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Impact of ADC resolution and its reference

Engineers always want to get all they can from their circuits; this holds for analog-to-digital converters (ADCs). To maximize performance from an ADC, resolution is perhaps the primary spec to focus on. However, the sad fact is that we have defined the maximum single-read resolution once we pick the ADC and its reference. For example, let’s say we use a 10-bit ADC with a 5-V reference. This means that our reading resolution is 5 V / (1023) or 4.888 mV per digital step. But what if we had this ADC system and had to apply it to a sensor that had an output of 0 to 1 V? The ADC resolution stays at 4.888 mV, but that means there are only 1 V /4.888 ms, or ~205 usable steps, so in essence, we have lowered the sensor’s resolution to 1 part in 205.

What if we were designing a device to measure the voltage across an inductor when a DC step voltage is applied through a series resistor? You can see in the curve below (Figure 1), in the first couple of seconds we probably would get decent data point readings, but after that, many of the data points would have the same value since the slope is shallow. In other words, the relative error would be high.

Figure 1 Sample inductor voltage versus time curve for a circuit measuring the voltage across an inductor when a DC step voltage is applied through a series resistor. Note the flat slope after 3 seconds, which will increase the relative error of the measurement.

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There are two basic ways to change this:

• Change the ADC to one with more bits (such as 12, 14, or 16 bits) or,
• Change the ADC’s reference voltage.

(There are also more exotic ways to change resolution, such as using delta-sigma converters.) Changing the number of bits would mean an external ADC or a different microcontroller. So, what if we designed a system with an adjustable reference? This resolution could change automatically as needed—let’s call this adaptive resolution.

Adaptive resolution demo

Let’s look at an easy method first. The Microchip ATMEGA328P has three settings for the internal ADC reference: the Vcc voltage, an internal 1.1-V reference, and an external reference pin (REF). So, for demonstration, the simplest setup is to use an Arduino Nano, which uses the ATMEGA328P.

The demonstration uses one of the analog inputs, which can connect to a 10-bit ADC, to measure voltage or the sensor output. The trick here is to set the reference to Vcc (+5 V in this design) and take an ADC reading of the analog input.

If the reading, after being converted to a voltage, is greater than 1.1 V, use that value as your measurement. If it is not greater than 1.1 V, change the reference to the internal 1.1-V band-gap voltage and retake the reading. Now, assuming your sensor or measured voltage is slow-moving relative to your sample rate, you have a higher-resolution reading than you would have had with the 5-V reference.

Referring to our inductor example, Figure 2 illustrates how this adaptive resolution will change as the voltage drops.

Figure 2 Change in adaptive resolution using the Microchip ATMEGA328P’s internal ADC with either reference Vcc voltage of 5 V or internal reference of 1.1 V.

Adaptive resolution code

The following is a piece of C code to demonstrate the concept of adaptive resolution.

[An aside: As a test, I used Microsoft Copilot AI to write the basic code, and it did a surprisingly good job with good variable names, comments, and offered a clean layout. It also converted the ADC digital to the analog voltage correctly. As I was trying to get Copilot to add some logic changes, it got messier, so at that point, I hand-coded the modifications and cleanup.]

// Define the analog input pin const int analogPin = A0; // Variable to store the reference voltage (in mV) const float referenceVoltage5V = 4753.0; // Enter the actual mv value here const float referenceVoltage1p1V = 1099.0; // Enter the actual mv value here // Types and variable to track reference state enum ReferenceState {Ref_5, Ref_1p1}; ReferenceState reference = Ref_5; void setup() { // Initialize serial communication at 9600 bits per second Serial.begin(9600); // Set the analog reference to 5V (default) analogReference(DEFAULT); reference = Ref_5; // Set reference state } void loop() { int sensorValue = 0; int junk = 0; float voltage = 0; sensorValue = analogRead(analogPin); // Take a reading using the current reference if (reference == Ref_5) { voltage = (sensorValue / 1023.0) * referenceVoltage5V; //Convert reading if (voltage < 1100) { // Check if the voltage is less than 1.1V // Change the ref voltage to 1.1v and take a new reading analogReference(INTERNAL); // Set the analog reference to 1.1V (internal) reference = Ref_1p1; // Set reference state junk = analogRead(analogPin); // Take a throw-away read after ref change sensorValue = analogRead(analogPin); // Take a new reading using 1.1v ref voltage = (sensorValue / 1023.0) * referenceVoltage1p1V; //Convert reading } } else // Reference is currently set to 1.1v voltage = (sensorValue / 1023.0) * referenceVoltage1p1V; //Convert reading if (sensorValue == 1023) { // Check if the ADC is at maximum (>= 1.1v) // Voltage is 1.1 volts or greater, so change to 5v ref and reread analogReference(DEFAULT); // Set the analog reference to 5V (default) reference = Ref_5; // Set reference state junk = analogRead(analogPin); // Take a throw-away read after reference change sensorValue = analogRead(analogPin); // Take a reading using the 5v reference voltage = (sensorValue / 1023.0) * referenceVoltage5V; //Convert reading } // Print the analog value and voltage to the serial monitor if (reference == Ref_5) Serial.print("Analog value with 5V reference: "); else Serial.print("Analog value with 1.1V reference: "); Serial.print(sensorValue); Serial.print(", Voltage: "); Serial.println(voltage / 1000,4); // Delay for a moment before the next loop delay(1000); }

