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ZHCSMZ6B December 2020 – July 2022 ADC3664

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8.3.4.5 Decimation Filter

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.

Table 8-2 Decimation Filter Summary and Maximum Available Output Bandwidth

REAL/COMPLEX DECIMATION	DECIMATION SETTING N	OUTPUT RATE	OUTPUT BANDWIDTH	OUTPUT RATE (F_S = 125 MSPS)	OUTPUT BANDWIDTH (F_S = 125 MSPS)
Complex	2	F_S / 2 complex	0.8 × F_S / 2	62.5 MSPS complex	50 MHz
	4	F_S / 4 complex	0.8 × F_S / 4	31.25 MSPS complex	25 MHz
	8	F_S / 8 complex	0.8 × F_S / 8	15.625 MSPS complex	12.5 MHz
	16	F_S / 16 complex	0.8 × F_S / 16	7.8125 MSPS complex	6.25 MHz
	32	F_S / 32 complex	0.8 × F_S / 32	3.90625 MSPS complex	3.125 MHz
Real	2	F_S / 2 real	0.4 × F_S / 2	62.5 MSPS	25 MHz
	4	F_S / 4 real	0.4 × F_S / 4	31.25 MSPS	12.5 MHz
	8	F_S / 8 real	0.4 × F_S / 8	15.625 MSPS	6.25 MHz
	16	F_S / 16 real	0.4 × F_S / 16	7.8125 MSPS	3.125 MHz
	32	F_S / 32 real	0.4 × F_S / 32	3.90625 MSPS	1.5625 MHz

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.