AD1885
PRODUCT OVERVIEW
Sample Rates and D2S
The AD1885 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 AD1885 sample rate
generator allows the Codec to instantaneously change and process
sample rates from 7040 Hz 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 AD1885 uses a 4-bit
Σ∆ structure and D2S to enhance noise immunity on mother-
boards and in PC enclosures, and to suppress idle tones below
the device’s quantization noise floor. The D2S process pushes
noise and distortion artifacts caused by errors in the multibit
DAC to frequencies beyond the auditory response of the human
ear and then filters them.
The AD1885 Codec meets the Audio Codec ’97 2.1 Extensions,
adding support for multiple Codecs and variable sample rates.
In addition, the AD1885 SoundPort Codec is designed to meet
all requirements of the Audio Codec ’97, Component Specification,
Revision 1.03, © 1996, Intel Corporation, found at www.Intel.com.
The AD1885 also includes other Codec enhanced features such
as communicating to three Codecs on the same link, integrated
headphone driver and built-in PHAT Stereo 3D enhancement.
The AD1885 is an analog front end for high-performance PC
audio, modem, or DSP 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 Con-
verters (ADCs), mixer, and I/O.
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 out-
put may be attenuated from 0 dB to –94.5 dB in 1.5 dB steps
or muted.
The main architectural features of the AD1885 are the high
quality analog mixer section, two channels of Σ∆ ADC conver-
sion, two channels of Σ∆ DAC conversion and Data Direct
Scrambling (D2S) rate generators.
FUNCTIONAL DESCRIPTION
Analog Outputs
This section overviews the functionality of the AD1885 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.
The AD1885 offers a line output controlled by the Master Volume
control and an integrated headphone driver with independent
control.
Host-Based Echo Cancellation Support
Analog Inputs
The AD1885 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.
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).
Telephony Modem Support
The AD1885 contains a V.34-capable analog front end for sup-
porting host-based and data pump modems. The modem DAC
typical dynamic range is 90 dB over a 4.2 kHz analog output
passband where FS = 12.8 kHz. The left channel of the ADC
and DAC may be used to convert modem data at the same
sample rate in the range between 7040 Hz and 48 kHz. All pro-
grammed sample rates have a resolution of 1 Hz. The AD1885
supports irrational V.34 sample rates with 8/7 and 10/7 select-
able multiplier coefficients.
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 and HP_OUT) duplicates mono chan-
nel data on both the left and right LINE_OUT and HP_OUT.
Additionally, the PC attention signal (PC_BEEP) may be mixed
with the line output and headphone. A switch allows the output
of the DACs to bypass the PHAT Stereo 3D enhancement.
Power Management Modes
The AD1885 is designed to meet notebook and ACPI power
consumption requirements through flexible power management
control of all internal resources. The following subsections may
be independently controlled:
Digital Audio Mode
The AD1885 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 DC ’97 controller or the host,
and may be used during simultaneous capture and playback at
different sample rates.
ADCs and Input Mux Power-Down
DACs Power-Down
Analog Mixer Power-Down
Digital Interface Power-Down
Internal Clocks Disabled
Analog-to-Digital Signal Path
ADC and DAC Power-Down
VREF Standby Mode
Low-Power Mixer Mode—CD Mixer Alive Only Mode
Mixer Bypass Mode (Digital Audio)
Headphone
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 enter-
ing 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 channel data at different sample rates.
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ADI [ ADI ]
