Most accurate signal generator

[BennoG]

Or even better use a scope, then you can see what you are measuring.
There are cheap scopes that even will go to 1Mhz.

Personally I use usb based scopes (Picotech) but everyone has his / her own preferences for scopes.

Benno

[shapirus]

Or even better use a scope, then you can see what you are measuring.

But even the not so cheap ones can hardly meet the required measurement accuracy. Frequency yes definitely, even cheap scopes are quite good at that, but amplitude not so much.

It may make sense to build a relatively simple bipolar peak detection circuit that will allow to measure positive and negative amplitude peaks and fine tune the generator's output to the desired AC level and remove the DC offset.

Can also be done, reasonably well at this frequency, using a simple ADC like MCP3304 (but then again you'll need a suitable DMM to calibrate it).

[nctnico]

The OP probably does not understand that the output load needs to be 50 ohm. If you not load the generator with 50 ohm the output voltage is usually double the output voltage you set on the generator.

Or for the el cheapo chinese the unloaded output is the set voltage and as soon as you put a load on the output the voltage drops.

Benno

The E1DA ADC has input impedance of 640 Ohm while the Scaler has input impedance of 200k Ohm. What would happen to the signal generator with 50 ohm output impedance in them?

With the generator set to High-Z mode (which is just an amplitude reading scale factor), you'll need to adjust the amplitude reading by a factor from the resistie divider of 50 / 640 Ohm or 50 / 200k Ohm. Another option is to put the generator in 50 Ohm mode and put a resistor parallel with the load to make the load resistance equal to 50 Ohm.

Using High-Z mode is likely the most accurate because the deviation of the internal resistance influences the result the least. With Low-Z mode you have to assume the output resistance of a cheap generator is actually 50 Ohm. A difference of a few Ohm makes a large error.

[Fungus]

No. I just wrote 1.00001V to drive the point that it should not be 1.2V or 0.9V but exactly 1V. It doesn't have to be 1.00001V but only 1.01 volt for example. It is enough.

My multimeter has this specs up to 500Hz only. What best inexpensive multimeter that can measure at least 10Hz to 20000Hz with accuracy of 1/100000th (ops, i mean just accurate enough in 2.01V or 3000.01 Hz?

Beware: Multimeter bandwidth ratings are dubious at best. I wouldn't use one with less than "100kHz" rating to measure a 20kHz signal.

I wouldn't use a multimeter at all for this, not when you can get a good-enough oscilloscope for $30.

https://www.aliexpress.com/item/1005004986731615.html

(get the 18MHz version with the proper oscilloscope probe, not just the crocodile clips...)

Verify the oscilloscope's voltage accuracy by measuring a fixed DC voltage (not an AC signal) and comparing with your multimeter. I'm sure it'll be close enough for your needs though (I own two of those 'scopes).

[Anthocyanina]

for your original 200$ budget, i would get an owon HDS242S.  it's a very reasonable oscilloscope, multimeter and generator for the price, here's the owon's generator in yellow, vs a keysight 33212a in blue, both set for the same frequency and amplitude of 1.8vpp. you can see the measured Vpp and frequency for both channels to the right of the waveforms.

keep in mind that the output of both generators is going to a high impedance load (the analog discovery's 1Mohm inputs) and will be halved if you connect them to a 50 ohm load. the owon can output 5vpp to high impedance loads and 2.5vpp to 50 ohm loads, so if that doesn't work for you, then yeah, this won't work, but within that voltage range, the generator of the owon is pretty reasonable for the frequency range you want, and you also get an oscilloscope and multimeter.

[egonotto]

Hello,

blue has small disturbances in the image 5khz.png.

Best regards
egonotto

[Anthocyanina]

Hello,

blue has small disturbances in the image 5khz.png.

