About Circuit Cellar Staff

Circuit Cellar's editorial team comprises professional engineers, technical editors, and digital media specialists. You can reach the Editorial Department at editorial@circuitcellar.com, @circuitcellar, and facebook.com/circuitcellar

Issue 308: EQ Answers

Problem 1—The circuit shown below is an audio amplifier with a slightly unusual topology. Explain how to analyze its DC operating point.eq0675_fig1

 Answer 1—For the DC analysis, start by calculating the Thevenin equivalent of the bias network: 8.0 V and 16.67 kΩ. This sets the emitter of Q1 at about 7.3 V.

Now, consider R6. Since the voltage across it is limited to 0.7 V, it is carrying at most about 0.15 mA. If we assume for the moment that the contribution of Q3’s base is negligible (we’ll verify this shortly), then that same current is flowing through R12, which gives it a voltage drop of 1.5 V, setting the collector voltage of Q3 at about 5.8 V.

This means that R10 is carrying a total current of about 1.23 mA, which means that the remaining current (1.08 mA) is flowing through Q3. If Q3 has a gain of 100, then its base current is about 10.8 µA, which is less than 10% of the R6 current, as surmised.

You could iterate through this analysis a few more times to get more exact figures, but that’s what circuit simulators are for.

Problem 2—What is the AC gain of the circuit, and what is its lower cutoff frequency?

Answer 2—As far as the AC analysis goes, Q1 by itself has a gain that is set by R6 and R8 to about 21, but since Q3 has no emitter resistor, its voltage gain is very large. Therefore, the overall gain of the circuit is almost entirely controlled by the negative feedback (R12 and R8), which makes the gain about 46.

Each of the capacitors has a high-pass effect on the circuit:

  • C1 working with the impdeance of the bias network has a time constant of 16.67 ms, which corresponds to a corner frequency of 9.5 Hz.
  • C2 working with R8 has a time constant of 22 ms, which corresponds to a corner frequency of 7.2 Hz.
  • C5 working with R10 and Rload has a time constant of 26.7 ms, which corresponds to a corner frequency of 6.0 Hz.

The overall circuit response will be dominated by the input network, for a cutoff frequency of about 10 Hz.

Problem 3—What is the analog video bandwidth required for a VGA display of 640 × 480 pixels at 60 frames/second?

 Answer 3—For a good-quality computer video display, where fine vertical lines show the same contrast as fine horizontal lines, the video bandwidth should be able to pass at least the 3rd harmonic of the fastest square wave that appears in the image.

The fastest square wave is alternating dark/light pixels, so its fundamental frequency is half the frequency of the dot clock. For VGA at 25.175 MHz, this would be 12.59 MHz. Three times this fundamental frequency is 37.76 MHz.

Problem 4—Some radar systems use a “chirped pulse”. What exactly is a chirped pulse, and what are its advantages?

 Answer 1—The basic problem in radar is to get both adequate power for total range and good timing resolution for range resolution. It is hard to build high-power amplifiers for microwave frequencies. You want to have a lot of energy in each transmitted pulse, but you also want to keep the pulse short.

There is a kind of all-pass filter (constant amplitude response) that has the property that it delays different frequency components by different amounts (linear phase response). When given a narrow pulse at its input, it produces a waveform that starts at a high frequency and then ramps down to a low frequency, over a much longer period of time. When done at audio frequencies, the result sounds like the chirp of a bird or insect, which is where the name comes from. This stretched pulse allows the power amplifier to operate at a lower peak power for a longer time in order to get the same total pulse energy.

Now, in radar, it doesn’t matter if you don’t compress the pulse again before feeding it to the antenna — the chirped pulse works just as well as the compressed pulse in terms of detecting objects.

In fact, you gain additional advantages when the reflections come back. You can amplify the chirped signal in the receiver (getting some of the same advantages as in the transmitter amplifier regarding peak-to-average power). And you can use a “matched filter” (which has the opposite phase characteristic from the transmit filter) to compress the pulse just prior to detection. This filter has the additional advantage of rejecting a lot of potential interference sources as well. The narrow pulses coming out of the receiver filter provide the required time resolution (range resolution).

Electrical Engineering Crossword (Issue 311)

The answers to Circuit Cellar’s June 2016 electrical engineering crossword puzzle are now available.


