Low noise N-JFET ?

Jon Elson <elson@wustl.edu> wrote:


Pieter wrote:

I did not find information on noise from 0 - 10 Hz yet. Seems that
there are only a few specialists.
Because the news is very bad down there, they don't WANT you to know.
Try to find op-amp specs for very low F noise, it is practically absent.
One op amp with really GOOD LF noise, and tey SPEC it too in the data
sheets, it the AD706. It got us out of a bind where we had a LOT of
extremely low-F noise. Our circuit would sit there runnign perfectly
stable for minutes, then suddenly it would jump millivolts. The AD706
was the only thing in the entire book that had a guaranteed spec for
.001 - 1 Hz. The spec wasn't that astonishingly low, but the fact they
were willing to guarantee the 1/f curve out to .001 Hz was big news.
Click to expand...
Specs need to be tested. A noise spec at 0.001 Hz needs a at least 1000
seconds to measure. This will make the test very expensive, as the tester
can only test 86 chips per day.

--
Uwe Bonnes bon@elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik Schlossgartenstrasse 9 64289 Darmstadt
--------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------
 
On Tue, 06 Nov 2007 16:50:25 -0600, Jon Elson <elson@wustl.edu> wrote:

Pieter wrote:
For this project, I am searching a low noise N-JFET for the input
stage. This will be followed by a very low noise opamp like the AD797
or LT1028. The drain current will probably be something like 10 mA.


We used the InterFet IF9030 and found it to be exceptional.
We ran it at about 4.5 mA to get the best noise performance.
I think Interfet got bought out by somebody since we bought these.

Jon
Click to expand...
Hi,

The website is still there, and yes, the specs are exceptional. Only
the capacitance is high, that that does make sens for a FET optimized
for noise.

Pieter
 
On Tue, 06 Nov 2007 16:57:33 -0600, Jon Elson <elson@wustl.edu> wrote:
Pieter wrote:
I did not find information on noise from 0 - 10 Hz yet. Seems that
there are only a few specialists.
Because the news is very bad down there, they don't WANT you to know.
Try to find op-amp specs for very low F noise, it is practically absent.
One op amp with really GOOD LF noise, and tey SPEC it too in the data
sheets, it the AD706. It got us out of a bind where we had a LOT of
extremely low-F noise. Our circuit would sit there runnign perfectly
stable for minutes, then suddenly it would jump millivolts. The AD706
was the only thing in the entire book that had a guaranteed spec for
.001 - 1 Hz. The spec wasn't that astonishingly low, but the fact they
were willing to guarantee the 1/f curve out to .001 Hz was big news.

Jon
Click to expand...
I was planning to use the AD797 or LT1028.

Pieter
 
Jon Elson wrote:
Pieter wrote:

I did not find information on noise from 0 - 10 Hz yet. Seems that
there are only a few specialists.
Because the news is very bad down there, they don't WANT you to know.
Try to find op-amp specs for very low F noise, it is practically absent.
One op amp with really GOOD LF noise, and tey SPEC it too in the data
sheets, it the AD706. It got us out of a bind where we had a LOT of
extremely low-F noise. Our circuit would sit there runnign perfectly
stable for minutes, then suddenly it would jump millivolts. The AD706
was the only thing in the entire book that had a guaranteed spec for
.001 - 1 Hz. The spec wasn't that astonishingly low, but the fact they
were willing to guarantee the 1/f curve out to .001 Hz was big news.
Click to expand...
That is surprising, although 17nV/rtHz at 10Hz is indeed not much to
write home about. But it does have the knee nice and low.

--
Regards, Joerg

http://www.analogconsultants.com/
 
Jon Elson wrote:
Pieter wrote:

I did not find information on noise from 0 - 10 Hz yet. Seems that
there are only a few specialists.
Because the news is very bad down there, they don't WANT you to know.
Try to find op-amp specs for very low F noise, it is practically absent.
One op amp with really GOOD LF noise, and tey SPEC it too in the data
sheets, it the AD706. It got us out of a bind where we had a LOT of
extremely low-F noise. Our circuit would sit there runnign perfectly
stable for minutes, then suddenly it would jump millivolts. The AD706
was the only thing in the entire book that had a guaranteed spec for
.001 - 1 Hz. The spec wasn't that astonishingly low, but the fact they
were willing to guarantee the 1/f curve out to .001 Hz was big news.
Click to expand...
This one is also quite good even though the graph ends at 10Hz. But I
never had to go lower than 5Hz or so:

http://www.national.com/ds/LM/LM833.pdf

--
Regards, Joerg

http://www.analogconsultants.com/
 
Le Tue, 06 Nov 2007 16:57:33 -0600, Jon Elson a ĂŠcrit:

