Hi Sir,
In our system the VS+ will have some deviation it will from 4.9V~5.3V.
We found the VS+ will cause the output level change , you can see below picture , is there any reason for this different?
for VS+ = 5.3V , VS= 5V , The Vp-p equal to 5.16Vp-p
VS+ = 4.9V , VS- = -5V , The Vp-p equal to 4.86V.
Hi Guenter,
Thanks for take care this question.
Please see the below circuit.
We have try to fixed the Vpole , Vgain , Voffset , Vpeak by external power supply and also verify the input signal level is stable during the V+ changing.
The input signal is come from AD8143 , AD8143 also use same VS+ , VS- with AD8123.
But we see the video signal is very stable even the VS+ changing.
We understand the Vpole , Vgain , Voffset , Vpeak will relate to output level , so we have tested it to set Voffset to 0 to make sure the Video offset level.
AD8123 is really old product for VGA signal extention , but some customer will design auto calibration and use sync-on color circuit , before the VGA output , the circuit need separate the H/Vsync , normally need rely to circuit like compactor, if the Video signal level and offset vibration that will get some effect with H/Vsync.
However , customer already modify thier H/Vsync recover circuit , but just not understand the reason for the level change during V+ change.
As datasheet mentioned , the voltage will relate to common mode voltage , so i guess it maybe reason to get output DC offset change during V+ change.
But i can't find any idea for the signal level change. 