  1. BELL—Was incorrectly credited for Antonio Santi Giuseppe Meucci’s invention
  2. ZEPTO—z; 10<super>–21
  3. NOISE—Hiss
  4. FEMTO—1,000<super>–5
  5. MICROCODE—Firmware
  6. AMORPHOUS—Silicon used in LCDs and solar cells
  7. PLASMA—”Anything formed”
  8. VELOCITY—m/s
  9. TACHOMETER—Measures a shaft’s rate of revolution


  1. VOLT—Potential energy/charge
  2. THOMSON—Discovered electron in 1896
  3. ELECTROSCOPE—A “gold-leaf” apparatus used to detect electric charge
  4. BUTTERWORTH—BT filter
  6. BOLTZMANN—Constant, k <sub> B
  7. MIXEDSIGNAL—IC with digital and analog circuits [2 words]
  8. PYRAMID—Volume: 1/3Bh, where B is the base’s area and h is height
  9. ELECTRON—E <super> –
  10. PLACEMENT—The step before routing in PCB design
  11. BOHR—Danish physicist (1885–1962), atomic structure, quantum theory


Electrical Engineering Crossword (Issue 310)

The answers to Circuit Cellar’s May 2016 electrical engineering crossword puzzle are now available.


  2. TRANSDUCER—Sensor, passive, active, actuator
  3. LOGICGATE—XOR, NOR, AND, OR [two words]
  4. KILBY—Physics Noble Prize in 2000
  5. ZUSE—German engineer; Turing-Complete Z3
  6. SOLDERMASK—Layer atop copper foil
  7. PETABYTE—1 Exabyte is 1,024 of these
  8. PHOTODIODE—Converts light to current
  9. BOLD—<b>
  10. SIGNIFICAND—Coefficient, mantissa


  2. HYPERSONIC—> Mach 5
  3. FERMI—Chicago Pile-1, induced radioactivity, Los Alamos
  4. MERCURY—Hg, Atomic number 80
  5. CODEC—Code decoder
  6. NORMALLYOPEN—NO [two words]
  7. LITZ—Wire for AC
  8. TOUCH—Haptics
  9. SWITCH—Breaks a circuit

16.        PERIODIC—Regular intervals


Electrical Engineering Crossword (Issue 309)

The answers to Circuit Cellar’s April 2016 electrical engineering crossword puzzle are now available.


  1. STASIS—Inactive
  2. DIODE—Current flows through it in one direction
  3. HEAT—BTUs; joules
  4. BUS—LIN
  5. CLI—Text shell
  6. BINARY—Offs and Ons
  7. BUFFER—Location to hold data temporarily
  8. ASIC—The opposite of a general-purpose IC
  9. PENTODE—Five-terminal transistor
  10. ISOTROPIC—Equal in all ways or directions
  11. HENRY—Inductance


  1. GAUSS—G
  2. TESLA—Flux density
  3. DECIBEL—One-tenth Bel
  5. EMITTER—Base, collector, and what?
  6. ATARI—Yars’ Revenge, Q*bert
  7. PHASE—Relationship between current and voltage
  8. TOP—Upper frequency range
  9. CHILD—UNIX directory below Parent


Electrical Engineering Crossword (Issue 308)

The answers to Circuit Cellar’s March 2016 electrical engineering crossword puzzle are now available.


  2. MICROMETER—Device for measuring a small object’s thickness
  3. TRACE—Conductive line
  4. VHF—Between 30 and 300 MHz
  5. TERA—10 to the 12
  6. APERIODIC—Irregular
  7. ATARI—Company Bushnell founded in 1972
  8. SHORT—Messaging service
  9. NODE—Circuit junction
  10. GENERATOR—Electromechanical transducing device that uses rotational energy to produce electricity


  1. PISO—74HC166
  2. BOM—List of sources
  4. RECTIFIER—Passes current one way
  5. DECIBEL—The smallest perceptible volume change to the average person
  6. NONVOLATILE—Stores data without an external power source
  7. FLOWRATE—Fluid velocity
  8. NTSC—Analog TV
  9. DELTA—Temperature difference
  10. PERIOD—“T” in T = 1/f

Temperature Logger for Long Duration Sessions

Maxim’s new DS1925 iButton data logger makes it possible to monitor cold chain and other temperature-sensitive products or processes for longer duration sessions. Temperature-sensitive products and processes can be damaged when exposed to overly high or low temperatures. The DS1925 provides longer monitoring sessions due to its 122 KB data log memory. In addition, it offers high accuracy over a wide temperature range and measures battery life. It also retains measurements even if the battery life ends before the logger is replaced.Maxim DS1925 iButton

The DS1925’s advantages and characteristics:

  • Largest storage capacity: 122-KB data log memory (compared to 16 KB)
  • Better accuracy over widest temperature range: ±0.5°C over –40°C to 85°C
  • Stainless steel enclosure
  • Small size (17.35 mm × 5.89 mm)

Evaluation kits are now available with hardware, software, host system source code, accessory products, and system solution references. Pricing starts at $45.25 in quantities of 1,000 or more.

