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Analog Designers Face Low Power Challenges

By John Blyler, Chief Content Officer

Can mixed signal designs achieve the low power needed by today’s tightly integrated SoCs and embedded IoT communication systems?

System level power budgets are affected by SoC integration. Setting aside the digital scaling benefits of smaller geometric nodes, leading edge SoCs achieve higher performance and tighter integration with decreased voltage levels at a cost. If power is assumed to be constant, then that cost is the increased current flow (P=VI) delivered to an ever larger number of processor cores. That’s why SoC power delivery and distribution remain a major challenge for chip architects, designers and verification engineers.

As with digital engineers, analog and mixed signal power designers must consider ways to lower power consumption early in the design phase. Beyond that consideration, there are several common ways to reduce the analog mixed signal portion of a power budget. These ways include low-power transmitter architectures; analog signal processing in low-voltage domains; and sleep mode power reduction. (ARM’s Diya Soubra takes about mixed signal sleep modes in, “Digital Designers Grapple with Analog Mixed Signal Designs.”)

To efficiently explore the design space and make basic system-level trade-offs, SoC architects must adapt their modeling style to accommodate mixed-signal design and verification techniques. Such early efforts will also help prevent overdesign in which globally distributed and cross-discipline (digital and analog) design teams don’t share information. For example, if designers are creating company-specific intellectual property (IP) cores, then they may not be aware how various IP subsystems are being used at the full chip level.

Similarly, SoC package level designers must also understand how IP is used at the higher board level. Without this information, designers tend to over compensate their portion of the design, i.e., over design to ensure their portion of the design stays within the allocated power budget. But that leads to increased cost and power consumption.

Power Modes

From an architectural viewpoint, power systems really have two categories; active and idle/standby modes. With all of the physical level (PHY) link integration occurring on SoCs, active power considerations must apply not only to digital but also analog and input-output power designs.

Within the modes of active and idle/standby power are the many power states needed to balance the current load amongst various voltage islands. With increased performance and power demands on both digital and analog designs, there is growing interest in Time- and Frequency-Domain Power Distribution (or Delivery) Network (PDN) analysis. Vic Kulkarni, VP and GM at Apache Design, believes that a careful power budgeting at a high level enables the efficient design of the power delivery network in the downstream design flow. (See, “System Level Power Budgeting.”)

SoC power must be modeled throughout all aspects of the design implementation.  Although one single modeling approach won’t work, a number of vertical markets like automotive have found success using virtual prototypes.  “System virtual prototypes are increasingly a mix – not just of hardware and software, but also of digital, control, and analog components integrated with many different sensors and actuators,” observed Arun Mulpur of The Mathworks. (See, “Chip, Boards and Beyond: Modeling Hardware and Software.”)

Communications Modes

Next to driving a device screen or display, the communication subsystem tends to consume the most power on a SoC. That’s why several low power initiatives have recently arisen like Bluetooth Low Energy. Today there are three mainstream standards for Bluetooth in use – Bluetooth 2.0 (often referred to as Bluetooth Classic), Bluetooth 4.0, which offers both a standard high-speed mode and a low-energy mode with limited data rate referred to Bluetooth LE; and a single-mode Bluetooth LE standard that keeps power consumption to a minimum.  (See, “Wearable Technologies Meet Bluetooth Low Energy.”)

Power profiling of software is an important part of designing for cellular embedded systems. But cellular is only one connectivity option when designing the SoC or board level device. Other communication types include short range subsystems, Bluetooth, Zigbee, 6LowPAN and mesh networks. If Wi-Fi connectivity is needed, then there will be choices for fixed LAN connected things using Ethernet or proprietary cabling systems. Further, there will be interplay amongst all this different ways to connect that must be simulated at an overall system-level.  (See, “Cellular vs. WiFi Embedded Design.”)

It has only been in the last decade or so that mixed signal systems have played a more dominant role in system level power budgets. Today’s trend toward a highly connected, Internet-of-Things world (IoT) means that low power, mixed signal communication design must begin early in the design phase to be considered part of the overall system-level power management process.

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