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AXT Inc of Fremont, CA, USA — which makes gallium arsenide (GaAs), indium phosphide (InP) and germanium (Ge) substrates and raw materials at plants in China — has closed its underwritten public offering of 8,163,265 shares of common stock at a price to the public of $12.25 per share, including the full exercise of the underwriters’ option to purchase an additional 1,064,773 shares. The firm received total gross proceeds of about $100m, before deducting the underwriting discounts and commissions and other offering expenses...

Recently, frequent Design Idea (DI) author Christopher Paul showcased an innovative and high performance true-two-wire current source using a depletion mode MOSFET as the pass device in “A precision, voltage-compliant current source.”

In subsequent comments the question arose whether similar performance is possible using a bipolar junction transistor instead of Christopher’s FET in a similar (looking) topology?

Wow the engineering world with your unique design: Design Ideas Submission Guide

It posed an intriguing design problem for which I offer here a possible (if implausible) solution. Bizarrely, it’s (roughly) based on the classic discrete transistor model of an SCR, shown in Figure 1.

Figure 1 SCR positive feedback loop suggests an unlikely basis for a BJT current source.

Figure 2 shows the nonlinear positive feedback loop of the thyristor morphing into a linear current source.

Figure 2 Q1 and Q3 current mirror, regulator Z1, and BJT Q1 comprise precision 2-wire current source. The source current is 1.05 * 1.24/R1, or 1.30/R1. * = 0.1% precision resistor

Shunt regulator Z1 and pass transistor Q2 form a very familiar precision current source circuit. In fact, it looks a lot like the one Christopher Paul uses in his MOSFET-based design. Negative feedback from current sense resistor R1 makes shunt regulator Z1 force Q2 to maintain a constant emitter current of 1.24v/R1.

Also, similar (looking) to Christopher Paul’s topology, bias for Z1 and Q2 is provided by a PNP current mirror. However, unlike the symmetrical mirror in Christopher Paul’s design, this one is made asymmetrical to accommodate Z1’s max recommended current rating.

Significant emitter degeneration (~2.5 volts) is employed to encourage accurate current ratios and keep positive feedback loop gain manageable so Z1 can ride herd on it.

Startup resistor R3 is needed because the bias for the transistors and regulator is provided by the SCR-ish regenerative positive feedback loop. R3 provides a trickle of current, a few hundred nanoamps, sufficient to jumpstart (trigger?) the loop when power is first applied.

To program the source for a chosen output current (Io).

 If Io > 5 mA, then:
R1 = 1.30/Io
R2 = 49.9/Io
R4 = 2.40/Io

 If Io < 5 mA, then:
R1 = 1.55/Io
R2 = 8/Io
R4 = 2/Io

Minimum accurate Io = 500 µA.  Maximum = 200 mA.

And for a finishing touch, frequent commentator Ashutosh points out that it’s good practice to protect loads against erroneous and possibly destructive fault currents. Figure 3 suggests a flexible and highly reliable insurance policy. Wire one of these gems in series with Figure 2 and fault current concerns will vanish.

Figure 3 Accurate, robust, fast acting, self-resetting, fault current limiter where Ilimit = 1.25/R1.

In closing, I leave it to you, the reader, to decide whether Figure 2’s resemblance to Christopher Paul’s design is merely superficial, truly meaningful, outright plagiaristic, or just weird.

Stephen Woodward’s relationship with EDN’s DI column goes back quite a long way. Over 100 submissions have been accepted since his first contribution back in 1974.

 Related Content

• A precision, voltage-compliant current source
• Active current mirror
• A current mirror reduces Early effect
• A two-way mirror—current mirror that is
• A two-way Wilson current mirror

The post SCR topology transmogrifies into BJT two-wire precision current source appeared first on EDN.

Have you ever had a duty-cycle resolution issue in your digitally controlled power supply?

In a digital pulse width modulation (DPWM)-controlled power supply, the duty-cycle adjustment is not continuous, but has a minimum step. This is one significant difference between digital control and analog control.

