Products > Test Equipment

Most accurate signal generator

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radiolistener:

--- Quote from: loop123 on March 26, 2024, 05:59:05 am ---You mean its difficult even to produce accurate 1.8V sine wave?  Is the voltage or sine wave more difficult to make or which one is more affected by a crystal/clock? usually what are the errors in crystal just to have an idea? but then if crystals vary how do wifi or cell phone even connect?

--- End quote ---

yes, it is difficult, especially if you're doing it with digital circuit. With analog circuit it is more easy, but still hard if you want to get very clean sine with low enough harmonics and distortion levels.

Precise voltage is not an issue for audio ADC. The issue is a level of distortions, noise and spurs.

In order to test your ADC, you can use two tone generator 700 Hz + 1900 Hz and see on FFT result.
You can easily see and measure distortion artifacts due to non linearity of ADC when using such two tone signal test.
And there is no needs to have precise voltage for such test.
For example, see pictures in this article: https://www.nxp.com.cn/docs/en/engineering-bulletin/EB38.pdf

But the issue here is to make clean enough signal generator which don't have distortions on the output within 170 dB for your tests... Such dynamic range is not trivial, so don't expect it from universal lab signal generators.

radiolistener:

--- Quote from: JeremyC on April 02, 2024, 12:21:52 am ---I'm guessing DAC in your computer is 24bit and in theory you have 144dB dynamic range.

--- End quote ---

I'm afraid there is no 24-bit DAC in the world which has 144 dB dynamic range  :-//

JeremyC:

--- Quote from: loop123 on April 02, 2024, 02:34:52 am ---
--- Quote from: JeremyC on April 02, 2024, 12:21:52 am ---
--- Quote from: loop123 on March 25, 2024, 09:11:30 pm ---
--- Quote from: radiolistener on March 25, 2024, 02:25:32 pm ---I think SDG6022X signal accuracy should be good enough for amateur needs.
https://siglentna.com/product/sdg6022x/

But its performance is not the best. So, if you want better performance, there is may be a sense to look for some specialized signal generator for your needs?

What do you mean when talking "most accurate"? Less noise / less spurs / high dynamic range? 

If you're interested in precise amplitude, then there is a sense to look for RF generator. They have pretty clean sine output and allows to setup calibrated amplitude. But note, all signal generators have fixed output impedance, usually 50 Ω (sometimes there is a switch between 50 Ω and 600 Ω). And if your load is not 50 Ω, then you're needs to recalculate amplitude, that is normal and expected behavior.

--- End quote ---

The use is specifically to test the E1DC Cosmos ADC to see if for example it's 0dB corresponds to 1.7V or 1.8V in its lowest setting (with best dynamic range). Just to test its overall accuracy. My present 2 signal generators don't even produce output where I can be certain it's 1V or 1.5V for example. So I need one where I can produce accurate 1.7V or 1.8V to see which voltage would clip it and establish the baseline because different units vary according to the manufacturer. I didn't know choosing signal generator is that complicated that is why didn't post the entire picture below in the original message. In the following is the -128dB noise floor of my E1DA I tested using REW RTA. My budget for the stand alone signal generator is less than $200. Please recommend which one specifically I should get knowing my requirements. Thanks.

--- End quote ---

Why you are not using the signal generator from the REW suite? I'm guessing DAC in your computer is 24bit and in theory you have 144dB dynamic range.

Link to documentation: https://www.roomeqwizard.com/help/help_en-GB/html/siggen.html#top

--- End quote ---

I used Microsoft Surface Pro 2017. How is its DAC? if bad. What external usb DAC can I get?

