Do you mean a circuit which compares two unknown volt levels? A differential amplifier is used. Usually a long-tail pair does this job. You may need to experiment to find a good operating point so it works properly.
A comparator usually drives an output high or low. Resolution has to do with its ability to distinguish the smallest difference between input A and input B. Transistor gain is a parameter that is no doubt involved in calculating resolution. If your long-tail pair have extremely high gain, then that might be sufficient to send the output fully high or low. Is that the calculation you wish to do?
Do you plan to modify the differential amplifier so as to improve resolution?