# PWM output signal noise

#### chatur

Joined Oct 15, 2021
2
Hi,
I have problem in PWM output signal,how can I resolve it and get clean signal.please suggest

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#### DickCappels

Joined Aug 21, 2008
7,981
What is the source of the PWM signal, and what can you tell us about it?

#### chatur

Joined Oct 15, 2021
2
What is the source of the PWM signal, and what can you tell us about it?
Dear sir,
I used frequency to voltage converter circuit ,it's input is pwm signal through plc.

#### DickCappels

Joined Aug 21, 2008
7,981
Can't tell much from that. You may have the ground for your scope probe in the wrong place. I would try grounding the probe at the ground connection to the PLC.

#### crutschow

Joined Mar 14, 2008
28,201
Without a schematic, your description makes little sense.
Showing a picture of the waveform does nothing to help us know what the source of the problem is or how to eliminate the noise.
What's the purpose of the frequency to voltage converter?
What does the PLC do?
What's the purpose of the circuit?

#### MisterBill2

Joined Jan 23, 2018
9,824
Indeed Cruts is right! Unless the signal is coming from the scope connection we need a lot more information.

In addition, the explanation, " I used frequency to voltage converter circuit ,it's input is pwm signal through plc. "does not make sense. Th output of a frequency to voltage converter is a DC level, not a square wave.
OR, are you using a PLC to generate a Pulse Width Modulated signal in an attempt to get an analog voltage from a PLC (Programmable Logic Controller) that doe not have an analog output?
Showing us a noisy waveform and asking how to get a clean signal is not going to get much useful response.
I can clean up the wave with either a schmitt gate IC or a comparator, but neither of those will get rid of the noise on the signal shown. But the resulting signal will be at the logic circuit voltage, not the voltages shown.
So an explanation of how the signal is generated and what the output circuit is, along with the related supply voltage, is needed.

#### DickCappels

Joined Aug 21, 2008
7,981
Indeed Cruts is right! Unless the signal is coming from the scope connection we need a lot more information.

In addition, the explanation, " I used frequency to voltage converter circuit ,it's input is pwm signal through plc. "does not make sense. Th output of a frequency to voltage converter is a DC level, not a square wave.
I often regard a monostable multivibrator followed by a low pass filter as a F-to-V converter, but if that's the case, what PLC do to the signal, other than to possibly add noise.

Agree: We can't help much because we don't know much about the circuit.

#### MisterBill2

Joined Jan 23, 2018
9,824
I often regard a monostable multivibrator followed by a low pass filter as a F-to-V converter, but if that's the case, what PLC do to the signal, other than to possibly add noise.

Agree: We can't help much because we don't know much about the circuit.
DC, please read what Bob Pease had to say about F to V and V to F converters. He was brilliant in that area as well as many others.

#### DickCappels

Joined Aug 21, 2008
7,981
I may have already read those articles. I realize his importance in the F-to-V and V-to-F converters and his inheriting the bandgap reference responsibilities from Bob Widlar. He was quite an engineer. I admire him so much I styled my current office after his: