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HMP9701A

AC’97 Audio Codec

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Functional Block Diagram

HMP9701A

HMP9701A AC’97 AUDIO CODEC

MIC1

MIC2

LINE_IN

CD

VIDEO

AUX

PHONE

GAIN

0dB / 20dB

MONO_OUT

MONO

VOL

G

A

M

LINE_OUT

MASTER

VOL

∑

PC_BEEP

GAM

∑

GGGGG

AAAAA

MMMMM

∑

∑

RECORD

GAIN

Σ∆ A/D

Σ∆ A/D

Σ∆ A/D

AC’97

CONTROL/CONFIGURATION

(64 REGISTERS)

GAM

Σ∆ D/A

Σ∆ D/A

SYNC

BIT_CLK

SDATA_OUT

SDATA_IN

RESET

STEREO SIGNAL PATH

MONO SIGNAL PATH

Functional Description

The HMP9701A is a full-duplex stereo audio codec compliant

to the AC’97 Codec specification. This component is designed

for use in multimedia and business personal computers. The

codec includes full duplex stereo converters, a mic pass

through ADC, complete on-chip anti-alias filtering, and a 5

channel analog mixer with programmable gain and attenuation.

Analog Inputs

The HMP9701A has 4 stereo inputs (LINE_IN, CD, VIDEO,

and AUX), two microphone level inputs (MIC1 and MIC2), and

one mono line level input (PHONE). A multiplexer is provided

to independently select the right and left record sources from

the analog inputs listed above. In addition, the output stereo

mix (LINE_OUT) or its mono equivalent may also be selected

as a record source. A gain block is available to amplify the

MIC inputs by 20dB to compensate for the difference between

line levels and typical condenser microphone levels.

Besides being fed to the Record Select Mux, all analog

inputs can be mixed (see Analog Mixer) with the stereo out-

put from the Playback DACs. Note: all analog inputs except

PHONE and PC_BEEP can be output on MONO_OUT.

There is a dedicated analog input, PC_BEEP, for the

standard “Beep” signal provided on most PC/Compatible

computers for power on self test and boot audio status

indication. This input is mixed into each channel of the

stereo line outputs.

Record ADCs

The HMP9701A provides 3 Σ∆ ADCs to record one dedi-

cated microphone input and 2 user selectable analog inputs.

The user selectable analog inputs are routed to the stereo

ADCs via an programmable Input Multiplexer. The multi-

plexer is programmed to select the 2 record channels via the

Record Select register (1Ah).

Each of the record channels pass through a programmable

gain block before each ADC. The record gain for each chan-

nel is set individually and ranges from 0dB to 22.5dB in

1.5dB increments (see Record Gain Registers 1Ch and

1Eh). The gain block can also be used to mute each chan-

nel. Note: an additional gain block provides 20dB of gain on

the MIC channel if activated (see MIC Volume register 0Eh).

The HMP9701A uses oversampling Σ∆ ADCs which only

require a single pole passive filter for anti-alias filtering. The

filter for the left, right and MIC channels is realized by placing

a 1nF capacitor between the AFILT1, AFILT2, and AFILT3

pins and analog ground respectively.

Playback DACs

The HMP9701A uses oversampling single bit Σ∆ DACs to

convert the stereo playback sample to an analog line level

output. The output of the DACs pass through internal recon-

struction filters that do not require any external components.

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