Project Analog - February 2008 - (Page 8) Selecting an Audio codec for Portable Apps By Larry Gaddy AKM Semiconductor / San Jose, CA www.akm.com Contents Viewpoint Digital potentiometer application circuits Smart ADC architecture Layout techniques for high accuracy and resolution ADCs Analog news Today’s devices integrate many features that affect audio quality, system cost, power requirements, and design complexity A udio codec ICs are at the heart of many different portable devices that feature both record and playback capabilities. While the basic product selection of input and output channels with their respective performance may be simple, today’s devices offer many integrated features that can affect audio quality, as well as system cost, power requirements, and design complexity. Understanding what these features bring to a portable application is needed to make the best choice. SyStem architecture The audio system in a portable record and play appliance includes more than the basic converters. These devices almost always include a stereo DAC, a mono or stereo ADC, a microphone amplifier, and outputs that may include a headphone and/or a speaker amplifier, and a line level output. Additional features can include a programmable gain amplifier (PGA), input and output automatic level controls (ALCs), a PLL, and an analog mixer. Codecs are available that address both the most basic system and the most complex. Once the full list of desired features has been determined, there are secondary considerations, including the control interface, amplifier interface, and clocking requirements (see Fig. 1). microphone inputS and adc Placement of the microphone and routing of its signal can be a critical factor. The microphone is mounted near the user’s mouth, but this is often far away from the codec. Most applications employ single-ended microphones, but when the signal is routed over a long distance, it is prone to noise interference. Con- the audio system in a portable record and play appliance includes more than the basic converters. Microchip analog page Mixed-signal overview Sample center microchipDIRECT Reference designs/ app notes Technical training 8 · Project AnAlog · feb 08 http://www.akm.com http://www.microchip.com http://www.microchip.com/analog http://www.microchip.com/analog http://www.microchip.com/mixedsignal http://sample.microchip.com/Default.aspx?testCookies=true http://www.microchipdirect.com/catalogselection.aspx?returnURL=default.aspx http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1469&filter1=function&redirects=appnotes http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1469&filter1=function&redirects=appnotes http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1423
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