Schmitt Trigger Input

Hi guys,

I would like to know what is Schmitt Trigger?

How is it differ from a TTL buffer?

For example the microcontroller port buffer type is Schmitt Trigger Input can i just send a logic high of 5V to it simillar to TTL buffer? If no? How does the interface circuit look like ( Do recommend me a chip to do it )

Hope I'm not asking too much. Thanks

A Scmidt Trigger is simply a device or circuit with hysteresis built into the input threshold. Hysteresis is a condition in which the trigger threshold changes when the output changes in such a way as to maintain the output level. For example when the input goes high and the output changes state, feedback from the output lowers the threshold a small amount so that the input must drop a small amount for the output to change back this change is the hysteresis voltage.
Schmidt triggers are usually used for either noisy or slowly changing signals so that the output is less noisy.
Logic devices use Schmidt Triggers and any analog comparator can be configured as a Schmidt Trigger.
An input with a Schmidt Trigger will interface directly to any input with the same voltage. You can check this by reading the specification of the chip. It will give you the low, high and hysteresis levels.

Hi,
There are many application of Schmitt Trigger.
It can be used to generate rectangular signals from periodic signals.

The main use of Schmitt Trigger is to prevent the output to change in the presence of Noise Spikes. This is due to the hysteresis property of the Schmitt Trigger

Thanks
Shaikh Sarfraz

here is a file "Oscillators for Microcontrollers"
it may clarify your questions
h**p://www.intel.com/design/mcs51/applnots/23065901.pdf#search=%22schmitt%20trigger%20VS%20TTL%20buffer%20inurl%3Aintel%22

it is to convert noisy sine signal in to perfect noise free square signal.....so it is self explained it can be used in digital circuits to regenerate perfect square signal from affected signals...

schmitt input has different high input threshold and low input voltage

threshold, this will help eliminate some noise at near threshold and

avoid output oscilating.

best regards

zhiling0229 said:

Hi guys,

I would like to know what is Schmitt Trigger?

How is it differ from a TTL buffer?

For example the microcontroller port buffer type is Schmitt Trigger Input can i just send a logic high of 5V to it simillar to TTL buffer? If no? How does the interface circuit look like ( Do recommend me a chip to do it )

Hope I'm not asking too much. Thanks

Click to expand...

A schmitt trigger takes a slow changing or noisy signal that would create many pulses as it crosses a set logic threshold (ie 1/2 Vcc in CMOS) and cleans it up into a single clean pulse by using hysteresis ( feedback) to create two distinct thresholds to change state.

This means the signal can't osillate at a single input voltage.

zhiling0229 said:

Hi guys,

I would like to know what is Schmitt Trigger?

How is it differ from a TTL buffer?

For example the microcontroller port buffer type is Schmitt Trigger Input can i just send a logic high of 5V to it simillar to TTL buffer? If no? How does the interface circuit look like ( Do recommend me a chip to do it )

Hope I'm not asking too much. Thanks

Click to expand...

Hi

Any schmitt device has got fixed voltage level for logic 0 and logic 1

Any voltage under 0.9v count as logic 0 and over 0.9v respect to supply to the device cont as logic 1
Look in the data sheet of CD4093 you will see that

Rajguru

Hi Rajguru,
Im sorry, but you must minimum so detailed check for a Schmittrigger_input data sheet...
On a CD 4093 data collection i.e. I cannot find a 0.9V limit, than I dont know "fixed logic level" logic devices :-(,
I mean-their are logic threshold defined (of course), but their value is some variant, nothing is absolutely fixed in our life...
In your CD4093 data sheet i.e. is exactly to find: input low is every time less as 1.3V(5V supplying) and less as 4.5V (15V supplying) and so on.
Same for input highs: higher as 2.75V & 8.1V... I can see nothing over 0.9V and fixed thresholds-sorry.
Best greetings!
K.