dimanche 30 avril 2017
samedi 29 avril 2017
"Network management" on Verizon Unlimited explained
Since the introduction of Verizon Unlimited, there has been some confusion about what the network experience is like once you use 22 GB. Click here for more.
from Cellular News http://bit.ly/2oST2NU
vendredi 28 avril 2017
Checking Out Some New (and Old) Automotive Technology
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Team Berkeley’s Hyperlane concept took first place in the AEM Infrastructure Vision 2050 challenge, which presented concepts for U.S. transportation and infrastructure at the Tech Experience at ConExpo CON/AGG. Hyperlane’s separate reserved lane allows self-driving cars to roll along at 120 mph.
“UC Berkeley graduate students, Baiyu Chen and Anthony Barrs see self-driving cars as the transportation of the future,” reports Leah Scully from our sister brand, Machine Design. “Their Hyperlane would take up real estate on existing highways and drive down the price point of constructing new infrastructure like high-speed rails. They expect their Hyperlane concept to be feasible by 2050, as major car companies like Tesla and Ford continue to invest in technologies for self-driving vehicles like car-to-car communications and physical sensors.”
New York Auto Show
The New York International Auto Show (Fig. 2) dates back to 1900 and will have nearly 1,000 cars and trucks on display. Machine Design editors had a preview of the show and captured some photos of the latest tech. Check out Jaguar/Panasonic’s FIA Formula E Championship electric-powered race car. The racing circuit consists of 10 teams and 20 drivers. Sebastien Buemi of Switzerland, driving a Spark-Renault Z.E. 15 was last season’s winning driver.
The International Auto Show highlights the latest and greatest cars and technology, including electric and self-driving cars, but there are a lot of cool cars that have a few years behind them. According to Machine Design once again, “The Summit Racing Equipment’s Piston-Powered Auto-Rama roared into Cleveland’s International Exposition Center (I-X Center) a few weekends ago, bringing more than 1,000 customized and classic cars, motorcycles, boats, aircraft, antique trucks, monster trucks, military vehicles, and historic construction equipment.” (see “Gallery: Hot Rods & Cool Cars” on machinedesign.com). The show’s motto is “If a piston makes it go, it’s in this show.”
One of the highlight cars is a 1930 Ford Roadster that started out as a 1930 Ford coupe. It now has 350-in.3 engine and overbored the cylinders by .030 in. to add another 5 in.3 of displacement. Jesse Woost also added two 50-mm turbochargers that add 30 psi to the incoming air. The orange hot rod hit 130 mph.
Electronics and self-driving cars may be cutting edge tech but sometimes the classics are worth enjoying.
from Electronic Design - Engineering Essentials Curated By Experts http://bit.ly/2pdAnji
A LoRa home environment monitoring gateway
When you’re away from your home, perhaps you’d like to know what is going on there. A camera system is one solution, but is fairly data-intensive and might not be the right method if you’d like to monitor information such as temperature and humidity in several zones. For this, Rod Gatehouse decided to build his own LoRa environment monitoring system using an Arduino Mega.
To keep an eye on things, Gatehouse (aka “RodNewHampshire” on Instructables) came up with an excellent LoRa IoT gateway that can be controlled via four push buttons and an LCD screen. This device can take input from remote stations wirelessly, and can put this data online or push it to a user as a text message.
The system enables a homeowner to monitor the home environment via an Internet accessible dashboard, receive periodic SMS environmental notifications, receive real-time SMS alerts when monitored environmental parameters exceed preset thresholds, and log environmental data to the cloud.
For more details on how Gatehouse set up this project and on his design choices, check out his Instructables page here.
from Arduino Blog http://bit.ly/2pugFA9
SanDisk Founder Sanjay Mehrotra Is Micron’s New Chief
Micron’s hunt for its next chief executive has ended with the company hiring Sanjay Mehrotra, the founder and former chief of memory chip rival SanDisk. The move, unveiled Thursday, ends the three-month effort to find a replacement for current chief Mark Durcan, who announced his retirement in February.
The changing of the guard – effective May 8 – is not without uncertainties. Micron is enjoying soaring prices for its DRAM and NAND flash chips, but the memory market is staring down new competition in China and chasing new categories of memory like 3D XPoint and carbon nanotubes.
Mehrotra, 58, is an elder statesman in the memory business. SanDisk, the company he founded with Eli Harari and Jack Yuan in 1988, made flash memory for cameras and other gadgets into an inexpensive product now sold next to chewing gum and tabloids at grocery stores. NAND flash is special for saving information even after losing power.
Mehrotra, who stayed close to SanDisk’s engineering team for over two decades, become chief executive when Harari retired from the role in 2011. In the next five years, he revitalized the business by shifting its NAND memory off store shelves and into solid-state drives for servers. Its good fortunes continued until Western Digital bought it in late 2015 for $19 billion.