In order to really understand the resolution issue, let’s look at the exaggerated DPWM waveform in Figure 1.

Figure 1 An exaggerated DPWM waveform where the DPWM is acting as the output by comparing its clock counter with a preset comparison value. Source: Texas Instruments

DPWM is acting as the output by comparing its clock counter with a preset comparison value; when the counter equals the comparison value, it will generate a trigger signal, and flip the PWM outputs. When you adjust the comparison to different values, the flipping edge will act earlier or later. Because the counter value can be the only integer, the minimum adjustment step of the duty cycle is expressed by Equation 1:

Oscillation caused by low duty-cycle resolution

The duty-cycle resolution of DPWM brings a disturbance to power-supply control. If the duty-cycle resolution is too low, it may bring limit cycle oscillations (LCOs) to the control loop and cause output voltage ripple. This problem is more serious in high-switching-frequency systems.

Let’s take a 48-V to 5-V synchronous buck converter as an example, as shown in Figure 2.

Figure 2 A 48-V to 5-V synchronous buck converter example. Source: Texas Instruments

Assuming a 500-kHz switching frequency when using 120-MHz PWM frequency, recalling Equation 1, the minimum duty-cycle step is . The minimum duty-cycle adjustment brings the voltage difference with , which means 4% voltage ripples of the output, shown in Figure 3. This is obviously unacceptable.

Figure 3 A low-resolution duty cycle causes output voltage ripple. Source: Texas Instruments

Increase duty-cycle resolution

The most direct way to resolve this duty-cycle resolution issue is to use high-resolution PWM (HRPWM). HRPWM is a powerful peripheral that can reduce the adjustment step significantly—to the 10ps level—but it is typically only available in high-performance MCUs, which may be too powerful or expensive for the design.

Is there a simple method to resolve the duty-cycle resolution issue without extra cost? Can you increase the duty-cycle resolution by using software, or an algorithm?

Looking again at the DPWM waveform, the duty cycle is generated by two variables: the comparison value and the period value, which Equation 2 calculates as:

The common method of adjusting the duty cycle is changing the comparison value and keeping the ‘Period’ value in constant; in other words, the buck converter is operating in fixed switching frequency. What happens if you adjust the duty-cycle by varying the switching frequency? Mostly, a small variation of the switching frequency is not harmful but helpful to power converters, it will reduce the electromagnetic interference and help to pass the EMI regulations.

If you keep the comparison value unchanged, but adjust one count to the period value, how much is the duty-cycle variation? Is it larger or smaller than adjusting the comparison value? Please look into the Equation 3:

Keeping in mind that, the duty-cycle variation by adjusting the comparison value is , because D is always smaller than 1, and  is nearly equal to , you can see that  will be always smaller than .

Which means, adjusting the period value will generate smaller variation to the duty-cycle than adjusting the comparison value.  The improvement is more significant when the duty cycle is much smaller than 1. If you point out the duty-cycle values on one numerical axis with varying the period value, you will clearly see that, when you adding the period value with fixed comparison value, the duty cycle will reduce with a smaller step, as shown in Figure 4.

Figure 4 Duty-cycle values when varying both period and comparison. Source: Texas Instruments

Varying the frequency

Based on the analysis above, it is possible to generate a higher resolution by adjusting the period value. But, in power converter, the switching frequency generally can’t vary much, otherwise the magnetic component design will become very challenge. So, the next question is, how to generate the expected duty cycle with the combination of these two variables?

The method is, first, decided the comparison value with a preset period value, and then, finetune the period value to get the closed duty cycle. The fine tune process either can by increasing the period value with the larger the comparison value, or by reducing the period value with the smaller the comparison value. Figure 5 shows the flowchart of the software by increasing the period value with the larger comparison value, the decreasing method will be similar to this, just need reverse the calculate direction.

Figure 5 Software flowchart for adjusting both the comparison and period values simultaneously. Source: Texas Instruments

At last, I need to figure out that, this software method is principally independent of HRPWM hardware technology, such as a micro-edge positioner. So it is applicable to a digital control loop with HRPWM peripherals same.

