Hewlett-packard Company

Roland Hassun

Albert W Kovalick

In direct digital synthesizers in the prior art, the output signal maintains a phase continuity whenever it switches, or hops, frequency. This phase continuity shows up as a smooth change in phase from one frequency to the next; the phase of the last frequency transitions into the phase of the new frequency without any discernable disruption. Thus, whenever the output signal returns to a switched frequency that it previously has, the output signal at the newly returned switched frequency has a new phase relative to its previous one at that frequency. For some applications, like simulating continuous different frequency sources, this phase continuity is not desirable. To overcome this disadvantage, the preferred embodiment of the present invention provides phase memory to a direct digital synthesizer so that regardless of the frequency that the output signal switches to, the output signal at that frequency is able to maintain a constant phase relative to a reference system clock pulse. In other words, switching and returning the synthesizer output signal to a selected frequency does not change the phase of the output signal at that frequency; the output signal at each frequency has the same constant phase as it has previously at that frequency. As a result, the synthesizer in accordance with the present invention appears to have a source of numerous continuous oscillators to which it can switch for a number of different frequencies, each having a constant phase.

Digital synthesizer with phase memory

A novel signal synthesizer provides high frequency synthesized waveforms for the user. By converting phase information into digital outputs in parallel and by selectively coupling these digital outputs, an ordered digital output is formed to provide the high frequency waveforms. This ordered digital output, which represents points on a sine function, is converted to an analog signal for the synthesizer output. Furthermore, frequency and phase modulations of the synthesized waveforms are easily implemented with this novel signal synthesizer; the modulation information is simply added to the digital outputs prior to selectively coupling. Thus when the ordered digital output is converted to an analog signal, the analog signal contains the modulation information.

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San Carlos, CA, United States of America

Roland Hassun