A Sub-6GHz Wideband Transmitter with LO Harmonic Rejection RF Front-Ends Using Frequency-Adaptive Calibration

This paper presents a broadband 0.1–6GHz transmitter that integrated a 0.1–2.5GHz local oscillator (LO) harmonic rejection (HR) RF front-end (RFFE) based on the LO frequency-adaptive calibration scheme. In the HR-RFFE, a programmable RC network is set to achieve the intermediate frequency domain harmonic rejection and pre-calibration. In the 8-phase LO generator, the cross-connected Gilbert phase detector provides the detection of the orthogonality of 90° shifted LO signals for the calibration of the LO phase errors due to the frequency variation. The in-phase (I) and quadrature (Q) signals are calibrated separately and summed in the power amplifier. Implemented in 40nm CMOS, the transmitter occupies 1.1×1.1mm². With the baseband and RFFE, the transmitter achieves a gain of over 26dB, a P1dB compression point of 16.1dBm, and a system efficiency of 25.9%, while operating at 0.1–6GHz. With the calibration techniques, the 3rd and 5th LO harmonic rejection ratios are over 46.9 dBc and 53.5 dBc, respectively.