APPLICATIONS INFORMATION
CONNECTING TO AUDIO CODECS
The ICS-40300 output can be connected to a dedicated codec microphone input (see Figure 12) or to a high input impedance gain
stage (see Figure 13.) A 0.1 µF ceramic capacitor placed close to the ICS-40300 supply pin is used for testing and is recommended to
adequately decouple the microphone from noise on the power supply. A DC-blocking 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.
A minimum value of 22 µF is recommended in Figure 12 because the input impedance of some codecs
highest PGA gain setting, which results in a high-pass filter corner frequency at 3.6 Hz. At lower gain settings, where the codec input
impedance is also lower, a smaller AC-coupling capacitor can be used. Figure 13 shows the ICS-40300 connected to an op amp
configured as a non-inverting preamplifier.
Figure 12. ICS-40300 Connected to a Codec
Figure 13. ICS-40300 Connected to an Op Amp
DYNAMIC RANGE CONSIDERATIONS
To fully utilize the 99 dB dynamic range of the ICS-40300 in a design, the preamp, ADC, or codec circuit following it must be chosen
carefully. A typical codec may have a 100 dB dynamic range with V
DD
= 3.3 V. To match the dynamic ranges between the microphone
and the ADC input of the codec, some gain must be added to the ICS-40300 output. For example, at the 130 dB SPL maximum acoustic
input, the ICS-40300 outputs dBV rms signal. The full-scale input voltage of a codec may be 0 dBV; therefore, 9 dB of gain must be
added to the signal to match the dynamic range of the microphone with the dynamic range of the codec.
ADC
OR
CODEC
ICS-40300
GND
OUTPUT
INPUT
MICBIAS
22 µF
MINIMUM
0.1 µF
VDD
GAIN = (R1 + R2)/R1
ICS-40300
GND
OUTPUT
1 µF
MINIMUM
0.1 µF
47 k
R1
R2
VDD
V
REF
V
OUT
V
REF
AMP
1.8-3.3 V
Page 9 of 16
Document Number: DS-ICS-40300-00
Revision: 1.0