This code continuously reads the ADC connected to analog pin A0. It starts by using Vcc (~5 V) as the reference for the ADC. If the reading is less than 1.1 V, the ADC reference is switched to the 1.1-V internal reference. This reference is continued to be used until the ADC returns its maximum binary value of 1023, which means the A0 voltage must be 1.1 V or greater. So, in this case, the reference is switched to Vcc again. After taking a valid voltage reading, the code prints the reference value used along with the reading.

The 5 V and 1.1 V references must be calibrated before use to get accurate readings. This should be done using a reasonably good voltmeter (I used a calibrated 5½ digit meter). These measured voltages can then be entered into the code.

Note that towards the top of the code, the 5-V reference voltage variable (“referenceVoltage5V”) is set to the actual voltage as measured on the REF pin of the Arduino Nano, when the input on A0 is greater than 1.1 V. The 1.1-V reference voltage variable (“referenceVoltage1p1V”) should also be set by measuring the voltage on the REF pin when the A0 voltage is less than 1.1 V. Figure 3 below illustrates this concept.

Figure 3 This code continuously reads the ADC connected to analog pin A0. If A0 voltage < 1.1 V, the ADC reference is switched to 1.1 V. If A0 > 1.1 V, the ADC reference is switched to Vcc.

Relative error between 1.1 V and 5 V references

A few pieces of data showing the improvement of this adaptive resolution are as follows: Around 1.1-V, the 5-V referenced reading can have a resolution error of up to 0.41% while the 1.1-V reference reading can have up to a 0.10% error. At 100 mV, a reading that references 5 V could have up to a 4.6% error, while a 1.1-V referenced reading may have up to a 1.1% error. When we reach a 10-mV input signal, the 5 V reference may err by 46% while the 1.1 V reference reading will be 10.7% or less.

Expanding reference levels External DAC method

If needed, this concept could be expanded to add more levels of reference, although I wouldn’t go more than 3 or 4 levels on a 10-bit ADC due to diminishing returns. The following are a few examples of how this could be done.

The first uses a DAC with its own reference tied to the Nano’s REF pin. The DAC controlled by the Nano could then be adjusted to give any number of reference values. An example of such a DAC is the MAX5362 DAC with I2C control (although its internal reference is 0.9xVcc, so the max reading would be roughly 4.5 V). In this design, the Nano’s REF pin would be set to “EXTERNAL.” See Figure 4 below for more clarity.

Figure 4 Using an external DAC (MAX5362) controlled by the Arduino Nano to provide more reference levels.

Nano’s PWM output method

Another way to create multiple reference voltages could be by using the Arduino Nano’s PWM output. This would require using a high-frequency PWM and very good filtering to obtain a nice flat DC signal, which is proportional to the 5-V reference value. You would want a ripple voltage of about 1 mV (-74 dB down) or less to get a clean, usable output. The outputs would also need to be measured to calibrate it in the code. This technique would require minimal parts but would give you many different levels of reference voltages to use. Figure 5 shows a block diagram of this concept.

Figure 5 Using the Arduino Nano’s PWM output and a lowpass filter to obtain the desired DC signal to use as a voltage reference.

Resistor ladder method

Another possibility for an adjustable reference is using a resistor ladder and an analog switch to select different nodes in the ladder. Something like the TI TMUX1204 may be appropriate for this concept. The resistor ladder values can be selected to meet your reference requirements. Figure 6 shows that two digital outputs from the Nano are also used to select the appropriate position in the resistor ladder.

Figure 6 Using a resistor ladder and an analog switch, e.g., TI TMUX1204, to select different nodes on the ladder to generate tailored voltage reference values.

