An I/Q Imbalance Detection and Calibration Scheme for mm-Wave Direct-Conversion Transmitter

Abstract

Transmitter (TX) modulation accuracy and spectral purity are a key requirement for the mm-Wave communication system. In this paper, we present an Inphase/Quadrature (I/Q) imbalance detection and calibration scheme for mm-Wave direct-conversion TX. By analyzing the relationship between the Local Oscillator (LO) I/Q Imbalance and Image Rejection Ratio (IRR), we proposed the LO I/Q imbalance detection and calibration scheme which can optimize the IRR. The proposed detection and calibration scheme is composed of 1-stage tunable RC-Poly Phase Filter (PPF) with variable resistor, Phase Detector (PD), 1-bit Phase-to-Digital Converter (PDC), Serial Peripheral Interface (SPI), 9-bit Resistive Digital-to-Analog Converter (RDAC) and Successive Approximation Register (SAR) algorithm. This scheme adjusts the cut-off frequency of PPF to LO input frequency by tuning the resistance of the PPF. For the first time, the simple and efficient SAR algorithm with 1-bit PDC was used to detect and calibrate I/Q imbalance automatically, which breaks the limitation of IRR in mm-Wave direct-conversion TX. To verify the proposed scheme, prototype is fabricated in 65-nm CMOS process. Using the proposed scheme, the measured IRR are better than 40 dB for 1 MHz-2 GHz tone-spacing and peak IRR is 68 dB. Also, the proposed scheme achieves maximum IRR improvement of 27.5dB. The proposed scheme enables -26.23 dB, -26.84 dB, -27.29 dB rms Error Vector Magnitude (EVM) for 3.2 Gb/s 16-QAM signal, 4.0 Gb/s 32-QAM signal, and 4.8Gb/s 64-QAM signal, respectively, without digital predistortion. The proposed TX provides Gain, OP1dB, PSAT of 13.8 dB, 12.6 dBm, and 13.7 dBm. The efficiency of TX is 17.4% and the DC power consumption is 135.1mW.