Spurious free wideband phase and frequency modulator using a direct digital synthesis alias frequency band
First Claim
1. A direct digital synthesis modulator for modulating a video signal, comprising:
- a digital state machine receiving a digital video input signal;
a direct digital synthesis module receiving an output signal from said digital state machine for providing direct digital synthesis of the output signal;
a tuned frequency local oscillator providing a modulating output signal from a transmitter frequency control signal; and
an exciter receiving the modulating output signal from said tuned frequency local oscillator for providing a modulated video signal to be transmitted.
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Abstract
A wideband phase and frequency modulator using a direct digital synthesis alias frequency band is described. The modulator is spurious free by the utilization of a fixed frequency at the output of the direct digital synthesizer wherein only certain submultiples of the clock frequency are used. Known frequency ratios relative to the clock frequency of the direct digital synthesizer (DDS) cause the DDS to function as a simple divider resulting in extremely low spurious levels when additional conditions are met. An additional frequency synthesizer may be utilized to achieve a tuning range since the DDS output is preferably held at a fixed frequency. At least one additional mixing operation is utilized for upconversion to a microwave frequency. Since fixed frequency ratios are used, implementation simpler than a full DDS may also be constructed consisting of digital modulators, multiplexers, digital to analog convertors, and filters.
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Citations
29 Claims
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1. A direct digital synthesis modulator for modulating a video signal, comprising:
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a digital state machine receiving a digital video input signal; a direct digital synthesis module receiving an output signal from said digital state machine for providing direct digital synthesis of the output signal; a tuned frequency local oscillator providing a modulating output signal from a transmitter frequency control signal; and an exciter receiving the modulating output signal from said tuned frequency local oscillator for providing a modulated video signal to be transmitted. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 28)
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14. An alias band bandpass sampler for a video modulator, comprising:
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a direct digital synthesizer providing a digital sinusoidal output, said direct digital synthesizer being driven with a clock signal; a multiplexer receiving said digital sinusoidal output from said direct digital synthesizer for providing a multiplexed output signal; a digital-to-analog converter receiving the multiplexed output signal from said multiplexer for converting the multiplexed output signal into an analog signal; and a filter receiving the analog signal for removing undesired frequency components from the analog signal to provide an output signal. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21)
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22. An alias band bandpass sampler for a video modulator, comprising:
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a direct digital synthesizer providing digital sine and cosine outputs, said direct digital synthesizer being driven with a clock signal; a multiplexer receiving said digital sine and cosine outputs from said direct digital synthesizer for providing a multiplexed output signal; a digital-to-analog converter receiving the multiplexed output signal from said multiplexer for converting the multiplexed output signal into an analog signal; and a filter receiving the analog signal for removing undesired frequency components from the analog signal to provide an output signal. - View Dependent Claims (23, 24, 25, 26, 27, 29)
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Specification