Texas Instruments Corporation

Leonardo Curradi

Frank Vanselow

In a circuit configuration for the compensation of leakage currents in a voltage-controlled oscillator ( ) of a PLL circuit ( ), a control voltage is applied to the oscillator by way of a loop filter ( ), which is generated by a phase detector ( ) as a function of the phase difference between the phase of a reference signal (f ) and the phase of the signal output by the voltage-controlled oscillator ( ). This oscillator ( ) contains varicap diodes ( ), as circuit elements to influence the frequency, to which the control voltage is applied via a control line ( ). A compensation circuit (K) is provided with varicap diodes ( ) in the same configuration as those in the oscillator ( ), and a voltage-follower-mode connected operational amplifier ( ) with a differential output is provided which has an input ( ) that is connected to the control line ( ). It reproduces at one of its outputs ( ) the control voltage which it applies to the varicap diodes ( ) in the compensation circuit (K). From its other output ( ) it supplies a current equal to the leakage current of the varicap diodes ( ) in the compensation circuit (K). A current shunt-off branch leads from the control line ( ), by way of which a current flows from the control line ( ) which corresponds to the current supplied by the operational amplifier ( ).

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Milan, Italy

Leonardo Curradi