ICS-40310

APPLICATIONS INFORMATION

OUTPUT IMPEDANCE CONSIDERATION

The ICS-

40310 has an output impedance of 4.5 kΩ, which is significantly higher than the impedance of many other MEMS

microphones. This higher output impedance enables the microphone to operate with a very low supply current, but also needs to be

considered in the design of the signal chain following the microphone. The input impedance of the device to which the microphone’s

output is connected should be much higher than 4.5 kΩ to ensure no loss of signal amplitude through the signal chain. A minimum

input impedance of 47

kΩ is recommended for the device connected to the ICS-40310’s output. An input with this impedance will

reduce the microphone’s output signal level by only 0.8 dB.

CODEC AND AMPLIFIER CONNECTIONS

The ICS-40310 output can be connected to a dedicated codec microphone input (see Figure 8), or to a high input impedance gain

stage (see Figure 9). A 0.1 µF ceramic capacitor placed close to the ICS-40310 supply pin is used for testing and is recommended to

adequately decouple the microphone from noise on the power supply. An AC-coupling capacitor is required at the output of the

microphone. This capacitor creates a high-pass filter with a corner frequency at

where R is the input impedance of the codec or amplifier.

A codec input connected to the ICS-40310’s output should be high impedance, as described above in the Output Impedance

Consideration section. The size of the AC-coupling capacitor should be chosen such that the high-pass filter that it forms at the

codec’s input does not affect the microphone’s low frequency performance. For high-impedance (>47

kΩ) inputs, a 100 nF or larger

AC-coupling capacitor will be sufficient. See Figure 8 for a schematic of this connection.

Figure 9 shows the ICS-40310 connected to an op amp configured as a noninverting preamplifier.

Figure 8. ICS-40310 Connected to an ADC or Codec

Figure 9. ICS-40310 Connected to an Op Amp

ADC

OR

CODEC

ICS-40310

GND

OUTPUT

INPUT

MICBIAS

0.1 µF

MINIMUM

0.1 µF

VDD

GAIN = (R1 + R2)/R1

ICS-40310

GND

OUTPUT

0.1 µF

MINIMUM

0.1 µF

47 k

Ω

R1

R2

VDD

VREF

VOUT

VREF

AMP

0.9-1.3 V

Page 8 of 14

Document Number: DS-ICS-40310-00

Revision: 1.2