You get the idea

There are other ways to construct the reference voltages, but you get the idea. The bigger picture here is using multiple references to improve the resolution of your voltage readings. This may be a solution looking for a problem, but isn’t that what engineers do—match up problems with solutions?

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.

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Amid persistent macroeconomic uncertainty and cyclical market softness, discrete device designer and manufacturer Nexperia of Nijmegen, the Netherlands (which operates wafer fabs in Hamburg, Germany, and Hazel Grove Manchester, UK) says that in fiscal year 2024 it demonstrated resilience, achieving stable revenues and maintaining profitability through a strong focus on execution and a commitment to innovation...

With the launch of its very first 3nm chip design facilities in Noida and Bengaluru, India has made a significant leap in semiconductor technology. These cutting-edge facilities were inaugurated by the Ministry of Electronics & Information Technology (MeitY), led by Union Minister Ashwini Vaishnaw, marking a new era in India’s semiconductor sector.

A Notable Milestone in India’s Semiconductor Sector

Renesas Electronics India’s newly established 3nm chip design centres are a milestone for India’s semiconductor technology. Previously India worked on 7nm and 5nm chip designs, but with the change to 3nm technology, the country is among the global leaders in semiconductor technology.

Vaishnaw emphasized that designing at 3nm is truly next-generation, highlighting India’s growing expertise in semiconductor design. The Noida facility, in particular, is expected to play a crucial role on developing a pan- India semiconductor ecosystem, leveraging the country’s skilled workforce. He emphasized the industry’s increasing confidence by pointing to large investments firms like Applied Materials and Lam Research.

Government Strategy and Industry Investments

India’s chip roadmap stretches beyond design, to fabrication, advanced packaging (ATMP), equipment and material supply chains. In developing a self-dependent and globally competitive semiconductor ecosystem, the government is encouraging strategic collaborations, infrastructure development and home-grown innovation.

As part of further enhancing the talent pipeline, Vaishnaw launched a new semiconductor learning kit that was designed to impart engineering students with practical exposure in hardware design. More than 270 educational institutions that are already utilizing cutting-edge EDA (Electronics Design Automation) tools under the India Semiconductor Mission (ISM) will now be provided with these kits.

“Renesas Electronics, CEO, Hidetoshi Shibata, appreciated India’s growing influence in embedded systems as well as semiconductor innovation and said that Indo-Japan strategic partnership would be instrumental in shifting the semiconductor trend globally.”

Conclusion:

India’s opening of 3nm chip design hubs is a landmark moment in the country’s semiconductor journey, placing the country among the world leaders in the field of chip innovation. With its government-supported semiconductor strategy taking root, India is now moving beyond chip design to fabrication, advanced packaging (ATMP) and the materials supply chains, creating a sustainable semiconductor ecosystem.

The post Redefining Semiconductor Excellence: India Sets the Stage with 3nm Designs appeared first on ELE Times.

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POET Technologies Inc of Toronto, Ontario, Canada — designer and developer of the POET Optical Interposer, photonic integrated circuits (PICs) and light sources for the hyperscale data-center, telecom and artificial intelligence (AI) markets — has appointed Ghazi M. Chaoui PhD MBA as its senior VP of global manufacturing & digital transformation. An industry veteran of nearly 40 years, Chaoui recently concluded a multi-year assignment as chief procurement officer of Coherent Corp...

At its global headquarters in Morrisville, PA, USA on 16 May, Mitsubishi Chemical Group company Gelest Inc (which manufactures specialty silicones, organosilanes, metal-organics and acrylate monomers) has opened its new 50,000ft2 production facility in a ribbon-cutting ceremony attended by company executives, local officials, and community members. The new building will increase Gelest’s production capabilities and support customer applications from microelectronics and medical devices to advanced thermal coatings and mobility. ..

For first-quarter 2025, POET Technologies Inc of Toronto, Ontario, Canada — designer and developer of the POET Optical Interposer, photonic integrated circuits (PICs) and light sources for the hyperscale data-center, telecom and artificial intelligence (AI) markets — has reported non-recurring engineering (NRE) and product revenue of $166,760, up from $29,032 last quarter and just $8710 a year ago...

The rapid advancement of semiconductor technologies has transformed industries across the globe, from data centers to consumer devices, and even critical infrastructure. With the ever-growing reliance on interconnected devices, robust security systems are paramount. Among the unsung heroes in ensuring this security are the firmware systems that power these devices, particularly security firmware embedded within semiconductor components.

