Controlling Portable Devices With Low-Power FPGAs - Ultra-low power, programmability and development platforms offer significant advantages - Gary Sugita, Director, Corporate Applications Engineering, Actel Corporation

Publication date: 30 September 2008

Controlling Portable Devices With Low-Power FPGAs - Ultra-low power, programmability and development platforms offer significant advantages - Gary Sugita, Director, Corporate Applications Engineering, Actel Corporation

As portable devices become increasingly feature rich, the task of managing and controlling various features within the device becomes more complex. Portable manufacturers desire to keep power at a minimum to ensure maximum battery life, but added features usually increase the power consumption of the end system.

Storage, light-emitting diodes (LEDs) for backlight and display, keypads and motors have grown commonplace. However, highly competitive markets and evolving standards make it increasingly difficult to support these features within tight cost and time-to-market constraints.

Portable designers have typically relied on microcontrollers, application-specific standard products (ASSPs), applications-specific integrated circuits (ASICs) or complex programmable logic devices (CPLDs) to handle these control functions.

ASICs take a long time and are very costly to develop, and they lack the flexibility required to respond to a rapidly changing market. Similarly, CPLDS, ASSPs and microcontrollers may be faster and cheaper to implement, but are often either too small, consume too much power or do not offer the level of integration, flexibility or sophistication required for most applications.

Designers are forced to seek out new technology. The good news is that semiconductor makers are responding, giving them the option to implement a new breed of low-power field-programmable devices (FPGAs) to take on the complex task of storage, display, human machine interface (HMI) tasks and miniature motor control in portable devices.

Constantly evolving, FPGAs combine the benefits of reprogrammability, low-power, integration, sophisticated features and fast time-to-market to provide an attractive option for motor control in portable systems.

The Challenge

To deliver successful portable products to the market, system designers must work within significant constraints. Very low power consumption, extended battery life, small form factor, low development cost, and rapid time to market requirements combine to create a seemingly difficult design challenge.

While new product versions require improved performance and additional features that consume more power, demand for longer battery life increases. To compound the problem, highly competitive markets and evolving standards can abbreviate product lifecycles, creating pressure to develop more advanced products more rapidly.

As a result, designers are forced to seek out new solutions. A few milliwatts, or even microwatts, can make a big difference. The good news is that semiconductor makers are responding with new technologies that can address these challenges.

For example, low-power devices with power-optimization modes allow engineers to meet tight power budgets, while small footprint packages and high levels of integration help minimize system size and cost.

Historically, FPGAs have been considered too power hungry for portable applications, but new, low-power FPGAs are gaining traction in the portable market. ASICs, by comparison, require a serious investment in development time and costs, and they lack flexibility required to respond to a rapidly changing market.

CPLDs are faster and cheaper to develop, but are too small, consume too much power and lack the features required for most applications. FPGAs continue to evolve, are feature rich, allow fast time to market and now offer very low-power solutions. In particular, ultra low-power FPGAs are an attractive option for the unique demands of portable systems makers.

Today, FPGA technology is increasing in usage in portable, battery-operated applications, but not all programmable technologies are up to the challenge. FPGA technology advances have lowered unit prices, making FPGAs a more attractive implementation option for handheld applications.

However, some innovations have come at the cost of higher power due to transistor leakage. Different FPGA technologies have varying power profiles, some of which can have a profound impact on overall system design and power budgets.

Figure 1: The comparative power-up power profile (left) and the operation power profiles (right) of SRAM-based FPGAs and flash/antifuse nonvolatile FPGAs 

Nonvolatile, flash-based FPGAs have inherently lower power consumption than their conventional SRAM-based FPGA competitors. The SRAM cell structure incurs substantial leakage and requires power-consuming configuration cells that have high static current. By contrast, flash-based cells have no leakage path, and thus have 1000x lower leakage per cell than SRAM, and do not require power-consuming configuration cells.

Portable Device Components

Whether a smart phone, MP3 player, PDA, or digital camera, some basic components are common to portable systems, each with varying levels and types of design challenges:

Storage

Today, most portable devices require storage for pictures, music, address books, calendars, etc. As a result, there have been rapid advances and ready availability of storage devices and associated storage interfaces, such as SD, SDIO, microSDTM, MMC and CE-ATA, in a variety of devices in the handheld market.

As the storage device market expands, with ever changing protocols and interface standards, design teams are challenged to reduce design cycle time, yet create newer, portable devices that support the latest standards.

These devices typically employ a combination of these interfaces, and must support multiple interfaces for different applications.

A single, reconfigurable hardware platform, such as a low-power reprogrammable FPGA, can help a system target multiple hard disk and flash storage standards. Using FPGAs, it's possible to implement a variety of storage functions without having to redesign an entire system to accommodate changing storage interface requirements.

Customizable FPGAs provide the flexibility needed to bridge between different storage standards or to interface to different application-processor buses and protocols. Other FPGA benefits include port expansion for processors like those from Marvell or Freescale.

One or more storage interface controllers can be programmed into a low-power FPGA for a flexible implementation that can be easily reprogrammed when standards evolve, without requiring a device change. FPGA technology that also allows for ultra-low power standby or sleep options can drastically reduce power consumption.

