Thunderbolt spurs on 10MHz output at 100Hz and 200Hz from signal.
Yes, I fear a timepod is a bit out of my budget (I can dream tho'). Over here in the UK PN measurement kit is a bit thin on the ground too.
So I looked at http://www.wenzel.com/documents/measuringphasenoise.htm but that seemed a little thin on details. Or were you referring to something else?
Dave
On 9/21/2016 9:01 AM, David C. Partridge wrote:
Yes, I fear a timepod is a bit out of my budget (I can dream tho'). Over here in the UK PN measurement kit is a bit thin on the ground too.
So I looked at http://www.wenzel.com/documents/measuringphasenoise.htm but that seemed a little thin on details. Or were you referring to something else?
The Wenzel note is at: http://www.wenzel.com/documents/circuits1.htm
as a pdf under link: "Low noise amplifier for Phase Noise measurements"
or try: www.wenzel.com/wp-content/uploads/lowamp.pdf
Pretty much all there, but the FET is hard to find now.
Dan
On Wed, 21 Sep 2016 09:16:18 -0700
Dan Rae danrae@verizon.net wrote:
On 9/21/2016 9:01 AM, David C. Partridge wrote:
Yes, I fear a timepod is a bit out of my budget (I can dream tho'). Over here in the UK PN measurement kit is a bit thin on the ground too.
So I looked at http://www.wenzel.com/documents/measuringphasenoise.htm but that seemed a little thin on details. Or were you referring to something else?
The Wenzel note is at: http://www.wenzel.com/documents/circuits1.htm
as a pdf under link: "Low noise amplifier for Phase Noise measurements"
or try: www.wenzel.com/wp-content/uploads/lowamp.pdf
Pretty much all there, but the FET is hard to find now.
If you want to build such an amplifier, then the first stage (aka the
jFET input and the first opamp) is the critical component. There are
other, more modern descriptions for this kind of application, in case
you don't want to just replace the jFET by one if its modern cousins.
One well known is AN124[1] and it's more current cousin AN159[2].
For the later, Bruce commented that an jFET input stage would
probably be more quiet. Gerhard Hoffman has designed a similar
system[3] that uses a couple of paralel low noise opamps instead
of a jfet stage and claims a noise floor of 220pV/sqrt(Hz). All of
these would need to be adapted to imporve thier frequency response
up to 10MHz (or actually a bit higher), but then the input stage
gets also a bit simpler as you don't need the huge capacitors anymore.
I also recommend a look at [4] which lists a couple of issues with jFET
input stages for opamps and how to get around them.
Attila Kinali
[1] "775 Nanovolt Noise Measurement for A Low Noise Voltage Reference",
by Jim Williams, Linear AN124, 2009
[2] "Measuring 2nV/sqrt(Hz) Noise and 120dB Supply Rejection
on Linear Regulators", by Todd Owen and Amit Patel, Linear AN159, 2016
[3] "A 220 pV/sqrt(Hz) low noise preamplifier", by Gerhard Hoffman, 2014
http://www.hoffmann-hochfrequenz.de/downloads/lono.pdf
[4] "Some Tips on Making a FETching Discrete Amplifier", by George Alexandrov
and Nathan Carter, Analog Dialog 47-10, 2013
http://www.analog.com/library/analogdialogue/archives/47-10/discrete_amplifier.html
--
Malek's Law:
Any simple idea will be worded in the most complicated way.
On Wed, September 21, 2016 1:59 pm, Attila Kinali wrote:
On Wed, 21 Sep 2016 09:16:18 -0700
Dan Rae danrae@verizon.net wrote:
Pretty much all there, but the FET is hard to find now.
If you want to build such an amplifier, then the first stage (aka the
jFET input and the first opamp) is the critical component. There are
other, more modern descriptions for this kind of application, in case
you don't want to just replace the jFET by one if its modern cousins.
If you do want to just substitute newer parts into the same style design,
you should be able to get Linear Systems jfets. They are not as quiet,
but much lower capacitance, so you could put more in parallel to get
reduced noise.
http://linearsystems.com/products_details.php?pr=jfet-amplifiers--duals&pro_id=65
--
Chris Caudle
On Wednesday, September 21, 2016 08:59:18 PM Attila Kinali wrote:
On Wed, 21 Sep 2016 09:16:18 -0700
Dan Rae danrae@verizon.net wrote:
On 9/21/2016 9:01 AM, David C. Partridge wrote:
Yes, I fear a timepod is a bit out of my budget (I can dream tho').
Over here in the UK PN measurement kit is a bit thin on the ground
too.
So I looked at
but that seemed a little thin on details. Or were you referring to
something else?>
The Wenzel note is at: http://www.wenzel.com/documents/circuits1.htm
as a pdf under link: "Low noise amplifier for Phase Noise
measurements"
or try: www.wenzel.com/wp-content/uploads/lowamp.pdf
Pretty much all there, but the FET is hard to find now.
If you want to build such an amplifier, then the first stage (aka the
jFET input and the first opamp) is the critical component. There are
other, more modern descriptions for this kind of application, in case
you don't want to just replace the jFET by one if its modern cousins.
One well known is AN124[1] and it's more current cousin AN159[2].
