EMI/EMC diagnostic and debugging

Transcription

1 EMI/EMC diagnostic and debugging 1

2 Introduction to EMI The impact of Electromagnetism Even on a simple PCB circuit, Magnetic & Electric Field are generated as long as current passes through the conducting medium Both the E & H-field will penetrate adjacent conducting medium and induce noise on it 2

3 Introduction to EMI Today s Electronic Design & EMI Debugging Trend for Embedded System Design ı Faster clock speed ı Smaller form factor ı More data lines for communications ı More design include RF technology ı Power has more impact on signals with smaller amplitude Via s Tiny-ITX motherboard More EMI issues ı Higher speed design introduces more EMI issues ı Bad PCB Layout (stacking) causing worse EMI ı RF features impact & be susceptible to EMI ı Driven by the discontinuities and resonances of the transmission path ı Extends to much higher harmonics than SI issues Cell Phone 3

4 Top Common Causes of EMI Problems (In no particular ranked order) 1 Ground Impedance 6 Stray Internal Coupling Paths 2 Poor Cable Shielding 7 Component Parasitics 3 4 Emissions from Switching Power Supplies Power Supply Filters 8 Inadequate Signal returns 9 Discontinuous Return Paths 5 LCD Emissions 10 ESD in Metallized Enclosures Ten common EMI Problems by William D. Kimmel and Daryl D. Gerke 4

5 Top Common Causes of EMI Problems Radio Frequency Interference Electro-Magnetic Interference Simultaneous Switching Noise LCM Power Supply

6 Introduction to EMI EMI Measurements in different design phases Conventional Compliance Process Testing in final phases of the product design Failing product need to be fixed Compliance Report does not provide EMI causes Product fixed cost time & resources Design Manufacturing R&D Prototype Pre-Production Manufacturing Design verifications Specifications Testing Product reviews Pre-Compliance QA Testing implementation Compliance Test EMI Test during product development Non-Compliance Feature Found problem in time & immediate adjustment Base on hardware knowledge to quickly find the possible cause Using EMI standards and design with margin CISPR 6

7 EMI Debugging with R&S Oscilloscope ı Most Common Tool for Engineers Analog Signals, Digital Bus Parallel, Serial Bus Analysis & Decode Mix Signal Oscilloscope FFT Analysis Complex Trigger Time Correlated Events ı Concerns Slow acquisition missed intermittent fault Limited Dynamic Range No correlation to Time Domain Captures Spectrum cannot be used for trigger Complicated settings EMI Filters, Detectors, and Averaging 7

8 EMI Debugging with R&S Oscilloscope 3. Important consideration #1 Acquisition speed 150 khz ~ 30MHz is scan at 9 khz at 1s Measuring Time (Smallest is 100us) RTO Spectrum Analysis is live and no sweep involve 8

9 EMI Debugging with R&S Oscilloscope 3. Important consideration #2 Ability to detect weak Signals EMI tends to be weak, to detect such signals, oscilloscope need to be able to detect them without limiting the bandwidth 1mV/div Low Noise and High Sensitivity at Full Bandwidth 9

10 EMI Debugging with R&S Oscilloscope Selecting the right tools Sniffer Probes ı Basically the probes are antenna that pickup the magnetic & electric field variation ı Depending on the position & orientation, it picks up different reading 10

11 EMI Debugging with R&S Oscilloscope Locate position of EMI faults I) General Approach ı Wide Span scan fundamental of interfering signals are usually lower than 1GHz, a span of <1GHz is sufficient as a start ı Identify abnormal spike or behavior and its location while moving the probe around ı Narrow down to smaller span and RBW, change to smaller probe for better analysis 11

12 EMI Practical Diagnosis example Locating Abnormal Spike Source with FFT Gating Our observation tell us it s an interfering signals with 80us frequency, therefore one can search through the board with Observe spikes We The Utilize Setup can interfering Culprit Notice deduced FFT Analyze Mask Gating found! that Violation signals that the interfering The tothe spike breakdown rightly signals to signal occurs detect signals appeared will that spike signals again occur behavior causes occurrence 200us at after into 80us EMI portion 80us before too such signals behaviour 12

13 Touch Panel 14

14 Other Practical Example Win 8 Tablet Testing (Courtesy from RS Taiwan) Noise from Touch Panel Acoustic Noise At 8 KHz 15

15 EMI Measurements in different design phases Design Manufacturing R&D Prototype Pre-Production Manufacturing Design verifications Specifications Testing Product reviews Pre-Compliance QA Testing implementation Compliance Test New ESR3/7 Top performance High accuracy Beyond specs verifications Real- time spectrum Fast captures of spurious noise CISPR16 compliance High speed time domain scan Pre-certification EMI Test Fast & reliable Correlate time & frequency domain Fast & accurate measurements Entry level Combo of EMI test receiver & spectrum Fully automated Entry level spectrum analyzer Light weight & compact Hi performance Wide variety of measurements Good level of accuracy Reliable Many meas. functions Fastest EMI test receiver - Time domain scan - Real time spectrum - Frequency Mask Trigger - Spectrogram - Persistence Mode 16

16 R&S Oscilloscope EMI Debugging Solution RTO HZ14 9kHz 1GHz HZ15 30MHz 3GHz HZ16 (For HZ15) EMI Debugging Set (Up to 4GHz) Oscilloscope 2x H-field probes E-field probe with built-in preamplifier Preamplifier for H-field probes Test jig for H-field probes 3x H-field probes 2x E-field probes Preamplifier 20dB 17

17 EMI Debugging with R&S Oscilloscope Summary ı The modern oscilloscope with hardware DDC and overlapping FFT is capable to do more than what the traditional oscilloscope is meant for. ı EMI Debugging with Oscilloscope correlate interfering signals with time domain with a very fast and lively update rate. ı FFT together with other mixed signal analysis on oscilloscope will allow engineers to gain different approach to isolate and converge the debugging effort easily.