The hottest Circuit Design Substack posts right now

And their main takeaways
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Cursed circuits #3: true mathematics

lcamtuf’s thing • 3877 implied HN points • 22 Dec 25
🕹 Technology Circuit Design
  1. An op-amp simply amplifies the voltage difference between its inputs by a huge factor, and with feedback you force its inputs to be nearly equal so passive parts (resistors, diodes, caps) can be arranged to perform math instead of just gain.
  2. Addition and subtraction are straightforward: resistor networks can average or sum signals and a non‑inverting amplifier scales them to produce a true sum, while difference amplifiers give Vout ≈ VA − VB and can be biased to work on a single supply.
  3. Harder operations are possible too: multiplication/division can be done with log/antilog converters that use the diode’s exponential V–I curve plus a summing stage, and integration is implemented by charging a capacitor with a controlled current to produce precise ramps, though these analog tricks need careful biasing and have practical limits (rails, linearity, noise).

Cursed circuits #2: switched capacitor lowpass

lcamtuf’s thing • 3265 implied HN points • 04 Dec 25
🕹 Technology Circuit Design
  1. You can build a lowpass filter using just capacitors and a switch instead of resistors. This method is simpler and can lead to interesting circuit designs.
  2. The switch in this setup changes the connection of the capacitors, allowing them to charge and affect the signal based on their voltages. This simulates resistor-like behavior, even though no resistors are used.
  3. By adjusting the frequency of the switching, you can control how the filter responds to different input signals. This gives you flexibility in analog signal processing.

PCBs, ground planes, and you

lcamtuf’s thing • 7142 implied HN points • 28 Jan 25
🕹 Technology Circuit Design
  1. Copper pours on PCBs help improve signal quality by providing better pathways for electrical currents. They make it easier for circuits to work well at high speeds.
  2. These copper areas also help reduce radio frequency interference to meet certain regulations. This is important for keeping devices running smoothly and within legal limits.
  3. While using copper pours can make PCB design easier, it's essential to be careful. Poorly executed layouts can create problems, especially in high-speed projects.

Which filters are Noisier – Analog or Digital? Part 2

filterwizard • 19 implied HN points • 19 Sep 24
🕹 Technology Circuit Design
  1. When comparing analog and digital filters, analog filters tend to perform better in terms of noise, especially at low frequencies. Digital filters can introduce quantization noise that isn't present in analog filters.
  2. Digital filters, specifically the Direct Form filter, can have significant noise gain, which means they can amplify noise from quantization, making their performance worse in certain situations.
  3. To improve the noise performance of digital filters, increasing the bit depth of the processing can help, but there are also alternative filter topologies that can reduce noise without needing more bits.

When the mask slips - a cautionary (if ancient) tale of IC quality

filterwizard • 59 implied HN points • 01 Sep 24
🕹 Technology Circuit Design
  1. Don't assume that all ICs perform the same, even if they look similar. Small changes in production can lead to big differences in quality.
  2. Working with audio equipment requires attention to detail in filtering processes. It's essential to ensure that all components meet specific performance standards.
  3. When using older components, always check for changes in manufacturing. Even slight variations can drastically affect audio quality, as seen with the NE5532 op-amps.
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Choosing an op-amp for your project

lcamtuf’s thing • 4081 implied HN points • 03 Jan 25
🕹 Technology Circuit Design
  1. When selecting op-amps for projects, avoid using older models like LM741 and LM324, as modern options perform much better and are easier to use.
  2. Look for op-amps with rail-to-rail input and output capabilities, which allow for better voltage range handling and simplify your circuit design.
  3. Focus on key parameters like bandwidth, output current, and noise specifications, but remember that many modern op-amps have decent performance that meets the needs of most hobby projects.

Building a decent microphone amplifier

lcamtuf’s thing • 2856 implied HN points • 30 Mar 23
🕹 Technology Circuit Design
  1. Building a good far-field microphone kit requires attention to microphone sensitivity and selecting a suitable op-amp.
  2. Creating a basic but effective circuit architecture for a microphone amplifier involves understanding current-to-voltage conversion and noise reduction techniques.
  3. To avoid issues like over-amplification and background noise, solutions such as manual gain control and automatic gain control (AGC) can be implemented in microphone amplifier circuits.

❄️Cubits in a Fridge: Make Quantum Great Again (Feat Himadri of SemiQon)❄️

State of the Future • 19 implied HN points • 04 Dec 24
🕹 Technology Circuit Design
  1. Silicon spin qubits are smaller and cheaper than other types, making them more scalable. They can potentially revolutionize quantum computing by using existing semiconductor technology.
  2. Cryo-CMOS technology allows quantum computers to operate at very low temperatures, which is essential for maintaining quantum states. This can also help reduce cooling costs for data centers, which spend billions on keeping their systems cool.
  3. The focus in quantum computing is shifting from just the number of qubits to how efficiently they perform operations. Spin qubits might have an advantage here due to their longer coherence times and faster gate operations.

Yet More On Decoupling, Part 1: The Regulator’s Interaction with capacitors

filterwizard • 0 implied HN points • 07 Sep 24
🕹 Technology Circuit Design
  1. Using Y5V capacitors can be tricky. Always check how the DC voltage affects their capacitance because it can drop much lower than expected.
  2. Linear dropout regulators (LDOs) can have increasing output inductance when the load current decreases. This can cause unexpected peaks in impedance, so adding a bypass capacitor can help smooth things out.
  3. Simulating circuits before building them is really helpful. It helps catch problems early and saves time in the long run.

Yet More On Decoupling, Part 4 – Don’t Get Into A Macromuddle!

filterwizard • 0 implied HN points • 08 Sep 24
🕹 Technology Circuit Design
  1. Many op-amp simulation models don’t accurately show how they react to power supply changes. This makes it hard to trust the results from these models.
  2. Just because an op-amp is high quality doesn't mean its simulation model will behave well in tests. It's important to check each model individually.
  3. Finding a reliable op-amp model for testing took a lot of effort. Even after trying many, only a few performed as expected.

Yet More On Decoupling, Part 5 – When Harry Regulator Met Sally Op-Amp

filterwizard • 0 implied HN points • 08 Sep 24
🕹 Technology Circuit Design
  1. Choosing the right decoupling and regulator output capacitors is important. These choices can affect how well your op-amp circuits work.
  2. Temporary signals on an op-amp's supply pins can impact its output. This can be critical if your system needs to be very accurate.
  3. Using too much of a certain type of capacitor can lead to unexpected issues. It's better to choose components that match the recommendations from manufacturers.

Yet More On Decoupling, Part 6 – steering in the right direction

filterwizard • 0 implied HN points • 08 Sep 24
🕹 Technology Circuit Design
  1. The choices you make on power supply and decoupling components can significantly affect how accurately an op-amp performs. It's important to choose components wisely.
  2. Using larger decoupling capacitors generally leads to better performance by reducing fluctuations in the power supply that can affect the output of the amplifier.
  3. Don't assume low ESR capacitors are always best; sometimes, adding a bit of resistance can actually improve performance by helping to manage fluctuations in power.