On 14 Mar 2015 14:30:24 -0700, Winfield Hill <hill@rowland.harvard.edu> wrote:>John Larkin wrote... >> >>On 14 Mar 2015 13:32:45 -0700, Winfield Hill >><hill@rowland.harvard.edu> wrote: >> >>>George Herold wrote... >>>> >>>> Hi guys (and dolls), So if you read in JL's TI opamp thread, >>>> I am having noise issues in our laser diode. >>>> I turns out (I think) that the extra noise is coming >>>> from my Piezo drive. >>>> The original circuit used a PA141 from Apex. >>>> (I can't find a schematic on-line, but I have a hard copy.) >>>> Several years ago this HV opamp went away and the >>>> recommended replacement from Apex was the PA314 >>>> https://apexanalog-public.sharepoint.com/Resources/PA341U.pdf >>>> >>>> I basically plugged it in, it worked, and I forgot about it. >>>> Well it's not quite the same... a few differences but the big one >>>> is the noise... Some gawd awful 350 uV rms in a 10 k Hz BW... >>>> (~350nV/rt Hz.) And no spec on the low freq. 1/f noise. >>>> >>>> So I've been trying to beat the noise down in the current circuit, >>>> but with no luck. I use it as a x10 inverting amp. Rin= 10 k ohm and >>>> Rf= 100k ohm. I tried rolling off the gain with 100pf in parallel >>>> with Rf, but this lead to low level oscillations.. (scratch scratch.) >>>> I then tried adding more compensation capacitance from 10 pF to ~70 pF >>>> but this did nothing. >>>> >>>> Any ideas for trying to salvage this circuit? >>>> I could live with a bandwidth of 5 kHz or so. >>>> >>>> TIA >>>> George H. >>> >>> Yep, most of the APEX opamps made with MOSFET input transistors >>> are very noisy, especially at low frequencies. For example, the >>> PA141 spec says 50uV rms, over a 10kHz bandwidth. By comparison >>> the PA341 spec is 337uV rms. Whoa!! Their JFET-input opamps >>> are much better, for example the PA97 specs 2uV rmw over 10kHz. >>> So you could change to one of those types. >>> >>> Or you could make your own HV amplifier, using a low-voltage >>> JEFT opamp to control MOSFET power transistors. We show an >>> example in Figure 3.75 in AoE 2nd edition (also see Figure >>> 6.47). These amplifiers can be even more quiet. I updated >>> the circuit for AoE-III, see Figure 3.111. [Note, AoE-III >>> is being printed and will be shipping in a week or two.] >>> >>> A more advanced circuit is set for the AoE x-Chapter book >>> (for the time being it's Figure 4x.50 in section 4x.18), >>> where there's a lengthy careful analysis of the design, >>> and its performance into large capacitive loads, etc. >>> >>> A refined version of that circuit is in development for a >>> freebie PCB, so y'all can easily make your own. It's my >>> Rowland EE Labs AMP-62A project, and here's a schematic: >>> https://www.dropbox.com/s/cqpoyr2toj1c7pt/AMP-62A-2_sch_r3_fast.pdf?dl=0 >>> https://www.dropbox.com/s/0e5x0mhr5ldwjho/AMP-62A-2_pcb_r3_3D-image.JPG? >dl=0 >> >> I don't understand the Q8-Q10 string. Is that safe? > > Absolutely. Avalanche is your friend, provided you keep > the power dissipation under control. If we assume about > 600V avalanche, at 0.5mA that's a very relaxed 300mW. > The lowest-current series current-source avalanches first, > then the next highest, and so on. So the current-source > varies by about maybe up to 0.1mA over voltage. But hey, > that's far better than using 2W carbon pullup resistors! > > Another scheme I like is the MOSFETs wired in cascode, > but this requires six series resistors to handle 1kV. > But it does let you double or triple the pullup current.LND150 data sheets don't mention an avalanche rating. Looks like Microchip acquired Supertex. -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Apex HV opamp issues.
