Help design white noise generator

[verytasty]

I need some help designing a white noise generator. Anybody here have a circuit diagram I could use or point me in the right direction?

Needs to have uniform power spectral density over a range of 10 hz to 1 mhz.
Output impedance should be 50 ohms or less
output voltage should be at least 1 mv rms/hz of noise bandwidth.

Anbody?? Please, this is really imporant..

 

[ebaycj]

this might help

http://www.howstuffworks.com/question47.htm

or, more likely, THIS might help.

http://world.std.com/~reinhold/truenoise.html

and i am no genius. i just know how to use google. seriously. at least CHECK a good search engine before asking sh!t like this. unless you're ABSOLUTELY POSITIVE that no one else has created what you are trying to create (as in: it has no name therefore no terms to search on), its likely someone has created it and that specs of some kind are on the net somewhere.

ebaycj

 

[verytasty]

I'm not stupid I already checked google for that stuff. And I need to design one with analog circuit components, not purchase one that will do the exact same thing. Thanks for your help though.

 

[Menelaos]

Isn't there something like a white noise diode? Will try to get you link.

Menel.

 

[crypticlogin]

<< I'm not stupid I already checked google for that stuff. >>


Funny, I just checked google and within the first 20 hits, I found 3 schematics and 2 white papers on how to design one. I think you need to try again...

edit: hint: I used three search terms, all of which are contained in your first post.

 

[verytasty]

Yes, but if you read the post it has to contain only analog components, not digital devices. I found a couple of schematics that produce white noise but are not:

a. proper output impedance
b. proper circuit elements

 

[PottedMeat]

heh isnt it a little late to start your 321k project?
the instructions description basically take a zener diode in series with a resistor to generate some shot noise, then amplify it
theres some equations in the thomas book i guess that say how much noise you generate based on the current you pass though the reversed biased diode. something like this might work?

Vbias----0----/\/\/\-------|<|-------------ground
/\
|

maybe this is where you can take the output and stick it into a noninverting amplifier
for the low output impedance maybe a jfet would work, you would probably have to adjust theoutput resistors to get wahat you need -good luck

 

[Harvey]

PottedMeat is on the right track. We don't have graphics, so here's how to do it with a single power supply, a zener diode and an op-amp:

1. Bias the zener diode by connecting it to a voltage source through a resistor as shown in his diagram. A zener voltage around 6 to 8 volts with a nominal zener current around 5 mA would be a good value.

2. Use an op-amp as a buffer to provide a low output impedance. Configure an op-amp as a voltage follower by connecting the output to the inverting (-) input. The op-amp must have sufficient bandwidth and be stable at unity gain. A good, inexpensive choice would be an LF351 (National) or TL071 (Texas Instruments).

3. Connect the non-inverting (+) input to the junction of the resistor and the zener.

4. Connect a 50 ohm resistor from the output of the op-amp to positive side of an output capacitor. Connect the other lead of the capacitor to a "tie down" resistor (around 100 kOhms) to ground. The value of the capacitor depends on the input impedance of the test equipment. If the input impedance is greater than 10 kOhms, a 22 uF capacitor will be sufficient. The junction of the capacitor and the tie down resistor is your output terminal.

5. Power the op-amp with either single positive or a bipolar voltage supply. +12 to 15 volts or +/- 12 to 15 volts would be a good value for the power supply. Be sure to add a decoupling cap (0.1 uF ceramic) from the power supply (pin 6) to ground. This will help prevent the op-amp from oscillating.

If you happen to have a dual op-amp (LF353 or TL072), you can safely defeat the second amp by configuring it as a voltage follower and grounding the non-inverting input.

If you need to amplify the white noise signal, you will need a few more components The easiest way to allow for this would be to power the op-amp with a bipolar supply and operate the circuit around 0 volts DC. To do this, add a coupling cap from the junction of the zener diode and bias resistor to the non-inverting input of the op-amp and a "tie down" resistor from the non-inverting input of the op-amp to ground. The cap can be in the range of 22 uF. The resistor can be between 10 kOhms and 100 kOhms.

This will center the AC (noise) signal around ground, so if you amplify the signal, you will not also amplify the DC reference voltage beyond the limits set by the power supply.

 

[edfcmc]

Harvey rules!