# Run SPICE on Your Imported Altium and Cadence Boards Run built-in ngspice on imported Altium and Cadence boards in Flux. See reset and supply RC results from BeagleBone Black and LimeSDR designs. Written by [Nico Tzovanis](https://flux.seobdtools.com/nico) Published Nov 2026 - 4 min read ![Run SPICE on Your Imported Altium and Cadence Boards](https://flux.seobdtools.com/p/assets/blogs/spice-simulation-imported-altium-cadence-boards/main.webp) Flux runs SPICE on existing circuits in imported Altium and Cadence designs with built-in ngspice. We used a BeagleBone Black reset network and a LimeSDR supply filter to get DC voltage, cutoff frequency, and rise time from the imported circuits. ## Import the board. Ask for the response. The workflow starts with the design you already have. Import it into Flux, identify the circuit question, and ask the AI hardware engineer to select the network, state the model, and run the analyses. For the six-layer, 459-part BeagleBone Black Rev D Cadence/Allegro import, the question was reset timing: > Simulate the existing reset RC network. Run a DC operating point, an AC sweep, and a transient startup. Report the steady-state voltage, corner frequency, and 10–90% rise time. Explain how the results relate to the imported resistor and capacitor values. For the 12-layer, 858-part LimeSDR-USB Altium import, the question was supply filtering: > Simulate an existing supply RC filter from this design. Use a 1 mA load. Report the DC output, cutoff frequency, 10–90% rise time, and attenuation at 100 kHz. 1. **Read the circuit.** Flux identifies the resistor, capacitor, source, and output node in the imported schematic. 2. **Run ngspice.** It runs the operating point, AC sweep, and transient analysis for the selected network. 3. **Explain the results.** It reports numerical measurements and connects them to the circuit's RC time constant. ## The model behind the measurements Flux modeled each network with ideal sources, resistors, and capacitors: an unloaded reset RC for BeagleBone Black, and a supply RC with a constant 1 mA load for LimeSDR. Rise time is measured from 10% to 90% of the output step. The three analyses answer different questions. The DC operating point gives the settled output. The AC sweep gives the small-signal response over frequency. The transient analysis shows how the output changes with time after the input rises. ## BeagleBone Black: reset timing The simulated network is R14 (10 kΩ) and C24 (2.2 µF), driven by an ideal 3.3 V source, with the output measured at C24 pin 1 relative to GND\_SIGNAL. The imported reset network produced **3.300000 V DC**, a **7.23 Hz corner**, and a **48.3 ms rise time**. ![Flux ngspice results for the BeagleBone reset network, including a 3.300000 V operating point and a 48.33894 ms 10–90% rise time](https://flux.seobdtools.com/p/assets/blogs/spice-simulation-imported-altium-cadence-boards/reset-results.webp) DC and transient measurements from the reset RC simulation in Flux. For a first-order RC network, the corner frequency is `fc = 1 / (2πRC)`. A 7.23 Hz corner corresponds to a time constant of about 22 ms. The 10–90% rise time is approximately `2.2 × RC`, which gives 48.4 ms and agrees with the simulated 48.3 ms. That turns an imported reset circuit into a timing result. The useful question is no longer just which parts are connected, but how long the reset node takes to rise. ## LimeSDR: supply filtering under load The simulated network is R33 (10 Ω) and C74 (1 µF), with an ideal 1.8 V source on VCC1P8\_LMS and the output measured at NetC74\_1 relative to ground. The supply RC produced **1.790 V DC at a 1 mA load**, a **15.9 kHz corner**, a **22.0 µs rise time**, and **−16.07 dB at 100 kHz**. ![Flux simulation output showing 1.790000 V DC with a 1 mA resistor current and frequency-response measurements including minus 16.0722 dB at 100 kHz](https://flux.seobdtools.com/p/assets/blogs/spice-simulation-imported-altium-cadence-boards/supply-results.webp) The supply filter's DC drop and AC attenuation are measured in the same workflow. The 15.9 kHz corner corresponds to a time constant of about 10 µs. Multiplying by 2.2 predicts a 22 µs rise time. At 100 kHz, the frequency is about 6.3 times the corner, so the first-order low-pass response predicts about −16.1 dB, consistent