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Editor’s note: In this Design Idea (DI), contributor Bonicatto designs a digital filter system (DFS. This is a benchtop filtering system that can apply various filter types to an incoming signal. Filtering range is up to 120 kHz.

In Part 1 of this DI, the DFS’s function and hardware implementation are discussed.

In Part 2 of this DI, the DFS’s firmware and performance are discussed.

Selectable/adjustable bench filter

Over the years, I have been able to obtain a lot of equipment needed for designing, testing, and diagnosing electronic equipment. I have accumulated power supplies, scopes, digital voltmeters (DVMs), spectrum analyzers, signal generators, vector network analyzers (VNAs), LCR meters, etc., etc.

One piece of equipment I never found is a reasonably priced lab bench filter—something that would take in a signal and filter it with a filter whose parameters could be set on the front panel.

There are some tools that run on a PC’s sound card, but I don’t like to connect my electronic tests on my PC for fear that I’ll damage the PC. The other issue is that I am looking for something that can go up to 100 kHz or so, which is not typical of many soundcards. So, it was time to try to design one.

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

What I came up with in a small bench-top device with one BNC input for the signal you want filtered and one BNC output for the resulting filtered signal (Figure 1). It has a touchscreen LCD to select a filter type and the cutoff/center frequency. So, what can it do?

Figure 1 The finished digital filter system that allows you to select a low-pass, high-pass, band-pass, or band-stop filter type.

You can select a low-pass, high-pass, band-pass, or band-stop filter type. The filter can also be either a two-pole Butterworth or a four-pole.

For the frequency, you can select anywhere from a few Hz to 120 kHz. The are also three gain controls (an analog input gain knob, an analog output gain, and an internal digital gain.)

The cost to build the filter is around $75, as well as some odds and ends you probably already have around.

I also included a download for a 3D printable enclosure. Let’s take a deeper look at this design.

The circuit

The design is centered around a digital filter executed in a Cortex M4 microcontroller (MCU). The three main blocks of the system are an analog front end (AFE), which is composed of four op-amps providing input gain adjustment and antialiasing filtering.

Next is a single board computer (SBC) powered by a Cortex M4. This provides an input for the ADC, controls the LCD and touchscreen, executes the digital filters, and controls the output DAC.

The last block is the analog back end (ABE), which again consists of four op-amps that make up the analog gain circuit and the analog output reconstruction filter.

Let’s take a look at the schematic to see more detail (Figure 2).

Figure 2 The DFS schematic showing the AFE, the ABE, and SBC that provides an input for the ADC, controls the TFT display, executes the digital filters, and controls the output DAC.

Here you can see the blocks we just talked about and a few other minor pieces. Let’s dive a little deeper.

The AFE

The AFE starts by AC-coupling the external signal you want to filter. Then, the first op-amp, after the protection diodes, provides an adjustable gain for the input. This uses a simple single-supply inverting op-amp circuit. RV1 is a potentiometer on the front panel (see Figure 1 above) that allows for a gain of the input from 1x to 5x.

Again, looking at the schematics, we next see a single-pole low-pass filter, which is tuned to 120 kHz. Next are a pair of 2-pole Sallen-Key low-pass filters with components selected to create a Butterworth filter set to 120 kHz.

So now our input signal has been filtered at a frequency that will allow the MCU’s ADC to sample without aliasing. I designed this filter and the ABE filter using TI’s WEBENCH Circuit Designer.

So, we have a 5-pole low-pass filter frontend that will give us a roll-off of 30 dB per octave, or 100 dB per decade.

The flywheel RC circuit is next. As explained in a previous article, the capacitor in this RC circuit provides a charge to hold up the voltage level when the ADC samples the input. More on this can be found at: ADC Driver Ref Design Optimizing THD, Noise, and SNR for High Dynamic Range

The ABE

We’ll skip the MCU for now and jump to the right side of the schematic. Here we see a circuit very similar to the AFE, but this is used as a reconstruction filter that removes artifacts created by the discrete steps used in the MCU’s DAC.

So, starting from the DAC output from the SBC, we see an adjustable gain stage which allows the user, via the output potentiometer, to increase the output level, if desired. This output gain can be adjusted from 1x to 5x.

Next in the schematic, you’ll see two stages of two-pole Sallen-Key low-pass filters configured exactly like the pair in the AFE. So again, they are configured as a 120 kHz Butterworth filter. 

The last op-amp circuit in the ABE is a 2x gain stage and buffer. Why a 2x gain stage? I’ll explain more later, but the gist is that the DAC has a limited slew rate compared to the sample rate I used. So, I reduced the value in the DAC by 2 and then compensated for it in this gain stage.

A note about the op-amps used in this design: The design calls for something that can handle 120 kHz passing through a gain of up to 5 and also dealing with the Sallen-Key filters (the TI WEBENCH shows a gain-bandwidth requirement of at least 6 MHz). I also needed a slew rate that could deal with a 120 kHz signal with a level of 3.3 Vpp. The STMicroelectronics TSV782 fit the bill nicely.

The last two components are the resistor and the capacitor before the output BNC connector. The resistor is used to stabilize the op-amp circuit if the output is connected to a large capacitance load. The 1uF capacitor provides AC coupling to the output BNC.

The MCU

The brains used in this design is a Feather M4 Express SBC, which contains a Microchip Technology’s ATSAMD51 that has a Cortex M4 core. This is primarily powered by a USB connection (or a battery we will discuss in Part 2).  

