Design Of RF Front-end For Ultra Wideband System

UWB communication technology has promising application aspects. This design adopts one sub-band (6336MHz-6864MHz) of UWB communication system as its communication band. Zero-IF receiver architecture is adopted after comparing several different receivers. Designing goals of RF front-end are derived. RF front-end consists of low noise amplifier (LNA) and Mixer. According to the designing goals of RF front-end, the targets of LNA and Mixer are made explicit.LNA needs wideband input impedance matching on the basis of system requirements. After comparing several common wideband LNA architectures, the LNA uses differential common gate amplifier as the basis of the design. Capacitive cross-coupling structure is used for lower NF and power and Positive feedback technology is also used for optimizing voltage gains by enhancing the equivalent input impedance. Variable voltage gains are achieved by controlling the status of the input end. Changing signal current flows reasonably can get both excellent input impedance matching and variable gains.Active mixers are selected to achieve conversion gain. In this thesis, some active mixers are introduced. After weighing advantages and disadvantages, double balanced mixer is chosen. The source voltage provided by TSMC 0.13um CMOS technology is 1.2V. So folded Gilbert mixer is adopted and variable gains are achieved by changing the load impedance. To reduce the influence of LO power, LO buffer circuit is investigated.LNA and Mixer are all designed in TSMC 0.13 um CMOS process. Layout is carefully designed and design verification is completed. After extracting parasitic parameters, post simulation is made. According to post simulation results, indicators of the LNA are as follows:voltage gain is 25dB/19dB/14dB/8dB, the return loss S11 is lower than -10dB in all modes, noise figure (NF) is less than 3dB at highest gain mode. Indicators of the Mixer are as follows:conversion gain is 2.2dB/10.2dB, DSB NF is less than 8dB in all modes, IP1dB and IIP3 are -3.4dBm and 6.5dBm at high gain mode, ⅠP1dB and ⅡP3 are -1.6dBm and 8.4dBm at low gain mode. Simulation results show that the proposed LNA and Mixer meet design requirements.