Schmitt Trigger IC Switching Noise Countermeasure (Patreon)

The CD40106 Schmitt Trigger IC is often used as an oscillator in DIY synthesizers.

I designed a metallic noise circuit using the CD40106 for a Hi-hat module design.

However, I got terrible noise on the power supply line in sync with the switching of the CD40106.

I installed a 100uF electrolytic capacitor on VDD, but it did not have much effect. As you can see in the picture, there is about 500mV of ripple noise on the 12V power line.

Next, I limited the VDD current with a 330 Ohm resistor and installed a 100uF electrolytic capacitor. This measure was effective and reduced the ripple noise on the power supply line.

The Schmitt trigger circuit of the BOSS DR-110 also takes measures to install a limiting resistor on the VDD line.

The supply voltage of the DR-100 is 6 V and the limiting resistor is 100 ohms.

If you suffer from power supply noise in logic ICs, not limited to Schmitt triggers, installing a limiting resistor of several hundred ohms and an electrolytic capacitor on VDD may be a solution.