A 0.7-3 GHz GaAs QPSK/QAM direct modulator

A vector modulator which contains a 90 degrees phase-shifter, two pairs of differential amplifiers, two double balanced FET mixers, and a differential output stage within a single chip is described. The QPSK and 16 QAM (quadrature amplitude modulation) constellations are measured with a vector network analyzer. The output spectrum of the SSB (single sideband) modulation is shown, demonstrating that the carrier suppression and the sideband suppression are better than 40 dBc. Third-order intermodulation tones are less than -40 dBc, while carrier suppression is better than 40 dBc.<
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