Three types of headset detection to embed in audio converters

December 22, 2014

In mobile electronics, a single device suffices to cover various daily usages: calling, taking pictures, playing music, geolocating, etc… All of these common features should fit in one’s hand. To adequately implement these new functionalities, audio electronics must not be limited to basic plug and play functionalities any longer. Smartphone applications should be compliant with new user practices by enabling more interactivity and giving more possibilities to control the inner functionalities.
If we focus on the audio application domain, the new usages of the headset is an important concern for every system maker. In so many situations, the headset becomes an essential accessory which replaces the touchscreen of the device. Indeed, users now want to control their Smartphone without taking it out of their pocket for not only hand-free phone calls but also for other applications, such as voice recognition. Buttons on the hand-free module can be used to pick-up a new call or control volume, play or stop music, jump to next or previous tracks, as well as for more advanced control operations which can be imagined by customizing long or multiple touches.
 Today, audio devices need to handle more functionalities between the headset and the audio converter, at least more that simply carrying the audio signal. But this capability cannot be handled otherwise than directly by the analog front-end. The audio converter needs to manage not only one hook button, but up to three buttons. Most of the time, this functionality is left to an external component but even when it is embedded in Integrated Components; the functionality is often limited to a dedicated headset and application schematic. The result is that each device uses its own headset, provided with the mobile phone or the tablet. As a consequence, users buying a new headset from a different maker generally lose the initial functionalities. The main risks are to have a non-working control button or a not recognized microphone by the application or, even worse, a notably deteriorated quality of sound.
 The reasons are that no unified standard exists, neither for headset schematics nor for the connectors themselves. Different microphones may also have different electrical models, especially equivalent resistance and current consumption, leading to different detection conditions from one microphone to another. Added with the fact that different application schematics are used, it is merely impossible for one circuit to support all headset button modules. Moreover, the drivers of the application interface may be trapped by false or ambiguous detection sequences, which can lead to extra development cost and duration.

 We will strive to detail in the following article the main issues and will highlight that solutions exist to achieve a robust, adaptive and easy to use design.

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