Using a CNT/DLY Block as a Deglitch Filter

Using a CNT/DLY Block as a Deglitch Filter

Signal Conditioning Technique

This technique can be used in any GreenPAK, since each GreenPAK includes CNT/DLY blocks.

Deglitch / debounce filters are common when it’s necessary to eliminate glitches - spurious signal transitions. Glitches may occur in many cases: for example, when a button is being pressed/released, or when a voltage level is very close to a threshold (of an input PIN or analog comparator) and there is no hysteresis or Schmitt trigger.

Figure 13 Example Deglitch Delay Options

 

There are 3 possible edge-triggered options to configure a deglitch delay: rising, falling or both. In this case delay block will filter pulses shorter then delay value with corresponding polarity: active High for rising edge, active Low for falling edge, both High and Low for both edge delay. See diagram below:

Figure 14 Edge Delay Behavior

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