Also see our Application Notes

• Amplifier Closed-Loop Bandwidth Considerations in High Resolution A/D Converter Applications - Amplifier Bandwidth Limitations Amplifier closed-loop bandwidth-limited accuracy considerations are critical when driving high resolution A/D Converters (ADCs). It is useful to be able to predict, for any closed loop gain, the required gain-bandwidth (GBW) product of an op amp to achieve a specified level of accuracy in terms of the minimum ADC resolution. Other sources of error include offset, noise, and distortion, which are beyond the scope of this article. A simple equation will be developed below that relates the minimum closed-loop bandwidth of an op amp to the resolution requirements of a given ADC.

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• Using Power to Improve Signal-Path Performance - System-level hardware designers pay careful attention to picking the right analog signal path ICs for their specific applications. Whether designing consumer MP3 players or medical ultrasound equipment, engineers care about making the right trade-offs while maintaining high performance. After reviewing and prioritizing specifications such as Signal-to-Noise Ratio (SNR), resolution, Total Harmonic Distortion (THD), input offset voltage, slew rate, jitter, and supply current, the analog signal path ICs can be selected. Picking the right signal path ICs leads to the best sight and sound experience for the user. Each of these signal path ICs need "clean" power. Often, power management is the last part of the system design.

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• A Voltage-Controlled Filter - In the area of sound and music synthesis, voltage- controlled filters are used to shape the envelope of the sound being generated. A web search on the term "voltage controlled filter" will locate many commercially available products for use with music synthesizers and sound effects generators. Most of what is available is not suitable for embedded systems because of the cost and number of components used. An alternative to these types of circuits is an amplifier which has the feature that its supply current is continuously variable over a range of 1 µA to 400 µA. One of the side effects of this is that the gain bandwidth of the amplifier is a function of the supply current.

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• Enabling HDTV Capabilities in Today's Systems - High Definition TV (HDTV) is now more prolific than ever. With a tremendously distinguishable difference in picture quality from traditional NTSC video, there is good reason why HDTV has been receiving high acclaim from videophiles as well as lay consumers. Today, the adoption of HDTV by the broadcast industry is on the incline as the percentage of worldwide TV service operators rapidly increases the offering of HD programming. Even video game console makers have joined the High Definition Video movement in recent years.

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• A Quick Sine Wave Generator - In various design and test situations, a sine wave signal with an arbitrary frequency may be needed. The following design, and accompanying Excel spreadsheet implement a sine wave generator that can be quickly assembled with a dual op amp and small number of resistors and capacitors.

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• Photo-Diode Current-to-Voltage Converters - Converting the small output current of a photo-diode transducer to a fast responding voltage is often challenging. Here are some ways to use high-speed current feedback and voltage feedback op amps to do the job.

• Unlimited Capacitive Load Drive Op Amp Takes Guesswork Out Of Design - Whether or not an op amp circuit is capable of driving a capacitive load successfully, depends on several factors:
  - Op amp internal architecture (e.g. ROUT, phase margin, compensation, etc.)
  - Closed loop gain and output loading
  - Load capacitance value

• An OrCAD PSPICE Library For The VIP10 High-Speed Op Amp - Creating the op amp SPICE model from the ground-up for simulation is esoteric and often time consuming. National Semiconductor Corporation has an OrCAD Capture library (nationalhighspeed.olb) and PSPICE (nationalhighspeed.lib) model library for the industry-leading VIP10 process high-speed operational amplifiers.

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• Lower System Cost Solution for Transmitting Video - There are many types of video systems that require the source of a video signal to be located several hundred feet from a video display. A good example of this is a video surveillance system where the camera and display are located at opposite ends of a building.

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• A Multi-Band GSM/GPRS Power Amplifier Controller - Global System for Mobile Communications (GSM) is the most popular cellular phone system in the world. In a GSM cellular phone or DCS/PCS phone network, Time Division Multiple Access (TDMA) scheme is used in the same cell to provide duplex communication. The Gaussian Minimum Shift Keying (GMSK) modulation scheme is used in both forward and reverse link.

