Why termination resistor is needed

In RS, the twisted pair cable used is defined to have a characteristic impedance of Ohm. By adding a ohm resistor at the end of an RS transmission line, the signal will be dampened by the resistor instead of reflected into the bus. If the value of the resistor does not match the characteristic impedance of the cable, reflection may occur. In most RS configurations, two termination resistors are used. One of each is placed at the extreme end of the twisted pair cable. However, if the system is configured in a way where only one device is transmitting and the transmitter is located at one end of the cable, only a single termination resistor is needed on the far end of the cable.

At this point, you may wonder if there are instances where the transmission line would work fine without any terminating resistors. Theoretically, a differential pair signal will be distorted, if the reflection signal loses significant amplitude before the next bit is sampled by the receiver. But that defeats the purpose of differential pair cable, which is supposed to provide reliable communications over long distance without sacrificing speed.

The bottom line is, make it a practice to install termination resistors on differential pair transmission lines. The cost of the resistors and installation is insignificant compared to the potential problems caused by signal rebound. You will not need a termination resistor if the particular hardware is not the first or the last on the transmission line. It halves the value and creates a potential signal rebound.

What is termination voltage? Battery discharge termination voltage is the minimum allowable discharge voltage. Nominal voltage electrode potential from the electrode material and the internal electrolyte concentration. What is the color code for a ohm resistor? What is a terminated cable? Cable Termination is the connection of the wire or fiber to a device, such as equipment, panels or a wall outlet, which allows for connecting the cable to other cables or devices.

Remember the cable connection is not complete until all terminations are properly identified and labeled! How is CAN bus voltage measured? Disconnect all devices from the network except for the Device you wish to test and turn power on.

CAN bus diagnosis? Close search. Regular price 25 EUR. If you prefer, you can of course also contact us. Error Quantity must be 1 or more. Add to cart. What role does CAN bus termination play?

Do you have any questions? Reflection occurs when a signal travels down the length of a conductive medium and encounters an impedance mismatch. This can occur due to natural imperfections within a trace, line, or cable. However, even if there were no imperfections throughout the length of a transmission line, the ends would still represent a huge impedance mismatch, because the physical line itself comes to an abrupt end. The amount of energy of your signal that gets reflected can be calculated from the impedance mismatch using a reflection coefficient.

This is where the termination resistor comes in. Much of routing in PCB design can be considered an exercise in impedance matching, where you try to make sure the input impedance of an electrical load matches the output impedance of its signal source. The easiest way to maintain these impedances is through the careful placement of termination resistors. Parallel termination is easy to implement because the value of the resistor is easy to obtain, you only need one extra component, and it perfrorms well with distributed loads.

The only major con with parallel termination is power dissipation via a continuous DC current path to ground. The power dissipation can add up across a circuit when you start terminating multiple nets.

Another way to match the load and trace impedances is to use two load-end resistors whose parallel combination equals the trace impedance. This variation of the parallel termination can also perform well in distributed loads at the expense of a constant current leakage from Vcc to ground.