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AS7058

Functional description

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7.7.2

BioZ/GSR measurement system

Bioelectrical impedance analysis is a method of assessing body composition, such as body fat,

fluid levels, and tissue mass. A small AC current is applied, which flows through the body, and

the voltage is measured so the bioimpedance can be calculated. The bioimpedance channel

consists of an input MUX, a capacitive-coupled amplifier, I/Q demodulation mixers, two anti-

aliasing filters, a pseudo-sine current DAC, and an internal reference resistor that is used to

calibrate the errors in the signal path and used as a measuring scale. A simplified system

block diagram of the BioZ/GSR measurement system is shown in Figure 44.

Figure 44: BioZ/GSR block diagram

The included MUX can freely combine the BIOZ1 pin to BIOZ4, as well as the input and output

of the current DAC and the BioZ amplifier. The selection can be set with BIOZ_SELECT (see

chapter 8.1 Register overview).

Two different modes can be chosen:

•

Body impedance measurement (BioZ)

•

Galvanic skin response (GSR)/Electro Dermal Activity (EDA)

AS7058

short

2 k

1 k

0.5 k

1 M

0° /90°

clk

BIOZ4

BIOZ2

BIOZ1

BIOZ3

ECG_LPF

ECG

GSR

BIOZ_I

BIOZ_Q

ECG_IMUX_GAIN

Buffer

TEMP

ECG_LEAD

MOD 3

Current input

delta-sigma

ECGMOD_IMUX_SEL2<2:0>

BIOZ_SELECT<6:0>

IDAC

Current DAC

10 µA - 100 µA

1 kHz – MHz

BIOZ_EXCIT_CURR<2:0>

BIOZ_EXCIT_FREQ_SEL<3:0>

BIOZ_GAIN

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