On Fri, 13 Mar 2015 10:10:38 -0700 (PDT), George Herold <gherold@teachspin.com> 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.How about the MP118... Spice model on my website, by yours truly ;-) Model includes .AC and .TRAN ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Apex HV opamp issues.
Started by ●March 13, 2015
Reply by ●March 13, 20152015-03-13
Reply by ●March 13, 20152015-03-13
On 3/13/2015 4:17 PM, George Herold wrote:> On Friday, March 13, 2015 at 4:04:28 PM UTC-4, mako...@yahoo.com wrote: >>>>>> >>>>>> So I've been trying to beat the noise down in the current circuit, but >>>>>> with no luck. >> >> try reading this >> http://www.ti.com/lit/ml/sloa082/sloa082.pdf >> >> especially about the different contributions of >> noise voltage and noise current >> >> Mark > > Thanks Mark, (I've read plenty about noise.) > This opamp seems to have a ton of 1/f noise > with a 1/f corner freq. that looks to be >10 kHz! > > > George H. >Cheer up, I've measured pHEMTs with 1/f corners of 50 MHz. ;) (It was the otherwise excellent SKY65050.) 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 ●March 13, 20152015-03-13
On Friday, March 13, 2015 at 4:45:17 PM UTC-4, John Larkin wrote:> On Fri, 13 Mar 2015 10:10:38 -0700 (PDT), George Herold > <gherold@teachspin.com> 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. > > Apex used to use an AT&T high-voltage CMOS analog process that was > astoundingly noisy, 140 nv/rtHz or something crazy like that. Maybe > the PA141 was one of those. There was an appnote on compounding that > dog with a good low-voltage opamp. > > These days, most of their products are regular surfmount parts on PC > boards. > > You could try my cheap and almost-famous optocoupler-based HV > amplifier. > > https://dl.dropboxusercontent.com/u/53724080/Optos/HVamp.JPGThanks but I think I'll try the LTC thing first. The Apex amp sticks out and can be cut off, and a pcb soldered in place. My only problem is my HV supply is a bit high. right now it runs off ~+155 and -12. (LTC6090 max is 150V) I don't need all the HV ~110-130 would be fine. And low current, I don't know the C of my piezo stack, but max freq is 3kHz. A few mA of current at most. Could I just do a series (beefy) zener? ~20V. With some RC filtering behind if needed. George H.> > > -- > > John Larkin Highland Technology, Inc > picosecond timing precision measurement > > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.com
Reply by ●March 13, 20152015-03-13
On Friday, March 13, 2015 at 6:29:41 PM UTC-4, Jim Thompson wrote:> On Fri, 13 Mar 2015 10:10:38 -0700 (PDT), George Herold > <gherold@teachspin.com> 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. > > How about the MP118... Spice model on my website, by yours truly ;-)Woah this? http://www.digikey.com/product-search/en?vendor=0&keywords=MP118 That even more $! George H.> > Model includes .AC and .TRAN > > ...Jim Thompson > -- > | James E.Thompson | mens | > | Analog Innovations | et | > | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | > | San Tan Valley, AZ 85142 Skype: skypeanalog | | > | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | > | E-mail Icon at http://www.analog-innovations.com | 1962 | > > I love to cook with wine. Sometimes I even put it in the food.
Reply by ●March 13, 20152015-03-13
On Fri, 13 Mar 2015 16:29:22 -0700 (PDT), George Herold <gherold@teachspin.com> wrote:>On Friday, March 13, 2015 at 6:29:41 PM UTC-4, Jim Thompson wrote: >> On Fri, 13 Mar 2015 10:10:38 -0700 (PDT), George Herold >> <gherold@teachspin.com> 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. >> >> How about the MP118... Spice model on my website, by yours truly ;-) > >Woah this? >http://www.digikey.com/product-search/en?vendor=0&keywords=MP118 > >That even more $! > >George H. >>[snip] You can use it to launch satellites ;-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●March 13, 20152015-03-13
On Friday, March 13, 2015 at 6:55:40 PM UTC-4, Phil Hobbs wrote:> On 3/13/2015 4:17 PM, George Herold wrote: > > On Friday, March 13, 2015 at 4:04:28 PM UTC-4, mako...@yahoo.com wrote: > >>>>>> > >>>>>> So I've been trying to beat the noise down in the current circuit, but > >>>>>> with no luck. > >> > >> try reading this > >> http://www.ti.com/lit/ml/sloa082/sloa082.pdf > >> > >> especially about the different contributions of > >> noise voltage and noise current > >> > >> Mark > > > > Thanks Mark, (I've read plenty about noise.) > > This opamp seems to have a ton of 1/f noise > > with a 1/f corner freq. that looks to be >10 kHz! > > > > > > George H. > > > Cheer up, I've measured pHEMTs with 1/f corners of 50 MHz. ;)Well it just means filtering is pointless... (in retrospec, I should have measured the noise first) Replacing the entire opamp with a pcb is something that I can get (some) customers to do in the field. (a TO-3-8 package, eight fat pins and two mounting holes) George H.> (It was the otherwise excellent SKY65050.) > > 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 ●March 13, 20152015-03-13
