Direct digital synthesizer system and related methods
View Patent ↗A direct digital synthesizer (DDS) has reduced spurious signals and includes a DDS core that produces a digital representation of a signal to be synthesized. A plurality of DDS circuits are operatively connected to the DDS core, each having a digital-to-analog converter connected to the DDS core for receiving the digital representation and converting it into a signal. A modulator is operatively connected to an oscillator circuit and digital-to-analog converter for receiving signals from the digital-to-analog converter and producing a modulated output signal. The individual frequencies of the respective DDS circuits are randomly and continuously changed from each other. A mixer receives and mixes the modulated output signals from the plurality of DDS circuits to create a mixed output signal at a selected and fixed frequency.
1. A direct digital synthesizer (DDS) having reduced spurious signals comprising:
a DDS core that produces a digital representation of a signal to be synthesized;
an oscillator circuit;
a plurality of DDS circuits operatively connected to the DDS core, each having a digital-to-analog converter connected to the DDS core for receiving the digital representation and converting it into a signal and a modulator operatively connected to said oscillator circuit and digital-to-analog converter for receiving signals from the digital-to-analog converter and producing a modulated output signal, wherein individual frequencies of the respective DDS circuits are randomly and continuously changed from each other; and
a mixer that receives and mixes the modulated output signals from said plurality of DDS circuits to create a mixed output signal at a selected and fixed frequency.
2. A direct digital synthesizer according to claim 1 , wherein said plurality of DDS circuits comprise first and second DDS circuits.
3. A direct digital synthesizer according to claim 1 , wherein said mixer is operative for summing the modulated output signals without multiplication or frequency gain.
4. A direct digital synthesizer according to claim 1 , wherein the sum of frequencies at the mixer of the modulated output signals is constant.
5. A direct digital synthesizer according to claim 1 , wherein the modulated output signals have frequencies that vary randomly.
6. A direct digital synthesizer according to claim 1 , and further comprising a bandpass filter that receives the mixed output signal for selecting a desired frequency and filtering wideband noise.
7. A direct digital synthesizer according to claim 6 , and further comprising a multiplier circuit that receives a signal from the bandpass filter that increases spur level on an instantaneous basis.
8. A direct digital synthesizer according to claim 7 , and further comprising a bandpass filter that receives a multiplied signal from the multiplier circuit.
9. A direct digital synthesizer according to claim 1 , wherein the DDS core comprises a field programmable gate array.
10. A direct digital synthesizer according to claim 1 , wherein said oscillator circuit comprises a voltage controlled oscillator and phase-locked loop circuit.
11. A direct digital synthesizer (DDS) having reduced spurious signals comprising:
a DDS core that produces a digital representation of a signal to be synthesized;
first and second voltage controlled oscillator/phase-locked loop circuits;
first and second DDS circuits operatively connected to the DDS core, each having a digital-to-analog converter connected to the DDS core for receiving the digital representation and converting it into a signal and a modulator operatively connected to said digital-to-analog converter and respective first and second voltage controlled oscillator/phase-locked loop circuits for receiving signals from the digital-to-analog converter and producing a modulated output signal, wherein individual frequencies of the first and second DDS circuits are randomly and continuously changed from each other; and
a mixer that receives and mixes the modulated output signals from said first and second DDS circuits to create a mixed output signal at a selected and fixed frequency.
12. A direct digital synthesizer according to claim 11 , and further comprising a switch circuit operative with said first and second voltage controlled oscillator/phase-locked loop circuits for switching between the modulators within respective first and second DDS circuits.
13. A direct digital synthesizer according to claim 12 , and further comprising a hybrid circuit operative with said switch circuit.
14. A direct digital synthesizer according to claim 11 , wherein said mixer is operative for summing the modulated output signals without multiplication or frequency gain.
15. A direct digital synthesizer according to claim 11 , wherein the sum of frequencies within the mixer of the modulated output signals is constant.
16. A direct digital synthesizer according to claim 11 , wherein the modulated output signals have frequencies that vary randomly.
17. A direct digital synthesizer according to claim 11 , and further comprising a bandpass filter that receives the mixed output signal for selecting a desired frequency and filtering wideband noise.
18. A direct digital synthesizer according to claim 17 , and further comprising a multiplier circuit that receives a signal from the bandpass filter that increases spur level on an instantaneous basis.
19. A direct digital synthesizer according to claim 18 , and further comprising a bandpass filter that receives a multiplied signal from the multiplier circuit.
20. A direct digital synthesizer according to claim 11 , wherein the DDS core comprises a field programmable gate array.
21. A method for synthesizing a signal, which comprises:
forming a digital representation of a signal within a direct digital synthesizer (DDS) core;
converting the digital representation into a signal within a plurality of DDS circuits, each having a digital-to-analog converter connected to the DDS core for receiving the digital representation and converting it into a signal and a modulator operatively connected to said digital-to-analog converter for receiving signals from the digital-to-analog converter and an oscillator circuit and producing a modulated output signal, wherein individual frequencies of the respective DDS circuits are randomly and continuously changed form each other; and
mixing each modulated output signal to create a mixed output signal at a selected and fixed frequency.
22. A method according to claim 21 , which further comprises converting the digital representation within first and second DDS circuits and modulating the converted signal within modulators operatively connected to first and second voltage controlled oscillator/phase-locked loop circuits and producing a modulated output signal.
23. A method according to claim 22 , which further comprises switching between the first and second voltage controlled oscillator/phase-locked loop circuits and a modulator.
24. A method according to claim 21 , which further comprises summing the modulated output signals without multiplication or frequency gain.
25. A method according to claim 21 , which further comprises filtering the mixed output signals for selecting a desired frequency and filtering wideband noise.
26. A method according to claim 21 , which further comprises multiplying the signal to increase spur levels on an instantaneous basis.