Secure firmware, especially in devices like self-encrypting drives (SEDs), is crucial in safeguarding sensitive data. As data breaches and cyberattacks become more sophisticated, ensuring that the foundation of technology—semiconductors—remains secure is critical. The secure firmware embedded in these systems enables the encryption and decryption of data in real time, ensuring that sensitive information remains protected without compromising performance.

Figure 1 SEDs provide hardware-based encryption for robust data protection. Source: Micron

While often invisible to the end user, this technology has a far-reaching impact. It secures everything from financial transactions to personal health data, laying the groundwork for secure, scalable, and efficient systems that are vital for industries in both the public and private sectors. In this context, the evolution of secure firmware can be seen as an essential pillar of digital safety, contributing to national and global security priorities.

Role of security protocols and standards

In the world of secure firmware, several protocols and standards ensure that systems remain resilient against evolving threats. These include advanced cryptographic algorithms, trusted platform modules (TPMs), and the implementation of standards set by organizations like National Institute of Standards and Technology (NIST) and Trusted Computing Group (TCG). These technical frameworks serve to safeguard sensitive data and build trusted systems from the hardware level up.

1. Security Protocol and Data Model (SPDM)

SPDM is a protocol developed by the Distributed Management Task Force (DMTF) to provide a standardized framework for secure communication between devices, especially in scenarios involving trusted hardware such as TPMs and secure boot mechanisms.

Figure 2 The security standard enables system hardware components such as PCIe cards to have their identity authenticated and their integrity verified. Source: OCP Security

It ensures secure data exchange by supporting authentication, integrity checks, and confidentiality for devices in a distributed environment. By embedding SPDM into security firmware, semiconductor systems can ensure end-to-end security from device initialization to secure communication with other networked devices.

2. NIST Cybersecurity Framework

NIST provides a comprehensive set of standards and guidelines that address the security requirements for information systems in various industries. The NIST Cybersecurity Framework, along with specific guidelines like NIST SP 800-53 and NIST SP 800-171, defines best practices for managing cybersecurity risks and ensuring system integrity.

Figure 3 The cybersecurity framework provides a structured approach to cybersecurity risk management, incorporating best practices and guidance. Source: NIST

These standards heavily influence the design and implementation of secure firmware within semiconductor systems, helping organizations meet regulatory compliance and industry standards. With strong encryption, secure boot processes, and robust key management, firmware embedded in semiconductor chips must comply with NIST standards to ensure that systems are protected against evolving threats.

3. Trusted Computing Group (TCG)

TCG defines industry standards for hardware-based security technologies, including TPMs, which are widely used in semiconductor systems for secure authentication and encryption. TCG’s specifications, such as the TPM 2.0 standard, enable the creation of a hardware-based root of trust within a device.

This ensures that even if the operating system is compromised, the underlying hardware remains secure. The integration of TCG standards into firmware helps strengthen the security posture of semiconductor devices, making them resilient to physical and remote attacks.

Impact of firmware security on different Industries

Secure firmware embedded in semiconductors is crucial in advancing various sectors, ensuring the protection of data and systems at a foundational level. Here’s how it’s benefiting key segments:

1. Financial sector

Secure firmware is essential in safeguarding financial transactions and sensitive data, particularly in banks, payment systems, and online platforms. Self-encrypting drives and hardware-based encryption ensure that financial data remains encrypted, even when stored on physical drives.

Implementing security protocols such as Secure Hash Algorithm (SHA), Advanced Encryption Standard (AES), and public-key cryptography standards ensures that financial data is protected against cyber threats, reducing the risk of data breaches and fraud.

2. Healthcare

The healthcare sector is increasingly relying on digital technologies to manage patient data. Secure firmware is critical in ensuring that health information remains protected across devices, from medical records to diagnostic machines.

By using encrypted semiconductor solutions and ensuring compliance with standards like Health Insurance Portability and Accountability Act (HIPAA), patient data is safeguarded from unauthorized access. The integration of secure boot processes and data encryption protocols, such as AES-256 and RSA, prevents data leakage and ensures that sensitive health records remain confidential.

3. Government and national security

Government agencies rely heavily on secure hardware solutions to protect sensitive national data. Secure firmware within semiconductor devices used by government systems ensures that classified information, defense data, and communications remain secure.

Through the implementation of NIST-approved cryptographic algorithms and TCG’s trusted hardware standards, government systems can resist both local and remote threats. This security infrastructure supports national defense capabilities, from intelligence gathering to military operations, indirectly enhancing national security.

