ADS1294 datasheet(23/88 Pages) TI

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MUX[2:0]=101

TempP

MUX[2:0]= 100

MvddP

(1)

MUX[2:0]= 011

FromLoffP

MUX[2:0]= 000

MUX[2:0]= 110

MUX[2:0]= 001

ToPgaP

ToPgaN

MUX[2:0]= 001

RLDIN

MUX[2:0]= 010

RLD_MEAS

AND

MUX[2:0]= 111

VINP

VINN

MUX[2:0]= 000

FromLoffN

RLD_REF

MUX[2:0]= 010

RLD_MEAS

AND

MvddN

(1)

TempN

MUX[2:0]= 100

MUX[2:0]= 101

ADS129x

MUX

TestP

TestN

TESTP_PACE_OUT1

INT_TEST

TESTN_PACE_OUT2

INT_TEST

MUX[2:0]= 011

EMI

Filter

(AVDD+AVSS)

ADS1294, ADS1294R

ADS1296, ADS1296R

ADS1298, ADS1298R

www.ti.com

SBAS459H

– JANUARY 2010 – REVISED OCTOBER 2011

THEORY OF OPERATION

This section discusses the details of the ADS129x internal functional elements. The analog blocks are reviewed

first, followed by the digital interface. Blocks implementing ECG-specific functions are covered in the end.

Throughout this document, fCLK denotes the frequency of the signal at the CLK pin, tCLK denotes the period of the

signal at the CLK pin, fDR denotes the output data rate, tDR denotes the time period of the output data, and fMOD

denotes the frequency at which the modulator samples the input.

EMI FILTER

An RC filter at the input acts as an EMI filter on all of the channels. The

–3dB filter bandwidth is approximately

3MHz.

INPUT MULTIPLEXER

The ADS129x input multiplexers are very flexible and provide many configurable signal switching options.

Figure 24 shows the multiplexer on a single channel of the device. Note that the device has eight such blocks,

one for each channel. TEST_PACE_OUT1, TEST_PACE_OUT2, and RLD_IN are common to all eight blocks.

VINP and VINN are separate for each of the eight blocks. This flexibility allows for significant device and

sub-system diagnostics, calibration, and configuration. Selection of switch settings for each channel is made by

writing the appropriate values to the CHnSET[2:0] register (see the CHnSET: Individual Channel Settings section

for details) and by writing the RLD_MEAS bit in the CONFIG3 register (see the CONFIG3: Configuration Register

3 subsection of the Register Map section for details). More details of the ECG-specific features of the multiplexer

are presented in the Input Multiplexer subsection of the ECG-Specifc Functions section.

(1)

MVDD monitor voltage supply depends on channel number; see the Supply Measurements (MVDDP, MVDDN)

section.

Figure 24. Input Multiplexer Block for One Channel

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