This paper presents an analytical model to characterize the performance of multi-state modulation used by IQ modulators in backscatter communication. The definition of the differential RCS, originally used in the RFID technology for two states modulation, is extended to N states and allows one to characterize and compare the performance of different transponders. Read range can also be directly extracted theoretically from the internal impedance of the device. All the results are confirmed considering a transponder based on a PIC architecture. Multistate modulation is obtained by changing the configuration of two GPIOs directly connected to a dipole antenna, in real time during runtime. Obtained delta RCS is compared to the one of classical UHF tags for passive and semi-passive technology. Associated read range is estimated in real environment.