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Industrial gas company Taiyo Nippon Sanso Corp (TNSC) of Tokyo, Japan (part of Nippon Sanso Holdings Group) says that a TNSC SR4000HT metal-organic chemical vapor deposition (MOCVD) reactor is being purchased by the University of South Carolina for R&D of advanced ultrawide-bandgap nitride materials and device technology...

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 partnered with Lessengers Inc of Seoul, South Korea — which provides optical components based on its patented direct optical wiring (DOW) technology — to offer a differentiated 800G DR8 transceiver. The transceiver will include POET’s transmit and receive optical engines and Lessenger’s Direct Optical Wiring (DOW) technology for a cost-effective solution for AI and hyperscale data center applications...

Sivers Semiconductors AB of Kista, Sweden (which supplies RF beam-former ICs for SATCOMs and photonic lasers for AI data centers) has announced a strategic partnership with optical communications device maker O-Net Technologies (Group) Co Ltd of Shenzhen, China to produce high-performance external laser sources, a critical component enabling next-generation AI data center architectures...

Editor’s note:

In this DI, high school student Tommy Liu modifies a popular low-cost DIY oscilloscope to enhance its input noise rejection and ADC noise with anti-aliasing filtering and IIR filtering.

Part 1 introduces the oscilloscope design and simulation.

Part 2 will show the experimental results of this oscilloscope.

Introduction

A digital oscilloscope is one of the most essential pieces of equipment for high school electrical and electronic labs. As useful and popular as it is for high schoolers, the cost of an oscilloscope can often be prohibitive. Professional digital oscilloscopes are generally expensive, with the entry cost of a basic model ranging from several hundred dollars to over a thousand dollars. One can argue that the advanced specifications and functionalities of these oscilloscopes often exceed most high school needs.

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

Low-cost DIY digital oscilloscopes provide another option for high schools—these oscilloscopes are inexpensive and typically cost less than a hundred dollars. The problem with DIY oscilloscopes is their performance—they lack measurement precision and the capability of noise immunization. Most DIY oscilloscopes only reach an effective resolution of 6 to 8 bits—even for those with a 12-bit ADC—due to poor noise isolation and rejection. These drawbacks limit DIY digital oscilloscopes from precision measurement and other more demanding applications in high school labs and clubs.

The first part of this design idea (DI) describes a practical, low-cost, and high-performance digital oscilloscope solution suitable for professional high school use, including precision signal measurement and analysis. The second part of this DI describes the experimental results obtained after building it.

The oscilloscope is based on a popular low-cost DIY platform. Analog and digital signal processing techniques, namely anti-aliasing filtering, and infinite impulse response (IIR) digital filtering, respectively, are implemented on the platform, significantly improving the noise rejection and measurement precision of the oscilloscope, with only a minor increase in cost.

Specifications ENOB

In many high school applications of oscilloscopes, an effective resolution of 6 bits to 8 bits is usually sufficient. However, for the most demanding professional high school STEM projects, sometimes a measurement precision within a few mV is required. As the full-scale range of these signals are typically within 3.3 V or 5 V, this requires a measurement precision of about one in a thousand (1/1000), or an effective number of bits (ENOB) of around 10 bits. Since the ENOB of ADCs is lower than their resolution, to achieve 10 bits of effective resolution, the scope’s ADC usually needs to be 12-bit or higher.

Signal bandwidth

Most high-school electronic projects deal with signals from DC to audio frequency (20 Hz to 20 kHz). An analog bandwidth (-3 dB) of 100 kHz is chosen, and the oscilloscope needs to maintain an effective resolution of 10 bits with an input frequency up to 20 kHz.

Table 1 summarizes the major specifications of the oscilloscope, including the precision requirement, input bandwidth, and necessary functions for various high-school users on electrical and electronic projects. As a low-cost solution for high schools, we determined the build of materials (BOM) cost should be less than fifty dollars.