The block diagrams in Figure 3 show how different storage interface standards can be supported using an ultra low-power flash-based FPGA.

Display

Lower costs and ease of mass manufacturing have increased LCD panel usage in various markets. In particular, the handheld market has witnessed a surge in LCD usage as a result of the increased popularity of personal media players, digital cameras, PDAs and other handheld devices.

When creating devices that meet ever-increasing consumer demands and needs, designers must choose LCD panels that are the right size for their application, have the best resolution, and offer the greatest color depth.

After the design process begins, they often face an even greater obstacle — newer displays with better capabilities and lower cost are launched. As a result, the designer must begin another long, difficult cycle of panel selection, display controller configuration, and system redesign.

To address the variability of display requirements and technology, portable display support circuitry requires a flexible implementation. Using FPGA technology, all types of displays can be supported with a single, modular board. In addition, timing control and image manipulations can be implemented on the same FPGA and modified as needed.

Human machine interface (HMI)

A growing number and variety of input devices such as keypads, switches, buttons and scroll wheels serve as the interface between portable device and user. Support for the broad range of possible interfaces can be easily achieved using a combination of FPGA-based logic and IP. This approach dramatically reduces time-to-market while customizing the end product to keep in step with customer preferences.

In addition to display and storage functions, portable devices have one or more types of HMI by which users interact with the application. In newer portable devices, HMI interfaces such as alphanumeric or qwerty keypads, touch keypad/displays with white or color LED backlighting, programmable keys/switches, joysticks, scroll wheels, and buzzers/speakers are becoming more and more prevalent.

Designers of portable HMI applications face several design challenges, resulting primarily from rapidly changing HMI requirements, small form factor and demand for extended battery life.

Low-power FPGAs help designers surmount HMI design challenges. Reprogrammable FPGAs enable designers to quickly adapt to changing HMI specifications and system requirements, as well as to take advantage of the latest advancements in portable interfaces.

In addition, multiple functions, such as motor control and level shifting, can be consolidated onto a single FPGA, making it possible to reduce form factor and system cost. HMIs in a portable system are not always active, and an HMI controller that employs power saving sleep or standby during periods of inactivity can save significant power and extend battery life.

Figure 4a. This keyboard control design supports a standard, 18-key cell phone keypad, but can be retargeted for any application requiring a keyboard interface in row-column matrix form.

Figure 4b. This brightness control circuit for white LEDs manages power and enhances battery life by manipulating the duty cycle of the PWM control input of the LED driver.

Figure 4c. This circuit controls color mixing for Red Green Blue (RGB) LEDs, and can be used to generate keypad or LCD backlight of any color. Individual RGB LEDs are illuminated in time-multiplexed fashion to reduce power consumption, and PWM brightness control helps extend battery life.

Figure 4d. This design generates audio tones of the desired frequency, volume and duration for applications that require an audible signal output. A flexible implementation that controls tone frequency and duration allows for the generation of a sequence of tones or the creation of music. Tone modulation can also be employed for enhanced user experience.

Miniature motor/servo control

The use of miniature motors in portable devices is growing dramatically. Examples of brushless DC and stepper motors used in portable medical, industrial and consumer systems include respirations, infusion and volumetric pumps, smart phones and security cameras.

As motors have grown commonplace, portable designers have typically relied on microcontrollers, ASSPs or CPLDs to handle miniature motor control functions. However, microcontrollers and ASSPs do not provide adequate flexibility and CPLDs do not offer the levels of integration or sophistication of FPGAs.

FPGA-based solutions can provide a platform-based design approach, enabling portable designers to quickly and easily address changing requirements, implement custom algorithms, and make quick and easy design changes through device reprogramming.

Further, feature-rich, low-power FPGAs can absorb additional glue logic and multiple functions into a single chip, thereby reducing bill of materials, board area, power consumption and cost. Finally, since power-hungry motors are not always active, low-power FPGAs that support flexible low-power implementation modes make it possible to save significant power and extend battery life by putting devices in ultra-low power mode when idle.

Figure 5. This FPGA-based implementation of a controller for brushless DC and stepper motors includes commutation logic and PWM for brushless DC motor control, a state machine for driving a stepper motor sequence, and control circuitry for managing input commands.
Summary

Today’s portable system designers are increasingly seeking ways to quickly deliver low-power, richly featured devices to the market. Ultra-low power, flash-based FPGA technologies that feature power saving modes, IP cores and advanced application solutions give designers the flexibility and agility they need to respond to changing market dynamics.

With the ability to economize on battery life through innovative design, the use of FPGAs in industrial, medical, and consumer portable devices will continue to grow. Power matters in portable system design, and low-power FPGA technology gives these developers the power to succeed.

GARY SUGITA - Director, Corporate Applications Engineering

Mr. Sugita joined Actel in 2007, bringing more than 15 years technology experience to the company. Sugita joined the company from Altera where he held senior director positions in solutions marketing and customer applications engineering. He holds a bachelor’s of science degree in electrical engineering from Santa Clara University.

For Further Information, Please Visit http://www.actel.com