Calibration of Direct-Conversion Transceivers

Due to its architectural simplicity, the direct conversion scheme is attractive for low-cost, low-complexity and/or reconfigurable transceiver design. Unfortunately, this scheme comes with moderate performance due to its sensitivity to circuit impairments such as transmitter and receiver quadrature imbalance, carrier feedthrough and receiver dc-offset. In this paper, a calibration method is presented to estimate and compensate for these circuit impairments such that their distortions at the transmitter and receiver output are eliminated. The proposed method is noniterative and enables calibration during normal transmit operation. The calibration is directly applicable on most direct-conversion transceivers embedding two frequency synthesizers as the increase of complexity is concentrated in the digital domain only. The performance has been evaluated based on measurements of three different systems operating on frequencies corresponding to major wireless interface standards, namely WLAN, WiMAX, WiFi, DVB-T/H, and even 60-GHz multi-gigabit wireless. The calibration improved the system performance significantly, exceeding standard compliancy.