The ADC3664 supports complex decimation by 2, 4, 8, 16 and 32 with a pass-band bandwidth of ~ 80% and a stopband rejection of at least 85 dB. Table 8-2 gives an overview of the pass-band bandwidth of the different decimation settings with respect to ADC sampling rate F_S. In real decimation mode the output bandwidth is half of the complex bandwidth.

The decimation filter responses normalized tot he ADC sampling clock frequency are illustrated in Figure 8-21 to Figure 8-30. They are interpreted as follows:

Each figure contains the filter pass-band, transition band(s) and alias or stop-band(s) as shown in Figure 8-20. The x-axis shows the offset frequency (after the NCO frequency shift) normalized to the ADC sampling rate F_S.

For example, in the divide-by-4 complex setup, the output data rate is F_S / 4 complex with a Nyquist zone of F_S / 8 or 0.125 × F_S. The transition band (colored in blue) is centered around 0.125 × F_S and the alias transition band is centered at 0.375 × F_S. The stop-bands (colored in red), which alias on top of the pass-band, are centered at 0.25 × F_S and 0.5 × F_S. The stop-band attenuation is greater than 85 dB.

Figure 8-20 Interpretation of the Decimation Filter Plots

Figure 8-21 Decimation by 2 complex frequency response

Figure 8-23 Decimation by 4 complex frequency response

Figure 8-25 Decimation by 8 complex frequency response

Figure 8-27 Decimation by 16 complex frequency response

Figure 8-29 Decimation by 32 complex frequency response

Figure 8-22 Decimation by 2 complex passband ripple response

Figure 8-24 Decimation by 4 complex passband ripple response

Figure 8-26 Decimation by 8 complex passband ripple response

Figure 8-28 Decimation by 16 complex passband ripple response

Figure 8-30 Decimation by 32 complex passband ripple response