EMC analysis workflow

Transcription

1 EMC analysis workflow Antonio Ciccomancini Scogna, CST of America

2 EMC/EMI Applications Emissions Susceptibility E3

3 Typical Emissions Issues 1 2 Image courtesy of Johnson Controls Inc. 1 Slots in ground plane radiate onto cable, DM to CM current conversion Coupling between heat sink and connector bypasses signal path through PCB Coupling through vent in enclosure EMC design involves minimizing the noise, absorbing the noise, containing the noise (shielding) and diverting/filtering the noise. Stray fields/couplings/radiation are critical in EMC/EMI. Capturing these effects accurately often requires full system-level simulation.

4 USB Channel Application USB cable 3 meter radiated emissions results USB differential pair with intended differential mode signals and unintended common mode signals Several potential coupling paths that may lead to emissions effects

5 Emissions Workflow: USB Channel Import PCB layout into CST PCB STUDIO and run CST BOARDCHECK to identify critical nets Perform detailed analysis of critical nets using CST Microwave STUDIO and compute transient CM voltage Use transient CM voltage to simulate radiation from USB cable Cascading approach is only valid if the system can be decoupled

6 CST BOARDCHECK EMC Rules Checking for PCB Designs 1. Deal with a new PCB layout 5. Obtain EMC rules for layout engineers Design Cycle 2. Analyze PCB in EMC rule checker 4. Perform simulations and analyze results 3. Decide which structures need simulation

7 EMC Rule Checking Workflow Import PCB Design Altium (ODB++), Cadence, Mentor Graphics, Zuken Select EMC Rules Categories: Signal reference, Wiring/Crosstalk, Decoupling, Placement Select Nets Tag critical nets, differential pairs, or power and ground nets Select Components Tag ICs, clock drivers, stitching or decoupling capacitors, or connectors Start EMC Rule Check Press one button and wait for the EMC violations to be listed

8 CST BOARDCHECK: Rules EMC rules SI rules

9 EMC Rule Check Violations Critical Differential Net Length Matching and Spacing Critical Net Near I/O Net Critical Net Near Edge of Reference Plane

10 Partitioning of the Model / USB Channel choke to connector pins CM choke driver to choke

11 CM Signals in Channel 1 2 DM to CM coupling Source of CM voltage at connector? 1. DM to CM coupling in line 2. coupling via neighbouring line in line -25 db S 21 in db via neighbouring line -55 db frequency in GHz

12 CM Signals in Channel DM CM 1 Without CM choke With CM choke Driver output skew set to 100ps Non perfect balanced lice increases skew and CM conversion CM voltage in V 1.5 V 80 mv time in ns

13 Radiated Emissions Prediction (I) Cable shield Without CM choke 63 dbµv/m Convolution of impulse response with periodic CM noise With CM choke 34 dbµv/m 3 meter emissions scan

14 System Assembly and Modeling Schematic View Assembly View Chassis PCB Heat sinks Vented Panel

15 PCB Near Field Source Modeling Portion of chassis modeled to capture reflections

16 Chassis Emissions Baseline Case Near field source (automatically positioned based on PCB location) Heat sinks Included Heat sink Clone block

17 Vented Panel Optimization Vented Panel Plane wave excitation Parametric Sweep Task to determine optimum hole dimensions Chassis including Vented Panel Optimized vented panel positioned behind fans

18 Vented Panel Optimization Without Vented Panel With Vented Panel Surface Current 5GHz

19 Key Features for Emissions Workflows CST BOARDCHECK Identify critical nets Integrated workflows PCB + connector + cable Transient co-simulation Broadband response, field/circuit coupling (CM chokes etc.) Efficient cable and aperture modeling CS complex cable bundles, TLM compact aperture models Simulation of EMC test setup External ground plane, far-field probes, cylinder scan System Assembly and Modeling (SAM) System-level simulation of design variants

20 Typical Susceptibility Issues 4 1 Source 3 5 x Victim 2 Power Line (or other interconnecting cables) Failure criteria depends on the test A No degradation in performance, operates as intended at all times B Degradation allowed during the test, full performance must be restored following the test, without user intervention C Degradation allowed during the test, and after the test, provided that full performance can be restored automatically or by user intervention

21 ESD Generator Model The motivation for developing a detailed full 3D model of the generator is to correctly simulate the asymmetric fields generated by the discharge and their coupling to the system. Discharge current at gun tip Induced voltage in semi-circular loop Full wave model for simulating Noiseken ESD Generator Dazhao Liu; Nandy, A.; Pommerenke, D.; Soon Jae Kwon; Ki Hyuk Kim; IEEE Symposium on EMC,17-21 Aug Time animation confirms the asymmetric field distribution. This may affect the coupling to the system under test