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• Audio Amplifier Drives Thermoelectric Cooler For OC-48 Laser Module - A common problem faced by designers of laser-based fiber optic communication systems is maintaining the laser’s characteristics over temperature. As the temperature drifts, the center frequency of the laser will also drift.

• Optimizing Portable Applications with D/A Converters - Designers of portable electronic devices have several methods available for using general-purpose Digital-to-Analog Converters (DACs) to digitally adjust voltages and enhance the performance of portable devices.

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• Intermediate Frequency (IF) Sampling Receiver Concepts - This article will discuss Intermediate Frequency (IF) sampling concepts of sub-sampling (or under sampling), noise processing gain, and the effects of interfering signals. Examples will be based on the GSM/EDGE communications standard where the channel bandwidth is 200 kHz and the sample rate is typically a multiple of 13 MHz.

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• High-Performance Analog Front Ends - High-speed conversion systems, especially in the telecommunications field, allow the input to the ADC to be AC-coupled either through a transformer, a capacitor, or a combination of both. For the test and measurement industry however, the frontend design is not as simple because this application area often requires the input signal to be DC-coupled as well as provide the capability for AC-coupling. The design of an active front end that delivers good pulse response and low distortion from DC up to frequencies of 500 MHz (and beyond) is challenging. This issue of the Analog EdgeSM will provide a few design ideas and suggestions for an analog front end for use with high-performance ADCs suitable for high-speed data capture.

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• Energy Scavenging for Remote Sensors - A recent concept being implemented to power circuits is using energy scavenging. This makes use of energy collection through solar cells, piezoelectric generators, or other energy conversion devices. These devices collect energy from diffuse sources, convert it to electricity, and typically store it in a capacitor until it is required. In many situations, the sensor circuitry is not required to operate continuously and the energy storage is replenished during the sensor off periods. In this example, a solar cell and a one-farad capacitor are used to power a remote motion-detector that uses an RF link to transmit the occurrence of any moment to a central monitor. This type of sensor is advantageous because wiring is not required and battery replacement is eliminated.

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• Data Converter Serial LVDS Interface Improves Board Routing - Systems often require signaling where common-mode signals are not welcome or difficult to handle. Some designs turn single-ended signals from the output of transducers to fully differential signals, then send this signal to a differential-input ADC downstream. The advantage of this is that most noise that gets introduced on this differential line is common to both lines. (This is assuming that the differential lines are laid out symmetrically.)

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• A precision interface for a Resistance Temperature Detector (RTD) - Resistance Temperature Detectors (RTDs) are temperature sensors that make use of the temperature dependence of a metal's resistance. They are used in a wide variety of temperature measurement and control instrumentation. These circuits are based on using a 100W Platinum RTD (PRTD), versions of which are readily available from many sources.

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• Interleaving ADCs for Higher Sample Rates - Designers have often attempted to combine more than one analog-to-digital converter in an effort to increase the effective sample rate. While the flash converter was available before the advent of high-speed fabrication processes, the process technology limitations restricted those early flash converters to speeds on the order of 10 to 20 Msps. Today we have process speeds and architectures that permit sampling at gigahertz rates.

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• The problem of ADC and mixed-signal grounding and layout for dynamic performance while minimizing RFI/EMI - Obtaining the best performance from Analog-to-Digital Converters has long eluded many circuit designers. Many designers have concluded that getting the performance claimed in data sheets is not possible in practical circuits. Previous articles describe methods that help improve the performance of mixed-signal circuits, particularly those using ADCs.

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• Analog Signals are Still Driving Digital Displays - Modern digital video display devices are ever present. Digital video projectors are reaching new heights of performance versus price. Dropping prices, and the obvious space advantages of flat-panel displays are driving a rapid shift away from traditional CRT monitors for corporate and consumer users. Advanced home entertainment displays of various technologies and formats are the hot consumer item for many buyers.

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• Ultra-High Speed ADCs Revolutionize Digital Receiver Design - This article demonstrates how ultra high-speed, high-analog input bandwidth ADCs can be used in digital receivers to replace RF tuners and also to offer functionality not possible with current receivers. The conventional receiver architecture requires an RF tuner for channel selectivity in the analog domain prior to digitization and digital signal processing.

