Texas Instruments ADS1298RECG-FE, User Manual

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D D V = R I = 0.11 29.15 = 3.2 V
B
m · ·
D - - W
R = R77 R77 || R76 = 330 329.89 = 0.11
I =
B
VREFP VREFM
R77 + R78 + R79 + R96 + R97
-
2.4
82.33k
= = 29.15 A
m
DC_V =
DC_V =
· -
(VREFP VREFM)
·
2.4 = 67.9mV
R77 + R78 +R79
R96 + R97 + R77 + R78 +R79
0.33k + 1k +1k
40k + 40k + 0.33k + 1k +1k
Evaluation of the ADS1298R Respiration Function
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42 SBAU181B – March 2011 – Revised Janurary 2016
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ADS1298R
The remainder of the circuit is necessary for respiration measurements with both the onboard circuitry and
patient simulator. Resistors R96 and R97 limit the amount of AC current that flows into the body.
Capacitors C108 and C109 block any DC current from flowing into the body from the transmission side.
Capacitors C99 and C100 serve the same purpose on the receiver side. The respiration capability is
available on Channel 1. The respiration signals are routed to Channel 1 when the two shunts on JP33 are
in the respective default locations, shorting pins 5-6 and 7-8 as shown in
Figure 36 .
5.2.2 Software Configuration
The Respiration Control Register works in conjunction with Configuration Register 4 (CONFIG4). Certain
bit changes must be done in order to activate the respiration circuitry of the ADS1298R.
For internal respiration with an internal clock, set the following:
• Configuration Register 4
– Respiration Frequency to 32kHz
• CHxSET registers
– Normal Electrode
– Gain to 6
• RESP register set to:
– Respiration Demodulation to Enabled
– Respiration Modulation to Enabled
– VREF to VREFP
– Respiration Phase to 112.5 deg
– Respiration Control to Internal Respiration with Internal Clock
Next, switch U11 must be toggled at the desired respiration frequency by applying a square wave via
JP36. An onboard MSP430G2121 is provided to give approximately 0.1Hz through 0.5Hz. The MSP430
circuitry is selected when JP36 is loaded with a shunt jumper that shorts pins 1-2 (default). An external
function generator can also be used for this purpose by applying a signal to SMA connector J6 and
moving the shunt jumper on JP36 to cover pins 2-3. Data can be acquired by clicking on the
Acquire tab.
Figure 37 shows the results for a 0.5Hz toggling of the switch.
The expected DC output can be calculated using Equation 2 .
(2)
The expected peak-to-peak output as a result of the impedance change can be calculated with
Equation 3 ; this value is the current flowing through the body:
(3)
The Δ impedance and peak-to-peak output can be calculated with Equation 4 and Equation 5 .
(4)
(5)
The results shown in Figure 37 are taken using a data rate of 500SPS. To obtain better resolution, these
results must be low-pass filtered. Figure 38 shows the result after the signal has been processed through
a 2Hz low-pass filter.