Accommodating the ever-expanding range of accessories which can be connected to the headphone socket has a myriad of challenges, including jack detection, impedance sensing, multi-button detection, and reconfiguring the system's audio signal path. This can tie up valuable GPIO pins on the processor and complicate software development.
More recently, some advanced dedicated audio chips have integrated the ability to intelligently detect the type of accessory connected to the headphone jack, and can seamlessly manipulate the signal-path configuration, such as changing gains and associated supplies and biases to automatically switch to the new use case, effectively offloading this task from the applications processor. Load-impedance, headset and switch / button detection are all featured in Wolfson's first audio SoC, WM5100, and will feature in future products.
System level connectivity
Connecting a range of system ICs together, which have a range of signal formats and amplitudes at the analogue outputs, and mixing them effectively without adding noise and DC offsets, to accommodate a range of use cases and audio effects, can be problematic, as can adding more-complex devices such as dedicated DACs and CODECs. A dedicated audio converter will typically improve the system audio performance, but this isn't always possible for a number of reasons; namely BOM cost, availability of a dedicated digital audio interface on the processor, and the additional software complexity associated with configuring such a product. If the budget and project scope allows, this is the recommended approach.
Alternatively, using a dedicated audio amplifier, which has multiple analogue inputs with dedicated programmable gain amplifiers and mixers for every input, allows system designers to carefully condition the various audio streams for each playback path before final amplification at the output stage.
Figure 8 – Fully featured audio input stage
One of the easiest ways to address the majority of these problems is to use a range of products from Wolfson's audio portfolio, from Audio SoC, hubs and audio amplifiers. For more information, go to http://www.wolfsonmicro.com/products/audio_amplifiers/ or http://www.wolfsonmicro.com/products/audio_hubs/.
About the author:
David Brown holds a BEng in Electronics and Electrical Engineering from the University of Edinburgh and a CIM Professional Diploma in Marketing. He joined Wolfson five years ago as an applications engineer for portable audio products and is currently product line manager for Wolfson's audio amplifiers and converter products.
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