What is the difference between IDC and crimp?

Transmission line impedance matching

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For other uses, see Termination

In electronics, electrical termination is the practice of ending a transmission line with a device that matches the characteristic impedance of the line. Termination prevents signals from reflecting off the end of the transmission line. Reflections at the ends of unterminated transmission lines cause distortion, which can produce ambiguous digital signal levels and misoperation of digital systems. Reflections in analog signal systems cause such effects as video ghosting, or power loss in radio transmitter transmission lines.

Transmission lines

Signal termination often requires the installation of a terminator at the beginning and end of a wire or cable to prevent an RF signal from being reflected back from each end, causing interference, or power loss. The terminator is usually placed at the end of a transmission line or daisy chain bus (such as in SCSI), and is designed to match the AC impedance of the cable and hence minimize signal reflections, and power losses. Less commonly, a terminator is also placed at the driving end of the wire or cable, if not already part of the signal-generating equipment.[1]

Radio frequency currents tend to reflect from discontinuities in the cable, such as connectors and joints, and travel back down the cable toward the source, causing interference as primary reflections. Secondary reflections can also occur at the cable starts, allowing interference to persist as repeated echoes of old data. These reflections also act as bottlenecks, preventing the signal power from reaching the destination.

Transmission line cables require impedance matching to carry electromagnetic signals with minimal reflections and power losses. The distinguishing feature of most transmission line cables is that they have uniform cross-sectional dimensions along their length, giving them a uniform electrical characteristic impedance. Signal terminators are designed to specifically match the characteristic impedances at both cable ends. For many systems, the terminator is a resistor, with a value chosen to match the characteristic impedance of the transmission line and chosen to have acceptably low parasitic inductance and capacitance at the frequencies relevant to the system. Examples include 75-ohm resistors often used to terminate 75-ohm video transmission coaxial cables.

Types of transmission line cables include balanced line such as ladder line, and twisted pairs (Cat-6 Ethernet, Parallel SCSI, ADSL, Landline , XLR audio, USB, Firewire, Serial); and unbalanced lines such as coaxial cable (Radio antenna, CATV, 10BASE5 Ethernet).

Types of electrical and signal terminators

Passive

Passive terminators often consist of a single resistor; however, significantly reactive loads may require other passive components such as inductors, capacitors, or transformers.

Active

Active terminators consist of a voltage regulator that keeps the voltage used for the terminating resistor(s) at a constant level.

Forced perfect termination

Forced perfect termination (FPT) can be used on single ended buses where diodes remove over and undershoot conditions. The signal is locked between two actively regulated voltage levels, which results in superior performance over a standard active terminator.[2]

Signal Termination Applications

SCSI

All parallel SCSI units use terminators. SCSI is primarily used for storage and backup. An active terminator is a type of single-ended SCSI terminator with a built-in voltage regulator to compensate for variations in terminator power.[citation needed]

Controller Area Network

Controller area network, commonly known as CAN Bus, uses terminators consisting of a 120 ohm resistor.

Dummy load

Dummy loads are commonly used in HF to EHF circuits.

Ethernet coaxial 50 ohm

10BASE2 networks absolutely must have proper termination with a 50 ohm BNC terminator. If the bus network is not properly terminated, too much power will be reflected, causing all of the computers on the bus to lose network connectivity.

Antenna network 75 ohm

A terminating resistor for a television coaxial cable is often in the form of a cap, threaded to screw onto an F connector. Antenna cables are sometimes used for internet connections; however, RG-6 should not be used for 10BASE2 (which should use RG-58) as the impedance mismatch can cause phasing problems with the baseband signal.

Unibus

The Digital Equipment Corporation minicomputer Unibus systems used terminator cards with 178 Ω pullup resistors on the multi-drop address and data lines and 383 Ω on the single-drop signal lines.[3]

Terminating resistor values of 78.7 ohms 2 watt 1% are used on the MIL-STD- bus. At the two ends of the bus, resistors connect between the positive (high) and negative (low) signal wires either in internally terminated bus couplers or external connectorized terminators.

The MIL-STD-B bus must be terminated at both ends to minimize the effects of signal reflections that can cause waveform distortion and disruption or intermittent communications failures.

Optionally, a high-impedance terminator ( to ohms) may be used in vehicle applications to simulate a future load from an unspecified device.

Connectorized terminators are available with or without safety chains.

