ADS1294 datasheet(73/88 Pages) TI

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Ch1

ADC

Modulation

Block

Demodulation

Block

RESP_CTRL[1:0]

Ch1

PGA

RespirationClock

Generator

CLK

I/O

RESP_CTRL[1:0]

GPIO3

GPIO4

GPIO2

RESP_MODP

RESP_MODN

IN1P

IN1N

EMI

Filter

MUX

ADS1294, ADS1294R

ADS1296, ADS1296R

ADS1298, ADS1298R

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SBAS459H

– JANUARY 2010 – REVISED OCTOBER 2011

Internal Respiration Circuitry with Internal Clock (RESP_CTRL = 10b, ADS1294R/6R/8R Only)

Figure 67 shows a block diagram of the internal respiration circuitry. The internal modulation and demodulator

circuitry can be selectively used. The modulation block is controlled by the RESP_MOD_EN bit and the

demodulation block is controlled by the RESP_DEMOD_EN bit. The modulation signal is a square wave of

magnitude VREFP

– AVSS. In this mode, the output of the modulation circuitry is available at the RESP_MODP

and RESP_MODN terminals of the device. This availability allows custom filtering to be added to the square

wave modulation signal. In this mode, GPIO2, GPIO3, and GPIO4 can be used for other purposes. The

modulation frequency can be 64kHz or 32kHz, as set by the RESP_FREQ[2:0] bits in the CONFIG4 register. The

phase of the internal demodulation signal is set by the RESP_PH[2:0] bits in the RESP register.

The ADS1294R/6R/8R channel 1 with respiration enabled mode cannot be used to acquire ECG signals. If the

RA and LA leads are intended to measure respiration and ECG signals, the two leads can be wired into channel

1 for respiration and channel 2 for ECG signals.

Figure 67. Internal Respiration Block Diagram

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