Analog bandwidth (-3dB)	100 kHz
Resolution of ADC	12-bit
Maximum real-time sampling rate	1 MSPS
Effective resolution (ENOB)	10 bits (input from DC to 20 kHz)
Maximum input voltage	50 V (peak-peak)
Voltage division range	10 mV/div – 5 V/div
Time division range	5 s/div – 10 µs/div
Trigger sources	Internal/External
BOM cost	$50 max

Table 1 the major specifications of the oscilloscope, including the precision requirement, input bandwidth, and necessary functions for various high-school users on electrical and electronic projects.

Pros and cons of common DIY scope

The DSO138-mini, a popular type of DIY oscilloscope on the market, was chosen as the base platform for our oscilloscope. DSO138-mini uses STM32F103C8 MCU as its main processing unit, which offers built-in 12-bit, 1 MSPS ADCs [1]. It also has all the essential functions, such as input range and DC/AC selection, voltage division and time division control, along with trigger source control. Besides an LCD display, the DSO138-mini also supports an UART/USB link so that captured waveforms can be sent to a PC for higher resolution display, data measurement, and data storage. Priced at under $40, the DSO138-mini includes a standard oscilloscope probe, which gives value among DIY oscilloscopes with its functionalities and features.

The major issues with DSO138-mini, like many other DIY types of oscilloscopes, are inadequate measurement precision and noise rejection. As will be discussed in the next few sections, DSO138-mini lacks adequate anti-aliasing filtering capability, making it susceptible to input high-frequency noises. It also has large ADC noises, possibly coupled from noisy power rails of digital circuitry inside the microcontroller, making the effective resolution less than 9 bits even in its own self-test mode when there is no external input signal. These two problems of inadequate anti-aliasing filtering capability and large ADC noises make the DSO138-mini unsuitable as a precision signal measurement device in high school labs.

The new oscilloscope

To fix these issues, a new anti-aliasing filter and a digital filter (1st-order IIR) are implemented on the DSO138-mini platform. The experiment results (Part 2 of this DI) show that the new oscilloscope has a significant improvement over the original DSO138-mini in terms of input noise rejection and ADC noise reduction and is capable of precision signal measurement up to 10 bits (or 1/1000).

The block diagram of the oscilloscope is illustrated in Figure 1. The analog input is first processed by the signal conditioning circuit for input range setup and voltage division selection. The ADC in the MCU converts the analog input signal into digital code. The scope control program of MCU processes and formats the digital data, and sends it over to LCD display, and/or to PC via UART/USB link. Note that the blocks in the blue color, namely the anti-aliasing filter, and the digital post-processing, are the new functions that were added to the DSO138-mini, to bring up its measurement precision to above 10 bits.   

Figure 1 Block diagram of the modified DSO138-mini DIY oscilloscope platform where the blue blocks are the new functioned added.

Analog signal processing Anti-aliasing filter introduction

Digital oscilloscopes rely on ADCs to convert the analog input into digital code for further signal processing and storage, one important phenomenon that could damage the conversion precision is called aliasing. Shannon theorem states that if the highest input frequency exceeds one-half of the ADC sampling frequency, or Nyquist frequency, aliasing will happen; meaning that the high frequency components will fold back to the signal bandwidth and contaminate the input signal, Figure 2

Figure 2 When the highest input frequency exceeds the ADC sampling frequency (fs), aliasing will occur, and the sampled frequency will not represent the original input signal.

In theory, ADC sampling frequency should be set two times above the input signal bandwidth to avoid aliasing. In practice, this is usually not sufficient since analog input signals often contain high frequency noises coupled from noisy parts of the system, e.g., the power supply, and high frequency harmonic tones generated by the signal sources.

In high precision applications, anti-aliasing filters of low-pass type are used to filter away these high frequency components. Ideally, a high-order low-pass filter (LPF) with a sharp roll off is preferred and the cut-off frequency of the filter should be placed near the Nyquist frequency, or one half of the sampling frequency. Due to the slow roll off rate (-20 dB/dec) of low-cost 1st order LPFs, the -3dB cut-off frequency often needs to be set significantly lower than the ADC sampling frequency to be effective.