Best regards
egonotto

yeah, that's a 50khz switching noise signal riding on it. i connected the keysight using long alligator clips as that's what i had laying around the closest to me, for later captures i just disabled the "acquire noise" option on the AD2

[loop123]

Guys. Besides needing 1.8V, 3000Hz to calibrate the E1DA ADC. I also need a 10uV signal generator at least 1000Hz with differential output to test my 16 channel USBamp bioamplifier directly in differential inputs. as well as the BMA bioamplifier. I got the following at Audacity. I can't figure out if its due to the Netech EEG simulator output that has noise or those amplifiers. Do you know any 10uV signal generator at 1000Hz (what is the highest possible without noise) that won't produce any noise or at least imperceptible?

[ebastler]

Do you know any 10uV signal generator at 1000Hz (what is the highest possible without noise) that won't produce any noise or at least imperceptible?

Before you start buying more equipment, you should read up on fundamental noise contributions and limitations. For starters, there is resistor noise (Johnson noise) which you can't avoid, even with the most expensive source and detector -- unless you go to cryogenic cooling.

The web page below explains some fundamentals and has a handy calculator. You will find that at room temperature, for 10 kHz bandwidth and 1 MOhm input resistance (as found on oscilloscopes), the Johnson noise is already 13 µVrms.  https://www.omnicalculator.com/physics/resistor-noise

[loop123]

Do you know any 10uV signal generator at 1000Hz (what is the highest possible without noise) that won't produce any noise or at least imperceptible?

Before you start buying more equipment, you should read up on fundamental noise contributions and limitations. For starters, there is resistor noise (Johnson noise) which you can't avoid, even with the most expensive source and detector -- unless you go to cryogenic cooling.

The web page below explains some fundamentals and has a handy calculator. You will find that at room temperature, for 10 kHz bandwidth and 1 MOhm input resistance (as found on oscilloscopes), the Johnson noise is already 13 µVrms.  https://www.omnicalculator.com/physics/resistor-noise

I know all the noises in my BMA amplifier. The following is the computation of the approx total noise. I need to get a high quality 10uV 1000Hz signal source because I'm going to build a 1nV/Sqrt (Hz) noise INA849. So please give the 10uV signal generator of purest quality with the highest bandwidth possible.

main noise sources in the signal path of the BMA are:
Source resistance (e.g. 10 kOhm)
2x 5k protection resistors
2x op amps (8 nV/sqrt Hz for the the OPA2132P)
Instrumentation amp (5 nV/sqrt Hz for the AMP01).

For bandwidth of 1 kHz:
So the calculation becomes:
10k Source resistance: 0.13 * Sqrt (10000) * Sqrt (BW) = 411 nV rms
2x 5k Protection resistors: Sqrt(2) * 0.13 * Sqrt (5000) * Sqrt (BW) = 411 nV rms
2x OP amps: Sqrt(2) * 8 * Sqrt (BW) = 357 nV rms
I amp: 5 * Sqrt (BW) = 158 nV rms

The noise powers sum:
Total = Sqrt (411 ^2 + 411 ^2 + 357 ^2 + 158 ^2) =
          = Sqrt (168,921 + 168,921 + 127449 + 24,964)
          = Sqrt (659,176)
          = 812 nV rms  = 0.812uV rms x 6.6 = 5.3592uV peak to peak
Without source impedance of 10k Ohm.
Total noise =  566.83nV = 0.566uV rms  x 6.6  = 3.7356uV peak to peak

 Bad for 10uV. So will go for the ultimate 1nV/Sqrt (Hz) INA849.  Does anyone know of any complete equipment that uses the INA849?

[nctnico]

Guys. Besides needing 1.8V, 3000Hz to calibrate the E1DA ADC. I also need a 10uV signal generator at least 1000Hz with differential output to test my 16 channel USBamp bioamplifier directly in differential inputs. as well as the BMA bioamplifier. I got the following at Audacity. I can't figure out if its due to the Netech EEG simulator output that has noise or those amplifiers. Do you know any 10uV signal generator at 1000Hz (what is the highest possible without noise) that won't produce any noise or at least imperceptible?

Simple: get a step attenuator and connect it to the output of a signal generator.

