A white noise circuit could be interesting part of a modular synthesizer. This design has no 1/f component, meaning no annoying repeating sounds in the white noise.
In this noise-generator circuit, the amplifier (MAX4238) has no 1/f component in its input voltage noise. It amplifies its own input-voltage noise with a feedback network made with low-value resistors, to avoid adding noticeable 1/f noise either from the resistors or from the amplifier’s input noise current.
Thanks rsdio!
For the app note lovers, thanks for letting us know you’re out there!
Wait a minute: 1/f does not mean repeating sounds (annoying or otherwise).
1/f means that the amplitude of the output is a 1/x function of frequency, f. In other words, 1/f is pink noise. This circuit does not have a 1/f component, so it is white noise instead of pink noise.
Repeating sounds come from shift-register-based digital noise sources, but that’s entirely unrelated to 1/f components.
Very cool, but I have a question: What is so darn special about the MAX4238 in this application? Wouldn’t any similar opamp work here? Or, is it the autocorrelating offset zeroing which is creating the noise???? Inquiring minds want to know!!!
That circuit with that values is bullshit. MAX4238 has 1.5MHz GBW and with amplifier gain 15k/75R=200 the effective bandwidth is 5kHz. The only significantly amplified noise component comes from the OpAmp with Vn=30nV/rtHz, i.e. 30nV*sqrt(5kHz)=2.2µV => 2.2µV*200=424µV effective white noise output with just 5kHz bandwidth.
the basic idea is good – a neg feedback opposed to signal ground
the datasheet noise density – https://datasheets.maximintegrated.com/en/ds/MAX4238-MAX4239.pdf (fig. – DC to 10kHz NOISE – pg.7)- looks having a peak near above 100kHz
amazingly the the corresponding graph – https://www.maximintegrated.com/en/app-notes/index.mvp/id/4527 – shows quite a flat region there ???