| 摘要 |
The invention described herein provides a method and apparatus that allows direct digital to IF/RF conversion using pulse-shaping. The method facilitates obtaining a flat or near flat output spectrum after digital to analog conversion with a minimal loss in signal energy. As opposed to pulse-shortening, where the DAC output pulse and consequently the energy per sample are reduced to a fraction a<l of the maximum, the pulse-shaping does not shorten the DAC pulse. For each sample, pulse-shaping first stores the energy delivered by DAC and then releases the stored energy to the output during a short period of time aT. This way little signal energy is lost even for very small values of a. With pulse-shaping, the duration aT of the output pulse contributes to the spectral flatness in a way similar to that pulse-shortening, but has the additional benefit that the shape of the output pulse contributes significantly to a flat spectrum. Two embodiments of the pulse-shaping method are described in the context of two types of DAC that are used: one with current output and the other with voltage output. Then, two examples of pulse-shaping implementation are given for a single-ended current-output DAC and for a differential current-output DAC.
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