Pieter wrote:

I did not find information on noise from 0 - 10 Hz yet. Seems that
there are only a few specialists.
Because the news is very bad down there, they don't WANT you to know.
Try to find op-amp specs for very low F noise, it is practically absent.
One op amp with really GOOD LF noise, and tey SPEC it too in the data
sheets, it the AD706. It got us out of a bind where we had a LOT of
extremely low-F noise. Our circuit would sit there runnign perfectly
stable for minutes, then suddenly it would jump millivolts. The AD706
was the only thing in the entire book that had a guaranteed spec for
.001 - 1 Hz. The spec wasn't that astonishingly low, but the fact they
were willing to guarantee the 1/f curve out to .001 Hz was big news.
Click to expand...
http://www.analog.com/UploadedFiles/Data_Sheets/AD706.pdf
Where did you find the 1mH-1Hz curve?
It's specified, as many others, between 0.1Hz and 10Hz, and the noise
curves don't get under 1Hz.

Noise wise the AD706 is an ordinary one and many others outperform them
by far. Their virtue is more in the low bias current over temperature
range and I wouldn't use them for anything else.


--
Thanks,
Fred.
 
Pieter wrote:

I did not find information on noise from 0 - 10 Hz yet. Seems that
there are only a few specialists.
Because the news is very bad down there, they don't WANT you to know.
Click to expand...
Try to find op-amp specs for very low F noise, it is practically absent.
One op amp with really GOOD LF noise, and tey SPEC it too in the data
sheets, it the AD706. It got us out of a bind where we had a LOT of
extremely low-F noise. Our circuit would sit there runnign perfectly
stable for minutes, then suddenly it would jump millivolts. The AD706
was the only thing in the entire book that had a guaranteed spec for
..001 - 1 Hz. The spec wasn't that astonishingly low, but the fact they
were willing to guarantee the 1/f curve out to .001 Hz was big news.

Jon
 
Pieter wrote:
My problem is that I not only need the noise from 0 - 1MHz, but also
the low-frequency noise from 0 - 10 Hz. And it is unclear to me what
is does there.
Click to expand...
We needed low noise in the sub-Hz region, too. The Interfet IF9030 I
mentioned in another reply is a full mm square device, so that brings
down the noise a lot. (Obviously their processing is also optimized to
lower the noise.)

Jon
 
Pieter wrote:
For this project, I am searching a low noise N-JFET for the input
stage. This will be followed by a very low noise opamp like the AD797
or LT1028. The drain current will probably be something like 10 mA.
Click to expand...

We used the InterFet IF9030 and found it to be exceptional.
We ran it at about 4.5 mA to get the best noise performance.
I think Interfet got bought out by somebody since we bought these.

Jon
 
P

Pieter

Guest
Hi,

I am building a device that can measure noise from resistors and
semiconductors. The source resistance ranges 0.2 Ohm to 20 MOhm.

But mostly semiconductors have to measured, and the range that is most
important is 500 Ohm to 2500 Ohm. That is the basic resistance of
those devices.

The frequency ranges to be measured are 0-10 Hz and 0-1 MHz. And the
noise is low, maximum of the semiconductor devices is 10 dB (compared
to the resistance 500 to 2500 Ohm), probably less.

For this project, I am searching a low noise N-JFET for the input
stage. This will be followed by a very low noise opamp like the AD797
or LT1028. The drain current will probably be something like 10 mA.

My questions:
What N-FETs (BFxxx? 2Nxxxx?) are really low-noise? Searching
datasheets is hopeless.
Does anyone here have advice about the input stage? Do you think a FET
input with opamp following it will do? Or can you think of better ones
that have lower noise, and lower input capacitance?

Any help or comment is welcome.

Thanks in advance,
Pieter
 
Pieter <dit3_werkt_ook_niet@hotmail.com> wrote:
Hi,

I am building a device that can measure noise from resistors and
semiconductors. The source resistance ranges 0.2 Ohm to 20 MOhm.

But mostly semiconductors have to measured, and the range that is most
important is 500 Ohm to 2500 Ohm. That is the basic resistance of
those devices.

