Ring oscillator help
Hi!👋
Does anyone know how to make a ring oscillator , using inverters, which will be connected to a buffer and then subsequently to an LED to “show” to frequency? I’ve been stuck on this for TWO days now😢😅. I tried using tinkercad and LTspice but to no avail. Also, I can seem to get my frequency to less than 5Hz to see the LED flashing the frequency.
I’ve attached a screenshot of the question as well as my LTspice simulation.
I’ve tried on tinkercad and kept on blowing the IC. Any help is appreciated. 🙏 I tried calculations too
1
u/kthompska 8h ago
What do your inverters look like? For very large RC time constants in a topology like this, you need to use extremely weak inverters. If you don’t, the slow rise and fall times will keep the inverter conducting a lot of totem pole current (from Vdd to gnd).
You have an RC time constant of 1.6s (8s for 5 stages) but unless you have a large hysteresis built into each inverter, the very slow signals will hover all around your inverter trip point. This will make the frequency fast and consume even more totem pole current.
There are much better ways to do ring oscillators. Current starving each inverter will help a lot (separate current sources into each inverter power pin). Also for very low frequencies you either need a very large number of series inverters (very wasteful) or much better to just run the ring at a higher natural frequency and divide down the output.
1
u/Worldly-Device-8414 5h ago
As is, your LED drive is not from a buffer, but from one of the slow switching sections which, as mentioned, is likely to be causing heating.
Consider using a chip (assuming CMOS) with hysteresis on the inputs.
Increasing the 10k's will slow the frequency.
2
u/alexforencich 9h ago
Well, if you keep blowing the chip then you're probably doing something wrong with the power and ground connections, and looking at your simulator schematic is not going to help, need a pic of the breadboard.