Composite amps

On Thursday, 27 February 2020 19:20:03 UTC, plastco...@gmail.com wrote:

For gas sensor :
4 keV / 30 = 133ē
For scintillator - SiPM !

http://ixbt.photo/?id=photo:1330019

eh?

 

Best result OPA140+BF862 (L=1mH+1mH drain load):
http://ixbt.photo/?id=photo:1329969

Rf=91k and Rf=1M
http://ixbt.photo/?id=photo:1330021

Pushmi-Pullyu
dual accelerator - input JFET, output pnp BJT
DC precision
power supply +-3.8V
active probe - bootstrapped dual JFET half-bridge CPH6904 (out=in+0.86V)
(mediocre, better jfet+ADA4860 or FVF (Flipped Voltage Follower) with BF998)
http://ixbt.photo/?id=photo:1330027

Tortoise outrun Achilles !
time: 1.25us
ĐĄircuit speed indifferent to input capacitance !
http://ixbt.photo/?id=photo:1330025

ĐĄheetah enters the arena:
http://ixbt.photo/?id=photo:1330022
only 1M + 2200pF + OPA656
poor substitute, OPA140+jfet better

The final, a curtain.
OPA656 + BF862
http://ixbt.photo/?id=photo:1330023
GBW=31 GHz ? ((

 

[George Herold]

On Thursday, February 27, 2020 at 6:10:34 PM UTC-5, plastco...@gmail.com wrote:

Best result OPA140+BF862 (L=1mH+1mH drain load):
http://ixbt.photo/?id=photo:1329969

I'm confused about the two traces are here.
The BF862 is unfortunately no more...
You can only surf so long on the trailing edge of technology.

Rf=91k and Rf=1M
http://ixbt.photo/?id=photo:1330021

Is this for me? Hard to tell the shape of the response
for the 91k. But the 1M looks more like a two pole response
now anyway.

Pushmi-Pullyu
dual accelerator - input JFET, output pnp BJT
DC precision
power supply +-3.8V
active probe - bootstrapped dual JFET half-bridge CPH6904 (out=in+0.86V)
(mediocre, better jfet+ADA4860 or FVF (Flipped Voltage Follower) with BF998)
http://ixbt.photo/?id=photo:1330027

So all the stuff on the left is an active probe?
To look at the inverting node without loading down with capacitance?
So is this right? The jfet is taking the fast part of the
current signal and sending it through to the non-inverting input?

I don't know what the pnp is doing on the output. Unless
it's a driver for some coax cable output?
It looks the the 'output' (your arrow between collector
of pnp and 1k R to -V) should be near -V... are you
now biasing PD via the output?

Tortoise outrun Achilles !
time: 1.25us
ĐĄircuit speed indifferent to input capacitance !
http://ixbt.photo/?id=photo:1330025
Well at least to C on the inverting node.

ĐĄheetah enters the arena:
http://ixbt.photo/?id=photo:1330022
only 1M + 2200pF + OPA656
poor substitute, OPA140+jfet better

The final, a curtain.
OPA656 + BF862
http://ixbt.photo/?id=photo:1330023
GBW=31 GHz ? ((

Huh the opa656 looks nice.. +/- 5V.
Thanks

Have you been lurking here long... I'm just reminded of
Jan Pantelje (sp) Which is a good thing. I like Jan.

George H.

 

Rf=91k and Rf=1M
http://ixbt.photo/?id=photo:1330021
Is this for me? Hard to tell the shape of the response
for the 91k. But the 1M looks more like a two pole response
now anyway.
With Rf=91k now Cf>0pF must be present

Pushmi-Pullyu
dual accelerator - input JFET, output pnp BJT
DC precision
power supply +-3.8V
active probe - bootstrapped dual JFET half-bridge CPH6904 (out=in+0.86V)
(mediocre, better jfet+ADA4860 or FVF (Flipped Voltage Follower) with BF998)
http://ixbt.photo/?id=photo:1330027

So all the stuff on the left is an active probe?
To look at the inverting node without loading down with capacitance?

Yes, the circuit is very sensitive to the probe capacitance.
Non-inverting node !

So is this right? The jfet is taking the fast part of the
current signal and sending it through to the non-inverting input?
JFET is input AC amplifier with feedback through Op Amp TIA))

I don't know what the pnp is doing on the output. Unless
it's a driver for some coax cable output?
It looks the the 'output' (your arrow between collector
of pnp and 1k R to -V) should be near -V... are you
now biasing PD via the output?

