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Audio signal chain chips target media-player phone handsets

Codecs, power controllers and headphone/speaker amps feature in mixed-signal chips

Wolfson Microelectronics has followed its recent course of combining its high-quality-audio signal path expertise with power management functions, in mixed-signal ICs, and has produced a new series of ICs for the portable audio market. One of these, the WM8900, is a low-power audio codec, with integrated class-G headphone amplifier. Wolfson designed this chip very specifically for use in media-player mobile phone handsets; the company has made clear its intention to add other parts aimed at alternative portable media devices at a later stage. The key to the performance of the 8900 is that it conserves power when it is driving loads at typical levels. Typical audio levels are from 0.1 mW per channel to a maximum of 2 mW per channel, Wolfson says; and, at those levels, its chip can yield an extra 11 hours of battery life compared to a non-class-G-equipped design. The amplifier is ground-referenced and an on-chip dual input, level shifting, intelligent charge pump generates symmetrical (positive and negative) power rails; +/- 1.2V from 2.4V in, or +/- 0.9V from 1.8V in. You can eliminate high-value capacitors from the output and improve bass response. If you demand power levels over 2 mW, the chip will switch to a different mode of operation that is somewhat less efficient. Automatic control of the charge pump maintains the most power efficient operating state during headphone playback. This is done with no intervention required from the operator or host software. The WM8900’s quiescent headphone playback power consumption is under 6 mW in voice mode and under 11mW in Hi-Fi mode; its designers also optimised it for the handset market with a 0.5-mm-high, 40-pin package. The ground-referenced class-G amplifier also eliminates, Wolfson says, many sources of pops and clicks during power-up, power-down, mute and unmute. The WM8900 costs $1.70 (10,000)
This chip follows two others introduced in the last few days. The WM9001 takes some aspects of the company’s AudioPlus (the ‘plus’ being power management) and optimises them for use in a phone handset, although the chip can be used elsewhere, Wolfson says. It is a mono, 1W switchable Class AB/D speaker driver for portable designs, that delivers up to 500 mW in class AB or 1W in class D. You can select class of operation, single ended or differential input modes, device clocking and speaker boost gain. 3x3mm QFN-16 and 1.64x1.64mm CSP package options allow you to place the chip close to a speaker to minimise any possible EMI concerns when in class D. RF noise suppression is also improved and external component count reduced by an integrated oscillator for clocking the class D outputs. Low leakage, high PSRR and pop/click suppression enable the speaker supply to be connected directly to the battery without compromising battery life or audio quality. The chip costs 0.45 in quantities of 10,000. It connects directly to a third new audio chip, the WM8400, and ‘audio hub codec’. Intended as the core of a portable audio architecture, the chip combines multimedia CODEC, on-chip FLL, two DC-DC converters and four LDO regulators, in a 6x6mm BGA package. It has eight analogue inputs and nine outputs; its low power audio CODEC delivers 98dB SNR performance and supports the signal switching, audio conversion and voice mixing requirements of next-generation mobile phones, Wolfson says. It has an on-board 1-W speaker driver (adding a 9001 gives you stereo) and you can select class AB or D operation in software: you might for example, operate in class AB for minimum noise if a GPS functions were also running – or switch to class D for highest output and efficiency. Replacing, the company says, three or more separate ICs, the 8400 comes in a 105-pin 6x6mm BGA package.