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• Power Supply Effects on Noise Performance - Understanding the PSRR (Power Supply Rejection Ratio) of analog circuits is an important step to improving overall mixed-signal system performance. Once you know the effects of PSRR you can compensate for them.

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• Tiny Temperature Sensors for Portable Systems - The last year has seen the introduction of silicon temperature sensors in revolutionary small packages, ideal for portable systems. This brief will discuss trade-offs in accuracy, as well as how to choose between thermistors and analog output IC temperature sensors.

• Four-Speed Fan Control Using Simple Remote Diode Temperature Sensor - The circuit controls the speed of a 12V DC fan using an LM88 Remote Diode Temperature Sensor (RDTS) IC. The LM88 is a dual remote diode temperature sensor with 3 digital comparators and has 3 open-drain outputs (O_SP0, O_SP1 and O_CRIT) that can be used as interrupts or to signal system shutdown.

• Autonomous Fan Control For Processor Systems Using The LM85 - To lower cost, many embedded processor systems include a hardware monitor for rudimentary system diagnostics. This helps ensure that the right person is sent to fix the problem with proper replacement parts. The system diagnostics include detection of power supply over/under voltage, system fan malfunction, and system component overheating.

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• Send High-Speed ADC Data Remotely And Quietly - In the world of Analog-to-Digital conversion, it is often desired to transport the digital data downstream using a minimal group of wires. This problem is sometimes addressed by using ADCs that are serial data output capable. This solution however, has its set of challenges.

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• Improving Video Clock Generation in Modern Broadcast Video Systems - The old adage "timing is everything" is well embodied in the modern broadcast studio, where precise timing of video clock and synchronization signals are essential to create, acquire, edit, and distribute analog and digital video. Today's broadcast systems must support industry-standard SD/HD formats, such as NTSC, PAL, 720p, 1080i, and 1080p, over analog and digital interfaces such as composite, component, and Serial Digital Interface (SDI). With high-speed SDI video equipment being increasingly used throughout the studio, improved video sync separation can more effectively produce video clocks with low jitter, which is crucial to meeting the stringent specifications of new SDI standards.

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• Overcoming Impedance Discontinuities in High-Speed Signal Paths by Using LVDS - At data rates from 400 Mbps to 1.5 Gbps, data signal paths become transmission lines. At these speeds the signal path model must include the reactive parasitic components in the cable or backplane. It is not just the data rate itself - the fast edge rates contain even higher frequency energy that react worse in distributed impedance environments. Ignoring parasitic impedances and impedance discontinuities above 200 Mbps will cause added noise in the transmission line, and data bit errors will occur.

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• Combating Noise Effects In Adaptive Cable Equalizer Designs - The adaptive cable equalizer is an essential component in the receiver front-ends of serial digital video (SDV) broadcast and serial telecommunications equipment. These equalizers can also be used in other types of wired communications systems. Equalizers interface directly with the transmission line and restore the signal amplitude and bandwidth loss caused by the cable.

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• Hundreds of Megabits @ Hundreds of Meters: Extending the Transmission Length for LVDS - Low-Voltage Differential Signaling (LVDS) is becoming the preferred differential interface standard as it delivers high data rates while consuming significantly less power than competing technologies. LVDS technology allows products to address applications with data rates of hundreds of Mbps in many market segments wherever the need for robust transmission of signals at high speed and low power exists.

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• 3.3V Cable Driver and Equalizer Drive Mega-Bits @ Many Meters - Transmitting data over long distances is necessary in a wide range of applications. These include telecom and video electrical interfaces running at data rates of up to 400 Mbps over appreciable distances. Long-haul data transmission is easily accomplished with existing devices.

• 2.5 Gbps LVDS 4 x 4 Crosspoint Switch - The unique architecture, diminutive size and flow through pinout of the DS90CP04 (Figure 1) make it an ideal building block for today’s high performance systems. This 4 x 4 crosspoint switch easily expands to build larger or uniquely shaped switch arrays. Digital control pins give the designer direct access to common building block functionality.

