Filtered D-sub Connectors

L, C, LC and Pie Black filtered D Sub-miniature Connectors

Standard d-sub connectors can not guarantee protection from EMI/RFI, even when enclosed in shielded hoods. Filter d connectors and adaptors are an ideal solution to reduce or eliminate EMI.



EMI can be any unwanted electrical or electromagnetic energy that causes undesirable responses, degraded performance or failure in electronic equipment. Radio Frequency Interference (RFI) is a more specific term often used interchangeably to describe the phenomenon. A filtered d-sub connector is widely recognised as a very effective way to reduce noise either entering or exiting an EMI enclosure because it can often be incorporated into a product late into the design process; even after emission problems have been detected. Noise induced on a signal line within the box can be removed as it passes through the filter D, hence preventing radiation to adjacent equipment. Filtered dsub connectors are also used to provide system immunity from external noise sources. Filters integrated into D-sub connectors to achieve a reduction in conducted EMI have evolved over the years using a variety of elements and materials to achieve varying degrees of noise suppression. These filters are broadly identified as low-pass filters. A low-pass filter allows lower frequencies to pass through the filter with minimal reduction in signal strength, while attenuating signals with higher frequency.

A filter element achieves this by essentially becoming a variable resistor connected between the signal lines and ground. The resistive value is inversely proportional to the frequency of the signal it is conducting. As the frequency increases, the resistance of the filter decreases, providing a lower impedance path to ground. The capacitors strip off the interfering noise from the signal as it passes through the filter device whilst diodes are used to clamp the voltage below a certain value, thereby protecting the electronic circuitry.
Filters can selectively attenuate specific frequency bands by introducing controlled impedance mismatches into the line. A low-pass filter effectively strips higher frequencies to ground while allowing desirable lower frequencies to pass through the filter. Filtered connectors are typically bi-directional, in that they can attenuate noise originating from either side of the filter, an important advantage when considering immunity.

Many different configurations of filters have been developed to address a variety of circuit requirements. The simplest design is the C or feed-through filter which consists of a single capacitor inserted between the signal line and ground. As the conducted signal frequency increases, the effective resistance of the capacitor decreases, and therefore shunting higher frequencies to ground. The result is a filter that passes lower frequencies while attenuating higher frequencies.

The so-called C-filter is arguably the common standard. In this single-stage low-pass filter, each contact of the connector is connected with a capacitor to the connector housing (ground). Other options that can be used depending on the problem to be solved are the two-stage LC and the three-stage PI filters (C-L-C), which are also available in various connector configurations in the standard product range.

With a large differential between operating and interference frequencies, a single C-filter is often a sufficient solution for the EMI problem. If the differential is small, multistage filter configurations can be used. A C-filter suppresses the interferences from the “3dB point” by approx. 20 dB, an LC filter with approx. 40 dB and a PI filter with approximately 60 dB per decade.


Key Features

Key Features

  • L Filters- The L filter consists of one Capacitive element and one inductive element. This type of filter may be used with either a low impedance source and a high impedance load or a high impedance load. “L” ferrite filter connectors are ideal for applications where a small amount of filtering is required or the elimination of parasitic frequencies. “L” filter connectors are very cost effective.”L” filter connectors are available in the standard D-subminiature format from 9 to 37 positions and in the high density format from 15 to 62 positions.
  • C Filters- “C” filter connectors are made with patented planar filter technology. Planar Arrays are extremely effective at filtering high-frequency interference. The C Filter is a low inductance, feed through capacitor. It is used to attenuate high frequency signals. For special filter requirements such as selective filters, other types of filters can be implemented. “C” filter connectors are available in the standard D-subminiature format of from 9 to 50 positions, and in high density format from 15 to 78 positions.
  • LC Filters- for certain applications it may be necessary to use ferrites and capacitance to achieve the filtering requirements. “LC” filter series of connectors increases the insertion loss by approx. 5 dB depending on the frequency range. The ferrite block is attached externally to the connector contacts. The attachment of the ferrite block does not change the physical size of the connector.
  • Pie Black Filters- using planar technology these connectors offer an insertion loss of 45dB at 100 MHz and as high as 90dB at higher frequencies. PI filter connectors can be implemented where high performance in high frequency applications is required. PI filter connectors utilise two patented planar filters and one inductive element. The PI filters provide low impedance at the source and the load. PI filter connectors provide better performance if compared to C or L type filters. PI filters are available in adapter, right angle, PC and solder cup configurations.
  • Footprints, board fixings and accessories as per standard or High Density D connectors.
  • Versions available with Dielectric Withstand Voltage of up to 1500 Vdc.
  • Filtered mixed layout styles available
  • Popular versions such as 2W2C, 3W3, 3W3C and 5W5 are available with totally integrated capacitance filters.
  • The filter capacitance ranges from 1.3nF to 100nF on each contact position.
  • Contacts with current ratings from 10A to 40A are available with solder bucket, straight PC, 90º PC or Press Fit tails.
  • MIL-DTL-24308 D-Subminiature filter connectors are designed to meet or exceed all applicable requirements of the military specification. The filter connectors are intermateable and interchangeable with standard non-filtered connectors from all quality connector manufacturers.



