audio/videoZONE Products for the week of August 16, 2004
AKM Says . . .
AAK4730: Multi-Reference Class-D Audio Amplifier Modulator
Asahi Kasei Microsystems Co., Ltd. (AKM) a leading supplier of audio ICs for professional and consumer markets, introduced a new Class-D two channel modulator generating a remarkable 110dB signal-to-noise ratio and industry-leading sound reproduction.
The AK4730 marks AKM's first entry into the high-power amplifier world and is aimed at both professional and consumer products.
AKM's AK4730 exceeds Class-AB performance with Class-D efficiency. The input to AK4730 is digital and supports two-channel, 192kHz sampling. The chip combines a two-channel PWM modulator with pre-driver circuitry for external MOSFETs.
Unlike other solutions that use two voltage levels for modulation (H-Bridge), AKM's Class D products utilize an advanced multi-reference E-Bridge architecture (JAM Technologies, Inc.) that achieves higher linearity and SNR performance for audio playback with fidelity closer to the original sound.
With an integrated driver, the AK4730 MOSFET output stage is a simple
circuit and is easily incorporated into an audio system. Output power to
suit system requirements can be readily achieved by changing the MOSFETs.
analogZONE Says...
One of the major problems with conventional H-Bridge modulation in Class-D audio is crossover distortion and linearity. Vendors will push overall THD and SNR numbers but will carefully avoid discussing linearity and crossover. And, of course, the marketing arms have been pushing the "no EMI filtering needed" as long as the IC is less than x (any small number) of cm away from the speaker terminals.
The E-Bridge (a simplification of Σ) is an architecture crafted by JAM Technology who are out of Boston, MA. They are licensing their technology and AKM seems to be one of the first companies to pick up on it and get into a market that has not been traditional for them. In many ways AKM seems to be tackling the market with the same attitude as Wolfson Microsystems, but batting for the higher end users.
The E-Bridge technology is said to sum multiple partial products at the load rather than processing the two phases of the signal complete. The multiple-level, PCM-type, approach makes a lot of sense and we will be asking JAM Technology to offer a simple explanation for readers in a future TechNote.
This standalone modulator from AKM is in a HQFP-80 and needs 4.75 V - 5.25 V for the modulator and 10.8 V - 13.2 V for the output buffer. SNR is claimed as 110 dB with 192 kHz sampling capability with formats of 24-bit MSB, 24-/20-/16-bit LSB justified, or I2S. Level control is offered in five different modes with 256 levels in 0.5-dB steps. Tone control is also provided at 100 Hz ±10 dB and 10 kHz ±10 dB, both is 1-dB steps.
Combining AK4730s with the AK4113 digital audio interface would allow the simplified production of multiple-channel audio systems simply requiring the addition of external power MOSFETs to drive the loudspeakers. The amount of output power available would depend on the choice of MOSFETs and the voltage they are run at. A number of vendors make suitable device to power certainly 100 W channels. Those vendors wanting to avoid "entrapment" by a single vendor of H-Bridge products will certainly want to look carefully at this product. The graphs that I have seen of the output spectrum from a AK4730-powered channel show dramatic improvements in out-of-channel emissions.
Both 70 W and 100 W evaluation boards are available from AKM.
There was no response to my request for a data sheet and a price from
AKM.