A 5-GHz CMOS quadrature modulator for direct conversion transmitters

A direct up-conversion quadrature modulator operating for the 5-GHz wireless LAN system is presented. As the key component in the transmitter, the doubly balanced quadrature modulator was designed and fabricated in a 0.18mum CMOS process. To improve the linearity of the quadrature modulator, a negative feedback technique is adopted in the transconductor design. The modulator chip consumes only 8mA with 1.8V supply voltage. The measured single end input 1-dB compression point is larger than -0.45dBV. The quadrature modulator has the accordant performance at 5-GHz with the process and temperature variations