Improvement results

Let’s return to the example of the 48-V to 5-V synchronous buck converter in Figure 2. After adopting this software method, it’s possible to reduce the duty-cycle resolution too; the output voltage ripple drops tremendously to <40 mV, as shown in Figure 6. This is acceptable to most of the electrical appliance.

Figure 6 Improved output voltage ripple using the software method. Source: Texas Instruments

This method doesn’t need to use HRPWM to solve the duty-cycle resolution problem, but slightly increasing the duty-cycle resolution with a software algorithm can make your product more competitive by enabling the use of a low-end MCU.

Furthermore, this method is a purely mathematical algorithm; in other words, it is not limited to low-resolution PWM only but also works for HRPWM. So it can be used in some extremely high requirement conditions to further increase the duty-cycle resolution with HRPWM.

Desheng Guo is a system engineer at Texas Instruments, where he is responsible for developing power solutions as part of the power delivery industrial segment. He created multiple reference designs and is familiar with AC-DC power supply, digital control, and GaN products. He received a master’s degree from the Harbin Institute of Technology in power electronics in 2007, and previously worked for Huawei Technology and Delta Electronics.

Related Content

• Digital PWM Motor Control
• Power Controller with Six DPWM Outputs
• Bus-Compatible DPWM Controller
• High efficiency resonant mode implementation using digital control

The post Power Tips #148: A simple software method to increase the duty-cycle resolution in DPWM appeared first on EDN.

Got a table saw recently so I went a little overboard with the French cleats. I also made a scope cart from the remains of my last desk. Fume extraction is a work in progress and I think I need a bigger flare on the hood. Next steps are better parts storage and filling out the relay rack with test gear. If anyone has any test lead/ cable storage suggestions, I’d love to hear them submitted by /u/jellzey [link] [comments]

From ancient compasses to modern smartphones, magnetometers have quietly shaped how we sense and navigate the world. Let us explore the fundamentals behind these field-detecting devices.

Magnetic fields are all around us, yet invisible to the eye. Magnetometers turn those hidden forces into measurable signals, guiding everything from navigation systems to consumer electronics. Well, let us dive into the principles that allow a simple sensor to translate invisible forces into actionable data.

A magnetometer is a device that measures magnetism: the direction, strength, or relative change of a magnetic field at a given location. Measuring the magnetization of a magnetic material, such as a ferromagnet, is one example. A compass is a simple magnetometer: it detects the direction of the ambient magnetic field, in this case the Earth’s.

The Earth’s magnetic field can be approximated as a dipole, offset by about 440 kilometers from the planet’s center and inclined roughly 11 degrees to its rotational axis. At the surface, its strength averages around 0.4 to 0.5 gauss, about 40–50 microtesla, which is quite small compared to laboratory magnetic fields.

Only a few types of magnetometers are sensitive enough to detect such weak fields, including mechanical compasses, fluxgate sensors, Hall-effect devices, magnetoelastic instruments, and magneto resistive sensors.

One of the landmark magnetoresistive sensors from the 1990s was KMZ51 from Philips. Released in 1996, it offered high sensitivity by exploiting the magnetoresistive effect of thin-film permalloy. At its core, the device integrated a Wheatstone bridge structure, which converted changes in magnetic resistance into measurable signals.

To enhance stability and usability, Philips added built-in compensation and set/reset coils: the compensation coil provided feedback to counter drift, while the set/reset coil re-aligned the sensor’s magnetic domains to maintain accuracy. These design features made KMZ51 particularly effective for electronic compasses, current sensing, and detecting the Earth’s weak magnetic field—applications where precision and reliability were essential. KMZ51 remains a classic example of how clever sensor design can make the invisible measurable.