Durcan’s role as chief executive of Micron also lasted five years. Durcan, 55, steered the Boise, Idaho-based firm through choppy financial waters that resulted from low prices for its memory chips. Because the chips are largely interchangeable, prices change based on supply and demand, not unlike those for dairy or steel.
Last year, Micron struggled mightily to counteract the falling prices of its short-term computer memory and long-term storage for data centers. It announced that it would cut 7.5% of its 32,000-person staff. The cutbacks, it said, would save an estimated $300 million, softening a 25% decline last year in third quarter sales.
In contrast, Mehrotra is taking the reins with memory prices surging. IC Insights, a semiconductor research firm in Scottsdale, Arizona, projects a 37% rise in the average selling price of DRAM, up last year from a 12% decline, and an increase of 22% increase in average selling price of NAND flash, up from a 1% decline last year.
Durcan also escorted several new types of memory out of Micron. Last year, the company started selling 3D NAND in enterprise products and shared details of its Quantx chips, which are based on the secretive 3D XPoint memory it devised with Intel. The chips, it says, have four times the capacity of DRAM and ten times lower latency than NAND.
In 2015, Durcan tiptoed through a $23 billion buyout offer from China’s Tsinghua Unigroup, the public face of Beijing’s ambitions to become a memory superpower. With virtually zero-chance of regulatory approval, Micron quietly declined. But the episode underscored the looming threat of China’s domestic chip industry.
The country is investing heftily to increase production. Tsinghua, which has hired the former chief of Micron’s Inotera Memories unit, is building a $30 billion memory fab in Nanjing, where it hopes foreign language schools and other perks will lure engineering talent. The factory will make DRAM and flash storage chips.
For now, it appears that Mehrotra will be tasked with keeping Micron on course. “The board is not looking to revise Micron’s direction, but rather to ensure we continue to invest in areas of the business that will accelerate Micron’s market and technology position,” Micron said in a statement.
But the company seems confident that Mehrotra is the right person for that job. “Sanjay has an outstanding track record of business success and exceptional knowledge of the memory and storage industry,” said Robert E. Switz, the chairman of Micron’s board, in a statement.
Mehrotra, who holds more than 70 patents, has also served as SanDisk’s the chief operating officer, head of engineering, and chief of product development. He was also the architect of SanDisk’s 17-year partnership on NAND flash manufacturing with Toshiba, the inventor of the technology.
With the change in roles, Durcan is planning to retire. He joined the memory business as a process integration engineer in 1984, climbing the ranks to chief technology officer and later president. In 2012, Durcan postponed his retirement to take over for chief executive Steve Appleton, who died in an airplane crash in Boise.
Durcan will step down as chief executive and from Micron’s board early next month, but he will serve as an advisor to the company into August. Mehrotra will split time between Micron’s offices in Milpitas – a few miles from SanDisk’s California headquarters – and Boise.
"Innovation in memory and storage technology is enabling new products, improved customer experience and growth across multiple markets," Mehrotra said in a press statement. “I am thrilled to have the opportunity to lead such a talented global team.”
from Electronic Design - Engineering Essentials Curated By Experts http://bit.ly/2oFVsE0
Single-/Dual-Supply Precision Analog Limiter Handles Wideband Signals
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As the name implies, a limiter circuit (sometimes called a “clipper”) prevents a signal from exceeding desired thresholds, which would otherwise cause saturation and overload of the following stage. The circuit in Figure 1 precisely limits the wideband input signal Vi at the VREF level and can be used with both single and dual power supplies.
Output signal Vo1 of the first stage, U1_1 (one-half of an LT1810, a dual 180-MHz, 350-V/µs low-distortion op amp), is precisely limited at the level of VREF , but with inverse polarity compared with the input signal. U1_1 has a gain of ‒1 for the input signal Vi, and a gain of +2 for the reference signal VREF.
Since the positive input of U1_1 is referenced to VREF, the output signal is referenced to 2 × VREF. Thus, while the input signal rises from zero to VREF, the output signal of the first stage decreases from 2 × VREF to VREF. The second stage of limiter U1_2 is an inverting amplifier with the gain of ‒1. It’s referenced to the VREF as well, and restores the original dc level and polarity of the input signal.
1. This analog circuit, based on the LT1810 op amp, precisely limits input signal Vi at reference level VREF.
For the output of the first stage, Vo1 = 2 × VREF - Vi if Vi ≤ VREF and Vo1 = VREF if Vi ≥ VREF, while the output signal of the second stage is Vo2 = 2 × VREF ‒ Vo1 = Vi, if Vi ≤ VREF, and Vo2 = VREF if Vi ≥ VREF. (Note that the output-dc level, along with the limiting point, may be shifted by an optional network of R6 and R7; otherwise, that network isn’t used.)
