Low Power Electronics

Introduction

Low-power design in electronic products aims to minimize average power consumption. This design philosophy is critical at both hardware and software levels. The benefits of low-power design are multi-fold, ranging from extending battery life to reducing the carbon footprint.

The Importance of Low Power in Carbon Footprint Reduction

Although it may seem trivial, low-power design can significantly reduce carbon emissions. For instance, reducing idle screen-on time for TVs from 4 hours to 30 minutes annually can save emissions equivalent to 250,000 cars. Such findings underscore the importance of power-conscious design in electronic products.

The goal of this article is to provide systems engineers, systems architects, and electrical engineers with insights into the impact of their work on carbon emissions and to offer technical guidance on addressing this issue.

Background

Key Terms

• Power States: Different levels of power consumption (active, idle, suspend, and off) that a device goes through.

• Connectivity: The capability to interact wirelessly or through wired connections with other devices in a network.

• System on Chip (SoC): A multi-functional chip that includes both general and special-purpose processors, along with internal memories and peripheral controllers.

Design Philosophy

Low-power design is a multifaceted approach that extends beyond mere component selection or isolated software techniques. It is a holistic strategy that incorporates hardware specialization, intelligent software control, and even the choice of components. These elements are orchestrated by a Power Management Unit (PMU) and the operating system’s resource scheduler to achieve optimal power efficiency.

Specialization and Division of Tasks

Much like in a factory, where specialization and division of labor improve efficiency, electronics benefit from similar principles. Special-purpose processors within the System on Chip (SoC), such as Graphics Processing Units (GPUs) or Audio Digital Signal Processors (DSPs), perform dedicated tasks, reducing the workload on the main processor and thus contributing to low-power operation.

Software’s Role in Power Management

Software isn’t just an end-user interface but plays an integral part in power management. From implementing sleep modes to deciding when to offload tasks to specialized hardware, software algorithms work in conjunction with the hardware to optimize power usage effectively.

Component Selection for Power Efficiency

Even the choice of components, down to the type of memory or clock source, can have a significant impact on power consumption. Opting for components specifically designed for low-power applications can contribute to power savings at a fundamental level.

Framework of Low-Power Design in Electronics

The diagram above serves as a high-level roadmap of low-power design, illustrating its main components and their interrelationships. Let’s break down its key elements:

• Low-Power Design: This is the overarching theme, capturing the essence of our focus — designing electronic systems that consume less power.

• Hardware-Level Optimization: This encompasses techniques like choosing power-efficient electronics, appropriate clock sources, and using low-power components. These are foundational to designing systems that are power-efficient at the hardware level.

• Software-Level Optimization: This focuses on how software can be designed to make efficient use of hardware resources. Techniques like sleep modes and hardware/software co-design fall under this category.

• Power Management: This is the central hub that interfaces with both hardware and software optimizations, ensuring that power consumption is minimized across all system levels.

By understanding these categories and how they interact, we set the stage for diving deeper into specific optimization strategies that can make a tangible impact on power consumption and, by extension, on sustainability and carbon footprint.

Optimization Strategies

Software-Level Optimization

Power State Design

Typical Smart TVs have four power states:

• Active: The TV screen is on.

• Idle: The screen is off, but hardware remains active.

• Suspend: Minimal hardware is active.

• Off: The TV is completely powered off.

The key to low-power design is to minimize the time spent in high-power states and transition to lower-power states whenever possible. This strategy requires designing various power modes and wake-up architectures that function cohesively across both hardware and software layers.

Low-Power Sensor Design

Sensors are fundamental components that constantly stream data, such as temperature, motion, and object orientation, to update the state of electrical devices. This data feeds into specialized processing cores, often referred to as “sensor fusion cores,” for real-time analytics and event detection.

The Role of the Sensor Hub

A key strategy in low-power sensor design is the use of an always-on, low-power microcontroller, commonly known as a “sensor hub.” This microcontroller offloads event detection tasks from the main application processor, thereby saving power.

Implementation

In practical terms, the sensor hub processor can either be embedded within the System on Chip (SoC) or function as a standalone microcontroller supplementing the main processor. This architecture allows the device to maintain high functionality while minimizing power consumption.

Sleep Modes and Wake-Up Triggers

Managing idle periods effectively is crucial for low-power design. Sleep modes and wake-up triggers play a pivotal role in this context.

Levels of Sleep Modes

Devices can have multiple levels of sleep modes, each consuming a different amount of power:

• Deep Sleep: Almost all circuits are off, and only essential functions like real-time clocks are running.

• Light Sleep: Core functions are suspended, but peripheral activities like timers may still run.

Intelligent Wake-Up Triggers

The device can be programmed to wake up based on specific conditions:

• Timer-based Wake-Up: The device wakes up at predetermined times to check for tasks.

