FROM EDN EUROPE: Class D audio comes with low noise floor

Zetex plans soon to release an all-digital version of its Class D audio-amplifier-driver chip as a complement to the analogue-input ZCXD1000 that is now available for sampling. The 1000 comprises a PWM converter and drivers for output-power MOSFETs. Zetex claims best-in-class THD and noise figures for designs based around this chip: less than 0.1% at 1 kHz, 1W and less than 0.2% at power rating as high as 90%, both measured open loop. Typical circuit topologies include H-bridge-connected MOSFETs in the output stage. Zetex's MSOP8-packaged ZXM64N03X and p03X provide power outputs as high as 50W, and the company provides reference designs for designs of 25 to 100W.

As always with Class D, efficiency is a key specification point; this design offers efficiency of more than 90%. If you are deriving your audio signal from a digital source, you must place an A/D converter ahead of this chip. In the version due for release in the next few weeks, Zetex will eliminate that conversion, and the all-digital system will accept standard digital-audio bit streams directly into the amplifier driver IC.

Zetex Semiconductors, +44 161 622 4422, www.zetex.com.