Hello Valentin Buryak,
I am pasting my response on tech support case #00319883 here again.
Input pins (IN0 and IN0#) of CY2DL1504 are biased internally as in the attached document. IN0 pin is biased at VDD/3 and IN0# pin is biased at VDD/2. So, we suggest you to bias IN0 pin close to VDD/2 by using external potential dividers. E.g. Connect a potential divider of two 1K resistors on IN0 pin, which will bias IN0 pin to voltage close to VDD/2 and you can connect your AC coupled signal to this pin. Or, if your AC coupled signal has peak to peak amplitude more than VDD/3, then you can connect it directly to IN0 pin without any external potential dividers. As the resistors shown in the diagram are semiconductor resistors, its value can change from device to device but their ratio will remain the same.
Please let us know if you need any further assistance.
Thanks and Regards,