Looking for some insight into mosfets and their effects on a digital signal. I am planning to use a mosfet to switch on and off a digital signal based on button commands and I am curious the effect the mosfet will have on the signal if any. Specifically referring to threshold voltage and the possibility that it could dilute or add too much noise to my digital waveform. insight or opinions?

 

Don't really understand what you are trying to do.
Why are you using a MOSFET to switch a digital signal?
Need to post a schematic.

 

I don't have a schematic because this is something new i am trying to implement into a larger system, but i need to know this first before I try anything. All I'm asking is if a digital signal can pass through a mosfet without distortion.

 

I don't have a schematic because this is something new i am trying to implement into a larger system, but i need to know this first before I try anything. All I'm asking is if a digital signal can pass through a mosfet without distortion.

Yup.

 

If you properly design the circuit.

 

Here is a commercially-available device that claims .3nSec of propagation delay

 

Ok guys. I tested this scenario the way i thought it would work and it did not work. SO, I am trying to use a mosfet as a switch to open and close a channel for a PWM signal. I am doing this to work around some issues caused by doing this setup through an existing system. This provides me the results i need without having to seriously alter the external systems, if i can get it to work. Attached is a crude schematic of what i am trying to accomplish. I need to be able to apply a PWM signal to my S and have it come out my D side when i open the gate. When i attempted this all i get on the D side is an analog high signal no matter what duty cycle my PWM input is set to. What can i do to make this work?

 

Your questions so far are missing a YUGE amount of information:

What is the nature of the signal source - microcontroller output pin, PWM chip output, 5 amp 120 Vdc drive power to a 1 horsepower blower - ?
What is the p-p voltage of the pwm "signal"?
What is the PWM frequency?
What is the peak current into the load?

And the biggie - what is the gate drive voltage swing from on to off? Note that what is important here is Vgs, the voltage from the gate to the source. Since the source voltage is varying, a simple DC signal from the gate to GND probably isn't enough.

ak

 

What you want is an AND gate between the signal source and the output. The signal goes to one input, the control signal to the second input. When the control signal is high, the PWM signal is passed through. When the control signal is low, the output is held low.

Bob

 

If you insist on using a MOSFET. Put a resistor (say 100 Ohm) between the input and the output. The put an N-channel MOSFET from the output to ground (D to resistor, S to ground). Now a high control voltage will turn off the PWM signal.

This all assumes that the "signal" is indeed a standard logic signal, and not a power source.

Bob