Joerg wrote:
> 
> Phil Hobbs wrote:
> > So I finally got the amplifier all measured up, with three different
> > pHEMTs: Skyworks SKY65050, Avago ATF38143, and Avago ATF34143.  Joerg's
> > suggestion of bodging in a bypass right at the collector load made the
> > amp stable even with the Avago parts, which are hotter than the Skyworks
> > one.  I dremelled down to the ground plane, so the inductance is only
> > 1-2 nH.
> >
> > Executive summary: horrible 1/f noise, but 0.28-0.4 nV noise in the
> > flatband, and < 1 pF input capacitance.  Second stage contribution
> > becomes important above ~100 MHz.  See
> > http://electrooptical.net/www/sed/pHEMT_probe/pHEMT_probe.html .
> >
> > Measuring all that was interesting--getting decent accuracy for noise
> > levels that small at high frequency is hard.
> >
> 
> 1/f is nearly always horrid with RF parts. If it's true wideband
> amplification you are after the only way is probably to diplex in a
> decent LF amp for the stuff under 20MHz. Of course that may not be
> helping much with phase noise in the GHz range.
> 
> I have done such splits before in FO gear but I had the luxury of a
> "dead band" (the client didn't need any signals from inseide there) from
> a few hundred kHz to a couple MHz or so. Meaning my diplexing could be
> rather crude.
> 
> --
> Regards, Joerg
> 
> http://www.analogconsultants.com/

Actually, it's okay for fast bootstraps and some TIAs--the
differentiating action of the input capacitance gets rid of most of the
low frequency schmutz.  It's pretty good medicine for the 1 nA/100 MHz
problem, which actually looks like it might be doable.  

Cheers

Phil Hobbs
-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

On Wed, 21 Mar 2012 10:01:48 -0700, Joerg <invalid@invalid.invalid>
wrote:

>Phil Hobbs wrote:
>> So I finally got the amplifier all measured up, with three different
>> pHEMTs: Skyworks SKY65050, Avago ATF38143, and Avago ATF34143.  Joerg's
>> suggestion of bodging in a bypass right at the collector load made the
>> amp stable even with the Avago parts, which are hotter than the Skyworks
>> one.  I dremelled down to the ground plane, so the inductance is only
>> 1-2 nH.
>> 
>> Executive summary: horrible 1/f noise, but 0.28-0.4 nV noise in the
>> flatband, and < 1 pF input capacitance.  Second stage contribution
>> becomes important above ~100 MHz.  See
>> http://electrooptical.net/www/sed/pHEMT_probe/pHEMT_probe.html .
>> 
>> Measuring all that was interesting--getting decent accuracy for noise
>> levels that small at high frequency is hard.
>> 
>
>1/f is nearly always horrid with RF parts. If it's true wideband
>amplification you are after the only way is probably to diplex in a
>decent LF amp for the stuff under 20MHz. Of course that may not be
>helping much with phase noise in the GHz range.
>
>I have done such splits before in FO gear but I had the luxury of a
>"dead band" (the client didn't need any signals from inseide there) from
>a few hundred kHz to a couple MHz or so. Meaning my diplexing could be
>rather crude.

We run into that same issue. The superfast parts, like distributed
amps, are inherently AC coupled, so we have to split the signal path
and squirt the DC part back in at the very end, with a wideband
inductor. If there are multiple places in the fast path that are AC
coupled, the DC path gets messy, and it's hard to get flat step
response.


-- 

John Larkin, President
Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation

Phil Hobbs wrote:
> So I finally got the amplifier all measured up, with three different
> pHEMTs: Skyworks SKY65050, Avago ATF38143, and Avago ATF34143.  Joerg's
> suggestion of bodging in a bypass right at the collector load made the
> amp stable even with the Avago parts, which are hotter than the Skyworks
> one.  I dremelled down to the ground plane, so the inductance is only
> 1-2 nH.
> 
> Executive summary: horrible 1/f noise, but 0.28-0.4 nV noise in the
> flatband, and < 1 pF input capacitance.  Second stage contribution
> becomes important above ~100 MHz.  See
> http://electrooptical.net/www/sed/pHEMT_probe/pHEMT_probe.html .
> 
> Measuring all that was interesting--getting decent accuracy for noise
> levels that small at high frequency is hard.
> 

1/f is nearly always horrid with RF parts. If it's true wideband
amplification you are after the only way is probably to diplex in a
decent LF amp for the stuff under 20MHz. Of course that may not be
helping much with phase noise in the GHz range.

I have done such splits before in FO gear but I had the luxury of a
"dead band" (the client didn't need any signals from inseide there) from
a few hundred kHz to a couple MHz or so. Meaning my diplexing could be
rather crude.