MMBTH81 is amplifier with gain~10
look in the upper right corner of the book AoE))
no photodiode offset !
slew rate only doubles((
overall gain increases

Capacitance SiPM 60035 = 3400pF
Dmitriy P.

 

On Friday, 28 February 2020 00:44:11 UTC, George Herold wrote:

On Thursday, February 27, 2020 at 6:10:34 PM UTC-5, plastco...@gmail.com wrote:

Best result OPA140+BF862 (L=1mH+1mH drain load):
http://ixbt.photo/?id=photo:1329969

I'm confused about the two traces are here.
The BF862 is unfortunately no more...
You can only surf so long on the trailing edge of technology.

Russia is expert at that game.


NT

 

[Phil Hobbs]

On 2020-02-26 21:18, jlarkin@highlandsniptechnology.com wrote:

On Wed, 26 Feb 2020 16:57:25 -0500, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2020-02-26 13:36, George Herold wrote:
On Monday, February 24, 2020 at 2:47:45 PM UTC-5, Phil Hobbs wrote:
On 2020-02-24 11:47, George Herold wrote:
On Monday, February 24, 2020 at 6:55:54 AM UTC-5, plastco...@gmail.com wrote:
1) grounded detector, grounded source/emitter HF transistor
2) true zero-bias operation of detector
3) my circuit is simpler
I like to read books))

OK, what do you find better about zero bias operation?
I should admit that for many years I ran all my PD's at
zero bias. I thought this gave me better 'zero' light detection.
(No DC offset with no light... but the dark current from
PDs is generally pretty low.)
Running with some bias has two main advantages.
1.) reduced C.. faster
2.) Higher saturation current (light intensity) without bias the
electrons build up in the junction and it saturates.. more light
gives no more electrons.

George H.
(who is addicted to reading... I need to find a few new fiction writers)


Zero bias is better in one respect: you can get zero leakage current.
For jobs such as very wide range, very slow photometers, that's a win.
Garry Epeldauer et al. wrote a beautiful paper about getting 14 orders
of magnitude in photocurrent, if you don't mind being stuck with
millihertz bandwidths:

https://electrooptical.net/www/optics/eppeldauer14decadephotocurrent.pdf
Hi Phil, I downloaded the above and was chewing through it last night.
Great stuff!
1.) Rs (PD shunt resistance... I've always just treated this as
infinite. Can I measure leakage current and get Rs?
2.) pg 3094 has a nice discussion of 1/f noise.
3.) Are there even better low current opamps these days?
4.) Nice effective BW calcs in App A.
I would add to that, the ENBW for a two pole filter, f_3dB and Q,
is
ENBW = f_3dB * Q *pi/2 = ~1.11 f_3dB (Q=0.707.. Butterworth)


Re: noise BW
Yeah, it's like 1.22x for two noninteracting RC poles, so 1.11 for
Butterworth sounds roughly right.

Re: shunt resistance

For bias voltages << kT/e, both the forward and reverse diffusion
currents are contributing to the conductance--it's just dI/dV, and so is
fairly far from zero for a large-area diode run at zero bias.

Ideally the effective shunt resistance goes up by a factor of 2 or so
with 50 mV of reverse bias, because you shut off the reverse diffusion
current without introducing significant additional leakage. That's a
super useful trick with InGaAs diodes in dim light.

re: 1/f noise
Haven't read it recently, but in photodiodes you actually can get
significant 1/f noise at zero bias, unlike in the case of resistors.

re: low current op amps

BITD I used to really like the OPA111. Its performance was easy to
remember: 1 MHz bandwidth, 1 mV offset, 1 uV/K drift, 1 pA input bias.
(See? I haven't used one in 30 years and I still remember.)

It was one of the primo op amps used in early tunnelling and atomic
force microscopy. Of course it's noisy, but not nearly as bad as the
other popular super-high-Z op amp of the day, namely the LM11.

Nowadays there are much better choices, e.g. JL's fave OPA197.

Cheers

Phil Hobbs

I don't use that as a low noise high-performance amp, but as a
general-purpose gumdrop. It's stable with a big output cap, 3.3u film
or 100u polymer.

