On 07/18/2016 09:24 PM, George Herold wrote:> On Monday, July 18, 2016 at 4:03:24 PM UTC-4, Phil Hobbs wrote: >> On 07/18/2016 03:28 PM, SilverLeo wrote: >>> Il giorno domenica 17 luglio 2016 09:56:50 UTC+2, SilverLeo ha >>> scritto: >>> >>>> cut >>> >>> I'm replying to myself: I apologize, this seems the only action >>> Google groups let me to do. >>> >>> So: interesting the cap multiplier approach; I'll do some math, maybe >>> it'll be handy in the future. I cannot move the TIA close to the >>> phototransistor: it's a retrofit for an old device for estimate the >>> density of filled paper tubes (filters for very specific application) >>> through the detection of diffused light. The more filled is the tube, >>> the less is the light diffused. Phototransistor is buried inside a >>> cast iron frame, far away from any conditioning electronic. >>> >>> The main reason that lead to the TIA approach was the fact that >>> pototransistor with classic resistor on collector will fall into >>> saturation (Vce near or below Vcesat), actually messing up density >>> estimation. A TIA, as far as the opamp keeps doing its magic, will >>> force Vce=Vbias, running the phototransistor deep in active region. >> >> Except that with the same size resistor and power supply, both will >> saturate at about the same light level--the TIA doesn't help that at >> all. Phototransistors have horrible linearity anyway, so the swing at >> the collector is the least of your worries. >> >>> >>> This in theory: in real world application the TIA output shows 50mV >>> of noise voltage, that does not correspond to a 10uA of current >>> noise, because with the simple resistor there is no evidence of it. >>> This noise comes out when some valves or motors are running. >> >> If you don't understand what I said about not hanging cables on summing >> junctions, just trust me. Your load resistor trick will work a lot better. >> >>> >>> TIA input impedance should be zero (as stated in books) because of >>> virtual ground at inverting input. But, because emitter is at -12V, >>> the phototransitor will see a variable resistor matched to drop >>> exactly 12V for any current. So, for "small" currents this resistor >>> becomes big", and for big current this resistor turns "small". Is >>> this right,somehow? >> >> No. It's the transistor that adjusts, not the load. >> >>> >>> I could add a resistor from inverting input to ground (10K range) to >>> set a limit to input impedance, >> >> That won't make any difference except to increase the noise a little. >> >>> and a capacitor in parallel to that >>> resistor (nF range) to bypass everything the opamp will not be able >>> to follow due to bandwidth limitation. Useless or not? >> >> You really don't want to hang a capacitor to ground on a summing >> junction. It's very likely to make the whole thing oscillate. > > Hey, I think it's a good idea for people who don't understand > TIA's and input C, to hang more on the inverting input and see > what happens.Yup. And then do the math so they understand why. It's just a few lines of algebra. Otherwise one might as well just wave a dead chicken over the circuit and fiddle till it sort of works. 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 hobbs at electrooptical dot net http://electrooptical.net
Phototransistor fed to a transimpedance amplifier
Started by ●July 17, 2016
Reply by ●July 19, 20162016-07-19
Reply by ●July 19, 20162016-07-19
On Monday, July 18, 2016 at 10:02:08 PM UTC-4, John Larkin wrote:> On Mon, 18 Jul 2016 18:28:33 -0700 (PDT), George Herold > <gherold@teachspin.com> wrote: > > >On Monday, July 18, 2016 at 5:19:35 PM UTC-4, John Larkin wrote: > >> On Mon, 18 Jul 2016 14:10:45 -0700, Joerg <news@analogconsultants.com> > >> wrote: > >> > >> >On 2016-07-17 04:14, Phil Hobbs wrote: > >> >> Why not put the TIA at the sensor? > >> >> > >> >> Putting long leads on the summing junction of an op amp is a > >> >> guaranteed way of getting into trouble. > >> >> > >> > > >> >... or the combination of the innards of a PMT plus a way too long > >> >socket, resonating all over the place. Don't ask ... > >> > > >> > > >> >> With equal resistors