Frequency reference signal generating system and method for frequency synthesizers
A system for generating a frequency reference signal comprising an oscillator, a direct digital synthesizer coupled to the oscillator and configured to receive a signal output from the oscillator, a digital to analog converter coupled to the direct digital synthesizer and configured to receive a sampled signal from the direct digital synthesizer and to convert the sampled signal to an analog waveform, and a bandpass filter coupled to the digital to analog converter and configured to select an aliased output signal from the digital to analog converter at a Nyquist zone other than a first Nyquist zone and to output the frequency reference signal.
1. A system for generating a frequency reference signal comprising:
an oscillator;
a direct digital synthesizer coupled to the oscillator and configured to receive a signal output from the oscillator;
a digital to analog converter coupled to the direct digital synthesizer and configured to receive a sampled signal from the direct digital synthesizer and to convert the sampled signal to an analog waveform; and
a bandpass filter coupled to the digital to analog converter and configured to select an aliased output signal from the digital to analog converter at a Nyquist zone other than a first Nyquist zone and to output the frequency reference signal.
2. The system of claim 1 , wherein the Nyquist zone selected by the bandpass filter is a third Nyquist zone.
3. A method for generating a frequency reference signal, the method comprising:
synthesizing a signal output received from an oscillator with a direct digital synthesizer;
converting a sampled signal received from the direct digital synthesizer to an analog waveform with a digital to analog converter;
selecting an aliased output signal from the digital to analog converter at a Nyquist zone other than a first Nyquist zone with a bandpass filter; and
outputting the frequency reference signal from the bandpass filter.
4. The method of claim 3 , wherein the Nyquist zone selected by the bandpass filter is a third Nyquist zone.
5. A system for generating a frequency reference signal comprising:
an oscillator;
a digital signal generator coupled to the oscillator and configured to receive a signal output from the oscillator;
a digital to analog converter coupled to the digital signal generator and configured to receive a sampled signal or a sideband signal from the digital signal generator and convert the received signal to an analog waveform; and
a bandpass filter coupled to the digital to analog converter and configured to select an aliased output signal from the digital to analog converter at a Nyquist zone other than a first Nyquist zone and to output the frequency reference signal.
6. The system of claim 5 , wherein the digital signal generator is further configured to generate a counting sequence according to a frequency control word stored by digital signal generator.
7. The system of claim 5 , wherein the digital signal generator comprises a direct digital synthesizer.
8. The system of claim 5 , wherein the digital signal generator comprises a numerically controlled oscillator.
9. The system of claim 8 , wherein the oscillator comprises a crystal oscillator.
10. The system of claim 9 , wherein the crystal oscillator is at a frequency of 10 MHz.
11. The system of claim 5 , wherein the Nyquist zone selected by the bandpass filter is a second Nyquist zone.
12. The system of claim 5 , wherein the Nyquist zone selected by the bandpass filter is a third Nyquist zone.
13. The system of claim 5 , wherein the frequency reference signal is at a frequency of approximately 13 MHz.
14. A method for generating a frequency reference signal comprising:
receiving a signal output from an oscillator by a digital signal generator coupled to the oscillator;
receiving, by a digital to analog converter, a sampled signal or a sideband signal from the digital signal generator;
converting, by the digital to analog converter, the received signal to an analog waveform; and
selecting, by a bandpass filter coupled to the digital to analog converter, an aliased output signal from the digital to analog converter at a Nyquist zone other than a first Nyquist zone and to output the frequency reference signal.
15. The method of claim 14 , further comprising generating, by the digital signal generator, a counting sequence according to a frequency control word stored by digital signal generator.
16. The method of claim 14 , wherein the digital signal generator comprises a direct digital synthesizer.
17. The method of claim 14 , wherein the digital signal generator comprises a numerically controlled oscillator.
18. The method of claim 17 , wherein the oscillator comprises a crystal oscillator.
19. The method of claim 18 , wherein the crystal oscillator is at a frequency of 10 MHz.
20. The method of claim 14 , wherein the Nyquist zone selected by the bandpass filter is a second Nyquist zone.
21. The method of claim 14 , wherein the Nyquist zone selected by the bandpass filter is a third Nyquist zone.
22. The method of claim 14 , wherein the frequency reference signal is at a frequency of approximately 13 MHz.