More energy efficiency in analog chips

Modern edge devices, as used in the IoT or in Industry 4.0, are becoming more and more intelligent while continually shrinking in size. And an increasing number of functionalities and sensors are being integrated into the chips. All of this requires a significant reduction in electricity consumption: energy-efficient analog ICs extend both battery and product life and improve the responsiveness of the system.

The earlier that energy consumption is factored into the design process, the greater the potential to conserve power. This means that energy efficiency should be considered a functional design requirement and evaluated in early stages of design implementation. Furthermore, there are several ways to minimise the energy consumption of analog circuits. This starts with using advanced circuit topologies and optimisation measures at block level, and also includes choosing the right system architecture and devising a signalling scheme – which makes it possible to reduce the complexity of the circuit.

The semiconductor industry has also developed new technologies and processes as solutions to help reduce the energy consumption of analog chips.

Nanopower technology

Typical battery-operated applications are in idle mode most of the time, and are simply waiting for something to happen. Once something does happen, the system takes the appropriate action, for example reading out a sensor. After this, it goes back into standby mode and waits for the next event to occur. This means that reducing the standby current of the power supply is an important factor in improving the energy efficiency of chips, as it makes the largest contribution to a system’s electricity consumption when it is in standby mode. This is where nanopower technology comes in, enabling the production of ICs with a standby current that is less than a microampere. It also enables housings to be built much smaller in size, with smaller and fewer external components, thus saving up to 50% of the space formerly required.

High performance and low standby power

Analog precision circuits can be realised more cheaply in older silicon technologies (e.g. 300 nm), while digital circuits can be shifted more easily to smaller structures and thus have lower silicon consumption. A compromise must therefore be found for mixed-signal circuits. Major efforts are therefore under way to develop new processes (e.g. 65 nm) that enable low consumption and sufficient precision for analog circuits.

For digital processes, optimisation is realised either in terms of speed or standby consumption. SOTB – developed by Renesas – is one of the innovative processes that enables high speed and low standby power.

This transistor technology is based on SOI (Silicon on Insulator) wafers and makes it possible to significantly reduce active and standby energy consumption. As a result, SOTB-based products are ideal for applications that require a longer battery life or that “harvest” their energy from the environment.

The SOTB process involves applying a thin insulating oxide layer (BOX, buried oxide) onto the silicon substrate, which in turn is covered by a very thin silicon layer. This creates a contamination-free channel transistor under the gate, which lowers the threshold voltage variance and thus enables a very low operating voltage. This construction enables high performance, low-voltage operation with very low leakage current and a very low operating current.

Neural networks with analog components

Solutions for machine-based learning (ML) are being used in an increasing number of sectors. At the moment, they are still based on digital logic, since digital technologies make neural networks easy to scale. They also provide the simplification that digital abstraction offers. But a significant challenge is the energy consumption of these systems, both during learning and inference – especially for edge applications.

Replacing digital circuits with analog ones allows electricity consumption to be considerably reduced to some extent. An analog solution becomes particularly useful when the raw data that it works with is also analog-based. This applies to a lot of sensors, for example microphones with an analog output.

Some voice recognition systems – ones that are activated via a wake-up word – already use analog chips. In this case, the analog block does not replace the entire audio chain: the task of the always-on circuit is solely to search for a “wake-up” word. All the while, the digital circuits remain switched off. It is only when the analog block detects a wake-up word that the rest of the (digital) audio chain is activated, which then processes the content of the command.
 

Save energy with new semiconductor materials

One conventional application area of analog semiconductors is controlling and converting currents. With the use of new semiconductor materials – known as Wide-Band-Gap (WBG) semiconductors – it is possible to significantly improve semiconductor efficiency and power density. Silicon carbide (SiC) and gallium nitride (GaN), in particular, have established themselves as breakthrough materials for such applications. Their use represents an important step towards an energy-efficient world, because SiC and GaN semiconductors enable a higher performance efficiency, a reduction in size, a reduction in weight and lower overall costs – or all of the above combined.

Whether for battery-powered applications, such as e-bikes, robotics or drones, drive systems and board systems in the mobility sector, or IT infrastructure – all of these areas rely on efficient, compact electronics. As a result, power electronics based on silicon carbide (SiC) and gallium nitride (GaN) make it possible to design smaller drives with a higher efficiency. For example, WBG components reduce power semiconductor losses by up to 80% in servo drives, compared to existing Si-based IGBT solutions.

SiC and GaN-based semiconductors offer considerable advantages in computers, smartphones and other consumer electronics systems too. Take chargers for mobile phones and computers, for example: They have become increasingly slimmer and more powerful over the last ten years. Since the trend is to continue and even to place USB-C chargers into wall outlets, chip solutions are needed that can produce more power in a restricted amount of space. Novel architectures, like variations of the active clamp flyback converter, in combination with GaN FETs, offer a significant improvement in adapter efficiencies and size, allowing very high power densities.

The audio sector is another area where devices are being made increasingly smaller, more light-weight yet higher in performance, with consumers expecting a constant improvement in audio quality. Most impressive in this regard are class-D amplifiers that allow even compact systems to deliver a high sound quality and high audio output power. Analog chips based on GaN maximise the output of class-D audio amplifiers and make it possible to achieve an output that almost matches that of the theoretical ideal output. They are a prerequisite for maximising audio output and minimising power losses in class-D audio amplifiers, while improving linearity and EMI performance. These types of chips can be used in all manner of applications – from intelligent loudspeakers through to high-quality home audio systems.
 

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