Started by ●March 13, 2015
Reply by ●March 14, 20152015-03-14
Reply by ●March 14, 20152015-03-14
John Larkin wrote...> Winfield Hill wrote: >> John Larkin wrote... >>> Winfield Hill wrote: >>>> George Herold wrote... >>>>> >>>>> Hi guys (and dolls), So if you read in JL's TI opamp thread, >>>>> I am having noise issues in our laser diode. >>>>> I turns out (I think) that the extra noise is coming >>>>> from my Piezo drive. >>>>> The original circuit used a PA141 from Apex. >>>>> (I can't find a schematic on-line, but I have a hard copy.) >>>>> Several years ago this HV opamp went away and the >>>>> recommended replacement from Apex was the PA314 >>>>> https://apexanalog-public.sharepoint.com/Resources/PA341U.pdf >>>>> >>>>> I basically plugged it in, it worked, and I forgot about it. >>>>> Well it's not quite the same... a few differences but the big one >>>>> is the noise... Some gawd awful 350 uV rms in a 10 k Hz BW... >>>>> (~350nV/rt Hz.) And no spec on the low freq. 1/f noise. >>>>> >>>>> So I've been trying to beat the noise down in the current circuit, >>>>> but with no luck. I use it as a x10 inverting amp. Rin= 10 k ohm and >>>>> Rf= 100k ohm. I tried rolling off the gain with 100pf in parallel >>>>> with Rf, but this lead to low level oscillations.. (scratch scratch.) >>>>> I then tried adding more compensation capacitance from 10 pF to ~70 pF >>>>> but this did nothing. >>>>> >>>>> Any ideas for trying to salvage this circuit? >>>>> I could live with a bandwidth of 5 kHz or so. >>>>> >>>>> TIA >>>>> George H. >>>> >>>> Yep, most of the APEX opamps made with MOSFET input transistors >>>> are very noisy, especially at low frequencies. For example, the >>>> PA141 spec says 50uV rms, over a 10kHz bandwidth. By comparison >>>> the PA341 spec is 337uV rms. Whoa!! Their JFET-input opamps >>>> are much better, for example the PA97 specs 2uV rmw over 10kHz. >>>> So you could change to one of those types. >>>> >>>> Or you could make your own HV amplifier, using a low-voltage >>>> JEFT opamp to control MOSFET power transistors. We show an >>>> example in Figure 3.75 in AoE 2nd edition (also see Figure >>>> 6.47). These amplifiers can be even more quiet. I updated >>>> the circuit for AoE-III, see Figure 3.111. [Note, AoE-III >>>> is being printed and will be shipping in a week or two.] >>>> >>>> A more advanced circuit is set for the AoE x-Chapter book >>>> (for the time being it's Figure 4x.50 in section 4x.18), >>>> where there's a lengthy careful analysis of the design, >>>> and its performance into large capacitive loads, etc. >>>> >>>> A refined version of that circuit is in development for a >>>> freebie PCB, so y'all can easily make your own. It's my >>>> Rowland EE Labs AMP-62A project, and here's a schematic: >>>> https://www.dropbox.com/s/cqpoyr2toj1c7pt/AMP-62A-2_sch_r3_fast.pdf?dl=0 >>>> https://www.dropbox.com/s/0e5x0mhr5ldwjho/AMP-62A-2_pcb_r3_3D-image.JPG? >>dl=0 >>> >>> I don't understand the Q8-Q10 string. Is that safe? >> >> Absolutely. Avalanche is your friend, provided you keep >> the power dissipation under control. If we assume about >> 600V avalanche, at 0.5mA that's a very relaxed 300mW. >> The lowest-current series current-source avalanches first, >> then the next highest, and so on. So the current-source >> varies by about maybe up to 0.1mA over voltage. But hey, >> that's far better than using 2W carbon pullup resistors! >> >> Another scheme I like is the MOSFETs wired in cascode, >> but this requires six series resistors to handle 1kV. >> But it does let you double or triple the pullup current. > > LND150 data sheets don't mention an avalanche rating.Right, when you see an official "avalanche" rating, it's actually a thermal-mass parameter, for use with pulsed high-power levels. It's consistent with and derivable from the Transient Thermal Impedance plots. But in this circuit we're not subjecting the part to any transient high-power dissipation.> Looks like Microchip acquired Supertex.Oops, we'll see what happens next. Fingers crossed. You may have noticed (lower left corner of the schematic) my enthusiasm for Infineon BSS126, instead of "my favorite" LND150. It's a higher-current, higher-voltage part. BTW, these SOT-23 MOSFETs have different pinouts. Just saying. -- Thanks, - Win