I didn't mean that you thought it was the best one, but it's sure better
than an OPA111.

I'm also partial to the OPA140, which is just about the perfect JFET op
amp: 0.5 pA typical Ibias at 25C, 5 nV 1-Hz flatband noise, 30 Hz 1/f
corner, 11 MHz BW, 220 uV max offset over temperature, 0.25 uV/K typical
drift, $2. Not horrible at all.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

I remembered where the zero offset of the photodiodes is still important !
Excellent mid-infrared photodiodes from Russia -
http://www.mirdog.spb.ru/products.htm
Ro = 5 Ί ... 10 k

Dmitriy P.

 

[George Herold]

On Friday, February 28, 2020 at 2:15:33 AM UTC-5, plastco...@gmail.com wrote:

Rf=91k and Rf=1M
http://ixbt.photo/?id=photo:1330021
Is this for me? Hard to tell the shape of the response
for the 91k. But the 1M looks more like a two pole response
now anyway.
With Rf=91k now Cf>0pF must be present


Pushmi-Pullyu
dual accelerator - input JFET, output pnp BJT
DC precision
power supply +-3.8V
active probe - bootstrapped dual JFET half-bridge CPH6904 (out=in+0.86V)
(mediocre, better jfet+ADA4860 or FVF (Flipped Voltage Follower) with BF998)
http://ixbt.photo/?id=photo:1330027

So all the stuff on the left is an active probe?
To look at the inverting node without loading down with capacitance?
Yes, the circuit is very sensitive to the probe capacitance.
Non-inverting node !

So is this right? The jfet is taking the fast part of the
current signal and sending it through to the non-inverting input?
JFET is input AC amplifier with feedback through Op Amp TIA))

I don't know what the pnp is doing on the output. Unless
it's a driver for some coax cable output?
It looks the the 'output' (your arrow between collector
of pnp and 1k R to -V) should be near -V... are you
now biasing PD via the output?
MMBTH81 is amplifier with gain~10
look in the upper right corner of the book AoE))
no photodiode offset !
slew rate only doubles((
overall gain increases

OK got it, thanks. I'm so-so at single transistor design.

George H.

Capacitance SiPM 60035 = 3400pF
Dmitriy P.

 

Composite voltage follower
CFA ADA4860 + BF862
http://ixbt.photo/?id=photo:1330880

Output signals
yellow - circuit A
white - circuit B (bootstrapped)
http://ixbt.photo/?id=photo:1330881

Rise time circuit B (bootstrapped)
http://ixbt.photo/?id=photo:1330882

 

very simple - imagine that a capacitor 2200pF is a photodiode with pulse photocurrent ~ 1 ÂľA

 

[George Herold]

On Saturday, March 7, 2020 at 3:15:17 AM UTC-5, plastco...@gmail.com wrote:

Composite voltage follower
CFA ADA4860 + BF862
http://ixbt.photo/?id=photo:1330880

Huh? scratch scratch. Dmitriy, I have no idea what
you are doing? What is the input? (for one)
You'd have to describe what you are doing if you wanted some
sort of input/ critic/ ideas. Which would most likely come not
from me, I mostly just ask questions.

George H.

Output signals
yellow - circuit A
white - circuit B (bootstrapped)
http://ixbt.photo/?id=photo:1330881

Rise time circuit B (bootstrapped)
http://ixbt.photo/?id=photo:1330882

 

A unity-gain buffer removes the photodiode's parasitic capacitance :
circuit A - 2200pF >> 15pF
circuit B - 2200pF >> 0.8pF
Bootstrap photodiodes known since 1984, may have been used before.
The operation of the circuit "A" is limited by the capacitance gate-drain of the JFET transistor.

 

Versatile composite amplifier configuration

https://www.researchgate.net/publication/271747584_Versatile_composite_amplifier_configuration

 

"Shunt bootstrapping technique to improve bandwidth of transimpedance amplifiers"
https://www.researchgate.net/publication/3380589_Shunt_bootstrapping_technique_to_improve_bandwidth_of_transimpedance_amplifiers

fig.3 Output of bootstrap amplifier

my composite voltage follower -
http://ixbt.photo/?id=photo:1332241

output signal from ADA4860 with photocurrent 1.23ÂľA
http://ixbt.photo/?id=photo:1332242

output signal from OPA656 with photocurrent 1.23ÂľA
http://ixbt.photo/?id=photo:1332243

rise time 70ns, noise 150mVp-p
Channel 2 = output ADA4860

I wish you all good health.