Figure 1 Simplified circuit diagram of KMZ51 illustrates its Wheatstone bridge and integrated compensation and set/reset coils. Source: Philips

On a related side note, deflection, compass, and fluxgate magnetometers represent three distinct stages in the evolution of magnetic sensing. The deflection magnetometer, essentially a large compass box with a pivoted needle, measures the Earth’s horizontal field by observing how an external magnet deflects the needle under the tangent law. The familiar compass magnetometer, in its simplest form, aligns a magnetic needle with the ambient field to indicate direction, a principle that has been carried forward into modern electronic compasses.

Fluxgate magnetometers, by contrast, employ a soft magnetic core driven into alternating saturation; the resulting signal in a sense coil reveals both the magnitude and direction of the external field with far greater sensitivity. Together, these instruments illustrate the progression from basic mechanical deflection to precise electronic detection, each expanding the engineer’s ability to measure and interpret the invisible lines of magnetism.

Tangent law and Tan B position in compass deflection magnetometers

In the Tan B position, the bar magnet is oriented so that the magnetic field along its equatorial line is perpendicular to the Earth’s horizontal magnetic field component. Under this arrangement, the suspended magnetic needle deflects through an angle β, and the tangent law applies:

Tanβ= B/BH

B is the magnetic field produced at the location of the needle by the bar magnet.

BH is the horizontal component of the Earth’s magnetic field, which tends to align the needle along the geographic north–south direction.

This relationship shows that the deflection angle β depends on the ratio of the magnet’s equatorial field to the Earth’s horizontal field. This simple geometric relationship makes the Tan B position a fundamental method for determining unknown magnetic field strengths, bridging classroom demonstrations with practical magnetic measurements.

Figure 2 The image illustrates magnetometer architectures—from pivoted needle to fluxgate core—across design generations. Source: Author

Quick take: Magnetometers on the workbench

Magnetometers range from fluxgate arrays orbiting in satellites to quantum sensors probing in research labs—but this session is just a quick take. The spotlight here leans toward today’s DIY enthusiasts and benchtop builders, where Hall-effect sensors and MEMS modules serve as practical entry points. Think of it as a wake-up call, sprinkled with a few lively detours, all pointing toward the components that make magnetometers accessible for everyday projects.

Hall-effect sensors remain the most approachable entry point, translating magnetic fields into voltage shifts that DIY-ers can easily measure with a scope or microcontroller. MEMS magnetometers push things further, offering compact three-axis sensing in modules that drop straight into maker projects or wearables.

These devices not only simplify experimentation but also highlight how magnetic sensing has become democratized—no longer confined to aerospace or geophysics labs but are available in breakout boards and low-cost modules.

For the benchtop builder, this means magnetometers can be explored alongside other familiar sensors, integrated into Arduino or Raspberry Pi projects, or used to probe the invisible magnetic environment around everyday circuits. In short, the practical face of magnetometers today is accessible, modular, and ready to be wired into experiments without demanding a physics lab.

Getting started with magnetometers is straightforward, thanks to readily available pre-wired modules. Popular options often incorporate ICs such as the HMC5883L, LIS3MDL, and TLV493D, among others.

Although not for the faint-hearted, it’s indeed possible to build fluxgate magnetometers from scratch. The process, however, demands precision winding of coils, careful core selection, stable drive electronics, and meticulous calibration—all of which can be daunting for DIY enthusiasts. These difficulties often make home-built designs prone to noise, drift, and inconsistent sensitivity.

For those who want reliable results without the engineering overhead, ready-made fluxgate magnetometer modules are a practical choice, offering calibrated performance and ease of integration straight out of the box. A good example is the FG-3+ fluxgate magnetic field sensor from FG Sensors, which provides compact and sensitive measurement capabilities for hobbyist and applied projects.

FG-3+ is a high-sensitivity fluxgate magnetic field sensor capable of measuring Earth’s magnetic field with up to 1,000-fold greater precision than conventional integrated IC solutions. Its output is a stable 5-volt rectangular pulse, with the pulse period directly proportional to the magnetic field strength.

