using Source Rotation

Ahstract- In this paper, the dipole-moment based reciprocity method is used to perform desense prediction and mitigation from the DDR noise source to the nearby RF antenna. The noise source is from the DDR signals between the application processor and the memory IC. Radiation physics of the noise source is analyzed by understanding of the current flow. Firstly, the random nature of the DDR signals is analyzed using the measurement data. Based on the measurement data, the setup of the near field scanning is further determined. The desense prediction procedures are decomposed into two steps: the forward problem and the reverse problem. In the forward problem, the noise source is approximately regarded as a single magnetic dipole moment based on the near field scanning above this specific electronic device. In the reverse problem, the transfer function from the magnetic dipole moment to the victim antenna is obtained by measuring the H field when the victim antenna radiates. Based on the measurements of forward and reverse problem, the coupled noise to the victim antenna can be analytically estimated. The estimated RFI results are compared with direct RFI measurement to validate the dipole-moment based reciprocity method. Lastly, a few methods to mitigate the desense are also discussed.

Desense Prediction and Mitigation from DDR Noise Source

A device is described. The device includes a data interface connector, an application processor, and interface circuitry. The application processor can receive signals via an antenna. The interface circuitry can be coupled between the application processor and the data interface connector. The data interface circuitry can determine a change in a signal property of one of the signals, the change being caused by an impedance mismatch between the data interface connector and a media consumption device. The data interface circuitry can also send the application processor a signal property setting corresponding with the change. The application processor can adjust the signal property of a subsequent one of the signals, in response to the signal property setting from the interface circuitry, to obtain an adjusted signal. The application processor can also send the adjusted signal to the media consumption device.

Adaptive impedance matching interface

Unintended Electromagnetic interference (EMI) is a common occurrence in all consumer electronics, which can often fail compliance margins of FCC and/or CE, when best practices of grounding, shielding and overall system integration are not followed. The measurement of EMI for regulatory compliance has been studied extensively and there are standard test labs which certifies for EMI. However, predicting the EMI radiation from a consumer electronic device through simulation is very challenging due to the complexities involved in modeling the device and noise source. This paper introduces a workflow for simulating one case of EMI radiation from a 208 MHz single-ended I/O clock generated from the System-on-Chip (SoC) in an electronic device. Through a full wave 3D solver, the radiated far field transfer function of the clock is obtained. Additionally, the spectral content of clock is measured in both time and frequency domain. Then the clock spectrum is combined with transfer function to predict EMI radiation envelope. The simulated results are then compared with the measured results from an FCC compliant laboratory. Based on the simulated and measured results, mitigation techniques are proposed to reduce the EMI to acceptable levels.

Accurate Prediction and Mitigation of EMI from High-Speed Noise Sources using Full Wave Solver

In this paper, a dipole-moment based reciprocity method is applied to a consumer electronic device. The dipole moment is then used to predict radio-frequency interference (RFI) from a high-speed connector to two nearby RF antennas. The connector has a 3D structure with data pins verticallyoriented, for which the near H field pattern around the connector shows a half magnetic dipole pattern. This is different from typical complete dipole patterns over planar printed PCB (printed circuit board) structures. To tackle this problem, a magnetic dipole is placed in full-wave simulation with a similar connector structure. Using the reference near field data from simulation an equivalent magnetic dipole moment for the measured field is obtained. Further reciprocity theorem is applied to predict RFI based on the equivalent dipole magnitude and the antenna reverse H field. The predicted RFI shows a fairly good match with the measured RFI for both victim antennas.

Jagan Rajagopalan

Papers

Desense Prediction and Mitigation from DDR Noise Source

A Novel RFI Mitigation Method Using Source Rotation

Adaptive impedance matching interface

Accurate Prediction and Mitigation of EMI from High-Speed Noise Sources using Full Wave Solver

Accurate RFI prediction of 3D non-planar connector with half magnetic dipole pattern