An Integrated 8-12 GHz Fractional-N Frequency Synthesizer in SiGe BiCMOS for Satellite Communications

We present an integrated fractional-N low-noise frequency synthesizer for satellite applications. By using two integrated VCOs and combining digital and analog tuning techniques, a PLL lock range from 8 to 12 GHz is achieved. Due to a small VCO fine tuning gain and optimized charge pump output biasing, the phase noise is low and almost constant over the tuning range. All 16 sub-bands show a tuning range above 900 MHz each, allowing temperature compensation without sub-band switching. This makes the synthesizer robust against variations of the device parameters with process, supply voltage, temperature and aging. The measured phase noise is 87 dBc/Hz and 106 dBc/Hz at 10 kHz and 1 MHz offset, respectively. In integer-N mode, phase noise values down to 98 dBc/Hz at 10 kHz and 111 dBc/Hz at 1 MHz offset, respectively, were measured.