with the ngspice result. The DC result answers the load question. The AC result answers the filtering question. The transient result shows the settling speed. Together, they describe the selected circuit more clearly than its component values alone. ## Ask a specific circuit question Start with the network and the decision you need to make. For reset, ask when the node reaches its threshold. For a supply filter, specify the load and the frequency you want to attenuate. Ask Flux to state the model and report the measured quantities. If your imported board has a first-spin symptom instead, see [how Flux diagnosed and corrected a regulator divider on an imported Altium design](https://flux.seobdtools.com/p/blog/first-spin-debug-imported-altium-board). That example follows the fault from the symptom through the saved resistor value and BOM. Source designs: [BeagleBone Black by BeagleBoard.org](https://github.com/beagleboard/beaglebone-black) (CC BY-SA 3.0) and [LimeSDR-USB by MyriadRF](https://github.com/myriadrf/LimeSDR-USB) (CC BY 3.0). Screenshots show results from the imported designs. [Start Free Trial](https://flux.seobdtools.com/signup) ## About the author [Nico Tzovanis](https://flux.seobdtools.com/nico) Nico is a professional electronics and PCB design engineer at Flux. Find him on Flux [@nico](https://flux.seobdtools.com/nico) Let’s start building Build your big idea together with Flux. All you need to do is describe what you want to make, or what problem you want to solve. Flux will work with you to make it a reality. ![Close-up photo of a PCB made with Flux, with an ESP32 module, buttons, and a microSD slot.](https://flux.seobdtools.com/p/assets/blogs/miscellaneous/sidebar-cta-pcb.webp) [Try it Free](https://flux.seobdtools.com/signup) ## Related Content [ ![Teal isometric illustration of an SDR circuit board in an open enclosure, with a regulator feedback divider highlighted for inspection](https://flux.seobdtools.com/p/assets/blogs/first-spin-debug-imported-altium-board/main.webp) ### Debug an Imported Altium Board From the First-Spin Symptom 3 Min Read](https://flux.seobdtools.com/p/blog/first-spin-debug-imported-altium-board)[ ![a space-themed background with stars and a floating astronaut helmet to the left. Large, bold text reads '6 Prompting Tips to Get the Most Out of Copilot', indicating a focus on maximizing the use of a digital assistant or tool.](https://flux.seobdtools.com/p/assets/blogs/copilot-6-prompting-tips/main.webp) ### 6 Prompting Tips to Get the Most Out of Copilot 6 Min Read](https://flux.seobdtools.com/p/blog/6-prompting-tips-to-get-the-most-out-of-copilot)[ ![Isometric teal line drawing on a dark background: a circuit board and its open enclosure on a workbench, with connected checkpoints that lead from a plan to a finished device](https://flux.seobdtools.com/p/assets/blogs/ai-adoption-hardware-teams-customer-success/main.webp) ### AI Adoption Is a People Problem: How Flux Customer Success Gets Hardware Teams to ROI 7 Min Read](https://flux.seobdtools.com/p/blog/ai-adoption-hardware-teams-customer-success)[ ![Glowing teal isometric line art of an isolated AC/DC power board with a transformer across a slot, next to a metal enclosure, on a dark background](https://flux.seobdtools.com/p/assets/blogs/creepage-and-clearance-pcb/main.webp) ### Creepage vs. Clearance: A Worked Example on an Isolated Power Board 10 Min Read](https://flux.seobdtools.com/p/blog/creepage-and-clearance-pcb)[ ![Flux for Librarians](https://flux.seobdtools.com/p/assets/blogs/flux-for-librarians/main.webp) ### Flux for Librarians 4 Min Read](https://flux.seobdtools.com/p/blog/flux-for-librarians)[ ![Handwritten sketches of a modern electronic device prototype](https://flux.seobdtools.com/p/assets/blogs/hardware-startup-ideas/main.webp) ### Is Your Hardware Startup Idea Worth Building? 7 Min Read](https://flux.seobdtools.com/p/blog/is-your-hardware-startup-idea-worth-building) See All (6) ## Let’s start building. Let’s build your idea together. All you need to do is describe what you want to make, or what problem you want to solve. Flux will work with you to make it a reality. [Try it Free](https://flux.seobdtools.com/signup) ![Close-up of a Flux-designed printed circuit board](https://flux.seobdtools.com/p/assets/homepage-v2/mission-visual.webp)