Reply by ●March 14, 20152015-03-14
On Sat, 14 Mar 2015 12:19:06 -0700, John Larkin wrote:> On Sat, 14 Mar 2015 13:43:41 -0500, Tim Wescott <tim@seemywebsite.com> > wrote: > >>On Sat, 14 Mar 2015 09:11:16 +0000, Jan Panteltje wrote: >> >>> On a sunny day (Fri, 13 Mar 2015 13:45:11 -0700) it happened John >>> Larkin <jlarkin@highlandtechnology.com> wrote in >>> <jji6gadtd50u67np8f9e1d15f3rdv7nt3g@4ax.com>: >>>> >>>>You could try my cheap and almost-famous optocoupler-based HV >>>>amplifier. >>>> >>>>https://dl.dropboxusercontent.com/u/53724080/Optos/HVamp.JPG >>> >>> Thats is a keeper. >> >>Ooooh, I wish I were still working at FLIR. Our head analog engineer >>was excellent, but very averse to odd topologies and to circuits that he >>didn't think would simulate well. Tossing this schematic in front of >>him in a meeting would be like tossing a cat into a cage full of >>antisocial dogs. > > If he was adverse to odd designs, how did the E45 software wind up so > weird? It's not a regular camera interface, it's a network device over > USB with a bizarre cable. > > If you use it one one USB port, and change ports next time, even a > different slot on a hub, the PC software forgets that it exists. > > The thermal part works pretty well.I'm pretty sure that the handheld stuff is still all done in Sweden. I worked on the high-dollar airborne imaging stuff. While we did make some profoundly stupid products from time to time (usually heralded by a company officer getting all of us into a room and telling us how smart he was to kick off the project), more often than not we made good chit. When I started there, a mechanical drawing had to be checked by two people in addition to the engineer who designed the part. A circuit had to be checked by one, other than the engineer. Software had to be checked not at all -- you just gave them a floppy with a hex file and signed on the dotted line. I took that to mean that software was considered to be magic, not engineering (other aspects of engineering management's behavior kind of confirmed that). -- www.wescottdesign.com
Reply by ●March 15, 20152015-03-15
On Saturday, March 14, 2015 at 4:33:06 PM UTC-4, Winfield Hill wrote:> George Herold wrote... > > > > Hi guys (and dolls), So if you read in JL's TI opamp thread, > > I am having noise issues in our laser diode. > > I turns out (I think) that the extra noise is coming > > from my Piezo drive. > > The original circuit used a PA141 from Apex. > > (I can't find a schematic on-line, but I have a hard copy.) > > Several years ago this HV opamp went away and the > > recommended replacement from Apex was the PA314 > > https://apexanalog-public.sharepoint.com/Resources/PA341U.pdf > > > > I basically plugged it in, it worked, and I forgot about it. > > Well it's not quite the same... a few differences but the big one > > is the noise... Some gawd awful 350 uV rms in a 10 k Hz BW... > > (~350nV/rt Hz.) And no spec on the low freq. 1/f noise. > > > > So I've been trying to beat the noise down in the current circuit, > > but with no luck. I use it as a x10 inverting amp. Rin= 10 k ohm and > > Rf= 100k ohm. I tried rolling off the gain with 100pf in parallel > > with Rf, but this lead to low level oscillations.. (scratch scratch.) > > I then tried adding more compensation capacitance from 10 pF to ~70 pF > > but this did nothing. > > > > Any ideas for trying to salvage this circuit? > > I could live with a bandwidth of 5 kHz or so. > > > > TIA > > George H. > > Yep, most