Flytop Circuit Limited tells you that the characteristic impedance of the transmission line, also known as the characteristic impedance, is a concept that we often mention when designing high-speed circuits. When the signal is transmitted in the transmission line, at a point where the signal arrives, an electric field will be formed between the transmission line and the reference plane. Due to the existence of the electric field, an instantaneous small current will be generated. This small current exists at every point in the transmission line. . Flytop Circuit Limited tells you that the signal also has a certain voltage at the same time, so that during the signal transmission process, each point of the transmission line will be equivalent to a resistance, and this resistance is the characteristic impedance of the transmission line we mentioned. A concept must be distinguished here, that is, the characteristic impedance is for AC signals (or high-frequency signals). For DC signals, the transmission line has a DC impedance, which may be much smaller than the characteristic impedance of the transmission line. Once the characteristics of the transmission line are determined (line width, distance from the reference plane, etc.), then the characteristic impedance of the transmission line is determined.
According to the above formula, we can better understand several factors that affect the characteristic impedance of the transmission line:
1. The line width is inversely proportional to the characteristic impedance. Increasing the line width is equivalent to increasing the capacitance, which reduces the characteristic impedance, and vice versa.
2. Flytop Circuit Limited tells you that the dielectric constant is inversely proportional to the characteristic impedance. Also increasing the dielectric constant is equivalent to increasing the capacitance.
3. The distance from the transmission line to the reference plane is proportional to the characteristic impedance. Increasing the distance between the transmission line and the reference plane is equivalent to reducing the capacitance, thus reducing the characteristic impedance, and vice versa.
4. The length of the transmission line has nothing to do with the characteristic impedance. It can be seen from the formula that both L and C are parameters of the transmission line per unit length, and have nothing to do with the length of the transmission line.
5. Flytop Circuit Limited tells you that the wire diameter is inversely proportional to the characteristic impedance. Due to the skin effect of high-frequency signals, the influence is smaller than other factors.
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