Product category: Capacitors
News Release from: Cap-XX | Subject: BriteSound
Edited by the Electronicstalk Editorial Team on 13 June 2007

Supercapacitors boost cellphone audio

Handset power architecture uses supercapacitors to satisfy peak demands while playing music

Cap-XX has announced its BriteSound power architecture for mobile phones. In a BriteSound phone, a Cap-XX supercapacitor provides a boost in peak power (more than 5V) that can double and sometimes triple audio power for richer-sounding music, and eliminate the buzzing and distortion that's common when transmitting wireless data while listening to music.

'With MP3-ready handsets growing in popularity, consumers want an iPod-quality audio experience without the distortion that interrupts music when the phone has to handle other peak-power functions', says Cap-XX CEO Anthony Kongats.

'We are working with key mobile-phone manufacturers and expect the first designs that are power-boosted by our Supercapacitors to hit the market in 2008'.

BriteSound is the second Cap-XX BritePower architecture for mobile phones, joining the BriteFlash solution for high-brightness LED flash.

In a power-management role supporting the battery, thin-form supercapacitors improve talk time, battery life, flash power, and audio quality, without compromising the handset's thin profile.

A mobile phone's audio quality depends on its audio amplifiers' power output and its speakers' impedance.

Typically, a standard 3.6V battery powers two class D amplifiers to drive a pair of 8ohm speakers.

In the Cap-XX tests, this setup delivered peak power of 1.2 to 2.25W.

This lack of power can result in thin-sounding music with a weak bass beat.

Another problem arises when the battery becomes taxed from simultaneous peak power demands to transmit wireless data and respond to a network poll (networks periodically poll phones to locate them and determine needed transmit power) while the user is also listening to music.

The battery voltage droops, and the audio amplifier supply voltage may droop enough to cause distortion which the user hears as a 'click'.

This problem is worse in GSM/GPRS/Edge phones that require particularly high power for RF transmission.

In addition, a 1A or greater peak-power demand on the battery will cause a ripple in the audio amplifier supply voltage which the user hears as audio noise, or as a 217Hz buzz during a phone call.

In the BriteSound power architecture, a 2.4mm-thin 0.55F 85mohm dual-cell Cap-XX HS206 supercapacitor delivers 5W power bursts to drive peak-power functions such as audio and LED Flash.

A battery covers the phone's average audio power needs of 0.5 to 1W, recharging the supercapacitor between bursts.

This leaves enough battery power to handle data transfers and network polls without compromising audio power, eliminating both the distortion and 'clicks' normally heard.

The supercapacitor powers the audio amplifier at 5V, compared with 3.6V directly from a battery, thereby doubling peak audio power for full-sounding music with a strong bass beat.

The supercapacitor also reduces noise by supplying peak power with less voltage droop than the battery would, and eliminates any 217Hz buzz when a GSM/GPRS/Edge phone transmits by protecting the audio amplifier from other peak loads the battery supplies such as the RF power amplifier.

Because the supercapacitor supplies high-peak currents, designers can use higher-quality 4ohm instead of standard 8ohm speakers, further doubling peak audio power.

Designers also save space and cost because they can size the phone's battery and power circuitry to cover average power consumption rather than peak loads.

Cap-XX used three cases for comparing audio quality and power, testing typical mobile-phone audio circuits both with and without a supercapacitor.

To test the difference in power that 4 versus 8ohm speakers would make, Cap-XX simulated the effect by attaching a second set of identical 8ohm speakers in the supercapacitor-powered setups.

To test a bass beat and a network poll, Cap-XX built two test circuits each with two class D audio amplifiers, one powered by a battery to drive a pair of 8ohm speakers, the other supported by a supercapacitor to drive two pairs of 8ohm speakers.

Cap-XX used a 100Hz bass beat lasting 120ms repeated every 0.5s to test speaker power and battery current.

The supercapacitor tripled peak audio power from 1.65 to 5.2W for fuller-sounding music.

Cap-XX simulated a GSM/GPRS/Edge network poll while listening to music by applying a 2A 1.15ms power pulse while the audio amplifier was playing a 1kHz tone.

The supercapacitor protected the audio amplifier from the battery voltage droop, eliminating distortion during wireless transmission.

Cap-XX used a set of SonyEricsson MPS60 external speakers and audio amplifier as a testbed.

Engineers modified one set with a supercapacitor charged to 5V to power the audio amplifier, then connected a second pair of 8ohm speakers to the original pair.

The company played a piece of music to compare the unmodified MPS60 to the supercapacitor-powered one.

The supercapacitor-modified setup more than doubled peak audio power from 2.24 to 4.96W, so music sounded fuller and richer.

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