Figure 3 The FG-3+ fluxgate magnetic field sensor integrates seamlessly into both experimental and applied projects. Source: FG Sensors

Closing thoughts

This marks the end of this quick-take post on magnetometers, presented in a deliberately unconventional style. We have only scratched the surface; the field is rich with subtleties and deflections that deserve deeper exploration. If this overview piqued your interest, I encourage you to experiment with sensor modules, study fluxgate designs, and share your findings with the engineering community.

And while magnetometers probably will not help you track UFOs, at least not yet, they remain a fascinating gateway into sensing the invisible forces all around us. The more we build, test, and exchange ideas, the stronger our collective understanding becomes. Onward to the next signal.

T. K. Hareendran is a self-taught electronics enthusiast with a strong passion for innovative circuit design and hands-on technology. He develops both experimental and practical electronic projects, documenting and sharing his work to support fellow tinkerers and learners. Beyond the workbench, he dedicates time to technical writing and hardware evaluations to contribute meaningfully to the maker community.

Related Content

• Tiny magnetometer ups sensitivity
• Fundamentals of digital magnetic sensors
• Differential Magnetic Current and Position Sensing
• Magnetometer basics for mobile phone applications
• Deliberate diamond defect yields ultrasensitive magnetometer

The post Magnetometers: Sensing the invisible fields appeared first on EDN.

Що відкрили для себе студенти КПІ в Національному музеї літератури України kpi ср, 12/31/2025 - 13:00

Space Forge of Cardiff, UK (which has operations on Florida’s Space Coast) has generated plasma aboard its ForgeStar-1 satellite, marking a world-first for commercial in-space manufacturing and a step toward producing a new class of high-performance semiconductor materials on orbit...

submitted by /u/SpecialistRare832 [link] [comments]

submitted by /u/canadianchasers [link] [comments]

NUBURU Inc of Centennial, CO, USA — which was founded in 2015 and developed and previously manufactured high-power industrial blue lasers — has given an update outlining multiple near-term strategic execution milestones expected to be achieved in January. These reflect continued progress across the firm’s previously announced defense platform expansion, financial strengthening initiatives, and transformation into an integrated Defense & Security Hub...

submitted by /u/Life-Name3309 [link] [comments]

Пам'яті Звезди Дмитра Володимировича kpi вт, 12/30/2025 - 17:36

Co-packaged optics (CPO) technology, a key enabler for next-generation data center architectures, promises unprecedented bandwidth density and power efficiency by tightly integrating optical engines with switch silicon. But after nearly a decade of existence, where does this next-generation optical interconnect technology stand in terms of broad commercial realization?

But before we delve into CPO’s technology roadmap and its future deployment prospects, here is a brief introduction to this silicon photonics architecture and how it empowers artificial intelligence (AI), high-performance computing (HPC), and high-speed networking applications where electrical signaling over copper wires is reaching its limits.

Figure 1 CPO integrates optical transceivers directly with switch ASICs or processors to enable low-power, high-bandwidth links. Source: Broadcom

CPO, which integrates optical components directly into a single package, minimizes the electrical path length, significantly reducing signal loss, enhancing high-speed signal integrity, and containing latency. In other words, CPO enhances data throughput by leveraging high-bandwidth optical engines that deliver higher data transfer rates and are less susceptible to electromagnetic interference (EMI) than traditional copper connections.

Moreover, this silicon-photonics integration improves power efficiency by reducing the need for high-power electrical drivers, repeaters, and retimers. Case in point: by shortening the copper trace, CPO could improve the link budget enough to remove digital signal processor (DSP) or retimer functionality. That significantly reduces the overall power per bit, a key metric in AI data center management.

Below is a sneak peek at major CPO activities during 2025; it offers a glimpse of product launches and the actual readiness of CPO’s basic building blocks.

CPO’s 2025 progress report

In January 2025, Marvell announced advances in its custom XPU architecture integrated with CPO technology. The company showcased how its custom AI accelerator architecture combines XPU compute silicon, HBM, and other chiplets with its 3D SiPho engines on the same substrate using high-speed SerDes, die-to-die interfaces, and advanced packaging technologies.