-- 
Regards, Joerg

http://www.analogconsultants.com/

John Larkin wrote:
> 
> On Wed, 21 Mar 2012 10:59:18 -0400, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
> 
> >So I finally got the amplifier all measured up, with three different
> >pHEMTs: Skyworks SKY65050, Avago ATF38143, and Avago ATF34143.  Joerg's
> >suggestion of bodging in a bypass right at the collector load made the
> >amp stable even with the Avago parts, which are hotter than the Skyworks
> >one.  I dremelled down to the ground plane, so the inductance is only
> >1-2 nH.
> >
> >Executive summary: horrible 1/f noise, but 0.28-0.4 nV noise in the
> >flatband, and < 1 pF input capacitance.  Second stage contribution
> >becomes important above ~100 MHz.  See
> >http://electrooptical.net/www/sed/pHEMT_probe/pHEMT_probe.html .
> >
> >Measuring all that was interesting--getting decent accuracy for noise
> >levels that small at high frequency is hard.
> >
> >Cheers
> >
> >Phil Hobbs
> 
> Hi, Phil,
> 
> Did you ever get the NE3509 to stop screaming? I measured its gate
> capacitance at about half a pF.
> 

I'll try that next.  Its pinout is different, so it isn't as easy to use
in this amp.

Cheers

Phil 

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

On Wed, 21 Mar 2012 10:59:18 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>So I finally got the amplifier all measured up, with three different
>pHEMTs: Skyworks SKY65050, Avago ATF38143, and Avago ATF34143.  Joerg's
>suggestion of bodging in a bypass right at the collector load made the
>amp stable even with the Avago parts, which are hotter than the Skyworks
>one.  I dremelled down to the ground plane, so the inductance is only
>1-2 nH.
>
>Executive summary: horrible 1/f noise, but 0.28-0.4 nV noise in the
>flatband, and < 1 pF input capacitance.  Second stage contribution
>becomes important above ~100 MHz.  See
>http://electrooptical.net/www/sed/pHEMT_probe/pHEMT_probe.html .
>
>Measuring all that was interesting--getting decent accuracy for noise
>levels that small at high frequency is hard.
>
>Cheers
>
>Phil Hobbs


Hi, Phil,

Did you ever get the NE3509 to stop screaming? I measured its gate
capacitance at about half a pF.


-- 

John Larkin, President       Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com   

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

So I finally got the amplifier all measured up, with three different
pHEMTs: Skyworks SKY65050, Avago ATF38143, and Avago ATF34143.  Joerg's
suggestion of bodging in a bypass right at the collector load made the
amp stable even with the Avago parts, which are hotter than the Skyworks
one.  I dremelled down to the ground plane, so the inductance is only
1-2 nH.

Executive summary: horrible 1/f noise, but 0.28-0.4 nV noise in the
flatband, and < 1 pF input capacitance.  Second stage contribution
becomes important above ~100 MHz.  See
http://electrooptical.net/www/sed/pHEMT_probe/pHEMT_probe.html .

Measuring all that was interesting--getting decent accuracy for noise
levels that small at high frequency is hard.

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

On Tue, 13 Mar 2012 23:26:47 +0100, Fred Bartoli <" "> wrote:

>josephkk a =E9crit :
>> On Sun, 11 Mar 2012 15:30:47 -0700 (PDT), dagmargoodboat@yahoo.com =
wrote:
>>=20
>>>>>> Thanks, Fred.  The Dremelled hand-made proto oscillated at about =
12 GHz,
>>>>>> which I measured by watching the amplitude go up and down as I =
moved my
>>>>>> hand within an inch or two of the surface.  It went from peak to =
valley
>>>>>> in about 1/4 inch, ergo, roughly 12 GHz.=20
>>>>>>
>>>>> He he, nice!
>>>>>
>>>>> 12GHz is pretty high. Just think that a 1nH via is 75R at that =
frequency=20
>>>>> for example.
>>>> Yup, so it's hard to ground the sources of the phemt with just a
>>>> couple of vias. I suggest a topside copper pour, with a lot of vias,
>>>> and maybe extend the topside pour to pick up other nearby grounds, =
and
>>>> maybe a cap or RC from drain to source copper.
>>> ISTM the pHEMT source is effectively "not grounded" at 12GHz.
>>> And, feedthrus might even couple and feed back (though I'm
>>> not saying they are).
>>>
>>> 1uF ceramic C1 won't be stiff at UHF either, not the ones I
>>> scouted anyhow.
>>>
>>> An old r.f. rule was that inductive source + inductive load
>>> an oscillator makes.  My first 1GHz amplifier breadboards
>>> much preferred oscillating at 5GHz to amplifying at 1GHz :-).
>>>
>>> Phil, even a frequency counter would give you really good insight
>>> about if/how layout contributes to the oscillation.  If a wire
>>> passed through Q1's source via(s) tunes f.osc up, for example...
>>>
>>> Fred's finger-probe is a good idea.  Fred needs to send Phil his
>>> finger.
>>>
>> The problem is that the finger is calibrated only attached to Fred.
>>> --=20
>>> Cheers,
>>> James Arthur
>
>Sure, I won't let my, ahem, calibrated tools go that easily...
>
>But I still can send 470pF+100R as a transfer standard.

