A good scope for measuring low levels of noise (e.g., Linear PS noise)

[2N3055]

For bandwidth of 3 MHz there is also 16bit picoscope 4262.. It has 8uV RMS noise at 2mV/div.
With a 100x amplifier in front it can see pretty much anything. Problem is amp noise, if anything.
Without the amp you can reliably measure 50 uV and up. Without amp it is pretty much enough for most uses.

[Sighound36]

Good Call 2N3055,

I have one of these scopes they are for the outlay rather good and have that low noise floor, just keep your lap top off the main lab power circuit when using it.

[2N3055]

Good Call 2N3055,

I have one of these scopes they are for the outlay rather good and have that low noise floor, just keep your lap top off the main lab power circuit when using it.

I also have Alldaq USB3 isolator, so scope has isolated ground from PC. Isolator comes with nice medical grade PSU, so it's cleaner than what usually comes from laptop, or worse, from desktop PC.
It shaves off few spurs down in the grass. Also, by experimenting, I found one cable ferrite that, with exactly two loops of USB cable trough it, shaves off few dB more on some peaks....

[Sighound36]

I have made something similar with a fully linear psu (we used to make these for audio when the usb computer craze strated) only instead of using Never connected technology these days we use our own propitiatory ultra quiet supply.

As you say does reduce the noise a few points to make it worth while.

Thinking outside the box again 2N3055 good man 

[Andreas]

I also have Alldaq USB3 isolator,

 I found one cable ferrite that,

Hello,

which one of the isolators exactly?
that with the 5V adapter: ADQ-USB-ISO-PS
or that with the external 10-30V input: ADQ-USB-ISO-W

Can you also give a pointer to the cable ferrite?

Thanks in advance

Andreas

[2N3055]

I also have Alldaq USB3 isolator,

 I found one cable ferrite that,

Hello,

which one of the isolators exactly?
that with the 5V adapter: ADQ-USB-ISO-PS
or that with the external 10-30V input: ADQ-USB-ISO-W

Can you also give a pointer to the cable ferrite?

Thanks in advance

Andreas

Andreas,

Not a problem.  It is ADQ-USB 3.0-ISO. I got that one so I can also use it with 3406D USB3.
Ferrite is an old one I found in a box, it came with some computer equipment god knows how many years ago...
Regards,
Sinisa

[egonotto]

Good Call 2N3055,

I have one of these scopes they are for the outlay rather good and have that low noise floor, just keep your lap top off the main lab power circuit when using it.

Hello,

one can improve the noise through addition the same signal.

Best regards
egonotto

[2N3055]

Good Call 2N3055,

I have one of these scopes they are for the outlay rather good and have that low noise floor, just keep your lap top off the main lab power circuit when using it.

Hello,

one can improve the noise through addition the same signal.

Best regards
egonotto

Yes, I see you used well that whitepaper... 

[tautech]

Yes well even probing techniques matter down in the uV never mind any environmental or scope internal noise.
This screenshot was done with a 1x probe where even LED lighting SMPS would badly impact measurements as the probes reference lead acts as a fine RF loop.......so done in the dark !

12V SLA battery, so pure DC just to see what the bottom level of noise/ripple measurements might be with a SDS2104X Plus.

[wn1fju]

Here is a curious oscilloscope that can see small signals my other scopes miss.  It is an HP 1200B, dual-channel, 500 kHz bandwidth relic from the 1970s with Volts/div settings down to 100 uV.  Shown in the picture is a 100 kHz sine wave at ~25 uVrms from an RF signal generator.  The 1200B has differential inputs plus all the usual dual-channel modes (alt, chop, etc.). 

Obviously, the very limited bandwidth makes it a dinosaur for modern electronics.  I guess HP was targeting the "audio crowd" back then.  The spec says the noise is "less than 20 uVrms measured tangentially at full bandwidth," whatever tangentially means.

I picked it up in broken (no horizontal sweep) condition for $40 a few days ago.  The fix involved hooking up a dangling power supply wire and replacing a defective vertical amplifier 2N3440 transistor.

[wn1fju]

To MasterTech: 

Thanks for the reference to the paper explaining a tangential noise measurement.  I learned something new today!

I did the measurement on the HP 1200B scope and got 9.7 uV which is fine given HP's "less than 20 uV" spec.

[David Hess]

To MasterTech: 

Thanks for the reference to the paper explaining a tangential noise measurement.  I learned something new today!

I did the measurement on the HP 1200B scope and got 9.7 uV which is fine given HP's "less than 20 uV" spec.

The 1 MHz Tektronix 7A22 is suppose to be 16 microvolts rms so comparable.  That may seem low but the differential cascode inputs that these instruments use extract a severe penalty in noise performance; a 500 kHz or 1 MHz single ended non-cascode input would have much lower noise.

My benchmark though is my 75 MHz 7A18 which I measured at 28 microvolts RMS which is smaller than its displayed trace at its maximum sensitivity and why I laugh at modern 100 MHz oscilloscopes which claim low noise.

[maginnovision]

...I laugh at modern 100 MHz oscilloscopes which claim low noise.

That's just silly.

[schratterulrich]

I like Tektronix HiRes Mode for this kind of measurements.

This measurement shows the noise of a XC6201P502 LDO.
Tektronix TDS744A (8-Bit Scope), direct connected with a coax cable, AC-coupling, 20 MHz BW limit:

and when unpowered (this should be the noise floor of scope, probe and environment):


In HiRes Mode the signal is lowpass filtered with 0.44 x Sample Rate. This can be an advantage because there will not be any aliasing artifacts and you can adjust the BW by choosing an appropriate Sampling Rate.


I have no chance to measure this noise with a TDS3032 9-Bit Scope:

[joeqsmith]

If I need to go lower than 20 or so mV, I will normally use some form of external amplifier.   I have a few different ones I use for RF and this lower one for DC-100KHz or so.   It has a 10,100 and 1000X gain select and AC or DC coupling.   

Shown for example is a 100mVp-p square attenuated by 80dB.  Amplifier is set to the 100X gain.   The scope is shown in full BW, no filters or averaging.     Then with 20MHz BW, 10 sweep average.