Hello,
Don´t understand: a 10K to 10R divider has 10R (ok 9.99 R) impedance at the output
You can also measure the resistors with a DMM to get more accuracy than the resistor tolerance.
10 or 100 Hz is nothing where I would worry about.
The only thing you have to keep in mind is that the input resistance of the amplifier is 1K.
So with 10R impedance at the input you have 1% loss (-1dB) by the 10R to 1K voltage divider.
with best regards
Andreas
If very low noise is measured, one should also know the amplifiers own noise to subtract it. So the first test should be checking the noise the amplifier itself, both with a short and open.
The amplifier circuit is running without feedback at the input stage. So the amplification will not be very stable.
The critical part is only the first JFET - due to the gain of the first stage, the second stage (P-MOS) is not critical. For this application, there is no need to have differential amplification - just one side is enough. However this leads to a little more distortion - the differential version reduces distortion and DC drift, but also increases noise. However real life the matching will not be that good - so there will be some drift and distortion.
I have got few more LNAs stashed from pipelie
Not sure what "A" index means on 3 of the units.
I have got few more LNAs stashed from pipelie
Not sure what "A" index means on 3 of the units.
Thank you!
schematic added
I have got few more LNAs stashed from pipelie
Not sure what "A" index means on 3 of the units.
Are you going to sell some perhaps?
I'm still have some LNAs. if you want to have it, send me a PM.
Thanks.
i have been playing around with LTspice hovering around these ULNA schematics intermittently. out of the blue, i remember J diddy P 's circuit on ESR, both sides of the probe could be floating w/o a GND. so in theory, the isolation cap will not be charging? should a differential style be more "instant" or "stable" ?? (see pic)
V1 = 2nV pp, output is nearly 14uV pp
what could i have missed in this? as it appears to be too "simple" for a ULNA?
a side track question, what kind of amplification is this normally called? a Bifet? JFET + PMOS?
How sensitive is this or any other design shown here in matters of humans hand? The 0.1-10Hz LNA design I copied by Andreas needs a cookie box with good ground connection to the scope, otherwise the amplifier is pretty sensitive to humans body. The aluminium profile case I used is not enough shielding.
-branadic-
How sensitive is this or any other design shown here in matters of humans hand? The 0.1-10Hz LNA design I copied by Andreas needs a cookie box with good ground connection to the scope, otherwise the amplifier is pretty sensitive to humans body. The aluminium profile case I used is not enough shielding.
-branadic-
How sensitive is this or any other design shown here in matters of humans hand? The 0.1-10Hz LNA design I copied by Andreas needs a cookie box with good ground connection to the scope, otherwise the amplifier is pretty sensitive to humans body. The aluminium profile case I used is not enough shielding.
-branadic-
I've not had any issues with external static or EMI fields with mine. I can pick it up and move it around without any noticeable effects.
At the very low level also the electrolytic cap can react to mechanical stress. So not sure it's the caps at the output that make it vibration sensitive.
The 10 Hz upper limit might be a good idea to get direct 0.1-10 Hz readings to compare to a data-sheet. However if used in combination with an FFT, it might be an advantage if a higher upper (and maybe lower lower) frequency limit is possible too.
Also keep in mind that with just adding an extra 2 nd order low pass behind the existing LP will lower the effective upper limit a little. It would be nice to have the calculated frequency response for the amplifier in the instructions. Giving just a frequency range for a noise measurement is tricky, as the filters are not ideal brick-wall and the type of role of can make a difference. For the lower end one might assume a 1/f type noise and thus could get an effective lower limit that works most of the time. But at 10 Hz, it depends on the noise source - the effective upper limit is different if there is dominant 1/f noise at 10 Hz or not.
With an aluminum case the contact to the case can be tricky. Sometimes aluminum does not make a good contact due to a strong oxide layer.
I finally decided to reprint my PCB of the Andreas based noise amplifier along with other PCB I made and today I completed the assembly.
Just build one and here are my first results (with 3,3mF ~2nA leakage, circuit without any enclosure):
--> there is essentially no relevant difference between low noise voltage source and short at input
what manufacturer/type of 3,3 mF capacitor did you use (2 nA is really low: at which voltage?).
the first picture with the "artefact" in division 9+10 makes me think of some interference (perhaps with a switchmode supply).
I would put all into a metal cookies box.
what manufacturer/type of 3,3 mF capacitor did you use (2 nA is really low: at which voltage?).
the first picture with the "artefact" in division 9+10 makes me think of some interference (perhaps with a switchmode supply).
I would put all into a metal cookies box.
The caps are Panasonic Series: M Typ: A 85°C 2000h.
Had two 3,3mF 25V for first test, one went down to ~2nA, the other to ~3,5nA @~11,5V.
They were formed @11,5V 48h + ~1week disconnected @20°C and <30%rH.
Perhaps my cheap SMPS with "high ripple" had an effect on that, for rechargeable batteries the positive effect with reflex/pulse charging is well known...
Tested with ADA4530-1 @12V as buffer for 12h with recording of voltage drop.
So the 2nA are before soldering, did not test after.
The scope was set with BW-limit to 20MHz (only option for this Rigol) and hires-mode turned on.
As it was a first test with bodged wires, I do not give a thougt on any residues or interference in the readings.
Sure it will go into metal cookie box with coax-cables and BNC-connectors and repeat the measurements