DC to 200KHz white noise generator - Page 1
Forum section: electronics / projects

author: ricko_uk
author_rank: Super Contributor
timestamp: December 02, 2020, 06:42:14 pm
content: Hi,for testing purposes, how can I generate white noise covering DC (i.e. as low as possible) to 200KHz?I was thinking to use Audacity but was told that the output from DACs even if they are 192KHz rate they are "probably" filtered down to 20KHz at the output. Does anybody know if that is true?Thank you

author: ejeffrey
author_rank: Super Contributor
timestamp: December 02, 2020, 08:03:06 pm
content: Does it need to be gaussian distributed? If not you can use a digital IO with a LFSR. Clock it at 10 MHz or higher and you will get plenty of bandwidth. AC couple it for whatever LF cutoff you want.Otherwise use a non audio DAC with high enough sample rate.

author: bdunham7
author_rank: Super Contributor
timestamp: December 02, 2020, 08:29:39 pm
content: Quote from: ricko_uk on December 02, 2020, 06:42:14 pmMost ARB/DDS signal generators have a noise option, even the low-end FeelTech models (no guarantee on how well they implement that). If you need to limit the bandwidth to 200kHz, you may need to construct your own filter.

author: Zero999
author_rank: Super Contributor
timestamp: December 02, 2020, 08:53:35 pm
content: 192kHz sample rate will only ever give a bandwidth of 97kHz.I'd do it the old fashioned analogue way.The easiest way is with a reverse biased zener diode and a suitable amplifier. It needs to be a relatively high voltage zener diode, >15V, to get a decent amount of noise and some experimentation to find the optimum noisy bias current is required.

author: TimFox
author_rank: Super Contributor
timestamp: December 02, 2020, 09:24:11 pm
content: If you need very low frequency noise, watch out for the inevitable 1/f component in analog noise generators (e.g., Zener diodes). One of my old General Radio 1381 analog generators (seehttps://www.ietlabs.com/pdf/Manuals/GR/GENRAD%201381%20IM.pdf) filters the noise (bandpass filter from 100 to 200 kHz) before heterodyning it (carrier at 150 kHz) down to baseband to reduce the contribution of 1/f "flicker" noise in the output (see page 15 of the manual). The final result is flat down to 2 Hz, with a selectable upper frequency (max 50 kHz). You could try this technique with a higher-frequency carrier.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: December 03, 2020, 04:06:08 pm
content: What are you testing ?Take a transistor for noise, select a good one, they all can differ in a badge depending on brand.Transistor noise is not flat like digital noise, thats why i am asking.Digital 200KHz is to fast for 8 bit chip, why waste more money on noise ?Let me know.

author: exmadscientist
author_rank: Frequent Contributor
timestamp: December 04, 2020, 06:32:25 am
content: Art of Electronics 3e has a few variations on this theme. The best starting point is probably Figure 8.93, showing a 10Hz to 100kHz white, pink, or red noise generation circuit. It looks like it would easily extend to higher frequencies.

author: jonpaul
author_rank: Super Contributor
timestamp: December 04, 2020, 11:09:51 am
content: Your OP confuses FS = sample rate 192 kHz with audio BW 20 kHz.A DAC eg ESS or TI or AKM may have the input digital audio SAMPLE RATE anything 28 k ...192 k..384 k BUT all have digital filters on output for audio = 20 kHz.Whats your exact application? DC noise implies very high 1/F or flicker. You are SURE you require "DC noise"The 1960s GENRAD 1390B OLD TUBE creates wideband noise to 5 MHz. It uses a 6D4 argon thyratron triode, in a strong transverse magnetic field to create the wideband noise.https://www.ietlabs.com/pdf/Manuals/GR/1390%20Noise%20Generator.pdfI have 4 of these excellent generators.BEWARE that newer solid state GENRAD 1381, 1382 etc use a noise diode and only have BW 50 kHz!Bon chance,Jon

author: jonpaul
author_rank: Super Contributor
timestamp: December 04, 2020, 12:11:23 pm
content: Hello again I unearthed and fired up 3 of the GenRad 1390-BOne has only hum output, bad PSU lytics.One is OK and one is perfect.TEK 7L5 show fine noise spectra.BUT how do you define "noise DC-200KHZ" since DC and noise are inconsistent: DC is a fixed voltage! THERE IS NO NOISE AT ZERO FREQ DC by definition.Jon