This ATSAMD51 has a few ADCs and DACs, and we use one of each in this design. It also has plenty of memory (512 kB of program memory and 192  kB of SRAM).

It runs at a usable 120 MHz and is enhanced with a floating-point processor. All this works nicely for the digital filtering we will explain in Part 2. Other features I used include a number of digital I/O ports, an SPI port, and a few other ADC inputs.

One feature I found very nice on the SBC was a 3.3 VDC linear regulator that not only powers the MCU, but has sufficient output to power all other devices in the design.

On the schematic (Figure 1), you can see that the AFE connects to an ADC input on the SBC, and an SBC DAC connects to the ABE circuit. Another major component is the TFT LCD and touchscreen, powered by the 3.3 VDC coming from the SBC.

Miscellaneous schematic items

That leaves a few extra items on the schematic.

Voltage reference

There are 2 simple ½ voltage dividers to generate 1.65 VDC from the 3.3 VDC supply. One is used on the AFE to get a mid-voltage reference for the single supply op-amp design. This reference is simply two equal resistors and a capacitor connected to ground, and from the center of the series-connected resistors.

A second reference was created for the ABE circuit. I used two references as I was laying this out on a protoboard, and the circuits were separated by a significant distance (without a ground plane).

LED indicator

There is also an LED used to indicate that the ADC is clipping the signal because the input is too large or too small. Another LED indicates the DAC is clipping for the same reasons. There will be more discussion on this in the firmware section in Part 2.

Floating ground

An interesting feature of the SBC is that it contains the charging circuit for a lithium polymer 3.7-V battery. This is optional in the design, but it does allow you to operate the DFS with a floating ground and a quiet voltage supply, which may help in your testing.

Enable

A somewhat unique feature, which turns out to be helpful, is an enable that is used to turn off the system if you pull it to ground.

If you use a battery, along with the USB, and want to use a typical power on/off switch, you would need to break the incoming USB line and the battery line, which makes it a 2-pole switch.

So, to get the DFS to power down, I pull the enable line to ground using a 3-pole SPDT switch, which I found has the typical “O/I” on/off indications. You can use a SPST switch; this will have to be switched to “I” to shut it down and “O” to turn it on.

USB voltage display

A ½ voltage divider, with a filter capacitor, is connected to the USB input and used as an input to one of the ADCs, so we can display the connected USB voltage.

Optional reset

The last item is an optional reset. I did not provide a hole to mount a pushbutton, but you can drill a hole in the back of the enclosure for a normally-open pushbutton.

More information

This device is a fairly easy to build. I built the circuit on a protoboard with SMT parts (thru-hole would have been easier). Maybe someone would like to lay out a PCB and share the design. I think you’ll find this DFS has a number of uses in your lab/shop.

The schematic, code, 3D print files, links to various parts, and more information and notes on the design and construction can be downloaded at: https://makerworld.com/en/@user_1242957023/upload

Editor’s Note: Stay tuned for Part 2 to learn more about the device’s firmware.

Damian Bonicatto is a consulting engineer with decades of experience in embedded hardware, firmware, and system design. He holds over 30 patents.

Phoenix Bonicatto is a freelance writer.

Related Content

• Non-linear digital filters: Use cases and sample code
• A beginner’s guide to power of IQ data and beauty of negative frequencies – Part 1
• A Sallen-Key low-pass filter design toolkit
• Designing second order Sallen-Key low pass filters with minimal sensitivity to component tolerances
• Toward better behaved Sallen-Key low pass filters
• Design second- and third-order Sallen-Key filters with one op amp

The post A digital filter system (DFS), Part 1 appeared first on EDN.

This Design Idea (DI) offers an alternative solution for an application borrowed from frequent DI contributor R. Jayapal, presented in: “A 0-20mA source current to 4-20mA loop current converter.” 

It converts a 0/20mA current mode input, such as produced by some process control instrumentation, into a standard industrial 4/20mA current loop output.

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

Figure 1 shows the circuit. It’s based on a (very) old friend—the LM337 three-legged regulator. Here’s how it works.

Figure 1 U1 plus R1 through R5 current steering networks convert 0/20mA input to 4/20mA output.

The fixed resistance of the R1 + R2 + R3 series network, working in parallel with the adjustable R4 + R5 pair, presents a combined load of 312 ohms to the 1.25v output of U1. That causes a zero-input current draw of 1.25/312 = 4 mA, trimmed by R5 (see calibration sequence detailed later).

Summed with this is a 0 to 16 mA current derived from the 0 to 20 mA input, controlled by the 4:1 ratio current split provided by the R1/R2/R3 current divider and fine trimmed by R2 (ditto). 

Note that 4 mA is below the guaranteed minimum regulation current specification for the LM337. In fact, most will work happily with half that much, but you might get a greedy one. So just be aware.

The result is a precision conversion of the 0 to 20mA input to an accurate 4 to 20mA loop current. Conversion precision and stability are insensitive to R2 trimmer wiper resistance due to the somewhat unusual input topology in play.

Calibration proceeds in a four-step linear (iteration-free one-pass) sequence consisting of:

1. Set input = 0.0 mA.
2. Adjust R5 for 4.00 mA loop current.
3. Set input = 20.00 mA.
4. Adjust R2 for 20.00 mA loop current.

Done.

The input voltage burden is a negative 1.0 volt. The output loop voltage drop is 4 volts minimum to 40 volts maximum. The maximum ambient temperature (with no U1 heatsink) is 100oC. Resistors should be precision types, and the trimmer pots should be multiturn cermet or similar.

