A CMOS Switched Load Harmonic Rejection Mixer for DTV Tuner Applications

In this paper, a switched load harmonic rejection mixer (HRM) structure with one single mixer core and a pair of switched load resistors is proposed. Different from the traditional three-phase HRM which is widely used in DTV tuners, this HRM performs the harmonic rejection function by vector multiplication rather than superposition. Sharing most of its parts with an ordinary Gilbert mixer, the proposed HRM shows greater simplicity in structure. The single mixer-core structure is also more power efficient than a traditional three-phase HRM. In order to verify the effectiveness of this approach, a proof-of-concept prototype is designed and fabricated in 0.18- μm RFCMOS technology. Measurements indicate that 38 dB for 3rd and 34.5 dB for 5th harmonic rejection ratio can be achieved. The HRM including a buffer stage consumes a low bias current of 3 mA under 1.8 V supply voltage and has equivalent performance such as CG, NF, and IIP3 to an ordinary Gilbert mixer. With the load switch inactivated, this HRM can be easily transformed into an ordinary Gilbert mixer, which increases its flexibility for different applications.