[loop123]

Guys. Besides needing 1.8V, 3000Hz to calibrate the E1DA ADC. I also need a 10uV signal generator at least 1000Hz with differential output to test my 16 channel USBamp bioamplifier directly in differential inputs. as well as the BMA bioamplifier. I got the following at Audacity. I can't figure out if its due to the Netech EEG simulator output that has noise or those amplifiers. Do you know any 10uV signal generator at 1000Hz (what is the highest possible without noise) that won't produce any noise or at least imperceptible?

Simple: get a step attenuator and connect it to the output of a signal generator.

In Op-Amps or INA. Noise characteristics are in the form of nV/Sqrt (Hz). How many about signal generators? Are the noises also in nV/Sqrt (Hz)?

Since my differential input is 10uV (microvolt). The noise peak to peak has to be less than 1uV. So noise should not be more than 1uV peak to peak or in rms  is 1uV/6.6 = 0.00000015 or 0.15uV rms noise. This is at 1000Hz. My Netech ECG simulator even with step attenuator used still has noises. Therefore what 1.8V signal generator  has noise of 0.15uV rms at 1000Hz?  Since I'd be using it not just on the E1DA but directly on the bioamplifier signal input too (just thought of yesterday). My budget is back to $200 from $50. But since I can only buy one $200. Please suggest one with guaranteed noise of at least 0.15uV rms at 1000Hz or below with differential output.

If noises in signal generator are not in nV/Sqrt (Hz), then what they are in? The quantization has to be lesser than 0.15uV rms too (or what its equivalent in quantization error)?

[gf]

If your budget is low, why don't you try in the first place what I suggested here:
https://www.eevblog.com/forum/testgear/most-accurate-signal-generator/msg5413988/#msg5413988
That cost's you a few cents for two 1% resistors.
You are asking for a SINAD of ~35dB. That's not really challenging for a signal generator.
I guess that even your FNIRSI toy can reach that, at least at the full scale level of the DAC
(EDIT: and 10µV are then obtained by dividing (say) 1V by 100,000 with a voltage divider, which does not increase SINAD).
The noise floor of your DUT (see your other threads) is significantly higher anyway.

EDIT:
And if I look at the spectrum plots in your other thread, then I cannot see that your ECG simulator did increase the random noise floor significantly. But yes, its signal obviously contains several undesired spurs. Additionally, your setup seems to pick up mains hum (and possibly some other noises) from the environment. I don't know, but I rather don't think this is coming out from your ECG simulator. So also take measures to minimize any pick-up of undesired signals from the environment.

[nctnico]

Shielding is everything with these kind of low signal levels; I don't think it is sensible to try and measure low level signals without being inside a shielded room. Also the grounding needs to be good so so you get noise from differences in ground levels.

[loop123]

If your budget is low, why don't you try in the first place what I suggested here:
https://www.eevblog.com/forum/testgear/most-accurate-signal-generator/msg5413988/#msg5413988
That cost's you a few cents for two 1% resistors.
You are asking for a SINAD of ~35dB. That's not really challenging for a signal generator.
I guess that even your FNIRSI toy can reach that, at least at the full scale level of the DAC
(EDIT: and 10µV are then obtained by dividing (say) 1V by 100,000 with a voltage divider, which does not increase SINAD).
The noise floor of your DUT (see your other threads) is significantly higher anyway.

EDIT:
And if I look at the spectrum plots in your other thread, then I cannot see that your ECG simulator did increase the random noise floor significantly. But yes, its signal obviously contains several undesired spurs. Additionally, your setup seems to pick up mains hum (and possibly some other noises) from the environment. I don't know, but I rather don't think this is coming out from your ECG simulator. So also take measures to minimize any pick-up of undesired signals from the environment.

My Netech simulator only has frequency choices of 0.1Hz, 2Hz, 5Hz, 50Hz, 60Hz only. I dont know how a frequency of 1000Hz would appear given the amplifier has 1000Hz bandwidth selected and ADC 48kHz in all cases in my setup. Based on the following. Can you describe how 1000Hz version of it would look like instead of just 50Hz.  Again In both cases my amplifier has switch selected to 1000Hz bandwidth. Can the sine wave at say 900Hz still be distinguished with the noises in the following becoming imperceptible or would 900Hz appear like a blur with no sine waves seen?

