科研之友
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摘要
A wideband (0.8每6ˋGHz) receiver front-end (RFE) utilizing a shunt resistive feedback low-noise amplifier (LNA) and a micromixer is realized in 90ˋnm CMOS technology for software-defined radio (SDR) applications. With the shunt resistive feedback and series inductive peaking, the proposed LNA is able to achieve a wideband frequency response in input matching, power gain and noise figure (NF). A micromixer down converts the radio signal and performs single-to-differential transition. Measurements show the conversion gain higher than 17ˋdB and input matching (S11) better than ˋ7.3ˋdB from 0.8 to 6ˋGHz. The IIP3 ranges from ˋ7 to ˋ10ˋdBm, and the NF from 4.5 to 5.9ˋdB. This wideband receiver occupies 0.48ˋmm2 and consumes 13ˋmW. 1. Introduction Software-defined radio was designed to process any signal within a certain bandwidth [1]. For an SDR in 0.8每6ˋGHz region, it includes signals of GSM, 3ˋG, WLAN, Bluetooth, WiMAX, and GPS applications. Such an idea can be realized by using an ultra-high speed ADC for direct sampling, but the power consumption of the high speed ADC is too large to accept. Relatively, a SDR receiver that down-converts signals before ADC appears to be a more practical approach. The intuitive SDR receiver topology is to connect front-ends of different standards in parallel as shown in Figure 1(a); nevertheless, the chip size of such topology would be too large. A wideband radio [2每6] and a tunable-band radio [7每9] (see Figure 1(b)) are good candidates for this purpose. The most challenging problem is how to design an LNA and a mixer that meet all the requirements in such a wideband from 800ˋMHz to 6ˋGHz. Figure 1: (a) Multiband receiver architecture. (b) Wideband or tunable-band receiver architecture. A wideband RFE can be implemented by several circuit structures. Conventional common-gate LNAs feature wide input matching and gain bandwidths [4]. However, the multiple stages required by such circuits for gain and noise flatness can be power hungry. A shunt-shunt feedback LNA followed by a passive mixer [2, 5, 6] can be an option, but its gain degrades at high frequency due to the large capacitance at its input and output stages. Besides, the trade-off between noise figure and bandwidth remains an issue. Tunable-band receivers switching its frequency with tunable passive devices [7每9] would be promising, except that the size of passive devices is too costly to accept. Designs of mixers can be also challenging for SDR. Passive mixers are widely used for frequency down-conversion. Very large power is needed for LO input to drive these
