LVDS 100 Ohm termination on driver side

[IADanilov]

lvds termination

Hello.

For which data rates it is necessary to use 100 Ohm termination resistor on driver side?

 

[coolstuff07]

sata termination

Hi,

Termination is done at receiving end and it does not depend on data rate.

Bye.

 

[dipnirvana]

100 ohm terminator

I think this depends on the rise/fall time of the signal you are transmitting. As a thumb rule , termination resistor not required to have if rise time of a signal is at least four times longer than the one-way propagation delay through the cable.

And data rate normally depends on rise time as buad rate <=0.3 rise time

 

[IADanilov]

differential signal 100 ohm termination

coolstuff07, I mean additional 100 Ohm resistor.

 

[PaloAlto]

lvds100

termination resistor not required to have if rise time of a signal is at least four times longer than the one-way propagation delay through the cable.

I don't understand that. When you say rise time, you mean the 10% to 90% time?

And data rate normally depends on rise time as buad rate <=0.3 rise time

And I don't understand this either, baud-rate is in bits per second, and rise time in seconds, how do you relate them?

Thanks

 

[FvM]

lvds 100 ohm termination

Apart from this particular confusion, the quoted answer is missing the LVDS discussion completely. As said, the LVDS standard is based on a receiver side termination. It's not optional (e.g. depending on the signalling rate) but required, also to achieve the specified signal level.

It's allowed however, to use an impedance matched transmitter as well, but not required for the signal rates covered by the standard. Faster differential standards as PCIe or SATA are requiring termination at both sides.

 

[PaloAlto]

why is a 100 ohm resistor needed for lvds

It's allowed however, to use an impedance matched transmitter as well, but not required for the signal rates covered by the standard. Faster differential standards as PCIe or SATA are requiring termination at both sides.

Oh! I see, so, you think that for rates up to say 1Gbps, impedance matched transmitter is not needed?

What about common mode? What should its BW be? If it is the same as differential, wouldn't that consume way too much power?

 

[FvM]

100ohm termination

LVDS receivers are required to have a high common mode impedance, so the drivers common mode properties are mainly a matter of susceptibility to interferences, I think. A commonly used architecture involves switched current sources and common mode voltage feedback path to balance them. If the bandwidth is sufficient below the signaling rate (most likely it is), it will also affected by the common mode load capacitance (connected cable length).