Anti-aliasing filter design

While many DIY oscilloscopes less than fifty dollars do not have any anti-aliasing filters at all, the DSO138-mini does provide limited LPF functions in its input signal conditioning circuits. Figure 3 illustrates the conceptual schematic of the analog front-end signal path of the DSO138-mini.

Figure 3 Conceptual schematic of the analog front-end signal path of DSO138-mini.

The first amplifier stage consists of input voltage division selection, LPF/frequency compensation, and a unity gain amplifier. The second stage is a non-inverting amplifier serving as a gain stage and a buffer to drive the ADC, with some attenuation adjustment capability at its input. The overall cut-off frequencies of the signal path are inadequate to effectively remove high frequency noises away from the input signal to avoid aliasing.

Table 2 summarizes the SPICE simulation results of the -3-dB cut-off frequencies at the oscilloscope’s different voltage division and attenuation configurations.

Voltage Division	Attenuation	Cut-off Frequency (-3dB)
10 mV	x1	599 kHz
	x2	598 kHz
	x5	593 kHz
0.1 V	x1	488 kHz
	x2	487 kHz
	x5	483 kHz
1 V	x1	813 kHz
	x2	805 kHz
	x5	798 kHz

Table 2 Cut-off frequencies (-3 dB) at different voltage division / attenuation configurations.

The -3dB cut-off frequencies range from about 500 kHz to 800 kHz, depending on the input range and attenuation settings. The built-in ADC of the MCU of DSO0138-mini has the highest sampling rate of 1 MSPS, and 500 KSPS or below is frequently used as the highest sampling frequency in many applications.

Apparently, these cut-off frequencies are too high for 500KSPS or even 1MSPS—they are all close to or higher than Nyquist frequency at 1MSPS. Severe aliasing and subsequent degradation in measurement precision would happen if the analog input contained high frequency noises. To resolve this problem, we need to introduce an LPF with lower cut-off frequencies.  

The right value of the cut-off frequency depends on the sampling rate or time division setup and the analog input bandwidth of the oscilloscope. Ideally, a customized anti-aliasing filter is implemented for each sampling rate/time division configuration. However, customized anti-aliasing filters will add hardware complexity and cost. In most high-school projects, we are mainly interested in the frequency from DC to audio frequency (20 kHz), with the highest sampling frequency of 500 KSPS to 1 MSPS. A cut-off (-3dB) frequency of around 100kHz is chosen for these applications.

Although the new anti-aliasing filter could be implemented at various locations in the input signal conditioning circuits, the best place is at the second amplifier stage, i.e., the ADC driver stage, so that the cut-off frequency is not affected by the input range and voltage division selections.

Figure 4 illustrates the conceptual schematic of the new anti-aliasing filter [2]. The capacitor, C_Filter, is added to the original second amplifier stage and put in parallel with the resistor, R6, forming a first-order LPF in an inverting amplifier configuration.

Figure 4 Conceptual schematic of the new first-order anti-aliasing LPF in an inverting amplifier configuration.

The -3 dB cut-off frequency is determined by the value of the C_Filter and R2 and given by the Equation 1.

Figure 5 shows the SPICE simulation results of the frequency response of the input conditioning circuits, including the newly added anti-aliasing filter, at Voltage Division of 0.1 V, Voltage Attenuation of 0 dB, and the C_Filter value of 1nF (R6 is 1.1 kΩ). The -3 dB cut-off is at 100 kHz. The filter cut-off frequency was found to be centered well around 100 kHz among all other voltage division and attenuation setups.

Figure 5 SPICE simulation results with frequency response of the input conditioning circuits, including the new anti-aliasing filter.

There is one additional benefit of C_Filter; it also lowers the output impedance of the amplifier which interfaces and drives the ADC. A lower output impedance can reduce the kick-back noise coming from the switch capacitor operation of the ADC [3].

