RFID reader system which is based on passive RFID tags typically takes the zero-IF receiving solution.This solution will cause carrier leakage between the sender and receiver of RF signal.This carrier leakage will cause two undesirable results:one is that it's easier for the front of receiver to become saturated which will reduce the communication distance of system;the other is that the DC offset phenomenon will be caused then the bit error rate of system will be increased.Therefore

two measures are proposed in this paper to solve this problem.Firstly

the carry cancellation technology is be applied in the RFID reader at 2.45GHz band

and the microstrip circuit is used in the design.By simulation and prototyping test

the results of leakage power of improved circulator are given.Secondly

a wideband and high-gain DC amplifier with DC feedback loop is proposed

it is used as the baseband signal amplifier without distortion and it can compensate the DC component brought by the mixer automatically.Thus

it will reduce the bit error rate of RFID readers when the electronic tags are readed.