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Issue 69

October 23, 2012


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Vikas Vinayak QUANTANCE Interview with Vikas Vinayak - CEO & Co-Founder


Featured Products Highs and Lows of Resistance Measurements: Can You Trust Your Test? Part 3


BY JONATHAN TUCKER WITH KEITHLEY How measuring resistances of mega-ohms or more comes with its own set of challenges and requires different measurement methods.


Homemade Tools - Part 2 BY PAUL CLARKE WITH EBM-PAPST After detailing the beginnings of a homemade temperature data logger in Part 1, this second installment describes how to finish the project using an mbed.


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Vikas Vinayak QU 4 26

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Quantance is a venture-backed semiconductor company based out of Silicon Valley. Their goal is to ensure that PAs transmit higher power and operate more efficiently for mobile devices. We spoke with Vikas Vinayak, the CEO and Co-founder, about his history in tech start-ups, the qBoost Envelope Tracking technology and how Quantance is well on its way to changing the LTE market.

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EEWeb PULSE Can you tell us about your work experience before becoming the CEO and Co-Founder at Quantance? After graduating from college, and as the first Gulf War was ending, the monopolistic hold of the Indian government on Indian television was loosened with the emergence of CNN. Suddenly during prime time you could view more than planting wheat – you could watch CNN and learn what was happening in the world. Then came MTV, and I thought people would certainly prefer music videos to planting wheat. As a result, I believed there was an enormous opportunity for products targeting the growing cable television (CATV) market in India. Will you tell us about cofounding TouchBeam Systems? What were your roles and responsibilities at this company? My friends and I decided to go after this opportunity, and we founded TouchBeam Systems to address the CATV market. I became the co-CEO. TouchBeam produced and delivered the first Vestigial Sideband Modulator for the CATV market in India, and expanded that to 85 hardware products designed to meet the growing needs of CATV operators. We’re talking about the distribution of equipment used by cable operators in homes across India. Our products got the signal from the satellite to the receiver in those homes.

mission is to enable high PA (power amplifier) efficiency and associated RF Front End cost reduction while significantly increasing data throughput from 3G and 4G mobile terminals. In this pursuit, we have

better power supplies if two different power supplies could be combined. However, combining these two different power supplies is challenging, and we founded Quantance to discover a way to accomplish this task.

“Quantance is working on delivering an optimized system solution – an ecosystem – that uses a patented algorithmic approach to adjust the voltage available to the power amplifier for voice and data.”

In our people, Quantance has a deep knowledge about RF transceiver and digital baseband solutions. Our developers use that knowledge to focus on the battery and the antenna – the two most critical aspects of the mobile device – and the path connecting them.

developed a unique, high-speed, high-efficiency power supply technology known as qBoost™. It does not add cost to a wireless device, yet enables the cellular chipset to track the RF

Can you tell us about Quantance and the technology you are developing?

signal envelope, supplying only the minimum power required by the PA in real time. This approach to closely managing the PA is known in the industry as “Envelope Tracking” or simply “ET.” The qBoost ET solution replaces the DC/DC switching power supply currently used to provide APT (average power tracking) power solutions, and upgrades that functionality.

Quantance is a fabless semiconductor company that makes the industry’s highest performance power supplies. Our

We noticed an underlying theorem governing the partitioning of energy flow in all power supplies, which could be exploited to make


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We created a new architecture, which had an interesting and unanticipated consequence of making an AC Boost power supply out of a high performance buck convertor. This solved all the front-end problems of heat, mismatch, broadbanding, throughput, unwanted antenna radiation and signal clarity in a unified way. There are many ways to solve one or more of these problems with other engineering techniques, but we believe our approach is the only holistic and systemic one. Now we have commercialized this power supply over three generations of continually improving and evolving product designs. A lot of companies are building chips to solve a growing pain for the electronics industry – how to deal with the greater power needed for data in handsets/technology originally designed for voice. If you think about it, the radio signals, or RF, used to transmit voice on a handset are not optimized for data, which requires more power to transfer. Current models are operating inefficiently, creating excessive heat and causing batteries to drain faster. Quantance is working on delivering an optimized system solution – an