and the same power rails, your TIA and load > >> >> resistor circuits will saturate at about the same light level. > >> >> > >> >> What's it for? > >> >> > >> > > >> >Silvio: In a pinch you can try 100ohms or so in series with the TIA > >> >input, right at the TIA opamp. > >> > >> Run a fiberoptic cable from the light source to the photodiode. Fiber > >> is 100% EMI immune. > >> > >> > >I like the fiber idea, you've gotta keep the (input) end clean. > > > >George H. > > Sure, like you gotta keep the phototransistor clean.Yup... I'm just back from vacation, where I took Mark Johnson's "Photodetection and Measurement" to the beach for reading. https://www.amazon.com/Photodetection-Measurement-Maximizing-Performance-Optical/dp/0071409440 He spends a chapter on making measurements in industrial environs. (The book would be a good predecessor for Phil's optics text...) George H.> > The big fat cheap plastic fiber, like toslink, has a big aperature to > let light in, but it has a lot of attenuation and wouldn't like high > temperatures. There is fat glass fiber, but it tends to be expensive. > > > -- > > John Larkin Highland Technology, Inc > > lunatic fringe electronics
Reply by ●July 19, 20162016-07-19
On 07/19/2016 09:39 AM, George Herold wrote:> On Monday, July 18, 2016 at 10:02:08 PM UTC-4, John Larkin wrote: >> On Mon, 18 Jul 2016 18:28:33 -0700 (PDT), George Herold >> <gherold@teachspin.com> wrote: >> >>> On Monday, July 18, 2016 at 5:19:35 PM UTC-4, John Larkin wrote: >>>> On Mon, 18 Jul 2016 14:10:45 -0700, Joerg <news@analogconsultants.com> >>>> wrote: >>>> >>>>> On 2016-07-17 04:14, Phil Hobbs wrote: >>>>>> Why not put the TIA at the sensor? >>>>>> >>>>>> Putting long leads on the summing junction of an op amp is a >>>>>> guaranteed way of getting into trouble. >>>>>> >>>>> >>>>> ... or the combination of the innards of a PMT plus a way too long >>>>> socket, resonating all over the place. Don't ask ... >>>>> >>>>> >>>>>> With equal resistors and the same power rails, your TIA and load >>>>>> resistor circuits will saturate at about the same light level. >>>>>> >>>>>> What's it for? >>>>>> >>>>> >>>>> Silvio: In a pinch you can try 100ohms or so in series with the TIA >>>>> input, right at the TIA opamp. >>>> >>>> Run a fiberoptic cable from the light source to the photodiode. Fiber >>>> is 100% EMI immune. >>>> >>>> >>> I like the fiber idea, you've gotta keep the (input) end clean. >>> >>> George H. >> >> Sure, like you gotta keep the phototransistor clean. > Yup... I'm just back from vacation, where I took Mark Johnson's > "Photodetection and Measurement" to the beach for reading. > https://www.amazon.com/Photodetection-Measurement-Maximizing-Performance-Optical/dp/0071409440 > > He spends a chapter on making measurements in industrial environs. > (The book would be a good predecessor for Phil's optics text...) >Yup, good book. I gave it a nice review on Amazon about a dozen years ago. Mark and I corresponded for a couple of years before the book came out, and have occasionally since. He's particularly good at hands-on demos (the 'Try It' sections) and on demystifying lock-in amplifiers, which as he shows work exactly like narrow bandpass filters followed by downconverters. I just recently received a paper to review from SPIE's Optical Engineering journal whose main idea was one that I recognized from Johnson (it's on P. 185). I doubt the authors were expecting anyone to notice. (Peer review is such a joke nowadays.) Cheers Phil Hobbs> George H. > > >> >> The big fat cheap plastic fiber, like toslink, has a big aperature to >> let light in, but it has a lot of attenuation and wouldn't like high >> temperatures. There is fat glass fiber, but it tends to be expensive. >> >> >> -- >> >> John Larkin Highland Technology, Inc >> >> lunatic fringe electronics >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 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●July 19, 20162016-07-19
You need a differential TIA with good common mode rejection. And to get good common mode the two diff inputs need to present the same Z to ground. (unlike the typical diff amp) Goggle common mode rejection M
