Built-In Self-Test and Digital Calibration of Zero-IF RF Transceivers

We propose a self-test method for zero-IF radio frequency transceivers using primarily loopback, aided by a small built-in self-test (BIST) circuitry, to determine critical performance parameters, such as I/Q imbalance and nonlinearity coefficients. The transceiver is placed in the loopback mode by couplers, specifically designed to be asymmetric with respect to the primary path and the BIST path. The loopback path is also designed to include two traces with slightly different delays to enable parameter deembedding. Transceiver parameters are analytically computed using baseband I and Q signals over two frames, each of which is 200 mu s in duration. Overall, measurement time is <10 ms, including computation time. In addition to loopback hardware support and the associated parameter deembedding methodology, we propose a complimentary BIST circuit to measure the transmitter (TX) gain. The measured parameters can be used for predistortion or postdistortion to calibrate the transceiver, both at production time and in the field. Both simulation and hardware measurement results show that the proposed method can determine the target performance parameters with adequate accuracy for digital calibration. Measurement and the subsequent calibration are shown to reduce TX error vector magnitude more than fivefold, even for significantly impaired systems.