A Second Harmonic Self-Oscillating Mixer Incorporating Resonant Cell Structure

A downconverting second harmonic self-oscillating mixer (SOM) is developed for low-cost wireless communications applications. Incorporating resonant cell in the SOM, we can provide suitable oscillation for generating LO and terminations to all major unwanted mixing products, leading to high conversion gain design. The proposed SOM was measured with 8.5？dB downconversion gain at the RF frequency of 8.2？GHz RF, LO frequency of 4.0？GHz, and IF frequency of 0.2？GHz. The proposed design achieves higher conversion gain than that of the SOM without resonant cell. 1. Introduction Compact, inexpensive, and low-power-consumption front-end transceivers are the crucial elements in the future wireless systems. Self-oscillating mixer (SOM), which combines both functions of local oscillator (LO) and frequency conversion, will be a good candidate for the compact wireless systems. Over this decade, SOM has found interests in the many radio frequency (RF)/microwave transceivers, as the SOM exhibits smaller size and potentially lower overall DC power consumption compared to their conventional counterpart arrangement of separated active mixer and oscillator. Since the first field-effect transistor (FET) SOM was introduced in [1], a number of different variations of the SOM design have been demonstrated such as dual-gate and balanced FET SOM configurations [2, 3]. Moreover, in certain short-range applications, it is even possible to use a SOM with high conversion gain integrated into an antenna [4], thus allowing for the development of a low-cost and ultra-compact-size single-element RF/microwave transceiver. Harmonic SOM is one of the extensions from the standard SOM technique: instead of mixing the RF signal with the fundamental LO frequency, one of its harmonics is used. A satisfactory isolation between the RF, LO, and IF can be easily achieved by simple filtering techniques. However, the performance such as conversion gain is not as good as the fundamental SOM. Recently, a third-harmonic SOM with high conversion gain has been developed pushing the state-of-the-art in modern SOM design towards high-order sub-harmonic architectures [5]. Recently, various works on resonant cells were found application of designing various microwave components [6]. In this paper, an improved resonant cell structure is proposed as a part of series feedback of SOM design. We can provide proper return paths for the RF, IF and other unwanted mixing products simultaneously, leading to a very high conversion gain design without sacrificing the circuit size. 2. Proposed SOM Circuit Figure 1 shows