Reply by ●July 19, 20162016-07-19
On 07/19/2016 09:49 AM, makolber@yahoo.com wrote:> You need a differential TIA with good common mode rejection. > And to get good common mode the two diff inputs need to present the same Z to ground. (unlike the typical diff amp) > > Goggle common mode rejection > > M > >The circuit is so slow that there's no reason I can see not to use the phototransistor barefoot with a load resistor, and bypass the receiving end like mad. If there's some really gross amount of RF around, 1 nF from B-C right down at the phototransistor will help. 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 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●July 19, 20162016-07-19
On Tuesday, July 19, 2016 at 9:46:01 AM UTC-4, Phil Hobbs wrote:> On 07/19/2016 09:39 AM, George Herold wrote: > > On Monday, July 18, 2016 at 10:02:08 PM UTC-4, John Larkin wrote: > >> On Mon, 18 Jul 2016 18:28:33 -0700 (PDT), George Herold > >> <gherold@teachspin.com> wrote: > >> > >>> On Monday, July 18, 2016 at 5:19:35 PM UTC-4, John Larkin wrote: > >>>> On Mon, 18 Jul 2016 14:10:45 -0700, Joerg <news@analogconsultants.com> > >>>> wrote: > >>>> > >>>>> On 2016-07-17 04:14, Phil Hobbs wrote: > >>>>>> Why not put the TIA at the sensor? > >>>>>> > >>>>>> Putting long leads on the summing junction of an op amp is a > >>>>>> guaranteed way of getting into trouble. > >>>>>> > >>>>> > >>>>> ... or the combination of the innards of a PMT plus a way too long > >>>>> socket, resonating all over the place. Don't ask ... > >>>>> > >>>>> > >>>>>> With equal resistors and the same power rails, your TIA and load > >>>>>> resistor circuits will saturate at about the same light level. > >>>>>> > >>>>>> What's it for? > >>>>>> > >>>>> > >>>>> Silvio: In a pinch you can try 100ohms or so in series with the TIA > >>>>> input, right at the TIA opamp. > >>>> > >>>> Run a fiberoptic cable from the light source to the photodiode. Fiber > >>>> is 100% EMI immune. > >>>> > >>>> > >>> I like the fiber idea, you've gotta keep the (input) end clean. > >>> > >>> George H. > >> > >> Sure, like you gotta keep the phototransistor clean. > > Yup... I'm just back from vacation, where I took Mark Johnson's > > "Photodetection and Measurement" to the beach for reading. > > https://www.amazon.com/Photodetection-Measurement-Maximizing-Performance-Optical/dp/0071409440 > > > > He spends a chapter on making measurements in industrial environs. > > (The book would be a good predecessor for Phil's optics text...) > > > > Yup, good book. I gave it a nice review on Amazon about a dozen years > ago. Mark and I corresponded for a couple of years before the book came > out, and have occasionally since.Hmm, do you have his email address... I wanted to send him a thanks for the book. And also talk a little about 'scope FFT's and Zener diode noise sources... (I made notes in the book margins.) Perhaps send it to me off-line. George H.> > He's particularly good at hands-on demos (the 'Try It' sections) and on > demystifying lock-in amplifiers, which as he shows work exactly like > narrow bandpass filters followed by downconverters. > > I just recently received a paper to review from SPIE's Optical > Engineering journal whose main idea was one that I recognized from > Johnson (it's on P. 185). I doubt the authors were expecting anyone to > notice. (Peer review is such a joke nowadays.) > > Cheers > > Phil Hobbs > > > > George H. > > > > > >> > >> The big fat cheap plastic fiber, like toslink, has a big aperature to > >> let light in, but it has a lot of attenuation and wouldn't like high > >> temperatures. There is fat glass fiber, but it tends to be expensive. > >> > >> > >> -- > >> > >> John Larkin Highland Technology, Inc > >> > >> lunatic fringe electronics > > > > 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 > > hobbs at electrooptical dot net > http://electrooptical.net
Reply by ●July 19, 20162016-07-19