Finally, when choosing the filter capacitor value in this type of topology, we also need to make sure that it does not cause issues of op-amp output slew rate and/or stability.

Digital signal post-processing Digital filter introduction

There are other noise sources in oscilloscopes that can damage measurement precision. Among them, noises on the ADC inside the MCU are of particular concern. This is because ADCs are sensitive to noises on their power supply rails and references. MCUs are known for their large digital switching noises and as a result, the signal-to-noise ratio (SNR) of their embedded ADCs are limited by these digital noises. The situation worsens in DIY oscilloscopes as little resources are available to be spent on reducing these digital noises.

The DSO138-mini, for example, has high frequency noises and ripples on its captured data even when the input analog signal is clean (with well-designed anti-aliasing filters). These ripples make precision measurement difficult.

Digital post-processing can be used to reduce these power supply and reference-induced noises. The ADC output digital code, or the raw data, goes through a digital LPF, with some of its high-frequency components (often noise) removed, before presenting to the display or other format of data output. The digital filter algorithms can be implemented either in MCU firmware or in PC programs when a PC is used for final display and data measurement. 

Digital filter design

DSO138-mini has two “terminals” for displaying waveforms. One is through an LCD for real-time waveform display. Because of its low resolution (320 x 240), the LCD is mainly used for bench waveform observation and monitoring. The oscilloscope also supports a UART/USB interface to transmit captured waveform data to a PC, where most precision measurements and signal analysis are performed. We therefore implement the digital post-processing program on the PC.

A first-order IIR filter is adopted for the digital signal post-processing [4]. The output and input relationship of a first order IIR filter is as follows:

The flow chart of the first-order IIR filter is shown in Figure 6.

Figure 6 Flow chart of the first-order IIR filter. IIR filters are widely used in various applications thanks to their simplicity and effectiveness.

The frequency response of the first-order IIR filter is shown in Figure 7. The pass-band width is decided by the coefficient, α. The smaller the α, the more attenuation to high frequency noises, with the cost of a smaller passband. Three different α values (0.5, 0.25, and 0.125) were plotted to compare their performances.

Figure 7 The frequency response of the IIR filter with three different α values: 0.5, 0.25, and 0.125.

The trade-off is between noise attenuation and useful signal bandwidth. Smaller α values can reject a wider band of noises but result in a smaller analog bandwidth.

For most high school projects, the input signal is from DC up to audio frequency (20 kHz). Therefore, we choose the value of α to be 0.25 as our default value for these purposes, with a -3 dB bandwidth of 23 kHz when ADC samples at 500 KSPS. The value of α is made programmable so that users can easily tune it for different applications.

Digital signal post-processing, if used properly, can significantly reduce the noises and ripples on oscilloscopes and improve measurement accuracy. We will demonstrate the effect of digital post-processing in Part 2.

Tommy Liu is currently a junior at Monta Vista High School (MVHS) with a passion for electronics. A dedicated hobbyist since middle school, Tommy has designed and built various projects ranging from FM radios to simple oscilloscopes and signal generators for school use. He aims to pursue Electrical Engineering in college and aspires to become a professional engineer, continuing his exploration in the field of electronics.

Related Content

• Designing antialias filters for ADCs
• Delta-sigma antialiasing filter with a mode-rejection circuit
• Three alternatives to your aliasing problems
• FIR and IIR digital filter design guide
• Fixed-point-IIR-filter challenges
• How to create fixed- and floating-point IIR filters for FPGAs

References

1. ST Microelectronics. (n.d.). Datasheet of STM32F103x8, Medium-density performance line Arm®-based 32-bit MCU with 64 or 128 KB Flash, USB, CAN, 7 timers, 2 ADCs, 9 com. interfaces. https://www.st.com/resource/en/datasheet/stm32f103c8.pdf
2. Franco, S. (1998). Design with operational amplifiers and Analog Integrated Circuits. McGraw Hill.
3. Reeder, R. (2011, June 20). Kicking back at high-speed, unbuffered adcs. Electronic Design. https://www.electronicdesign.com/technologies/analog/article/21798279/kicking-back-at- high-speed-unbuffered-adcs
4. of EECS, University of Michigan, Ann Arbor. (2002, August 2). IIR Filters IV: Case Study of IIR Filters, https://www.eecs.umich.edu/courses/eecs206/archive/spring02/notes.dir/iir4.pdf

The post Building a low-cost, precision digital oscilloscope appeared first on EDN.