One last thing, how big is that fingertip?  In mm by mm please.  And if
you have it the sheet resistivity in ohms per square.

?-)

On 03/13/2012 04:26 PM, Nemo wrote:
> dagmargood wrote:
>
> Might need fancy treatment, like a
>> bootstrapped
>> shield.
>
> I tried a bootstrapped shield the other day, and found it made things
> worse. Eventually I decided it was (probably) because the signal I was
> interested in measuring was around a nanoamp, and the BF862 I was using
> had a similar level of noise ~1nV/rt Hz - so I was adding more than I
> was cancelling (yeah I'm mixing units, but my point is both were small
> so the voltage was probably significant). Surely Phil will face the same
> problem with his 62-electron signal...?

Bootstrapping is really worthwhile if the bootstrap amp is quiet and 
accurate enough, but it still introduces a noise current equal to its 
input noise voltage differentiated by the capacitive reactance.  This is 
the same problem faced by TIAs, of course, but interestingly, you win by 
combining them.  They work sort of independently, though not exactly 
so--in arm-waving terms, the capacitance improvement adds linearly, and 
the noise only in RMS.

It's also initially pretty surprising how small the gain and phase error 
in a bootstrap has to be, if you want it to make the effective 
capacitance to go down by a factor of 10 or more.  With a BF862, it's 
very worthwhile using a current source load, and hanging a couple of 
really fast emitter followers (also with current source loads) on the 
FET's source.  Use one follower to bootstrap the BF862's drain and the 
other one to drive the capacitance.   Spice says that one's good for a 
factor of 300, if the capacitance to ground from the sensitive node (a 
photodiode in that case) is below about 0.1 pF.  That's the sort of 
place where a bootstrapped shield makes a lot of sense--there's no other 
way to get the capacitance to ground that low.

Cheers

Phil Hobbs



-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

josephkk a �crit :
> On Sun, 11 Mar 2012 15:30:47 -0700 (PDT), dagmargoodboat@yahoo.com wrote:
> 
>>>>> Thanks, Fred.  The Dremelled hand-made proto oscillated at about 12 GHz,
>>>>> which I measured by watching the amplitude go up and down as I moved my
>>>>> hand within an inch or two of the surface.  It went from peak to valley
>>>>> in about 1/4 inch, ergo, roughly 12 GHz. 
>>>>>
>>>> He he, nice!
>>>>
>>>> 12GHz is pretty high. Just think that a 1nH via is 75R at that frequency 
>>>> for example.
>>> Yup, so it's hard to ground the sources of the phemt with just a
>>> couple of vias. I suggest a topside copper pour, with a lot of vias,
>>> and maybe extend the topside pour to pick up other nearby grounds, and
>>> maybe a cap or RC from drain to source copper.
>> ISTM the pHEMT source is effectively "not grounded" at 12GHz.
>> And, feedthrus might even couple and feed back (though I'm
>> not saying they are).
>>
>> 1uF ceramic C1 won't be stiff at UHF either, not the ones I
>> scouted anyhow.
>>
>> An old r.f. rule was that inductive source + inductive load
>> an oscillator makes.  My first 1GHz amplifier breadboards
>> much preferred oscillating at 5GHz to amplifying at 1GHz :-).
>>
>> Phil, even a frequency counter would give you really good insight
>> about if/how layout contributes to the oscillation.  If a wire
>> passed through Q1's source via(s) tunes f.osc up, for example...
>>
>> Fred's finger-probe is a good idea.  Fred needs to send Phil his
>> finger.
>>
> The problem is that the finger is calibrated only attached to Fred.
>> -- 
>> Cheers,
>> James Arthur

Sure, I won't let my, ahem, calibrated tools go that easily...

But I still can send 470pF+100R as a transfer standard.

-- 
Thanks,
Fred.

dagmargood wrote:

Might need fancy treatment, like a
> bootstrapped
> shield.

I tried a bootstrapped shield the other day, and found it made things
worse. Eventually I decided it was (probably) because the signal I was
interested in measuring was around a nanoamp, and the BF862 I was using
had a similar level of noise ~1nV/rt Hz - so I was adding more than I
was cancelling (yeah I'm mixing units, but my point is both were small
so the voltage was probably significant). Surely Phil will face the same
problem with his 62-electron signal...?