Datasheet

ADAU1772 Data Sheet
Rev. B | Page 28 of 116
THEORY OF OPERATION
The ADAU1772 is a low power audio codec with an optimized
audio processing core, making it ideal for noise cancelling
applications that require high quality audio, low power, small
size, and low latency. The four ADC and two DAC channels
each have an SNR of at least +96 dB and a THD + N of at least
−88 dB. The serial data port is compatible with I
2
S, left justified,
right justified, and TDM modes, with tristating for interfacing
to digital audio data. The operating voltage range is 1.8 V to
3.63 V, with an on-board regulator generating the internal
digital supply voltage. If desired, the regulator can be powered
down and the voltage can be supplied externally.
The input signal path includes flexible configurations that can
accept single-ended analog microphone inputs as well as up to
four digital microphone inputs. Two microphone bias pins provide
seamless interfacing to electret microphones. Each input signal
has its own programmable gain amplifier (PGA) for volume
adjustment.
The ADCs and DACs are high quality, 24-bit Σ-Δ converters
that operate at a selectable 192 kHz or 96 kHz sampling rate.
The ADCs have an optional high-pass filter with a cutoff
frequency of 1 Hz, 4 Hz, or 8 Hz. The ADCs and DACs also
include very fine-step digital volume controls.
The stereo DAC output is capable of differentially driving a
headphone earpiece speaker with 16 Ω impedance or higher.
One side of the differential output can be powered down if
single-ended operation is required. There is also the option to
change to line output mode when the output is lightly loaded.
The core has a reduced instruction set that optimizes this codec
for noise cancellation. The program and parameter RAMs can
be loaded with custom audio processing signal flow built using
the SigmaStudio™ graphical programming software from
Analog Devices, Inc. The values stored in the parameter RAM
control individual signal processing blocks. The ADAU1772 also
has a self-boot function that can be used to load the program
and parameter RAM along with the register settings on power-
up using an external EEPROM.
The SigmaStudio software is used to program and control the core
through the control port. Along with designing and tuning a signal
flow, the tools can be used to configure all of the ADAU1772
registers. The SigmaStudio graphical interface allows anyone with
digital or analog audio processing knowledge to easily design the
DSP signal flow and port it to a target application. The interface
also provides enough flexibility and programmability for an
experienced DSP programmer to have in-depth control of the
design. In SigmaStudio, the user can connect graphical blocks
(such as biquad filters, volume controls, and arithmetic operations),
compile the design, and load the program and parameter files into
the ADAU1772 memory through the control port. SigmaStudio
also allows the user to download the design to an external EEPROM
for self-boot operation. Signal processing blocks available in the
provided libraries include the following:
• Single-precision biquad filters
• Second order filters
• Absolute value and two-input adder
• Volume controls
• Limiter
The ADAU1772 can generate its internal clocks from a wide range
of input clocks by using the on-board fractional PLL. The PLL
accepts inputs from 8 MHz to 27 MHz. For standalone operation,
the clock can be generated using the on-board crystal oscillator.
The ADAU1772 is provided in a small, 40-lead, 6 mm × 6 mm
LFCSP with an exposed bottom pad.