Wireless Transmitter IQ Balance and Sideband Suppression



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).

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