Researchers are exploring a combination of optoelectronics components, artificial intelligence (AI), and analog drivers and amplifiers to seek new frontiers in biomedical sensing. Bill Schweber explores the design example of a non-invasive blood pressure monitor developed using LEDs, photosensors, and AI algorithms.

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Indium phosphide (InP)-based optical communications device developer and manufacturer HieFo Corp of Alhambra, CA, USA (formed from management buy-out of the chips business and wafer fabrication operations of Emcore Corp in May 2024) has launched multiple new high-efficiency continuous wave distributed feedback (DFB) InP lasers, designed to address the ever-increasing demands of silicon photonics-based optical transceivers....

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As vehicle architectures transition to hybrid and electric models, conventional battery systems are increasingly being supplemented or replaced by 48 V power sources. This shift is expected to become the new standard for future electric vehicles, as 12 V and 24 V power net systems reach their limits. 48 V systems enable advanced features, enhance passenger comfort, and improve efficiency by reducing currents and simplifying wire harness complexity. Additionally, the electrification of both primary and secondary power distribution systems requires replacing conventional relays and fuses. To support this development, Infineon Technologies AG (FSE: IFX / OTCQX: IFNNY) is launching the Power PROFET + 24/48V switch family, developed for the requirements of modern vehicle power systems.

The Power PROFET + 24/48V switch family is housed in a compact, TO leadless package and includes two high-side switch variants: the BTH50030-1LUA with an RDS(ON) of 3.0 mΩ and the BTH50015-1LUA with an RDS(ON) of 1.5 mΩ, which enables minimal power losses in high-current applications. The devices are ideal for the demanding requirements of today’s automotive electrical systems and for commercial and hybrid vehicles, as well as the next generation of electric cars, where they enable a safer, greener and more comfortable driving experience.

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Built-in protection and diagnostic functions such as short-circuit, over-current and over-temperature protection provide safety of the device. Diagnostic signals enable advanced fault detection and increase the reliability of the entire vehicle by preventing failure modes in the power supply network. The switches are housed in an 8-pin TO leadless package, reducing the footprint by 23 percent compared to, for example, D2PAK packages with similar thermal performance. The accuracy of the load current sense is ±5 percent after calibration and can be easily determined by reading an analog voltage at the IS pin. In addition, the switch family is PRO-SIL ISO switch 26262-ready and comes with a safety application note that supports the evaluation of hardware elements according to ISO 26262.

To enable seamless integration, the Power PROFET + 24/48V family is supported by the online simulation tool Infineon Automotive Power Explorer which is available in the Infineon Developer Center. The tool helps to calculate intrinsic fuse characteristics and visualize the sense current range for specific load currents, ensuring accurate and efficient implementation.

The post Power PROFET + 24/48V smart power switch family with lowest ohmic resistance optimizes automotive power distribution appeared first on ELE Times.

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Lumentum Holdings Inc of San Jose, CA, USA (which designs and makes optical and photonic products for optical networks and lasers for industrial and consumer markets) has announced new advancements in foundational indium phosphide (InP) photonic chip technologies designed to deliver higher bandwidth and more power-efficient connectivity for next-generation AI-driven data centers. Its latest InP innovations — enabling future 400Gbps-per-lane optical links, more efficient 200Gbps-per-lane optical links, and co-packaged optics — are being showcased in live demonstrations and a technical presentation in booth #2119 at the Optical Fiber Communications Conference & Exposition (OFC 2025) in San Francisco (1–3 April)...

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