如何给便携式设备添加音乐和数据传输功能

作者：Wade Gillham
Silicon Laboratories Inc.

便携式设备领域的一个新趋势，就是不仅提供音乐播放功能，还要添加数据和语音传输服务。数字媒体正变得越来越受欢迎，但我们不应该忘记人们对于AM和FM广播的需求以及它们的流行度。对于半导体厂商来说，如何以低成本高效率的方式将这些流行功能增加到移动设备上，并且保持设备的小外形，是一个极大的挑战。AM广播尤其是个大问题，因为它需要大的天线。因此，很多小型的电池供电型多功能便携式设备都不具备AM广播收听功能。

本文讲解了如何将音乐和AM广播功能添加到一部全功能的便携式设备中，而不会扩大产品的外形大小，同时保持较低的功耗需求。

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英文原文：

How To: Adding Music and Data Transmission to Portable Devices

Wade Gillham
Silicon Laboratories Inc.

Portable devices have become one of main sources of demand for the semiconductor industry. The high volumes of these products are driving significant semiconductor innovation to add new features in a very small footprint. This also requires low power dissipation. One of the emerging trends in portable devices is offering music along with data and voice transmissions. Digital media is becoming increasingly popular, but we shouldn’t forget about the demand for and popularity of AM and FM radio. The challenge for semiconductor suppliers is to enable these popular features cost effectively and in a very small footprint. AM radio in particular is very challenging due to the large antenna required. As are result, for very small, battery powered, multi-function portable devices do not have a large penetration of AM radio. AM radio is extremely common in around the world and therefore it is well understood to be a popular potential feature, but how does a system designer overcome the challenges?

A major innovation in AM radio for portable devices, particularly cell phones is the use of a digital low-IF architecture that allows many analog functions to be replaced with digital signal processing (DSP). Functions implemented with DSP techniques include selectivity filtering, adjustable channel bandwidth filters, FM and AM demodulation, stereo decoding, signal strength measurement, signal-to-noise measurements, automatic gain control (AGC), automatic frequency control (AFC), RDS/RBDS decoding, audio processing including volume control, soft mute and stereo blend. The high integration level and digital-intensive architecture provides many customer benefits, including a reduction in the bill of materials (BOM) and a reduction in board space by more than 95 percent when compared with traditional AM/FM receivers.

This high level of integration allows a system designer to add AM capability to a full featured portable device without having to make compromises on the size of their end product.

By leveraging new, innovative architectures, AM radio footprint can be reduced from more than 45 components and 1,000 mm2 to a single chip and two external components requiring only 15 mm2 of board space. This tiny footprint and low power requirements make it possible to offer an AM/FM receiver into mobile phones and MP3 players. But the designer may be asking the question, what about the antenna?

A flexible design enables the use of a wide-variety of ferrite antenna options. Historically, it was thought that low cost antennas would result in poor reception and sound quality, however, the high performance enabled in a digital low-if architecture is less reliant on a strong antenna and enables the use of very small, low cost AM antennas while still delivering similar or better sound quality than competing solutio