SBAS872 December 2020 ADC3683
The ADC368x supports complex decimation by 2, 4, 8, 16 and 32 with a stopband rejection of at least 85 dB and a pass-band bandwidth of ~ 80%. Table 8-3 gives an overview of the pass-band bandwidth of the different decimation settings with respect to ADC sampling rate FS. In real decimation mode the output bandwidth is half of the complex bandwidth.
|REAL/COMPLEX DECIMATION||DECIMATION SETTING N||OUTPUT RATE||OUTPUT BANDWIDTH||OUTPUT RATE |
(FS = 65 MSPS)
|OUTPUT BANDWIDTH |
(FS = 65 MSPS)
|Complex||2||FS / 2 complex||0.8 × FS / 2||32.5 MSPS complex||26 MHz|
|4||FS / 4 complex||0.8 × FS / 4||16.25 MSPS complex||13 MHz|
|8||FS / 8 complex||0.8 × FS / 8||8.125 MSPS complex||6.5 MHz|
|16||FS / 16 complex||0.8 × FS / 16||4.0625 MSPS complex||3.25 MHz|
|32||FS / 32 complex||0.8 × FS / 32||2.03125 MSPS complex||1.625 MHz|
|Real||2||FS / 2 real||0.4 × FS / 2||32.5 MSPS||13 MHz|
|4||FS / 4 real||0.4 × FS / 4||16.25 MSPS||6.5 MHz|
|8||FS / 8 real||0.4 × FS / 8||8.125 MSPS||3.25 MHz|
|16||FS / 16 real||0.4 × FS / 16||4.0625 MSPS||1.625 MHz|
|32||FS / 32 real||0.4 × FS / 32||2.03125 MSPS||0.8125 MHz|
Each figure contains the filter pass-band, transition band(s) and alias or stop-band(s) as shown in Figure 8-24. The x-axis shows the offset frequency (after the NCO frequency shift) normalized to the ADC sampling rate FS.
For example, in the divide-by-4 complex setup, the output data rate is FS / 4 complex with a Nyquist zone of FS / 8 or 0.125 × FS. The transition band (colored in blue) is centered around 0.125 × FS and the alias transition band is centered at 0.375 × FS. The stop-bands (colored in red), which alias on top of the pass-band, are centered at 0.25 × FS and 0.5 × FS. The stop-band attenuation is greater than 85 dB.