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.

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• Single phase mains cycle skipping controller sans harmonics
• Two-wire remote sensor preamp

The post Silly simple precision 0/20mA to 4/20mA converter appeared first on EDN.

The shift from Industry 4.0 to 5.0 is not an easy task. Industry 5.0 implementation will be complex, with connected devices and systems sharing data in real time at the edge. It encompasses a host of technologies and systems, including a high-speed network infrastructure, edge computing, control systems, IoT devices, smart sensors, AI-enabled robotics, and digital twins, all designed to work together seamlessly to improve productivity, lower energy consumption, improve worker safety, and meet sustainability goals.

(Source: Adobe Stock)

In the November/December issue, we take a look at evolving Industry 4.0 trends and the shift to the next industrial evolution: 5.0, building on existing AI, automation, and IoT technologies with a collaboration between humans and cobots.

Technology innovations are central to future industrial automation, and the next generation of industrial IoT technology will leverage AI to deliver productivity improvements through greater device intelligence and automated decision-making, according to Jack Howley, senior technology analyst at IDTechEx. He believes the global industry will be defined by the integration of AI with robotics and IoT technologies, transforming manufacturing and logistics across industries.

As factories become smarter, more connected, and increasingly autonomous, MES, digital twins, and AI-enabled robotics are redefining smart manufacturing, according to Leonor Marques, architecture and advocacy director of Critical Manufacturing. These innovations can be better-interconnected, contributing to smarter factories and delivering meaningful, contextualized, and structured information, she said.

One of those key enabling technologies for Industry 4.0 is sensors. TDK SensEI defines Industry 4.0 by convergence, the merging of physical assets with digital intelligence. AI-enabled predictive maintenance systems will be critical for achieving the speed, autonomy, and adaptability that smart factories require, the company said.

Edge AI addresses the volume of industrial data by embedding trained ML models directly into sensors and devices, said Vincent Broyles, senior director of global sales engineering at TDK SensEI. Instead of sending massive data streams to the cloud for processing, these AI models analyze sensor data locally, where it’s generated, reducing latency and bandwidth use, he said.

Robert Otręba, CEO of Grinn Global, agrees that industrial AI belongs at the edge. It delivers three key advantages: low latency and real-time decision-making, enhanced security and privacy, and reduced power and connectivity costs, he said.

Otręba thinks edge AI will power the next wave of industrial intelligence. “Instead of sending vast streams of data off-site, intelligence is brought closer to where data is created, within or around the machine, gateway, or local controller itself.”

AI is no longer an optional enhancement, and this shift is driven by the need for real-time, contextually aware intelligence with systems that can analyze sensor data instantly, he said.

Lisa Trollo, MEMS marketing manager at STMicroelectronics, calls sensors the silent leaders driving the industrial market’s transformation, serving as the “eyes and ears” of smart factories by continuously sensing pressure, temperature, position, vibration, and more. “In this industrial landscape, sensors are the catalysts that transform raw data into insights for smarter, faster, and more resilient industries,” she said.

Energy efficiency also plays a big role in industrial systems. Power management ICs (PMICs) are leading the way by enabling higher efficiency. In industrial and industrial IoT applications, PMICs address key power challenges, according to contributing writer Stefano Lovati. He said the use of AI techniques is being investigated to further improve PMIC performance, with the aim of reducing power losses, increasing energy efficiency, and reducing heat dissipation.

Don’t miss the top 10 AC/DC power supplies introduced over the past year. These power supplies focus on improving efficiency and power density for industrial and medical applications. Motor drivers are also a critical component in industrial design applications as well as automotive systems. The latest motor drivers and development tools add advanced features to improve performance and reduce design complexity.

The post Transitioning from Industry 4.0 to 5.0: It’s not simple appeared first on EDN.

The Universal Serial Bus (USB) started out as a data interface, but it didn’t take long before progressing to powering devices. Initially, its maximum output was only 2.5 W; now, it can deliver up to 240 W over USB Type-C cables and connectors, processing power, data, and video. This revision is known as Extended Power Range (EPR), or USB Power Delivery Specification 3.1 (USB PD 3.1), introduced by the USB Implementers Forum. EPR uses higher voltage levels (28 V, 36 V, and 48 V), which at 5 A will deliver power of 140 W, 180 W, and 240 W, respectively.

USB PD 3.1 has an adjustable voltage supply mode, allowing for intermediate voltages between 9 V and the highest fixed voltage of the charger. This allows for greater flexibility by meeting the power needs of individual devices. USB PD 3.1 is backward-compatible with previous USB versions including legacy at 15 W (5 V/3 A) and the standard power range mode of below 100 W (20 V/5 A).

The ability to negotiate power for each device is an important strength of this specification. For example, a device consumes only the power it needs, which varies depending on the application. This applies to peripherals, where a power management process allows each device to take only the power it requires.

The USB PD 3.1 specification found a place in a wide range of applications, including laptops, gaming stations, monitors, industrial machinery and tools, small robots and drones, e-bikes, and more.

Microchip USB PD demo board

Microchip provides a USB PD dual-charging-port (DCP) demonstration application, supporting the USB PD 3.1 specification. The MCP19061 USB PD DCP reference board (Figure 1) is pre-built to show the use of this technology in real-life applications. The board is fully assembled, programmed, and tested to evaluate and demonstrate digitally controlled smart charging applications for different USB PD loads, and it allows each connected device to request the best power level for its own operation.

