ADPD7000 datasheet(21/127 Pages) AD

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Data Sheet

ADPD7000

THEORY OF OPERATION

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Rev. 0 | 21 of 127

Table 10. TIA Connections in the BIA Channel (Continued)

Bit Name

Setting

Connection

010

EXCP

011

RINT_SN2

100

IMPIP

101

EXCN

110

ECG RLD (EDA only)

111

ECGIP (EDA only)

BIOZ_PCHAN_x

000

HPTIA_p1

001

IMPIP

010

EXCN

011

RINT_SP2

100

IMPIN

101

EXCP

110

ECGIN (EDA only)

111

ECGIP (EDA only)

1 HPTIA_n and HPTIA_p refer to the two terminals of the TIA resistor.

2 RINT_SN and RIN_SP refer to the two terminals of the internal resistor.

The frequency of the generated sine wave is controlled by the

BIOZ_SINEFCW_x_x bits, whereas the amplitude of the sine

wave is controlled by the BIOZ_SINEAMPLITUDE_x bits. The

BIOZ_SINE_PHASE_OFFSET_x bits are used to control the sine

wave phase.

Use the following equations to set the voltage output (VOUT) am-

plitude and sine wave frequency with these bits, respectively, as

follows:

VOUT=0.8×BIOZ_SINEAMPLITUDE_x

211

V p‐p (2)

Frequency=32M×BIOZ_SINEFCW_x_x

226

Hz (3)

The TIA gain can be accessed through the BIOZ_TIA_RGAIN_x

bits.

After digitizing the measurement, the ADC output is sent to the

datapath of the BIA channel, which includes filters, gain controls,

and DFT. The DFT result is I data and Q data of the received sine

wave, and the data format is 3 bytes or 4 bytes and is controlled by

the BIOZ_DATA_SIZE_x bit.

When the chain turns on, the DFT path can wait before

performing the DFT. The waiting time is controlled by the BI-

OZ_ADC_CONV_DLY_x registers.

For accurate measurement, the chip must perform ratio measure-

ment. That is, the chip must measure the known internal resistor at

RINT, and then measure the unknown resistor. Use the ratio method

to calculate the resistor under test.

EDA SIGNAL PATH

EDA, also known as galvanic skin response (GSR), measures the

electrical activity conducted through sweat glands in the skin, which

indicates the intensity of an emotion experienced.

The ADPD7000 supports three measurement modes: AC voltage,

DC voltage, and DC current. To calculate the unknown impedance,

measure the current (I) flow into the unknown impedance and also

measure the voltage across the unknown impedance (VZ

UNKNOWN).

Use the following equation to calculate the unknown impedance:

Z =VZUNKNOWNI

(4)

Typically, the use of two electrodes can measure the EDA (see

Figure 34). The excitation signal is a low frequency excitation, and

the measurement result is the combination of the skin impedance

and the electrode contact impedance.

Figure 34. EDA Measurement Method

FIFO

The FIFO is never written with partial packets of data. If there is not

enough room for the data that is written to the FIFO for all enabled

time slots and any selected status bytes, no data is written from

any of the time slots during that period and the INT_FIFO_OFLOW

status bit is set.

The order of samples written to the FIFO (if selected) is dark data

followed by lit data. Table 11 shows the byte order for multibyte

words.

Table 11. Byte Order for FIFO Writes

Size

Byte Order (After Shift)

[7:0]

[15:8], [7:0]

[23:16], [15:8], [7:0]

[31:24], [23:16], [15:8], [7:0]

The FIFO size is 704 bytes. When the FIFO is empty, a read

operation returns 0xFF, and the INT_FIFO_UFLOW status bit is set.

ECG Data Format

The data in the ECG is channel is 24-bit unsigned data with a

status byte as a header. Figure 35 shows the data in the ECG

channel.

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