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
f
C
= 1/(2π × C × R)
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 0.1 µF 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
OU
TPUT
INPUT
MICBIAS
0.1 µF
MINIMUM
0.1
µF
VDD
G
AIN = (R1 + R2)/R1
ICS-40310
GND
OUTPUT
0.
1 µF
MINIMUM
0.1 µF
47 kΩ
R
1
R2
VDD
V
REF
V
OUT
V
REF
AMP
0.9-1.3 V
Page 8 of 13
Document Number: DS-ICS-40310-00
Revision: 1.0
