INTRODUCTION
Direct complex modulation has increasingly become the architecture of choice for implementing transmitter signal chains for end applications, such as cellular base stations, WiMAX, and wireless point-to-point applications. This technique directly modulates the output IQ signals of a digital-to-analog converter onto an RF carrier (direct conversion), which eliminates the need for an intermediate IF stage and the associated filtering. A typical direct conversion transmitter is shown in Figure 1.
It is widely known that during the analog modulation process, gain and phase mismatches of IQ signals have a direct impact on sideband suppression performance. This results in degraded error vector magnitude (EVM) at the receiver, which in turn degrades the bit error rate (BER).