Figure 1: MCP19061 USB DCP board (Source: Microchip Technology Inc.)

The board shows an example charging circuit with robust protections. It highlights charge allocation between the two ports as well as dynamically reconfigurable charge profile availability (voltage and current) for a given load. This power-balancing feature between ports provides better control over the charging process, in addition to delivering the right amount of power to each device.

The board provides output voltages from 3 V to 21 V and output currents from 0.5 A to 3 A. Its maximum input voltage range is from 6 V to 18 V, with 12 V being the recommended value.

The board comes with firmware designed to operate with a graphical user interface (GUI) and contains headers for in-circuit serial programming and I2C communication. An included USB-to-serial bridging board (such as the BB62Z76A MCP2221A breakout board USB) with the GUI allows different configurations to be quickly tested with real-world load devices charging on the two ports. The DCP board GUI requires a PC with Microsoft Windows operating system 7–11 and a USB 2.0 port. The GUI then shows parameter and board status and faults and enables user configuration.

DCP board components

Being a port board with two ports, there are two independent USB PD channels (Figure 2), each with their own dedicated analog front end (AFE). The AFE in the Microchip MCP19061 device is a mixed-signal, digitally controlled four-switch buck-boost power controller with integrated synchronous drivers and an I2C interface (Figure 3).

Figure 2: Two independently managed USB PD channels on the MCP19061-powered DCP board (Source: Microchip Technology Inc.) Figure 3: Block diagram of the MCP19061 four-switch buck-boost device (Source: Microchip Technology Inc.)

Moreover, one of the channels features the Microchip MCP22350 device, a highly integrated, small-format USB Type-C PD 2.0 controller, whereas the other channel contains a Microchip MCP22301 device, which is a standalone USB Type-C PD port controller, supporting the USB PD 3.0 specification.

The MCP22350 acts as a companion PD controller to an external microcontroller, system-on-chip or USB hub. The MCP22301 is an integrated PD device with the functionality of the SAMD20 microcontroller, a low-power, 32-bit Arm Cortex-M0+ with an added MCP22350 PD media access control and physical layer.

Each channel also has its own UCS4002 USB Type-C port protector, guarding from faults but also protecting the integrity of the charging process and the data transfer (Figure 4).

Traditionally a USB Type-C connector embeds the D+/D– data lines (USB2), Rx/Tx for USB3.x or USB4, configuration channel (CC) lines for charge mode control, sideband-use (SBU) lines for optional functions, and ground (GND). The UCS4002 protects the CC and D+/D– lines for short-to-battery. It also offers battery short-to-GND (SG_SENS) protection for charging ports.

Integrated switching VCONN FETs (VCONN is a dedicated power supply pin in the USB Type-C connector) provide overvoltage, undervoltage, back-voltage, and overcurrent protection through the VCONN voltage. The board’s input rail includes a PMOS switch for reverse polarity protection and a CLC EMI filter. There are also features such as a VDD fuse and thermal shutdown, enabled by a dedicated temperature sensor, the MCP9700, which monitors the board’s temperature.

Figure 4: Block diagram of the UCS4002 USB port protector device (Source: Microchip Technology Inc.)

The UCS4002 also provides fault-reporting configurability via the FCONFIG pin, allowing users to configure the FAULT# pin behavior. The CC, D+/D –, and SG_SENS pins are electrostatic-discharge-protected to meet the IEC 61000-4-2 and ISO 10605 standards.

The DCP board includes an auxiliary supply based on the MCP16331 integrated step-down switch-mode regulator providing a 5-V voltage and an MCP1825 LDO linear regulator providing a 3.3-V auxiliary voltage.

Board operation

The MCP19061 DCP board shows how the MCP19061 device operates in a four-switch buck-boost topology for the purpose of supplying USB loads and charging them with their required voltage within a permitted range, regardless of the input voltage value. It is configured to independently regulate the amount of output voltage and current for each USB channel (their individual charging profile) while simultaneously communicating with the USB-C-connected loads using the USB PD stack protocols.

All operational parameters are programmable using the two integrated Microchip USB PD controllers, through a dynamic reconfiguration and customization of charging operations, power conversion, and other system parameters. The demo shows how to enable the USB PD programmable power supply fast-charging capability for advanced charging technology that can modify the voltage and current in real time for maximum power outputs based on the device’s charging status.

The MCP19061 device works in conjunction with both current- and voltage-sense control loops to monitor and regulate the load voltage and current. Moreover, the board automatically detects the presence or removal of a USB PD–compliant load.

When a USB PD–compliant load is connected to the USB-C Port 1 (on the PCB right side; this is the higher one), the USB communication starts and the MCP19061 DCP board displays the charging profiles under the Port 1 window.

If another USB PD load is connected to the USB-C Port 2, the Port 2 window gets populated the same way.

The MCP19061 PWM controller

The MCP19061 is a highly integrated, mixed-signal four-switch buck-boost controller that operates from 4.5 V to 36 V and can withstand up to 42 V non-operating. Various enhancements were added to the MCP19061 to provide USB PD compatibility with minimum external components for improved calibration, accuracy, and flexibility. It features a digital PWM controller with a serial communication bus for external programmability and reporting. The modulator regulates the power flow by controlling the length of the on and off periods of the signal, or pulse widths.

