Patent ID: 7821344
Filing Date: 2010-10-26
Classification: H03L

Abstract:
1. A VCO driving circuit that inputs a control signal to a control terminal of a voltage controlled oscillator, the VCO driving circuit comprising: a coarse adjustment DAC that receives digital data having a coarse adjustment frequency to output an analog signal; a fine adjustment DAC that receives digital data having a fine adjustment frequency to output an analog signal; a first LPF that removes noise from an output signal from the coarse adjustment DAC and then provides the resultant signal as an input to the control terminal of the voltage controlled oscillator, the first LPF having frequency pass characteristics that allow only a low frequency component to pass therethrough; a second LPF that converts an output signal from the fine adjustment DAC to a voltage to thereby smooth the signal, the second LPF having frequency pass characteristics that allow frequency components higher than the frequency component allowed by the first LPF to pass therethrough; a resistor that connects an input stage of the first LPF to an input stage of the second LPF; and a capacitor that provides a capacitive coupling such that the output of the second LPF is added to the output of the first LPF.