D1 is a part of the negative feedback of U1_1, making it an "ideal diode"—as soon as Vi reaches the VREF level, U1’s output voltage increases until it compensates for voltage drop Vd of the diode. When Vi is less than VREF and D1 is turned off, diode D2 is on and sends the output current of U1 directly to its input. This prevents U1 from negative saturation, which would significantly decrease the switching speed of the first stage.
The voltage level on the output pin of U1_1 is (2 × VREF) ‒ Vi + Vd, and it reaches its maximum level with the minimum level of the input signal. This determines the maximum possible level of VREF, which doesn’t cause the distortion of the limiter's output signal at its minimum level of VREF = [(V+) + Vi - Vd]/2. Here, V+ is the maximum output voltage of op amp at the chosen VCC, which is almost equivalent to VCC for the rail-to-rail op amp.
For the same reason, the minimum level of VREF should not be lower than Vd; however, the input signal may significantly exceed VREF.
2. The LTspice simulation shows the limiter's response for a 1-MHz sine-wave signal (a) and a 2-µs piecewise-linear signal (b).
The LTspice simulation shows the limiter's responses for a 1-MHz sine-wave signal with 8-V peak-to-peak amplitude (Fig. 2a), and for a 10-V, 2-µs piecewise linear (PWL) signal crossing the limitation level several times (Fig. 2b), both with VREF of 5.5 V. The limiter is quite accurate within the entire output-voltage range of the op amp. The simulation demonstrates that limitation errors don’t exceed 8 mV and output setting time is within 30 ns around the limitation point. When compared to the "simple op amp clipper" of Ref. 1, this limiter works at much-higher frequencies and with significantly lower distortion.
References
1. Thomas Mosteller and Aaron Schultz, "Op Amps Make Precision Clipper, Protect ADC" Electronic Design, November 2016.
2. Datasheet, LT1810 - Dual 180MHz, 350V/µs Rail-to-Rail Input and Output Low Distortion Op Amps.
from Electronic Design - Engineering Essentials Curated By Experts http://bit.ly/2pcm0f0
LED Drivers Expand Control of Automotive Lighting
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The automotive industry makes extensive use of light-emitting diodes (LEDs) in high-beam headlights, brake and position lights, and side and rear direction lights. In an LED driver design, the brightness intensity of the various illuminating devices is not equal; rather, it depends on their specific function.
Needless to say, then, that LEDs operate at different brightness levels—for example, at full brightness for braking and from 10% to 25% for the rear lights. LED dimming circuits are used to differentiate the brightness level through a pulse-width-modulation (PWM) driving technique, which modulates the width of the current pulses applied to the LEDs. LED driver solutions integrate a PWM system to control the brightness by providing a ramp generator, thus simplifying the driver design.
PWM has been adopted as the preferred dimming technique for high-quality LED lighting. An essential aspect of the lighting control system is the power management provided by integrated-circuit (IC) drivers in several configurations, such as buck and buck-boost topologies. The ease of controlling LEDs makes them an intelligent lighting system.
LED Driver Features
LED solutions require a constant current in order to produce uniform brightness. The accuracy of the source and the fluctuations in terms of voltage and other parameters are the fundamental design parameters for the correct driver. Fluctuations that occur with the vehicle’s power supply must therefore be strongly considered. Moreover, other requirements, which are reflected in the design phase, include temperature and humidity, voltage range, electromagnetic interference (EMI) and compatibility (EMC), as well as the reliability requirements dictated by the qualification tests.
1. The delay exhibited by the LED driver is in response to its PWM signal. These delays result in the contrast ratio (CR) factor of the system. Here, tD represents the propagation delay from when VDIM (PWM signal) goes high to when there’s a response from the If (forward current) driving the LED (tSU and tSD are the LED forward-current slew-up time and slew-down time, respectively). DMIN and DMAX are the minimum and maximum duty cycle, respectively.
High-reliability demands in automotive applications indicates that protection circuitry is essential within the IC driver, which provides protection from overvoltage, undervoltage, reverse polarity, overcurrent, short circuits, and higher and lower temperatures that don’t belong in the working range. Harsh automotive environments require protection circuits to prevent problems in case of failures. The devices also should demonstrate reliable operation over an extended temperature and humidity range, and the ability to withstand continuous vibration.
The ability to adjust light intensity in interior lighting systems is a normal requirement. For outdoor lighting applications, however, the same LED must have different levels of brightness. For example, the stop and position lights or low-beam and high-beam headlights are defined at two brightness levels. In some cases, integrating a suitable driver into the design can satisfy both situations with the same LED.
The main drivers have generally been designed with integrated PWM dimming. Many chips incorporate a PWM generator to determine the driver's ON and OFF cycle. A key factor in the PWM technique is the frequency fDIM—the minimum value of this frequency is determined by the eye’s sensitivity to flicker. Lowering fDIM generally facilitates a higher contrast ratio (CR), expressed as the inverse of the minimum on-time (Fig. 1).