The operation of the MCP19061 enables efficient power conversion with the capability to operate in buck (step-down), boost (step-up), and buck-boost topologies for various voltage levels that are lower, higher, or the same as the input voltage. It provides excellent precision and efficiency in power conversions for embedded systems while minimizing power losses. Its features include adjustable switching frequencies, integrated MOSFET drivers, and advanced fault protection. The operating parameters, protection levels, and fault-handling procedures are supervised by a proprietary state machine stored in its nonvolatile memory, which also stores the running parameters.

Internal digital registers handle the customization of the operating parameters, the startup and shutdown profiles, the protection levels, and the fault-handling procedures. To set the output current and voltage, an integrated high-accuracy reference voltage is used. Internal input and output dividers facilitate the design while maintaining high accuracy. A high-accuracy current-sense amplifier enables precise current regulation and measurement.

The MCP19061 contains three internal LDOs: a 5-V LDO (VDD) powers internal analog circuits and gate drivers and provides 5 V externally; a 4-V LDO (AVDD) powers the internal analog circuitry; and a 1.8-V LDO supplies the internal logic circuitry.

The MCP19061 is packaged in a 32-lead, 5 × 5-mm VQFN, allowing system designers to customize application-specific features without costly board real estate and additional component costs. A 1-MHz I2C serial bus enables the communication between the MCP19061 and the system controller.

The MCP19061 can be programmed externally. For further evaluation and testing, Microchip provides an MCP19061 dedicated evaluation board, the EV82S16A.

The post Expanding power delivery in systems with USB PD 3.1 appeared first on EDN.

The state variable active filter (SVAF) is an active filter you don’t see mentioned much today; however, it’s been a valuable asset for us old analog types in the past. This became especially true when cheap dual and quad op-amps became common place, as one can “roll their own” SVAF with just one IC package and still have an op-amp left over for other tasks!

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

The unique features of this filter are having low-pass (LP), high-pass (HP), and band-pass (BP) filter results simultaneously available, with low component sensitivity, and an independent filter “Q” while creating a quadratic 2nd order filter function with 40-dB/decade slope factors. The main drawback is requiring three op-amps and a few more resistors than other active filter types.

The SVAF employs dual series-connected and scaled op-amp integrators with dual independent feedback paths, which creates a highly flexible filter architecture with the mentioned “extra” components as the downside.

With the three available LP, HP, and BP outputs, this filter seemed like a nice candidate for investigating with the Bode function available in modern DSOs. This is especially so for the newer Siglent DSO implementations that can plot three independent channels, which allows a single Bode plot with three independent plot variables: LP, HP, and BP.

Creating a SVAF with a couple of LM358 duals (didn’t have any DIP-type quad op-amps like the LM324 directly available, which reminds me, I need to order some soon!!), a couple of 0.01-µF mylar Caps, and a few 10 kΩ and 1 kΩ resistors seemed like a fun project.

The SVAF natural frequency corner is simply 1/RC, as shown in the notebook image in Figure 1 as ~1.59 kHz with the mentioned component values. The filter’s “Q” was set by changing R4 and R5.

Figure 1 The author’s hand-drawn schematic with R1=R2, R3=R6, and C1=C2, resistor values are 1 kΩ and 10 kΩ, and capacitors are 0.01 µF.

This produced plots of a Q of 1, 2, and 4 shown in Figure 2, Figure 3, and Figure 4, respectively, along with supporting LTspice simulations.

The DSO Bode function was set up with DSO CH1 as the input, CH2 (red) as the HP, CH3 (cyan) as the LP, and CH4 (green) as the BP. The phase responses can also be seen as the dashed color lines that correspond to the colors of the HP, LP, and BP amplitude responses.

While it is possible to include all the DSO channel phase responses, this clutters up the display too much, so on the right-hand side of each image, the only phase response I show is the BP phase (magenta) in the DSO plots.

Figure 2 The left side shows the Q =1 LTspice plot of the SVAF with the amplitude and phase of the HP (magenta + dashed magenta), the amplitude and phase of the LP (cyan + dashed cyan), and the amplitude and phase of the BP (green + dashed green). The right side shows the Q =1 DSO plot of the SVAF with HP (red), LP (cyan), BP (green), and phase of the BP (magenta).

Figure 3 The left side shows the Q =2 LTspice plot of the SVAF with the amplitude and phase of the HP (magenta + dashed magenta), the amplitude and phase of the LP (cyan + dashed cyan), and the amplitude and phase of the BP (green + dashed green). The right side shows the Q =2 DSO plot of the SVAF with HP (red), LP (cyan), BP (green), and phase of the BP (magenta).

Figure 4 The left side shows the Q =4 LTspice plot of the SVAF with the amplitude and phase of the HP (magenta + dashed magenta), the amplitude and phase of the LP (cyan + dashed cyan), and the amplitude and phase of the BP (green + dashed green). The right side shows the Q =4 DSO plot of the SVAF with HP (red), LP (cyan), BP (green), and phase of the BP (magenta).

The Bode frequency was swept with 33 pts/dec from 10 Hz to 100 kHz using a 1-Vpp input stimulus from a LAN-enabled arbitrary waveform generator (AWG). Note how the three responses all cross at ~1.59 kHz, and the BP phase, or the magenta line for the images on the right side, crosses zero degrees here.

If we extend the frequency of the Bode sweep out to 1 MHz, as shown in Figure 5, well beyond where you would consider utilizing an LM358. The simulation and DSO Bode measurements agree well, even at this range. Note how the simulation depicts the LP LM358 op-amp output resonance ~100 kHz (cyan) and the BP Phase (magenta) response.

