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 for IoT hub applications that integrated a 0.1-2.5GHz local oscillator (LO) harmonic rejection (HR) RF front-end (RFFE) with a frequency-adaptive calibration scheme. In the HR-RFFE, a programmable RC network is proposed 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 delay adjustment to calibrate the LO phase errors due to the frequency variation. Implemented in TSMC 40nm CMOS, the proposed transmitter core occupies 1.1mm × 1.1mm. With the baseband and RFFE, the transmitter achieves a conversion gain of over 26dB, a P1dB 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.