Electrical termination

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Types of terminators

Passive

Passive terminators consist of a simple resistor. Limited usage for highspeed applications. There are two types: a resistor between signal and ground like in Ethernet, or a resistor from the positive rail to signal and a resistor from the signal to negative rail like in SCSI. vrla batteries

Active battery separator

Active terminators consist of a voltage regulator that keeps the voltage used for the terminating resistor(s) at a constant level. 12v motorcycle battery

Forced Perfect Termination (FPT)

Forced Perfect Termination 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.

Applications

SCSI terminator.

SCSI

All parallel SCSI units use terminators. SCSI is primarily used for storage and backup.

Dummy load

Main article: Dummy load

Dummy loads are commonly used in HF to EHF frequency 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.

MIL-STD-1553

Terminating resistors values of 78.7 ohms 2 watt 1% are used on the MIL-STD-1553 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-1553B 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 (1000 to 3000 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

Electrical connector

Electrical network

MIL-STD-1553

Issues

Signal reflection

Impedance matching

Biasing

External links

MIL-STD-1553B Concepts and Considerations from MilesTek Corporation

Terminators from MilesTek Corporation

Other meaning

Electrical termination sometimes refers to manufacturing operations which connect wires together. This includes crimping, soldering, and related operations. See electrical connector.

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