Figure 5 The left side shows the Q =7 LTspice plot of the SVAF with the amplitude and phase of the HP (magenta + dashed magenta), the amplitude and phase of the LP (cyan + dashed cyan), and the amplitude and phase of the BP (green + dashed green). The right side shows the Q =7 DSO plot of the SVAF with HP (red), LP (cyan), BP (green), and phase of the BP (magenta).

I’m honestly surprised the simulation agrees this well, considering the filter was crudely assembled on a plug-in protoboard and using the LM358 op-amps. This is likely due to the inverting configuration of the SVAF structure, as our experience has shown that inverting structures tend to behave better with regard to components, breadboard, and prototyping, with all the unknown parasitics at play!

Anyway, the SVAF is an interesting active filter capable of producing simultaneous LP, HP, and BP results. It is even capable of producing an active notch filter with an additional op-amp and a couple of resistors (requires 4 total, but with the LM324, a single package), which the interested reader can discover.

Michael A Wyatt is a life member with IEEE and has continued to enjoy electronics ever since his childhood. Mike has a long career spanning Honeywell, Northrop Grumman, Insyte/ITT/Exelis/Harris, ViaSat and retiring (semi) with Wyatt Labs. During his career he accumulated 32 US Patents and in the past published a few EDN Articles including Best Idea of the Year in 1989.

Related Content

• Unusual 2N3904 transistor circuit
• Simple diff-amp extension creates a square-law characteristic
• DIY isolation transformer enhances Bode analysis with modern DSOs
• Injection locking acts as a frequency divider and improves oscillator performance

The post Simple state variable active filter appeared first on EDN.

At the tail end of my September 1 teardown of EBL’s first-generation 8-bay battery charger:

I tacked on a one-paragraph confession, with an accompanying photo that as usual, included a 0.75″ (19.1 mm) diameter U.S. penny for size comparison purposes:

I’ll wrap up with a teaser photo of another, smaller, but no less finicky battery charger that I’ve also taken apart, but, due to this piece as-is ending up longer-than-expected (what else is new?), I have decided to instead save for another dedicated teardown writeup for another day:

An uncertain lineage

That day is today. And by “finicky”, as was the case with its predecessor, I was referring to its penchant for “rejecting batteries that other chargers accepted complaint-free.”

Truth be told, I can’t recall how it came into my possession in the first place, nor how long I’ve owned it (aside from a nebulous “really long time”). Whatever semblance of an owner’s manual originally came with the charger is also long gone; tedious searches of both my file cabinet and online resources were fruitless. There’s not even a company name or product code to be found anywhere on the outer device labeling, just a vague “Smart Timer Charger” moniker:

The best I’ve been able to do, thanks to Google Image Search, is come across similar-looking device matches from a company called “Vidpro Power2000” (with the second word variously alternatively referred to as “Power 2000”) listed on Amazon under multiple different product names, such as the XP-333 when bundled with four 2900 mah AA NiMH batteries:

and the XP-350 with four accompanying 1000mAh AAA batteries, again NiMH-based:

My guess is that neither “Vidpro Power2000” nor whatever retail brand name was associated with this particular charger was actually the original manufacturer. And by the way, those three plastic “bumps” toward the top of the front panel, above the battery compartment and below the “Power2000” mark, aren’t functional, only cosmetic. The only two active LEDs are the rectangular ones at the front panel’s bottom edge, seen in action in an earlier photo.

Anyhoo, after some preparatory top, bottom, and side chassis views as supplements to the already shared front and back perspectives:

A few screws loose

Let’s work our way inside, beginning (and ending?) with the visible screw head in between the two foldable AC plug prongs:

Nope, that wasn’t enough:

Wonder what, if anything, is under the back panel sticker? A-ha:

There we are:

“Nice” unsightly blob of dried glue in the upper left corner there, eh?

No more screws, clips, or other retainers left; the PCB lifts away from the remainder of the plastic chassis straightaway:

As I noted earlier, those “three bumps” are completely cosmetic, with no functional purpose:

Dual-tone and contract manufacturer-grown

And speaking of cosmetics, the two-tone two-sided PCB is an unexpected aesthetic bonus:

As you may have already noticed from the earlier glimpse of the PCB’s backside, the trace regions are sizeable, befitting their hefty AC and DC power routing purposes and akin to those seen last time (where, come to think of it, the PCB was also two-tone for the two sides). But the PCB itself is elementary, seemingly with no embedded trace layers, therein explaining the between-regions routing jumpers that through-hole feed to the other side:

We’ve also finally found a product name: the “TL2000S” from “Samyatech”. My Google search results on the product code were fruitless; let me know in the comments if you had any better luck (I’m particularly interested in finding a PDF’d user manual). My research on the company was more fruitful, but only barely so. There are (or perhaps more accurately in this case, were) two companies that use(d) the “Samyatech” abbreviation, both named “Samya Technology” in full. One is based in Taiwan, the other is in South Korea. The former, I’m guessing, is our candidate:

Samya Technology is a manufacturer of charging solutions for consumer products. The company manufactures power banks, emergency chargers, mobile phone battery chargers, USB charging products, Solar based chargers, Secondary NiMH Batteries, Multifunction chargers, etc. The company has two production bases, one in Taiwan and the other in China.

The website associated with the main company URL, www.samyatech.com, is currently timing out for me. Internet Archive Wayback Machine snapshots suggest two more information bits:

• The main URL used to redirect to samyatech.com.tw, which is also timing out, and
• More generally, although I can’t read Chinese, so don’t take what I’m saying as “gospel”, it seems the company shut down at the start of the COVID-19 lockdown and didn’t reopen.