Source: Maxim Integrated

Compact COM Express Module with Intel Celeron N3xxx Processors

WIN Enterprises recently launched the compact MB-73450 COM Express module with Type 6 pinouts. The module supports a variety of dual- and quad-core SoC processors, including Intel Celeron and Pentium N3000 product families (4–10 W). In addition the unit supports the cost-efficient Intel Atom quad-core x5-E8000. Turbo-boost frequencies range from 2 up to 2.56 GHz across the various processor options for MB-73450.WinEnt MB-73450

Notable features and characteristics:

  • Supports Intel Celeron N3x processor family
  • Up to 8-GB non-ECC dual-channel DDR3L
  • Two DDI channels, one LVDS, up to three independent displays
  • GbE, 2× SATA 6 Gbps, 4× USB 3.0 and 8× USB 2.0
  • Five PCIe ×1 (Gen2)
  • Supports TPM 1.2/2.0
  • Wide-range voltage input 8.5 to 20 V
  • Wide range operating temperature: –40°C to 85°C (optional)
  • A maximum of up to 8-GB DDR3L memory.

The MB-73450 processor options featured robust turbo burst frequencies for IoT applications where processors must serve functions incremental to their primary application function, such as encryption/deencryption and virus protection. MB-73450 supports Trusted Platform Module (TPM) for more secure communications.

Source: WIN Enterprises

Complete USB Type-C Reference Design

Silicon Labs recently announced a complete USB reference design for developing cables and cable adapters based on the USB Type-C specification. The USB Type-C reference design features EFM8 microcontrollers, USB Power Delivery (PD) protocol stacks certified by the USB-IF, and USB Billboard Device source code.Silicon Labs USB CDue to the rapid adoption of USB Type-C (USB-C), demand is increasing for dongles and adapters to connect with legacy and existing products. The Silicon Labs reference design provides a complete solution for a USB Type-C to DisplayPort (DP) adapter, making it easy to communicate with legacy products.


Qualified developers can access the reference design for free. In addition to schematics, it includes software libraries and stacks, source code, code examples, and access to Simplicity Studio development tools.

Silicon Labs USB Type-C solution highlights:

  • Comprehensive hardware/software reference design based on ultra-low-power EFM8 8-bit microcontrollers
  • Complete software solution, including a USB PD stack library, billboard device source code, and sample code for USB-C to DP applications available in Simplicity Studio library format
  • USB-IF certified USB Power Delivery silicon
  • Complete reference design solution for USB Type-C to DisplayPort adapters
  • Support for USB-C video adapter dongle and USB PD controller functions including attach/detach detection, power contract negotiation, and Alternate mode detection/selection
  • Billboard device support communicating Alternate Mode failure to host

The Silicon Labs USB Type-C reference design deliverables (schematics, PD stack library, billboard device source code and sample code) are available to qualified developers for free.

Source: Silicon Labs

June Engineering Challenge: Find the Schematic Error


Find the error.

Find the error in this  schematic. Submit your answer via the online form by the 20th of the month.

The June Electrical Engineering Challenge (sponsored by Technologic Systems) is now live! Review the schematic on the challenge webpage and find the error for a chance to win prizes, such as a TS-7250-V2 High-Performance Embedded Computer or a Circuit Cellar Digital Subscription.


Circuit Cellar’s technical editors purposely inserted an error in the schematic diagram. It could be a design error, symbol-related error, value error (e.g., 10k vs 100k), incorrect part usage, or some other problem that negatively affects the electronics. Find the error and submit your answer via the online form by the deadline (2 PM EST on the 20th of the month).



Circuit Cellar will randomly select winners from the pool of respondents who submit the correct answer. For more information, read the Rules, Terms, & Conditions.

Produced in Spain: Startup for Hardware Security Solutions

When you talk about a startup, you likely envision bearded hipsters drinking fancy coffee at their expensive Macs. But not all startups are cut from the same cloth. Consider the following case. We recently met with a small team of talented long-time engineers in Madrid that is swimming against the tide. After working for many years in the electronics design industry, the engineers now innovating secure hardware products at a startup with big ideas and lofty goals.

