ADAS1000 datasheet(39/80 Pages) AD

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Data Sheet

ADAS1000/ADAS1000-1/ADAS1000-2

filtered, and synchronously demodulated in the digital domain;

the result is a digital signal that represents the total thoracic or

respiration impedance, including cable and electrode contri-

butions. While it is heavily low-pass filtered on-chip, the user is

required to further process it to extract the envelope and perform

the peak detection needed to establish breathing (or lack thereof).

Respiration measurement is available on one of the leads (Lead I,

Lead II, or Lead III) or on an external path via a pair of dedicated

pins (EXT_RESP_LA, EXT_RESP_RA, or EXT_RESP_LL).

Only one lead measurement can be made at one time. The

respiration measurement path is not suited for use as additional

ECG measurements because the internal configuration and

demodulation do not align with an ECG measurement; however,

the EXT_RESP_LA, EXT_RESP_RA, or EXT_RESP_LL paths

can be multiplexed into one of the ECG ADC paths, if required,

as discussed in the Extend Switch On Respiration Paths section.

The respiration signal processing path is not reconfigurable for

ECG measurements, as it is specifically designed for the respiration

signal measurement.

Table 12. Maximum Allowable Cable and Thoracic Loading

Cable Resistance

Cable Capacitance

R < 1 kΩ

C < 1200 pF

1 kΩ < R < 2.5 kΩ

C < 400 pF

2.5 kΩ < R < 5 kΩ

C < 200 pF

RTHORACIC < 2 kΩ

Internal Respiration Capacitors

The internal respiration function uses an internal RC network

(5 kΩ/100 pF), and this circuit is capable of 200 mΩ resolution

(with up to 5 kΩ total path and cable impedance). The current

is ac-coupled onto the same pins that the measurement is sensed

back on. Figure 69 shows the measurement on Lead I, but,

similarly, the measurement can be configured to measure on

either Lead II or Lead III. The internal capacitor mode requires

no external capacitors and produces currents of ~64 µA p-p

amplitude when configured for maximum amplitude setting

(±1V) through the RESPCTRL register (see Table 30).

External Respiration Path

The EXT_RESP_xx pins are provided for use either with the

ECG electrode cables or, alternatively, with a dedicated external

sensor independent of the ECG electrode path. Additionally, the

EXT_RESP_xx pins are provided so the user can measure the

respiration signal at the patient side of any input filtering on the

front end. In this case, the user must continue to take precautions

to protect the EXT_RESP_xx pins from any signals applied that

are in excess of the operating voltage range (for example, ESIS

or defibrillator signals).

Figure 69. Simplified Respiration Block Diagram

LA CABLE

ECG1_LA

EXT_RESP_LA

ECG2_LL

EXT_RESP_LL

ECG3_RA

EXT_RESP_RA

ADAS1000

OVERSAMPLED

5kΩ

100pF

RESPIRATION DAC

DRIVE +

±1V

CABLE AND ELECTRODE

IMPEDANCE < 5kΩ

LL CABLE

RA CABLE

FILTER

RESPIRATION

MEASURE

RESPIRATION DAC

DRIVE–

HPF

IN-AMP AND

ANTI-ALIASING

MAGNITUDE

AND

PHASE

SAR

ADC

46.5kHz TO

64kHz

46.5kHz TO

64kHz

LPF

fc=10kHz

fc=150kHz

7Hz

Rev. B | Page 39 of 80

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