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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 burning 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 keep the parameters and quantity of the filter capacitor on the power supply pin of the main chip consistent with the reference design. PCB design layout is close to power supply pin. Analog ground and digital ground shall be separated, and single point connection shall be conducted by means of resistance (one 0603 package) or copper coating. The analog power supply AVDD selects 2R and capacitor to form a filter network. See the reference design for details.

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 is analog ground and needs to be isolated from the digital ground. The microphone has positive and negative polarities. Please note that the positive and negative polarities are consistent with the chip requirements when using, otherwise the recognition effect will be affected.

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 for the design of the echo cancellation (AEC) circuit?

When designing the AEC circuit, note that the AEC loop of the analog power amplifier is taken from the back end of the power amplifier (SPK+or SPK -). There are two kinds of AEC circuits for digital power amplifier

  1. It is taken from the front end of the power amplifier, that is, the place where the filtering is completed (the requirement for AEC is not high).

  2. It is taken from the back end of digital power amplifier and added with filter circuit (requiring high AEC as smart speaker).

Note the difference between the AEC sampling circuit of digital power amplifier and analog power amplifier. It is recommended to design according to the reference circuit provided by our company.

If it is a dual microphone AEC circuit, pay special attention to the correct connection of the polarity. If it is reversed, the power amplifier will output stereo sound SKL+. SKR+will be inverted, and it will be silenced after combining. It is recommended to design according to the reference circuit provided by our company.