Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Measurement of Radiated Emissions from Integrated Circuits—Surface Scan Method (Loop Probe Method) 10 MHz to 3 GHz
SAE J1752-2 defines a standardized approach for evaluating near-field electric or magnetic components at the surface of an integrated circuit (IC). Using loop probes and precision scanning, this method identifies internal RF sources and produces color-enhanced field strength maps. It is an essential diagnostic tool for IC architectural analysis, functional floor planning, and power distribution optimization.
This method is intended for comparative IC diagnostics, not for predicting far-field radiated emissions. For consistent results, use the standardized test board specified in the standard.
🔍 Understanding the Surface Scan Method
The technique involves mechanically scanning an electric or magnetic field probe over the IC surface in a plane parallel or perpendicular to the package. The probe is connected to an RF measuring instrument (spectrum analyzer or receiver) and a preamplifier. Data is captured at each point and computer-processed to generate a color-enhanced map of field strength at a specific frequency.
According to the standard, “The resolution of the pattern is determined by the characteristics of the probes used and the precision of the mechanical probe positioner.” The method is usable over 10 MHz to 3 GHz with current probe technology.
🛠️ Key Test Setup Requirements
Proper setup is critical for repeatable measurements. The standard specifies requirements for shielding, probes, scanning system, and calibration. Below are essential elements:
| Component | Requirement |
|---|---|
| Shielding | Ambient electromagnetic noise must be minimized; a shielded room or enclosure is recommended. |
| RF Measuring Instrument | Spectrum analyzer or receiver covering 10 MHz to 3 GHz. |
| Preamplifier | Sufficient gain to improve signal-to-noise ratio. |
| Near-Field Probes | E-field and H-field probes with known characteristics; size determines spatial resolution. |
| Scanning System | Computer-controlled X-Y-Z positioner with precision of at least 0.1 mm. |
| Test Board | Use standardized board per SAE J1752-1 for comparable results. |
⚠️ Common mistakes include using a non-standardized test board, insufficient calibration, and misinterpreting near-field data as far-field radiation. Always perform an ambient check and operational verification before scanning.
Data Interpretation and Engineering Design Insights
The electric and magnetic field scans reveal the relative strength of sources within the IC package. This allows engineers to compare architectures and identify emission hotspots. Key design insight: Resolution is limited by probe size and positioning precision; smaller probes provide finer detail but may have lower sensitivity. Both E-field and H-field scans offer complementary information about emission mechanisms.
As stated in the standard, “The electric and magnetic field pattern over the surface of the IC is related to the electromagnetic radiation potential of the IC and of the electronic module of which it is a part. However, this procedure is intended to provide a comparative measure for ICs and not to predict far field levels.”
For post-processing, the appendix hints at total energy calculation, wave impedance analysis, and other techniques to extract maximum insight from scan data.
Frequently Asked Questions
1. How do I set up and calibrate the scanning system?
Follow the standard’s guidance: calibrate the system including cables and preamplifier, define the scan area and step size, and ensure the probe is oriented correctly (vertical for magnetic field, horizontal for electric field in typical configurations). Regular calibration with a known reference is recommended.
2. What probe characteristics are needed for different frequency ranges?
Probes must have sufficient bandwidth and sensitivity. For frequencies up to 3 GHz, small loop probes (e.g., 1 mm diameter) are common. The probe size affects resolution: smaller probes offer better spatial resolution but lower sensitivity. Refer to probe manufacturer specifications for frequency response.
3. How can I ensure repeatability and comparability of scans?
Use the standardized test board for comparisons, verify ambient noise levels, and maintain consistent probe height and scanning parameters. Document all settings to facilitate correlation between measurements.
4. How do I interpret the field strength maps to identify emission sources?
Color-enhanced maps show relative field strength; hot spots indicate areas of high RF activity. Compare scans with IC floor plans to associate emissions with functional blocks. Wave impedance analysis (ratio of E-field to H-field) can distinguish between electric and magnetic field dominated sources.
