Design Of Low Noise Amplifier And Mixer Used In Wireless Local Area Networks

CMOS technology has been able to use in radio frequency (RF)circuit designs. This paper introduces RFICs of receiver. A low noiseamplifier (LNA) with an active balun and a current-mode mixer arepresented.The output signal of wireless’s antenna is usually unbalances singlesignal. An additional discrete chip is needed to convert unbalanced signal todifferent balanced signals. However using discrete chips would result inlower integration of system and certain insertion losses of passive chipsrequire other active chips to provide higher gains. The conversion circuit isintegrated into the LNA in order to improve the integration of system andreducing insertion losses of discrete passive chips. The conversion circuit isimproved on conventional structure and it has a better performance in phaseerror of differential output signals. The structure of proposed LNA in thearticle is cascode common-source and common-gate circuit. The cascodecircuit not only ensure sufficient power gain also have good isolations. Byoptimizing the cascode circuit of amplifier, a flat gain is obtained over a wideband. A5.15~5.725GHz LNA integrated with signal conversion circuit ispresented in this paper. The simulated results show that performances of theproposed LNA in this paper are improved obviously.The traditional mixer needs high power supply voltage for its three stagestransistor stacked structure and it couldn’t work with low power voltage.Improvements have been made in conventional mixer to get a low voltagemixer with better performances. A current-mode circuit is used instead of avoltage-mode one, and then the power supply voltage could be reduced. Theeven harmonics of improved tranconductance circuits could be canceled byusing cross current feedback technology. A better linearity of mixer isobtained. The output circuit of mixer is simplified by replacing the passive load with crossed active transistors. Simulation results of the proposed mixershows that it can achieve low voltage power supply and have a good linearityat the same time. Improvements of mixer performances have shown thefeasibility of proposed mixer circuit.