EMI/EMC Conducted immunity, using CDNs

EN 61000-4-6 calibration set up using EMCview PRO 

• Test Level 1: 1V RMS, 1 kHz / 80% AM modulated 
• Test Level 2: 3V RMS, 1 kHz / 80% AM modulated 
• Test Level 3: 10V RMS, 1 kHz / 80% AM modulated 
• Test Level X: special (unspecified)

The specified test levels are open circuit voltages at the EUT port of the CDN.

The voltages measured during calibration must be multiplied by 3 to allow for the 50 Ohm to 150 Ohm conversion and again by 2 to reach the open circuit voltage.

Hence, the measured voltage at the output of the 150 Ohm to 50 Ohm adapter is 1/6 th the voltage of the desired stress level. In logarithmic figures, the measured voltage is 15.5 dB lower than the open circuit voltage.

Example: Test level 2

U0= 3V RMS open circuit voltage at the EUT port of the CDN = 3V/6 = 0.5V RMS at the output of the 100 Ohm to 50 Ohm adapter

The required power at the output of the modulated amplifier is:

U0/6 [dBm] + CDN insertion loss + 6 dB (Attenuator) + 5.1 dB (80% AM RMS)

Assuming 10 dB insertion loss for the CDN, the required RF power is:

7 dBm + 10 dB + 6 dB + 5.1 dB = 28.1 dBm = 0.65 Watt

During calibration, EMCview Pro will make a stepped sweep, for each frequency adjusting the tracking generator level in order to achieve 7 dBm + 5.1 dB -30 dB = -17.9 dBm at the spectrum analyzer input. The tracking generator level table will then be used to set levels during the actual immunity test.

The typical insertion loss of a CDN with attached 150 Ohm to 50 Ohm adapter is 10 dB.

Adding the 6 dB attenuator and 5.1 dB for the AM RMS conversion results in a quasi-insertion loss of 10 dB + 6 dB + 5.1 dB = 21.1 dB

For open circuit voltages of 1V, 3V and 10V, the corresponding power at the output of the 150 Ohm to 50 Ohm adapter is -2.6 dBm, 7 dBm, 17.4 dBm RMS CW. Add 5.1 dB to cover the RMS power of 80% AM modulation.

Consequently, the required power at the input of the 6 dB attenuator for class 1/2/3 is 18.5 dBm / 28.1 dBm / 38.5 dBm.

The table below reflects the insertion loss versus frequency of a real CDN in order to set the required input power for the TBMDA5.

Table - measured input power settings for the TBMDA5 in order to achieve stress level 1 and 2

The maximum output power of the TBMDA5 is approximately 3 dB short with respect to power level 3. As a compromise, the 6 dB attenuator could be replaced by a 3 dB attenuator.

EMCview PRO has the capability to automatically adjust the tracking generator level in order to achieve the desired stress level voltage. The output is a calibration table, which is loaded and applied during the immunity test.

EN 61000-4-6 immunity test set up using EMCview PRO