Electronic – Voltage shifter distorts signal


I am trying to downshift a 5V TTL signal to 3V logic signal using NTB0102 level shifter. The connection is described below:

enter image description here

However, my oscilloscope measurements are distorted. Even the input signal (out of the microcontroller pin-pin connected) does not look like a true TTL 0-5V signal:

enter image description here

Placing caps on VCC does not help. Reversing the propagation way (0-3V input to 0-5V output) also produces ugly picture. Pulling UP/DOWN microcontrollre's output pin does not make a difference. Any ideas about what's going on?

The layout:

enter image description here

After someone suggested using 10x probes, I have an improvement in the output signal, but it still does not like a square wave:

enter image description here

Best Answer

Two more guesses:

  1. The scope probe compensation is set badly. The blue trace in your bottom scope plot looks like the poster case for this.

  2. You have the "coupling" for that traces set to AC instead of DC.