92hd98 Integrated Device Technology, 92hd98 Datasheet - Page 32

• Manufacturer Part Number: 92hd98
• Description: Datasheet
• Manufacturer: Integrated Device Technology

92HD98
SINGLE CHIP PC AUDIO SYSTEM, CODEC+MONO SPEAKER AMPLIFIER+CAPLESS HP+LDO
IDT CONFIDENTIAL
©2009 INTEGRATED DEVICE TECHNOLOGY, INC.
2.19. EQ
2.20. Combo Jack Detection
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.
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.
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.
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.
Figure 10. Combo Jack
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92HD98