The frequency ranges to be measured are 0-10 Hz and 0-1 MHz. And the
noise is low, maximum of the semiconductor devices is 10 dB (compared
to the resistance 500 to 2500 Ohm), probably less.

For this project, I am searching a low noise N-JFET for the input
stage. This will be followed by a very low noise opamp like the AD797
or LT1028. The drain current will probably be something like 10 mA.

My questions:
What N-FETs (BFxxx? 2Nxxxx?) are really low-noise? Searching
datasheets is hopeless.
Does anyone here have advice about the input stage? Do you think a FET
input with opamp following it will do? Or can you think of better ones
that have lower noise, and lower input capacitance?
Click to expand...
The BF862 is very low noise.

Look at the Linear Technology site to use it in conjunction with low noise
fast Op-Amps.

--
Uwe Bonnes bon@elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik Schlossgartenstrasse 9 64289 Darmstadt
--------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------
 
Uwe Bonnes schrieb:
Pieter <dit3_werkt_ook_niet@hotmail.com> wrote:
Hi,

I am building a device that can measure noise from resistors and
semiconductors. The source resistance ranges 0.2 Ohm to 20 MOhm.

But mostly semiconductors have to measured, and the range that is most
important is 500 Ohm to 2500 Ohm. That is the basic resistance of
those devices.

The frequency ranges to be measured are 0-10 Hz and 0-1 MHz. And the
noise is low, maximum of the semiconductor devices is 10 dB (compared
to the resistance 500 to 2500 Ohm), probably less.

For this project, I am searching a low noise N-JFET for the input
stage. This will be followed by a very low noise opamp like the AD797
or LT1028. The drain current will probably be something like 10 mA.

My questions:
What N-FETs (BFxxx? 2Nxxxx?) are really low-noise? Searching
datasheets is hopeless.
Does anyone here have advice about the input stage? Do you think a FET
input with opamp following it will do? Or can you think of better ones
that have lower noise, and lower input capacitance?

The BF862 is very low noise.

Look at the Linear Technology site to use it in conjunction with low noise
fast Op-Amps.
Click to expand...
The BF682 (IDSSS = 10 .. 25 mA, Yfs = 45 mS typ) seems to come in a
surface-mount package only. Some Japanese through-hole counterparts
(all Toshiba) are:

2SK117, 2SK184: IDSSS = 1.2 .. 14 mA, Yfs = 15 mS typ
2SK170: IDSSS = 2.6 .. 20 mA, Yfs = 22 mS typ
2SK370: IDSSS = 2.6 .. 20 mA, Yfs = 28 mS typ
2SK369, 2SK371: IDSSS = 5 .. 30 mA, Yfs = 40 mS typ
2SK389: monolithic 2SK170 pair

A higher transfer admittance Yfs means a changed channel geometry
corresponding to a paralleling of FETs with lower Yfs. It translates
into smaller noise, as the dominant source of white noise is resistive
noise from the channel. On the other hand, this means higher FET
capacitances.

Similar to bipolar transistors, FET noise also involves a 1/f
component below some corner frequency. However, while the designers of
the bipolar MAT02, MAT03, LT1028, and AD797 managed to push this
corner down to the 1 .. 10 Hz range, the noise of the above FETs
already starts to rise below the 1 .. 10 kHz range. Compare the
Toshiba datasheets.

Also note that the LT1028 has a noise peak around 400kHz (see page 9
of the Linear Technology datasheet).

Martin.
 
Uwe Bonnes wrote:
Pieter <dit3_werkt_ook_niet@hotmail.com> wrote:
Hi,

I am building a device that can measure noise from resistors and
semiconductors. The source resistance ranges 0.2 Ohm to 20 MOhm.

But mostly semiconductors have to measured, and the range that is most
important is 500 Ohm to 2500 Ohm. That is the basic resistance of
those devices.

The frequency ranges to be measured are 0-10 Hz and 0-1 MHz. And the
noise is low, maximum of the semiconductor devices is 10 dB (compared
to the resistance 500 to 2500 Ohm), probably less.

For this project, I am searching a low noise N-JFET for the input
stage. This will be followed by a very low noise opamp like the AD797
or LT1028. The drain current will probably be something like 10 mA.