Up top is the AC-to-DC conversion circuitry, along with other passives:

And at the bottom are the aforementioned LEDs and their attached light pipes:

Back to the PCB backside, this time freed of its previous surrounding-chassis encumbrance:

That blotch of dried glue sure is ugly (not to mention, unlike its same-color counterparts on the other side that keep various components in place, of no obvious functional value), isn’t it?

Algorithmic (over)simplicity

The IC nexus of the design was a surprise (at least to me, perhaps less so to others who are already more immersed in the details of such designs):

At left is the AZ324M, a quad low-power op amp device from (judging by the company logo mark) Advanced Analog Circuits, part of BCD Semiconductor Manufacturing Limited, and subsequently acquired by Diodes Incorporated.

And at right? When I first saw the distinctive STMicroelectronics mark on one end of the package topside, I assumed I was dealing with a low-end firmware-fueled microcontroller. But I was wrong. It’s the HCF4060, a 14-stage ripple carry binary counter/divider and oscillator. As the Build Electronics Circuits website notes, “It can be used to produce selectable time delays or to create signals of different frequencies.”

This all ties to, as I’ve been able to gather from my admittedly limited knowledge and research, how basic battery chargers like this one work in the first place (along with why they tend to be so fickle). Perhaps obviously, it’s important upfront for such a charger to be able to discern whether the batteries installed in it are actually the intended rechargeable NiMH formulation.

So, it first subjects the cells to a short-duration, relatively high current pulse (referencing the HCF4060’s time delay function), then reads back their voltages. If it discerns that a cell has a higher-than-expected resistance, it assumes that this battery’s not rechargeable or is instead based on an alternative chemistry such as alkaline or NiCd…and terminates the charge cycle.

That said, rechargeable NiMH cells’ internal resistance also tends to increase with use and incremental recharge cycles. And batteries that are in an over-discharge state, whether from sitting around unused (a particular problem with early cells that weren’t based on low self-discharge architectures) or from being excessively drained by whatever device they were installed in, tend to be intolerant of elementary recharging algorithms, too.

That said, I’ve conversely in the past sometimes been able to convince this charger to accept a cell that it initially rejected, even if the battery was already “full” (if I’ve lost premises power and the charger acts flaky when the electricity subsequently starts flowing again later, for example) by popping it into an illuminated flashlight for a few minutes to drain off some of the stored electrons.

So… And again, as I mentioned back in September, a more “intelligent” (albeit also more expensive) charger such as my La Crosse Technology BC-9009 AlphaPower is commonly much more copacetic with (including being capable of resurrecting) cells that simplistic chargers comparatively reject:

Some side-view shots in closing, including closeups:

And with that, I’ll turn it over to you for your thoughts in the comments. A reminder that I’m only nominally cognizant of analog and power topics (and truth be told, I’m probably being overly generous-of-self in even claiming that), dear readers—I’m much more of a “digital guy”—so tact in your responses is as-always appreciated! I’m also curious to poll your opinions as to whether I should bother putting the charger back together and donating it to another, as I normally do with devices I non-destructively tear down, or if it’d be better in this case to save potential recipients the hassle and instead destine it for the landfill. Let me know!

—Brian Dipert is the Principal at Sierra Media and a former technical editor at EDN Magazine, where he still regularly contributes as a freelancer.

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The post A budget battery charger that also elevates blood pressure appeared first on EDN.

Delta-sigma (ΔΣ) converters may sound complex, but at their core, they are all about precision. In this post, we will peel back the layers and uncover the fundamentals behind their elegant design.

At the heart of many precision measurement systems lies the delta-sigma converter, an architecture engineered for accuracy. By trading speed for resolution, it excels in low-frequency applications where precision matters most, including instrumentation, audio, and industrial sensing. And it’s worth noting that delta-sigma and sigma-delta are interchangeable terms for the same signal conversion architecture.

Sigma-delta classic: The enduring AD7701

Let us begin with a nod to the venerable AD7701, a 16-bit sigma-delta ADC that sets a high bar for precision conversion. At its core, the device employs a continuous-time analog modulator whose average output duty cycle tracks the input signal. This modulated stream feeds a six-pole Gaussian digital filter, delivering 16-bit updates to the output register at rates up to 4 kHz.

Timing parameters—including sampling rate, filter corner, and output word rate—are governed by a master clock, sourced either externally or via an on-chip crystal oscillator. The converter’s linearity is inherently robust, and its self-calibration engine ensures endpoint accuracy by adjusting zero and full-scale references on demand. This calibration can also be extended to compensate for system-level offset and gain errors.

Data access is handled through a flexible serial interface supporting asynchronous UART-compatible mode and two synchronous modes for seamless integration with shift registers or standard microcontroller serial ports.

Introduced in the early 1990s, Analog Devices’ AD7701 helped pioneer low-power, high-resolution sigma-delta conversion for instrumentation and industrial sensing. While newer ADCs have since expanded on their capabilities, AD7701 remains in production and continues to serve in legacy systems and precision applications where its simplicity and reliability still resonate.

The following figure illustrates the functional block diagram of this enduring 16-bit sigma-delta ADC.

Figure 1 Functional block diagram of AD7701 showcases its key architectural elements. Source: Analog Devices Inc.