Driver Topologies
LEDs typically require constant current to produce a uniform light output. Therefore, an LED driver must be able to vary the output voltage to maintain a constant current. The output voltage is related to many parameters, such as the temperature of the LED matrix and the number of LEDs in series. The designer must be able to predict with great accuracy the maximum output voltage in order to select the optimal regulator topology and, therefore, the driver IC and associated components.
The right power supply enables high-quality lighting with maximum conversion efficiency (in terms of lumens per watt), thereby prolonging the life of LEDs. The quality of the light produced is determined primarily by the light-intensity stability, which requires a precise regulation of the current with constant working points in all voltage and temperature conditions. It may be useful to employ drivers with integrated or external transistors, depending on the power of the given LEDs. However, the integration of the MOSFET for the LED driver reduces the number of external components, thus saving space on the board and simplifying the circuit.
2. Energy is stored through the inductor in this buck-converter design, with the production of an output voltage always lower than input.
The LED driver can be divided into three categories: linear regulators; charge pumps characterized by a capacitor; and the switching driver characterized by an inductor (reactive electronic component). The latter have found a wide range of applications, thanks to their flexibility and ever-increasing efficiency. Moreover, they allow wide ranges of input voltage to be accepted, and have the potential to be electrically insulated for operation in high temperatures.
Linear regulators provide a simple control and don’t require filters for EMI. However, their power dissipation can become excessive for high-power applications. Switching drivers come in four flavors: buck, boost, buck/boost, and single-ended primary inductor converter (SEPIC).
As in a typical switched-mode device, a switch controls the transfer of energy. The output voltage of an ideal buck converter (Fig. 2) depends on the product of the switching cycle time and its supply voltage. The boost converter, instead, consists of four main elements: inductor, power switch (MOSFET, IGBT), diode, and capacitor.
The buck-boost configuration (Fig. 3), which employs an inductor in parallel to the input voltage, provides an advantage in terms of flexibility. The SEPIC converter (Fig. 4) topology is a buck/boost converter without the inverted voltage. It requires an additional inductor and a blocking capacitor, which is the disadvantage to this design.
3. The inductor, which is discharged through the diode, provides current to the load in this buck-boost converter.
Depending on whether the LED application is automotive or general lighting, use of a multi-topology LED driver with maximum flexibility of input- and output-voltage range makes it easier to select the correct driver. The voltage range for the automotive sector extends from 9 to 16 V (nominal 14 V) and includes extreme conditions, such as reversal of the battery polarity (‒12 V), fault conditions like load dump (which occurs when the battery is disconnected from the alternator), and other transient voltages.
Among their other benefits, the buck-boost SEPIC configurations ensure constant brightness in all battery-voltage variations. When the need arises to control several LEDs in series, a buck-boost topology can address a variety of application requirements, including the ability to manage extreme voltage values.
In some automotive exterior-lighting applications, the LED array or matrix may be located at a distance from the driver/controller. In these cases, a boost converter can be a more appropriate topology choice. Carefully choosing the buck regulator can allow for PWM dimming frequencies in the kilohertz range. While this feature perhaps isn’t necessary for traditional lighting, it can be effective in applications such as high-speed stroboscopic effect for recognition activities (imaging) in the industrial and automotive sectors.
4. A SEPIC is similar to a traditional buck-boost converter, but has the advantage of a non-inverted output (the output voltage has the same polarity of the input voltage) and isolation between input and output (provided by a capacitor in series).
LEDs Create a Better Driving Experience
LED lighting and other secondary optics solutions significantly boost road safety simply due to well-lighted vision and overall improved efficiency of night driving. The characteristics of longer-duration LEDs—high performance, high brightness efficiency, and low-heat-dissipation energy consumption—are the main features of an ideal automotive lighting solution.
As more lighting technologies come onto the scene, new LED driver technologies for internal and external lighting help produce an added level comfort in a wide range of vehicles. The goal is to provide linear LED dimming with a large contrast ratio. The correct procedure is to operate the LEDs at the manufacturer-recommended forward current/forward voltage.
Conclusion
LEDs are becoming a significant force in the lighting market due to their long lifetime and the ability to control specific lighting requirements. More integration of systems-on-a-chip (SoCs) will continue to reduce the size of driver ICs, leading to faster product development cycles and accurate management of high-level lighting features.
The LED driver market for lighting is estimated to have a compound annual growth rate (CAGR) of about 27% in the near future. The key driving factors responsible for the upswing in the LED driver market includes the greater efficiency exhibited by power-management circuits and the strong demand for LEDs in commercial and industrial applications.
from Electronic Design - Engineering Essentials Curated By Experts http://bit.ly/2oTvXeA
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