Frequency synthesizer systems and methods for three-point modulation with a DC response

A frequency synthesizer which generates an output frequency, comprising:

• a controlled oscillator which is responsive to a frequency control input signal, to generate the output frequency;
• a programmable frequency divider which is responsive to the output frequency and to a divider control input, to divide the output frequency by a first integral ratio or by a second integral ratio in response to the divider control input, to thereby produce a divided signal;
• a phase comparator which is responsive to a reference frequency signal and to the divided signal, to compare the reference frequency signal and the divided signal and thereby produce a first error signal;
• a sigma-delta modulator which is responsive to a modulation input, to produce the divider control input;
• a loop filter which is responsive to the first error signal to thereby produce the frequency control input signal;
• and
• a direct modulation injector which is responsive to the loop filter and to the modulation input, to produce the frequency control signal.

A frequency synthesizer which generates an output frequency, comprising:

• a controlled oscillator which is responsive to a frequency control input signal, to generate the output frequency;
• a programmable frequency divider which is responsive to the output frequency and to a divider control input, to divide the output frequency by a first integral ratio or by a second integral ratio in response to the divider control input, to thereby produce a divided signal;
• a phase comparator which is responsive to a reference frequency signal and to the divided signal, to compare the reference frequency signal and the divided signal and thereby produce a first error signal;
• a sigma-delta modulator which is responsive to a modulation input, to produce the divider control input;
• a loop filter which is responsive to the first error signal to thereby produce the frequency control input signal;
• a scaler which is responsive to the ripple compensation signal;
• and
• a compensation injector which is responsive to the scaler and to the first error signal, to produce a compensated first error signal, and to provide the compensated first error signal to the loop filter.

A frequency synthesizer which generates an output frequency, comprising:

• a controlled oscillator which generates the output frequency;
• a programmable frequency divider which divides the output frequency by a first or second integral ratio to thereby produce a divided signal;
• a phase comparator which is responsive to a reference signal and to the divided signal, to compare the reference frequency signal and the divided signal;
• and
• a three point modulator which is responsive to a modulation signal, and generates a sampled and quantized approximation of the modulation signal and provides the sampled and quantized approximation to the frequency divider to control the first or second integral ratio, which generates a phase error compensation waveform from the modulation signal and combines the phase error compensation waveform and the output of the phase comparator to produce a first control signal, and which combines the modulation signal and the first control signal to produce a second control signal which is applied to the controlled oscillator to generate the output frequency.

A modulator which modulates a frequency synthesizer with a digital data stream to produce a modulated output signal at a carrier frequency, the frequency synthesizer including a controlled oscillator, a loop filter, a phase comparator and a programmable frequency divider, the modulator comprising:

• an input register which stores a predetermined portion of the digital data stream;
• a counter which increments at a multiple of the symbol rate of the digital data stream;
• and
• a memory including a first address input which is connected to the input register and a second address input which is connected to the counter, the memory storing predetermined bit sequences;
• the memory providing at least one bit as a function of the first address input and the second address input, to produce a control signal for the programmable frequency divider;
• wherein the programmable frequency divider is connected to the counter to clock the counter.

A modulator which modulates a frequency synthesizer with a digital data stream to produce a modulated output signal at a carrier frequency, the frequency synthesizer including a controlled oscillator, a loop filter and a phase comparator, the modulator comprising:

• a digital waveform generator which is responsive to the digital data stream to generate numerical samples which represent the modulation waveform;
• a digital sigma-delta converter which is responsive to the digital waveform generator to convert the numerical samples into a stream of sigma-delta modulation symbols at a symbol rate which is determined by a clock signal;
• and
• a programmable frequency divider which divides the controlled oscillator output by an integer determined by the sigma-delta modulation symbols, to produce the clock signal.

A modulator which modulates a frequency synthesizer with a digital data stream to produce a modulated output signal at a carrier frequency, the frequency synthesizer including a controlled oscillator, a loop filter, a phase comparator and a programmable frequency divider, the modulator comprising:

• a digital waveform generator which is responsive to the digital data stream to generate numerical samples which represent the modulation waveform;
• and
• a digital sigma-delta converter which is responsive to the digital waveform generator to produce a control signal for the programmable frequency divider;
• wherein the digital sigma-delta converter also produces a ripple compensation signal which is applied to the loop filter;
• and
• wherein the digital sigma-delta converter also produces a direct compensation signal which is applied to the controlled oscillator.

A frequency synthesizing method for generating a modulated output signal at a desired frequency, comprising the steps of:

• generating the modulated output signal using a controlled oscillator having a frequency control signal input;
• sigma-delta converting a modulation input to produce a second error signal and a stream of sigma-delta modulation symbols at a symbol rate determined by a clock signal;
• dividing the modulated output signal by an integer ratio selected from at least a first integer ratio or a second integer ratio in response to the symbols and a frequency control input, to produce the clock signal;
• comparing the clock signal with a reference frequency signal to thereby produce a first error signal;
• and
• loop filtering the first and second error signals to thereby produce the frequency control signal input to the controlled oscillator.

A modulating method for a frequency synthesizer which generates an output frequency, the frequency synthesizer comprising a controlled oscillator which generates the output frequency;

• a programmable frequency divider which divides the output frequency to thereby produce a divided signal;
• and a phase comparator which is responsive to a reference signal and to the divided signal, to compare the reference frequency signal and the divided signal;
• the modulating method comprising the steps of:
• generating a sampled and quantized approximation of the modulation signal and providing the sampled and quantized approximation to the frequency divider;
• generating a phase error compensation waveform from the modulation signal and combining the phase error compensation waveform and the output of the phase comparator to produce a first control signal;
• and
• combining the modulation signal and the first control signal to produce a second control signal which is applied to the controlled oscillator to generate the output frequency.

A modulating method for modulating a frequency synthesizer with a digital data stream to produce a modulated output signal at a carrier frequency, the frequency synthesizer including a controlled oscillator, a loop filter, a phase comparator and a programmable frequency divider, the modulating method comprising the steps of:

• generating numerical samples from the digital data stream, which represent the modulated output signal;
• and
• digital sigma-delta converting the numerical samples to produce a control signal for the programmable frequency divider, wherein the digital sigma-delta converting step further comprises the steps of:
• producing a ripple compensation signal which is applied to the loop filter;
• and
• producing a direct compensation signal which is applied to the controlled oscillator.