That eliminates the need for electrical signals to leave the XPU package into copper cables or across a PCB. Furthermore, connections between XPUs can achieve faster data transfer rates and distances that are 100x longer than electrical cabling. Marvell’s 3D SiPho engine supports 200 Gbps electrical and optical interfaces.

Figure 2 XPU with integrated CPO enhances AI server performance by increasing XPU density from tens within a rack to hundreds across multiple racks. Source: Marvell

“AI scale-up servers require connectivity with higher signaling speeds and longer distances to support unprecedented XPU cluster sizes,” said Nick Kucharewski, senior VP and GM of the Network Switching Business Unit at Marvell. “Integrating co-packaged optics into custom XPUs is the logical next step to scale performance with higher interconnect bandwidths and longer reach.”

Four months later, in May 2025, Broadcom offered a glimpse of its third-generation 200G per lane CPO technology. The company’s CPO journey began in 2021 with the Tomahawk 4-Humboldt chipset, and the second-generation Tomahawk 5-Bailly chipset became the industry’s first volume-production CPO solution.

“Broadcom has spent years perfecting our CPO platform solutions, as evidenced by the maturity of our second-generation 100G/lane products and the ecosystem readiness,” said Near Margalit, VP and GM of the Optical Systems Division at Broadcom. The company also claims that, in addition to edge switch ASICs and optical-engine technology, it offers a comprehensive ecosystem of passive optical components, interconnects, and system solutions partners.

Figure 3 CPO offers a sustainable path forward by addressing the power constraints and physical limitations of traditional pluggable optics. Source: Broadcom

In October 2025, Broadcom claimed that Meta has tested its CPO solutions for one million link hours without a single link flap in a high-temperature lab characterization environment. A link flap is a brief connectivity disruption; it’s a critical reliability metric in high-performance data center networks.

Besides CPO heavyweights like Broadcom and Marvell, there are notable startups in the silicon photonics realm, striving to overcome electrical I/O bottlenecks. For instance, Ayar Labs, a supplier of optical interconnect solutions, has incorporated its TeraPHY optical engines into ASIC design services of Global Unichip Corp. (GUC), a Hsinchu, Taiwan-based chip developer.

In November 2025, Ayar Labs announced that it has integrated its optical engines into GUC’s advanced packaging and ASIC workflow, a critical step toward future CPO deployment. The joint design effort helps address key challenges of CPO integration: architectural, power and signal integrity, mechanical, and thermal.

Figure 4 In this CPO, two TeraPHY optical engine chiplets (left) are shown with a customer FPGA (center) within the same SoC package. Source: Ayar Labs

“The future of AI and data center scale-up will not be possible without optics to overcome the electrical I/O bottleneck,” said Vladimir Stojanovic, CTO and co-founder of Ayar Labs. “Working with GUC on advanced packaging and silicon technologies is an important step in demonstrating how our optical engines can accelerate the implementation of co-packaged optics for hyperscalers and AI scale-up.”

CPO in 2026 and beyond

While CPO proponents are eager to claim that the CPO revolution is at our doorstep, industry watchers like Yole Group see large-scale deployments between 2028 and 2030. Meanwhile, pluggable modules—inserted into the front panel of a switch sitting at the edge of the PCB—will remain competitive.

Market research firm LightCounting also predicts that optical modules will continue to account for the majority of optical links in data centers throughout the decade. At the same time, however, optical transceiver technology will continue to steadily shift toward placing the optics closer to the ASIC.

That’s because traditional pluggable optical modules are increasingly constrained by signal loss, power consumption, and latency due to long electrical traces between the switch ASIC and the optical engine. CPO overcomes these limitations by placing the optical engine much closer to the switching silicon.

The migration of the optical engine closer to the switch ASIC shortens the length of copper trace used for electrical signalling, thereby improving electrical performance. However, the seamless attachment of optical engines to switch ASICs or XPUs requires a range of packaging approaches, including 2.5D interposers, through-silicon vias (TSVs), fan-out wafer-level packaging, and 3D integration enabled by hybrid bonding.

