An integrated fractional-N frequency synthesizer for software-defined radio applications

We present an integrated fractional-N frequency synthesizer providing in-phase / quadrature phase signal over the frequency bands 0.6-4.6 GHz, 5-7 GHz, 10-14 GHz, and in-phase signal over 20-28 GHz for software-defined radio applications. An integrated voltage controlled oscillator (VCO) with 34 % tuning range and a set of high speed dividers are used to accomplish all the frequencies. By employing a multi-bit, single-loop sigma delta modulator and an 8-bit reference divider, the synthesizer can achieve a frequency step size of less than 10 Hz. The measured PLL phase noise is -132 dBc/Hz and -121 dBc/Hz at 1 MHz offset for 884 MHz and 3.5 GHz, respectively. Fabricated in a 0.25 ¿m SiGe-BiCMOS process, the VCO including buffer draws 45 mA from a 5 V supply and the rest draws 150 mA from a 3 V supply.