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DTV codec eases audio signal management

Posted: 03 Oct 2007 ?? ?Print Version ?Bookmark and Share

Keywords:DTV audio codec? DTV system designs? signal management?

Cirrus Logic Inc. believes that it has greatly simplified the challenge of audio signal management within complex DTV system designs with the introduction of the CS42324 and CS42325 DTV codecs.

In their need to accommodate audio signals from numerous incoming sources, many DTV audio systems incorporate complex circuitry, including external muxes, operational amplifiers and input buffers. The highly integrated CS42324 and CS42325 provide system designers a single IC solution that manages the audio signal routing, eliminating the need for many of these separate components.

Among its features, the CS42324 includes a stereo ADC, a four-channel DAC, an I/O mux, line-level input buffers and output drivers, and the ability to run the ADC and DACs at asynchronous sample rates. On the analog front-end, its 5:1 stereo input mux allows for the selected audio source signal to be passed through either a data converter or to the output drivers directly. The CS42324 accepts line-level inputs up to 2Vrms, ensuring compliance with the SCART European standard. There are six 2Vrms output drivers which can be driven by either of the stereo DACs or by the inputs directly. Each output channel uses Cirrus Logic's patented Popguard technology that minimizes the effects of output transients commonly associated with single-ended, single-supply converters.

According to Carl Alberty, senior marketing manager of mixed-signal audio division at Cirrus Logic, "DTV audio hardware engineers can significantly reduce the complexity of the analog and digital audio signal routing and data conversion in their designs. The CS42324 and CS42325 provide a single-chip IC that simplifies their design, reduces the board area required for the audio circuitry, minimizes external components, and helps lower system cost."

The CS42324's independent serial ports allow for the onboard ADCs and DACs to operate at different, asynchronous sample rates, which simplifies system-level design issues related to managing audio streams that often have different sample rates, such as S/PDIF receivers, memory card interfaces, HDMI inputs and TV tuners. The codec operates from a single 3.3V digital supply and 9V or 12V analog supply for 2Vrms I/O drive capability while performing advanced multibit Delta-Sigma data conversion at up to 24bit resolution and sample rates up to 96kHz. Individual digital volume controls with 0.5dB step sizes and selectable soft ramp and zero crossing transitions ensure click-free changes. Channel muting can be implemented with either hardware or software control to further enhance sound quality and eliminate pops and clocks during power cycling, source switching and clock changes.

The CS42325 is hardware and software compatible with the CS42324 and includes on-chip stereo headphone drivers on one of the three stereo output pairs. The compatibility provides manufacturers a scalable audio solution to minimize development efforts for their entire product lineup.

Samples of the CS42324 and CS42325 are currently available in a 48-pin LQFP package and are priced at $2.05 and $2.15 in quantities of 10,000.

- Dennis Barker
Digital TV Designline

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