I have used TC1796 as a micro-controller to read the voltage values, by using FADC. The read values are ok. However, the FADC signal has spikes, when the are incremental encoder signal (A and B) are fed into the microcontroller.

The TC1796 only deals with 3.3 V. In the beginning, I found that the encoder signals are 0/5 V, then I have modified to 0/3.3V, but the noise (spikes) in FADC signal still exists.

The spikes usually occurs while the shaft of encoder is being moved, especially when it is faster then the higher noises occur.

I have done :

- The zener-diode is connected before going to the FADC in order to protect the higher voltage.
- Grounds are connected together.

How should the spikes can be removed?

 

Just put capacitors on the two micro input pins, which should remove all high freq noise (fast spikes).

Then the low freq edges should be debounced using a typical quadrature decoder in software.

 

I have already added C for both ENC signals , C=5nF, the spikes of FADC are still available. I have look through the pin plan. At 40 pins (for microcontroller input), the signal of FADC pin is opposite to ENC pins. Should C be added to the FADC input pin also?

 

I think you should show your schematic, that will make things easier.

Also if you have a 'scope photo of the "spikes" that helps too.

 

It was a mistake, when C was connected. I have decided to put RC filter then I found the wrong connection. After adding RC filter, everything is better.

Thanks so much for your suggestion.