An I/Q Imbalance Calibration Scheme for 5G Direct-Conversion Transmitter

This brief presents an I/Q imbalance calibration scheme for a 5G direct-conversion transmitter (TX). By utilizing a simple 1-bit phase-to-digital converter and 9-bit digital-to-analog converter, a quadrature phase error associated with fabrication tolerances can be minimized effectively using a binary search algorithm. This approach implements a continuous, real-time calibration that adaptively adjusts the resistive components of the type-I polyphase filter in response to detected phase errors, thereby ensuring precise phase alignment by dynamically compensating for I/Q imbalance without interrupting the primary signal path. The proposed idea is demonstrated in the LO path of a 5G direct-conversion transmitter in a 65-nm bulk CMOS technology. The measured image rejection ratio and LO feedthrough suppression ratio are maintained less than −52 dBc and −37 dBc, respectively, in the range of 27.5-29.5 GHz. The TX can support a peak data rate of 4.8 Gb/s at 28.5 GHz using 64-QAM and an error vector magnitude of −27.3 dB.