The Future Role of Analog

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This paper is an opinion piece commenting on observations about the possible death of analog in the near future. In practice, analog is growing in areas such as analog processing (replacing DSP code), adaptive systems and energy harvesting. This paper will examine the role analog plays today and how important it is in our future. Examples on Home Land Security and Body Area Networking for health care will be examined.

In a world that seems dominated by digital devices such as personal computers, mobile handsets and fantastically complex medical imaging devices, one may wonder if there is an end of the road for analog functions. After all, Digital Signal Processing (DSP) has supplanted many analog functions already. If the trend is extended into the next decade would analog simply disappear as the functions are absorbed into giant digital mega-chips?

Near the end of the 20th century it was also believed that the Internet would obsolete traditional business models. “On-line” shopping would eliminate the need for “real” physical stores where people would visit to buy their goods. Obviously, retail stores are still here and expanding their reach using the Internet for additional business. The human need to touch and feel is fundamental in not only the shopping experience, but an important factor in human existence itself.

The Real World
We live in a world of light, sound, touch, taste and smell – all senses that rely on our ability to perceive the physical world around us. This is the analog domain where even at imperceptible levels the world around us remains continuous in nature. It is only when we approach atomic levels that the world begins to be discrete and finite in quanta. And even then, there are non-discrete components (such as the difference in strength between nuclear and electric forces).

Our world is analog and requires us to deal with ever varying physical phenomena. This is not to say that digital technology has not enabled new capabilities, but it’s what is accomplished in the analog domain that provides the raw “bits” for digital systems to process. In addition, modern digital processes have shrunk in feature size (gate geometries in CMOS processes are well below 65 nanometers today) providing the ability to place billions of transistors on a single die. All of these transistors consume power, and it is the domain of analog electronics that provides the closely regulated voltages to power these devices.

Applications of Analog Electronics
Analog is adapting to new requirements in both higher density digital systems-on-a-chip (SoC) and the power they require.

Digital processes use power in a non-linear fashion (see equation 1) and the energy they consume is increasing due to higher chip densities. There are analog systems (assisted by digital means) that are being employed to curb the increasing power demands of these high density processes. One example is Adaptive Voltage Scaling or (AVS) pioneered by National Semiconductor.

This technology provides closed loop control of the energy consumed in large digital devices and can reduce average power by 40% or more in many cases (over a fixed Vdd core voltage). It incorporates both digital intellectual property and analog technology to solve this problem. Without the analog components of this solution the power savings would not be possible.

Another area of high importance today is security including personal, corporate and homeland. In many cases, analog technology will play an ever increasing role in sensing and detection as well as energy harvesting. Sensors can detect the presence of pathogens or radiation, however they often provide signals that vary in current, voltage, resistance or capacitance (all analog phenomena) as their outputs. These signals may be very weak and require amplification or other analog processing before they can be converted into bits and processed by digital signal processors.

An example of this is radiation detectors used for finding hidden radioactive materials (or other contraband) in cargo containers. Modern detectors use a solid state sensor or scintillation crystal (a material that emits extremely small flashes of light when exposed to radiation) and analog electronics to increase the output levels. There is a long chain of analog signal processing that is required to enable the detection of radiation. Once the signals are properly processed by the analog chain, they are passed to digital processors for filtering and other complex tasks (such as image reconstruction). The system can then discriminate between various types of radiation such as α (alpha), β (beta) and γ (gamma) and whether the levels present are of concern. Without the analog signal processing, analog to digital conversion and the complex power supplies, this system would not be possible.

Analog’s Future
As we continue our journey into the 21st century, health care technology will greatly contribute to the quality of life we experience. One aspect of this is the ability to monitor – in real time – a patient’s health. Personal health monitors have been around for some time, but the next generation will use some innovative techniques to be as unobtrusive as possible. This requires reducing or eliminating heavy and bulky batteries. Energy must be scavenged from the environment and conditioned for use by the system. For the health monitors, mechanical vibration is a good candidate.

Mechanical energy harvesting uses either Piezo or magnetic techniques to create energy from the movement of a person. While wearing the monitoring device and moving around, these mechanical generators produce power. The problem is the rate of which energy is scavenged from the motion of the patient. There can be times of rapid movement such as running to catch a plane, or periods of low output while sitting at a computer. The power supplies must adapt to this ever changing energy input and provide mechanisms to capture and store the energy. They must also provide continuous regulated power to the electronics to maintain their function.

Sensors around the body may also use energy harvesting techniques for power as well and communicate through a patient’s skin using low power AC fields. Microsoft patented a technique for not only communicating over a human (or animal), but for powering the devices as well (patent no. 6,754,472). IBM and others have been experimenting with Personal Area Networks (PANs) since the late 1990’s and soon they may start showing up in medical monitoring systems. The advantage of these systems will be to allow somewhat normal life activities for long periods without the problem of recharging or replacing batteries – there will be only super capacitors that are charged by the user’s activity.

Another area of interest is saving power through analog processing – that is, moving some information processing back into the analog signal chain. DSPs use considerable power while processing data, while analog systems use much less. An example application in homeland security would be to have sensors (powered by energy harvesters such as solar cells) do some of the identification processing in the analog domain. An example might be listening for the vibrations of people or vehicles approaching a border line. Upon determining a good probability of detection, the higher power processing of the DSP could be brought on-line to verify the analog subsystem’s findings. This saves a great deal of energy since the DSP is off-line and powered down most of the time. Systems designed in this manner can run without service indefinitely which is highly important for applications in remote areas.  
 

Without analog techniques, processes and subsystems modern digital systems would lack a means of power, input and output. Analog’s future is bright – more so now than ever. Like the vision of a world filled only with virtual stores, a prediction of the demise of analog technology may have been premature. Modern electronics te
chnology will play an ever increasing role in the quality and variety of our lives. The role of analog semiconductors and systems will only increase as we become more personal with our technology. 

Richard Zarr Chief PowerWise technologist, National Semiconductor

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