| 摘要 |
<p>A D/A converter (8) includes a DELTA SIGMA modulator (9) applying Delta-Sigma modulation to a digital signal S1 in order to generate a code sequence S2, and first and second post-filters (10,11) as a first-order analog low-pass filter, respectively, which is connected in cascade to the subsequent stage of the modulator (9), in which low-pass filtering on the code sequence S2 is executed so as to output an analog signal Sout. The post-filter (10) is set to have a cutoff frequency fcb which falls in the frequency range from fca to fHa, where the fca is a cutoff frequecy of the post-filter (11) and the fHa is a maximum frequency thereof. Since the respective attenuation characteristics of post-filters (10 and 11) are synthesized, an overall attenuation characteristic Gab between the both filters is able to have the characteristics of a desired second-order filter. The synthesized attenuation characteristic Gab allows the D/A converter to simultaneously execute processing such as de-emphasis in the frequency range between the both cutoff frequency fca and fcb, and elimination of high-frequency noises over the frequency range of the cutoff frequency fcb. As a result, the D/A converter with a small circuit scale can be provided. <IMAGE></p> |
