A new 5-GHz CMOS MMIC for down conversion with an active balun and current-folded mixer

Abstract

ABSTRACT:A new 5-GHz CMOS MMIC for a down-conversion structure with an active balun and current-folded mixer is proposed for improving linearity, LO-to-RF isolation, and INTRODUCTIONOne of the critical requirements of modern RF transceivers [1] for portable telecommunication equipment is power consumption, which limits battery lifetime. In general, the best way to reduce power consumption is by reducing the power supply and current. However, due to the effect of transistor noise on the quiescent current, the only way to reduce power consumption in the mixer is by reducing the supply voltage. The conventional Gilbert mixer uses a three-stacked transistor configuration, which is ill-suited for low-voltage use. Therefore, the essence of low-voltage operation depends on reducing the number of stacked transistors and employing a current-folded scheme [2][3][4], which can solve the abovementioned problems. Some research studies [2, 4 -6] have used separate signal amplifiers to drive a Gilbert mixer and a balun transformer has been used to convert the single-ended input to a differential signal for the mixer, which occupies more board space and hence more power is consumed. In this paper, we propose a new CMOS MMIC current-folded mixer with a source-degeneration active balun. The circuit is constructed using a source-degeneration active balun and currentfolded mirror in order to achieve a low-voltage-supply, highlinearity, and cost-effective down-conversion mixer. DESIGN OF THE NEW CMOS MMIC MIXERIn this paper, a conventional active balun stage with source degeneration is applied, as shown in Figure 1. The transconductance G m can be obtained as follows [7,8]:where g m1 , g m2 , and denote the transconductance of M 1 , M 2 , and the body effect of M 2 , respectively. In Eq. (3), if the loadA schematic diagram of the proposed new CMOS MMIC mixer is shown in Figure 2. The circuit uses an active balun with source degeneration to improve the linearity and LO-to-RF isolation, which is constructed by a common source amplifier M 1 , common gate amplifier M 2 and source degeneration resistors R S . Then it cascodes with differential folded mirrors M 3 , M 10 , and M 4 , M 9 , which can reduce the number of series-connected transistors of the Gilbert mixer and result in the current-folded topology so as to achieve low voltage supply. This is followed by a Gilbert quad M 5 -M 8 , and IF output buffer stages M 11 and M 12 . As mentioned above, if we choose a suitable value of R S , then G m will be a weak function of g m1 and g m2 . Therefore, the linearity region of the proposed mixer can be expanded.With a small RF signal v RF , and a large LO signal v LO , as shown in Figure 2, the conversion gain (CG) of the proposed mixer can be calculated as follows. The differential small-signal drain current of M 9 and M 10 is given byWith respect to the Gilbert quad-mixer core [9], the output smallsignal IF current signals are given by Substituting Eqs. (5) and (6) into Eq. (7), the CG becomesLet R S Ͼ Ͼ 1/g m1 , g m1 ϭ g m2 , g m11...