INTERVIEW ecosystem – that uses a patented algorithmic approach to adjust the voltage available to the power amplifier for voice and data. By doing so, the solution would result in greater efficiency, reduced heat, improved battery life, and better performance in terms of fewer dropped calls. We are building this on the fastest power supply to deliver the exact amount of power required for a specific application at the exact time it’s needed. The Quantance qBoost ET solution is an entire ecosystem of innovation – soft wrapping around a hard product that delivers unique differentiation to our customers. Handsets are just the first market we’re targeting. The consumer electronics market is wide open and now with the growing use of wireless networks, most devices can benefit from our unique approach. Can you tell us more about Quantance’s products? Our main product is our third generation single-chip ET product known as the Q845. Featuring the latest qBoost ET innovations, the Q845 is a very high-speed power supply that generates the supply voltage to deliver the exact amount of power to the most power-hungry circuit inside a cell phone when needed. The most power-hungry circuit is the power amplifier that generates the radio frequency waves that carry the data bits back and forth from your handset to the base station many miles away. The power requirements of the circuit change very rapidly. As cell phones evolve from 2G to 3G to 4G, the rate at which these power requirements change becomes even more rapid and therefore, if you have a very high-speed and high-performance power supply, you can deliver the

exact amount of power, no more, no less. When you deliver only the exact amount of power, there is no excess power that gets burned up as heat and circuits get cooler and when circuits run cooler, they work faster. The net result is, with our technology, an increase in the upload speed of your phone by up to three times.

a car analogy: if you expect your car to go faster, you expect your engine to produce more power, not less. When you go from voice to data, you actually reduce the maximum power that you transmit. The reason is that when you go from voice to data, you add more variation to the signal that you’re transmitting, because you have to incorporate more bits. Because the maximum power of an amplifier is fixed, if you increase the maximum-to-average ratio, that average must go down, because the maximum absolute power is constant. Can you tell us about Quantance’s qBoost™ Envelope Tracking technology?

Does this technology compensate for other variables? The maximum power that a power amplifier can put out is normally constant. An interesting fact is that in every phone—big-name brands included—puts out half the power in data mode as compared to voice mode. Data obviously takes more bits per second than voice. To use

With qBoost, we are able to deliver the highest performing, end-toend ET ecosystem. It includes the Quantance power supply silicon, proprietary noise reduction algorithms that run on the cellular baseband, power amplifiers optimized for envelope tracking, backward compatibility with APT, field measurements audited by carriers, and unique removal of MPR (maximum power reduction) to increase data transmission speeds. Visit



“ When you deliver only the exact amount of power, there is no excess power that gets burned up as heat and circuits get cooler and when circuits run cooler, they work faster. The net result is, with our technology, an increase in the upload speed of your phone by up to three times. “ Our ET solution combines analog and digital power supplies using a patented and deeply mathematical approach involving algorithms from statistical communication theory to create very fast power supplies that work well with sensitive RF front-end circuits while meeting all system noise requirements. The result is fast, efficient power supply that boosts PA voltage above the battery level to meet RF peak demand for higher power and data throughput. It then lowers PA voltage to match reduced RF output power demand for higher efficiency and reduced current. Our power supply has the equivalent switching rate of 400 MHz for best-in-class ET technology. Do most power amplifiers in current phones work with your power supply technology? The power amplifiers that are being shipped to 800 million cell phones


a year are designed to work with very slow power supplies. They include capacitors to absorb the transients that occur in traditional designs. In ET systems these capacitors become both unnecessary and an impediment. For amplifiers, we need to remove this capacitor, which is normally a discrete capacitor in the PA module. In the last 12 months, the momentum behind this technology has been accompanied by a push and a pull. Every single carrier that we are aware of understands the benefits that envelope tracking brings to

