Shubhankar Marathe

A Frequency Tunable High Sensitivity H-Field Probe Using Varactor Diodes and Parasitic Inductance

A frequency-tunable resonant magnetic field probe is designed for near-field scanning applications for the radio frequency interference studies. Tunable resonance is achieved by using a varactor diode providing the required capacitance and the parasitic inductance of a magnetic loop (i.e., a parallel LC circuit). An equivalent circuit model for the probe is described, analyzed, and used for designing the probe for achieving maximum sensitivity. The resonance frequency of the designed probe is tunable in the frequency range of 900-2260 MHz that covers multiple radio bands, such as the GSM900, UMTS, and GPS bands. The sensitivity of the probe at the resonance frequency is about 7-9 dB higher than that of an equivalently sized broadband magnetic field probe throughout the tunable frequency range. The measured frequency response and sensitivity over a microstrip trace using the fabricated probe shows good agreement with the simulated results of the equivalent circuit model and the full-wave simulation model.

Broadband phase resolving spectrum analyzer measurement for EMI scanning applications

EMI scanning application requires phase and magnitude information for the creation of equivalent radiation models and for far-field prediction. Magnitude information can be obtained using rather an inexpensive spectrum analyzer (SA). Phase-resolving instruments such as vector network analyzers (VNA) or oscilloscopes are very expensive for frequencies above 5 GHz. For this reason, this paper proposes a method that utilizes a SA for phase-resolved magnitude measurements. The basic principle is to measure the sum or difference of two signals for different phase shifts and deduct the phase from the combined output of those measurements. The phase is retrieved using an optimization procedure. It is shown that the proposed approach can recover phase deviation within 20° when using six steps of variable attenuator control voltage for the test cases between 5 and 12 GHz.

Detection methods for secondary ESD discharge during IEC 61000-4-2 testing

When an ESD (electrostatic discharge) event reaches a non-grounded metallic part within a product, the voltage of this metal part with respect to ground will increase. If the isolation to ground is insufficient, a secondary ESD event can occur. As secondary ESD often leads to system upset or damage, and to poorly-reproducible results, it is important to detect the occurrence of secondary ESD. If the discharge current is monitored using an oscilloscope, the test equipment may miss the secondary discharge waveform. This is because the time delay between the primary and secondary discharge events can vary between nanoseconds to milliseconds. This delay depends on the amount that the secondary gap is overvoltaged, its shape, humidity, etc. Present oscilloscopes do not offer functionality to auto-detect a secondary discharge event. The goal of this study is to analyze different types of secondary discharge events acquired with different measurement setups. The data is analyzed with respect to the identification of parameters which allow an automatic detection of secondary ESD, with low, false or missed detection. Since ESD guns are known to produce pre-pulse and post-pulse events due to the switching of relays inside of the gun, this creates difficulty in distinguishing the secondary discharge from the pre- and post-pulses of the ESD gun. This is a necessary step toward developing methods to auto-detect secondary events while monitoring the discharge waveform either at the ESD gun tip or at the ground strap.

Effect of Inhomogeneous Medium on Fields Above GCPW PCB for Near-Field Scanning Probe Calibration Application

In this paper, a method is proposed to calibrate a probe by placing it into a known field and referencing its output voltage to the known field. A transmission line is a convenient structure for creating such a known field. This paper presents the effect of the inhomogeneous medium on the near-field generated over a grounded coplanar waveguide (GCPW) printed circuit board (PCB) and reports the field pattern over the GCPW. GCPW PCBs are used to determine the probe factor for near-field scanning applications. A near-field scan is performed to visualize the near-field sources over a device under test (DUT). The near-field is measured by using E- and H-field electromagnetic interference probes. The output of these probes is a voltage and using the probe factor, the field present over the DUT can be determined. To calculate the probe factor, the near-field strength needs to be known using the 3-D simulation. GCPW creates a quasi-TEM field. The effect of non-TEM modes is easily underestimated, such that non-TEM fields prevent the user from determining the unwanted field suppression of probes at higher frequencies.

