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ZHCSFU8B May 2016 – December 2021 ADC32RF80 , ADC32RF83

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RMP|72
- MPQF396A
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- MPQF526

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8.3.4.3 Decimation Filters

The stop-band rejection of the decimation filters is approximately 90 dB with a pass-band bandwidth of approximately 80%. Table 8-4 gives an overview of the pass-band bandwidth depending on decimation filter setting and ADC sampling rate.

Table 8-4 Decimation Filter Summary and Maximum Available Output Bandwidth

DECIMATION SETTING	NO. OF DDCS AVAILABLE PER CHANNEL	NOMINAL PASSBAND GAIN	BANDWIDTH		ADC SAMPLE RATE = N MSPS		ADC SAMPLE RATE = 3 GSPS
DECIMATION SETTING	NO. OF DDCS AVAILABLE PER CHANNEL	NOMINAL PASSBAND GAIN	3 dB (%)	1 dB (%)	OUTPUT RATE (MSPS) PER BAND	OUTPUT BANDWIDTH (MHz) PER BAND	COMPLEX OUTPUT RATE (MSPS) PER BAND	OUTPUT BANDWIDTH (MHz) PER BAND
Divide-by-4 complex	1	–0.4 dB	90.9	86.8	N / 4 complex	0.4 × N / 2	750	600
Divide-by-6 complex	1	–0.65 dB	90.6	86.1	N / 6 complex	0.4 × N / 3	500	400
Divide-by-8 complex	2	–0.27 dB	91.0	86.8	N / 8 complex	0.4 × N / 4	375	300
Divide-by-9 complex	2	–0.45 dB	90.7	86.3	N / 9 complex	0.4 × N / 4.5	333.3	266.6
Divide-by-10 complex	2	–0.58 dB	90.7	86.3	N / 10 complex	0.4 × N / 5	300	240
Divide-by-12 complex	2	–0.55 dB	90.7	86.4	N / 12 complex	0.4 × N / 6	250	200
Divide-by-16 complex	2	–0.42 dB	90.8	86.4	N / 16 complex	0.4 × N / 8	187.5	150
Divide-by-18 complex	2	–0.83 dB	91.2	87.0	N / 18 complex	0.4 × N / 9	166.6	133
Divide-by-20 complex	2	–0.91 dB	91.2	87.0	N / 20 complex	0.4 × N / 10	150	120
Divide-by-24 complex	2	–0.95 db	91.1	86.9	N / 24 complex	0.4 × N / 12	125	100
Divide-by-32 complex	2	–0.78 dB	91.1	86.8	N / 32 complex	0.4 × N / 16	93.75	75

A dual-band example with a divide-by-8 complex is shown in Figure 8-17.

Figure 8-17 Dual-Band Example

The decimation filter responses normalized to the ADC sampling clock are illustrated in Figure 8-17 to Figure 8-40 and can be interpreted as follows:

Each figure contains the filter pass-band, transition bands, and alias bands, as shown in Figure 8-18. The x-axis in Figure 8-18 shows the offset frequency (after the NCO frequency shift) normalized to the ADC sampling clock frequency.

For example, in the divide-by-4 complex, the output data rate is an f_S / 4 complex with a Nyquist zone of f_S / 8 or 0.125 × f_S. The transition band is centered around 0.125 × f_S and the alias transition band is centered at 0.375 × f_S. The alias bands that alias on top of the wanted signal band are centered at 0.25 × f_S and 0.5 × f_S (and are colored in red).

The decimation filters of the ADC32RF8x provide greater than 90-dB attenuation for the alias bands.

Figure 8-18 Interpretation of the Decimation Filter Plots