Effects of Current Probe Input Port Impedance during Bulk Current Injection (BCI) Test

The Bulk Current Injection (BCI) test method performs a conducted immunity test by means of injecting interference signal current into the wiring harness of the device under test (DUT) through a current probe as a transformer. However, for some DUTs, their functions are already affected and malfunctions occur when the current probe is merely clamped on the DUT wiring harness even without applying interference signal. That's because the impedance mismatch affects the DUT signal integrity. In this work, the effects of current probe input port impedance on transmission loss and signal integrity in DUT circuits are experimentally analyzed. The analysis shows that the transmission loss of the DUT circuit fluctuates significantly and the integrity of the transmission signal in the DUT circuit is obviously affected when the current probe is directly connected to the power amplifier. The transmission loss and signal integrity can be effectively improved by connecting a 6 dB attenuator between the current probe and the power amplifier.