My questions:
What N-FETs (BFxxx? 2Nxxxx?) are really low-noise? Searching
datasheets is hopeless.
Does anyone here have advice about the input stage? Do you think a FET
input with opamp following it will do? Or can you think of better ones
that have lower noise, and lower input capacitance?

The BF862 is very low noise.
Click to expand...
I was just going to suggest that one, it ought to be the lowest noise
JFET around. However, as Martin pointed out one may have to consider the
sub-audio region. NXP's data sheet is, ahem, rather skimpy. Do you (or
Martin) know about any study of the BF862 below, say, 20Hz?

Also, does anyone know what happened to the old 2N4417? Can't find it
anywhere these days.


Look at the Linear Technology site to use it in conjunction with low noise
fast Op-Amps.
Click to expand...
I am a bit partial to the Texas THS series. Mostly because many can be
used at +/-10V and more, resulting in lots of dynamic range.

--
Regards, Joerg

http://www.analogconsultants.com/
 
On Wed, 31 Oct 2007 12:06:38 -0700, Joerg
<notthisjoergsch@removethispacbell.net> wrote:

Uwe Bonnes wrote:
Pieter <dit3_werkt_ook_niet@hotmail.com> wrote:
Hi,

I am building a device that can measure noise from resistors and
semiconductors. The source resistance ranges 0.2 Ohm to 20 MOhm.

But mostly semiconductors have to measured, and the range that is most
important is 500 Ohm to 2500 Ohm. That is the basic resistance of
those devices.

The frequency ranges to be measured are 0-10 Hz and 0-1 MHz. And the
noise is low, maximum of the semiconductor devices is 10 dB (compared
to the resistance 500 to 2500 Ohm), probably less.

For this project, I am searching a low noise N-JFET for the input
stage. This will be followed by a very low noise opamp like the AD797
or LT1028. The drain current will probably be something like 10 mA.

My questions:
What N-FETs (BFxxx? 2Nxxxx?) are really low-noise? Searching
datasheets is hopeless.
Does anyone here have advice about the input stage? Do you think a FET
input with opamp following it will do? Or can you think of better ones
that have lower noise, and lower input capacitance?

The BF862 is very low noise.


I was just going to suggest that one, it ought to be the lowest noise
JFET around. However, as Martin pointed out one may have to consider the
sub-audio region. NXP's data sheet is, ahem, rather skimpy. Do you (or
Martin) know about any study of the BF862 below, say, 20Hz?

Also, does anyone know what happened to the old 2N4417? Can't find it
anywhere these days.


Look at the Linear Technology site to use it in conjunction with low noise
fast Op-Amps.


I am a bit partial to the Texas THS series. Mostly because many can be
used at +/-10V and more, resulting in lots of dynamic range.
Click to expand...
My problem is that I not only need the noise from 0 - 1MHz, but also
the low-frequency noise from 0 - 10 Hz. And it is unclear to me what
is does there.

I tried to simulate it in Multisim, but that gave very strange noise
results when I changed the frequency range (went from -110 dB to +33
dB).

Pieter
 
Pieter wrote:
On Wed, 31 Oct 2007 12:06:38 -0700, Joerg
notthisjoergsch@removethispacbell.net> wrote:

Uwe Bonnes wrote:
Pieter <dit3_werkt_ook_niet@hotmail.com> wrote:
Hi,
I am building a device that can measure noise from resistors and
semiconductors. The source resistance ranges 0.2 Ohm to 20 MOhm.
But mostly semiconductors have to measured, and the range that is most
important is 500 Ohm to 2500 Ohm. That is the basic resistance of
those devices.
The frequency ranges to be measured are 0-10 Hz and 0-1 MHz. And the
noise is low, maximum of the semiconductor devices is 10 dB (compared
to the resistance 500 to 2500 Ohm), probably less.
For this project, I am searching a low noise N-JFET for the input
stage. This will be followed by a very low noise opamp like the AD797
or LT1028. The drain current will probably be something like 10 mA.
My questions:
What N-FETs (BFxxx? 2Nxxxx?) are really low-noise? Searching
datasheets is hopeless.
Does anyone here have advice about the input stage? Do you think a FET
input with opamp following it will do? Or can you think of better ones
that have lower noise, and lower input capacitance?
The BF862 is very low noise.

I was just going to suggest that one, it ought to be the lowest noise
JFET around. However, as Martin pointed out one may have to consider the
sub-audio region. NXP's data sheet is, ahem, rather skimpy. Do you (or
Martin) know about any study of the BF862 below, say, 20Hz?