 

Composite amplifier EPHEMT + RGC + OPA656
Cdet=2200pF Rf=1M
ATF-54143 Igate= 18 nA
Bead on gate blm18bb050sn1d
http://ixbt.photo/?id=photo:1339025

Without e-phemt :
http://ixbt.photo/?id=photo:1339026

Rise time :
http://ixbt.photo/?id=photo:1339027
Dmitriy P.

 

Retrospective "composite amplifier" challenge))
Question for experts and authors of the AoE3.
What is the function of capacitors 10nF between base and emitter MMBT6429 ?
https://electronix.ru/forum/uploads/monthly_06_2016/post-21169-1466350930.png
Why is there only one capacitor in the service manual between base and emitter ?
https://electronix.ru/forum/uploads/monthly_06_2016/post-21169-1466350949.png
Dmitriy P.

 

[Winfield Hill]

plastcontrol.ru@gmail.com wrote...

Retrospective "composite amplifier" challenge))
Question for experts and authors of the AoE3.
What is the function of capacitors 10nF between base and emitter MMBT6429 ?
https://electronix.ru/forum/uploads/monthly_06_2016/post-21169-1466350930.png
Why is there only one capacitor in the service manual between base and emitter ?
https://electronix.ru/forum/uploads/monthly_06_2016/post-21169-1466350949.png
Dmitriy P.

You're right, my copy of the service manual
only shows one capacitor. The symmetrical
extra one came in, either when I made the
pencil drawing for the draftsman, or they
made a drafting error. As for the purpose
of the capacitors, we can only guess. It'd
be nice to be able to ask the HP engineer(s).

Did we point out in the text that those are
cascode transistors, whose only purpose is to
isolate the op-amp active nodes from the very
high capacitance of the huge IF3602 JFETs?
The Darlington is to insure all of the emitter
current ends up in the collector, and almost
none in the base.

The performance specs for their G=10,000
amplifier are pretty amazing. We have one of
those HP 34420A multimeters in my lab, but
it's rarely used, it's far too good! And the
special nanovolt input connector is awkward.


--
Thanks,
- Win

 

[Michael Terrell]

On Sunday, May 3, 2020 at 8:09:24 AM UTC-4, Winfield Hill wrote:

plastcontrol wrote...

Retrospective "composite amplifier" challenge))
Question for experts and authors of the AoE3.
What is the function of capacitors 10nF between base and emitter MMBT6429 ?
https://electronix.ru/forum/uploads/monthly_06_2016/post-21169-1466350930.png
Why is there only one capacitor in the service manual between base and emitter ?
https://electronix.ru/forum/uploads/monthly_06_2016/post-21169-1466350949.png
Dmitriy P.

You're right, my copy of the service manual
only shows one capacitor. The symmetrical
extra one came in, either when I made the
pencil drawing for the draftsman, or they
made a drafting error. As for the purpose
of the capacitors, we can only guess. It'd
be nice to be able to ask the HP engineer(s).

Did we point out in the text that those are
cascode transistors, whose only purpose is to
isolate the op-amp active nodes from the very
high capacitance of the huge IF3602 JFETs?
The Darlington is to insure all of the emitter
current ends up in the collector, and almost
none in the base.

The performance specs for their G=10,000
amplifier are pretty amazing. We have one of
those HP 34420A multimeters in my lab, but
it's rarely used, it's far too good! And the
special nanovolt input connector is awkward.

Some former HP engineers are on:

https://groups.io/g/HP-Agilent-Keysight-equipment

This replaced the old Yahoo HP group.

 

[Cursitor Doom]

On Sun, 03 May 2020 09:15:17 -0700, Michael Terrell wrote:

Some former HP engineers are on:

https://groups.io/g/HP-Agilent-Keysight-equipment

Yeah, but so is Gardner lately.

 

[Tom Gardner]

On 03/05/20 17:32, Cursitor Doom wrote:

On Sun, 03 May 2020 09:15:17 -0700, Michael Terrell wrote:

Some former HP engineers are on:

https://groups.io/g/HP-Agilent-Keysight-equipment

Yeah, but so is Gardner lately.

Best you stay away.

Or (attempt to) put me in your killfile (again).