FREQUENCY SYNTHESIZER CIRCUIT WITH LINEARIZED GAIN OF THE CONTROLLED OSCILLATOR

A frequency synthesizer circuit (100) for a car radar system is disclosed, the circuit (100) comprising: a phase locked loop (110) for providing a frequency chirp at a range of tuning voltages (140, 320), said phase locked loop (110) comprising: a phase detector (122) and a voltage controlled oscillator (150), wherein said phase locked loop (110) has an open loop gain dependent on the tuning voltage (140) and a gain of the voltage controlled oscillator (150); a first varactor (340, 410) unit for altering the gain (392) of the voltage controlled oscillator (150) over a first subset range of tuning voltages (344); and a second varactor (360, 430) unit for altering the gain (392) of the voltage controlled oscillator (150) over a second subset range of tuning voltages (364), wherein the second subset range of tuning voltages (364) is higher than the first subset range of tuning voltages (344); such that variations in the open loop gain (384, 394) over the first and second subset range of tuning voltages (344, 364) of the range of tuning voltages (320) are compensated for by the varactor units (340, 360).