For the later, Bruce commented that an jFET input stage would
probably be more quiet. Gerhard Hoffman has designed a similar
system[3] that uses a couple of paralel low noise opamps instead
of a jfet stage and claims a noise floor of 220pV/sqrt(Hz). All of
these would need to be adapted to imporve thier frequency response
up to 10MHz (or actually a bit higher), but then the input stage
gets also a bit simpler as you don't need the huge capacitors anymore.
I also recommend a look at [4] which lists a couple of issues with jFET
input stages for opamps and how to get around them.
Attila Kinali
[1] "775 Nanovolt Noise Measurement for A Low Noise Voltage
Reference",
by Jim Williams, Linear AN124, 2009
[2] "Measuring 2nV/sqrt(Hz) Noise and 120dB Supply Rejection
on Linear Regulators", by Todd Owen and Amit Patel, Linear AN159, 2016
[3] "A 220 pV/sqrt(Hz) low noise preamplifier", by Gerhard Hoffman, 2014
http://www.hoffmann-hochfrequenz.de/downloads/lono.pdf
[4] "Some Tips on Making a FETching Discrete Amplifier", by George
Alexandrov and Nathan Carter, Analog Dialog 47-10, 2013
er.html
2sk369BL are still available from:
http://www.ampslab.com/trans_2sk369.htm
I obtained some from them, they met the noise specs so are probably not
counterfeit.
One issue with the Wenzel preamp is that it has poor PSRR.
This can easily be improved substantially by redesigning the bias circuitry
for the opamp noninverting input.
Another issue is the requirement to trim the current sink for low output
offset. If one takes advantage of the fact that the PLL imposes a low
frequency cutoff to the PN measurements, the amplifier input can be AC
coupled, allowing dc bias feedback to be applied to the input device gate.
Use a parallel dc coupled JFET input opamp for the PLL
Using a single ended input stage is significantly quieter than using a
differential pair.
Paralleled BF862's can be substituted for the input JFET.
Bruce
Am 22.09.2016 um 00:24 schrieb Bruce Griffiths:
For the later, Bruce commented that an jFET input stage would
probably be more quiet. Gerhard Hoffman has designed a similar
I must insist in my second "n" Hoffmann :-)
system[3] that uses a couple of paralel low noise opamps instead
of a jfet stage and claims a noise floor of 220pV/sqrt(Hz). All of
these would need to be adapted to imporve thier frequency response
up to 10MHz (or actually a bit higher), but then the input stage
gets also a bit simpler as you don't need the huge capacitors anymore.
The ADA4898 has ft= 50 MHz, so that will be hard. It already takes some
cascoding
to get to 2 MHz with the new FET amp.
Another issue is the requirement to trim the current sink for low output
offset. If one takes advantage of the fact that the PLL imposes a low
frequency cutoff to the PN measurements, the amplifier input can be AC
coupled, allowing dc bias feedback to be applied to the input device gate.
Use a parallel dc coupled JFET input opamp for the PLL
Using a single ended input stage is significantly quieter than using a
differential pair.
Paralleled BF862's can be substituted for the input JFET.
Hi, Bruce and Attila (and ...),
the JFET version of my preamp is making progress. It supports either upto 16
BF862 or 2 pairs of Interfet IF3602. Upper bandwidth limit will be 2 MHz if
it runs like the simulation. There is also a low gain DC output for the PLL.
<
https://www.flickr.com/photos/137684711@N07/29193737144/in/dateposted-public/
One is populated with BF862, the other with Interfet. The 3rd will be
populated
according to the outcome of the first tests, so that I have 2 equal ones for
X correlation. There will be some leftover boards available, but not to
put them
into the drawer.
Soldered them last weekend, debug them on the next :-)
I expect 170 pV/rt Hz at least for the Interfet version. That is
probably pearls before
swine after a ring mixer, but then we are nuts.
Attila, you are just half an hour of driving away, at least during the
weekend!
regards, Gerhard
Am 22.09.2016 um 00:24 schrieb Bruce Griffiths:
Another issue is the requirement to trim the current sink for low output
offset.
And that FET is made from Unobtainium.
If one takes advantage of the fact that the PLL imposes a low
frequency cutoff to the PN measurements, the amplifier input can be AC
coupled, allowing dc bias feedback to be applied to the input device gate.
Use a parallel dc coupled JFET input opamp for the PLL
That's what I did. Original Burr-Brown opa2134, time to use them up..
Paralleled BF862's can be substituted for the input JFET.
Yep!
On Thursday, September 22, 2016 01:37:02 AM Gerhard Hoffmann wrote:
Am 22.09.2016 um 00:24 schrieb Bruce Griffiths:
Another issue is the requirement to trim the current sink for low
output
offset.
And that FET is made from Unobtainium.
If one takes advantage of the fact that the PLL imposes a low
frequency cutoff to the PN measurements, the amplifier input can be
AC
coupled, allowing dc bias feedback to be applied to the input device
gate.
Use a parallel dc coupled JFET input opamp for the PLL
That's what I did. Original Burr-Brown opa2134, time to use them up..
Paralleled BF862's can be substituted for the input JFET.
Yep!
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One still has to deal with the negative R in series with negative C input
impedance component which will cause peaking with source resistance
greater than a few ohms (typically 1k source resistance shows significant
gain peaking at high frequencies near the upper end of the amplifiers
bandwidth).
Bruce