A 7-8 GHz Serrodyne Modulator in SiGe for MIMO Signal Generation

An 8-bit 360o sawtooth modulated phase shifter is used to apply very small frequency offsets to RF signals between 7 and 8 GHz. Offsets between 6 Hz and 10MHz can be obtained. Such frequency offsets can be used to generate orthogonal signals, which are required in e.g. MIMO applications. Each undesired frequency component is suppressed to below -30 dBc. The phase modulator is realized in a 250 nm SiGe BICMOS technology.