92HD99B Datasheet, PDF (28/225 Pages) Integrated Device Technology – SINGLE CHIP PC AUDIO SYSTEM

92HD99
SINGLE CHIP PC AUDIO SYSTEM, CODEC+SPEAKER AMPLIFIER+CAPLESS HP+LDO
2.18.1. Filter Description
The high-pass filter is derived from the common biquadratic filter and provides a 12dB/octave roll-off.
The filter may be programmed for a -3dB response at: 100Hz, 200Hz, 300Hz, 400Hz, 500Hz, 750Hz,
1KHz, or 2KHz. The high pass filter is enabled by default with a cut-off frequency of 300Hz. The filter
may be bypassed using the associated verb (processing state verb).
The analog PC_Beep input is not affected by the digital high-pass filter. To ensure that the speakers
attached to the BTL amplifier are not harmed by low frequency audio entering the PC_Beep input, an
external filter must be implemented. Fortunately, it is common practice to implement an attenuation
circuit and DC blocking capacitor at the PC_Beep input. This attenuator/filter is easily adjusted to
restrict low frequency audio. The easiest approach is to reduce the value of the DC blocking capaci-
tor but other approaches are equally effective.
2.19. EQ
There are 5 bands of parametric EQ (bi-quad) per channel. Due to the flexibility of the bi-quad imple-
mentation, each filter band may be configured as a high-pass, low-pass, band-pass, high shelving,
low shelving, or other function.
Each band has an independent set of coefficients. A bi-quad filter has 6 coefficients. One coefficient
is normalized to 1 and 5 are programmed into the core. Each band supports up to +15dB boost or up
to -36dB cut.
2.20. Combo Jack Detection
4 conductor (combo) jacks are becoming popular. In the most common implementation the 4 con-
ductor plug has the same mechanical dimensions as a 3 conductor 3.5mm plug but the sleeve por-
tion has been split into two segments:S1 and S2. When a 4-conductor plug (headset) is inserted into
the jack T (Tip) = Left headphone audio, R (Ring) = Right headphone audio, S1 (First half of sleeve)
= microphone input, and S2 (Second half of sleeve) = return (GND). When a 3-conductor plug
(headphones) is inserted into the jack; T=Left audio, R=Right audio, S1=GND, S2=GND. By moni-
toring the S1 connection to see if it is shorted to ground, we can distinguish between headsets and
headphones. Please note that analog microphone plugs (3-conductor-Lmic/Rmic/GND) and optical
SPDIF plugs can not be supported using this implementation.
Figure 9. Combo Jack
GND _MIC
Plug insertion is reported on the headphone port using the switch integrated into the jack.
The internal circuit monitors the voltage at the jack to determine if a low impedance load is present.
IDT CONFIDENTIAL
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92HD99