ADS1294 datasheet(26/88 Pages) TI

26 / 88 page

PgaP

50k

20k

(forGain=6)

50k

FromMuxP

PgaN

FromMuxN

ToADC

ADS1294, ADS1294R

ADS1296, ADS1296R

ADS1298, ADS1298R

SBAS459H

– JANUARY 2010 – REVISED OCTOBER 2011

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PGA SETTINGS AND INPUT RANGE

The PGA is a differential input/differential output amplifier, as shown in Figure 28. It has seven gain settings (1,

2, 3, 4, 6, 8, and 12) that can be set by writing to the CHnSET register (see the CHnSET: Individual Channel

Settings subsection of the Register Map section for details). The ADS129x have CMOS inputs and hence have

negligible current noise. Table 6 shows the typical values of bandwidths for various gain settings. Note that

Table 6 shows the small-signal bandwidth. For large signals, the performance is limited by the slew rate of the

PGA.

Figure 28. PGA Implementation

Table 6. PGA Gain versus Small-Signal Bandwidth

NOMINAL BANDWIDTH AT ROOM

GAIN

TEMPERATURE (kHz)

237

146

127

The resistor string of the PGA that implements the gain has 120k

Ω of resistance for a gain of 6. This resistance

provides a current path across the outputs of the PGA in the presence of a differential input signal. This current

is in addition to the quiescent current specified for the device in the presence of a differential signal at the input.

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ADS1294 Datasheet(PDF) 26 Page - Texas Instruments