A 0.25μm CMOS Downconverter Mixer for 1.6GHz

This work shows the implementation of a CMOS double balanced mixer based in the Gilbert cell capable of providing high conversion gain and high linearity. The mixer includes a common mode feedback circuit to keep a fixed DC level at the output and to maintain the transistors in the saturation, since the triode operation reduces the conversion gain. It uses inductive source degeneration in the transconductance stage in order to provide impedance matching and to improve the linearity of the circuit. It also incorporates an active balun at the output to convert the differential, or balanced, signal to a single ended termination. The mixer was designed to work with an RF signal of 1.8 GHz, an LO of 1.6 GHz, thus producing an IF of 200 MHz. The circuit presents a conversion gain of 22.5 dB and an IIP3 of +2 dBm. The single sided band noise figure is 10.9 dB, input signal loss of just -35.5 dB. The power consumption is 22.5 mW for a power supply of 2.5 V