--- End quote ---

You Surface Pro has USB 3 port and you can connect external DAC/ADC.
If high quality is required I would recommend the MOTU M2, or the Focusrite Scarlett 2i2 3rd or 4th gen. They are in $170 - $200 price range.
You may get from ebay inexpensive 16bit (96dB) for $12 - $20. If you decide for the inexpensive option then don’t install the software but use generic Windows driver.
Example link to e-bay: https://www.ebay.com/itm/401755911322?itmmeta=01HTED6688A2FY27CRRW68F852&hash=item5d8a84b49a:g:Kk0AAOSwAUlc63WW&itmprp=enc%3AAQAJAAABIC0MCrhyW6Eac1oLB8M%2BzA3WXXHO7mUdAbGQOUArG8kGJufeddaLXqm%2BQQ686ENb1DaWBuvAgAQZW72V87C7gVzOJndb0l3vNtnllshfIkth3e1uBbF2X9nO3z49pbST%2Bm1Nv5KQURU7J9mnuNZ0qpRNQbKB906LOvGbQ3pHFyBRtaaPDHivWKCc%2BBBvCh5ER8FcVQ19EfgD1KN9AWFj2WK8SfNbGm5f7q8qVEY0H0MpmxrJ65i5wYDTSdAvVxGqNjETazvRgumcTtTb%2BCMAoIIT64NKPdXI903%2B%2FEjuuN8%2F2fOFibsGLXp%2FuTCiFNJMquiqowzNfnDqwwImxJ0MTUaJxJsKiezCi43xf93H5jr4Q60Av09vE5K0FSSh%2BcQY%2Bg%3D%3D%7Ctkp%3ABFBMpuSYzdNj

JeremyC:

--- Quote from: radiolistener on April 02, 2024, 03:11:25 am ---
--- Quote from: JeremyC on April 02, 2024, 12:21:52 am ---I'm guessing DAC in your computer is 24bit and in theory you have 144dB dynamic range.

--- End quote ---

I'm afraid there is no 24-bit DAC in the world which has 144 dB dynamic range  :-//

--- End quote ---

I agree, and that's why I wrote "in theory",  20 * log(2^24)=144
In reality those DACs have 110 - 120 dB dynamic range. My MOTU M2 for instance has 120dB.

In my opinion for audio work even 16bit sound card is more adequate than $1000 AWG.

loop123:

--- Quote from: gf on April 01, 2024, 12:16:58 pm ---
--- Quote from: loop123 on March 31, 2024, 10:53:58 pm ---I figured out the sine waves noises don't merge into one another because they don't affect the past. And at 1kHz amplifier setting. The noises of 50Hz vs 900Hz is identical because making it pulse faster (higher frequency below 1kHz) doesn't produce more noise. And I want to test this.

--- End quote ---

Sorry, I can't follow your thoughts. What do you mean with "noises of 50HZ vs. 900Hz"? You have noise, and you have your wanted signal. Just consider them as two independent signals. At the end, noise and wanted signal simply add up. The noise does not change if your wanted signal changes. You don't get a "different noise" if your wanted signal is 50Hz or 900Hz.

Nevertheless keep in mind that your noise is not white, but your amplifier also suffers from 1/f noise at low frequencies, and that you deal with bandwidth-limited noise (~1kHz). Both imply that your noise is not independent and identically distributed, but it is autocorrelated. So the deformation of the waveform due to noise (if you zoom-in) will definitively look different for a 50Hz sine wave signal and for a 900Hz sine wave signal. I have attached example plots for 1kHz-bandlimited (2nd order Butterworth) white noise and 12dB SNR. Note that for the 900Hz signal, the noise mostly affects the envelope. Keep in mind that these plots are still not represenative for the noise of your amplifier.

To get a more representative picture, can't you record the noise floor of your USBamp (e.g. with Audacity, as you already did it with your other amplifier) and then use Audacity to add an artificial sine wave signal to the recorded noise in order to see what you would get?


--- Quote ---Supposed my signal is 1V and I want to convert it to 10uV.

--- End quote ---

That's a factor of 100,000 or in other words 20*log10(100000) = 100dB.


--- Quote ---What button or number should I press?

--- End quote ---

The enabled stages simply add up. Example: If you turn on 20+16+2, then you get 38 dB.


--- Quote from: nctnico on April 01, 2024, 11:33:24 am ---That is an option but the step attenuator allows to make many different levels quickly which is handy while experimenting.

--- End quote ---

The OP was very much focused on accuracy. The chosen step attenuator is likely not a precision device. I wonder what total accumulated uncertainty can be achieved for the involved components (generator's no-load voltage, generator's output impedance, 8 attenuator stages, and the terminator impedance).  I have doubts that we are still within 1% at the end.

--- End quote ---

What software did you use on your attached waveforms? Id like to try it. I still dont know the context of bandwidth limited noise and still puzzled. See my last message for my questions. Tnx.

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