Investigation On Wideband Direct-Conversion Receiver And I/Q Mismatch Correction

Spectrum analyzer is the most basic and widely used measuring instruments in microwave radio field.With the rapid development of wireless communication technologies in recent years, the demand for the spectrum analyzer is also growing.Therefore, it is important to study the related technology of spectrum analyzer.Based on the spectrum analyzer application, a broadband direct-conversion receiver is designed, and the main performance indexes are measured. Compared to the super heterodyne and digital IF scheme, zero-IF scheme has the advantages of simple structure, low cost, no interference of the mirror and so on. But the problem of I/Q mismatche is inevitable in wideband quadrature demodulation receiver. The present of I/Q mismatches will affect the performance of receiver system. The effects of DC offset and I/Q imbalance on the receiver are analyzed in detail and three methods to I/Q imbalance calibration are introduced. However, these methods are rely on the assumption that the channel mismathch is frequency independent. Therefore, these methods can only be applied to a narrow band receiver system. In this paper, an I/Q mismatch correction method for wideband radio receivers is proposed.In this method, frequency dependent I/Q mismatches are first estimated by scanning a test signal over the band of interest. Based on the obtained mismatch information a digital filter is constructed to compensate them in the normal operation of the receiver. The results showed that image rejection ratio generally improved 30dBc after I/Q mismatch correction and the validity of this method is verified. In addition, the data acquisition, transmission and storage system based on FPGA is designed and implemented.