ADC32RF80_16 Datasheet, PDF (40/136 Pages) Texas Instruments – Dual-Channel, 3-GSPS Telecom Receiver and Feedback Devices

ADC32RF80, ADC32RF83
SBAS774A – MAY 2016 – REVISED DECEMBER 2016
A dual-band example with a divide-by-8 complex is shown in Figure 96.
ADC
NCO 1,
16 Bits
3 GSPS
IQ 3 GSPS
Filter
8
IQ
750 MSPS
IQ Output
Band 1
IQ 3 GSPS
NCO 2,
16 Bits
8
Filter
IQ
750 MSPS
IQ Output
Band 2
Band 2
fS/4
Band 1
Band 1
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fS/16
Band 2
fS/16
NCO 2
NCO 1
fS/2
Figure 96. Dual-Band Example
The decimation filter responses normalized to the ADC sampling clock are illustrated in Figure 96 to Figure 119
and can be interpreted as follows:
Each figure contains the filter pass-band, transition bands, and alias bands, as shown in Figure 97. The x-axis in
Figure 97 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.
Filter
Transition
Band
Bands That Aliases On
Top of Signal Band
Band That Folds Back On
Top of Transition Band
Figure 97. Interpretation of the Decimation Filter Plots
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