of the APEX opamps made with MOSFET input transistors > are very noisy, especially at low frequencies. For example, the > PA141 spec says 50uV rms, over a 10kHz bandwidth. By comparison > the PA341 spec is 337uV rms. Whoa!! Their JFET-input opamps > are much better, for example the PA97 specs 2uV rmw over 10kHz. > So you could change to one of those types. > > Or you could make your own HV amplifier, using a low-voltage > JEFT opamp to control MOSFET power transistors. We show an > example in Figure 3.75 in AoE 2nd edition (also see Figure > 6.47). These amplifiers can be even more quiet. I updated > the circuit for AoE-III, see Figure 3.111. [Note, AoE-III > is being printed and will be shipping in a week or two.] > > A more advanced circuit is set for the AoE x-Chapter book > (for the time being it's Figure 4x.50 in section 4x.18), > where there's a lengthy careful analysis of the design, > and its performance into large capacitive loads, etc. > > A refined version of that circuit is in development for a > freebie PCB, so y'all can easily make your own. It's my > Rowland EE Labs AMP-62A project, and here's a schematic: > https://www.dropbox.com/s/cqpoyr2toj1c7pt/AMP-62A-2_sch_r3_fast.pdf?dl=0 > https://www.dropbox.com/s/0e5x0mhr5ldwjho/AMP-62A-2_pcb_r3_3D-image.JPG?dl=0 >Wow! thanks, That's much more HV amp than I can afford to get my head around. (at the moment) (I'm glad JL ask about Q8-10) I'm going to try the LTC6090. My only issue for a retro fit is throwing away about 20-30 V of HV supply (@ 10 mA max.) A silly resistor divider takes too much power. I was thinking of a series Zener (1 Watt) I then wondered if I could run a three terminal voltage regulator (LM317) With the adjust pin driven from the input side? Which lead me to the voltage divider cap multiplier. Vin---+---+----|<|---+----+---+ | | | | | R \ />-----+ R C 1 --+-- l l | | o o +-----+ a a | | d d R C | | 2 1 | | gnd--+-----+-------------+---+ About 1mA flowing through R1/R2. George H.> > > > -- > Thanks, > - Win
Reply by ●March 18, 20152015-03-18
On Friday, March 13, 2015 at 1:10:42 PM UTC-4, George Herold wrote:> Hi guys (and dolls), So if you read in JL's TI opamp thread, > I am having noise issues in our laser diode. > I turns out (I think) that the extra noise is coming > from my Piezo drive. > The original circuit used a PA141 from Apex. > (I can't find a schematic on-line, but I have a hard copy.) > Several years ago this HV opamp went away and the > recommended replacement from Apex was the PA314 > https://apexanalog-public.sharepoint.com/Resources/PA341U.pdf > > I basically plugged it in, it worked, and I forgot about it. > Well it's not quite the same... a few differences but the big one > is the noise... Some gawd awful 350 uV rms in a 10 k Hz BW... > (~350nV/rt Hz.) And no spec on the low freq. 1/f noise. > > So I've been trying to beat the noise down in the current circuit, > but with no luck. I use it as a x10 inverting amp. Rin= 10 k ohm and > Rf= 100k ohm. I tried rolling off the gain with 100pf in parallel > with Rf, but this lead to low level oscillations.. (scratch scratch.) > I then tried adding more compensation capacitance from 10 pF to ~70 pF > but this did nothing. > > Any ideas for trying to salvage this circuit? > I could live with a bandwidth of 5 kHz or so. > > TIA > George H.Just the final update on apex opamps... (I'm still waiting on DK, but I had to leave early today.) It turns out that I'd forgotten the first apex update, where the PA141 went to the PA241... so here a noise plot (noise density is uncalibrated.. though I have the gain settings.) https://www.dropbox.com/s/1vguffiuj4noghz/Graph1.BMP?dl=0 (The black line has a slope of 1) Turns out the opamp got progressively worse... What's weird is that the "1/f" noise is not 1/f, but f^-2/3. Well since I don't understand 1/f, (1/f)^2/3 is no weirder. George H.
