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Simple state variable active filter
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!
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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.
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EDOM Seminar Explores the Next Generation of Physical AI Robots Powered by NVIDIA Jetson Thor
The wave of innovation driven by generative AI is sweeping the globe, and AI’s capabilities are gradually extending from language understanding and visual recognition to action intelligence closer to real-world applications. This change makes physical AI, which integrates “perception, reasoning, and action,” the next important threshold for robotics and smart manufacturing. To help Taiwanese industries grasp this multimodal trend, EDOM Technology will hold the “AI ×Multimodal Robotics: New Era of Industrial Intelligence Seminar” on December 3, showcasing NVIDIA Jetson Thor, the ultimate platform for physical AI and robotics, and featuring insights from ecosystem partners who will share innovative applications spanning smart manufacturing, autonomous machines, and education.
As AI technology rapidly advances, robotics is shifting from the traditional perception and response model to a new stage where they can autonomously understand and participate in complex tasks. The rise of multimodal AI enables machines to simultaneously integrate image, voice, semantic, and spatial information, making more precise judgments and actions in the real world, making it possible to “know what to do” and “know how to do it.” As AI capabilities extend from the purely digital realm to the real world, physical AI has become a core driving force for industrial upgrading.
Multimodal × Physical AI: The Next Key Turning Point in Robotics
The seminar focuses on the theme of “Physical AI Driving the Intelligent Revolution of Robotics”, explores how AI, through multimodal perception and autonomous action capabilities, is reshaping the technical architecture and application scenarios of human-machine collaboration. Through technical sharing and case analysis, the seminar will help companies grasp the next turning points of smart manufacturing.
This event will focus on NVIDIA Jetson Thor and its software ecosystem, providing a panoramic view of future-oriented multimodal robotics technology. The NVIDIA Jetson Thor platform combines high-performance GPUs, edge computing, and multimodal understanding to complete perception, inference, decision-making, and action planning all at the device level, significantly improving robot autonomy and real-time responsiveness. Simultaneously, the platform is deeply integrated with NVIDIA Isaac, NVIDIA Metropolis, and NVIDIA Holoscan, creating an integrated development environment from simulation, verification, and testing to deployment, thus accelerating the implementation of intelligent robots and edge AI solutions. NVIDIA Jetson Thor also supports LLM, visual language models (VLMs), and various generative AI models, enabling machines to interpret their surroundings, interact, and take action more naturally, becoming a core foundation for advancing physical AI.
In addition to the core platform analysis, the event features multiple demonstrations and exchange sessions. These includes a showcase of generative AI-integrated robotic applications, highlighting the latest capabilities of the model in visual understanding and action collaboration; an introduction to the ecosystem built by EDOM, sharing cross-field cooperation experiences from education and manufacturing to hardware and software integration; and a hands-on technology experience zone, where attendees can see the practical applications of NVIDIA Jetson Thor in edge AI and multimodal technology.
From technical analysis to industry exchange, Cross-field collaboration reveals new directions for smart machines:
- Analyses of the core architecture of NVIDIA Jetson Thor and the latest developments in multimodal AI by NVIDIA experts.
- Case studies on how Nexcobot introduces AI automation in smart manufacturing.
- Ankang High School, which achieved excellent results at the 2025 FIRST Robotics Competition (FRC) World Championship, showcases how AI and robotics courses can cultivate students’ interdisciplinary abilities in education.
- Insights into LLM and VLM applications in various robotic tasks given by Avalanche Computing.
Furthermore, EDOM will introduce its system integration approaches and deployment cases powered by NVIDIA IGX Orin and NVIDIA Jetson Thor, presenting the complete journey of edge AI technology from simulation to application implementation.
The event will conclude with an expert panel. Featuring leading specialists, the discussion covers collaboration, challenges, and international trends brought by multimodal robotics, helping industries navigate and anticipate the next phase of smart machine innovation.
Driven by physical AI and multimodal technologies, smart machines are entering a new phase of growth. The “AI × Multimodal Robotics: New Era of Industrial Intelligence Seminar” will not only showcase the latest technologies but also aim to connect the supply chain in Taiwan, enabling the manufacturing and robotics industries to seize opportunities in multimodal AI. The event will take place on Wednesday, December 3, 2025, at the Taipei Fubon International Convention Center, with registration and demonstration beginning at 12:30 PM. Enterprises and developers focused on AI, robotics, and smart manufacturing are welcome to join and stay at the forefront of multimodal technology. For more information, please visit https://www.edomtech.com/zh-tw/events-detail/jetson-thor-tech-day/
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Nuvoton Releases Compact High-Power Violet Laser Diode (402nm, 1.7W)
Nuvoton Technology announced today the launch of its compact high-power violet laser diode (402nm, 1.7W), which achieves industry-leading optical output power in the industry-standard TO-56 CAN package. This product realizes compact size, high output power, and long-life, which were previously considered difficult, through our proprietary chip design and thermal management technologies. As a result, it contributes to space-saving and long-life optical systems for a wide range of optical applications.
Achievements:
1. Achieves industry-leading optical output power of 1.7W at 402nm in the industry-standard TO-56 CAN package, contributing to the miniaturization of optical systems.
2. Realizes long-life through proprietary chip design and thermal management technologies, reducing the running costs of optical systems.
3. Expands the lineup of mercury lamp replacement solutions, improving flexibility in product selection according to application.
Latest Addition
In addition, this product is newly added to their lineup of mercury lamp replacement solutions using semiconductor lasers, providing customers with new options. This enables flexible product selection according to application, installation environment, and required performance, improving the freedom of system design.
Its applications include:
・ Laser Direct Imaging (LDI)
・ Resin curing
・ Laser welding
・ 3D printing
・ Biomedical
・ Display
・ Alternative light source for mercury lamps, etc.
Nuvoton Technology Corporation Japan (NTCJ) joined the Nuvoton Group in 2020. As a dedicated global semiconductor manufacturer, NTCJ provides technology and various products cultivated over 60 years since its establishment, and solutions that optimally combine them. We value relationships with our customers and partners, and by providing added value that exceeds expectations, we are working as a global solution company that solves various issues in society, industry, and people’s lives.
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