Datasheet

www.ti.com
COARSE GAIN AND PROGRAMMABLE FINE GAIN
ADS6145, ADS6144
ADS6143, ADS6142
SLWS198B – JULY 2007 – REVISED MARCH 2008
The ADS614X include gain settings that can be used to improve SFDR performance (compared to 0 dB gain
mode). The gain settings are 3.5 dB coarse gain and 0 dB to 6 dB programmable fine gain. For each gain
setting, the analog input full-scale range scales proportionally, as shown in Table 13 .
The coarse gain is a fixed setting of 3.5 dB and is designed to improve SFDR with little degradation in SNR (as
shown in Figure 13 and Figure 14 ). The fine gain is programmable in 1 dB steps from 0 dB to 6 dB. With fine
gain, SFDR improvement is also achieved, but at the expense of SNR (there is about 1 dB SNR degradation for
every 1 dB of fine gain).
So, the fine gain can be used to trade-off between SFDR and SNR. The coarse gain makes it possible to get the
best SFDR but without losing SNR significantly. At high input frequencies, the gains are especially useful as the
SFDR improvement is significant with marginal degradation in SINAD. The gains can be programmed using the
register bits <COARSE GAIN> (see Table 5 ) and <FINE GAIN> (see Table 10 ). Note that the default gain after
reset is 0 dB.
Table 13. Full-Scale Range Across Gains
GAIN, dB TYPE FULL-SCALE RANGE, V
PP
0 Default after reset 2.00
3.5 Coarse setting (fixed) 1.34
1 1.78
2 1.59
3 1.42
Fine gain (programmable)
4 1.26
5 1.12
6 1.00
46 Submit Documentation Feedback Copyright © 2007 – 2008, Texas Instruments Incorporated
Product Folder Link(s): ADS6145, ADS6144 ADS6143, ADS6142