ad1881a Analog Devices, Inc., ad1881a Datasheet - Page 10

• Manufacturer Part Number: ad1881a
• Description: Ac?97 Soundmax Codec
• Manufacturer: Analog Devices, Inc.

AD1881A
PRODUCT OVERVIEW
The AD1881A meets the Audio Codec ’97 2.0 and 2.1 Extensions. In
addition, the AD1881A SoundMAX Codec is designed to meet all
requirements of the Audio Codec ’97, Component Specification, Revi-
sion 1.03, © 1996, Intel Corporation, found at www.Intel.com.
The AD1881A also includes some other Codec enhanced fea-
tures such as the built-in PHAT Stereo 3D enhancement.
The AD1881A is an analog front end for high performance PC
audio applications. The AC’97 architecture defines a 2-chip
audio solution comprising a digital audio controller, plus a high
quality analog component that includes Digital-to-Analog
Converters (DACs), Analog-to-Digital Converters (ADCs),
mixer and I/O.
The main architectural features of the AD1881A are the high
quality analog mixer section, two channels of Σ∆ ADC conversion,
two channels of Σ∆ DAC conversion with Data Direct Scram-
bling (D
and DAC are compatible for modem applications supporting irra-
tional sample rates and modem filtering requirements.
FUNCTIONAL DESCRIPTION
This section overviews the functionality of the AD1881A and
is intended as a general introduction to the capabilities of the
device. Detailed reference information may be found in the
descriptions of the Indexed Control Registers.
Analog Inputs
The Codec contains a stereo pair of Σ∆ ADCs. Inputs to the
ADC may be selected from the following analog signals: tele-
phony (PHONE_IN), mono microphone (MIC1 or MIC2),
stereo line (LINE_IN), auxiliary line input (AUX), stereo CD
ROM (CD), stereo audio from a video source (VIDEO) and
post-mixed stereo or mono line output (LINE_OUT).
Analog Mixing
PHONE_IN, MIC1 or MIC2, LINE_IN, AUX, CD and VIDEO
can be mixed in the analog domain with the stereo output from the
DACs. Each channel of the stereo analog inputs may be inde-
pendently gained or attenuated from +12 dB to –34.5 dB in 1.5 dB
steps. The summing path for the mono inputs (PHONE_IN, MIC1,
and MIC2 to LINE_OUT) duplicates mono channel data on both
the left and right LINE_OUT. Additionally, the PC attention sig-
nal (PC_BEEP) may be mixed with the line output. A switch
allows the output of the DACs to bypass the PHAT Stereo
3D enhancement.
Digital Audio Mode
The AD1881A is designed with a Digital Audio Mode (DAM)
that allows mixing of all analog inputs independent of the DAC
output signal path. Mixed analog input signals may be sent to
the ADCs for processing by the controller or the host, and may
be used during simultaneous capture and playback at different
sample rates.
2
S) rate generators. The AD1881A’s left channel ADC
Analog-to-Digital Signal Path
The selector sends left and right channel information to the
programmable gain amplifier (PGA). The PGA following the
selector allows independent gain control for each channel entering
the ADC from 0 dB to +22.5 dB in 1.5 dB steps. Each channel
of the ADC is independent, and can process left and right chan-
nel data at different sample rates.
Sample Rates and D
The AD1881A default mode sets the Codec to operate at 48 kHz
sample rates. The converter pairs may process left and right
channel data at different sample rates. The AD1881A sample
rate generator allows the Codec to instantaneously change and
process sample rates from 8 kHz to 48 kHz with a resolution
of 1 Hz. The in-band integrated noise and distortion artifacts
introduced by rate conversions are below –90 dB. The AD1881A
uses a 4-bit D/A structure and Data Directed Scrambling (D
to enhance noise immunity on motherboards and in PC enclo-
sures, and to suppress idle tones below the device’s quantization
noise floor. The D
caused by errors in the multibit DAC to frequencies beyond the
auditory response of the human ear and then filters them.
Digital-to-Analog Signal Path
The analog output of the DAC may be gained or attenuated from
+12 dB to –34.5 dB in 1.5 dB steps, and summed with any of
the analog input signals. The summed analog signal enters the
Master Volume stage where each channel of the mixer output may
be attenuated from 0 dB to –94.5 dB in 1.5 dB steps or muted.
Line-Level Outputs
The AD1881A offers a true line-level output for notebook dock-
ing station and home theater applications. The line-level output
does not change with master volume settings.
Host-Based Echo Cancellation Support
The AD1881A supports time correlated I/O data format by pre-
senting MIC data on the left channel of the ADC and the mono
summation of left and right output on the right channel. The
ADC is splittable; left and right ADC data can be sampled at
different rates.
Power Management Modes
The AD1881A is designed to meet ACPI power consumption
requirements through flexible power management control of all
internal resources.
2
S process pushes noise and distortion artifacts
2
S
2
S)