On Fri, 21 Feb 2020 13:11:52 -0800 (PST), plastcontrol.ru@gmail.com wrote:>Capacitor 2200pF is my photodiode.That's a lot. You could drive a cascode emitter to keep the load impedance way down on the photodiode. The transistor collector, much lower capacitance, can drive the TIA. The problem there is that you should have a standing current in the cascode transistor, to keep the emitter impedance low. That makes an offset and maybe messes up the TIA. Hence the notion that a photodiode has two leads. Take the fast stuff from one end and the slow signal from the other. It's the Tektronix "feed-beside" idea. I'm expecting the first article of my GHz o/e converter any day now. It uses the feed-beside idea. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Composite amps
Started by ●May 27, 2018
Reply by ●February 21, 20202020-02-21
Reply by ●February 22, 20202020-02-22
Internal input capacitance OPA140 : differential Cd = 10 pF common mode Ccm = 7 pF Cascode transistor or voltage follower useless in this case. Zero bias voltage photodiode boosted TIA : http://ixbt.photo/?id=photo:1329322 OPA140 with internal compensation cap - amplifier like integrator.
Reply by ●February 22, 20202020-02-22
Reply by ●February 23, 20202020-02-23
On Saturday, February 22, 2020 at 4:56:56 PM UTC-5, plastco...@gmail.com wrote:> Metamorphoses : > > http://ixbt.photo/?id=photo:1329419 > > Bootstrapping TIA grounded photodiodeDmitriy, What's the advantage of this? At one point in your circuit evolution I thought you were going to move the non-inverting input away from ground to bias the photodiode (PD). (You can reduce PD capacitance ~factor of 3 or so with reverse bias.) Have you read Phil Hobb's book? Most of his ideas can be found for free online... check his website. George H.
Reply by ●February 24, 20202020-02-24
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))
Reply by ●February 24, 20202020-02-24
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)
Reply by ●February 24, 20202020-02-24
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> 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
Reply by ●February 24, 20202020-02-24
On Mon, 24 Feb 2020 14:47:33 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> 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> > >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 HobbsI know of a large organization that has wasted about a million dollars a year, since 2002, by running a lot of very expensive Hamamatsu photodiodes at zero bias. https://www.dropbox.com/s/wm3a3cpxa8tcarg/S8551_1.JPG?raw=1 -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●February 24, 20202020-02-24
On 2020-02-24 15:13, John Larkin wrote:> On Mon, 24 Feb 2020 14:47:33 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> 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> >> >> 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 > > I know of a large organization that has wasted about a million dollars > a year, since 2002, by running a lot of very expensive Hamamatsu > photodiodes at zero bias. > > https://www.dropbox.com/s/wm3a3cpxa8tcarg/S8551_1.JPG?raw=1 >I suspect I know the organization. ;) They have some very good folks though. 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
Reply by ●February 24, 20202020-02-24
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> > > 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.(Well thanks for trashing the first ~20 years of my PD career. :^) In defense of zero bias it's got great simplicity, doesn't break if put in backwards*. And if your DMM has a 200uA scale a ~10mm^2 PD makes an easy light detector. Lots of applications don't care so much about speed. (a bow to the lm324, I never used one, but enjoyed the schematics.)> > 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.George H. *I've never tried breaking a PD by forward biasing hard. my bpw34 looks about the same volume as a 1/4 watt resistor, so ~1/4 W, 0.6V and 0.4A> > 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
