Application case and specific test method of spectrum analyzer in DDI EMI test of mobile phone screen
DDI, or Display Driver IC, is a crucial component in display panels that "scans" digital image signals onto LCD or PDP screens. In the mobile phone industry, especially within Samsung and across the broader market, there's a clear shift in display technology development. Not only are major manufacturers expanding into the DDI space, but even smaller and mid-sized system suppliers are now entering this field. DDI technology is increasingly integrated into various electronic products, such as mobile devices, often combined with multimedia application processors (APs) to provide complete phone modules for more manufacturers.
For electronic products, especially mobile devices, electromagnetic compatibility (EMC) testing is one of the most critical and challenging assessments, particularly in foreign markets. Among these, EMI (Electromagnetic Interference) testing—especially the suppression of radiation noise—is notoriously difficult to pass.
One of the key tests we conduct during our customers' EMI testing is the DDI EMI Noise test. For instance, the RIGOL DSA815 can be used for basic EMI qualitative analysis on the DDI of a mobile phone screen. The test method and results are illustrated below:
Figure 1: Test connection method
Solution Configuration:
- Equipment Name: Spectrum Analyzer – RIGOL DSA815 (9kHz–1.5GHz)
- Near-field Probe: Germany Langer RF2
- PC Software: Ultra Spectrum
- External Preamp: Optional
- Fix Bracket: Customized according to need
During the test, we need to capture the peak values of 16 frequency points between 700MHz and 1GHz. However, the DSA815 only displays up to 10 peaks at a time, so we use the PC software for more detailed analysis:
Figure 2: Using PC software to analyze and read frequency point results
Test Conditions:
- Frequency Range: 700MHz - 1GHz
- RBW/VBW: 10kHz
- Sweep Points: 2000
- Number of Sweeps: 5
- Attenuation: 0dBm
- Test Environment: Clean, without other complex interference sources
Testing Process:
First, we reset the DSA815 to factory defaults, connect the near-field probe, set the start frequency to 700MHz, end frequency to 1GHz, and span to 300MHz. We turn on the preamplifier and set input attenuation to 0dB. This helps reduce the instrument’s internal noise floor, allowing us to detect weaker radiation signals. The number of sweeps is set to 5, and sweep points to 2000. The near-field probe is placed approximately 3mm away from the DDI at the top of the phone screen while the screen is lit in white. We scan the area systematically, moving from top to bottom and left to right. The test results are then viewed via the host computer software, which displays the peak values of the 16 frequency points.
Process Summary:
The most common application of a spectrum analyzer is in EMI pre-testing. Through qualitative EMI analysis, we can gradually improve product performance and ensure compliance with international standards. This not only reduces the cost of third-party testing but also saves significant time in the development cycle.
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