Whitepapers: Embedded Software Security Essentials (Sponsor: PRQA)

When it comes to embedded software, security matters. Programming Research Ltd (PRQA) helps its customers to develop high-quality embedded source code—software which is impervious to attack and executes as intended. PRQA solutions are widely adopted by organizations whose products need to perform securely and reliably in mission-critical and safety-critical environments, as well as any other industry where software must behave as intended.

Click here to access the following whitepapers on embedded software security: Addressing Security Vulnerabilities at the Source; How IoT Is Making Security Imperative for All Embedded Software; Developing Secure Embedded Software: Quality Doesn’t Equal Security; and Addressing Security Vulnerabilities in Embedded Applications.

High-Performance Laser Diode Driver

Intersil Corp. recently announced the ISL78365 laser diode driver for automotive heads-up display (HUD) systems. Capable of pulsing four high-intensity lasers up to 750 mA for projecting full-HD color video onto a windshield, the quad-channel ISL78365’s enables HUDs with high resolution, high color-depth, and high frame-rate projections.Intersil ISL78365

The only laser driver with a fourth channel for supporting a wide variety of laser diode configurations, the ISL78365 provides sub-1.5-ns rise and fall times. It also provides 10-bit color and 10-bit scale resolution to support a wide variety of contrast levels for each driver channel. Furthermore, it supports pixel rates up to 15 0 MHz or 1,900 pixels per line.

The ISL78365’s features and specs:

  • Up to 750 mA of peak current output per channel
  • Fast output switching speeds with pulse rise/fall times of 1.5 ns typical for crisp pixels
  • Supports up to 150-MHz maximum output pixel clock
  • Laser voltage sampler with integrated dynamic power optimization controller to conserve system power
  • Flexible data order supports multiple RGB laser diode optomechanical placement
  • Blanking time power reduction reduces laser diode driver current consumption
  • Programmable multi-pulse RTZ for maximum flexibility and speckle reduction
  • Single 3.3-V supply and 1.8-V video interface for low power operation
  • 3-wire serial peripheral interface
  • AEC-Q100 Grade-1 qualified for operation from –40°C to 125°C
  • Wettable flank QFN package enables the optical inspection of solder joints for lower manufacturing cost

You can combine the ISL78365 with the ISL78206 2.5-A synchronous buck regulator, ISL78201 2.5-A synchronous buck/boost regulator, ISL78233 3-A synchronous buck regulator, ISL78302 dual 302-mA LDO, and ISL29125 digital RGB color light sensor to provide a complete power supply system for automotive laser projection HUDs.

The quad-channel ISL78365 laser diode driver is available in a 6 mm × 6 mm 40-lead WFQFN package. It costs $9.82 in 1,000-unit quantities.

Source: Intersil Corp.

Imperas ARMv8 Support Advances Embedded Software Development

Imperas Software recently announced the availability of models and virtual platforms for the Cortex-A72 ARMv8 processors (in addition to the earlier models). Now the Imperas Open Virtual Platforms (OVP) processor model library comprises more than 160 models across a wide range of IP vendors. More than 40 ARM cores—including the Cortex-A, Cortex-R, and Cortex-M families—are supported.

The Imperas Cortex-A72 ARM processor models are available in single-core, multi-core, and multi-cluster configurations enabling high-performance simulations of platforms ranging from simple single cores to many core systems. Imperas also offers a model of the ARM GICv3 interrupt controller.

Also available are Extendable Platform Kits (EPKs)—which are virtual platforms of the target devices—for ARMv8 processor cores running Linux. Available on the OVP website, the EPKs enable you to run high-speed simulations of ARM-based SoCs and platforms on any suitable PC. You can extend and customize the functionality of the virtual platform. The platform and the peripheral models are open source.

Note that OVP models also work with the Imperas advanced tools for multicore software development, analysis, verification, and debugging, including M*SDK advanced software development solutions and key tools for hardware-dependent software development. The tools use the Imperas SlipStreamer patent-pending binary interception technology. SlipStreamer enables the analytical tools to operate without modification or instrumentation of the software source code.

Source: Imperas Software

Embedded Couplers for New Close Proximity Wireless Transfer Technology

Antenova M2M is now shipping its first orders for the TransferJet coupler, Zoma (SR4T014). In addition, it is working with Icoteq to build TransferJet designs for customers worldwide.Antenova SR4T014


Intended to transfer multimedia data (e.g., photos to a TV screen), TransferJet is a close-proximity wireless transfer technology that radiates very low-power radio waves. It combines the speed of ultra-wide band networking with near-field communications (NFC) and operates over short ranges. TransferJet uses a coupler as opposed to an antenna.