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• Auxiliary Power Extends PoE Applications - Power-over-Ethernet (PoE) has found utility in hundreds of applications from Voice over Internet Protocol (VoIP) telephony and wireless routers to security equipment. Many PoE applications employ auxiliary power sources, typically an AC "wall wart" power supply at the Powered Device (PD) or an Uninterruptible Power Supply (UPS) at the Power Sourcing Equipment (PSE). Integrating auxiliary power can be a challenging design task and the PoE designer must understand the various methods and inherent tradeoffs that exist with each. Three configurations are commonly used to add auxiliary power to PoE systems, and the possible combinations are to multiplex auxiliary power with PoE power (1) through the PD's front end hot-swap section, (2) directly to the input of the PD power supply controller, and (3) directly to the PD power supply's isolated output voltage.

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• Optimizing Power Management Solutions for Advanced Applications Processors - Power management solutions for today's portable applications processors are becoming highly integrated. Total power consumption, standby, and deep-sleep current consumption effect battery size, bill-of-material cost, and product acceptance. System designers must consider many variations of power supplies when designing portable devices such as smart phones or PDAs. Smart phones are becoming more power hungry and require highly-integrated power management solutions to meet the overall design requirements of maximum battery life in the smallest PCB area possible. Today's applications processors require separate power domains for the core, IOs, memory, and peripherals.

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• PWM DC-DC Controllers with Built-In Start-Up Regulators Simplify Switching Power Supply Design - Although PWM DC-DC switching power converters are based on simple topologies, making practical power supplies out of them requires the addition of various functions such as start-up bias, soft-start, switch driving, regulation, short circuit protection, over-voltage protection, over-temperature protection, etc. Today, most of these functions are usually implemented within a compact DC-DC PWM controller integrated circuit.

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• Powering Applications Processors with a Multifunction Integrated Power Solution - Power consumption and battery life are major obstacles that system designers have to consider when designing for portable battery-operated systems. One system that requires sophisticated power management to achieve maximum battery life is one that incorporates a high-performance applications processor. An example is Intel's PXA27x XScale® applications processor. This device requires up to 12 different power domains for the processor, IOs and internal subsystems to function with peak performance and optimized efficiency. Intel's PXA27x processor has multiple power-supply inputs which can be turned on and off as demanded by the CPU's power management software. Its flexible power management architecture controls the selection of the internal and external peripherals that can be powered at any given time.

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• MPL in cell Phones makes smaller, smarter serial links - Mobile Pixel Link (MPL) provides cell phone architects with a new low power, low-EMI serialized interface alternative to replace the high-power, non-standard, pin-consuming wide parallel interfaces commonly used in the video paths today. The interface challenge get more difficult as color depth increases or display resolution increases, as the pixel bandwidth demand greatly increases. (courtesy of Planet Analog)

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• Advanced Technology and New LDO Features for Highly Demanding Applications - Most designers would agree that linear regulators are one of the most easy-to-use types of regulator available and, for that same reason, usually their most preferred type. But in today's highly demanding applications, it is increasingly difficult to get a high-performance design running by utilizing only linear solutions.

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• Power Supply Design and the Thinking Engineer - Over the last 15 years, the design of switching power supplies has entered the mainstream. Now, no longer solely the responsibility of an expert, almost anyone involved in system design may end up putting together the switching power supply. Fortunately, people of all levels of expertise can use National’s WEBENCH® online tools to design switching regulators.

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• Three elements of architectural change represent a new piece in the distributed-power puzzle - In recent years we have seen a revolution in the distributed-power architecture for the rapidly evolving information infrastructure. This article reviews three elements of this architectural change: the introduction of the intermediate bus architecture, the advent of digital control, and the trend toward the manageability of power at the point of load.

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• Precision Method for Laser Diode Emission Control - In many applications where light is used to control a process, it is very important to maintain a constant light level. In some systems, a simple LED or laser diode is used to create a light source to provide illumination, however, even with initial calibration the light source will degrade with time. As the LED ages, its current-to-light emission ratio degrades and the level will decrease.

