ZHCSRJ6C June 2010 – January 2023 TLV320AIC3104-Q1
PRODUCTION DATA
The digital interpolation filter upsamples the output of the digital audio processing block by the required oversampling ratio before data are provided to the digital delta-sigma modulator and analog reconstruction filter stages. The filter provides a linear phase output with a group delay of 21 / fS. In addition, programmable digital interpolation filtering is included to provide enhanced image filtering and reduce signal images caused by the upsampling process that are below 20 kHz. For example, upsampling an 8-kHz signal produces signal images at multiples of 8-kHz (that is, 8 kHz, 16 kHz, 24 kHz, and so forth). The images at 8 kHz and 16 kHz are below 20 kHz and are still audible to the listener; therefore, these images must be filtered heavily to maintain a good quality output. The interpolation filter is designed to maintain at least 65-dB rejection of images that are below 7.455 fS. In order to use the programmable interpolation capability, program fS(ref) to a higher rate (restricted to be in the range of 39 kHz to 53 kHz when the PLL is in use), and the actual fS is set using the NCODEC divider, where NCODEC = NDAC = NADC. For example, if fS = 8 kHz is required, then fS(ref) can be set to 48 kHz and the DAC fS set to fS(ref) / 6. This setting ensures that all images of the 8-kHz data are sufficiently attenuated well beyond a 20-kHz audible frequency range.