• Event-driven Wake-Up: External events, like a button press or a sensor reading, wake the device up.

This combination of sleep modes and wake-up triggers allows for sophisticated control of power consumption during idle times.

Hardware/Software Co-Design

The optimization of hardware and software interactions is a crucial aspect of low-power design.

Task Scheduling

Efficient task scheduling algorithms can distribute computational work in a way that minimizes the time the processor spends in high-power states.

Resource Allocation

Intelligent resource allocation can also significantly reduce power consumption. For example, offloading tasks to specialized hardware can free up the main processor, allowing it to enter a low-power state more frequently.

Bluetooth Connectivity Low-Power Design

Bluetooth devices maintain a stable connection by agreeing on timed intervals for data and command exchange. The challenge lies in keeping these connections active while minimizing power consumption.

Connection Intervals and Power Consumption

The question at hand is: What’s the relationship between the frequency of these intervals and overall power consumption? This is a critical issue that low-power design aims to address.

Low-Energy vs. Classic Bluetooth

To find the optimal balance between connectivity and power usage, low-energy Bluetooth protocols are often preferred over classic Bluetooth. The main difference is that low-energy protocols offer lower data throughput and more flexible connection intervals, thus reducing the overall energy consumption.

Configurations for Optimal Power Consumption

One approach to achieve this balance is to adjust the slave latency parameters. This allows peripheral Bluetooth devices to skip some reconnection requests from the host device while maintaining an active connection and minimal response latency. This trade-off presents a challenge but is crucial for power-efficient design.

Hardware-Level Optimization

Efficient low-power design extends beyond software to include hardware system controls. Key areas in hardware-level optimization are, component selection, power electronics design and clock source selection.

Use of Low-Power Components

Choosing components designed for low power can have a significant impact on the overall power consumption of a device.

Examples of Low-Power Components

• Low-Power DDR Memory (LPDDR): Consumes less power compared to regular DDR memory.

• Low-Power Microcontrollers: Designed to operate at lower voltages and frequencies.

• Low-Power Transceivers: For wireless communications, optimized for low power.

By opting for components that are specifically designed for low-power applications, you can achieve significant power savings even before considering other optimization techniques.

Power Electronics Design

Power electronics components must be carefully selected based on their load requirements:

• Switch Mode Power Supplies: Ideal for high-power rails.

• Linear Regulators: Used for low-power loads requiring precise and clean output.

To achieve high efficiency, power rails and the sharing of these rails are optimized to minimize conversion losses at various power states.

Power Gating Technique

One advanced technique to save power is power gating. This involves completely powering off a subsystem by gating its power supply rails. This can be done using a load switch or by turning off the regulator entirely. However, this method requires careful planning to ensure that turning off one subsystem doesn’t risk or degrade the device’s other functions.

Clock Source Optimization

The choice of clock source is crucial for different hardware blocks:

• Slow Clocks: Ideal for low-power hardware blocks.

• Fast Clocks: Best for active and high-speed hardware blocks.

System electrical engineers are responsible for choosing the appropriate clock source for each hardware block. Options include standalone crystals, temperature-controlled oscillators (TCOs), or clock signals from a host device like an application processor or a Power Management IC.

Example Clock Design for Bluetooth Radio

When designing for low-power Bluetooth connectivity, different clock sources play a pivotal role in managing power consumption.

Fast and Slow Clocks

Bluetooth chips generally utilize two types of clocks:

• Slow Clock (32 kHz): This is ideal for managing precise connection intervals in low-power states. It also keeps certain hardware blocks active for monitoring interrupts or wake-up signals.

• Fast Clock (tens of MHz): This clock is used to activate the radio transceiver hardware and network processors for data transmission or reception.

By judiciously choosing these clock sources, the Bluetooth chip can transition quickly between low-power and active states, thus optimizing overall power consumption.

Summary & Conclusion:

Low-power design aims to reduce the overall average power consumption of a product during its usage, having a substantial impact on reducing the carbon footprint when scaled.

1. General Power States: Consumer electronics typically have four general power states: active, idle, suspend, and off.

2. Software-Level Goals: The primary objective at the software level is to transition devices from high-power states to lower-power states whenever possible.

3. Hardware-Level Goals: At the hardware level, the focus is on enhancing the overall efficiency of power delivery mechanisms.

4. Connectivity Devices: For devices requiring constant connectivity, like Bluetooth devices, minimizing re-connection frequency is the practical approach to reduce the power consumption of radio hardware.

5. Multi-Sensor Devices: For devices with multiple sensors, the best practice is to connect all sensors to a low-power sensor hub.

Low-power design is increasingly critical in today’s world, given the consumer demand for miniaturized, portable hardware products. The primary challenge is to maintain connectivity while also extending the device’s period of usage. As a systems engineer, it’s essential to integrate both hardware and software-level designs to meet user expectations and needs effectively.