Also, does anyone know what happened to the old 2N4417? Can't find it
anywhere these days.


Look at the Linear Technology site to use it in conjunction with low noise
fast Op-Amps.

I am a bit partial to the Texas THS series. Mostly because many can be
used at +/-10V and more, resulting in lots of dynamic range.

My problem is that I not only need the noise from 0 - 1MHz, but also
the low-frequency noise from 0 - 10 Hz. And it is unclear to me what
is does there.

I tried to simulate it in Multisim, but that gave very strange noise
results when I changed the frequency range (went from -110 dB to +33
dB).
Click to expand...
IME Spice is not very helpful here. I am afraid someone has to actually
measure it because Philips probably didn't. If you decide to do that
please post.

Hey, aren't you in the Netherlands? I've lived there many years ago and
most people I knew had some relative or acquaintance who worked at
Philips, or now NXP. Maybe ask someone?

--
Regards, Joerg

http://www.analogconsultants.com/
 
Joerg schrieb:
Uwe Bonnes wrote:
Pieter <dit3_werkt_ook_niet@hotmail.com> wrote:
Hi,

I am building a device that can measure noise from resistors and
semiconductors. The source resistance ranges 0.2 Ohm to 20 MOhm.

But mostly semiconductors have to measured, and the range that is most
important is 500 Ohm to 2500 Ohm. That is the basic resistance of
those devices.

The frequency ranges to be measured are 0-10 Hz and 0-1 MHz. And the
noise is low, maximum of the semiconductor devices is 10 dB (compared
to the resistance 500 to 2500 Ohm), probably less.

For this project, I am searching a low noise N-JFET for the input
stage. This will be followed by a very low noise opamp like the AD797
or LT1028. The drain current will probably be something like 10 mA.

My questions:
What N-FETs (BFxxx? 2Nxxxx?) are really low-noise? Searching
datasheets is hopeless.
Does anyone here have advice about the input stage? Do you think a FET
input with opamp following it will do? Or can you think of better ones
that have lower noise, and lower input capacitance?

The BF862 is very low noise.


I was just going to suggest that one, it ought to be the lowest noise
JFET around.
Click to expand...
No. The transfer function of low-IDSS BF862's closely corresponds to
that of high-IDSS 2SK170's, so at the same drain current the white
noise will be the same. The 2SK369 has a higher Yfs and its white
noise will be lower.

It is remarkable, though, that the BF862 achieves the same Yfs at a
third of the capacitances of the 2SK170.

However, as Martin pointed out one may have to consider the
sub-audio region. NXP's data sheet is, ahem, rather skimpy. Do you (or
Martin) know about any study of the BF862 below, say, 20Hz?
Click to expand...
That's why I referred to the Toshiba datasheets. The BF861 too seems
to be a close relative to the BF862. It's noise is specified down to
10 Hz (Fig. 15), and this curve should roughly apply here too.

Also, does anyone know what happened to the old 2N4417? Can't find it
anywhere these days.
Click to expand...
Was this one much different from the 2N4416 = PN4416 ?

(Correction to my first post: the 2SK370 is nothing but a 2SK170 in a
miniturised through-hole package, electrically they are the same. And
please read IDSS for IDSSS.)

Martin.
 
On Thu, 01 Nov 2007 00:22:12 GMT, Joerg
<notthisjoergsch@removethispacbell.net> wrote:

Pieter wrote:
On Wed, 31 Oct 2007 12:06:38 -0700, Joerg
notthisjoergsch@removethispacbell.net> wrote:

Uwe Bonnes wrote:
Pieter <dit3_werkt_ook_niet@hotmail.com> wrote:
Hi,
I am building a device that can measure noise from resistors and
semiconductors. The source resistance ranges 0.2 Ohm to 20 MOhm.
But mostly semiconductors have to measured, and the range that is most
important is 500 Ohm to 2500 Ohm. That is the basic resistance of
those devices.
The frequency ranges to be measured are 0-10 Hz and 0-1 MHz. And the
noise is low, maximum of the semiconductor devices is 10 dB (compared
to the resistance 500 to 2500 Ohm), probably less.
For this project, I am searching a low noise N-JFET for the input
stage. This will be followed by a very low noise opamp like the AD797
or LT1028. The drain current will probably be something like 10 mA.
My questions:
What N-FETs (BFxxx? 2Nxxxx?) are really low-noise? Searching
datasheets is hopeless.
Does anyone here have advice about the input stage? Do you think a FET
input with opamp following it will do? Or can you think of better ones
that have lower noise, and lower input capacitance?
The BF862 is very low noise.

