Solution for high-fidelity restoration of smartphone "music player"

The audio quality of a smartphone should include two aspects: first, the sound quality of a portable communication device; and second, the high-fidelity restoration of a smartphone “music player”. This issue newsletter will be based on high-fidelity (Hi-Fi) audio quality. Starting with chip selection, circuit design, and processing algorithms, NCN technology, equalizer filtering algorithm, PCB wiring skills, miniDSP Codec, and MEMS device selection are proposed. .

With the increasing expansion of the consumer group of smartphones and the high quality of people's lives brought by smartphones, consumers are required to be able to talk in a noisy environment and hear the other party's speech without being disturbed by echoes . As can be seen from various data, there are many factors that affect the audio effect, such as the introduction of high-resolution audio amplifiers, radio frequency interference, PCB wiring, and insufficient power, etc. can all affect the quality of the call. These factors that affect the consumer's audio experience have led manufacturers and system designers to integrate more advanced audio processing functions, including software and hardware, into portable communication devices to enable voice calls in noisy environments even if the sound is not loud Be heard clearly, and eliminate echoes. This has driven those audio processing solutions with high-fidelity (Hi-Fi) effects to become more popular with consumers.

These requirements pose challenges for designers because they usually have to be completed with smaller form factors and design constraints that do not affect power consumption (battery life), weight (battery size), and cost (consumer devices are particularly sensitive). The following is the research and solutions for some of the above factors, I hope to help engineers and developers:

Noise caused by high-resolution audio amplifier

Regardless of whether the network used by the mobile phone is GSM or TDMA, the switching action of the RF transmitter will produce noise that seriously affects the power supply, because the switching frequency of the RF power amplifier is 217 Hz. The power amplifier draws a lot of current from the power supply each time it switches (typically up to 1.7A), so that the battery's equivalent series resistance (ESR) will produce a sudden voltage drop of up to 500mV. For SoC designs with embedded high-resolution audio converters and audio amplifiers or highly sensitive MEMS, this change will jeopardize the overall performance of the SoC, especially the audio quality will be severely affected, and humming noise will be heard. This document proposes the concept of PSRR (PSRR represents the regulator's ability to keep the output voltage stable when the input voltage changes), and analyzes in detail the impact of PSRR and other power factors on the audio quality of mobile phones. example:

RF carrier interference

At present, there are more and more opportunities for audio amplifiers to be interfered by strong RF electric fields. Many audio amplifiers are not designed with high-frequency signal interference in mind, so it is easy to demodulate the RF carrier information into the audio frequency band, causing RF interference. This document proposes several methods to reduce the effects of RF noise:

1. Integrate the audio amplifier into the baseband device

2. Optimize circuit board design

3. Use audio amplifiers that are not affected by radio frequency

PCB wiring improves cellular phone sound quality

Cell phone circuit board wiring is a great challenge for PCB wiring engineers. Modern cell phones include almost all portable subsystems, and each subsystem has conflicting needs. A well-designed PCB must give full play to the performance advantages of each connected device while avoiding mutual interference between subsystems. Therefore, for conflicting requirements, the performance of each subsystem must be compromised. Although the audio functions of cellular phones continue to increase, little attention has been paid to the PCB layout of audio circuits. This document proposes the relationship between PCB wiring and the sound quality of cellular phones, and reduces the noise of smart phone calls from the wiring.

Advanced device selection to reduce call noise

More and more mobile devices, such as mobile phones, headphones, cameras and MP3s, use advanced noise reduction technology to eliminate background sounds and improve sound quality. For this reason, the MEMS microphone produced by EPCOS not only has the ability to resist radio frequency and electromagnetic interference, but also has a very small size, which is an ideal solution in line with the design of modern smartphones; Texas Instruments has launched ultra-low power miniDSP audio Codec integration The dual miniDSP core can provide high-performance voice and music processing capabilities for battery-powered portable products in the working state with low electrode consumption.

In 2009, global shipments of Feature phones and Smart phones will exceed 1 billion units, accounting for more than 80% of all mobile phone shipments. In the current Chinese mobile phone market, the development of Feature Phone and Smart Phone is also the fastest. In these mobile phones, mobile phone speakers used for music playback are already a standard configuration, it can be said that most mobile phones are now music phones. "I want to sing, sing loudly" is a requirement for music phones, but now mobile phones have encountered many problems in music playback, from MP3 source files, mobile phone amplifier hardware design, player software design, etc. will introduce noise , So that the original color is lost for the restored sound. The following is a technical overview of these factors from several aspects:

Non-breaking sound (NCN) technology

The so-called NCN technology means that when the volume increases or the power supply voltage changes, the loud sound in the music will not exceed the maximum undistorted amplitude, forming a broken sound, so that the sound quality is "large but not broken". The NCN function uses Compression & Limitation Technology (Compression & Limitation) in professional audio systems, with important parameters such as threshold threshold, start-up time and release time.

Audio processing algorithm

Improving the audio quality of mobile phones is not easy. The two main factors are the size of the mobile phone and the compression of audio files.

Obtaining high-quality audio effects in the small size of mobile phones is indeed a challenge. To meet this challenge, we can only rely on a cross-functional team composed of designers in the fields of industry, electromechanics, and electronics. The engineer proposed this initiative: the use of audio processing algorithms. In order to compress audio, audio is usually compressed into smaller files for users to download. File compression is achieved through encoding algorithms (such as MP3). The reduction of files may cause the loss of information and ultimately affect the audio effect. Therefore, audio processing Algorithms can also come in handy.

Noise and its solutions

In the current portable multimedia devices with concentrated functions, more and more functions are being integrated into smaller and smaller systems. Audio is the most basic function of any multimedia-enabled system on the market, but system designers usually pay more attention to "eye-catching" features, such as wireless connection, video processing, image capture, and display. As a result, where there is a little space between many important components, the audio circuit is crowded wherever, resulting in very general or even poor audio quality. However, with a little care, good audio quality can be seamlessly integrated into the system along with many other features required by users. This article provides some suggestions for excellent system design and PCB layout design related to the design of any portable system that includes audio playback and / or recording functions, and analyzes many analog audio in the portable audio system that causes poor quality audio Noise sources that affect sound quality on the signal.

HD voice technology

HD voice, also known as broadband voice, is an audio technology that can transmit high-definition, natural voice quality for cellular networks, mobile phones, and wireless headphones. Compared with traditional narrowband phones, high-definition voice greatly improves voice quality and reduces the hearing burden. As narrowband networks and devices transition to high-definition voice, a voice processing technology called bandwidth expansion (BWE) can be used to simulate call quality similar to high-definition voice on the receiving terminal device, providing devices that do not support high-definition voice A compromise solution. This article will introduce BWE technology in detail.