  • Shell – Steel
    Tin plated (Plugs EMI/RFI dimpled)
  • Insulator – Polyester GF, UL 94V-0
  • Contacts – Machined or S/Formed copper alloy, plated hard acid gold over nickel solder area tin plated
    Class 3 = 50 cycles
    Class 2 = 200 cycles
    Class 1 = 500 cycles


  • Capacitor values
Standard HDD
180pF +/-20% 180pF +/-20%
370pF +/-20% 370pF +/-20%
830pF +/-20% 830pF +/-20%
1300pF +/-20%
  • Current
    Standard 5A @ 20ºC.
    HDD 3A @ 20ºC.
  • Working Voltage
Standard HDD
Standard 100Vdc 100Vdc
High 100Vdc
Ultra High 200Vdc
  • Dielectric Withstand Voltage
Standard HDD
Standard 424Vdc 300Vdc
Standard () 300Vdc
High 707Vdc
Ultra High 1500Vdc
Ultra High ( & >1300pF) 1000Vdc
  • Voltage surge
10/700µs Standard HDD
Standard 300V
High 500V
  • Contact Resistance
    Before use – max 10m Ohm Sign
    After use – R max 10m
    Insulation Resistance – > 1 G @ 100Vdc


  • Mating/unmating forces
No. of Contacts Standard HDD
9 15 <30N <50N
15 26 <50N <83N
25 44 <83N <110N
37 62 <123N <170N
50 78 <167N
  • Mechanical operations –
    50 cycles
    200 cycles
    500 cycles


  • Working temperature:
    Standard D -25º to +105ºC
    HDD -25 to +85ºC
  • Humidity – 40ºC/85% relative humidity


Adaptor, C-LC-Pie Black-Filter
Plug and socket solder bucket L-Pie BlackFilter
Plug and socket straight PC C-Pie Black-Filter
Plug and socket 90º PC (0.318″) C-LC-Filter
Plug and socket 90º PC (0.350″) C-L-LC-Filter
Plug and socket 90º PC (0.370″) C-L-LC-Filter
Plug and socket 90º PC (0.370″) C-L-LC-Filter
Plug and socket 90º PC (0.590″) C-Pie Black-Filter
Dual port C Filter 90º PC (0.625″)
Dual port C Filter 90º PC (0.750″)
Filtered (mixed layout) D connectors
Ferrites for standard and High Density D connectors
EMI/RFI gasket connector shield
Hoods and accessories



Plastic In/Out connectors penetrating shielded enclosures can cause a breakdown in screening since the connector’s isolating body provides no shielding against any interference signals that may be present. Therefore high frequency interference signals can be passed in or out of the system without hindrance. The connector’s contacts may act as antennas that receive and transmit interference signals because filtering is typically implemented on the PC board. Interface connectors with integrated filters can be of benefit in these cases. Filter D-subminiature connectors contribute to the protection of EMC zones. The integrated filter inside the connector saves PCB-space and can be installed into an existing PCB layout. To replace an unfiltered connector with a filtered one is simple and effective, either at the design stage or retrospectively.

The de-facto standard filter is the so-called “C filter”. Depending on the problem situations, other possible variations can be employed; a two-stage LC filter and a three stage PI filter (C-L-C) are also available in various connector configurations within the standard product line. CONEC filter connectors are an effective way to guard against electromagnetic interference (EMI RFI).

In2Connect market a series of EMI-filtered connectors that provide near linear performance up to 1GHz and beyond. The EMI-filtered D-subminiature connector series features a proprietary ceramic planar that provides a higher linear performance with better insertion loss yet remains competitively priced with the ‘chip cap’ types. Traditional filter connectors that function from 100 to 300 MHz, used with on-board filter capacitors, cannot provide the same level of insertion loss, conserved board space, or reduced components count as these new EMI-filtered connectors.

Filtered d type connectors are available as solder bucket and straight or right angled PCB, in standard, high density and dual-port configurations.

Filtered, mixed layout d connectors are ideal for power line filtering. Their small size means that they can be installed directly onto the backplane, backpanel, or power supply cable. These connectors and Adaptors are UL and CSA approved.

Because of the wide range of configurations available (including waterproof IP 67), these connectors are built to order.