ADS4225 datasheet(83/104 Pages) TI1

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DigitalFunctions

(Gain,OffsetCorrection,TestPatterns)

Output

Interface

DDRLVDS

orCMOS

12-Bit(ADS422x)

14-Bit(ADS424x)

ENDIGITALBit

12-/14-Bit

ADC

ADS4222, ADS4225, ADS4226

ADS4242, ADS4245, ADS4246

www.ti.com

SBAS533C

– MARCH 2011 – REVISED JUNE 2011

DIGITAL FUNCTIONS

The device has several useful digital functions (such as test patterns, gain, and offset correction). These

functions require extra clock cycles for operation and increase the overall latency and power of the device. These

digital functions are disabled by default after reset and the raw ADC output is routed to the output data pins with

a latency of 16 clock cycles. Figure 165 shows more details of the processing after the ADC. In order to use any

of the digital functions, the EN DIGITAL bit must be set to '1'. After this, the respective register bits must be

programmed as described in the following sections and in the Serial Register Map section.

Figure 165. Digital Processing Block

GAIN FOR SFDR/SNR TRADE-OFF

The ADS424x/422x include gain settings that can be used to get improved SFDR performance (compared to no

gain). The gain is programmable from 0dB to 6dB (in 0.5dB steps). 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

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. Note that the

default gain after reset is 0dB.

Table 11. Full-Scale Range Across Gains

GAIN (dB)

TYPE

FULL-SCALE (VPP)

Default after reset

Fine, programmable

1.78

Fine, programmable

1.59

Fine, programmable

1.42

Fine, programmable

1.26

Fine, programmable

1.12

Fine, programmable

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Product Folder Link(s): ADS4222 ADS4225 ADS4226 ADS4242 ADS4245 ADS4246

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