Demonstration board and accessories

AN4146

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DocID023502 Rev 2

ground (due to the array board schematic) and this trace is used to switch off the LED D1

and to control the voltage-controlled switches SW1 and SW2 (IC1 and IC2 on the STEVAL-

MKI126Vx board). The LED switching off indicates that the array is connected and the

switches commutate the PDM input 1 and 2 from the data of the microphones onboard to

the data of the microphones on the array.

1.5.4

Output section

an operational amplifier used as the headphone driver. The STA321MP includes a PWM

modulator so it possible to export this signal and after a suitable filtering (refer to Figure 11)

an analog signal is obtained. This dual output option allows interfacing the microphones to

(filtered output).

Figure 11. Headphone out schematic - only one channel