WRN-441 WRN-442 WRN-443 WRN-520 WRN-521 K type thermocouples
WRN-441 WRN-442 WRN-443 WRN-520 WRN-521 K type thermocouples, this is the easiest and most commonly used termination method that we can think of. The output impedance of the transmitting end is relatively small, so we directly connect a resistor in series on the circuit, so that the total impedance of the output impedance plus the resistance value is equal to the transmission line impedance. This can ensure the continuity of the impedance and reduce the reflection of the signal. The series termination is relatively simple to implement and the disadvantages are obvious. The resistance in series in the line will affect the rise time of the signal, which may cause problems in high-speed circuits. In addition, the output of the transmitting end is reduced due to the voltage division of the resistor. The series-terminated resistor should be placed as close as possible to the transmitting end in order to play a better role.
When the input impedance of the receiving end is relatively large, we can consider terminating a resistor to ground or to the power supply in parallel at the receiving end. The resistance value is equal to the characteristic impedance of the trace. In this way, impedance matching is achieved. This method is as simple as series termination, and the disadvantage is that it consumes DC power. It can increase the driving ability when pulled up, and can improve the current absorption ability when pulled down.
Thevenin termination uses pull-up resistors and pull-down resistors to form a termination circuit together, so that Thevenin's equivalent impedance is equal to the characteristic impedance of the transmission line to achieve impedance matching. The Thevenin termination has the advantage that both pull-up and pull-down resistors can be used to absorb reflections. When there is no signal on the circuit, it can also provide a DC level for the circuit, which is suitable for bus applications. However, the disadvantage is also obvious, that is, due to the presence of resistance, there is a DC path between the power supply and ground, and the DC power consumption is large.
The RC network termination is an upgraded version of the parallel termination, which is to add a capacitor below the resistor connected in parallel to the ground. In this way, the reflection can be reduced as well as the parallel termination. At the same time, the DC is isolated due to the presence of the capacitor, which reduces the DC power consumption. Of course, the disadvantages are also obvious. The time constant of the RC circuit will affect the rise time of the signal. It must be carefully calculated in the use of high-speed circuits.