ESD susceptibility evaluation on capacitive fingerprint module

This paper reports on an investigation of ESD stresses on a fingerprint module. It shows that sparking to the flex connector, dielectric breakdown of the insulating layers, and transient electric and magnetic fields can cause damage. Test methods and simulation models are shown. An ESD generator and ESD field probe were used to expose the fingerprint module to currents and electromagnetic fields. Breakdown of the top insulating layer was observed. Damage due to ESD induced H-field injection occurred A 1 kŌ resistively grounded ring is proposed as an ESD protection solution for the fingerprint module system. Its effect on the discharge current is shown via simulation.

Effect of relative humidity and materials on triboelectric charging of USB cables

A USB cable can be triboelectrically charged by rubbing it against a piece of clothing, such as a sweater. If a charged cable is inserted into a connector, an ESD event can upset or damage attached equipment. To investigate charge levels and estimate the resulting voltages on a USB cable, a set of experiments has been performed in a climate chamber under five different environmental conditions. These experiments were conducted by rubbing 44 different cables against sweaters made of 100% cotton, 100% polyester, 50% wool/50% nylon, and 50% wool/50% acrylic. The resulting charge levels often reflected the material pairing, as expected from the triboelectric series. The maximum charge level reached −141 nC, or −7 kV, assuming a capacitance of 20 pF between the cable and ground.

Scenarios of ESD discharges to USB connectors

Different real world scenarios which may cause stress voltages on USB connected devices are investigated. This study identifies ESD discharge scenarios and their respective current and voltage levels, stress duration and the rise times for different USB cable shield types.

On secondary ESD event monitoring and full-wave modeling methodology

An adjustable spark gap structure is designed to generate Secondary ESD. The primary and the secondary discharge current are directly measured. The setup is modelled using CST full-wave simulation software. The goal is to predict secondary ESD induced current levels using simulation methods, to assist designers in product development in the early design stage.

ESD to the display inducing currents measured using a substitution PC board

ESD to a display may upset or damage the display or the touch circuit. The ESD may have a visible spark carrying current to the frame of the mobile device, to the connecting flex cable, or into the display by penetrating the glue between the glass layers. It may also be a sparkless ESD that causes corona charging on the surface of the glass having currents as high as 10 A. A measurement technique is presented that allows measurement of the currents on all traces, including ground of flex cables that connect from the display to the main board of a mobile device. The main board is substituted by a PCB that has the same connections to the body of the mobile device and the same shape, i.e., the same electromagnetic affects. However, all connections to the display are terminated in resistive structures that allow measuring the currents in the flex cable individually. Besides measuring ESD currents, the substitution board offers various other applications with respect to the coupling and propagation of self-interference causing signals or EMI problems.

IEC 61000-4-2 ESD test in display down configurationfor cell phones

During the IEC 61000-4-2 test the DUT is placed on a 0.5 mm insulating sheet, which is on the horizontal coupling plane (HCP). For discharge points on the back side of the phone this leads to a situation in which the display is facing the HCP. The phone or tablet forms a capacitance between 50 pF and 300 pF to the HCP. The capacitance value depends on the size of the phone, its screen flatness, and the flatness of the insulator which may deteriorate over time. The discharges to the phone lead to a large displacement current flowing through the display. This current has multiple paths to the body of the phone: via the touch electronics, via the display electronics, and directly to the body of the phone. As these currents can reach 30 A (at 8 kV contact mode) they can lead to upset and damage of both the display and the touch layers. This paper provides analysis of the display down test situation in order to show reproducibility problems. The effect of the capacitance variation is shown by the measurement and the PSPICE model. Full-wave model was used to help understand how much of the total current flows through the body of the phone. The Lichtenberg dust figure method was used to show the contribution of the corona discharge.