I was just going to suggest that one, it ought to be the lowest noise
JFET around. However, as Martin pointed out one may have to consider the
sub-audio region. NXP's data sheet is, ahem, rather skimpy. Do you (or
Martin) know about any study of the BF862 below, say, 20Hz?

Also, does anyone know what happened to the old 2N4417? Can't find it
anywhere these days.


Look at the Linear Technology site to use it in conjunction with low noise
fast Op-Amps.

I am a bit partial to the Texas THS series. Mostly because many can be
used at +/-10V and more, resulting in lots of dynamic range.

My problem is that I not only need the noise from 0 - 1MHz, but also
the low-frequency noise from 0 - 10 Hz. And it is unclear to me what
is does there.

I tried to simulate it in Multisim, but that gave very strange noise
results when I changed the frequency range (went from -110 dB to +33
dB).


IME Spice is not very helpful here. I am afraid someone has to actually
measure it because Philips probably didn't. If you decide to do that
please post.

Hey, aren't you in the Netherlands? I've lived there many years ago and
most people I knew had some relative or acquaintance who worked at
Philips, or now NXP. Maybe ask someone?
Click to expand...
Hi,

Yes, I live in the Netherlands. I have my own company now, and have in
the past also worked for several companies including Philips in
Eindhoven. NXP is former Philips Semiconductors in Nijmegen.

I did not find information on noise from 0 - 10 Hz yet. Seems that
there are only a few specialists.

Pieter
 
Uwe Bonnes <bon@hertz.ikp.physik.tu-darmstadt.de> wrote:
B.t.w.: Congratulations to the NXP web site developper :-(

Their search doesn't find the BF862.

Argh...
--
Uwe Bonnes bon@elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik Schlossgartenstrasse 9 64289 Darmstadt
--------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------
 
Pieter wrote:
On Thu, 01 Nov 2007 00:22:12 GMT, Joerg
notthisjoergsch@removethispacbell.net> wrote:

Pieter wrote:
On Wed, 31 Oct 2007 12:06:38 -0700, Joerg
notthisjoergsch@removethispacbell.net> wrote:

Uwe Bonnes wrote:
Pieter <dit3_werkt_ook_niet@hotmail.com> wrote:
Hi,
I am building a device that can measure noise from resistors and
semiconductors. The source resistance ranges 0.2 Ohm to 20 MOhm.
But mostly semiconductors have to measured, and the range that is most
important is 500 Ohm to 2500 Ohm. That is the basic resistance of
those devices.
The frequency ranges to be measured are 0-10 Hz and 0-1 MHz. And the
noise is low, maximum of the semiconductor devices is 10 dB (compared
to the resistance 500 to 2500 Ohm), probably less.
For this project, I am searching a low noise N-JFET for the input
stage. This will be followed by a very low noise opamp like the AD797
or LT1028. The drain current will probably be something like 10 mA.
My questions:
What N-FETs (BFxxx? 2Nxxxx?) are really low-noise? Searching
datasheets is hopeless.
Does anyone here have advice about the input stage? Do you think a FET
input with opamp following it will do? Or can you think of better ones
that have lower noise, and lower input capacitance?
The BF862 is very low noise.

I was just going to suggest that one, it ought to be the lowest noise
JFET around. However, as Martin pointed out one may have to consider the
sub-audio region. NXP's data sheet is, ahem, rather skimpy. Do you (or
Martin) know about any study of the BF862 below, say, 20Hz?

Also, does anyone know what happened to the old 2N4417? Can't find it
anywhere these days.


Look at the Linear Technology site to use it in conjunction with low noise
fast Op-Amps.

I am a bit partial to the Texas THS series. Mostly because many can be
used at +/-10V and more, resulting in lots of dynamic range.
My problem is that I not only need the noise from 0 - 1MHz, but also
the low-frequency noise from 0 - 10 Hz. And it is unclear to me what
is does there.

I tried to simulate it in Multisim, but that gave very strange noise
results when I changed the frequency range (went from -110 dB to +33
dB).

IME Spice is not very helpful here. I am afraid someone has to actually
measure it because Philips probably didn't. If you decide to do that
please post.

