Very-Near-Field Scanning Solutions for Pinpoint
Diagnosis of EMC Compliance Problems
Agenda
Introduction to Very-Near-Field
Very-Near-Field Implementation
High Resolution Scanner
Sample Results
Case Study
Other Applications
Conclusion
EMSCAN Introduction
World Leading Developer of Fast Magnetic VeryNear-Field Measurement Applications
Real-Time Visual Test Solutions for Antenna and
PCB Designers and Verification Engineers
Pre-Compliance Not Compliance
EMSCAN Products
EMxpert
– EMC/EMI diagnostic tool
enabling designers to rapidly
diagnose and solve EM problems
in a single design cycle in their
own lab environment
RFxpert
– APM tool enabling engineers to
quickly evaluate and optimize
their designs with real-time
antenna performance
characterization at their desk
Introduction to Very-Near-Field
Far-Field / Near-Field / Very-Near-Field
What is Very-Near-Field?
What we call the very-nearfield is the reactive region
Interaction with device under
test is unavoidable
Where the most information is
available
d
Far-Field (Chamber) Measurements
Compliance or compliance like results
Slow test time with possible queues for chamber time
No information about source of emissions
Image: www.geosig.com
Very-Near-Field Measurements
Origin of all emissions
Insight into root causes
Best applied at board level
Possible to extrapolate far-field from very-near-field
Not repeatable and difficult to get whole picture
Very-Near-Field Implementation
A Better Solution
Scanning Array of Probes
1218 probes in a 29 x 42 array
Magnetic field loop probes
– Sensitive down to -135 dBm
– Inefficient for EMI isolation
– Broadband
Scan area 21.8cm x 31.6cm
Real-time measurements ( <1 sec)
System Configuration
LAN/USB
USB
Software Application
External Trigger
Controller
Spectrum Analyzer
Control
RF
Sensor Array
Spectral Scan
Identify the frequencies of emission
Spatial Scan
Visualize where the emissions are coming from
High Resolution Scanner
Best of Both Worlds
Higher Resolution Spatial Scan
Use the same probe array for high speed testing
Probe spacing is 7.5mm
7.5mm
Higher Resolution Spatial Scan
Move the entire probe array to synthesize small
probe spacing
Level 1
Up to Level 7 (0.1mm)
Level 2
Higher Resolution Spatial Scan
Detail of small feature available
Even inside components like ICs
Level 1
Level 3
Sample Results
Following Emissions Across a PCB
Analyzing a PCB
First view of a scan give spectral content and aggregate spatial content
Analyzing a PCB
Jump around by frequency or location to follow signals
Load new PCB layers to correlate to features
Energy coupled onto power plane
Energy coupled onto control line
Analyzing a PCB
Able to follow the signal on the traces as it goes between layers.
Layer 1
Layer 2
Beginning of ground
plane shielding
control line
Layer 3
Via transition
to layer 2
Digital control
line on layer 1
Control line
continued on layer 2
Sample Results
Peering inside an IC
Emissions From Inside the IC
100 MHz
Emissions From Inside the IC
120 MHz
Different Profile
Emissions From Inside the IC
130 MHz
Comparable to Other Techniques
Probe Array
Method
Single Probe
Method
Case Study
Debugging an optical IC courtesy of
Optical Networking Unit
Passive optical network (PON)
Onboard bi-directional optical subassembly (BOSA)
Converts Wired LAN traffic to Optical Network
Chamber RE
GN25L95 (ONU) with power on
No data between GN25L95 and MAC
Chamber RE
GN25L95 with power on
Full EPON data between GN25L95 and MAC
Change Layout and Test in Chamber
Cut traces 10nF local
Fit 33R here instead.
May be better to not fit this resistor.
BOSA On Board – 2 layer PCB
Scan Conditions – Bottom Layer
Spectral Scan Results
Idle (1010)
Jitter pattern
Spatial Scan Results
Hotspots indicate high emission area.
All Ones 8b10b
Tx leads to
BOSA
All Zeroes 8b10b
Scan Conditions – Top Layer
Tx leads
Spectral Scan Results
Data of interest
Back ground noise
PRBS2^7-1
Data of interest
Back ground noise
PRBS2^23-1
Summary
The higher spectral content in the failed RE tests are due to the
patterns used for EMC compliance testing
The measured spectral content in the very-near-field scans aligns
with the theoretical FFT expectation and with chamber results
The emissions “hotspot” is the tx leads to the BOSA
Other Applications
Typical EMC Concerns
A/B Comparison
Obsolescence management
Production unit versus gold standard
Fault diagnosis
Effectiveness of Filters
Immediate feedback means trial and error can be used
Measure Self-Interference (Desense)
Sensitivity of the system can detect emissions from a conducted
power as low as -135dBm
Noise generated at 1575.039 MHz while camera is active
harms GPS performance
Other Applications
Chamber Predictions
Far-Field Prediction
VNF results to predict Open Area Test Site (OATS) or free space
radiated EMI of PCB
Far-Field Prediction
Measure the very-near-field emission from real source
Use this as a source model in a simulation package
Amplitude and phase needed
Far-Field Prediction
Standard IEC file format allows importation into many packages
Far-Field Prediction
Simulation could include large scale effect like cables, enclosures, etc.
3m
Conclusion
Very-Near-Field Array Based Measurement
Very-Near-Field Pros and Cons
Array based very-near-field testing can identify source of
emissions quickly
Changes in the lab can be validated before going to the
chamber
Intermittent or changing events can be captured
Extremely high resolution available
Very-Near-Field Pros and Cons
PCB diagnostic not product compliance
Some shapes not appropriate for testing
Trace or IC must be very close to get most benefit from
high resolution scanning
Thank You
www.emscan.com
info@emscan.com