See also

References

IDC or Crimp? When discussing options for cable assemblies, designers frequently ask if we recommend discrete wire cable assemblies with crimped contacts or insulation displacement connectors (IDC) with ribbon cable. Our answer is it depends on your application. Crimped connectors and IDC are both reliable connector systems and each has its own list of advantages and disadvantages.

Before we get to those lists, just to make sure we&#;re all on the same page, here are quick definitions of each connector type, courtesy of Wikipedia:

&#;An insulation-displacement contact (IDC), also known as insulation-piercing contact (IPC), is an electrical connector designed to be connected to the conductor(s) of an insulated cable by a connection process which forces a selectively sharpened blade or blades through the insulation, bypassing the need to strip the conductors of insulation before connecting. When properly made, the connector blade cold-welds to the conductor, making a theoretically reliable gas-tight connection.&#;

IDC cable assemblies are available on 1.27 mm pitch, 2.00 mm pitch, and 2.54 mm pitch. Most are double-row connectors, but a few are single row.

&#;Crimped connectors are a type of solderless connection, using mechanical friction and uniform deformation to secure a connector to a pre-stripped wire (usually stranded). Crimping is used in splice connectors, crimped multipin plugs and sockets, and crimped coaxial connectors. Crimping usually requires a specialised crimping tool &#;&#;

Discrete wire connectors come in a variety of centerlines, sizes, shapes, and wiring configurations.

Insulation Displacement Connectors (IDC)

IDC&#;s are quicker, and therefore less expensive, to manufacture. Literally dozens wires and contacts can be terminated at one time.

The insulation on the wires does not have to be stripped prior to termination, or soldered, or individually crimped. This saves a lot of time and therefore money.

Most IDC&#;s can be terminated by a basic hand press or other simple tool.  For that matter, generally, much lower forces are required to terminate the ribbon cable to the IDC contacts.

IDC has been around since the &#;s and is an accepted connector design. It&#;s so accepted that connector companies offer a large variety of design and manufacturing options. They are available in a variety of wire gauges, pin sizes and centerlines. Mating connectors for the IDC cable assembly incorporate options to increase the ruggedness of the assembly with features like locking clips, ejection latches, strain relief, and polarization, to name just a few.

Assuming you are purchasing your components from a reputable connector supplier (like Samtec!), IDC&#;s are gas-tight and vibration-proof because of the quality of the design and manufacture of the contacts and plastic insulators which house them.

In the assembly process the metal blades penetrate any surface oxides on the wire.

In our opinion one of the biggest disadvantages of ribbon cable and IDC is the cable is relatively inflexible and stiff, and the cable pretty much has to travel from one point of termination to another in a relatively straight line, or with minimal bends and angles.

Crimped Connectors (Discrete Wire)

Because cable assemblies with crimped connectors almost always incorporate discrete (individual) wires and not ribbon cable, these crimp cable assemblies can fit into some tight areas that ribbon cable can&#;t. They can bend, angle, and flex into some tight bends and small nooks and crannies. As mentioned previously, IDC cable assemblies pretty much have to go straight ahead and can&#;t bend. 

Discrete wire assemblies can break-out from a higher pin count connector to several smaller position connectors. You can also do this with IDC, but you have more flexibility and options with crimped connectors.

Crimped systems allow designers to use two or more wire sizes in one cable assembly, allowing the same connector to route both signal and power. This design can save board space, and it can allow the designer to use fewer connectors. It is popular on 2.54 mm pitch connectors because those contact systems accept a wide range of wire gauges, from 20 to 30 AWG.

Crimped connector assemblies let designers transition from one connector pitch to another. A common example is switching from 2.54 pitch to 2.00 mm pitch. Perhaps the most common application is a designer needs to connect their PCB to a PCB or device from another supplier. They may design a smaller pitch termination on their PCB to save real estate.

We frequently pull pins between &#; in other words, selectively populate &#; the plastic insulator to meet creepage and clearance requirements.

Like IDC, crimped contact systems are available in a large variety of design and manufacturing options:  a variety of wire gauges, pin sizes, centerlines, latches, and options to increase the ruggedness of the system.

The biggest disadvantage is cost, primarily in assembly and manufacturing time, and tooling and assembly can be more complex.

I&#;m sure if I thought longer I would come up with more differences between these two systems, but I think we&#;ve covered the main points.

IDC or Crimp?

Click here lean more about Samtec IDC cable assemblies and components.  And click here to learn more about Samtec crimped (discrete wire) assemblies and components. And finally, here&#;s a link to a blog I wrote a few years ago listing some of Samtec&#;s most requested discrete wire cable assemblies

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