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Testing the differential output differentially!? (Read 4360 times)
vakilia
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Testing the differential output differentially!?
Jun 02nd, 2003, 3:52pm
 
Hello;

It is mostly recommended to use differential input-output configuration to avoid common mode noises and that's why in the simulation time if we look at each output (eg. in a Diff. I/O OTA), it might have much more noise including switching noise and clock feedthrough (if the circuit is sampled data one) rather than the time that we look at the difference of the outputs. However we should be able to test a real circuit in the same manner. I mean we should be able to connect the spectrum analyzer (S.A.) differentially to the outputs of the circuit (if we consider the circuit can drive two 50ohm load and the S.A. has only one input channel) and it is like connecting one of the output to the ground of the S.A. with a 50ohm resistance and the other one to the input channel of the S.A., the process that I did and I couldn't get good results because it is not a good idea to connect a wide spread ground of the S.A. to the output of a circuit generally, as I guess.
Maybe there is a S.A. that has two channels but as I know they can not show the difference of the two channel to be able to simulate the differential output mathematically in the S.A.

Do you have any idea that how the people test the real circuits differentially?

Thanks
Babal


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Mighty Mouse
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Re: Testing the differential output differentially
Reply #1 - Jun 2nd, 2003, 5:52pm
 
You have to add a balun at the output to convert the differential signal to a single-ended signal.

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vakilia
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Re: Testing the differential output differentially
Reply #2 - Jun 3rd, 2003, 10:21am
 
And it will take care of the noise reduction effect of the differential output scheme?

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Babak
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Mighty Mouse
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Re: Testing the differential output differentially
Reply #3 - Jun 3rd, 2003, 10:36am
 
Yes, the balun will reject the common mode signal.

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