Iq Mismatch And The Dc Offset Compensation Of The Direct Conversion Receiver

Direct conversion receivers, which directly down covert the radio signal to baseband without any use of intermediate frequencies, are increasingly popular for use in mobile terminals due to advantages of physical size, weight and cost. However, a direct conversion receiver often suffers problems of leakage from LO-RF, DC offset and IQ mismatch.In this paper, IQ mismatch and DC offset in direct conversion receiver are investigated. The major work of this dissertation contains several points shown below:Heterodyne receivers and direct conversion receivers are compared. The main sources of problems of leakage from LO-RF, DC offset and IQ mismatch and the corresponding solving methods are discussed.The mixer, as an important part of direct conversion receivers, is analyzed theoretically, noise coefficient, loss, dynamic range and isolation are investigated, mixing distortion and selection of mixer are studied.Baseband signal model in direct conversion receivers with DC offset is built, the symbol error probability in QAM and PSK are analyzed, the LS method of DC offset is given and bit-error probability of the three kinds of receivers with BPSK, QPSK and 8-PSK codes are deduced and simulated.Baseband signal model in direct conversion receivers with DC offset and IQ mismatch is built. A new algorithm for estimating IQ mismatch and DC offset is proposed, and the performance of the estimator is analyzed.