92HD91 Datasheet, PDF (18/298 Pages) Integrated Device Technology – SINGLE CHIP PC AUDIO SYSTEM

92HD91
SINGLE CHIP PC AUDIO SYSTEM, CODEC+SPEAKER AMPLIFIER+CAPLESS HP+LDO
2.3. Mono output Band-Pass Filter
For many applications, the primary speakers are incapable of reproducing low frequency audio.
Therefore it is desirable to implement a woofer or sub-woofer speaker. The mono output is ideal for
this task.
However, the frequency response should be restricted to prevent interference with the primary
speakers. Typically an external filter, known as a cross-over filter, is used. The mono processing
path includes a band-pass filter with programmable high and low cut-off frequencies to eliminate the
need for an external filter.
2.3.1. Filter Description
The band-pass filter is derived from the common biquadratic filter and provides a 12dB/octave
roll-off. The filter may be programmed for a -3dB lower band edge of: 63Hz, 80Hz, 100Hz, 120Hz,
150Hz, 200Hz, 315Hz, or 400Hz. The filter may be programmed for a -3dB upper band edge of:
150Hz, 200Hz, 250Hz, 315Hz, 400Hz, 500Hz, 630Hz, or 800Hz.
The band-pass filter is enabled by default with a cut-off frequencies at 120Hz and 250Hz. The filter
may be bypassed using the associated verb (processing state verb).
The Analog PC_Beep input is not affected by the band-pass filter.
2.4. Mixer
The mixer supports independent gain (-34.5 to +12dB in 1.5dB steps) on each input as well as inde-
pendent mutes on each input. The following inputs are available:
• Port A
• Port C
• Port E
• Port F
• DAC 0
• DAC 1
2.5. ADC Multiplexers
The codec implements 2 ADC input multiplexers. These multiplexers incorporate the ADC record
gain function :(-16 to +30dB gain in 1dB steps) as an output amp and allow a preselection of one of
below possible inputs:
• Port A
• Port C
• Port E
• Port F
• Mixer Output
• DMIC 0
• DMIC 1
IDT™ CONFIDENTIAL
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92HD91