| BM5446EFV-BD5446EFV Class D Speaker Amp |  |
Class D Speaker Amplifier with On-board DSP Improves Audio Fidelity and Contributes to Increased Miniaturization
ROHM has announced the development of two Class D speaker amplifiers for LCD and panel TVs, mini-component systems, powered speakers, and gaming devices. The BM5446EFV (with on-board DSP) and BD5446EFV (without DSP) feature 20W + 20W output and digital input compatibility, preventing audio deterioration caused by D/A converters normally utilized in analog systems. The gain can be fine tuned (BM5446EFV: 16 steps, BD5446: 8 steps), enabling optimization of the S/N ratio, and analog audio output provides support for headphones as well as devices requiring line output.
The increasing trend towards larger screen size and thinner LCDs and plasma TVs places greater limitations on the shape, size, and locations of speakers, making it difficult to provide high sound quality. In order to provide a level of sound quality that matches high definition video, conventional manufacturers have resorted to integrating a specialized DSP in addition to the video processing system IC. This has resulted in additional problems, including increased costs and space requirements.
The BM5446EFV integrates a DSP for high-performance audio and is the first IC of its kind with a calculation function that automatically determines the equalizer filter coefficients (i.e. 7-band parametric equalizer, 3-band tone control). Conventional systems normally transmit the filter setting coefficients from the microcontroller, placing an enormous load on the system. ROHM’s automatic calculation function makes it easy to set the equalizer characteristics– simply send a small amount of setting data for the gain, center frequency, and Q (quality) factor. Besides the normal array of audio modes (e.g. volume, surround) a unique audio function, P2Audio (Perfect Pure Audio), is integrated, encompassing three distinct correction circuits: DRC (Dynamic Range Control), bass enhancement, and sound image localization optimization. A feedback circuit is also built in, eliminating the need for power circuitry (normally used for stabilization), resulting in increased PSRR (Power Supply Rejection Ratio) while enabling direct drive support with +24V power sources for LCD TV backlights. This not only reduces the number of components required, but ensures lower noise, distortion, and output impedance for superior audio quality.
The BD5446EFV, with no on-board DSP, is ideal as an add-on to existing audio systems that already have tone- and volume-adjusted digital signals.
1. Key Features
(1) On-board audio DSP optimized for volume and tone
adjustment in flat panel TVs (BM5446EFV only)
(2) Supports direct two-line digital audio signal input
(3) Built-in feedback circuit ensures high PSRR
characteristics and high sound quality
(4) Reduced popping noise during power ON/OFF
(5) Unique software swapping technology utilized for
high quality audio muting and smooth volume adjustment
(6) Built-in analog output allows selection from two-line
digital audio input, independent of speaker output
(7) Integrated S/PDIF (optical digital) output (BM5446EFV only)
(8) Compatible with a single power supply: Vcc = 10V to 26V
(9) Equipped with heat sink, enabling 20W + 20W output
(10) Multiple protection circuits built-in: thermal shutdown,
low voltage protection circuit, overcurrent protection,
speaker/clock stop protection
2. Terminology
Feedback Circuit
A circuit that feeds PWM output from the Class D power amp to the previous PWM modulator, eliminating noise caused by variations in the power source while correcting PWM output noise and distortion in the class D power amp.
7-band Parametric Equalizer
An equalizer function for fine tuning of the frequency characteristics in flat panel TV speakers. Conventional systems utilize a microcontroller to transmit the enormous amount of filter coefficient data required for setting equalizer characteristics. ROHM eliminates this by integrating a unique circuit that automatically calculates the filter coefficients, making it possible to set the equalizer characteristics utilizing only a small amount of data (i.e. gain, center frequency, and Q factor) from the microcontroller.
PSRR (Power Supply Rejection Ratio) Characteristics
This indicates the ability of the amplifier to maintain stable output voltage even during source voltage fluctuations. It is defined as the ratio between the source voltage variation and output voltage variation, and is expressed in decibels (dB).
P2Audio (Perfect Pure Audio)
Refers to three functions, uniquely developed by ROHM, that are considered indispensable for audio processing in thin-screen TVs.
- P2Volume (Perfect Pure Volume): A DRC (Dynamic Range Control)
function that suppresses loud sounds such as explosions and amplifies
quiet sounds (i.e. whispering) to make them easier to hear. It also
prevents deterioration of the S/N ratio when the sound is muted.
- P2Bass (Perfect Pure Bass): An amplification function for correcting
and strengthening bass sounds. Unlike ordinary bass boosts, it is
capable of reproducing strong bass sounds clearly without muddying
vocals and other audio signals.
- P2Treble (Perfect Pure Treble): A correction function designed to
improve sound localization by making it sound as if the audio is
originating from the center of the picture in cases where the
speakers are arranged below the screen, as in the majority of flat
panel TVs and monitors.
DRC (Dynamic Range Control) Function
A function that contracts and expands the dynamic range of the audio signal. Dynamic range refers to the value expressed as the ratio of the minimum value and the maximum value of the audio signal, and is expressed in decibels (dB).
S/N Ratio (Signal-to-Noise)
The value expressed as the ratio of audio signal to noise. Expressed in decibels (dB). The greater the S/N ratio the less noise is present. A low value indicates a relatively large amount of noise.
Technical note will be available mid of June, samples ~ July 2009.