- #1

- 2

- 0

Dear people,

it might be a simple question, but I have been on this for over 2 days now and can't find a proper explanation of this anywhere:

https://dl.dropbox.com/u/2264519/circuit.jpg [Broken]

Picture a RCL circuit which is kept at room temperature. Now even when there is no current going through the circuit, the resistor is still creating some thermal noise [itex]S_{R}(f) = 4k_{B}TR[/itex] due to the motioin of individual electrons. This is just simple white (/Johnson) noise, which is the same for all frequencies. I can work with Laplace transformations and stuff, calculating the resonance frequency of the circuit. Now my question is this:

Wouldn't the resistor also create a small portion of noise at the frequency that just so happens to be the resonance frequency of the RCL circuit? At all other frequencies the noise woudn't resonante through the circuit but decay, but what happens on this frequency?

Will this circuit just start to resonate out of nothing? Isn't that strange? Also, can you calculate what would be the current that will be resonating at this frequency? (I guess it would have to be T dependent, since a higher T causes more noise). What will the nosie spectrum of this circuit look like? What would I see when I measure the current through certain parts of the circuit?

A lot of questions, but I'm hoping to get a more clear picture of noise in electrical circuits ^^.

If anyone knows a nice essay that deals with noise in electrical circuits that would be great! I do know some mathematics, but as a physics student I don't work with electronics very often.

it might be a simple question, but I have been on this for over 2 days now and can't find a proper explanation of this anywhere:

https://dl.dropbox.com/u/2264519/circuit.jpg [Broken]

Picture a RCL circuit which is kept at room temperature. Now even when there is no current going through the circuit, the resistor is still creating some thermal noise [itex]S_{R}(f) = 4k_{B}TR[/itex] due to the motioin of individual electrons. This is just simple white (/Johnson) noise, which is the same for all frequencies. I can work with Laplace transformations and stuff, calculating the resonance frequency of the circuit. Now my question is this:

Wouldn't the resistor also create a small portion of noise at the frequency that just so happens to be the resonance frequency of the RCL circuit? At all other frequencies the noise woudn't resonante through the circuit but decay, but what happens on this frequency?

Will this circuit just start to resonate out of nothing? Isn't that strange? Also, can you calculate what would be the current that will be resonating at this frequency? (I guess it would have to be T dependent, since a higher T causes more noise). What will the nosie spectrum of this circuit look like? What would I see when I measure the current through certain parts of the circuit?

A lot of questions, but I'm hoping to get a more clear picture of noise in electrical circuits ^^.

If anyone knows a nice essay that deals with noise in electrical circuits that would be great! I do know some mathematics, but as a physics student I don't work with electronics very often.

Last edited by a moderator: