The invention relates to a phase-locked loop circuit (1) in a radio transceiver for the detection of the linear operation of a first voltage controlled oscillator (2). The phase-locked loop circuit also has a frequency divider (8), a reference oscillator (10), a phase detector (12) to compare the phases of the reference oscillator (10) with a divided frequency of the frequency divider (8), and a charge pump (14) connected to the phase detector (12) and is characterized in that the connection (13) between the phase detector (12) and the charge pump (14) has at least one branch-off line (15) connected to at least one filter (22) having an output voltage that is related to the linear operation of the voltage controlled oscillator (2).