Single point modulator having a PLL circuit
View Patent ↗A single-point modulator ( 1 ) has a PLL circuit ( 2 ) and a programmable frequency divider ( 7 ) whose control connection is connected to a circuit branch for injecting a digital modulation signal ( 15 ) which is arranged in the feedback path of the PLL circuit ( 2 ). The circuit branch contains a sigma-delta modulator ( 9 ) which, in turn, has a digital filter ( 24 ) having a transfer function H(z). The noise transfer function NTF(z) of the sigma-delta modulator ( 9 ) is given by the function NTF(z)=1−H(z).
1. A single-point modulator for phase or frequency modulation comprising a PLL circuit whose feedback path contains a programmable frequency divider whose control connection is connected to a circuit branch for injecting a digital modulation signal into the PLL circuit, wherein
the circuit branch contains a sigma-delta modulator,
the sigma-delta modulator has a digital filter having a transfer function H(z), and
a noise transfer function NTF(z) of the sigma-delta modulator in the frequency domain is given by a function NTF(z)=1−H(z).
2. The single-point modulator according to claim 1 , wherein
the digital filter is arranged in the feedback path of the sigma-delta modulator.
3. The single-point modulator according to claim 1 , wherein
it is possible to program the filter coefficients of the digital filter.
4. The single-point modulator according to claim 1 , wherein
the digital filter is an FIR filter.
5. The single-point modulator according to claim 1 , wherein
the sigma-delta modulator has a MASH structure.
6. The single-point modulator according to claim 1 , wherein
the PLL circuit comprises:
a voltage-controlled oscillator for providing a phase-modulated or frequency-modulated output signal at its output,
a phase frequency detector for determining a phase difference between a feedback signal and a reference signal and for driving the voltage-controlled oscillator as a function of the phase difference determined, and
a feedback path for providing the feedback signal.
7. The single-point modulator according to claim 1 , wherein the feedback signal is derived from the output signal.
8. The single-point modulator according to claim 1 , wherein
a Gaussian filter is connected upstream of the sigma-delta modulator.
9. A method for phase or frequency modulation comprising the steps of:
providing a PLL circuit whose feedback path contains a programmable frequency divider whose control connection is connected to a circuit branch for injecting a digital modulation signal into the PLL circuit,
providing a sigma-delta modulator within the circuit branch, wherein
the sigma-delta modulator has a digital filter having a transfer function H(z), and wherein
a noise transfer function NTF(z) of the signma-delta modulator in the frequency domain is given by a function NTF(z)=1−H(z).
10. The method according to claim 9 , further comprising the step of:
programming the filter coefficients of the digital filter.
11. The method according to claim 9 , wherein
the digital filter is an FIR filter.
12. The method according to claim 9 , wherein
the sigma-delta modulator has a MASH structure.
13. The method according to claim 9 , wherein
the PLL circuit comprises:
a voltage-controlled oscillator for providing a phase-modulated or frequency-modulated output signal at its output,
a phase frequency detector for determining a phase difference between a feedback signal and a reference signal and for driving the voltage-controlled oscillator as a function of the phase difference determined, and
a feedback path for providing the feedback signal.
14. The method according to claim 9 , comprising the step of deriving the feedback signal from the output signal.