Linear controlled temperature independent varactor circuitry

For the purpose of adjusting the VCO frequency a voltage controlled capacity (varactor) is needed. In CMOS technologies MOS transistors are commonly used as varactors in spite of (parasitic) diodes because of their larger tuning range and lower series resistance. Especially for high PSSR and low phase noise purpose the typically very small linear controlling range of a simple MOS varactor is disadvantageous. In this paper a new circuitry with a subdivided MOS varactor is proposed to solve these problems. Measurement results of a fabricated 2.4GHz VCO point out the favourable operation of this novel principle.