G
Gerhard Hoffmann
Guest
Am 17.03.2018 um 21:16 schrieb Castorp:
That would actually be good news, that the noise comes from the input
amplifiers. That would mean that one can use cross correlation on the
two channels. I had some fear that it might be phase noise from the
sampling clock since it is probably synthesized. That would be common
to both channels and would not average away.
> With a preamp built of 4 paralleled ADA4522s and LT5400 resistor arrays, I managed to get noise floor of about 5 nV/sqrtHz flat down to a few mHz. If there's interest, I can dig up those measurements. I used it to measure excess 1/f noise in resistors hooked up in a biased
Yes, especially the setup of the 89410.
Wheatstone bridge, like this:
Thanks to plowing with the power of a thousand chicken my setup is only
abt. 10 dB worse than that of Fred Walls, but without cross
correlation. I still can add that.
1000 chicken means averaging over 20 ADA4898 op amps .
If you want numbers on batteries that you actually can buy and not some
anonymous thingies that they happened to have in the lab, there is
<
http://www.hoffmann-hochfrequenz.de/downloads/NoiseMeasurementsOnChemicalBatteries.pdf
>
It is still limited by the 1/f of the 89410A and the undersized input
capacitor of the preamp (160 uF foil). I have replaced the foil caps
with wet slug tantal, 4700 u IIRC, but that is only a good decade
better, just a drop in the bucket.
An array of organic polymer electrolytics was too leaky. An array of
wet slug tantals costs too much if I have to pay for it from my own
money. :-(
BTW, two 3.7V Panasonic lithiums are quite OK, noisewise. They seem
hard to top.
<
https://www.flickr.com/photos/137684711@N07/39056813010/in/album-72157662535945536/
>
0 dB is 1nV / rt Hz, DC voltage is 7.3V. The 60 Ohm 1nV/rt Hz reference
resistor and the short switch are on the amplifier side of the coupling
capacitor, so everything looks much better.
The picture of the batteries is to the right.
cheers, Gerhard
I've used a number of 89410A devices, and they have exhibited some spread in the noise floor. Usually the flat part is around 8-9 nV/sqrtHz, and the 1/f corner could be in the kHz or tens of kHz. One device had popcorn-like noise in one channel.
That would actually be good news, that the noise comes from the input
amplifiers. That would mean that one can use cross correlation on the
two channels. I had some fear that it might be phase noise from the
sampling clock since it is probably synthesized. That would be common
to both channels and would not average away.
> With a preamp built of 4 paralleled ADA4522s and LT5400 resistor arrays, I managed to get noise floor of about 5 nV/sqrtHz flat down to a few mHz. If there's interest, I can dig up those measurements. I used it to measure excess 1/f noise in resistors hooked up in a biased
Yes, especially the setup of the 89410.
Wheatstone bridge, like this:
https://dcc.ligo.org/public/0002/T0900200/001/current_noise.pdf
Another nice trick with the 2-channel FFT is cross-spectrum measurement. With two good preamps and some patience it buys you another 10-20 dB downwards:
https://www.researchgate.net/publication/3622215_Measurement_of_voltage_noise_in_chemical_batteries
Thanks to plowing with the power of a thousand chicken my setup is only
abt. 10 dB worse than that of Fred Walls, but without cross
correlation. I still can add that.
1000 chicken means averaging over 20 ADA4898 op amps .
If you want numbers on batteries that you actually can buy and not some
anonymous thingies that they happened to have in the lab, there is
<
http://www.hoffmann-hochfrequenz.de/downloads/NoiseMeasurementsOnChemicalBatteries.pdf
>
It is still limited by the 1/f of the 89410A and the undersized input
capacitor of the preamp (160 uF foil). I have replaced the foil caps
with wet slug tantal, 4700 u IIRC, but that is only a good decade
better, just a drop in the bucket.
An array of organic polymer electrolytics was too leaky. An array of
wet slug tantals costs too much if I have to pay for it from my own
money. :-(
BTW, two 3.7V Panasonic lithiums are quite OK, noisewise. They seem
hard to top.
<
https://www.flickr.com/photos/137684711@N07/39056813010/in/album-72157662535945536/
>
0 dB is 1nV / rt Hz, DC voltage is 7.3V. The 60 Ohm 1nV/rt Hz reference
resistor and the short switch are on the amplifier side of the coupling
capacitor, so everything looks much better.
The picture of the batteries is to the right.
cheers, Gerhard