ADPD4100 datasheet(49/101 Pages) AD

49 / 101 page

Data Sheet

ADPD4100/ADPD4101

Rev. 0 | Page 49 of 101

Figure 56 shows a circuit that can be used for the two-electrode

lead off detection measurement. RBODY is the resistance of the

body.

CH1

IN1

IN2

470pF

VC2

ADPD4100/

ADPD4101

500kΩ

IN3

25kΩ

RBODY

47pF

Figure 56. Circuit Used for Two-Electrode Lead Off Detection Measurement

ECG and two-electrode lead off detection are measured as

follows:

1. ECG is measured in Time Slot A as defined in the ECG

Measurement with the ADPD4100/ADPD4101 section.

2. Lead off detection of the ECG electrodes is taken in

Time Slot B by making a single-ended measurement for

impedance between the E1 and E2 ECG electrodes into

Channel 1, as shown in Figure 56.

When the ECG electrodes are making contact with the skin

during the measurement, an ECG signal and a value for the

impedance measurement indicating that some current is

flowing through RBODY are visible. When either electrode stops

making contact with the skin, there is no ECG signal, and a

much smaller value at the ADC output is observed for the

impedance measurement indicating that there is no current

flowing through the low impedance RBODY. When both electrode

skin contacts are restored, the ECG signal appears immediately.

Because only one input and one channel are allocated to detect

lead off condition for two electrodes, the impedance measurement

shows a much smaller value when either electrode loses contact

with skin and, thus, it is a common indicator for both electrodes.

Figure 57 illustrates a representation of ADC output changes in

different cases. Before Time tA, both ECG electrodes make

contact with the skin. At Time tA, only E1 is disconnected from

the skin. At Time tB, it starts to make contact with the skin again

and both electrodes make contact until tC. At tC, only E2 is

disconnected from the skin and it stays disconnected until tD. At

tD, E2 starts making contact with the skin again, and they stay

connected until tE. At tE, both electrodes are disconnected. At

tF, both electrodes start making contact again. Therefore, lead

off detection measurement can be achieved for all cases, and

lead off condition is represented by lower ADC output for the

impedance measurement.

TIME

Figure 57. Graph of Two-Electrode Lead Off Measurement

The following configuration enables low dc offset ECG

measurement in Time Slot A and two-electrode lead off

detection in Time Slot B:

# ADPD4100 ECG Measurement with small DC

offset in Timeslot A and Two-Electrode

Lead-Off Measurement in Timeslot B

0009 0080

# 32MHz oscillator trim

000B 02B2

# 1MHz oscillator trim

000D 0D05

# Sampling rate 300 Hz

000F 0006

# 1MHz low frequency oscillator

0010 0100

# Timeslot A and B enabled

0020 2200

# Float input 1&2 and 3&4

during sleep

0021 0001

# IN1/IN2 configured as a

differential pair

# Timeslot configuration #

# ADPD4100 ECG Measurement with small DC

offset

0100 0000

# Input resistor 500

Ω

0101 00E6

# skip preconditioning,

bandpass filter bypassed

0102 0007

# IN1&IN2 differential pair to

channel 1

0103 0000

# float during preconditioning

0104 02C1

# TIA gain 100k

Ω, TIA_VREF =

0.88V

0105 0000

# LEDs off

0106 0000

# LEDs off

0107 0102

# 2 pulses

0108 1000

# float mode, minimum period

010A 0203

# Integrator pulse width,

bandpass filter powered down

010B 01A0

# Integrator pulse timing

offset

010C 0210

# Modulation pulse width and

offset

010D 0000

# Chopping mode disabled

010E 0000

# no ADC offset

010F 0000

# no ADC offset

ADPD4100 데이터시트(PDF) 49 Page - Analog Devices

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