No abstract

A down-converter insensitive to 2 nd and 3 rd harmonics and a digital assisting circuit that cancels residual sensitivity due to device mismatches are proposed. Measured 2 nd and 3 rd harmonic rejection ratios of over 60 dB are achieved. This performance allows a simple RF filter, and it is effective to reduce the die size. IntroductionBroad band receivers have a design issue of avoiding harmonic mixing [1][2][3]. In a traditional balanced mixer, the switching operation by the LO signal generates the odd harmonics; while the even harmonics are suppressed because of the balanced circuits structure. As the results, RF signals at the odd multiple frequencies are down-converted to the baseband.There are two attractive down-conversion techniques for the harmonic rejection. One is the double-quadrature mixing (DQM) [1] that executes multiplication of two complex signals. DQM requires RF/IF poly-phase filters as phase-shifters, and the filters occupy large area.The other one is the poly-phase mixing [2]. A conventional poly-phase down-converter consists of weighted-gain mixers driven by 8-phase LO signals. The reduction ratio is limited around 30dB because of gain mismatch. A digital assisting technique that enlarges the reduction with 8-phase mixing was proposed [3]. However, the digital assisting system is able to cancel only a single (3rd or 5th) harmonic, and even harmonics are assumed to be sufficiently rejected only with device matching. We propose a harmonic rejection down-converter with digital assist to eliminate 2 nd and 3 rd harmonics.

No abstract

No abstract