What is a Coupling Decoupling Network or CDN?

A CDN (Coupling Decoupling Network) is a device used in conducted immunity EMC tests that are performed as per IEC/EN 61000-4-6.  The main function of the CDN is as follows.

1. Couples the RF disturbance signal from the RF signal generator into the cable connected to the EUT.

2. Decouples (blocks) this RF signal from affecting powers source and/or other associated auxiliary equipment (AE). 

3. Provides standardized common-mode impedance (150 ohms) for the EUT power lines, which is independent of the external power line impedance.

The CDNs can be used to inject the common-mode signal as well as the differential mode signal to the EUT port.

EMC immunity tests are conducted during the product development stage to check whether the product operates properly when exposed to a significant level of RF interference. The EMC immunity tests are of two types - conducted immunity tests and radiated immunity tests (via air). The conducted immunity test is performed to check whether the equipment operates properly when subjected to the significant level of RF conducted disturbance. The RF conducted disturbance is created by injecting the RF inference signal (noise voltage/current) into the equipment under test (EUT) through the connection cable of EUT. There are three devices that can be used for the injection of the RF signal onto the cable: CDN, BCI (Bulk current injection clamp), and EM clamp. Usually, the CDN is the preferred device to inject the RF signal.

Coupling decoupling network (CDN)

Working principle of CDN:

The CDN device uses passive components like a resistor & coupling capacitor for injecting the RF disturbance into a cable and uses the decoupling inductor to decouple the RF inference signal between the RF input port and auxiliary equipment (AE) port. The basic CDN concept and its function are shown below.    

The RF signal path shows that the coupling capacitor & resistor provide a path for injecting the RF inference because it provides a low impedance path at RF frequencies. On the other side, the decoupling inductor provides a high impedance path at RF frequencies; hence the inductor blocks the RF signal from entering the other associated auxiliary equipment. 

CDN types:

Different types of CDNs are available to perform conducted immunity tests on equipment with several types of connecting cables like the main power line, balanced cable, screened cable, unscreened cable, and unshielded twisted pair (UTP). The CDNs are ideal for use in conducted immunity tests of EUT as per IEC/EN 61000-4-6.   

Specification details of coupling decoupling network (CDN):

Frequency range: Represents the operating frequency of the coupling decoupling network. Usually, the operating frequency range is from kHz to MHz. 

Cable type: Represents the CDN is designed to inject RF inference signal on this cable. The cable-type may be a main (main power line)/balanced lines/unbalanced lines/screened lines/unscreened lines/ coaxial cables/telecommunication ports/unshielded twisted pair (UTP).  

Number of lines: Represents the number of lines that can be RF injected by the CDN. It can inject the RF disturbance signal into the single line/ two lines/four lines/five lines…etc.

Common mode impedance: Represents the common-mode impedance of the EUT port of the CDN. Usually, it has a value of 150 ohms. 

Decoupling isolation: Represents the signal isolation between the RF input port and the auxiliary port. It is represented in dB.

Insertion loss: It is the loss due to the insertion of CDN in the measurement circuit (RF in –EUT). It is expressed in decibels (dB).   

EMC standards: Represents the EMC standards to which the CDN comply.

Input power: Represents the input power requirement of CDN. It is represented in Watts (W).

Connectors: Represents the connector type associated with the RF input port of the CDN.

Connector AE: Represents the connector type associated with the CDN for auxiliary equipment connection.

Connector EUT: Represents the connector type associated with the CDN for the EUT equipment connection.

Operating current: Represents the operating current of the coupling decoupling network. It is expressed in Ampere (A).

Weight: Represents the weight of the CDN in Kg.

Coupling Decoupling Networks, also known as CDNs from the leading manufacturers. View product details, download spec sheets, and request quotes on products that meet your requirement.