Frequency synthesizer with improved spurious performance

A frequency synthesizer, comprising:

• a phase frequency detector operable to produce an error signal indicative of a difference in phase or frequency between a reference signal and a feedback signal;
• a charge pump operable to generate a current pulse proportional to said error signal;
• a loop filter operable to filter said current pulse to produce a control voltage, wherein said loop filter includes:
• a first switched capacitor including a first metal capacitor having a first capacitance value and operable to charge to a first voltage corresponding to said current pulse, said first switched capacitor further including a first switch coupled to said first metal capacitor and operable in a first state to enable said first metal capacitor to charge to said first voltage and in a second state to discharge said first metal capacitor, and
• a second switched capacitor having a second capacitance value and operable to charge to a second voltage from said first voltage and produce said control voltage based upon said second voltage;
• wherein said loop filter has a bandwidth determined by a ratio of said second capacitance value to said first capacitance value;
• and
• an oscillator operable to produce an oscillation and said feedback signal based upon said control voltage.

A method within a frequency synthesizer, comprising:

• producing an error signal indicative of a difference in phase or frequency between a reference signal and a feedback signal;
• producing a current pulse proportional to said error signal;
• filtering said current pulse using a bandwidth determined by a ratio of a first capacitance value to a second capacitance value to produce a control voltage, said filtering including:
• charging a first switched capacitor having said second capacitance value to a first voltage corresponding to said current pulse,
• charging a second switched capacitor having said first capacitance value to a second voltage from said first voltage by enabling charge sharing between said first switched capacitor and said second switched capacitor to vary said second voltage over time as a function of said first voltage until said second voltage reaches a steady state voltage and ceasing charge sharing between said first switched capacitor and said second switched capacitor when said first voltage and said second voltage are equivalent to said steady state voltage, and
• producing said control voltage based upon said second voltage;
• and
• producing an oscillation based upon the control voltage.