Using The Evaluation Board; Adau1701 Sigmadsp; Power Supply; Analog Audio Input - Analog Devices EVAL-ADAU1701MINIZ Quick Start Manual

USING THE EVALUATION BOARD

ADAU1701 SIGMADSP

The ADAU1701 is a complete, single-chip, audio system with a
28-bit/56-bit audio DSP, ADCs, DACs, and microcontroller-like
control interfaces. Signal processing , which includes equalization,
crossover, bass enhancement, multiband dynamics processing,
delay compensation, speaker compensation, and stereo image
widening, can be used to compensate for real-world limitations
of speakers, amplifiers, and listening environments, providing
dramatic improvements of perceived audio quality.
This signal processing is comparable to that found in high-
end studio equipment. Most processing is done in full 56-bit,
double-precision mode, resulting in very good low level signal
performance. The ADAU1701 is a fully programmable DSP. The
easy-to-use SigmaStudio software allows the user to graphically
configure a custom signal processing flow using blocks, such as
biquad filters, dynamics processors, level controls, and GPIO
interface controls.
ADAU1701 programs can be loaded on power-up either from a
serial EEPROM through its own self-boot mechanism or from
an external microcontroller. On power-down, the current state
of the parameters can be written back to the EEPROM from the
ADAU1701 to be recalled the next time the program is run.
Two Σ-Δ ADCs and four Σ-Δ DACs provide a 98.5 dB analog
input to analog output dynamic range. Each ADC has a
THD + N of −83 dB, and each DAC has a THD + N of −90 dB.
Digital input and output ports allow a glueless connection to
additional ADCs and DACs. The ADAU1701 communicates
2
through an I C® bus or a 4-wire SPI® port.

POWER SUPPLY

The power supply circuit consists of a 5 V to 3.3 V ADP3336
dc regulator, filtering, and an LED indicator. The resistors and
capacitor connected to the FB pin of the ADP3336 set the
output voltage. Power can be supplied from the USBi board,
on power connector J2, or through a battery wired to J1.
When the USBi is used to power the EVAL-ADAU1701MINIZ
from the 5 V dc of the USB port (default setting), a jumper
should be connected to J3. When an external 5 V dc supply
is used on either J1 or J2, the jumper on J3 should be discon-
nected. On J1, Pin 1 is power and Pin 2 is ground, as labeled
on the board's silkscreen.
When the EVAL-ADAU1701MINIZ is powered, LED D3
illuminates green. The ADAU1701 digital circuitry operates
off of a 1.8 V supply generated from the IC's on-board regulator
and pass transistor, Q1.

ANALOG AUDIO INPUT

Each of the stereo analog input signals connects to an anti-
aliasing filter and ac coupling capacitor before connecting to
one of the ADAU1701 ADCs. The resistor in series with the
ADC input is used in conjunction with the ADC_RES resistor
on the ADAU1701 to set the full-scale rms input voltage of the
ADC. In this case, it has been set to 1.0 V rms.

ANALOG AUDIO LINE OUTPUT

The ADAU1701 includes four Σ-Δ DACs. The SNR of the DAC
is 104 dB and the THD + N is −90 dB. A full-scale output on the
DACs is 0.9 V rms (2.5 V p-p).
The DACs are in an inverting configuration. If a signal
inversion from input to output is undesired, it can be reversed.
Simply invert the signal in the ADAU1701 DSP program flow.
DAC 2 and DAC 3 are connected to a single-pole, passive low-
pass filter with a 50 kHz corner frequency, which is sufficient to
filter the DAC out-of-band noise.

CLASS-D AMPLIFIER OUTPUT

DAC 0 and DAC 1 of the ADAU1701 are connected to the
SSM2306, a 2 W filterless, Class-D amplifier with a built-
in output stage. It drives 2 W into 4 Ω and 1.4 W into 8 Ω.
Connect speakers to J4 according to Table 1.
Table 1. J4 Pinout
Pin
1 (bottom)
2
3
4 (top)

CLOCKING THE EVALUATION BOARD

The ADAU1701 on-chip clock oscillator can drive an external
crystal to create a master clock. Switch S1 allows the crystal to
be disconnected; an external MCLK signal, input on J7, is used
instead (see Table 2). Crystal Y1 is 12.288 MHz, thus, the
ADAU1701 runs at a sample rate of 48 kHz (12.288 MHz/256).
Table 2. Master Clock Source Settings
Clock Source
12.288 MHz Crystal
MCLK from Header J7

EXTERNAL DIGITAL AUDIO INPUT

To use the digital audio input port of the ADAU1701, the
serial data, BCLK, and LRCLK signals must be connected to
an external source using Header J7. The source needs to be
synchronous to the ADAU1701, thus, the MCLK should be
input to this header as well. On J7, the row of pins along the
edge of the board are ground and the inner row of pins are
the signals.
Within the SigmaStudio software, the digital input Channel 0
through Channel 7 are accessed in the input cell in Position 2
through Position 9, as shown in Figure 6. Position 0 and
Position 1 are inputs from the ADCs.
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EVAL-ADAU1701MINIZ
SSM2306 Output
Right −
Right +
Left +
Left −
S5 Setting
Right
Left