ADAU1701 is a complete single-chip audio system that integrates a 28/56-bit audio DSP, ADC, DAC, and a microcontroller interface. It supports various signal processing functions such as balance, mixing, bass enhancement, multi-band dynamic processing, delay compensation, and stereo image expansion. This chip helps to overcome the limitations of real-world speakers, amplifiers, and listening environments, and dynamically enhances the perceived audio quality.
The first circuit we present below uses the ADAU1701 SigmaDSP codec, the low-power SSM2306 Class D amplifier, and the ADP3336 LDO regulator to achieve analog audio input and Class D output. The circuit connects the ADAU1701 codec with an integrated SigmaDSP® core to the SSM2306 2 W stereo Class D amplifier and ADP3336 low-dropout regulator. With two built-in ADCs and four DACs, the ADAU1701 can process a stereo audio signal and simultaneously output separately processed signals to both a line-level output and an amplified output. This allows different signal processing techniques—such as custom EQ, chip-level compressor for specific outputs, or spatial effects adjusted based on speaker configurations—to be applied to each output independently.
The ADP3336 provides a 3.3 V power supply for the ADAU1701, while the SSM2306 is a high-efficiency 2 W stereo Class D amplifier with ultra-low idle current. It requires minimal external components and does not need a large inductor, making the system compact. The amplifier is powered directly from a 5 V system supply rather than the regulator. This design is ideal for applications like radios, multimedia docking stations, or PC speakers where audio signal processing is needed for low-efficiency amplifiers.
The DAC output of the ADAU1701 is connected to the SSM2306 via a resistor and capacitor at each amplifier input. A 0.1 μF capacitor and a 13 kΩ resistor are used in series between the ADAU1701 output and the SSM2306 input to create a 28 Hz high-pass filter. These resistors also set the amplifier gain to approximately 6 dB. With a full-scale output of 0.9 V RMS from the ADAU1701, the SSM2306 amplifies it to 1.8 V RMS (5.09 V peak-to-peak), which closely matches the amplifier's clamp level when VDD is 5 V.
The circuit uses the multi-purpose (MP) pin of the ADAU1701 to control the active-low enable pin of the SSM2306. This connection, along with a 10 kΩ pull-up resistor, allows the SigmaDSP program to cleanly disable the Class D amplifier without causing any noise or clicks.
To stabilize the SSM2306 output, a ferrite bead and a 1 nF capacitor are placed on each speaker pin. The SSM2306’s power supply is taken directly from a 5 V source, while the ADAU1701 requires a 3.3 V regulated supply generated by the ADP3336. The output voltage of the ADP3336 is set to 3.3 V using a feedback network of 140 kΩ and 78.7 kΩ resistors. A 1 μF capacitor is placed between the output and ground to ensure stability, and a 1 μF capacitor at the input decouples stray inductance between the board and the 5 V power supply. The regulator’s shutdown pin is simply connected to the input voltage, enabling the IC automatically when power is present.
In addition to the ADAU1701, this circuit can also be implemented using other SigmaDSP processors with integrated DACs, such as the ADAU1761. The ADAU1702 can also replace the ADAU1701, though the main difference lies in the size of the SigmaDSP program and data memory. Similarly, Class D amplifiers like the SSM2301, SSM2302, and SSM2304 differ slightly from the SSM2306 used in this design. These amplifiers do not require external resistors to set the gain, and the SSM2301 is a mono amplifier rather than a stereo one.
A digital audio system solution based on the ADAU1701 and ARM7 is also presented, featuring multiple application diagrams that illustrate different circuit implementations.
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