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WBLNA - Wide Bandwidth low noise amplifier
WBLNA - Wide Bandwidth low noise amplifier
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Old 12th October 2019, 08:14 AM   #1
Frex is offline Frex  France
diyAudio Member
 
Join Date: Nov 2009
Arrow WBLNA - Wide Bandwidth low noise amplifier

Hi all,

I designed some weeks ago a small tool to improve my noise instrumentation setup.
In fact, when doing wide-band noise measurement (well beyond what we can simply do with a sound card),
is is more difficult to measure low noise level.
One way is to use RMS measurement with an oscilloscope, but scope sensitivity doesn't go much less than a mV...
My latest AAPSU01 low noise PSU design is an example that can achieve low wide-band noise,
and so building this small tool has been motivate first by that.

So in practical manner, it's a small shielded box that include a low noise, high bandwidth and high gain amplifier.

The design specs are :
  • 20Hz to 20MHz measurement bandwidth (-3 dB)
  • 4th order Butterworth low pass filtering.
  • Individual +20 dB(x10) and +40 dB(x100) outputs BNC
  • 12 Vdc@50mA input supply.
  • Max input amplitude about 100mVpp (with 12V supply)
  • Output noise floor RTI ~ 12µVrms (Equal to En= 2.7nV/VHz)
  • Can handle +/- 20VDC input offset voltage (AC coupled)
  • Zin= 50 Ohms, AC or DC coupled (internal jumpers)
  • Fully shielded design.
  • Low cost design (full bom <30€ + PCB)

The design is based on LT6200-10 OPAMP from LinearTech (now AD).
It's a very high speed amplifier with 1.6GHz of GBW product
and less than 1nV/VHz of spectral noise density.


The full schematics is here : WBLNA_schematics


You can show below some picture of my unit and some measurements results.

PCB Kicad 3D view :

Click the image to open in full size.


Picture of the finished prototype :

Click the image to open in full size.


100ns pulse test input/output result :

Click the image to open in full size.


So, i have published this projects as open source and it is available
to download on the GitHub repository here : \OnEAudioProjects\WBLNA
The project has been designed with Kicad 5.0.2

All original design files are available :
  • Schematics
  • Bill of material (with Mouser order codes)
  • Mechanical drawing
  • LTspice design files
  • Gerbers files
  • Panels stickers print
and more...

So i hope that will interest some people.

(Note that i have few bare PCB's available(4) , anyone interested can get one
with the panel stickers for 6€ worldwide shipping included )

Regards.


Frex
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Old 12th October 2019, 08:30 AM   #2
jan.didden is offline jan.didden  Europe
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Join Date: May 2002
Location: Westende Resort, BE coast
Frex, you keep surprising us!

Do you have an idea of the distortion of this amplifier up to say 50kHz?

Jan
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Old 12th October 2019, 09:08 AM   #3
Frex is offline Frex  France
diyAudio Member
 
Join Date: Nov 2009
Hello,

I don't have done THD measurement on it, but LT6200-10 datasheet specs show very good THD figure
up to MHz range.I'll try to make some measurements if i found time.
Regards.

Frex
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Old 14th October 2019, 09:54 PM   #4
Mark Tillotson is offline Mark Tillotson
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Join Date: May 2018
Location: Cambridge UK
The LT6200 1/f knee is around 1kHz, not unusual for a high speed amp, but not ideal for audio work perhaps?


Do you have a measured noise-floor plot?
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Old 16th October 2019, 03:26 PM   #5
Frex is offline Frex  France
diyAudio Member
 
Join Date: Nov 2009
Hello,

It's not directly intended to audio stuff, but it can.

You can show on simulation of my design in LTSpice below
the noise spectra density between all bandwidth of 20Hz-20MHz.
It show an rms value of about 1mV, very near i had really measured on my prototype (1.2mV).
If you would take only audio bandwidth of 20Hz-20kHz, that would gave 31 µVrms that is 310nVrms RTI.
Regards.

Frex


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