PCB新聞 - PCB特性阻抗計算

訊號在傳輸過程中看到的暫態阻抗值。 訊號在每個傳播間隔中看到的阻抗Z與阻抗的基本定義一致

Z=V/I
The voltage V refers to the signal voltage added to the transmission line, 電流I是指在每個時間間隔δt內從電池獲得的總電荷量δQ, so
I=δQ/δt
The charge flowing into the transmission line (the charge ultimately comes from the signal source) is used to charge the capacitance δC formed between the newly added signal line 和 the return path in the signal propagation process to the voltage V, so
δQ=VδC
The capacitance caused by the signal traveling a certain distance during the propagation process is related to the capacitance value CL per unit length of the transmission line and the speed U of the signal propagating on the transmission line. 同時, 訊號移動的距離是速度U乘以時間間隔δt. so
δC = CL U δt
Combining all the above equations, the instantaneous impedance can be derived as:
Z=V/I=V/(δQ/δt)=V/(VδC/δt)=V/(V CL U δt /δt)=1/(CL U)
It can be seen that the instantaneous impedance is related to the capacitance value per unit transmission line length and the speed of signal transmission. 這也可以人為地定義為傳輸線的特性阻抗. 為了區分特性阻抗和實際阻抗Z, 特性阻抗中特別添加了一個下標0. The characteristic impedance of the signal transmission line has been obtained from the above derivation:
Z0 = 1/(CL U)
If the capacitance value per unit length of the transmission line and the speed at which the signal propagates on the transmission line remain constant, 然後，傳輸線在其長度內具有恒定的特性阻抗. 這種傳輸線稱為受控阻抗傳輸線.
從上面的簡要描述可以看出，有關電容的一些直觀知識可以與新發現的特性阻抗直觀知識聯系起來. 換句話說, 如果訊號接線在 PCB板 被加寬了, 傳輸線每組織長度的電容值將新增, 並且可以降低傳輸線的特性阻抗.

以上介紹了PCB特性阻抗的計算. Ipcb也提供給 PCB製造商 and PCB製造 科技