A 5 GHz-band SiGe-MMIC direct quadrature modulator using a doubly stacked polyphase filter

A 5 GHz-band SiGe-MMIC direct quadrature modulator using a doubly stacked polyphase filter (PPF) is described. The doubly stacked PPF can dramatically reduce the output phase and magnitude imbalance corresponding to the transmission line length inside the RC PPF networks. The quadrature modulator using two-stage doubly stacked PPF performs the error vector magnitude of 3.6 %rms, magnitude error of 3.0 %rms, and phase error of 1.2 deg at LO frequency of 5.8 GHz for /spl pi//4-shifted QPSK (2 Msps) modulated signals. Wideband characteristics from 5.0 to 6.5 GHz are also demonstrated. This modulator dissipates 11.3 mA at 3.3 V supply voltage.