A voltage controlled oscillator, VCO, CMOS regulator circuit (600, 650, 700) comprising a CMOS regulator being connectable to a VCO, the CMOS regulator including: a first voltage regulator (604, 654, 730) configured to regulate a first input voltage provided to the first voltage regulator (604, 654, 730), the first voltage regulator (604, 654, 730) including a P-type metal-oxide-semiconductor, PMOS, pass element; a second voltage regulator (606, 658, 750) configured to regulate a second input voltage provided to the second voltage regulator (606, 658, 750), the second voltage regulator (606, 658, 750) including an N-type metal-oxide-semiconductor, NMOS, pass element, wherein the first voltage regulator (604, 654, 730) is connected to the second voltage regulator (606, 658, 750); characterized in that the VCO CMOS regulator circuit (600, 650, 700) further comprises: a switch circuit (602, 652, 656, 710) connected to the CMOS regulator, the switch circuit (602, 652, 656, 710) being configured to select a voltage mode by selecting either a high voltage, HV, mode or a low voltage, LV, mode for the CMOS regulator, and to selectively activate at least one of the first voltage regulator (604, 654, 730) or the second voltage regulator (606, 658, 750) within the selected voltage mode, wherein the switch circuit (602, 652, 656, 710) is configured to select the HV mode based on pulling effects of the VCO connectable to the VCO CMOS regulator circuit (600, 650, 700), and to selectively activate the at least one of the first voltage regulator (604, 654, 730) or the second voltage regulator (606, 658, 750) based on the pulling effects. a first voltage regulator (604, 654, 730) configured to regulate a first input voltage provided to the first voltage regulator (604, 654, 730), the first voltage regulator (604, 654, 730) including a P-type metal-oxide-semiconductor, PMOS, pass element; a second voltage regulator (606, 658, 750) configured to regulate a second input voltage provided to the second voltage regulator (606, 658, 750), the second voltage regulator (606, 658, 750) including an N-type metal-oxide-semiconductor, NMOS, pass element, wherein the first voltage regulator (604, 654, 730) is connected to the second voltage regulator (606, 658, 750); characterized in that the VCO CMOS regulator circuit (600, 650, 700) further comprises: a switch circuit (602, 652, 656, 710) connected to the CMOS regulator, the switch circuit (602, 652, 656, 710) being configured to select a voltage mode by selecting either a high voltage, HV, mode or a low voltage, LV, mode for the CMOS regulator, and to selectively activate at least one of the first voltage regulator (604, 654, 730) or the second voltage regulator (606, 658, 750) within the selected voltage mode, wherein the switch circuit (602, 652, 656, 710) is configured to select the HV mode based on pulling effects of the VCO connectable to the VCO CMOS regulator circuit (600, 650, 700), and to selectively activate the at least one of the first voltage regulator (604, 654, 730) or the second voltage regulator (606, 658, 750) based on the pulling effects. a switch circuit (602, 652, 656, 710) connected to the CMOS regulator, the switch circuit (602, 652, 656, 710) being configured to select a voltage mode by selecting either a high voltage, HV, mode or a low voltage, LV, mode for the CMOS regulator, and to selectively activate at least one of the first voltage regulator (604, 654, 730) or the second voltage regulator (606, 658, 750) within the selected voltage mode, wherein the switch circuit (602, 652, 656, 710) is configured to select the HV mode based on pulling effects of the VCO connectable to the VCO CMOS regulator circuit (600, 650, 700), and to selectively activate the at least one of the first voltage regulator (604, 654, 730) or the second voltage regulator (606, 658, 750) based on the pulling effects.