ADS5295IPFP datasheet(64/93 Pages) TI2

64 / 93 page

Mapper

8:8

Multiplexer

OUT3A

OUT3B

OUT4A

OUT4B

LVDS Outputs

12-Bit

ADC

1/2 ADS5295

Channel 2

Channel 3

Channel 4

OUT1A

OUT1B

OUT2A

OUT2B

Digital Processing Block for Channel 1

Test

Patterns,

Ramp

Average of

2 Channels

Average of

4 Channels

Channel 1 ADC Data

Built-In Coefficients

Decimate

By 2, 4,

or 8

Custom Coefficients

12-Tap Filter

Gain

(0 dB to 12 dB,

in 1-dB steps)

Decimate

By 2 or 4

Channel 2 ADC Data

Channel 3 ADC Data

Channel 4 ADC Data

12-Bit

ADC

12-Bit

ADC

12-Bit

ADC

Digital Processing Block for Channel 2

Digital Processing Block for Channel 3

Digital Processing Block for Channel 4

23-Tap Tilter

(Odd Tap)

24-Tap Filter

(Even Tap)

23-Tap Filter

(Odd Tap)

24-Tap Filter

(Even Tap)

Channel 1

Serializer

Wire 1

Serializer

Wire 2

Channel 4

Serializer

Wire 1

Serializer

Wire 2

Channel 3

Serializer

Wire 1

Serializer

Wire 2

Channel 2

Serializer

Wire 1

Serializer

Wire 2

ADC Data:

ADS5295

SBAS595 – DECEMBER 2012

www.ti.com

DIGITAL PROCESSING BLOCKS

The ADS5295 integrates a set of commonly-used digital functions that can be used to ease system design.

These functions are shown in Figure 61 and are described in the following sections.

Figure 61. Digital Processing Block Diagram

Digital Gain

The ADS5295 includes programmable digital gain settings from 0 dB to 12 dB in 1-dB steps. The benefit of

digital gain is obtaining improved SFDR performance. However, SFDR improvement is achieved at the expense

of SNR; for each gain setting, SNR degrades by approximately 1 dB. Therefore, the gain can be used to trade-off

between SFDR and SNR.

For each gain setting, the supported analog input full-scale range scales proportionally, as shown in Table 9.

After reset, the device comes up in 0-dB gain mode. To use other gain settings, program the GAIN_CH[3:0]

Table 9. Analog Full-Scale Range Across Gains

GAIN_CH[3:0]

DIGITAL GAIN (dB)

ANALOG FULL-SCALE INPUT (VPP)

0000

0001

1.78

0010

1.59

0011

1.42

0100

1.26

0101

1.12

0110

0111

0.89

1000

0.8

1001

0.71

1010

0.63

1011

0.56

1100

0.5

Other combinations

Do not use

—

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