Fail safe input

It can be achieved easily if you connect a resistor to the power signal and this will place a high voltage on the input line. A look at TI's old design in LVDS drivers has the input lines connected to the power line thro' a high resistor(300k). But the simulations work for even a low resistor(say 1k).Why is it a very high value?Am i missing something fundamental about simulation program here.

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Well, simulations don't always behave like the real thing. SPICE models don't work outside their range of applicability. And simulations should never override common sense. I think all you need is common sense here.

The impedance of a typical LVDS cable/driver is 100 ohms so whether the resistor is 1K or 300K, it's a comparatively high-impedance connection to the voltage source.

What is your "high voltage"? If high voltage is greater than 5V then you will likely have degraded noise immunity/improper operation with a

1K resistor.


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Tim Shoppa

The high voltage is 2,5V.Thanks for the reply.

Is is possible to find a the resistance value that would give a good enough noise immunity?Cos 300K is a pretty high value and I want to know how a 100K would be any different considering 100k is still very high impedance compared to 100 ohm of a LVDS cable.

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