Hey, aren't you in the Netherlands? I've lived there many years ago and
most people I knew had some relative or acquaintance who worked at
Philips, or now NXP. Maybe ask someone?

Hi,

Yes, I live in the Netherlands. I have my own company now, and have in
the past also worked for several companies including Philips in
Eindhoven. NXP is former Philips Semiconductors in Nijmegen.
Click to expand...
Ah, finally another one with entrepreneurial spirit in Europe. But I
wouldn't use "dit werkt ook niet" in the email address :)

Randstad area? Or out in the country? I used to live in Zuid Limburg, by
many Dutch people not considered to be part of NL because they couldn't
understand us. And they also didn't get most of the Urbanus jokes while
we were rolling on the floor.


I did not find information on noise from 0 - 10 Hz yet. Seems that
there are only a few specialists.
Click to expand...
NXP's marketing is a mystery to me. Sometimes I wonder whether they
still have one. I found the BF862 by pure coincidence. Never got any
email announcement about it, just stuff like all those boring protector
diodes they make. Yawn. Yet this FET could really take off in the
marketplace if they'd advertise it _and_ provide a little more data or
at least cram some more info into an app note. And they should get a
better web design time but that's a whole 'nother story.

--
Regards, Joerg

http://www.analogconsultants.com/
 
clicliclic@freenet.de wrote:
Joerg schrieb:
Uwe Bonnes wrote:
Pieter <dit3_werkt_ook_niet@hotmail.com> wrote:
Hi,
I am building a device that can measure noise from resistors and
semiconductors. The source resistance ranges 0.2 Ohm to 20 MOhm.
But mostly semiconductors have to measured, and the range that is most
important is 500 Ohm to 2500 Ohm. That is the basic resistance of
those devices.
The frequency ranges to be measured are 0-10 Hz and 0-1 MHz. And the
noise is low, maximum of the semiconductor devices is 10 dB (compared
to the resistance 500 to 2500 Ohm), probably less.
For this project, I am searching a low noise N-JFET for the input
stage. This will be followed by a very low noise opamp like the AD797
or LT1028. The drain current will probably be something like 10 mA.
My questions:
What N-FETs (BFxxx? 2Nxxxx?) are really low-noise? Searching
datasheets is hopeless.
Does anyone here have advice about the input stage? Do you think a FET
input with opamp following it will do? Or can you think of better ones
that have lower noise, and lower input capacitance?
The BF862 is very low noise.

I was just going to suggest that one, it ought to be the lowest noise
JFET around.

No. The transfer function of low-IDSS BF862's closely corresponds to
that of high-IDSS 2SK170's, so at the same drain current the white
noise will be the same. The 2SK369 has a higher Yfs and its white
noise will be lower.

It is remarkable, though, that the BF862 achieves the same Yfs at a
third of the capacitances of the 2SK170.

However, as Martin pointed out one may have to consider the
sub-audio region. NXP's data sheet is, ahem, rather skimpy. Do you (or
Martin) know about any study of the BF862 below, say, 20Hz?

That's why I referred to the Toshiba datasheets. The BF861 too seems
to be a close relative to the BF862. It's noise is specified down to
10 Hz (Fig. 15), and this curve should roughly apply here too.
Click to expand...
Fig 14:
http://www.nxp.com/acrobat_download/datasheets/BF861A_BF861B_BF861C_4.pdf

Yuck, that's pretty bad. Puzzling: The BF861 is spec'd at 1.5nv/rtHz at
1MHz while the BF862 is spec'd at 0.8nv/rtHz at 100kHz:
http://www.nxp.com/acrobat_download/datasheets/BF862_3.pdf

So, is it "aggressive marketing" or is it really that much better? The
graph in the BF861 datasheet somehow tells another story.

I'll stay with the BCX70K for now where it doesn't have to be really
hi-Z. That's really low noise and much cheaper.


Also, does anyone know what happened to the old 2N4417? Can't find it
anywhere these days.

Was this one much different from the 2N4416 = PN4416 ?
Click to expand...
Nope, IIRC it is (was?) a small JFET.


(Correction to my first post: the 2SK370 is nothing but a 2SK170 in a
miniturised through-hole package, electrically they are the same. And
please read IDSS for IDSSS.)
Click to expand...
Well, but those are all not mainstream in the US.

--
Regards, Joerg

http://www.analogconsultants.com/
 
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