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• Choosing the Right Linear Regulator for Your Application - Linear regulators are often used as a band-aid by design engineers and are often chosen in later stages of the product development. The design engineer is concentrating more on how to make the complex BB or RF ASIC work, rather than the power/performance of the linear regulator that he or she may select.

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• Fixing EMI Across the Board - An ounce (okay 2 ounces!) of prevention are always better than cure. So here we look at some of the practical design aspects involved in controlling and testing EMI.

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• Communications System Power Supply Designs - Communications infrastructure equipment employs a variety of power system components. Power factor corrected (PFC) AC/DC power supplies with load sharing and redundancy (N+1) at the front-end feed dense, high efficiency DC/DC modules and point-of-load converters on the back-end. A power efficient design is required that supplies both the higher voltage analog circuits and multiple tightly regulated low-voltage supplies for the high-speed digital communications ASICs and FPGAs.

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• A USB-Powered Lithium-Ion Battery Charger - The Universal Serial Bus has become one of the most widespread and convenient ways to connect electronic devices to the PC. Countless modern portable products with built-in USB connectors readily use the USB data bus to transmit and receive data to and from PCs, but many of these battery-powered units still use a separate power supply for battery charging. Sometimes overshadowed by its data bus partner, each USB connection also contains a power supply bus connection.

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• Switched Capacitor Circuits Provide Efficient and Functional White-LED Drive - Since the conception of cellular phones, PDAs, and handheld computers, there has been a continuing push for more useful and dynamic displays. One of the more drastic changes in miniature display technology has emerged due to the availability of Internet content, pictures, and videos on ever shrinking personal devices. The promise of more content and functionality has caused a migration towards higher resolution color displays.

• Inductive-Based Switching Regulator Circuts Provide High-Efficiency White-LED Drives - Since the conception of cellular phones, PDAs, and handheld computers, there has been a continuing push for more useful and dynamic displays. One of the more drastic changes in miniature display technology has emerged due to the availability of Internet content, pictures, and videos on ever-shrinking personal devices. The promise of more content and functionality has caused a migration towards higher resolution color displays.

• Thermal Performance of National’s LLP Package, Highlighting the LM2750 Regulated Voltage Converter - National’s Leadless Leadframe Package (LLP) provides excellent power dissipation capability in a very small package footprint. The LLP is a chip scale package that requires minimum PCB footprint area. Unlike conventional leaded plastic packages, the LLP contains pads on the bottom of the package for PCB mounting.

• Wide-Input, High-Voltage Buck Converter - When the DC input voltage to a buck converter has a wide range, it becomes important to not only select a suitable switching regulator IC for the application, but to select the power components to handle the worst-case input voltage. For a given component, the worst case may be the maximum input voltage or the minimum input voltage, but in fact may also be somewhere in between.

• DDR-SDRAM Termination Simplified Using A Linear Regulator - With the advent of DDR-SDRAM as the industry standard for memory in desktop computers, laptops and videocards, power management has become a focal point for system designers. Active termination of bus interconnects has required the use of another regulator, increasing cost and system complexity. To specifically address this issue, National Semiconductor has just released the LP2995 DDR Termination Linear Regulator, offering a linear topology in a marketplace dominated by switchers.

• Sub-Miniature Buck Converters Tailored For Portable Power Applications - Although there are many step-down converters available in the market, they aren't as small and precise enough to meet the demands of portable system manufacturers. National Semiconductor has recently released a family of step-down converters that accommodate the need for smaller packages with enhanced performance and features. These are the 2.8V to 5.5V and can operate from a single Li-Ion cell.

• Integration Simplifies TFT Power Designs - Flat-panel video screens are becoming increasingly popular as the cost decreases and the performance increases. One major attraction of these screens is the vast amount of space saved versus the CRT displays that have been the standard for years.

• Powering Portable Devices: Alternatives To Linear Regulators In Step-Down Conversion - In portable products such as PDAs and laptop computers - powering the microprocessor from a Li-Ion battery generally means choosing a small and power-efficient step-down DC-DC converter. In terms of efficiency, a switching regulator is the best choice. However, when component height limitations rule out the use of inductors, a converter might take the form of a low dropout linear regulator.

