Nowadays, smart speakers are very common in our lives. They are a tool for everyone to access the internet. They can also play songs, shop online, make weather forecasts, turn on the lights, turn on the TV, open curtains, set the temperature of the refrigerator, and heat up the water heater. Smart speakers are a very smart home product with broad market prospects in the future.

What components are common smart speakers made of, what role do diodes and transistors play in smart speakers, and how they help smart speakers achieve more intelligent functions. In this issue, Heketai will introduce you to the application of diodes and transistors in smart speakers, helping you gain a deeper understanding of the role of diodes and transistors in smart speakers.

As is well known, diodes are one of the most fundamental components in electronic products. Usually, electronic products use diodes, resistors, capacitors, inductors, and other components to make reasonable connections, forming circuits with different functions, which can achieve various functions such as AC rectification, modulation signal detection, amplitude limiting and clamping, and power supply voltage stabilization.

A common intelligent speaker usually consists of several modules: microprocessor, audio processing circuit module, power management circuit module, interface circuit module, LED display circuit module, data storage circuit module, etc. The BOM usually includes SoC chips, mixed signal microcontrollers, WiFi/Bluetooth single chips, stereo audio amplifier chips, voice dedicated chips, DSP chips, storage chips, power management chips, LED drivers, MEMS microphone pickup arrays, PCB boards, diodes, transistors, resistors, capacitors, inductors, crystal oscillators, sensors, connectors, speakers, micro buttons, microphones, batteries, USB interfaces, etc.

Taking common echo cancellation circuits as an example, diode products will be used in this section. The accuracy challenge of intelligent speaker speech recognition is that the microphone picks up ambient noise. In order to filter out noise, one technique is echo cancellation, which can recognize the digital signal of playing music and then remove it from the microphone input. In order to better filter out environmental noise, the audio amplifier with echo cancellation function has an SDOUT signal, which is then fed into the SoC to filter out the music signal received by the microphone.

Taking the audio output module as an example, the audio source module of an intelligent speaker is usually divided into two parts: one is the digital part responsible for outputting digital signals, and the other is the decoding part responsible for digital/analog conversion of digital signals. The power amplifier section is also divided into pre amplifier and post amplifier. The pre amplifier is mainly responsible for signal voltage amplification, volume control, multi-channel sound source switching, tone adjustment, and impedance matching functions, while the post amplifier is specifically responsible for power amplification. Both parts will use transistor products.

The purpose of a power amplifier is to provide sufficient current driving capacity for the load to achieve power amplification. Class D power amplifiers, also known as digital amplifiers, use extremely high frequency conversion switching circuits to amplify audio signals, which has the advantages of high efficiency and small size. The typical D-class power amplifier topology consists of a triangular wave generator, a comparator, and a power output stage