Hardware Design¶
What precautions do you have for chip power supply design?¶
If the module is used for product design, it should be noted that the power supply of the module cannot exceed the specification requirements to avoid flashing the module and the power supply ripple is less than 50mV.
LDO is recommended for 3.3V power supply of the main chip, and DCDC is not recommended to avoid large ripple of DCDC output voltage affecting the recognition effect. The voltage parameter of LDO requires that the output voltage fluctuation shall not exceed 5%, the ripple shall be less than 20mV, and the output current shall be more than 150mA.
To reduce power consumption, the core power of the main chip, such as 1.2V, should be supplied by DCDC. If power consumption is not considered, LDO can also be used for power supply. It is recommended that the voltage fluctuation of the core power supply should not exceed 5%, the ripple should be less than 50mV, and the output current should be more than 500mA.
FB feedback sampling resistor of DCDC chip must use 1% accuracy. The inductance and saturation current of the power inductor must meet the requirements of the chip and the actual output current.
Please ensure that the parameters and quantity of the filter capacitors on the main chip’s power supply pins match those in the reference design. During PCB layout, position these components close to the power supply pins. The analog ground (AGND) and digital ground (DGND) should be separated and connected at a single point using either a resistor (0603 package) or a copper pour. For the analog power supply (AVDD), implement a filtering network using a 2Ω resistor in series with a capacitor. For specific details, please refer to the reference design.
In addition, it is recommended to consider adding test points when designing power supply to facilitate automatic testing.
What are the precautions for microphone circuit design?¶
When designing the microphone circuit, pay special attention to that the bias voltage of the input bias circuit of the microphone should meet the requirements of chip parameters.
The analog ground loop should be as short as possible to avoid interference from digital signals. The microphone input interface is reserved with ESD protection devices, and ESD can be added to products with high requirements for electrostatic protection.
The microphone input circuit uses an analog ground, which must be isolated from the digital ground. Microphones have polarity - ensure the positive and negative terminals match the chip’s requirements during use, as incorrect polarity will affect recognition performance.
What are the precautions for infrared circuit design?¶
The infrared sending circuit is controlled by PWM signal, and the pins with conflicting functions shall not be selected. Generally, 4-6 transmitting tubes are used. 3.3V power supply mode, pay attention to change the corresponding current limiting resistance.
The infrared receiving circuit uses ordinary GPIO to receive and decode signals. Note that pins with conflicting functions should not be selected, such as serial port upgrade pins. For the power supply of the receiver, pay attention to the RC filtering of 100R+10UF in series.
What are the considerations in the process of designing an acoustic echo cancellation (AEC) circuit?¶
When designing the AEC (Acoustic Echo Cancellation) circuit, note that for analog power amplifiers, the AEC loop should be taken from the output stage (SPK+ or SPK-). For digital power amplifiers, there are two AEC loop configurations:
Taken from the pre-amplifier stage (after filtering) - suitable for applications with lower AEC requirements. Taken from the digital power amplifier output with additional filtering circuitry - recommended for applications with higher AEC requirements, such as smart speakers. Pay attention to the differences between digital and analog power amplifier AEC sampling circuits. It is recommended to follow our company’s reference circuit design.
For dual-microphone AEC circuits, special attention must be paid to correct polarity connection. Incorrect polarity will cause the amplifier’s stereo outputs (SKL+ and SKR+) to be out of phase, resulting in audio cancellation during mixing. It is strongly advised to follow our company’s reference circuit design.