EEWeb | Electrical Engineering Community

the user experience and to network capacity, and they are creating the pull for it. Every single handset manufacturer is coming in to push this technology for additional smart phone performance benefits. Once the ecosystem has signed up to an explicit recognition of the need of this technology, every power amplifier manufacturer will embrace envelope tracking-compliant amplifiers. Today, we are engaged

INTERVIEW geographies and newer data standards, such as LTE, has forced an explosion in the RF transmit chains that must be supported in handsets. This is leading to increased strains on cost and size – which is critically important to device makers because of the cost and innovation required to meet consumer demands. Devices must be able to work in multiple modes and geographies, while supporting multiple frequency plans. All of this requires multiple power amplifiers. We hope that with judicious use of other technologies, Quantance can help to eliminate many of those problems.

with several PA manufacturers that have sampled us ET optimized PAs. What direction do you see Quantance heading in the next few years and what challenges do you foresee along the way? As the LTE market continues on its exponential growth path, we believe there will be a greater a need for a holistic way to solve the RF problem from the antenna back to the battery, and Quantance participates by contributing more to the system. Quantance will continue to deploy our unique power supply in all forms of wireless technologies. Many modern consumer devices – even beyond smartphones – transmit radio signals. Almost all of those devices can benefit from our technology. The



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EEWeb | Electrical Engineering Community


ghs and Lows of nce Measurements:

n You Trust r Test? Measuring resistances of mega-ohms or more comes with its own set of challenges and requires different measurement methods. The sources of error for high resistance measurements are also quite different than those that affect low ohms measurements. High impedance insulators are an integral part of today’s high performance electronic products. The purity of the materials used to construct these insulators can make the difference between a product that works properly and one that doesn’t work at all. For example, crystalline materials are fundamental to modern electronics and optoelectronics.



EEWeb PULSE Therefore, the electrical properties of these materials, such as their (anisotropic) conductivity and photoconductivity, as well as the temperature dependencies associated with these properties, are of great interest to researchers. The crystals grown using a number of crystallization techniques may be small in size and often exhibit very high resistances (Figure 1).

In this method, a constant voltage source (V) is placed in series with the unknown resistor (R) and an ammeter (IM). Given that the voltage drop across the ammeter is negligible, essentially all the test voltage appears across R. The resulting current is measured by the ammeter and the resistance is calculated using Ohm’s Law (R= V/I). High resistance is often a function of the applied voltage, which makes the constant-voltage method preferable to the constant-current method. By testing at selected voltages, a resistance vs. voltage curve can be developed and a voltage coefficient of resistance can be determined. Some of the applications that use this method include testing two-terminal high resistance devices, measuring insulation resistance, and determining the volume and surface resistivity of insulating materials.

Figure 1: High resistance measurement on crystalline material. (2003 photo courtesy of Dr. Felix Budde, formerly of the MacDiarmid Institute of Advanced Materials and Nanotechnology in Wellington, New Zealand)

The constant-voltage method requires measuring low current. The two most common error sources when measuring high resistance are electrostatic interference and leakage current. Electrostatic interference can be minimized by shielding the high impedance circuitry. Interferences due to leakage current can be controlled by guarding.

When resistances greater than one mega-ohm must be measured, an electrometer, SMU, or picoammeter/ voltage source combination is usually required. An electrometer may measure high resistance by either the constant-voltage or the constant-current method. Some electrometers allow the user to choose either method. The constant-voltage method uses an ammeter and a voltage source, while the constant-current method uses an electrometer voltmeter and a current source, similar to most DMMs. The most accepted method of measuring high resistance is to apply a large voltage to a sample and measure the small currents stimulated through that sample. However, for high resistance samples, the levels of current that must be measured are extremely low, so testing these materials accurately and repeatably can be a challenge. Other current sources, such as piezoelectric effects or discharging capacitive elements, can obscure the stimulated current that must be observable in order to calculate resistance. The basic configuration of the constant-voltage method using an electrometer or picoammeter is shown in Figure 2a. As shown in Figure 2b, an SMU can also be used for making high resistance measurements using the constant-voltage method.