On Fri, 13 Mar 2015 13:11:16 -0700, George Herold wrote:> On Friday, March 13, 2015 at 2:44:51 PM UTC-4, Tim Wescott wrote: >> On Fri, 13 Mar 2015 10:49:11 -0700, George Herold wrote: >> >> > On Friday, March 13, 2015 at 1:23:46 PM UTC-4, Jan Panteltje wrote: >> >> On a sunny day (Fri, 13 Mar 2015 10:10:38 -0700 (PDT)) it happened >> >> George Herold <gherold@teachspin.com> wrote in >> >> <ad164713-93a0-48f2-919e-b5f94b53a806@googlegroups.com>: >> >> >> >> >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. >> >> >> >> >> >> Sometimes {tm) >> >> ------||---10k ---- >> >> | 1n | >> >> |----------||------ | >> >> | 100p | >> >> 10k ----- 100 k----------------- >> >> | | >> >> --- - | >> >> > ----- >> >> --- + >> >> >> >> >> > OK, I'll give it a try... I was thinking some resistance in series >> > with the 100pF..(?) >> > >> > (I just ordered some LTC6090's from DK...) >> > >> > I also noticed that the PA341 has been replaced with the PA441.. 30 >> > times less noise! >> > >> > >> Maybe they were getting lots of complaints! Is it pin-compatible? > > Yup.. I order one of those too.. but only 1.. ~$50 each!Apex parts definitely make you pay for the privilege of not having to roll your own amp. It's worth it if your volume is low and the cost of failure is high. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Reply by ●March 13, 20152015-03-13
On Fri, 13 Mar 2015 14:09:26 -0400, Phil Hobbs wrote:> On 03/13/2015 01:10 PM, 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. >> > How about a resistor in series with the output? Your piezo is probably > in the nanofarads. > > Cheers > > Phil HobbsAt least with some of the Apex amplifiers, they depend on high output capacitance as part of the frequency compensation. Adding (too much) output resistance would make these amplifiers go unstable. Increasing the load capacitance might be part of reducing closed loop amplifier bandwidth. HTH-
Reply by ●March 13, 20152015-03-13
On Friday, March 13, 2015 at 8:08:22 PM UTC-4, Tim Wescott wrote:> On Fri, 13 Mar 2015 13:11:16 -0700, George Herold wrote: > > > On Friday, March 13, 2015 at 2:44:51 PM UTC-4, Tim Wescott wrote: > >> On Fri, 13 Mar 2015 10:49:11 -0700, George Herold wrote: > >> > >> > On Friday, March 13, 2015 at 1:23:46 PM UTC-4, Jan Panteltje wrote: > >> >> On a sunny day (Fri, 13 Mar 2015 10:10:38 -0700 (PDT)) it happened > >> >> George Herold <gherold@teachspin.com> wrote in > >> >> <ad164713-93a0-48f2-919e-b5f94b53a806@googlegroups.com>: > >> >> > >> >> >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. > >> >> > >> >> > >> >> Sometimes {tm) > >> >> ------||---10k ---- > >> >> | 1n | > >> >> |----------||------ | > >> >> | 100p | > >> >> 10k ----- 100 k----------------- > >> >> | | > >> >> --- - | > >> >> > ----- > >> >> --- + > >> >> > >> >> > >> > OK, I'll give it a try... I was thinking some resistance in series > >> > with the 100pF..(?) > >> > > >> > (I just ordered some LTC6090's from DK...) > >> > > >> > I also noticed that the PA341 has been replaced with the PA441.. 30 > >> > times less noise! > >> > > >> > > >> Maybe they were getting lots of complaints! Is it pin-compatible? > > > > Yup.. I order one of those too.. but only 1.. ~$50 each! > > Apex parts definitely make you pay for the privilege of not having to roll > your own amp. It's worth it if your volume is low and the cost of failure > is high.Yeah, we've been happily paying that cost for years. Now due to their crappy opamp, combined with my lack of due diligence... the return shipping costs to India will make it seem like nothing. (at least I found it now, I think we've only shipped one to India... and you never know we might find someone there who can handle a soldering iron.) George H.> > -- > > Tim Wescott > Wescott Design Services > http://www.wescottdesign.com
Reply by ●March 13, 20152015-03-13
On Sat, 14 Mar 2015 00:26:36 +0000 (UTC), Frank Miles <fpm@u.washington.edu> wrote:>On Fri, 13 Mar 2015 14:09:26 -0400, Phil Hobbs wrote: > >> On 03/13/2015 01:10 PM, 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. >>> >> How about a resistor in series with the output? Your piezo is probably >> in the nanofarads. >> >> Cheers >> >> Phil Hobbs > >At least with some of the Apex amplifiers, they depend on high output >capacitance as part of the frequency compensation. Adding (too much) >output resistance would make these amplifiers go unstable. > >Increasing the load capacitance might be part of reducing closed loop >amplifier bandwidth. > >HTH-The MP118, the one I wrote the Spice model for, uses pole-splitting compensation, plus a lead zero... external cap. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
