Datasheet

Maxim Integrated │ 90
MAX98090 Ultra-Low Power Stereo Audio Codec
www.maximintegrated.com
Digital Microphone Frequency Compensation
The digital microphone inputs can be configured to pro-
duce a wide range of digital microphone clock frequen-
cies. To optimize performance over the entire range of
available frequencies, the device provides configurable
frequency range and compensation settings. Once the
master clock (and thus prescaled clock) frequency is
decided, and the digital microphone clock divider is cho-
sen, the digital microphone frequency range bits should
be programmed to the correct range (DMIC_FREQ,
Table 14). If quick configuration mode is used and a
system clock bit is selected (Table 36), then the device
automatically calculates and selects the correct range
once the digital microphone clock divider is configured.
The digital microphone inputs also provide a configurable
frequency compensation filter with 9 frequency response
settings (Figure 8). Every sample rate and MCLK/PCLK
frequency (and the resulting digital microphone clock
frequency) combination results in a different baseline
frequency response. Table 15 to Table 20 provide the
recommended compensation filter settings for the most
commonly used PCLK frequency and sample rate com-
binations. Choose the PCLK divider that results in the
DMC clock frequency closest to the optimal frequency for
the built-in digital MIC hardware, and then set the correct
DMIC frequency range (DMIC_FREQ, Table 14). Then,
based on the desired sample rate, select the appropriate
compensation settings from Table 14 (DMIC_COMP).
If the system PCLK frequency does not match one of
these commonly used rates, then refer to the table for the
PCLK frequency that is closest (e.g., if the system PCLK
frequency is 12.5MHz, see Table 17 as 12.288MHz is the
closest common PCLK frequency). As before, choose
the PCLK divider that results in the optimal DMC clock
frequency, and set the appropriate DMIC frequency range
(DMIC_FREQ, Table 14). Then choose the compensation
settings based on the row that is the closest match to the
configured DMC frequency. Similarly, for nonstandard
sample rates choose the column with the common value
closest to the actual system sample rate.
In quick configuration mode, once both the system clock
and sample rate bits are selected (Table 36 and Table
37), the device automatically selects the recommended
response curve once the digital microphone clock divider
is configured. The digital microphone input does not sup-
port sample rates in excess of 48kHz (where DHF = 1,
Table 27).
Figure 8. Digital Microphone Compensation Filter Frequency
Response
DIGITAL MICROPHONE COMPENSATION FILTER
RESPONSE vs. NORMALIZED FREQUENCY
NORMALIZED FREQUENCY
COMPENSATION FILTER RESPONSE (dB)
0.4 x f
S
0.3 x f
S
0.2 x f
S
0.1 x f
S
0.5
1.0
1.5
2.0
2.5
0
0 x f
S
0.5 x f
S
DMIC_COMP = 6
DMIC_COMP = 5
DMIC_COMP = 4
DMIC_COMP = 3
DMIC_COMP = 2
DMIC_COMP = 1
DMIC_COMP = 0
DMIC_COMP = 8
DMIC_COMP = 7