[nctnico]

Filters do not have infinitely steep slopes. Likely the bandwidth filters on your equipment are first or second order at most in order not to create too much phase shifts. The source of the 1kHz signal can be anything (for example an intermodulation product from a noise source, including poor grounding). I'd start with measuring with the inputs of your ADC shorted and go from there.

[gf]

I'd start with measuring with the inputs of your ADC shorted and go from there.

This was already suggested by a member in the other thread, and loop123 already did this measurement.
I don't know why loop123 starts multiple threads on the same topic, having the consequence that context is lost

[loop123]

Filters do not have infinitely steep slopes. Likely the bandwidth filters on your equipment are first or second order at most in order not to create too much phase shifts. The source of the 1kHz signal can be anything (for example an intermodulation product from a noise source, including poor grounding). I'd start with measuring with the inputs of your ADC shorted and go from there.

I mean I want to get a signal generator so I can output 10uV and 1kHz to see what the waveforms and noises look like at 1kHz because all I experienced seeing are always 50Hz signal. I havent see what 1kHz signal with noise looks like.

[gf]

Filters do not have infinitely steep slopes. Likely the bandwidth filters on your equipment are first or second order at most in order not to create too much phase shifts. The source of the 1kHz signal can be anything (for example an intermodulation product from a noise source, including poor grounding). I'd start with measuring with the inputs of your ADC shorted and go from there.

I mean I want to get a signal generator so I can output 10uV and 1kHz to see what the waveforms and noises look like at 1kHz because all I experienced seeing are always 50Hz signal. I havent see what 1kHz signal with noise looks like.

The method I suggested with your FNIRSI generator can also be done at 1 kHz. Only the amplitude calibration (if you don't trust the generator) with the DVM needs to be done at a frequency which is within the spec of your DVM -- thereafter you can also tune the generator to a higher frequency. I would not expect the generator to show a significant amplitude deviation between 50 Hz and 1000 Hz.

To get a first impression what to expect, I would just capture the noise floor with shorted input and add an artificial 1kHz tone (with 3dB lower amplitude to account for the filter) in Audacity.

[loop123]

Filters do not have infinitely steep slopes. Likely the bandwidth filters on your equipment are first or second order at most in order not to create too much phase shifts. The source of the 1kHz signal can be anything (for example an intermodulation product from a noise source, including poor grounding). I'd start with measuring with the inputs of your ADC shorted and go from there.

I mean I want to get a signal generator so I can output 10uV and 1kHz to see what the waveforms and noises look like at 1kHz because all I experienced seeing are always 50Hz signal. I havent see what 1kHz signal with noise looks like.

The method I suggested with your FNIRSI generator can also be done at 1 kHz. Only the amplitude calibration (if you don't trust the generator) with the DVM needs to be done at a frequency which is within the spec of your DVM -- thereafter you can also tune the generator to a higher frequency. I would not expect the generator to show a significant amplitude deviation between 50 Hz and 1000 Hz.

To get a first impression what to expect, I would just capture the noise floor with shorted input and add an artificial 1kHz tone (with 3dB lower amplitude to account for the filter) in Audacity.

What I want to see is noise deviation between 50Hz and 1000Hz with all settings the same like bandwidth switch of 1000Hz selected at amplifier. Before today I was thinking that if there were many noises like in my 50Hz waveform shared in last message, the noises would be same size at higher frequency such that at 100Hz the sine wave become blur as they merge to the noise. But today I was thinking of the possibility the noises size gets smaller with more frequency such that with my amplifier set to 1kHz bandwidth. It would still show 900Hz signal assuming the Netech simulator can output 900Hz instead of just 50Hz?

[nctnico]

Aha, just do as I wrote before: get an RF step attenuator (like this one from Aliexpress: https://nl.aliexpress.com/item/32905603744.html ) and connect it between the generator output and the ADC. You'll need to terminate the step attenuator with 50 Ohm so you'll need a 50 Ohm feedthrough terminator.

