ADS1292 datasheet(17/69 Pages) TI

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ADS1291

ADS1292

ADS1292R

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SBAS502A – DECEMBER 2011 – REVISED MARCH 2012

THEORY OF OPERATION

This section contains details of the ADS1291, ADS1292, and ADS1292R internal functional elements. The

analog blocks are discussed first followed by the digital interface. Blocks implementing ECG-specific functions

are covered in the end.

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

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

frequency at which the modulator samples the input.

EMI FILTER

An RC filter at the input acts as an electromagnetic interference (EMI) filter on channels 1 and 2. The –3-dB filter

bandwidth is approximately 3 MHz.

INPUT MULTIPLEXER

The ADS1291, ADS1292, and ADS1292R input multiplexers are very flexible and provide many configurable

signal-switching options. Figure 19 shows the multiplexer for the ADS1291, ADS1292, and ADS1292R. Note that

TESTP, TESTM, and RLDIN/RLDREF are common to both channels. INP and INN are separate for each of the

three pins. This flexibility allows for significant device and sub-system diagnostics, calibration, and configuration.

Switch settings for each channel are selected by writing the appropriate values to the CH1SET or CH2SET

ECG-specific features of the multiplexer are discussed in the Input Multiplexer subsection of the ECG-Specifc

Functions.

Device Noise Measurements

Setting CHnSET[3:0] = 0001 sets the common-mode voltage of (VREFP + VREFN)/2 to both inputs of the

channel. This setting can be used to test the inherent noise of the device in the user system.

Test Signals (TestP and TestN)

Setting CHnSET[3:0] = 0101 provides internally-generated test signals for use in sub-system verification at

power-up. This functionality allows the entire signal chain to be tested out. Although the test signals are similar to

the CAL signals described in the IEC60601-2-51 specification, this feature is not intended for use in compliance

testing.

Test signals are controlled through register settings (see the CONFIG2: Configuration Register 2 subsection in

the Register Map section for details). INT_TEST enables the test signal and TEST_FREQ controls switching at

the required frequency.

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