On 07/19/2016 09:59 AM, George Herold wrote:> On Tuesday, July 19, 2016 at 9:46:01 AM UTC-4, Phil Hobbs wrote: >> On 07/19/2016 09:39 AM, George Herold wrote: >>> On Monday, July 18, 2016 at 10:02:08 PM UTC-4, John Larkin wrote: >>>> On Mon, 18 Jul 2016 18:28:33 -0700 (PDT), George Herold >>>> <gherold@teachspin.com> wrote: >>>> >>>>> On Monday, July 18, 2016 at 5:19:35 PM UTC-4, John Larkin wrote: >>>>>> On Mon, 18 Jul 2016 14:10:45 -0700, Joerg <news@analogconsultants.com> >>>>>> wrote: >>>>>> >>>>>>> On 2016-07-17 04:14, Phil Hobbs wrote: >>>>>>>> Why not put the TIA at the sensor? >>>>>>>> >>>>>>>> Putting long leads on the summing junction of an op amp is a >>>>>>>> guaranteed way of getting into trouble. >>>>>>>> >>>>>>> >>>>>>> ... or the combination of the innards of a PMT plus a way too long >>>>>>> socket, resonating all over the place. Don't ask ... >>>>>>> >>>>>>> >>>>>>>> With equal resistors and the same power rails, your TIA and load >>>>>>>> resistor circuits will saturate at about the same light level. >>>>>>>> >>>>>>>> What's it for? >>>>>>>> >>>>>>> >>>>>>> Silvio: In a pinch you can try 100ohms or so in series with the TIA >>>>>>> input, right at the TIA opamp. >>>>>> >>>>>> Run a fiberoptic cable from the light source to the photodiode. Fiber >>>>>> is 100% EMI immune. >>>>>> >>>>>> >>>>> I like the fiber idea, you've gotta keep the (input) end clean. >>>>> >>>>> George H. >>>> >>>> Sure, like you gotta keep the phototransistor clean. >>> Yup... I'm just back from vacation, where I took Mark Johnson's >>> "Photodetection and Measurement" to the beach for reading. >>> https://www.amazon.com/Photodetection-Measurement-Maximizing-Performance-Optical/dp/0071409440 >>> >>> He spends a chapter on making measurements in industrial environs. >>> (The book would be a good predecessor for Phil's optics text...) >>> >> >> Yup, good book. I gave it a nice review on Amazon about a dozen years >> ago. Mark and I corresponded for a couple of years before the book came >> out, and have occasionally since. > > Hmm, do you have his email address... I wanted to send him a > thanks for the book. And also talk a little about > 'scope FFT's and Zener diode noise sources... (I made notes in the > book margins.) Perhaps send it to me off-line. >Sent. He's also on LinkedIn. 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 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●July 19, 20162016-07-19
"Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message news:JsKdnfAN597esBPKnZ2dnUU7-X2dnZ2d@supernews.com...> Yup. And then do the math so they understand why. It's just a few > lines of algebra. Otherwise one might as well just wave a dead chicken > over the circuit and fiddle till it sort of works.Hey but dead chickens are great, I keep one by my scope at all times! Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Reply by ●July 19, 20162016-07-19
On Tue, 19 Jul 2016 09:38:11 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 07/18/2016 09:24 PM, George Herold wrote:[snip].>> >> Hey, I think it's a good idea for people who don't understand >> TIA's and input C, to hang more on the inverting input and see >> what happens. > >Yup. And then do the math so they understand why. It's just a few >lines of algebra. Otherwise one might as well just wave a dead chicken >over the circuit and fiddle till it sort of works. > >Cheers > >Phil HobbsYou forgot the most important "parts"... Eye of newt, and toe of frog, Wool of bat, and tongue of dog, Adder's fork, and blind-worm's sting, Lizard's leg, and howlet's wing,-- For a charm of powerful trouble, Like a hell-broth boil and bubble. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I'm looking for work... see my website.
Reply by ●July 19, 20162016-07-19
On 07/19/2016 10:32 AM, Tim Williams wrote:> "Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message > news:JsKdnfAN597esBPKnZ2dnUU7-X2dnZ2d@supernews.com... >> Yup. And then do the math so they understand why. It's just a few >> lines of algebra. Otherwise one might as well just wave a dead chicken >> over the circuit and fiddle till it sort of works. > > Hey but dead chickens are great, I keep one by my scope at all times! > > Tim >Yeah, but yours is deep fried, which doesn't count. ;) 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 hobbs at electrooptical dot net http://electrooptical.net
