Calibration of SDR Circuit Imperfections

Software defined radio (SDR) transceivers comprising a single highly reconfigurable circuit have proven to enable multi-mode multi-band operation at low-cost. However, distortion induced by circuit imperfections hampers standard compliancy over the diverse modes and bands. In this paper, a solution is presented and implemented in hardware to eliminate this distortion by using digital in-system calibration. The proposed calibration scheme offers system performance improvements beyond standard compliancy, achieving e.g. an error vector magnitude (EVM) of 1.8%, a quadrature imbalance of -46 dBc and -42 dBc at the transmitter and receiver output respectively and a carrier feedthrough of -38 dBc. This calibration scheme is very efficient and directly applicable on most SDR transceivers, even in a multiple antenna (MIMO) configuration.