ADS6123IRHB25 datasheet(46/67 Pages) TI1

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COARSE GAIN and PROGRAMMABLE FINE GAIN

ADS6125, ADS6124

ADS6123, ADS6122

SLAS560A – OCTOBER 2007 – REVISED MARCH 2008

ADS612X includes gain settings that can be used to get improved SFDR performance (compared to 0 dB gain

mode). The gain settings are 3.5 dB coarse gain and programmable fine gain from 0 dB to 6 dB. For each gain

setting, the analog input full-scale range scales proportionally, as shown in Table 15.

The coarse gain is a fixed setting of 3.5 dB and is designed to improve SFDR with little degradation in SNR (as

seen in Figure 13 and Figure 14). The fine gain is programmable in 1 dB steps from 0 to 6 dB. With fine gain

also, SFDR improvement is 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

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

reset is 0 dB.

Table 15. Full-Scale Range Across Gains

GAIN, dB

TYPE

FULL-SCALE RANGE, VPP

Default after reset

2.00

3.5

Coarse setting (fixed)

1.34

1.78

1.59

1.42

Fine gain (programmable)

1.26

1.12

1.00

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ADS6123IRHB25 Datasheet(PDF) 46 Page - Texas Instruments