请教LVDS接收器是否需要在差分输入端加上100Ω电阻

vszombie

需要实现上图这样的从 L号转换为CMOS信号的功能，要做一个LVDS接收器。
现在不清楚图中那个100Ω的终端匹配电阻只是在仿真时加上，还是要做在实际电路里，放在M1和M2之间。

方块forever

应该是在实际电路里也要加上的

gubels

Yes, required to balance the termination at both side TX and RX.

Also to maintain the DC common mode between two differential inputs.

vszombie

gubels 发表于 2021-5-14 21:51
Yes, required to balance the termination at both side TX and RX.

Also to maintain the DC common mod ...

谢谢。DC common不是由LVDS TX端发过来的吗?

是不是需要AC couple，然后在receiver差分输入这里另外给一个DC bias？

DamonTam

LVDS transmitter的话应该都是current mode，没有100ohm resistive loading的话输出会饱和的。

vszombie

DamonTam 发表于 2021-5-17 22:25
LVDS transmitter的话应该都是current mode，没有100ohm resistive loading的话输出会饱和的。 ...

谢谢。
意思是LVDS TX传输过来的是电流信号，然后需要这个电阻把它转成电压信号吗？

vszombie

糊涂了，LVDS传输的到底是电压信号还是电流信号...

磐磬

vszombie 发表于 2021-5-19 16:25
糊涂了，LVDS传输的到底是电压信号还是电流信号...

电流信号

vszombie

磐磬 发表于 2021-5-19 17:20
电流信号

那为啥LVDS定义的是350mV振幅的信号...不应该是多少电流么...

bo_feng

LVDS is a differential signaling system, meaning that it transmits information as the difference between the voltages on a pair of wires; the two wire voltages are compared at the receiver. In a typical implementation, the transmitter injects a constant current of 3.5 mA into the wires, with the direction of current determining the digital logic level. The current passes through a termination resistor of about 100 to 120 ohms (matched to the cable's characteristic impedance to reduce reflections) at the receiving end, and then returns in the opposite direction via the other wire. From Ohm's law, the voltage difference across the resistor is therefore about 350 mV. The receiver senses the polarity of this voltage to determine the logic level.

wiki上lvds的介绍。