ADAS1000BSTZ datasheet(37/80 Pages) AD

37 / 80 page

Data Sheet

ADAS1000/ADAS1000-1/ADAS1000-2

Rev. A | Page 37 of 80

a shield drive, an external amplifier connected to the CM_OUT

pin can be used.

RESPIRATION (ADAS1000 MODEL ONLY)

The respiration measurement is performed by driving a high

frequency (programmable from 46.5 kHz to 64 kHz) differential

current into two electrodes; the resulting impedance variation

caused by breathing causes the differential voltage to vary at the

respiration rate. The signal is ac-coupled onto the patient. The

acquired signal is AM, with a carrier at the driving frequency

and a shallow modulation envelope at the respiration frequency.

The modulation depth is greatly reduced by the resistance of the

customer-supplied RFI and ESIS protection filters, in addition

to the impedance of the cable and the electrode to skin interface

(see Table 12). The goal is to measure small ohm variation to sub

ohm resolution in the presence of large series resistance. The

circuit itself consists of a respiration DAC that drives the ac-

coupled current at a programmable frequency onto the chosen

pair of electrodes. The resulting variation in voltage is amplified,

filtered, and synchronously demodulated in the digital domain;

what results 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.

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 66 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 28).

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

Figure 66. 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

ADAS1000BSTZ датащи(PDF) 37 Page - Analog Devices

ADAS1000BSTZ датащи(HTML) 37 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

датащи скачать

ссылки URL