Resistor Current Noise

Thread Starter

bonkers31

Joined May 27, 2016
8
Hey all, I'm trying to measure 1/f noise from a resistor (using a bridge) connected to an op-amp, but for some reason I'm getting a region of white noise at a higher noise voltage than predicted (from thermal or shot). After this region it also returns to being pink again, not really sure why. Any help would be greatly appreciated, Thanks
 

Kermit2

Joined Feb 5, 2010
4,162
Is your circuit shielded to exclude EM radiation? Any radio or TV stations within 50 miles? Digital program modulation is a different beast from analog broadcasting. It might appear as white noise in certain freq. ranges.
 

crutschow

Joined Mar 14, 2008
34,285
Is your circuit shielded to exclude EM radiation? Any radio or TV stations within 50 miles? Digital program modulation is a different beast from analog broadcasting. It might appear as white noise in certain freq. ranges.
That's an interesting thing about digital modulation. For optimum usage of RF spectrum, the modulation should look like white noise, since that means the entire allotted modulation spectrum is being uniformly used, and modern digital modulation approaches that ideal.
AM modulation, on the other hand, tends to have a spectrum that looks like a comb, with the frequencies in between the comb peaks not well utilized.
 

Thread Starter

bonkers31

Joined May 27, 2016
8
Is your circuit shielded to exclude EM radiation? Any radio or TV stations within 50 miles? Digital program modulation is a different beast from analog broadcasting. It might appear as white noise in certain freq. ranges.
I don't belive there's any radio or TV stations near by. I did shield the op amp and bridge in a grounded metal box though.
 

Thread Starter

bonkers31

Joined May 27, 2016
8
I excited the bridge with a DC bias, zeroing the offset by connecting the bridge to a variable resistor and then recorded AC noise voltage from oscilloscope
 

Thread Starter

bonkers31

Joined May 27, 2016
8
I mean how did you connect the op amp when you measured its noise?
It was exactly the same as when measuring with the bridge, just with the bridge removed. I have been looking around online as well, is it possible it could have occurred due to LC/RLC oscillation?
 

crutschow

Joined Mar 14, 2008
34,285
It was exactly the same as when measuring with the bridge, just with the bridge removed. I have been looking around online as well, is it possible it could have occurred due to LC/RLC oscillation?
Okay, let's try again. :confused:
What, if anything was connected to the op amp input?
Post a circuit diagram for the op amp during this test.
 
Top