Delta-sigma ADCs and DACs

Delta-sigma converters—both analog-to-digital converters (ADCs) and digital-to-analog converters (DACs)—leverage oversampling and noise shaping to achieve high-resolution signal conversion with relatively simple analog circuitry.

In a delta-sigma ADC, the input signal is sampled at a much higher rate than the Nyquist frequency and passed through a modulator that emphasizes quantization noise at higher frequencies. A digital filter then removes this noise and decimates the signal to the desired resolution.

Conversely, delta-sigma DACs take high-resolution digital data, shape the noise spectrum, and output a high-rate bitstream that is smoothed by an analog low-pass filter. This architecture excels in audio and precision measurement applications due to its ability to deliver robust linearity and dynamic range with minimal analog complexity.

Note that from here onward, the focus is exclusively on delta-sigma ADCs. While DACs share similar architectural elements, their operational context and signal flow differ significantly. To maintain clarity and relevance, DACs are omitted from this discussion—perhaps a topic for a future segment.

Inside the delta-sigma ADC

A delta-sigma ADC typically consists of two core elements: a delta-sigma modulator, which generates a high-speed bitstream, and a low-pass filter that extracts the usable signal. The modulator outputs a one-bit serial stream at a rate far exceeding the converter’s data rate.

To recover the average signal level encoded in this stream, a low-pass filter is essential; it suppresses high-frequency quantization noise and reveals the underlying low-frequency content. At the heart of every delta-sigma ADC lies the modulator itself; its output bitstream represents input signal’s amplitude through its average value.

A block diagram of a simple analog first-order delta-sigma modulator is shown below.

Figure 2 The block diagram of a simple analog first-order delta-sigma modulator illustrates its core components. Source: Author

This modulator operates through a negative feedback loop composed of an integrator, a comparator, and a 1-bit DAC. The integrator accumulates the difference between the input signal and the DAC’s output. The comparator then evaluates this integrated signal against a reference voltage, producing a 1-bit data stream. This stream is fed back through DAC, closing the loop and enabling continuous refinement of the output.

Following the delta-sigma modulator, the 1-bit data stream undergoes decimation via a digital filter (decimation filter). This process involves data averaging and sample rate reduction, yielding a multi-bit digital output. Decimation concentrates the signal’s relevant information into a narrower bandwidth, enhancing resolution while suppressing quantization noise within the band of interest.

It’s no secret to most engineers that second-order delta-sigma ADCs push noise shaping further by using two integrators in the modulator loop. This deeper shaping shifts quantization noise farther into high frequencies, improving in-band resolution at a given oversampling ratio.

While the design adds complexity, it enhances signal fidelity and eases post-filtering demands. Second-order modulators are common in precision applications like audio and instrumentation, though stability and loop tuning become more critical as order increases.

Well, at its core, the delta-sigma ADC represents a seamless integration of analog and digital processing. Its ability to achieve high-resolution conversion stems from the coordinated use of oversampling, noise shaping, and decimation—striking a delicate balance between speed and precision.

Delta-sigma ADCs made approachable

Although delta-sigma conversion is a complex process, several prewired ADC modules—built around popular, low-cost ICs like the HX711, ADS1232/34, and CS1237/38—make experimentation remarkably accessible. These chips offer high-resolution conversion with minimal external components, ideal for precision sensing and weighing applications.

Figure 3 A few widely used modules simplify delta-sigma ADC practice, even for those just starting out. Source: Author

Delta-sigma vs. flash ADCs vs. SAR

Most of you already know this, but flash ADCs are the speed demons of the converter world—using parallel comparators to achieve ultra-fast conversion, typically at the expense of resolution.

Flash ADCs and delta-sigma architectures serve distinct roles, with conversion rates differing by up to two orders of magnitude. Delta-sigma ADCs are ideal for low-bandwidth applications—typically below 1 MHz—where high resolution (12 to 24 bits) is required. Their oversampling approach trades speed for precision, followed by filtering to suppress quantization noise. This also simplifies anti-aliasing requirements.

While delta-sigma ADCs excel in resolution, they are less efficient for multichannel systems. Architecture may use sampled-data modulators or continuous-time filters. The latter shows promise for higher conversion rates—potentially reaching hundreds of Msps—but with lower resolution (6 to 8 bits). Still in early R&D, continuous-time delta-sigma designs may challenge flash ADCs in mid-speed applications.

Interestingly, flash ADCs can also serve as internal building blocks within delta-sigma circuits to boost conversion rates.

Also, successive approximation register (SAR) ADCs sit comfortably between flash and delta-sigma designs, offering a practical blend of speed, resolution, and efficiency. Unlike flash ADCs, which prioritize raw speed using parallel comparators, SAR converters use a binary search approach that is slower but far more power-efficient.

Compared to delta-sigma ADCs, SAR designs avoid oversampling and complex filtering, making them ideal for moderate-resolution, real-time applications. Each architecture has its sweet spot: flash for ultra-fast, low-resolution tasks; delta-sigma for high-precision, low-bandwidth needs; and SAR for balanced performance across a wide range of embedded systems.

Delta-sigma converters elegantly bridge the analog and digital worlds, offering high-resolution performance through clever noise shaping and oversampling. Whether you are designing precision instrumentation or exploring audio fidelity, understanding their principles unlocks a deeper appreciation for modern signal processing.

Curious how these concepts translate into real-world design choices? Join the conversation—share your favorite delta-sigma use case or challenge in the comments. Let us map the noise floor together and surface the insights that matter.

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.

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The post Delta-sigma demystified: Basics behind high-precision conversion appeared first on EDN.