Antenova is working with Icoteq, which developed a sensor board for high-speed data upload using TransferJet. The 50 mm × 40 mm board feature an Atmel SAMS70/SAMV70 microprocessor and Antenova’s TransferJet coupler.

Source: Antenova

The Future of Sensor Technology for the IoT

Sensors are at the heart of many of the most innovative and game-changing Internet of Things (IoT) applications. We asked five engineers to share their thoughts on the future of sensor technology.

ChrisCantrellCommunication will be the fastest growth area in sensor technology. A good wireless link allows sensors to be placed in remote or dynamic environments where physical cables are impractical. Home Internet of Things (IoT) sensors will continue to leverage home Wi-Fi networks, but outdoor and physically-remote sensors will evolve to use cell networks. Cell networks are not just for voice anymore. Just ask your children. Phones are for texting—not for talking. The new 5G mobile service that rolls out in 2017 is designed with the Internet of Things in mind. Picocells and Microcells will better organize our sensors into manageable domains. What is the best cellular data plan for your refrigerator and toaster? I can’t wait for the TV commercials. — Christopher Cantrell (Software Engineer, CGI Federal)

TylerSensors of the future will conglomerate into microprocessor controlled blocks that are accessed over a network. For instance, weather sensors will display temperature, barometric pressure, humidity, wind speed, and direction along with latitude, longitude, altitude, and time thrown in for good measure, and all of this will be available across a single I2C link. Wide area network sensor information will be available across the Internet using encrypted links. Configuration and calibration can be done using webpages and all documentation will be stored online on the sensors themselves. Months’ worth of history will be saved to MicroSD drives or something similar. These are all things that we can dream of and implement today. Tomorrow’s sensors will solve tomorrow’s problems and we can really only make out the barest of glimpses of what tomorrow will hold. It will be entertaining to watch the future unfold and see how much we missed. — David C. Tyler (Retired Computer Scientist)

Quo vadis electronics? During the past few decades, electrical engineering has gone through an unprecedented growth. As a result, we see electronics to control just about everything around us. To be sure, what we call electronics today is in fact a symbiosis of hardware and software. At one time every electrical engineer worth his salt had to be able to solder and to write a program. A competent software engineer today may not understand what makes the hardware tick, just as a hardware engineer may not understand software, because it’s often too much for one person to master. In most situations, however, hardware depends on software and vice versa. While current technology enables us to do things we could not even dream about just a few years ago, when it comes to controlling or monitoring physical quantities, we remain limited by what the data sensors can provide. To mimic human intellect and more, we need sensors to convert reality into electrical signal. For that research scientists in the fields of physics, chemistry, biology, mathematics, and so forth work hard to discover novel, advanced sensors. Once a new sensor principle has been found, hardware and software engineers will go to work to exploit its detection capabilities in practical use. In my mind, research into new sensors is presently the most important activity for sustaining progress in the field of electronic control. — George Novacek (Engineer, Columnist, Circuit Cellar)

GustafikIt’s hard to imagine the future of sensors going against the general trend of lower power, greater distribution, smaller physical size, and improvements in all of the relevant parameters. With the proliferation of small connected devices beyond industrial and specialized use into homes and to average users (IoT), great advances and price drops are to be expected. Tech similar to that, once reserved for top-end industrial sensor networks, will be readily available. As electrical engineers, we will just have to adjust as always. After years of trying to avoid the realm of RF magic, I now find myself reading up on the best way to integrate a 2.4-GHz antenna onto my PCB. Fortunately, there is an abundance of tools, application notes, and tutorials from both the manufacturers and the community to help us with this next step. And with the amazing advances in computational power, neural networks, and various other data processing, I am eager to see what kind of additional information and predictions we can squeeze out of all those measurements. All in all, I am looking forward to a better, more connected future. And, as always, it’s a great time to be an electrical engineer. — David Gustafik (Hardware Developer, MicroStep-MIS)

MittalMiniature IoT, sensor, and embedded technologies are the future. Today, IoT technology is a favorite focus among many electronics startups and even big corporations. In my opinion, sensor-based medical applications are going to be very important in our day-to-day lives in the not-so-distant future. BioMEMS sensors integrated on a chip have already made an impact in industry with devices like glucometers and alcohol detectors. These types of BioMEMS sensors, if integrated inside mobile phones for many medical applications, can address many human needs. Another interesting area is wireless charging. Imagine if you could charge all your devices wirelessly as soon as you walk into your home. Wouldn’t that be a great innovation that would make your life easier? So, technology has a very good future provided it can bring out solutions which can really solve human needs. — Nishant Mittal (Master’s Student, IIT Bombay, Mumbai)