ADS58C28IRGCR Datasheet, PDF (51/67 Pages) Texas Instruments – Dual Channel IF Receiver with SNRBoost3G

ADS58C28
www.ti.com
SBAS509B – JUNE 2010 – REVISED OCTOBER 2010
Table 14. Complete List of SNRBoost^3G Modes (f_S = Sampling Frequency in MSPS) (continued)
SNRBoost^3G FILTER NUMBER
CENTER FREQUENCY OF THE BATHTUB
BANDWIDTH OF THE BATHTUB (MHz)
(MHz)
40
60 × (f_S/184)
46 × (f_S/184)
41
60 × (f_S/184)
46 × (f_S/184)
42
60 × (f_S/184)
30 × (f_S/184)
43
60 × (f_S/184)
30 × (f_S/184)
44
60 × (f_S/184)
62 × (f_S/184)
45
60 × (f_S/184)
62 × (f_S/184)
46
60 × (f_S/184)
40.5 × (f_S/184)
47
60 × (f_S/184)
40.5 × (f_S/184)
48
60 × (f_S/184)
37 × (f_S/184)
49
60 × (f_S/184)
37 × (f_S/184)
50
60 × (f_S/184)
53 × (f_S/184)
51
60 × (f_S/184)
50 × (f_S/184)
52
60 × (f_S/184)
54 × (f_S/184)
53
58 × (f_S/184)
58 × (f_S/184)
54
60 × (f_S/184)
62 × (f_S/184)
GAIN FOR SFDR/SNR TRADE-OFF
The ADS58C28 includes gain settings that can be used to get improved SFDR performance. The gain is
programmable from 0dB to 6dB (in 0.5dB steps) using the GAIN register bits. For each gain setting, the analog
input full-scale range scales proportionally, as shown in Table 15.
The SFDR improvement is achieved at the expense of SNR; for each gain setting, the SNR degrades
approximately between 0.5dB and 1dB. The SNR degradation is reduced at high input frequencies. As a result,
the gain is very useful at high input frequencies because the SFDR improvement is significant with marginal
degradation in SNR. Therefore, the gain can be used as a trade-off between SFDR and SNR.
After a reset, the gain function is disabled. To use gain:
• First, program the DIGITAL MODE 1 and DIGITAL MODE 2 bits (see Table 12) to enable the gain function.
• This setting enables the gain and puts the device in a 0dB gain mode.
• For other gain settings, program the GAIN register bits.
GAIN (dB)
0
1
2
3
4
5
6
Table 15. Full-Scale Range Across Gains
TYPE
Default after reset
Fine adjust, programmable
Fine adjust, programmable
Fine adjust, programmable
Fine adjust, programmable
Fine adjust, programmable
Fine adjust, programmable
FULL-SCALE (V_PP)
2
1.78
1.59
1.42
1.26
1.12
1
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