As mobile phones are turning into smartphones, a growing range of multimedia features are making their appearance, including Hi-Fi audio playback of MP3 or other file formats, video capture and touch-sensitive displays.

For all these functions, mixed-signal and analogue design is key to achieving the performance that users have come to expect, while shrinking the physical size of components and reducing power consumption.
A whole industry has sprung up around the sale of ring tones, generating extra income for network operators. Keeping ahead of the curve in this area allows manufacturers to appeal to both operators and end customers. Only a couple of years ago, hi-fi enthusiasts watched in disbelief as handsets first began to sprout a pair of coin-sized speakers to play polyphonic ring tones in stereo. Today, as a struggling music industry is jumping on the bandwagon, MP3 is set to replace MIDI as the standard ring tone format. Having an MP3 decoder on-board also enables the phone to double as an MP3 player.
All this audio requires, first and foremost, more transducers. A high-end clamshell phone might have the obligatory earpiece, a larger 'inside' speaker to take over when the user switches to hands-free, and two 'outside' speakers to play the latest chart-topper while the clamshell is closed.
Headsets also need to be stereo, with additional audio inputs and outputs to connect to in-car hands-free kits. But quantity is not enough: to win over the sceptics and convince the world that MP3 ring tones are worth paying for, they must sound good too.
Given the tiny speakers and the size and cost constraints in mobile phone design, this will require significant analogue expertise. Many component manufacturers achieve very high quality audio reproduction on their evaluation boards; the real challenge, however, is to accomplish the same on a tiny handset PCB crammed full of noisy RF and digital components.
Reducing the power consumption of analogue circuitry is also becoming increasingly important, as more and louder speakers could potentially reduce the all-important battery life. Dedicated and knowledgeable field applications support frommixed-signal chip vendors is therefore set to become even more critical than it is today.
Camera phones have met with much success in the last year. However, significant improvements in image quality are needed before camera phones can become a serious alternative to stand-alone digital cameras. This is not just a question of megapixels; analogue metrics like the signal-to-noise ratio of the sensor and A/D converter are just as important, as is the quality of the optical lens.

The same argument applies to video phones. As long as the slowdeployment of 3G networks and the cost of high-bandwidth services are delaying the widespread use of real-time video conferencing, 'video' tends to mean recording short clips that are just as likely to be viewed on a PCas on the tiny phone screen. This means that picture quality continues to matter, the other key differentiator for video being frame rate.
Quality video, of course, requires a quality audio track; even where users might tolerate a less than perfect picture in exchange for easy portability, keyring-sized MP3 players have set a high benchmark for audio performance, no matter how small the gadget.
With user interfaces becoming increasingly standardised, touchscreens are one of the features manufacturers can use to differentiate their design. True, a certain minimum screen size is needed for this function to make sense. But with screen sizes growing, it seems that interest in touchscreens is growing in the high-end market segment.

On the hardware side, touch is essentially amixed-signal function with a strong analogue component. Electromagnetic interference (EMI) and the three-way trade-off between conversion speed, accuracy and power consumption are just two of the analogue issues designers need to tackle.
There are of course those who remain unimpressed by the slew of new functions and services and concentrate instead on quality of service (QoS) in plain old voice transmission.
While QoS depends critically on a good network infrastructure, better mixed-signal hardware also plays a part. This includes the possibility for voice codecs to offer higher resolutions and sample rates. Whether future sales battles will be fought over new features or the quality of existing ones, everything indicates that the importance of analogue and mixed-signal functions as a differentiator will continue to grow.
Dr David Milne co-founded the Company with Jim Reid in 1985. He was formerly the director of the Wolfson Microelectronics Institute at the University of Edinburgh, which pioneered engineering CAD software and integrated circuit design techniques.
He is a Fellow of the Royal Academy of Engineering and the Royal Society of Edinburgh. He is a member of the Court of the University of Edinburgh and is an Hon Professor in the School of Engineering. He is non executive director of Edinburgh Research & Innovation and the Edinburgh Technology Fund.