Method to design low noise differential CMOS VCOs without tail current source

A low phase noise LC voltage-controlled oscillator (VCO) design method with differential varactors is proposed. This technique uses the VCO CMOS structure properties instead of a tail current source to limit the current. A VCO providing a 286 MHz signal is designed with 0.35-μμm standard CMOS technology. This VCO without current limiting MOS transistors has to fulfill APCO, TETRA and TETRAPOL phase noise requirements. The 286 MHz VCO phase noise measurement result is equal to -130dBc/Hz at 100 kHz.