AS7058 datasheet(52/199 Pages) AMSOSRAM

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AS7058

Functional description

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The chosen mode influences which excitation waveform, sine wave for the BioZ, and square

wave for GSR, is used. Furthermore, the applied current range and excitation frequency are

different. The choice between the two modes can be done in BIOZ_CFG register (see chapter

8.1 Register overview). Important to mention is that BIOZ_EN and GSR_EN must not be set to

1 at the same time. When BioZ is activated, the excitation frequency can be chosen in steps

from 1 kHz to 1 MHz on a sine waveform, and the current can be controlled from 10 µA to

100 µA. These settings can be chosen in BIOZ_EXCIT register. The settings will only be

applied when BIOZ_EN bit is set to one. The operating gain of the BioZ/GSR preamplifier can

also be extended to gain 2 via register bit BIOZ_GAIN.

When GSR is activated, the excitation frequency is half of the ECG sample frequency chosen

in a square waveform, and the current can be controlled from 200 nA to 85 µA. These settings

can be chosen in BIOZ_EXCIT. The settings will only be applied when GSR_EN bit is set to

one. The dynamic range that can be achieved is between 300 nS to 100 µS with 1 nS step

size.

7.7.3

ECG/BioZ signal processing overview

Similar to the PPG signal processing the ECG and BioZ data acquisition path supports also

various signal processing options. An overview of all options and a device signal flow is shown

in Figure 45.

The output of ADC modulator 3 is connected to the SINC filter block which acts as down

sampling filter. It is possible to select between 4th and 5th filter order via register

ECG1_SEL_ORDER and ECG2_SEL_ORDER as well as decimation rates between 16, 32,

64, 128 and 256 via register ECG1_SINC_DEC and ECG2_SINC_DEC. In order to further

improve SNR of the system there is an oversampling filter function, which is part of the down

sampling filter that can be enabled via register ECG1_SINC_OVS and ECG2_SINC_OVS. The

three-bit register allows for 7 different oversampling filter ratios to be enabled from factor 2 up

to 128. The oversampling filter function is disabled in default configuration. Please mind that by

enabling the oversampling filter function the active ADC modulator time is increased

influencing power consumption with the benefit of better noise behavior. Once the signal

passed the SINC decimation and optional oversampling filter the ECG/BioZ signal is feed into

a scaling block which converts the signal into 20-bit unsigned signal. The on-chip IIR filter

block is the last processing block which can be enabled to implement post processing filter

characteristics before the data is written to the FIFO memory. Please refer to chapter 7.8 for

more detail information regarding the IIR filter block.

AS7058 Datasheet(PDF) 52 Page - ams-OSRAM AG