Is this a good termination scheme?

[sys_eng]

I have a driver output impedance of 100 ohm, the line impedance is 50 ohm and the receiver gate input impedance of infinite.

so, to have a match impedance , on the output side, I throw a parallel 100 ohm with driver output 100 ohm , together it will give me 50 ohm to match the line impedance.

On the receiver side, the gate input impedance of infinite, therefore I throw a 50 ohm parallel termination resistor
50 || infinite =50 ohm to match the line impedance.

Is this a correct way to go?

 

[KlausST]

Hi,

I´d say it is correct.

But are you sure the driver with it´s 100 Ohms output impedance is the right choice?

Your output voltage signal will be 25% of the unloaded driver output signal.


Klaus

 

[ted2]

As a matter of fact, by eliminating the receiver termination, you would get 50% of the driver's open circuit voltage in the receiver end, without any problems. That configuration is called "series termination", and there the driver side is terminated correctly. Usually one uses a low-impedance driver with a resistor in series. In that termination mode the driver end produces only 50% to the cable, as you shunt/waste half of the signal in the driver side's extra terminator. When we look at the receiver side, the incoming signal in receiver end is fully reflected from an "open" (high-impedance) transmission line end, and that reflection lifts the received signal to double of the incoming one (which is now only 1/4 of the generator output, giving in the end 1/2 of generator's voltage). When the reflection arrives back to the driver side, it is absorbed by the termination, and is not re-reflected / disturbing later.

That is about the best you can do if you can't have lower impedance driver sending the signal out to the transmission line.

 

[albbg]

Are you sure the driver output is single ended: could it be, instead, a 100 ohm differential ?

However what about the frequency and the shape of your signal (square wave, sinwave, etc.) ?

 

[D.A.(Tony)Stewart]

in theory, this is a matched impedance system, but signal level , frequency, and cable quality depends on application for acceptable losses.