4. Critical infrastructure

The protection of critical infrastructure, such as power grids, transportation systems, and communications networks, is paramount for the functioning of society. Secure firmware in semiconductors enables these systems to operate securely, preventing cyberattacks that could compromise national safety.

Protocols such as SPDM help ensure that all components of critical infrastructure can communicate securely, while hardware-backed encryption ensures that even if systems are breached, data integrity is maintained.

5. Manufacturing and industrial control systems

In manufacturing environments, industrial control systems that manage production lines, robotics, and automated systems need to be protected from cyber threats. Secure firmware embedded in the semiconductor chips that control these systems helps prevent cyberattacks targeting production processes, which could lead to significant financial losses or safety issues.

For instance, the use of TCG’s TPM technology enables secure authentication and encryption of communication between devices, ensuring that industrial systems remain operational and tamper-free.

6. Defense and aerospace

In the defense and aerospace sectors, secure firmware is indispensable for the integrity of both commercial and military technologies. From satellites to weapon systems, semiconductor-based firmware security ensures the protection of classified military data and technologies from cyber espionage and attacks.

With the growing adoption of TPMs and other hardware-based security solutions, defense technologies become more resilient to attacks, ensuring the protection of national interests.

Implications for national and global security

As industries become more digitally interconnected, the need for secure hardware has never been more pressing. Secure firmware plays an essential role in protecting data at the hardware level, preventing unauthorized access and ensuring the integrity of information even in the event of physical tampering. This level of protection is vital not only for corporations but also for government institutions and critical sectors that rely on unbreachable security measures.

The ongoing development and refinement of firmware security in semiconductors align with broader global priorities surrounding cybersecurity. Through cutting-edge technologies like self-encrypting drives, secure firmware helps mitigate the risks associated with cyberattacks, such as data theft or system compromise, providing a layer of defense that supports global digital infrastructure.

The semiconductor industry is constantly evolving, pushing the boundaries of what is possible in terms of speed, efficiency, and security. As part of this progress, companies in the semiconductor industry are investing heavily in the development of advanced security measures embedded in their hardware solutions. This innovation is not only crucial for the companies themselves but has far-reaching implications for industries that rely on secure technology, from finance to healthcare, education, and government.

This innovation is not only beneficial for the industries adopting these technologies but also plays a significant role in driving broader policy and technological advancements. As organizations continue to develop and deploy secure semiconductor systems, they contribute to a more resilient and trustworthy digital ecosystem, indirectly bolstering national interests and global technological leadership.

The ongoing development of firmware security in semiconductor systems represents a critical effort in the fight against cyber threats and data breaches. While often unnoticed, the impact of these technologies is profound, helping to secure the digital infrastructure that underpins modern society.

As the semiconductor industry continues to innovate in this space, it contributes to the ongoing enhancement of security standards, indirectly supporting global technological leadership and contributing to a more secure digital world.

Karan Puniani is a staff test engineer at Micron Technology.

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The menu is navigated using a rotary encoder, and each channel has an LED indicator. Two lights can be set to either automatic or manual mode independently. The air pump operates at 30 Hz, and its duty cycle can be adjusted from 10% to 20% in 5% increments, super silent! (The bobbin was rewired to work with DC.) The water pump can be toggled on or off for maintenance purposes. A DS3231 real-time clock is used, powered by a custom lithium-ion backup battery with integrated charging circuitry. An AT24C32 EEPROM is used for memory storage. The software is developed using the Arduino IDE. submitted by /u/ElectronSurf [link] [comments]

Використання штучного інтелекту в публічному управлінні: виклики, можливості, перспективи kpi нд, 05/18/2025 - 14:47

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I've been wanting a curve tracer for some time, but I don't like the prices for "vintage" commercial equipment. I learned about the "Octopus" just recently and decided to give it a go. It still needs final touches, like mounting the transformer with double sided tape and adding a fuse, but otherwise it is done. I used the design found on qsl dot net. It seemed dead simple and there's always room to perform mods, like adjustable voltage and current. For now, we'll see how this works out. I built the BOM on mouser for under $60 shipped. Some items like the power cord, pomona test clips, and proto board I already had on hand. I used a drill press to drill the front and rear panels. I used MS Paint to create templates for drilling the banana jacks, power switch, and BNC jacks. Anyway, fun stuff! We'll see which of my scopes will do the best job. submitted by /u/vtfrotex [link] [comments]

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Лабораторія тунельної та електронної мікроскопії ФМФ – об'єкт національного надбання України kpi пт, 05/16/2025 - 21:59