Reply by ●March 18, 20152015-03-18
On Wednesday, March 18, 2015 at 6:45:12 PM UTC-4, George Herold wrote:> On Friday, March 13, 2015 at 1:10:42 PM UTC-4, George Herold wrote: > > Hi guys (and dolls), So if you read in JL's TI opamp thread, > > I am having noise issues in our laser diode. > > I turns out (I think) that the extra noise is coming > > from my Piezo drive. > > The original circuit used a PA141 from Apex. > > (I can't find a schematic on-line, but I have a hard copy.) > > Several years ago this HV opamp went away and the > > recommended replacement from Apex was the PA314 > > https://apexanalog-public.sharepoint.com/Resources/PA341U.pdf > > > > I basically plugged it in, it worked, and I forgot about it. > > Well it's not quite the same... a few differences but the big one > > is the noise... Some gawd awful 350 uV rms in a 10 k Hz BW... > > (~350nV/rt Hz.) And no spec on the low freq. 1/f noise. > > > > So I've been trying to beat the noise down in the current circuit, > > but with no luck. I use it as a x10 inverting amp. Rin= 10 k ohm and > > Rf= 100k ohm. I tried rolling off the gain with 100pf in parallel > > with Rf, but this lead to low level oscillations.. (scratch scratch.) > > I then tried adding more compensation capacitance from 10 pF to ~70 pF > > but this did nothing. > > > > Any ideas for trying to salvage this circuit? > > I could live with a bandwidth of 5 kHz or so. > > > > TIA > > George H. > > Just the final update on apex opamps... > (I'm still waiting on DK, but I had to leave early today.) > It turns out that I'd forgotten the first apex update, > where the PA141 went to the PA241... so here a noise plot > (noise density is uncalibrated.. though I have the gain settings.) > > https://www.dropbox.com/s/1vguffiuj4noghz/Graph1.BMP?dl=0 > (The black line has a slope of 1)Oh, I should add that the x-axis "bandwidth" is the low pass filter setting, and the signal was AC coupled with a 10 Hz HP.> > Turns out the opamp got progressively worse... > What's weird is that the "1/f" noise > is not 1/f, but f^-2/3. > > Well since I don't understand 1/f, (1/f)^2/3 is no weirder. > > George H.
Reply by ●March 19, 20152015-03-19
George Herold wrote...> > Just the final update on apex opamps... > (I'm still waiting on DK, but I had to leave early today.) > It turns out that I'd forgotten the first apex update, > where the PA141 went to the PA241... so here a noise plot > (noise density is uncalibrated.. though I have the gain settings.) > > https://www.dropbox.com/s/1vguffiuj4noghz/Graph1.BMP?dl=0 > (The black line has a slope of 1) > > Turns out the opamp got progressively worse... > What's weird is that the "1/f" noise > is not 1/f, but f^-2/3. > > Well since I don't understand 1/f, (1/f)^2/3 is no weirder.We discuss in detail how this can happen in our lengthy Chapter 8 in Art of Electronics 3rd edition, 40 tons of which is shipping now from the printer. It's largely due to offset shifts (i.e., popcorn-noise style) as well as large thermal offset-voltage drifts. A good solution is a "composite" amplifier, where the poor amplifier is wrapped with a good opamp. -- Thanks, - Win
Reply by ●March 19, 20152015-03-19
On 18 Mar 2015 20:10:37 -0700, the renowned Winfield Hill <hill@rowland.harvard.edu> wrote:>George Herold wrote... >> >> Just the final update on apex opamps... >> (I'm still waiting on DK, but I had to leave early today.) >> It turns out that I'd forgotten the first apex update, >> where the PA141 went to the PA241... so here a noise plot >> (noise density is uncalibrated.. though I have the gain settings.) >> >> https://www.dropbox.com/s/1vguffiuj4noghz/Graph1.BMP?dl=0 >> (The black line has a slope of 1) >> >> Turns out the opamp got progressively worse... >> What's weird is that the "1/f" noise >> is not 1/f, but f^-2/3. >> >> Well since I don't understand 1/f, (1/f)^2/3 is no weirder. > > We discuss in detail how this can happen in our lengthy > Chapter 8 in Art of Electronics 3rd edition, 40 tons of > which is shipping now from the printer.Excellent. As a send-off we need a re-write of Flanders and Swan's 20 Tons: https://www.youtube.com/watch?v=48waPFTXJvY Come the ghostly Magi bearing.. 