ADS58C48IPFPR datasheet(55/70 Pages) TI

55 / 70 page

ADS58C48

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SLAS689 – MAY 2010

GAIN FOR SFDR/SNR TRADE-OFF

ADS58C48 includes gain settings that can be used to get improved SFDR performance. The gain is

programmable from 0 dB to 6 dB (in 0.5 dB steps) using the <GAIN> register bits. For each gain setting, the

analog input full-scale range scales proportionally, as shown in Table 11.

The SFDR improvement is achieved at the expense of SNR; for each gain setting, the SNR degrades about 0.5

-1dB. The SNR degradation is less at high input frequencies. As a result, the fine gain is very useful at high input

frequencies as the SFDR improvement is significant with marginal degradation in SNR. So, the fine gain can be

used to trade-off between SFDR and SNR.

After a reset, the gain function is disabled. To use fine gain:

•

First, program the bits <DIGITAL MODE 1> and <DIGITAL MODE 2> as per the table above to enable the

gain function.

•

This enables gain and puts device in 0 dB gain mode.

•

For other gain settings, program the <GAIN> register bits.

Table 11. Full-Scale Range Across Gains

FULL-SCALE,

GAIN, dB

TYPE

VPP

Default after reset

1.78

1.59

1.42

Programmable gain

1.26

1.12

1.00

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ADS58C48IPFPR Datasheet(PDF) 55 Page - Texas Instruments