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Digitally-controlled analog volume ICs broaden dynamic range

Austin, Texas — Cirrus Logic Inc. says it's setting a new industry standard for analog volume control ICs with a multichannel device that provides unmatched control flexibility for high-end audio systems.

Touting a dynamic range of 127 dB, 118 dB adjustable range and negligible distortion, Cirrus' CS3318 analog volume control integrated circuit (IC) targets high-end surround sound consumer and multichannel professional audio applications like audio/video receivers, home theater systems, digital mixing consoles, outboard audio converters, PC sound cards and automotive entertainment systems.

“Unlike digital volume control devices that limit dynamic range, the CS3318 is a digitally-controlled analog volume control IC that offers much broader control flexibility while maintaining the original dynamic range,” said Jason Rhode, vice president of Cirrus' Mixed-Signal Audio Division.

Supporting eight channels of audio, such as for 7.1 surround-sound entertainment systems, the CS3318 operates from a ±9-volt power supply, with 118 dB adjustable range from +22 db to -96 dB, negligible distortion and interchannel isolation.

 
 
See CS3308 block diagram

The pin-compatible ±5-V version (CS3308) provides a dynamic range of 123 dB (see block diagram above).

“Both the CS3318 and CS3308 feature a .25 dB step size, which is improved from the industry standard of .5 dB — providing upgraded resolution to ensure considerably smoother, finer volume adjustment,” Rhode said.

Additionally, Cirrus' patent-pending technologies — dynamic address assignment, simultaneous master volume, and mute controls — across devices over a single serial control bus (eg. I2C/SPI) provides additional design and control flexibility, according to Rhode.

The CS3318 and CS3308 volume control ICs are now available and are priced at $9.22 and $6.97, respectively, in quantities of 10,000-piece quantities. Click here for the CS3318 and CS3308 data sheets.

Cirrus Logic , 1-800-625-4084, www.Cirrus.com.

This analog volume control IC duo is supposed to provide superior audio quality and design simplicity.

Cirrus has been shipping a stereo analog volume control chip (CS3310) for over 12 years. In terms of performance, Cirrus' CS3318 can achieve a significantly higher dynamic range at 127 dB compared to the older CS3310 at 116 dB.

Looking back, the best analog-to-digital (A/D) converters and digital-to-analog (D/A) converters didn't exceed 110 dB dynamic range when the CS3310 was introduced, said Carl Alberty, senior marketing manager of Cirrus' Mixed-Signal Audio Division.

Today, Cirrus' flagship mixed-signal audio products offer 120 dB for its A/D and D/A converters. “If you are able to decrease the noise level by 6 dB, that's half of what it used to be. We've made a 10 dB improvement in dynamic range and total harmonic distortion plus noise (THD+N) performance, compared to the CS3310,” Alberty said.

These are single chips with eight channels of volume control — instead of using four stereo or two, four-channel volume controls. There are also some competing eight-channel volume control ICs available that are geared toward entry-level audio applications, as opposed to professional equipment, Alberty said. “It's the combination of analog performance (127 dB), THD+N (-110 dB), the flexible control interface and eight-channel integration that makes these chips unique,” he said.

Eight channels is significant because the content from DVD or HDTV shows for high-end consumer AV receivers for home theatres is typically broadcast in a six- or eight-channel format, which is driven by surround sound standards like Dolby Digital and DTS. “Consequently, the cost per channel can be significantly reduced by using the eight-channel device,” Alberty said.

Interchannel isolation of 110 dB for the CS3318 should draw some attention from designers. “Typically, they look for at least 100-dB isolation,” Alberty said.

Even more important though is the capability for control that these devices provide. Volume can be adjusted on each channel, independently, for instance. Cirrus' proprietary master control feature offers the user the ability to control each channel's volume and mute on an individual and grouped basis. Furthermore, the control port allows independent control of up to 128 devices on the shared serial control bus.

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