Нові можливості дуальної освіти: КПІ ім. Ігоря Сікорського розширює співрацю з Melexis-Україна kpi пт, 05/16/2025 - 20:29

Tawazun Council (an independent government entity that works closely with the Ministry of Defence and security agencies in the United Arab Emirates), aerospace & defense company RTX of Arlington, VA, USA, and Emirates Global Aluminium (EGA, the world’s largest producer of ‘premium aluminium’, and the largest industrial firm in the United Arab Emirates outside the oil and gas industry) have signed a memorandum of understanding (MOU) to establish EGA as a new producer of gallium. EGA is equally owned by Mubadala Investment Company of Abu Dhabi and the Investment Corporation of Dubai, and is the largest company jointly owned by the two Emirates...

A recent Design Idea, “Three discretes suffice to interface PWM to switching regulators,” demonstrated one way to use PWM to control the output of a typical switching voltage regulator. There were some discussions in the comments section about circuit behavior, which influenced design modification. Here’s a low-cost design that evolved in light of those discussions. A logic gate IC, an op-amp, and a few resistors and capacitors buffer a PWM and supplies a signal to the regulator’s feedback pin, Figure 1.

Figure 1 A microprocessor produces a 12-bit, 20 MHz, PWM signal that controls a switching voltage regulator using an inverter IC, an op-amp, resistors, and capacitors to buffer the signal for the regulator’s feedback pin.

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

For various reasons, it’s difficult, if not impossible, to control a regulator’s output voltage beyond a certain level of accuracy. This design proceeds with a PWM having 12 bits of resolution in mind, operating at a frequency of approximately 4900 Hz.

It’s easy these days to find microprocessors (µPs) that can produce a PWM clocked at 20 MHz. However, the supply currents running through that IC’s power supply bonding wires can cause voltage drops. This means that the PWM signals don’t quite swing to the rails. Worse yet, if the currents vary significantly with the µP’s tasks, the voltage drops can change, and it might not be possible to calibrate the errors out. A simple solution is to buffer the µP with logic gates (typically inverters), which draw negligible current except during switching transients. The gates can be powered from a clean, accurate voltage source, the same as or close in value to that which powers the µP.

The inverter in Figure 1 is a 74LVC2G14GW,125 IC whose paralleled outputs drive an op-amp-based low-pass filter whose passive components are of sufficiently high impedances to negligibly load those outputs. When powered from 3 V or more, this dual inverter has an output resistance of less than 15 Ω from -40°C to +85°C. (If you need to operate the µP at 1.8 V, parallel the 6 inverters of a 74LVC14AD,118 for a less than 19 Ω result.)

The TLV333IDBVR op-amp has a maximum input offset voltage of 15 µV (the maximum offset is specified for a 5-V supply; an unknown increase can be expected if the supply voltage is lower).

Its typical (maximum are not specified) input currents are 150 pA from -40°C to +85°C, contributing an offset through R1, R2, and R3 of 115 µV. At 1.8 V, ½ LSb for a 12-bit signal is 220 µV (370 µV with a 3.0-V supply.) The filter settles to much less than that 12-bit ½ LSb voltage in 10mS and has a peak (not peak-peak) ripple of less than 50µV.

R4 and R5 should be chosen so that the intended most positive op-amp output voltage multiplied by R4 / (R4 + R5) is at most slightly greater than Vfb. This allows a regulator output of Vfb. This ratio could be smaller if the minimum desired regulator output is larger than Vfb. The resistors’ parallel combination should be the value specified by the regulator for the single resistor connected between Vfb and ground, typically 10 kΩ. R6 should be set in accordance with the desired range of output voltages.

The allowed range of PWM duty cycles should exclude extremes for at least two reasons. First, the op-amp output is only guaranteed to swing within 70 mV of each rail (with a 10k load connected to half of the supply voltage.) Second, the processor, GPIO in particular (but also the gate to some extent), likely has unequal rise and fall times and delays. Although these differences are small, they have their greatest effects on accuracy at duty cycle extremes, which therefore should be avoided. Fortunately, accommodating these limitations has a negligible effect on functionality.

In this design, the output voltage is linear with the duty cycle. The regulator’s loop gain is unchanged from that of standard operation. With the regulator disabled until the PWM filter output settles, there are no startup issues. Finally, there is negligible inherent injection of noise into the feedback pin from an external supply.

Christopher Paul has worked in various engineering positions in the communications industry for over 40 years.

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