A 2-V 2-GHz Si-bipolar direct-conversion quadrature modulator

A 2-GHz Si-bipolar direct-conversion quadrature modulator with a wide bandwidth is described. It operates at a low supply-voltage of 2 V and features a "current-folded" double-balanced mixer with a two-stacked-transistor configuration, and a tunable RC/CR 90/spl deg/ phase shifter that reduces the amplitude imbalance and the phase error over a wide bandwidth (0.8 to 2 GHz). The modulator is implemented using 18-GHz Si-bipolar technology and dissipates only 68 mW at 2 V. The image ratio at 2 GHz is about -37 dBc, corresponding to a phase error of 1.6/spl deg/. Moreover, both second-order and third-order products, and local signal leakage are less than -40 dBc.