Figure 2: Constant-voltage method for measuring high resistance

EEWeb | Electrical Engineering Community


Figure 3: Effects of cable resistance on high resistance measurements

Figure 4: Guarding cable shield to eliminate leakage resistance

Guarding Guarding high resistance test connections can significantly reduce the effects of leakage resistance and improve measurement accuracy. Consider the unguarded resistance measurement setup shown in Figure 3. Here, an electrometer ohmmeter is forcing a current (IR) through the unknown resistance (RS) and then measuring the voltage (VM) across the DUT. Assuming that the meter has infinite input resistance, the measured resistance is RM = VM / IR. However, because the cable leakage resistance (RL) is in parallel with RS, the actual measured resistance (RM) is reduced.

The loading effects of cable resistance (and other leakage resistances) can be virtually eliminated by driving the cable shield with a unity-gain amplifier, as shown in Figure 4. Given that the voltage across RL is essentially zero, all the test current (IR) now flows through RS, and the source resistance value can be accurately determined. The leakage current (IG) through the cable-to-ground leakage path (RG) may be considerable, but that current is supplied by the low impedance output of the Ă—1 amplifier rather than by the current source (IR). Visit



Figure 5: Settling time is the result of RSCSHUNT time constant

The settling time of the circuit is particularly important when making high resistance measurements. The settling time of the measurement is affected by the shunt capacitance, which is due to the connecting cable, test fixturing, and the DUT. As shown in Figure 5, the shunt capacitance (CSHUNT) must be charged to the test voltage by the current (IS). The time period required for charging the capacitor is determined by the RC time constant (one time constant, = RSCSHUNT). Therefore, it becomes necessary to wait four or five time constants to achieve an accurate reading. When measuring very high resistance values, the settling time can range up to minutes, depending on the amount of shunt capacitance in the test system. For example, if CSHUNT is only 10 pico-farads, a test resistance of one tera-ohm will result in a time constant of 10 seconds. Therefore, a settling time of 50 seconds would be required for the reading to settle to within 1% of final value. In order to minimize settling times when measuring high resistance values, keep shunt capacitance in the system to an absolute minimum by keeping connecting cables as short as possible. Also, guarding may be used to decrease settling times substantially. Finally, the source voltage, measure current method of resistance measurement is generally faster because of reduced settling times.

2. Keithley Instruments, Inc., Low Level Measurements Handbook, 6th Edition, 2004. 3. “Making High Resistance Measurements on Small Crystals in Inert Gas or High Vacuum with the Model 6517A Electrometer/High Resistance System,” Application Note #2464, Keithley Instruments, 2003. 4. Keithley Instruments, Inc., “Improving the repeatability of ultra-high resistance and resistivity measurements,” White Paper, 1997.

About the Author Jonathan Tucker is a Senior Marketer and Product Manager for Keithley Instruments in Cleveland, Ohio, which is part of the Tektronix test and measurement portfolio. He is responsible for business development of Keithley’s research and education business with emphasis in the areas of nanotechnology, semiconductor, energy, printable/organic electronics, and electrochem. He is also product manager for Keithley’s sensitive measurement instruments. He joined Keithley Instruments in 1987 and has held numerous positions, including test engineer, applications engineer, applications manager, and product marketer.

REFERENCES 1. Joseph F. Keithley, The Story of Electrical and Magnetic Measurements: From 500 BC to the 1940s, IEEE Press, 1999, p. 93.


