Patent ID: 7193479
Filing Date: 2007-03-20
Classification: H03L

Abstract:
1. A local oscillator circuit having a selectable frequency setting, comprising: a control voltage generator receiving a first current having a magnitude and a direction, generating a control voltage, and raising and lowering the control voltage according to the first current; a voltage-controlled oscillator generating an output signal having a frequency responsive to said control voltage; a frequency divider dividing the frequency of the output signal of the voltage-controlled oscillator by a frequency division ratio selectable according to said frequency setting, thereby generating a divided signal; a phase detector comparing phases of the divided signal and a reference frequency signal to generate a phase detection signal; and a current generator generating the first current, switching the direction of the first current according to the phase detection signal, switching the magnitude of the first current according to the frequency setting, thereby bringing the frequency of the output signal of the voltage-controlled oscillator to said frequency setting; wherein the current generator comprises: a first terminal switchably coupled to the control voltage generator, feeding the first current to the control voltage generator when the first current flows in one direction; a second terminal switchably coupled to the control voltage generator, drawing the first current from the control voltage generator when the first current flows in another direction; a first current source generating a second current; a first analog switch connected to the first current source and the first terminal, selectively feeding the second current to the first terminal, thereby increasing the first current; a second current source generating a third current; a second analog switch connected to the second current source and the first terminal, selectively drawing the second current from the first terminal, thereby decreasing the first current; a third current source generating a fourth current; a third analog switch connected to the third current source and the second terminal, selectively drawing the fourth current from the second terminal, thereby increasing the first current; a fourth current source generating a fifth current; and a fourth analog switch connected to the fourth current source and the second terminal, selectively feeding the fifth current to the second terminal, thereby decreasing the first current.