Frequency synthesizer modulation response linearization

Claim 1

A method of substantially flattening modulation response in a frequency synthesizer having a reference frequency and a variable frequency generator having a gain response that varies in response to an input parameter, comprising the steps of: providing a charge pump having: an output; a current source for providing a charging current at said output, said current source having a controllable gain that is responsive to said output; and a current sink for providing a discharging current at said output, said current sink having a controllable gain that is responsive to said output; providing a loop filter; providing a control signal to said variable frequency generator to cause generation of a synthesized frequency; scaling said synthesized frequency with a scalar to produce a scaled synthesized frequency; detecting any phase difference between said scaled synthesized frequency and said reference frequency, and providing a phase detection signal related to said difference; providing said phase detection signal to said charge pump current source when a phase difference in a first direction is sensed to cause provision of said charging current at said output; providing said phase detection signal to said charge pump current sink when a phase difference in a second direction is sensed, said second direction being opposite to said first direction, to cause provision of said discharging current at said output; providing said output of said charge pump to said loop filter to thereby develop said control signal having a gain response substantially the reciprocal of said gain response of said variable frequency generator; whereby the interaction of said variable frequency generator and said charge pump approximates a flat modulation response.

Claim 2

A method of substantially flattening modulation response in a frequency synthesizer having a reference frequency and a variable frequency generator having a gain response that varies in response to an input parameter, comprising the steps of: providing a charge pump having: an output; a current source for providing a charging current at said output, said current source having a controllable gain that is responsive to said output; and a current sink for providing a discharging current at said output, said current sink having a controllable gain that is responsive to said output; providing a loop filter; providing a control signal to said variable frequency generator to cause generation of a synthesized frequency; scaling said synthesized frequency with a scalar to produce a scaled synthesized frequency; detecting any phase difference between said scaled synthesized frequency and said reference frequency, and providing a phase detection signal related to said difference; providing said phase detection signal to said charge pump current source when a phase difference in a first direction is sensed to cause provision of said charging current at said output; providing said phase detection signal to said charge pump current sink when a phase difference in a second direction is sensed, said second direction being opposite to said first direction, to cause provision of said discharging current at said output; providing said output of said charge pump to said loop filter to thereby develop said control signal having a gain response substantially the reciprocal of said gain response of said variable frequency generator; whereby the interaction of said variable frequency generator and said charge pump approximates a flat modulation response.

Claim 6

A method of substantially flattening modulation response in a frequency synthesizer having a reference frequency and a variable frequency generator having a gain response that varies in response to an input parameter, comprising the steps of: providing a charge pump having: an output; an FET having a gate connected to said output; a first transistor that can provide a charging current at said output, said first transistor having a base that connects to a power terminal of said FET and through a first resistor to a voltage source; and a second transistor that can providing a discharging current at said output, said second transistor having a base that connects to another power terminal of said FET and through a second resistor to ground; providing a loop filter; providing a control signal to said variable frequency generator to cause generation of a synthesized frequency; scaling said synthesized frequency with a scalar to produce a scaled synthesized frequency; detecting any phase difference between said scaled synthesized frequency and said reference frequency, and providing a phase detection signal related to said difference; providing said phase detection signal to said charge pump current source when a phase difference in a first direction is sensed to cause provision of said charging current at said output; providing said phase detection signal to said charge pump current sink when a phase difference in a second direction is sensed, said second direction being opposite to said first direction, to cause provision of said discharging current at said output; providing said output of said charge pump to said loop filter to thereby develop said control signal having a gain response substantially the reciprocal of said gain response of said variable frequency generator; whereby the interaction of said variable frequency generator and said charge pump approximates a flat modulation response.

Claim 7

A method of substantially flattening modulation response in a frequency synthesizer having a reference frequency and a variable frequency generator having a gain response that varies in response to an input parameter, comprising the steps of: providing a charge pump having: an output; an FET having a gate connected to said output; a first transistor that can provide a charging current at said output, said first transistor having a base that connects to a power terminal of said FET and through a first resistor to a voltage source; and a second transistor that can providing a discharging current at said output, said second transistor having a base that connects to another power terminal of said FET and through a second resistor to ground; providing a loop filter; providing a control signal to said variable frequency generator to cause generation of a synthesized frequency; scaling said synthesized frequency with a scalar to produce a scaled synthesized frequency; detecting any phase difference between said scaled synthesized frequency and said reference frequency, and providing a phase detection signal related to said difference; providing said phase detection signal to said charge pump current source when a phase difference in a first direction is sensed to cause provision of said charging current at said output; providing said phase detection signal to said charge pump current sink when a phase difference in a second direction is sensed, said second direction being opposite to said first direction, to cause provision of said discharging current at said output; providing said output of said charge pump to said loop filter to thereby develop said control signal having a gain response substantially the reciprocal of said gain response of said variable frequency generator; whereby the interaction of said variable frequency generator and said charge pump approximates a flat modulation response.