These advanced packaging technologies are steadily evolving, and so is CPO deployment. IDTechEx projects that the CPO market will exceed $20 billion by 2036, growing at a robust CAGR of 37% from 2026 to 2036.

Related Content

• The Rise of Co-Packaged Optics
• AI Clusters Spur Optical Connectivity
• The advent of co-packaged optics (CPO) in 2025
• Global Insights into the Co-Packaged Optics Technology Platform
• AI Performance Now Depends on Optics (and CPO is the Front Line)

The post Where co-packaged optics (CPO) technology stands in 2026 appeared first on EDN.

The first hits from a Google search of the term “guard circuit” produce a series of references to the National Guard on some security circuit. Deep in the list is a printed circuit board company that touts that they design guard rings on critical circuits. So just what are they?

Wow the engineering world with your unique design: Design Ideas Submission Guide

Guard circuit

Analog Devices references guard shields around their op amps as well as the printed circuit traces [1]. These traces are called guard rings; they circle and shield critical circuits. Another well-known reference on electromagnetic interference (EMI) discusses guard shields in the early edition [2]. The use of op amp shields, together with shielded pairs, and grounded so as to eliminate differential input noise. This is accomplished by connecting the cable shield to the op amp shield. Another section discusses guarded meters.

In this example, the recommended connection should be made so as not to cause current flow through any measuring leads. The term “guard shield” is missing from the author’s subsequent book on the same topic [3].

High-power active devices can use guard shields, in the form of a thin conductive strip placed between two electrical insulating yet thermal conductive gaskets, used to mount the device to a heat sink [4]. The guard shield is returned to the circuit common. This results in lower leakage capacitance between the device case and the heat sink, and lower parasitic currents.

Active circuit guard wiring techniques

Guarding can be done using active circuit devices such as an operational amplifier, as shown in Figure 1. The amplifier is wired as a coupler or isolator; the feedback is between the output and the positive input. The coaxial shield is connected to that output, which is the active shield, a low impedance source equal to the input voltage. A large leakage resistor is shown to complete the Spice simulation. The center wire is connected to the measured devices or circuit.

Figure 1 An active circuit guarding with op amps wired as a coupler or isolator and the feedback is between the output and positive input. 

Guard circuit applications

Another possible application for the guard technique is interfacing a pulse signal. A pulse signal’s Fourier transform has a fundamental and odd harmonics. For high-frequency signal transmission, twisted pairs such as Cat 5 are frequently used. The source and load impedance should be equal to prevent reflections. But what if this is not the case? If a guarded circuit is used, the source is connected to the operational amplifier input, which has a high input impedance, and the wire is guarded from the return path.

An example where this circuit could be employed is interfacing industrial or process fluid flow meters. A variety of meters, such as positive displacement, which uses oval gears, and a pickup circuit to count revolutions. This includes turbine meters, which have blades internal to the meter and rotate proportionally to the flow rate.

The vortex flow meter is based on the Von Karman effect. As the fluid flows around a fixed body or blunt object, vorticity is shed alternately. The frequency of this vortex shedding is proportional to the fluid velocity. This signal can be sensed in several ways and is a pulse signal.

The Coriolis mass flow meters make use of two vibrating tubes. Flow through the tubes causes Coriolis forces to twist the tubes, resulting in a phase shift. The time difference between the waves is measured and is directly proportional to the mass flow rate.

All these meters have a calibration factor or K, which is a constant relating to the calibration, for example, K= 800 pulses per gallon. The pulses, electrical circuits, and internal resistances can vary depending on the meter. There are a variety of signal levels as well as input and output resistances between these meters and the input circuit cards.

A frequent application for these meters is to charge a known fluid volume in a tank. An accurate method is to count up or down pulses in an industrial controller. It is more accurate to measure the signal as a pulse, adding interface circuitry such as an analog flow rate signal, and integrating that signal will be subject to circuit inaccuracies and, assuming the operation is done in an industrial controller, be subject to scan sampling errors.

