CDNs - Coupling Decoupling Network

What is a CDN / What is a Coupling Decoupling Network?

Coupling- / Decoupling Networks are utilized to inject common mode disturbances into the Equipment under Test (EuT). In addition, the CDNs provide adequate isolation between Auxiliary Equipment (AE) and disturbance signals. IEC 61000-4-6 (Immunity to conducted disturbances induced by radio-frequency fields) describes the requirements for CDN and their application. CDNs have a 150-Ohm common mode impedance and are available for a variety of cable types and connectors.

Coupling Decoupling Networks, commonly called CDNs for IEC-61000-4-6 conducted immunity testing, serve the purpose of Injecting common mode disturbances These CDNs also ensures these signals do not interfere (decoupling) with auxiliary equipment connected to the device under test (DUT).

The disturbing signals are coupled to the DUT through several types of CDNs such as those designed for use on power line (M series OR Power series), unscreened unbalanced lines (AF Series), shielded line (S series OR Screened series) and unshielded balanced lines (T series OR Telecom series). The M type CDNs are also used to decouple injected signals, preventing them from being fed back into the building mains.

The typical IEC-61000-4-6 test is between 150 kHz and 80 MHz, but in some cases, where small-sized equipment is considered (dimension < λ/4), Some product family standards may prescribe that the stop frequency be extended up to a maximum of 230 MHz. When using this test method up to higher frequencies, results are influenced by the size of equipment, the type(s) of interconnecting cables used, and the availability of special CDNs, etc. Further guidance for proper application should be supplied in the dedicated product standards

In order to calibrate CDNs and set the test levels you require, specific shorting adapters (ADA-X) and a set of 150-Ω to 50-Ω adapters (ADA-515-X) are required. We recommend purchasing these adapters from Com-Power since they will be needed to calibrate the test levels prior testing actual product. Typical test levels given in IEC-61000-4-6 are 1, 3 and 10 V RMS.

The CDN are supplied with calibration traceable to the SI through NIST or recognized National Metrology Institute. Com-Power also offers ISO-17025 accredited calibration.

There are two other methods of injecting common mode noise listed in IEC-61000-4-6. The preferred test method CDN method:

1. BCI probe (Bulk Current Injection probes)
2. EM Clamp (Electromagnetic clamp)

Advantages of CDNs:

• CDN coupling method is more efficient than other two methods. It needs least amount of power for the highest test level.
• Ensures accurate control of stress levels applied to device under test. 
• Designed to have common mode impedance of 150 Ohms.
• Decoupling of the auxiliary equipment (AE).

Disadvantages of using CDN:

• CDNs for unshielded applications are specific to the number of conductors within a given cable used by the DUT. For example, it is not appropriate to couple noise onto a cable with 2 conductors using a CDN that is designed for 3 conductors. The proper noise level will not be injected to each conductor. 
• CDNs are also cable type and interface specific which can lead to multiple CDN being used for a single test. For example, CDN-USB-AE is for DUTs that have USB cables, CDN-T8E is for DUTs that have balanced cables, etc.

Com-Power offers a wide selection of CDNs specifically for IEC-61000-6 testing.