Noise reduction at the output

Hi,
In the following image


The normal value of the signal is at 5 V and it switches to 0 V on detection. Hence the number of high to low transitions taken as pulse count.

But in the steady state, the wave form oscillates between 5 to 3V and sometimes if noise is higher then voltage transition between 5 to 1.5v in the steady state. But my waveform will go to 0V on detection.

If voltage goes below 1.8 V( say 5 to 1.5V then from 1.5v to 5v) during normal state itself then controller takes this as a pulse, but it should not be happen.

So in the steady state even if the output oscillates between different levels i dont want it to go below 2.2 V. For doing this what should i do?

Thanks,
Murugesh

You could perhaps filter the waveform. What is the frequency of the pulses and the frequency of the noise? What is the pulse width?

The problem is in your signal source. The output is noisy as apparently there is no input to your device generating noise.
You may try to use a pull-up or pull-down resistor at the output but then your device might need a larger input to trigger the correct output.
Your device may have an internal level setting device to maintain the 5 V no-signal hen there is no input. Do you have the schematic?

Well thanks guys for your reply. I dont have the schematic though.
The time duration in which the output stays low is 100 micro seconds.

I got a idea but i need to check it out. If i connect the output to the base of the npn transistor with its emitter ground and connecting the one end of a 10K resistor to the collector of transistor and other end to 5V. I will take the output at the collector of transistor.

My thought is even if the output violates between 5 to 1.5V the output at the collector of transistor is 0V and when i get the proper zero signal during detection i will get 5V at the collector.

Will this work out?

Murugesh_89 said:

Well thanks guys for your reply. I dont have the schematic though.
The time duration in which the output stays low is 100 micro seconds.

I got a idea but i need to check it out. If i connect the output to the base of the npn transistor with its emitter ground and connecting the one end of a 10K resistor to the collector of transistor and other end to 5V. I will take the output at the collector of transistor.

My thought is even if the output violates between 5 to 1.5V the output at the collector of transistor is 0V and when i get the proper zero signal during detection i will get 5V at the collector.

Will this work out?

Click to expand...

I think that this transistor inverter will only transmit the ugly noise amplified. The problem is that the device you have no schematic of is generating the noise until triggered by a specified input level.
Please try to use a 10-100 k resistor connected to ground or +5 Vcc, and try to put the other end of it to various accessible points in the device circuit. There should be a comparator which processes the AM-demodulated signal to output TTL levels; without a proper input, the output is noisy as you observed. I had a similar experience with a TX-RX pair where the RX was super-regenerative detector which is also noisy without a RF input. By setting the comparator to get rid of the noise output, the system then worked well.