EDNE May 2012 - (Page 22)

By Ia n De n n Is • P r I s m s o u n D G r o u P Audio-converter-subsystem design challenges in the 21st century Some key StrAtegieS enAble you to Achieve optimum Audio-converter performAnce. he habitat of audio converters is ever-changing. of 130 dB and total harmonic distortion plus noise of 110 dB Designers built early converters into stand-alone rms, unweighted, in the audio band. The weak link in a converdigital-audio equipment. Later, they built them sion system is most often elsewhere. No case exists for applying as stand-alone conversion devices with dedicated design effort or budget to the data converter itself, except in the digital-audio connectivity. Nowadays, converters most exacting of applications, and where it has already been are increasingly available as peripherals for PCs applied in great measure to the rest of the converter subsystem. or computer networks. Meanwhile, performance targets have To get the best from your chosen data converter, you must apply been rising. In some ways, these changes have affected audio- painstaking design and relentless assessment. converter design; in other ways, it’s business as usual. It seems that the plan of campaign for most engineers set- Typical aDc anD Dac subsysTems ting out to design an audio-converter subsystem—that is, a Figures 1 and 2 show typical ADC and DAC subsystems. You stand-alone converter or that part of the equipment that deals with audio conversion—is as follows: First, choose PSU a data-converter device—an ADC, a DAC, or a codec chip—which will SYNCHRONOUS DIGITAL PARTS VREF meet the project’s requirements for perPLL formance, channel count, cost, and features. Then, implement a design ANALOG DIGITALSIGMA-DELTA DIGITAL DSP INPUT DECIMATION INTERFACE around the device using the manuMODULATOR OUTPUT FUNCTIONS INPUT CONDITIONING FILTER TRANSMITTER facturer’s application note plus whatever additional features and interfaces the design requires. Most converter figure 1 in a typical Adc, you must take special care of the analog bits (blue shading); subsystems, however, either always or several parts of the subsystem will try to make that task difficult. sometimes perform somewhat below the potential of their chosen data converter—usually because of several issues: clocking, unruly switch-mode PSU power supplies, low-quality analogsignal paths, lack of attention to the DIGITAL PARTS VREF PLL voltage reference, and digital parts that go awry. When digital audio was new, the INTERPOLATOR DIGITALDAC AND data converter itself was almost the ANALOG DIGITAL AND SIGMAOUTPUT DSP INTERFACE LOWPASS OUTPUT INPUT DELTA CONDITIONING FUNCTIONS RECEIVER FILTER only consideration because it was MODULATOR impossible to build one with as much dynamic range and linearity as the professional or high-end consumer dashed line user required in analog equipment. figure 2 in a typical dAc system, theEDN MS4434 Fig indicates where you might consider 1.eps DIANE Designers asked only, “What chip is isolating the analog parts (blue shading) and the digital parts, but many ways are availin it?” Nowadays, workmanlike data able for doing so, or you can opt not to isolate the parts. converters can exceed a dynamic range 22 EDN EUROPE | MAY 2012 www.edn-europe.com T http://www.edn-europe.com

Table of Contents for the Digital Edition of EDNE May 2012

Cover
Contents
International Rectifier
RS Components
Masthead
Comment
International Rectifier
Pulse
Analog Devices
Toshiba
Digi-key
Bergquist
Baker's best
Test & Measurement
Agilent Technologies
Digi-key
Audio-converter-subsystem design challenges in the 21st century
Coilcraft
Silicon Labs
Digi-key
Cover Story
Digi-key
Sensor & Test
Mechatronics in design
Vicor's insert
Understand and reduce dc/dc-switching-converter ground noise
Power MOSFETs continue to evolve
Design Idea
Product Roundup
Tales from the cube

EDNE May 2012