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• High voltage, single chip DC/DC regulator optimized for flyback, boost, or forward power converter applications - Telecom and industrial applications such as local area networks (LAN), telephone interfaces (SLICs), ISDN, and xDSL terminals often require low-power multi-output, non-isolated power supplies operating from a non-regulated 12-36 V bus.  The flyback converter is often the preferred solution because of its simplicity, size, low cost, and low part count. National Semiconductor’s newest high-voltage, single-chip, DC/DC regulator is a monolithic integrated circuit specially designed and optimized for flyback, boost, or forward power converter applications.

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• Designing wireless interfaces for patient monitoring equipment - Today's patients face a depressing situation: confined to a fixed area tethered to their monitoring equipment. However, recent advances in wireless technologies now make it possible to free patients from their equipment, allowing greater freedom and even making possible monitoring by their health provider while the patient is on the go. In this article we examine the technology, typical medical monitoring applications and some of the design issues related to employing short-range wireless technology to improve the patient experience. (courtesy of RF Design Magazine)

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• Reworking LLP Chip Scale Package - LLP is a “Leadless Leadframe Package” – there are no leads extending beyond the package body. The contact pads are exposed and flush with the bottom of the package, providing a more compact footprint. Exposed die attach pad when soldered to the board provides a direct path for heat to transfer from the package to the PCB providing excellent thermal performance.

• Delta Sigma PLLs Raise The Standard For Performance - The high performance, low power, and low cost requirements of today’s mobile telephone handsets sometimes put designers between a rock and a hard place. System issues such as integration level, type of architecture, and critical system performance all affect key parameters such as linearity, error rates, power consumption, cost, and time-to-market.

• Thermal Issues and Solutions in Power Management - Power converter design is a multidisciplinary process; an effective designer needs to understand analog and mixed-signal circuit design, wound components, electromagnetic compatibility, packaging, and thermal design. Packaging and thermal design are driven by increased power density and the many trade-offs in power topology selection. The challenging environment in equipment destined to power the expanding information infrastructure brings thermal design into sharp focus.

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• Temperature Sensor Solutions for Low-Voltage Systems - To follow Moore's law and provide higher performance and expanded features at lower cost, processor manufacturers have moved to lower geometry or deep sub-micron processes. One of the characteristics of smaller geometry processes is a drop in supply voltage. The supply voltage requirements vary based on process design. A drop in the supply voltage can be delayed but it cannot be prevented as the geometry size is reduced. For example, a 0.35 micron process has sufficient oxide isolation to accept a maximum supply voltage of 5V. However for 0.13 micron and 90 nm processes, the maximum supply voltage is 3.3V and 1.8V, respectively.

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• Silicon Temperature Sensors Protect Your System - Two facts in building electronic systems force system designers to think more and more about the temperature budget. One chief driver is that cost and size of the PCB and enclosures have to be reduced resulting in less air flow to cool semiconductors which are both power hungry and at the same time sensitive. The other factor is the need for ever higher performance from processors, DSPs and Microcontrollers. Moore's law of doubling processor power is having the side effect that power dissipation is raising proportionally.

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• Cost Effective Partitioning of IO and Management Functions in PCs - Introduction of SensorPath™ Technology - Early model personal computers used discrete devices to implement serial ports, parallel ports, keyboard controllers, floppy diskette controllers and other such I/O interfaces.  As technological capability increased, the Super I/O (SIO) device integrated these functions into a single device, along with system power shut-down and wake-up control logic.  The SIO device has become the catchall logic device where miscellaneous system functions go.

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• Partition IEEE 1149.1 SCAN Chains For Manageability! - The proliferation of IEEE 1149.1 supported devices is helping Design for Test (DfT) engineers solve complex test access problems during board test. As ICs become more complex and boards become denser, this dedicated 5-wire serial test bus provides simple, standardized access to internal test nodes unreachable with existing In-Circuit-Test (ICT) methods. Many new board designs are incorporating JTAG as a standard feature for test and programming access – in many cases there is simply no other methodology capable of achieving an acceptable level of board fault coverage, or a cost effective means of programming on-board.