I designed a circuit that has an analog signal conditioning portion, and a digital circuit to make some measurements on the signal. The analog circuit is powered by 15V supplys, thus the output is a 0-15V square wave. The digital circuit needs a 0-5V input. I tried using a voltage divider on the output of the analog circuit to bring the voltage down to a 0-5V square wave, which worked fine. When I connected the output of the voltage divider to a digital device, the result was the signal was offset. The offset was high enough that the digital device was only reading a high instead of a changing signal. I used seperate power and grounds for the analog circuits. Any ideas on how to fix this?