Composite amps

On 2020-02-25 16:06, plastcontrol.ru@gmail.com wrote:
> 
>>
>> It works a lot better if you run the pHEMT as a follower and return the
>> anode of the PD to the pHEMT source via a capacitor.
>>
> 
> IMHO, the follower or my wiring diagram does not make any difference - only the location of the symbol GND !
>  From the point of view of the photodiode, one circuit pulls on the lower terminal, the other circuit operates on the upper pin.
> All properties are similar.
> My JFET BF862 is installed more conveniently - single-supply compatible.
> It is very interesting to observe the voltage at the input of the amplifier.
> 
> http://ixbt.photo/?id=album:30781
> 
> Why no one broke the taboo - disconnect the non-inverting input Op Amp from GND ?
> 

Because you've got a 10 MHz op amp inside the feedback loop of a 12-GHz 
f_max pHEMT, which is just plain silly.

There's nothing special about ground anyway.

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

The capacitance of my detectors is below 300 pF and i use negative bias.
cap 2200 pF for picture only))

Very thin dead layer is important for photons 13 nm.
Responsivity of the detector for photons 1keV - 5keV is always the same = 0.27 A/W
Very funny detector this is a CCD camera without a window.
Only you need to connect it not to the TV, but to the oscilloscope and you can immediately analyze the materials by XRF. 

Phil Hobbs wrote:
>That's sort of silly, because it relies on the OPA140 to complete the
>loop, and that grossly limits the speed.

>Because you've got a 10 MHz op amp inside the feedback loop of
> a 12-GHz f_max pHEMT, which is just plain silly.

From bootstrapping photodiode to bootsrapping non-inverting input Op Amp.
The task of the bootstrap circuit is to keep the voltage at the photodiode constant by directing the photocurrent to the amplifier.
STOP ! Error detected))
The current should not go to the amplifier, but to the feedback resistor Rf !
Now you guess what needs to be changed in the circuit so that the amplifier OPA140 turns from a snail into a cheetah ?
Slew Rate OPA140 20 V/μs

http://ixbt.photo/?id=photo:1329866

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)

George H. 
  
> 
> Crappy PN photodiodes and solar cells don't respond well to large 
> reverse bias either.
> 
> For just about anything else, zero bias is a complete crock.
> 
> With almost any PIN diode, APD, MPPC, (etc) zero bias is a disaster. 
> Applying reverse bias to a PIN diode can reduce its capacitance by a 
> factor of 7 or so, which reduces the high frequency noise by the same 
> factor.
> 
> 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

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

-- 
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

On Wednesday, February 26, 2020 at 4:57:32 PM UTC-5, Phil Hobbs 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.
Yeah well the 1.11 number is in AoE so I figured everyone knew it. :^)
> 
> 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.
Huh OK... I did this measurement on bpw34 today. At modest voltages
(6 to 21V I got ~10 mV from a TIA with 100 meg FB ~0.1 nA.. 
at 10V rev.  that's ~100 G ohm..!? OK I was also seeing ~10 mVrms of 
60 Hz crude.. so I'm not sure of these numbers.  
> 
> 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.
Oh, probably simple stuff you know, but it resonated with me.  
1/f noise density (V^2) ~ Log(f_high/f_low) 
And then if you are recording a number (P) of separate measurements.
The low freq BW ~1/P and the noise density goes as Log(P) the number 
of measurements...
"Oh", I said to myself.   
> 
> 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.

Thanks, I saw the opa111 was the last time buy on DK.. for 
~$50 you can relive past. :^)  

George H. 
Re opa197: at least spec wise doesn't the opa192 knock it away? 
(maybe I'm missing something?) (5uV offset and 0.2 uV/C drift)
> 
> 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

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.



-- 

John Larkin         Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet. 
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"

On Wednesday, February 26, 2020 at 9:18:30 PM UTC-5, jla...@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.
> 
OK Thanks.  Is there some nice opamp like this (opa197 or 192) that 
has a little more GBW?  I'm looking at table 4X.2 (AoEx) High spped 
VFB's... there are a lot to choose from.  50-100 MHz would be nice.  

opa1611 looks OK 

George H. 
> 
> 
> -- 
> 
> John Larkin         Highland Technology, Inc
> 
> The cork popped merrily, and Lord Peter rose to his feet. 
> "Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"

On Tuesday, February 25, 2020 at 3:55:22 PM UTC-8, George Herold wrote:
> On Tuesday, February 25, 2020 at 2:13:52 PM UTC-5, plastco...@gmail.com wrote:

> > Russian photodiode for 13 nm, is expensive.
> > Example: 4keV photon,...

>.. easier to measure x-ray 
> energy from a pulse height or total current or something.)  

At 4 keV, I'd want a proportional counter with (Xenon?) gas,
or a fairly large volume ion chamber (leakage current in biased
parallel-plate capacitor).   Neither is a tiny solid detector.

A phosphor, of course, can generate light flashes when hit by X-rays,
and photodiodes can be efficient at detecting the secondary radiation.

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

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

torsdag den 27. februar 2020 kl. 19.59.42 UTC+1 skrev whit3rd:
> On Tuesday, February 25, 2020 at 3:55:22 PM UTC-8, George Herold wrote:
> > On Tuesday, February 25, 2020 at 2:13:52 PM UTC-5, plastco...@gmail.com wrote:
> 
> > > Russian photodiode for 13 nm, is expensive.
> > > Example: 4keV photon,...
> 
> >.. easier to measure x-ray 
> > energy from a pulse height or total current or something.)  
> 
> At 4 keV, I'd want a proportional counter with (Xenon?) gas,
> or a fairly large volume ion chamber (leakage current in biased
> parallel-plate capacitor).   Neither is a tiny solid detector.
> 
> A phosphor, of course, can generate light flashes when hit by X-rays,
> and photodiodes can be efficient at detecting the secondary radiation.

years ago I did X-ray fluorescence spectrometry with an Fe55 source (5.9keV)
and a CCD as detector, image processed to find all pixels with empty neighbours