Figure 2 Active circuit guarding, pulse interface circuit based on 200 feet RG-58 coax cable with distributed capacitance and resistance.

Test circuit

This proposed circuit was tested based on a pulse waveform based on a typical meter as discussed. The pulse assumed is 1-ms wide with a 3-ms period. The pulse is generated by a LMC555 wired in astable operation with a 1-kΩ pull up load to a 5-V supply.

The isolation operational amplifier is 1/4 LM324 wired such that the output is a non inverting unity amplifier. The guard circuit is a 40 foot RG-58 coaxial cable. The amplifier is powered by its own 9-V battery. The only connection between both supplies is the single conductor wire parallel to the coax.

The results are shown in Figure 3, the circuit was able to provide an output the same as the input, and able to interface with any input impedance.

Figure 3 Pulse waveforms where yellow is the output and green is the input.

These waveforms agreed with the Spice simulation. The output closely followed the input.

Note the output waveform when expanded time scale when rising. The rapid increase followed by a ramp to the steady state is because the op amp has a very high gain, and is charging based on its supply voltage. However when the outer coax is charged to a point below the steady state output, the RC equivalent circuit is still charging expecting that the steady state at supply voltage. However when input difference is zero, the ramp ceases.

Figure 4 The pulse waveforms where yellow is the output and green is the input. The time scale 1/100 the previous figure (Figure 3).

Because almost all these flow signal transmitters have isolated electronics, the third wire, signal common, may be the same wire as the power supply return. This supply power is typically supplied from the pulse sensing electronics.

If so, that conductive path or reference is already available, usually in the same pair as the supply wire, in the form of a twisted, shielded cable. This provides magnetic and electric field EMI protection. The user only needs to provide the coaxial cable to the flow meter.

More than a shield

A guard shield is more than just a shield, either a solid conductive surface or braided cylinder, it is in concert with thoughtful wiring techniques to both active and passive components that result in mitigating EMI.

Related Content

• Power Supply Guard Circuit
• Telephone Guard Circuit
• Understanding grounding, shielding, and guarding in high-impedance applications
• Analog layout: Why wells, taps, and guard rings are crucial

References

1. Sheingold, Daniel H., Transducer Interfacing Handbook, Analog Devices, Inc., Norwood, MA., 1980.
2. Ott, H. W., Noise Reduction Techniques in Electronic Systems, John Wiley & Sons, New York, New York, 1988.
3. Ott, H. W., Electromagnetic Compatibility Engineering, John Wiley & Sons, New York, New York, 2009.
4. Morrison, R., Grounding and Shielding Circuits and Interference, fifth edition, IEEE Press, John Wiley & Sons, New York, New York, 2007.

Bob Heider worked as an electrical and controls engineer for a large chemical company for over 30 years. This was followed by several years in academic and research roles with Washington University, St. Louis, MO. He is continuing to work part-time as well as mentor some student groups.

The post Guard circuit provides impedance matching appeared first on EDN.

AXT Inc of Fremont, CA, USA — which makes gallium arsenide (GaAs), indium phosphide (InP) and germanium (Ge) substrates and raw materials at plants in China — has announced the pricing of an underwritten public offering of 7,098,492 shares of common stock at a price of $12.25 per share...

📋 Для українських науковців продовжено безкоштовний доступ до міжнародних наукових ресурсів kpi вт, 12/30/2025 - 10:28

I've been buying stuff from thrift stores to learn more about electronics. I took this apart and found it had a broken circuit board. It took a couple hours and it's not pretty but it works! submitted by /u/jacobthejones [link] [comments]

Відкриття виставки кераміки «П'ять чаш» в Українсько-Японському центрі kpi пн, 12/29/2025 - 23:35

Move2Thz – Sustainable Indium Phosphide (InP) platform and ecosystem upscaling, enabling future mass market (sub-)THz applications – is a collaborative project to address existing indium phosphide (InP) shortcomings and build a mature European ecosystem to obtain a commercially and industry-viable platform for use in various mass-market applications utilizing the higher-frequency spectrum towards THz and beyond...