[loop123]

Aha, just do as I wrote before: get an RF step attenuator (like this one from Aliexpress: https://nl.aliexpress.com/item/32905603744.html ) and connect it between the generator output and the ADC. You'll need to terminate the step attenuator with 50 Ohm so you'll need a 50 Ohm feedthrough terminator.

Are the inside of the RF step attenuator composed of resistor dividers? I actually did the following before:




I connected 1Mohm in series with 1k ohm. Then when I want to lower the voltage by 0.001. I connect the input to the 1k ohm resistor, so that 1V become 1mV, and 1mV become 1uV. isn't this accurate? I don't use it with my cheap F-Nirst and FG-100 signal generators because I can't tell 1V from 2V and my multimeter is 20 year old and only up to 500Hz. Ok. I'll look and buy the best suggestions made here. Since it would take time for them to arrive. For those with signal generator, RF step attenuator and amplifier. Pls try the following:

Set your amplifier to bandwidth between 1kHz to 5kHz.

Set your signal generator to 10uV, 50Hz  using RF attenuator or resistor divider. Take the screenshot of the noise at 10uV, 50Hz. Now set your signal generator to 10uV, 1000Hz. I want the see noise difference between 50Hz and 1000Hz in the signal generator with the amplifier set to 1kHz in all settings. Please show the waveforms.  I want to see the noise deviation or appearance between 50Hz and 1000Hz. I want to know what to happen to the huge noise seen at 50Hz when signal generator is set to 1000Hz. whether you can still see the noise and to what degree. This is what I couldn't see all these months. Thanks.

[Anthocyanina]

Aha, just do as I wrote before: get an RF step attenuator (like this one from Aliexpress: https://nl.aliexpress.com/item/32905603744.html ) and connect it between the generator output and the ADC. You'll need to terminate the step attenuator with 50 Ohm so you'll need a 50 Ohm feedthrough terminator.

Are the inside of the RF step attenuator composed of resistor dividers? I actually did the following before:

(Attachment Link)


I connected 1Mohm in series with 1k ohm. Then when I want to lower the voltage by 0.001. I connect the input to the 1k ohm resistor, so that 1V become 1mV, and 1mV become 1uV. isn't this accurate? I don't use it with my cheap F-Nirst and FG-100 signal generators because I can't tell 1V from 2V and my multimeter is 20 year old and only up to 500Hz. Ok. I'll look and buy the best suggestions made here. Since it would take time for them to arrive. For those with signal generator, RF step attenuator and amplifier. Pls try the following:

Set your amplifier to bandwidth between 1kHz to 5kHz.

Set your signal generator to 10uV, 50Hz  using RF attenuator or resistor divider. Take the screenshot of the noise at 10uV, 50Hz. Now set your signal generator to 10uV, 1000Hz. I want the see noise difference between 50Hz and 1000Hz in the signal generator with the amplifier set to 1kHz in all settings. Please show the waveforms.  I want to see the noise deviation or appearance between 50Hz and 1000Hz. I want to know what to happen to the huge noise seen at 50Hz when signal generator is set to 1000Hz. whether you can still see the noise and to what degree. This is what I couldn't see all these months. Thanks.

that setup is very likely to pick up enough noise to make the 10uV signal indistinguishable from the background noise. you might have better chances soldering the resistors together, closely, and connecting the generator leads right where the resistor leads meet the resistor bodies

[nctnico]

There are resistors inside an RF step attenuator, but these have much lower values (single digit Ohm) as each section needs to maintain a 50 Ohm impedance at in & out. The step attenuator also has internal shielding to avoid signal leakage between sections. The low value resistors alone reduce noise compared to your breadboard setup. For your purpose, the breadboard setup is completely inadequate.

[Fungus]

Are the inside of the RF step attenuator composed of resistor dividers? I actually did the following before:

Yes, but to avoid noise you need high current (low impedance), short tracks, and shielding.