In recent years, the market for mobile / portable devices such as smartphones and notebook computers has continued to develop rapidly. While these products continue to integrate more new functions to enhance the user experience, there is still plenty of room for improvement in the user experience of basic voice communication functions, especially in noisy environments to improve voice clarity while maintaining natural voice fidelity. For example, when a user walks in a crowded commercial street, the surrounding environment may be full of car horns, engine roar, construction noise, noisy crowd noise, footsteps and even wind noise. When using a mobile phone to make a voice call, the traditional technology It is difficult to provide a clear voice communication effect. In addition, manufacturers are also adding video calling capabilities to emerging tablet PCs. When using these mobile / portable devices for teleconferences, the surrounding environment may also include a variety of noises, such as noisy human voices in the office, surrounding conversations, computer noises, stroke noises, and glassware knocking sounds. The call effect is also not easy. In these applications, to reduce or filter environmental noise and improve voice communication effects, different methods can be used, such as special noise reduction microphones, analog circuit noise reduction or digital circuit noise reduction. These methods have their own characteristics. In comparison, the noise reduction method using digital circuits is flexible, the acoustic design complexity is low, and the noise reduction effect is superior. Of course, in addition to providing good noise reduction effects, portable device designers are also faced with various design constraints and challenges, such as size, energy consumption, physical acoustic design, audio fidelity, and cost. Advanced dual microphone real-time adaptive noise reduction technology ON Semiconductor recently introduced the BelaSigna R261 high-performance voice capture system-on-chip (SoC) based on digital circuit noise reduction technology. The device uses advanced dual microphone noise reduction technology, which can help the design to provide excellent noise reduction effect (see Figure 1). This advanced signal processing technology accepts the signals of two microphones, can distinguish different types of signals, extract effective voice information and suppress environmental noise, thereby improving voice recognition. Figure 1: BelaSigna R261 uses an advanced real-time adaptive noise reduction algorithm. BelaSigna R261 has a speech extraction algorithm built into its integrated ROM memory. This algorithm uses one or more sensors to extract the waveform propagation signal without the need to know the sound source or sensor position in advance. This scheme uses global optimization criteria and works in the frequency, time, and space domains at the same time. There is no limit to the number of sound sources and the number of sensors, and it has nothing to do with the signal-to-noise ratio (SNR). It also works optimally, and is very suitable for applications such as mobile phones and portable computers that need to extract useful speech signals from different noise domains. This adaptive noise suppression algorithm provides 25 dB of noise suppression capability, which can separate the required speech and environmental noise in real time. It is suitable for various voice sources and voices in various positions, while ensuring natural sound quality (after other solutions) (Unnatural sound, not full), can effectively work with microphones of various qualities. Analysis of key features of BelaSigna R261 BelaSigna R261 is a high-performance voice capture SoC that integrates a digital signal processor (DSP), voltage regulator, phase-locked loop (PLL), level shifter, and ROM memory. Such a high level of integration is comparable to other solutions By comparison, the bill of materials (BOM) can be reduced. As shown in Figure 2, this device supports dual microphone direct input, noise reduction algorithm is built into the integrated ROM memory, DSP-based application controller provides high performance and ultra-low energy consumption, provides dual-pass analog output, and supports digital microphones Output. In addition, the built-in power management module supports supply voltages from 1.8 V to 3.3 V, the built-in on-chip PLL provides multiple frequency options, and also provides an I2C interface. Figure 2: Functional architecture of BelaSigna R261 high-performance voice capture SoC. It is particularly worth mentioning that the dual microphone real-time adaptive noise reduction algorithm used in BelaSigna R261 provides two basic algorithm modes, namely the long-distance pickup mode (algorithm mode 0) and the short-distance pickup mode (algorithm mode 1) . Algorithm mode 0 is optimized for long-distance sound pickup. It can pick up voices up to 6 meters away, while suppressing noise, and supports 360-degree sound pickup. It is suitable for laptop, hands-free phone / meeting or mobile hands-free call mode. . In this mode, even if the user does not point the microphone, or even away from the microphone, can provide excellent voice clarity, thereby enhancing the user's freedom of use. Algorithm mode 1 is optimized for short-distance pickup. At this time, the user is very close to the microphone (the distance is less than 5 cm), that is, picking up the voice at a short distance, effectively suppressing various environmental noises. Equipment working in a noisy environment. In addition to these two basic algorithm modes, BelaSigna R261 also provides customized algorithm modes to help manufacturers meet specific application needs. This algorithm mode supports special configurations and can be adjusted by loading new algorithm parameters through an external EEPROM or I2C control interface. The algorithm effect can be optimized according to the specific application, microphone type, position and other system parameters. Table 2: BelaSigna R261 supports different modes such as long-distance pickup, close-distance pickup and customization. As mentioned above, BelaSigna R261 provides high integration, built-in adaptive noise reduction algorithm, can be directly connected to the digital microphone interface or the microphone input of the main chip (baseband processor). Therefore, in addition to supporting multiple pickup modes, another important advantage of this device is that it is easy to integrate into the design, which can minimize the time and engineering work required for design-in, because the design team does not There is no need to design complex support and interface circuits to develop or acquire algorithms. This device also allows cost-conscious original equipment manufacturers (OEMs) to use two inexpensive (not necessarily matched) omnidirectional microphones in their designs, making the microphone layout more flexible and eliminating the need to debug the microphone on the production line, further saving Time and cost. This SoC is packaged in a very compact 5.3 mm2 WLCSP package (both 26-ball and 30-ball versions). It takes up much less board space than other alternatives. Even the most space-constrained form factor for portable consumer electronics products Worthy. In addition, the current consumption of this device at 3.3 V is 15 mA, and the energy consumption is extremely low. Main points of BelaSigna R261 application design Because BelaSigna R261's ROM-based noise reduction algorithm is very flexible, there are many possible options for microphone layout (physical acoustic design), but the default algorithm works best only when the microphone is laid out in the following manner: 1) Two microphones are facing the user Mouth; 2) The midpoint of the two microphones is within 10 to 25 mm from each microphone. Of course, other microphone layout configurations can also be used when using custom mode. In terms of circuit design, BelaSigna R261 is designed to support both digital and analog processing in a single system. Because of this mixed-signal circuit property, to maintain high audio fidelity, careful design of printed circuit board (PCB) wiring is critical. To avoid coupling noise into the audio signal path, keep digital signal traces away from analog signal traces. To avoid electrical feedback coupling, it is also necessary to isolate the input traces from the output traces. In terms of ground design, the ground layer should be divided into two parts, namely the analog ground layer (VSSA) and the digital ground layer (VSSD). The two ground planes should be connected together through a single point (that is, star connection point). The star connection point should be at the ground of the capacitor at the output of the power regulator. Of course, these are just some of the issues that designers need to pay attention to when applying BelaSigna R261 design. See reference 2 for detailed design points. to sum up: Designers of portable device audio systems need high-performance voice capture solutions that are easy to integrate into their systems while meeting their requirements for size, energy consumption, and cost. ON Semiconductor, as the leading high-performance silicon solution provider for energy-efficient electronic products, provides designers with a simple choice with BelaSigna R261 high-performance voice capture SoC. This device has high integration, built-in advanced adaptive noise reduction algorithm, supports multiple voice pickup modes, so that applications such as smartphones, walkie-talkies, notebooks and tablets can provide clear and comfortable voice communication, with extremely high design flexibility At the same time, the small size and low power consumption facilitate the selection of low-cost microphones, enabling manufacturers of various portable consumer electronics products to greatly improve voice recognition and customer satisfaction, and speed up the product listing process. 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