Rainbow Electronics MAX98088 - Manual (Page 98)

Stereo Audio Codec
with FLEXSOUND Technology
MAX98088
98
Speaker Amplifier Signal Processing
The IC includes signal processing to improve the sound
quality of the speaker output and protect transducers
from damage. An excursion limiter dynamically adjusts
the highpass corner frequency, while a power limiter and
distortion limiter prevent the amplifier from outputting too
much distortion or power. The excursion limiter is located
in the DSP while the distortion limiter and power limiter
control the analog volume control (Figure 28). All three
limiters analyze the speaker amplifier’s output signal to
determine when to take action.
Excursion Limiter
The excursion limiter is a dynamic highpass filter that
monitors the speaker outputs and increases the high-
pass corner frequency when the speaker amplifier’s out-
put exceeds a predefined threshold. The filter smoothly
transitions between the high and low corner frequency to
prevent unwanted artifacts. The filter can operate in four
different modes:
U
Fixed-Frequency Preset Mode. The highpass corner
frequency is fixed at the upper corner frequency and
does not change with signal level.
U Fixed-Frequency Programmable Mode. The high-
pass corner frequency is fixed to that specified by the
programmable biquad filter.
U Preset Dynamic Mode. The highpass filter automati-
cally slides between a preset upper and lower corner
frequency based on output signal level.
U
User-Programmable Dynamic Mode. The highpass
filter slides between a user-programmed biquad filter
on the low side to a predefined corner frequency on
the high side.
Table 23. Speaker Output Mixer Register
Speaker Output Volume
REGISTER BIT NAME DESCRIPTION
0x3D/0x3E
7 SPLM/SPRM
Left/Right Speaker Output Mute
0 = Disabled
1 = Enabled
4
SPVOLL/SPVOLR
Left/Right Speaker Output Volume Level
VALUE VOLUME (dB) VALUE VOLUME (dB)
0x00 -62 0x10 -10
0x01 -58 0x11 -8
3
0x02 -54 0x12 -6
0x03 -50 0x13 -4
0x04 -46 0x14 -2
0x05 -42 0x15 0
0x06 -38 0x16 +1
0x07 -35 0x17 +2
2
0x08 -32 0x18 +3
0x09 -29 0x19 +4
0x0A -26 0x1A +5
0x0B -23 0x1B +6
1
0x0C -20 0x1C +6.5
0x0D -17 0x1D +7
0x0E -14 0x1E +7.5
0x0F -12 0x1F +8