40 tons of AoE..>It's largely > due to offset shifts (i.e., popcorn-noise style) as > well as large thermal offset-voltage drifts. > > A good solution is a "composite" amplifier, where > the poor amplifier is wrapped with a good opamp.Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
Reply by ●March 19, 20152015-03-19
On Wednesday, March 18, 2015 at 11:10:45 PM UTC-4, Winfield Hill wrote:> George Herold wrote... > > > > Just the final update on apex opamps... > > (I'm still waiting on DK, but I had to leave early today.) > > It turns out that I'd forgotten the first apex update, > > where the PA141 went to the PA241... so here a noise plot > > (noise density is uncalibrated.. though I have the gain settings.) > > > > https://www.dropbox.com/s/1vguffiuj4noghz/Graph1.BMP?dl=0 > > (The black line has a slope of 1) > > > > Turns out the opamp got progressively worse... > > What's weird is that the "1/f" noise > > is not 1/f, but f^-2/3. > > > > Well since I don't understand 1/f, (1/f)^2/3 is no weirder. > > We discuss in detail how this can happen in our lengthy > Chapter 8 in Art of Electronics 3rd edition, 40 tons of > which is shipping now from the printer. It's largely > due to offset shifts (i.e., popcorn-noise style) as > well as large thermal offset-voltage drifts.Hi Win, I assume you are talking about 1/f noise ...(and not the 2/3rds power dependence.) I've read some stuff on 1/f. (Van-der-Ziel for one.) I guess the classic 1/f noise is from the old carbon comp. resistors. Here's a plot.... well it's a bit busy, I found a tiny hint of 1/f noise in (cheap, Xicon) metal film resistors. https://www.dropbox.com/s/y1jv60eawkj9oxd/1_OVER_F.BMP?dl=0 George H.> > A good solution is a "composite" amplifier, where > the poor amplifier is wrapped with a good opamp. > > > -- > Thanks, > - Win
Reply by ●March 19, 20152015-03-19
On 03/19/2015 12:30 PM, George Herold wrote:> On Wednesday, March 18, 2015 at 11:10:45 PM UTC-4, Winfield Hill wrote: >> George Herold wrote... >>> >>> Just the final update on apex opamps... >>> (I'm still waiting on DK, but I had to leave early today.) >>> It turns out that I'd forgotten the first apex update, >>> where the PA141 went to the PA241... so here a noise plot >>> (noise density is uncalibrated.. though I have the gain settings.) >>> >>> https://www.dropbox.com/s/1vguffiuj4noghz/Graph1.BMP?dl=0 >>> (The black line has a slope of 1) >>> >>> Turns out the opamp got progressively worse... >>> What's weird is that the "1/f" noise >>> is not 1/f, but f^-2/3. >>> >>> Well since I don't understand 1/f, (1/f)^2/3 is no weirder. >> >> We discuss in detail how this can happen in our lengthy >> Chapter 8 in Art of Electronics 3rd edition, 40 tons of >> which is shipping now from the printer. It's largely >> due to offset shifts (i.e., popcorn-noise style) as >> well as large thermal offset-voltage drifts. > > Hi Win, I assume you are talking about 1/f noise ...(and not the 2/3rds power dependence.) I've read some stuff on 1/f. (Van-der-Ziel for one.) > I guess the classic 1/f noise is from the old carbon comp. resistors. > Here's a plot.... well it's a bit busy, I found a tiny hint of 1/f noise in (cheap, Xicon) metal film resistors. > https://www.dropbox.com/s/y1jv60eawkj9oxd/1_OVER_F.BMP?dl=0 > > George H. >>IIRC most MF resistors are specified at 1E-7V/V per decade of frequency. I measured some as a voltage divider with a 9V alkaline, battery, and they were nowhere near that bad. 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
