Evaluation of the ADS1298R Respiration Function
41
SBAU181B – March 2011 – Revised Janurary 2016
Copyright © 2011–2016, Texas Instruments Incorporated
ADS1298R
5
Evaluation of the ADS1298R Respiration Function
5.1
Introduction
The ADS1298R allows for the measurement of respiration rate based on the principle of impedance
pneumography. The key concept of this approach is to measure the change in impedance of the thoracic
cavity during breathing (respiration). The ADS1298REVM provides two ways to test the respiration
circuitry: first, using onboard circuitry; and second, using a patient simulator with respiration outputs. This
section describe both approaches.
5.2
Testing with Onboard Circuitry
For additional information on Impedance Pneumography, please refer to the following
.
5.2.1
Hardware Configuration
The ADS1298REVM has onboard circuitry to test a respiration circuit. A simplified diagram illustrating only
the respiration portion of the circuit is shown in
; the onboard circuitry to generate the respiration
signal is within the red dotted box. By default, jumpers JP34 and JP35 connect the onboard circuitry for
respiration evaluation. R77 models the baseline impedance of the thoracic cavity. This component is a
surface-mount resistor located on the underside of the board; it can be changed if desired. R78 and R79
model the cable resistance (typically 1k
Ω
for patient monitoring). Capacitors C97 and C98 are used to
model the parasitic capacitance that may be present when real cables are used. Capacitors C113 and
C114 serve as a secondary means to prevent a single fault (such as a shorted C112 capacitor from a
carrier generator) from causing excessive DC currents through the electrodes.
The parameter of interest is the change in impedance during breathing. This change in impedance is
accomplished by switching 1M
Ω
impedance in parallel to R77 using an analog switch, U11. Two 1M
Ω
resistors (R82 and R83) have been added to provide a DC bias to this switch. Switch U11 must have a
control signal that toggles between AVSS and AVDD at the desired respiration frequency. This control
signal can be fed from either an onboard signal source or an external function generator via JP36.
Figure 36. Respiration Evaluation with Onboard Circuitry
