Chung-Hao Chen

Synthesis Model and Design of a Common-Mode Bandstop Filter (CM-BSF) With an All-Pass Characteristic for High-Speed Differential Signals

A new common-mode bandstop filter (CM-BSF) with an all-pass performance (from dc to 9 GHz) for differential signals is proposed by using a C-shaped patterned ground structure (PGS) with meandered signal lines on a two-layer printed circuit board (PCB). This technique can successfully generate two close transmission zeros in common-mode within the frequencies of concern. A corresponding equivalent circuit model is established to predict the filter behaviors, and a formula for common-mode transmission zeros is derived based on the circuit model. Next, a design method is developed and a synthesis procedure is proposed. According to the procedure, a wideband CM-BSF is synthesized and fabricated on a two-layer PCB. In addition, the simulation and experiment results are demonstrated to verify the technique and show excellent performance of the proposed CM-BSF. It is shown that common-mode noise can be suppressed over 10 dB from 1.9 to 8.9 GHz with 130% fractional bandwidth (FBW) while the insertion loss of differential-mode can be kept less than 3 dB from dc to 9 GHz. The electrical size is only 0.21 λg ×0.21 λg, where λg is the wavelength of the stopband central frequency. To sum up, the proposed CM-BSF has merits of low cost (two layer), a simple geometric structure, a compact size, and a large common-mode FBW. Most importantly, the filter can keep good signal integrity of the digital differential signals due to its all-pass characteristic.

Modeling and Analysis of Bandwidth-Enhanced Multilayer 1-D EBG With Bandgap Aggregation for Power Noise Suppression

A circuit model of multilayer electromagnetic bandgap (EBG) structure with application on bandgap aggregation design is investigated in this paper. A design concept for bandgap aggregation is merging the lowest two bandgaps into an equivalent wide bandgap by narrowing central passband. This goal could be achieved by optimizing pitch and arrangement of power/ground vias. The theoretical circuit model which only focuses on cutoff frequencies is proposed for efficient bandgap prediction. The accuracy of the proposed model is validated by comparison with full-wave simulation and measurement results. By using the circuit model, mechanism of bandgap aggregation can be explained well, and the influence of structural parameters can also be studied easily. Furthermore, effect on limiting excitation of propagation modes by narrowing central passband is also validated for merging adjacent bandgaps. Test boards with unit cell size 2.03 mm × 3.94 mm are fabricated and measured to validate the design concepts. Both simulation and measurement show the wide bandgap in insertion loss results, which ranges from 1.27 GHz to above 10 GHz by merging even higher bandgaps.

Miniaturized and bandwidth-enhanced multilayer 1-D EBG structure for power noise suppression

A one-dimensional multilayer electromagnetic bandgap (EBG) structure is investigated for size reduction and bandwidth enhancement. A design concept for bandwidth enhancement of the multilayer EBG structure focuses on merging multi-bandgap into one wide bandgap by making inner passbands as narrow as possible. Such goal could be achieved by optimizing the arrangement of power/ground vias. It is also shown that the first band would drop slightly and the third band would be raised significantly with the proper vias arrangement. In addition, size reduction is due to large capacitance characteristics of multilayer structure. The proposed ten-layer structure results in bandgap from 1.6 GHz to 6.3 GHz with merging first two bandgaps. Test boards are also fabricated and measured to validate the design concepts and simulation results. Wider bandgap for insertion loss results, which ranges from 1.27 GHz to above 10 GHz, is better than dispersion diagram due to higher bandgaps.

A novel measurement fixture for characterizing USB 3.0 radio frequency interference

USB 3.0 running at 5 Gbps can radiate and interfere with the wireless communication technologies integrated in mobile computer designs. The interference degrades the wireless performance such as data throughput and results in bad user experience. It is important to define compliance test methods to ensure good designs in both system and component levels. In this paper, a new and simple test fixture and the measurement methods for USB 3.0 radio frequency interference compliance testing are proposed.

Radio frequency interference due to USB3 connector radiation

USB3 devices use 5-Gbps signalling and the data spectrum can generate broadband noise in the 2.4-GHz ISM band. The noise can radiate from the USB3 connectors or cables and cause radio frequency interference (RFI) to a wireless receiver whose antenna is placed near a USB3 device. In this paper the root-cause for the radiation from USB3 receptacle connectors is presented. Simulation and measurement data are shown on an improved connector design that can reduce the amount of noise radiated.

Investigation of signal integrity issues in multi-path electrostatic discharge protection device

This paper studies signal integrity issues in a multi-path electrostatic discharge (ESD) protection device. A commercial four-path ESD protection device is investigated as a case study. The insertion loss, mode conversion and crosstalk of the test circuit are measured. Besides, a circuit model is proposed which has the ability to explain the behavior of the ESD protection device in insertion loss, mode conversion and crosstalk up to 10 GHz. The model is SPICE-compatible and can be used in SPICE-like simulator. Comparison between simulation by ADS and measurement results are also shown. By investigating the model, mechanisms for those non-ideal effects are discussed in this paper as well.

Gb/s USB: RFI risk analysis and test methodologies

Gb/s speed USB signals running at 5 Gbps or 10 Gbps can radiate and interfere with wireless communication receivers integrated in mobile computer designs. There are several coupling paths for the radiation, including the connectors and cables between the USB hosts and devices. The radiation causes radio frequency interference (RFI) to integrated wireless receivers and can results in degraded wireless performance such as data throughput and poor user experience. Effective shielding of the cables and connectors is critical for reducing the radiation due to the high speed signaling. In this paper, a simple new test fixture and measurement method for characterizing shielding effectiveness of a USB cable which can lead to cost-effective cable designs with optimized shielding are discussed.

Controlling common mode noise radiation through differential signalling IO buffer optimization

Non-ideal IO differential signaling from the silicon die or transmitter buffer propagating through the package, printed circuit board, connector, cable until to the external device, may cause undesirable common mode noise radiation. This common mode noise could be radiated effectively through the external cable causing the risk of EMI. Although controlling the common mode noise is critical, it is challenging to define a specification of the allowable common mode noise. This paper proposes an analytical method on estimating differential signal rise/fall time mismatch and timing skew allowable for the unintended common mode radiation on the cable that meet the regulatory requirements.

Cable radiation from common mode signals and differential mode signals

IO cable radiation is believed to be mainly from the unintentional common-mode signals transmitting on the differential lines. In this paper, an example is given by simulation and measurement that the IO cable radiation can be from the intentional differential-mode signals. This explains why populating common mode chokes to mitigate radiation is not effective.

RF Design, Power Handling, and Hot Switching of Waveguide Water-Based Absorptive Switches

This paper presents the first complete water-based waveguide absorptive switch from 25-40 GHz integrated with commercially available micropumps. The design exploits the absorptive properties of water in the microwave and millimeter-wave bands along with innovative techniques to achieve an optimized performance in both switching states. Besides its static RF performance, the hot-switching response is also experimentally characterized. Successful hot-switching measurements are presented for power levels of up to 32 and 0.16 W for circulating and noncirculating water, respectively. This is achieved with a circulation rate of only ~20 mL/min. We also show that this power handling can readily reach 125 and 1250 W if the circulation rate is increased to 30 and 300 mL/min, respectively. In addition, the dynamic scattering matrix under hot-switching conditions is also measured and compared to the cold-switching scattering matrix. Furthermore, critical temperature effects are also studied. In particular, contrary to common wisdom, we show that increased water temperature can result in improved RF isolation with the appropriate waveguide-switching design.