EVAL-ADMP441Z-FLEX AD [Analog Devices], EVAL-ADMP441Z-FLEX Datasheet - Page 10

• Manufacturer Part Number: EVAL-ADMP441Z-FLEX
• Description: Omnidirectional Microphone with Bottom Port and I2S Digital Output
• Manufacturer: AD [Analog Devices]

ADMP441
DIGITAL FILTER CHARACTERISTICS
The
high-pass filter eliminates unwanted low frequency signals.
A low-pass filter allows the user to scale the pass band with
the sampling frequency as well as perform required noise
reduction.
High-Pass Filter
The
dc and very low frequency components. Table 7 shows the high-
pass characteristics for a nominal sampling rate of 48 kHz. The
cutoff frequency scales with changes in sampling rate.
Table 7. High-Pass Filter Characteristics
Frequency
3.7 Hz
10.4 Hz
21.6 Hz
This digital filter response is in addition to the natural high-
pass response of the
has a −3 dB cutoff of 60 Hz.
Low-Pass Filter
The analog-to-digital converter in the
high order, sigma-delta (Σ-Δ) running at a high oversampling
ratio. The noise shaping of the converter pushes the majority of
the noise well above the audio band and gives the microphone a
ADMP441
ADMP441
incorporates a high-pass filter to remove unwanted
has an internal digital band-pass filter. A
ADMP441
Attenuation
–3.0 dB
–0.5 dB
–0.1 dB
MEMS acoustic transducer that
ADMP441
is a single-bit,
Rev. B | Page 10 of 16
wide dynamic range. However, it does require a good quality
low-pass filter to eliminate the high frequency noise.
Figure 13 shows the response of this digital low-pass filter
included in the microphone. The pass band of the filter extends
to 0.423 × f
ripple. The high frequency cutoff of −6 dB occurs at 0.5 × f
48 kHz sampling rate results in a pass band of 20.3 kHz and a
half amplitude corner at 24 kHz; the stop-band attenuation of
the filter is greater than 60 dB. Note that these filter specifica-
tions scale with sampling frequency.
–100
–10
–20
–30
–40
–50
–60
–70
–80
–90
0
0
Figure 13. Digital Low-Pass Filter Magnitude Response
S
and, in that band, has an unnoticeable 0.04 dB of
0.1
0.2
NORMALIZED FREQUENCY (
0.3
0.4
0.5
0.6
0.7
f
S
)
Data Sheet
0.8
0.9
1.0
S
. A