An integrated 3.6 GHz bidirectional direct quadrature modulator/demodulator

A bidirectional direct quadrature modulator/demodulator IC has been developed for high speed data communication applications in enhanced digital wireless communication systems operating in the 3.6 GHz fixed-wireless-access (FWA) band. The IC contains a precise quadrature phase shifter and a passive double balanced mixer core, as well as microwave band amplifiers and the associated signal conversion circuits. An important feature of the design is a passive double balanced mixer which allows the system to function as both a direct quadrature modulator in a transmit channel and a direct quadrature demodulator in a receive channel, which is advantageous for simplified transceiver realization. The mixer´s output has a 1-dB compression point of -20.4dB corresponds to a input signal level of -12.5dB and exhibits a high input and output port isolation. The silicon implementation was carried out using Cadence 0.18μm CMOS technology. Physical layout of the entire system occupies an area of 1.2mm² with a low power dissipation of 137mW at a single power supply of 3.3V.