DocID023502 Rev 2

13/30

AN4146

Demonstration board and accessories

Figure 10. Microphones and I/O interfaces - block diagram subsection

The inputs of the PDM interface depend on the group of selectors S12, S13, S14, S15, S16

and S17 called Data Level SEL (respectively the couples R64-R65, R70-R71, R66-R67,

R72-R73, R68-R69 and R74-R75). These selectors are set if the PDM inputs come from the

microphones or from the level shifter.

The level shifter (enabled through the level shifter EN) is used when the microphones

supply voltage is set to 1.8 V. Under this condition the sensors are a 1.8 V section while the

decoder is still a 3.3 V section. In order to match these two board portions, a level shifter is

needed to increase the PDM data output level before providing it to the processor.

In a default configuration the PDM inputs are directly connected to the microphones data, in

other words R65, R67, R69, R71, R73 and R75 are soldered.

other four inputs depend on the connection of the microphone adapter boards. If the user

wants to use the external microphone array, the microphone adapter boards must be

unplugged and then the user must connect the array to the array connector with the

dedicated cable. When the array is plugged in, pin 2 of the array connector is forced to

STA321MPL

I2S

(3x)

PDM Interface

L/R

Clk

Vdd

Out

gnd

S4

L/R

Clk

Vdd

Out

gnd

S5

L/R

Clk

Vdd

Out

gnd

S6

L/R

Clk

Vdd

Out

gnd

S7

L/R

Clk

Vdd

Out

gnd

S8

L/R

Clk

Vdd

Out

gnd

S9

S13

S14

S15

S16

S12

S17

Level shifter

Low

1.8V

3.3V

3.3V

LRCK

BICK

SDO12

SDO34

SDO56

PWM

OpAmp

HP Jack

MIC1

MIC2

MIC3

MIC4

MIC5

MIC6

High

3.3V

J4

J3

SW1

SW2

Array connector

3.3V

3.3V

APWlink

connector

connector

3.3V

a. Regarding MIC1 and MIC2, the board can host every type of ST digital microphone since it supports all the

footprints