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• ORing Down to 1V and Up to 20V with ISL6146A, ISL6146B, ISL6146D and ISL6146E

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Homemade Tools Part 1 22 Part Part Back in July I introduced the idea of building your Back in July I introduced the idea of building yourown own homemade homemade tools — stuff that can thatfeatures tools inthat the shops perhaps just toolsgive -- stuffyou thatfeatures can give you tools in thecan’t, shopsor can’t, or perhaps less available expensive in than those available in stores. less expensive thanjust those stores. In Part Two I will document the building of my ownhome home temperaIn Part Two I will document the building of my own temperature data ture data logger using an mbed. logger using an mbed.

18 22

EEWeb | Electrical Engineering Community


Paul Clarke Electronics Design Engineer


19 23


Using the mbed gets you right off the ground very fast with its microcontroller, compiler online, and wealth of tools, sample code, and available help. I started by looking at the temperature inputs I wanted, and I decided I wanted three temperature inputs. Two of these would use NTC temperature sensors, and the other a thermocouple.

cessing the variable using the read_u16 function as shown below:

The NTCs are resistors that change value as the temperature around them alters. Having a negative temperature coefficient (NTC) means that as the temperature rises the resistance drops. These sensors come in different shapes and sizes. The ones I have have a resistance of 10k at 25’c. You will find all NTCs have their resistance listed in this way.

The thermocouple input is a little more difficult as you can’t just connect it to your mbed. The theromocouple input needs a chip that can amplify the weak signal it generates and then pass it to the mbed. Old chips used to give you a analog voltage, but these days you can connect to these devices over communication buses like SPI. To make our life simpler I have selected the max31855 IC that does just this. And to make things even easier,I got this on a prototype board from TAUTIC. This means no fiddly surface mount soldering – you just have to connect the data and power pins.

My circuit for the NTC could not be more simple. I’m only looking for a basic input, so I will use the NTC as part of a resistor network across the mbeds supply. The center tapping will then be used as an input (analog) to the mbed. The input is very basic and has no filtering, gain, or range control. You could achieve this with a opamp, but I have found that for normal room temperature readings using a matched resistor in the fixed side of the network works well.

- Analog In Ain1(p19);

- some Value = Ain1.read_u16();

Thermocouple Input

To the right, you will see our NTC and 10k resistor. This gives a voltage of half rail voltage at 25’c. When the temperature goes up the voltage at the input goes down. NTC Circuit The mbed itself is just as easy to set up by using the AnalogIn class and telling the compiler what pin you have connected your signal too. Each time you want to read the value after that you just use the variable declared. However, for my code I have decided to use the raw values that come from the internal ADC, so I am acNTC Circuit


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The SPI interfaces to the max chip using a 32 bit block of data. However the pre-written function within the mbed that allows direct access to the SPI bus only goes up to a 16 bit format. This would have made interfacing to the device as easy as the NTC and analog pins. However SPI is really easy to deal with anyway, so below I have written my own code to interface to the device.


SPI_Code The last thing I’ll need to add this time round is a serial connection to use for debugging and then later for our Xbee. Once again this is really easy to add to your mbed. Add the Serial class with the pre-defined RX and TX pins and then install the mbed USB to serial driver on your PC, and you are done! I use a small free program called putty.exe that can be used as a serial terminal. Set the baud rate to 9600 and coms port (you can find this in device manager under “Serial Ports” in Windows) and then you can get data from your mbed. Last thing to do this time round is to send the collected data, one second at a time, and send it over the serial port (code below). The data from the NTCs is still raw ADC counts and not in T’c as yet but the data from the max chip is. Output Code

You will see that I only need the block of bits from bit 1 (where 0 is the first) to 11. The rest are thrown away. A little shift register in c code and you can quickly get your data from the max chip. I really should look at the timings on a scope but it’s working right now -- I will check the details later on but I suspect I’m well within limits.

Next time I will turn the raw ADC counts into T’c and also look at storing the data on the mbed’s flash. If you would like to see the full code you can download it form here: monpjc/code/temperature_logger_Pt2/

Output Code Visit


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