SDAA499 September   2026 AMC0306M25

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Detailed Description
    1. 2.1 Signal Integrity
    2. 2.2 Signal Filtering
    3. 2.3 Shielding
    4. 2.4 Results
  6. 3Summary
  7. 4References

2.4 Results

Example of Enveloping a CISPR Plot Figure 2-11 Example of Enveloping a CISPR Plot

Figure 2-11 shows a plot using enveloping to trace the top of the CISPR emissions plot. This is a clever method to simplify CISPR plots and allows them to be overlaid for easy comparison.

RC Filtering Results with Different Sized Capacitors Figure 2-12 RC Filtering Results with Different Sized Capacitors

Figure 2-12 shows the results of the RC filtering in CISPR emissions. The graph overlays the envelopes of the different sized capacitors in RC filters. As seen in the plot, using a larger capacitor lowers the RC filters cutoff frequency, which brings down the EMI. This effect is more pronounced at high frequencies. Note the 0pF line is just series terminated with no capacitor.

CISPR Test Setup Figure 2-13 CISPR Test Setup

Figure 2-13 shows the test setup for the CISPR32 standard, The CISPR11 standard was used over the course of creating this application note. The only major differences are the lack of anechoic tiles between the device under test and the receiver and the frequency measurement range. The device was rotated in increments of 90° for this test and the highest magnitude for each frequency was recorded.

Device Under Test Figure 2-14 Device Under Test

Figure 2-14 shows the device used to test EMI in the chamber. One of long traces was connected to the digital output of the AMC0306M25 and the other was left unconnected. Batteries were used to power the device during CISPR testing to reduce noise from the power source.