schmit trigger design

[Rockzinstruz]

Hi....

I designed the schmit trigger circuit for converting triangular,sine and square waves at 1Hz to 1MHz.The circuit is working fine.Im using the HD74LS14 with +5V power supply.
But the circuit needs the input voltage 15V to convert the input signal especially for triangular wave.Why this problem is occuring?
I attached the below circuit for your reference.


View attachment 66979


Thanks,
Rockzinstruz

 

[dougy83]

I designed the schmit trigger circuit for converting triangular,sine and square waves at 1Hz to 1MHz.The circuit is working fine.Im using the HD74LS14 with +5V power supply.
But the circuit needs the input voltage 15V to convert the input signal especially for triangular wave.Why this problem is occuring?
I attached the below circuit for your reference.

Hi. I have no idea what you are trying to say... Can you please rephrase or provide a picture explaining what you want, and also what you are currently seeing (describe what is wrong with it also).

 

[Rockzinstruz]

I wants to convert the 2v sine and triangular wave to square wave at the frequency range of 1Hz to 1MHz using HD74Ls14 schmit trigger.this circuit converts the sqaure wave upto few Hz range of frequency.if I need to convert the 1MhZ signal means I have to increase the amplitude level of input signal.
I attached the above image represents the amplifier circuit with schmitt trigger.Amplifier for strengthening the input signal.

 

[MikeMl]

Have you considered the effect of the series resistor and shunt capacitor at the input of the hysteresis gate? It acts as a low-pass filter which attenuates 1Mhz signals (not so much at 1Hz)


View attachment 66980

 

[Rockzinstruz]

then how to design the schmit trigger circuit with minimum input voltage ;it has to work at the frequency range of 1Hz to 1MHz.

 

[alec_t]

Why do you have that low-pass filter at the input to the Schmitt?
Have you ensured your op-amp output is biased at half the Schmitt supply voltage?
Is the op-amp gain enough to have an output swing crossing both Schmitt threshold voltages?

 

[Grossel]

Hi.

Without having looking at the opamps datasheet, have you considered the following possible problems:
* Output of the opamp. What is the maximum and minimum voltage it can provide. Is those maximums near supply voltage? Is the output type open collector?
* What does the actual wiring looks like? You may have got some unwanted stray capacitors and inductors?

 

[MikeMl]

then how to design the schmit trigger circuit with minimum input voltage ;it has to work at the frequency range of 1Hz to 1MHz.

Look up the various DIY "frequnecy counter" projects that are on the web. Most have an input amplifier and trigger stage that works from dc to ~50Mhz.

A high-speed comparitor chip (start with LM311 but use a modern equivalent) could do the amplification and Schmit Trigger function in one stage. Below 1MHz, you should be able to get a minimum sensitivity of ~10mV.

 

[MikeMl]

then how to design the schmit trigger circuit with minimum input voltage ;it has to work at the frequency range of 1Hz to 1MHz.

The AD811 seems to be way overkill for your application. If you want to use it, you need to pay attention to Table 3 in the data sheet.

https://www.analog.com/static/imported-files/data_sheets/AD811.pdf