22 ESD to Enclosure with Cable Entry External Cable Screen Bonded to Enclosure Bi-Directional co-simulation between the 3D field, cable and circuit simulations allows the effect of cable entry to be considered External Cable Screen not Bonded to Enclosure

23 ESD Transient co-simulation

24 Modeling details/ports Reader_p Reader_n tag_n tag_p Ports 3,4 (diodes) Port 1 Port 2

25 Results/currents Reader_n tag_n

26 Surface current

27 Hybrid Cable EMI Sensor SMPS Load RS485 screen Programmable switch mode power supply driving an intelligent sensor with high speed RS485 communications IGBT switching is used to generate Pulse Width Modulation waveforms to supply the sensor Import measured screen transfer impedance Interference between Power and Control circuits

28 Cable Parameter Extraction Analysis of mutual capacitance between Vpos and Vneg phase wires C +,- = pF/m C +,- = pF/m Vneg Vpos New curved tetrahedral elements in EMS electrostatic solver CST EMS can used to design cable cross section and extract parasitic values CST CS uses an internal 2D field solver to extract parasitic values for TL analysis

29 Interference Analysis Cable/circuit co-simulation CST CS used to investigate CM noise for different SMPS waveforms, cable lengths, cable screens and terminations CM Current in RS485 line Input SMPS PWM voltage

30 Typical E3 Issues I (A) 200kA peak 1.5µs rise, 88 µs fall t 300 V/m CW field 10 KHz to 40 GHz EMP E (V/m) 50 kv/m peak 1ns rise, 25 ns fall t Lightning channel HIRF Lightning Strike High Intensity Radiated Fields Electromagnetic Pulse Lightning and EMP are transient effects: peak fields and dissipated energy are critical HIRF requires analysis over an extremely wide spectrum (10 KHz to 40 GHz)

31 Field/Cable Co-Sim. Plane Wave Transient EMP Internal probe Good cable screen to chassis connection Simulation of incident EMP and effect of cable shield connection to enclosure Poor cable screen to chassis connection

32 Rotorcraft EMP Simulation Free standing curves for slots/seams Huge difference in scale! 500nm ITO thickness vs. airframe dimensions

33 Rotorcraft EMP Simulation ITO coated canopy reduces peak electric field inside cockpit from 8 KV/m to 800 V/m Solve time 200m on 8-core CPU / 4.3 GB RAM

34 EMP Protection Assessment Real world cable modeling True transient co-simulation Solid and braided screens can be added to cable model to investigate shielding Non-linear transient protection devices modeled by true transient co-simulation

35 Cosite Analysis Powerful workflows for antenna co-site and RADHAZ analysis Near Field Source

36 CST STUDIO to Saber Link Model exchange thru S-parameter and touchstone standard Fully automated Saber model export approach in CST Studio Suite Easy external model integration in Saber thru drag & drop Full support for transient & frequency analysis in Saber CST Studio Suite Saber Structural Component Model S-Parameter Computation Touchstone Exchange Format S-Parameter Model Block TR or AC Analysis

37 Common Mode Choke Example

38 Matching the Inductance Typical mue value for the ferrite was chosen Number of windings was adjusted to match inductance given in datasheet

39 Fine tuning - Common Mode Impedance Wire Resistance Inter wire capacitance 1e

40 Export into Synopsys Saber Drag and Drop the created files into the Saber library.

41 Frequency Analysis in Saber Place into Saber Schematic common mode +1V / +1V differential mode +1V / -1V

42 Hybrid Cable Example SMPS Sensor Load RS485 screen Programmable switch mode power supply driving an intelligent sensor with high speed RS485 communications Import measured screen transfer impedance into CST Cable Studio

43 S Parameters for Saber Export Broadband S parameter output to cover power harmonic spectrum Cable screens grounded Ports placed on power and RS485 pins for coupling analysis

44 Transient Analysis in Saber Place into Saber Schematic

45 Export Circuit to Synopsys Saber In addition to S parameter link, CABLE STUDIO can directly generate an equivalent circuit model for Saber Equivalent circuit derived from 2D cross section field solver and TL solver

46 Conclusions Powerful solutions for analyzing broad range of Emissions Susceptibility and E3 problems Coupling, shielding, ESD, lightning, EMP, HIRF Transient solver Direct time-domain analysis of transients such as ESD, EMP and lightning Co-simulation MWS+CS+DS co-simulation enables coupling between fields, cables and circuits Compact models Thin conducting panels, slots/gaps, joints/seams and ventilation panels Realistic cable models Twisted conductors, screens, connections to 3D structure New links between CST STUDIO SUITE and Synopsys Saber provide smooth workflow for system-level analysis