It is well known that if the impedance is not continuous in the circuit, it will cause signal reflection, causing signal distortion such as overshoot and ringing, which seriously affects signal quality. Therefore, impedance matching is an important consideration when designing circuits. Impedance control of our PCB traces is not a profound technology, basically the basic capabilities necessary for every hardware engineer. Then in the specific circuit, only considering the impedance of the trace is not enough. The actual circuit is composed of the transmitting end, the connecting line, and the receiving end. What we hope to achieve is that the impedance of the entire link is consistent. However, it is very difficult to do this in the actual circuit. Generally, the output impedance of the transmitting end will be relatively small, and the input impedance of the receiving end is very high. Therefore, to deal with this contradiction, the terminating becomes a natural means. Therefore, the nature of termination is still impedance matching, which is the top priority for PCB design. The common termination methods are as follows: series termination, parallel termination, Davining termination and RC network termination. Here is a brief introduction to the differences, advantages and disadvantages of several termination methods. (1) Termination termination. This is one of the easiest and most commonly used termination methods. The output impedance of the transmitting end is relatively small, then we directly connect a resistor in series with the circuit, so that the total impedance of the output impedance plus the resistance value is equal to the impedance of the transmission line, thus ensuring the continuity of the impedance and reducing the reflection of the signal. The serial termination is relatively simple to implement, and the disadvantages are also obvious. Since the resistors are connected in series in the line, the rise time of the signal is affected, which may cause problems in the high-speed circuit. In addition, due to the partial pressure of the resistor, the output of the transmitting end is reduced. The resistors in series termination should be placed as close as possible to the transmitter to perform better. (2) Parallel termination. When the input impedance of the receiving end is relatively large, we can consider connecting a resistor in parallel to the ground or to the power supply at the receiving end. The resistance of the resistor is equal to the characteristic impedance of the trace. Impedance matching is achieved in this way. This method is as simple as a serial terminal, and the disadvantage is that it consumes DC power. When pulling up, it can improve the driving ability, and when it is pulled down, it can improve the absorption capacity of current. (3) Davidin terminated. The Thevenin termination uses a pull-up resistor and a pull-down resistor to form a termination circuit that makes the Thevenin equivalent impedance equal to the characteristic impedance of the transmission line for impedance matching. The advantage of the Thevenin termination is that both the 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, suitable for bus applications. But the shortcoming is also obvious, that is, due to the existence of the resistor, there is a DC path between the power supply box ground, and the DC power consumption is large. (4) RC network termination. The RC network termination is an upgraded version of the parallel termination. Just add a capacitor under the resistor connected in parallel to ground. This can reduce the reflection as well as the parallel termination, while the DC is isolated due to the presence of the capacitor, reducing DC power consumption. Of course, the shortcomings are also obvious. The time constant of the RC circuit will affect the rise time of the signal, and it should be carefully calculated in the use of high-speed circuits. Back Seat Headrest Pillow Phone Holder Back Seat Headrest Pillow Phone Holder,Samsung Tablet Car Holder Back Seat,Car Back Seat Organiser With Tablets,Car Back Seat Tablet Holder Ningbo Luke Automotive Supplies Ltd. , https://www.car-phone-holder.com
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