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Class D Audio Subsystems provide 3D stereo enhancement.

January 29, 2008 - Intended for applications where speakers must be positioned close together, MAX9775 integrates mono, DirectDrive(TM), 80 mW receiver amplifier; stereo, DirectDrive, 80 mW headphone amplifier; and high-efficiency, Class D, stereo 1.5 W audio power amplifier, while MAX9776 employs mono, 80 mW receiver amplifier; stereo, DirectDrive 80 mW headphone amplifier; and mono Class D amplifier. Spread-spectrum modulation flattens wideband spectral components, minimizing EMI emissions.

Related categories: Electronic Components and Devices

Press Release
Release date: December 13, 2007

High-Efficiency Class D Audio Subsystems Enhance 3D Stereo Sound

SUNNYVALE, CA - December 13, 2007 - Maxim Integrated Products (Pink Sheets: MXIM) introduces the MAX9775/MAX9776 highly efficient Class D audio subsystems that provide 3D stereo enhancement. These devices are intended for cell phones or any application where audio quality is paramount and speakers must be positioned close together.

3D Enhancement of Stereo Sound

As stereo speaker applications become more compact, the quality of stereophonic sound is jeopardized. Close together in a handheld device, speakers almost sound mono.

With Maxim's 3D stereo enhancement in the MAX9775, it is now possible to emulate stereo sound in situations where the speakers must be positioned close together. Wave interference can be used to cancel the left channel in the vicinity of the listener's right ear, and vice versa. This 3D enhancement technique yields an "apparent" separation between the speakers that is a factor of four or greater than the actual physical separation!

Unprecedented Integration of Amplifiers

The MAX9775 integrates five output amplifiers: a mono, DirectDrive(TM), 80mW receiver amplifier; a stereo, DirectDrive, 80mW headphone amplifier; and a high-efficiency, Class D, stereo 1.5W audio power amplifier. The MAX9776 has four output amplifiers: the mono, 80mW receiver amplifier; the stereo, DirectDrive 80mW headphone amplifier; and a mono Class D amplifier. The MAX9775/MAX9776 are both designed around several of the Company's proprietary technologies, specifically spread-spectrum modulation, Active Emissions Limiting (AEL), Class D filterless amps, and DirectDrive Technology. The benefits of each of these design approaches will be discussed in turn.

Class D Speaker Efficiency and EMI

The MAX9775/MAX9776 Class D audio systems feature the Company's spread-spectrum modulation and third-generation filterless Active Emissions Limiting (AEL) technology. This proprietary architecture reduces EMI radiated emissions and ensures acceptance by international communications standards.

The efficiency of a Class D amplifier is attributed to the operation of the output stage transistors. In a Class D amplifier, the output transistors act as current-steering switches and consume negligible additional power. Any power loss associated with the Class D output stage is mostly due to the I²R loss of the MOSFET on-resistance and quiescent current overhead.

Patented spread-spectrum modulation* flattens the wideband spectral components, thus improving EMI emissions. Instead of a large amount of spectral energy present at multiples of the switching frequency, the energy is now spread over a bandwidth that increases with frequency. Above a few megahertz, the wideband spectrum looks like white noise for EMI purposes. Proprietary techniques ensure that the cycle-to-cycle variation of the switching period does not degrade audio reproduction or efficiency. The MAX9775/MAX9776 Class D speaker amplifiers exhibit greater than 70% efficiencies, while AEL circuitry keeps the EMI levels well below acceptable standards.

DirectDrive Design Improves Audio Performance and Saves Valuable Space

The devices' stereo headphone amplifier and receiver amplifier both feature the Company's patented DirectDrive architecture, which uses a charge pump to produce an internal negative supply voltage. This allows a ground-referenced output, almost doubling the dynamic range while operating from a single supply. This architecture removes the bulky DC-blocking capacitors required on the output. Instead of two large (typically 220µF) tantalum capacitors, the charge pump requires just two small ceramic capacitors. DirectDrive technology also provides comprehensive click-and-pop suppression. The overall design conserves board space, reduces cost, and improves the frequency response of the headphone driver.

Flexible Inputs and Outputs

The MAX9775/MAX9776 incorporate a user-defined input architecture that features an input mixer and multiplexer. Three flexible inputs can be configured as singled-ended stereo inputs or differential mono inputs. All input signals are summed into three unique signals before being routed to the amplifiers. This unique approach for the inputs and outputs gives the designer flexible options for each end application.

Samples and Further Information

Additional MAX9775/MAX9776 features include volume control, internal gain, and an I²C-compatible interface for software control.

The MAX9775 and MAX9776 are sampling now. Both are available in a standard 32-pin, 5mm x 5mm TQFN package or a 36-bump, 3mm x 3mm (RoHS-compliant) UCSP(TM). The MAX9775 is priced at $1.45, and the MAX9776 is $1.25 (10,000-up, FOB USA). Evaluation kits are available to speed designs. For more information on these products, please visit: http://www.maxim-ic.com/3D-Audio

*U.S. Patent #6,847,257
U.S. Patent #7,061,327

Company Information:
Name: Maxim Integrated Products
Address: 120 San Gabriel Dr.
City: Sunnyvale
State: CA
ZIP: 94086
Country: USA
Phone: 408-737-7600
FAX: 408-737-7194
http://www.maxim-ic.com

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