Part Number:ADC12J4000
Hi,
I'm would like to use a dc coupled line and the LVPECL standard for the communication around the ADC12J4000.
I've got some questions around the voltage values of the datasheet.
These values are shown here :
So, the common mode voltage has to be somewhere between 0VDC and 1.9VDC, and the differential swing between 0.4Vpp and 2Vpp.
First question : are those differential values |SYSREF+ - SYSREF-| ?
If it is, that would mean the minimum required single ended voltage swing is 0.4/2=0.2Vpp, meaning the single ended minimum values to be +/-0.1V.
I downloaded the ADC12J4000's IBS file, and simulated it being driven by the AD HMC7044 :
As the HMC7044's LVPECL's output common mode voltage is 2VDC, I tried to lower it to 1VDC with thoses resistors, keeping the 50R adaptation.
The results are shown here :
You've got the HMC7044's output on top, the ADC12J4000's input in the middle and the AC-coupled diff at the bottom, with the ADC's thresholds.
In the bottom right hand corner, you can see AC-coupled differential thresholds for the ADC12J4000 being +/-0.1V.
That does not correspond to my previous calculations, as I stated the single ended minimum swing should be +/-0.1V ...
If the IBS model is right, as the differential value received by the ADC12J4000 (red line in the simulation's output) is superior to the IBS threshold of the ADC, my application should be working.
If the IBS model is wrong and the real thresholds are +/-0.2V (as I understand the datasheet), my application might not work because my differential amplitude is just superior to 0.4Vpp, and I would like to have at least 150mVpp of margin.
Second question : are my previous calculations right ? If it is, is the IBS model wrong ?
Third question : Are the thresholds the same for both AC-coupled and DC-coupled modes ?
Thanks for reading, have a good day
Alexis