AD1816 Analog Devices, AD1816 Datasheet - Page 15

• Manufacturer Part Number: AD1816
• Description: Single Chip Plug And Play Multimedia Audio Subsystem
• Manufacturer: Analog Devices

REV. A
HOST INTERFACE
The AD1816A contains all necessary ISA bus interface logic on
chip. This logic includes address decoding for all onboard
resources, control and signal interpretation, DMA selection and
control logic, IRQ selection and control logic, and all interface
configuration logic.
The AD1816A supports a Type “F” DMA request/grant archi-
tecture for transferring data with the ISA bus through the 8-bit
interface. The AD1816A also supports DACK preemption. Pro-
grammed I/O (PIO) mode is also supported for control register
accesses and for applications lacking DMA control. The
AD1816A includes dual DMA count registers for full-duplex
operation enabling simultaneous capture and playback on sepa-
rate DMA channels.
Codec Functional Description
The AD1816A’s full-duplex stereo codec supports business audio
and multimedia applications. The codec includes stereo audio
converters, complete on-chip filtering, MPC Level-2 and
Level-3 compliant analog mixing, programmable gain and at-
tenuation, variable sample rate converters, extensive digital mixing
and FIFOs buffering the Plug and Play ISA bus interface.
Analog Inputs
The codec contains a stereo pair of
verters (ADC). Inputs to the ADC can be selected from the fol-
lowing analog signals: mono (PHONE_IN), mono microphone
(MIC), stereo line (LINE), external stereo synthesizer
(SYNTH), stereo CD ROM (CD), stereo audio from a video
source (VID) and post-mixed stereo or mono line output (OUT).
Analog Mixing
PHONE_IN, MIC, LINE, SYNTH, CD and VID can be mixed
in the analog domain with the stereo line OUT from the
digital-to-analog converters (DAC). Each channel of the stereo
analog inputs can be independently gained or attenuated from
+12 dB to –34.5 dB in 1.5 dB steps, except for PHONE_IN,
which has a range of 0 dB to –45 dB steps. The summing path
for the mono inputs (MIC, and PHONE_IN to line OUT) du-
plicates mono channel data on both the left and right line OUT,
which can also be gained or attenuated from +12 dB to –34.5 dB
in 1.5 dB steps for MIC, and +0 dB to –45.0 dB in 3 dB steps
for PHONE_IN. The left and right mono summing signals are
always identical being gained or attenuated equally.
Analog-to-Digital Datapath
The selector sends left and right channel information to the pro-
grammable gain amplifier (PGA). The PGA following the selec-
tor allows independent gain for each channel entering the ADC
from 0 dB to 22.5 dB in 1.5 dB steps.
For supporting time correlated I/O echo cancellation, the ADC
is capable of sampling microphone data on the left channel and
the mono summation of left and right OUT on the right channel.
The codec can operate in either a global stereo mode or a global
mono mode with left channel inputs appearing at both channels of
the 16-bit
sampling frequency (from 4 kHz to 55.2 kHz with 1 Hz resolution).
Digital Mixing and Sample Rates
The audio ADC sample rate and the audio DAC sample rates
are completely independent. The AD1816A includes a variable
sample rate converter that lets the codec instantaneously change
and process sample rates from 4 kHz to 55.2 kHz with a reso-
lution of 1 Hz. The in-band integrated noise and distortion
artifacts introduced by rate conversions are below –90 dB.
converters. Data can be sampled at the programmed
analog-to-digital con-
–15–
Up to four channels of digital data can be summed together and
presented to the stereo DAC for conversion. Each digital chan-
nel pair can contain information encoded at a different sample
rate. For example, 8 kHz .wav data received from the ISA inter-
face, 48 kHz MPEG audio data received from I
44.1 kHz CD data received from I
22.05 kHz music data may be summed together and converted
by the DACs.
Digital-to-Analog Datapath
The internally generated music synthesizer data, PCM data
received from the ISA interface, data received from the I
port and data received from the I
port passes through an attenuation mute stage. The attenuator
allows independent control over each digital channel, which can
be attenuated from 0 dB to –94.5 dB in 1.5 dB steps before be-
ing summed together and passed to the DAC, or the channel
may be muted entirely.
Analog Outputs and Phat Stereo
The analog output of the DAC can be summed with any of the
analog input signals. The summed analog signal enters the
Master Volume stage where each channel L_OUT, R_OUT and
PHONE_OUT may be attenuated from 0 dB to –46.5 dB in
1.5 dB steps or muted.
Analog Outputs and Phat Stereo
The AD1816A includes ADI’s proprietary Phat Stereo 3D
phase enhancement technology, which creates an increased
sense of spaciousness using two speakers. Our unique patented
feedback technology enables superior control over the width and
depth of the acoustic signals arriving at the human ear. The
AD1816A employs an electrical model of the speaker-to-ear
path allowing precise control over a signal’s phase at the ear. The
Phat Stereo circuitry expands apparent sound images beyond the
angle of the speakers by exploiting phase information in the audio
signal and creating a more immersive listening experience.
Digital Data Types
The codec can process 16-bit twos complement PCM linear
digital data, 8-bit unsigned magnitude PCM linear data and
8-bit -law or A-law companded digital data as specified in the
control registers. The AD1816A also supports ADPCM en-
coded in the Creative SoundBlaster ADPCM formats.
Host-Based Echo Cancellation Support
The AD1816A 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 OUT on the right channel. The
ADC sample rates are independent of the DAC sample rate allow-
ing the AD1816A to support ADC time correlated I/O data at
8 kHz and DAC data at any other sample rate in the range of
4 kHz to 55.2 kHz simultaneously.
Telephony Support
The AD1816A contains a PHONE_IN input and a
PHONE_OUT output. These pins are supplied so the AD1816A
may be connected to a modem chip set, a telephone handset or
down-line phone.
WSS and SoundBlaster Compatibility
Windows Sound System software audio compatibility is built
into the AD1816A.
SoundBlaster emulation is provided through the SoundBlaster
register set and the internal music synthesizer. SoundBlaster Pro
version 3.02 functions are supported, including record and Cre-
ative SoundBlaster ADPCM.
2
S(1) port, and the DSP serial
2
S(1) and internally generated
AD1816A
2
S(0), digital
2
S(0)