Forums

TI opamp

Started by John Larkin March 10, 2015
On Thursday, March 12, 2015 at 11:15:57 AM UTC-4, dagmarg...@yahoo.com wrote:
> On Tuesday, March 10, 2015 at 12:22:34 PM UTC-4, Gerhard Hoffmann wrote: > > Am 10.03.2015 um 15:57 schrieb John Larkin: > > > On Tue, 10 Mar 2015 08:44:40 -0500, John S <Sophi.2@invalid.org> > > > wrote: > > > > > >> On 3/9/2015 10:36 PM, John Larkin wrote: > > >>> > > >>> > > >>> Has anybody used this one? > > >>> > > >>> http://www.ti.com/product/lme49990 > > >>> > > >>> Sounds too good to be true. > > >> > > >> Note that the GBW is 110MHz on page 1 of the specs :) > > > > > > Yup. The ADI low-noise amps, still relatively noisy, are slow. The > > > LT1028 is below 1 nv/rthz but has issues. > > > > The AD797 is not significantly noisier or slower, if at all. > > I really like the ADA4898-2. > > > > Depending on how it's measured, a little bit lower ft than the LME, but > > more than twice the slew rate, no 300 KHz noise mole hill like LT1028, > > and with 2 amplifiers/SO-8 quite a good price, especially if you average > > 20 devices for _really_ low voltage noise from low impedance sources. > > > > < http://www.hoffmann-hochfrequenz.de/downloads/lono.pdf > > > > > and, related: > > > > < > > http://www.hoffmann-hochfrequenz.de/downloads/NoiseMeasurementsOnChemicalBatteries.pdf > > > > > Nice write-up, thanks. Nice amplifier. Surprising how much > 'noise' batteries make at 50Hz. ;-)
That is nice... Gerhard, I wonder if you say any microphonic pickup in the batteries. Back in grad school we used 9V transistor batteries to bias a bolometer, a few uA of current. (Low temperature FIR sensor.) There was this extra noise sometimes that we eventually traced back to microphonic pickup in the batteries... (If you talked loudly next to the battery bias box you saw the noise on the scan.) George H.
> > Cheers, > James Arthur
On Tue, 10 Mar 2015 17:22:27 +0100, Gerhard Hoffmann
<ghf@hoffmann-hochfrequenz.de> wrote:

>Am 10.03.2015 um 15:57 schrieb John Larkin: >> On Tue, 10 Mar 2015 08:44:40 -0500, John S <Sophi.2@invalid.org> >> wrote: >> >>> On 3/9/2015 10:36 PM, John Larkin wrote: >>>> >>>> >>>> Has anybody used this one? >>>> >>>> http://www.ti.com/product/lme49990 >>>> >>>> Sounds too good to be true. >>> >>> Note that the GBW is 110MHz on page 1 of the specs :) >> >> Yup. The ADI low-noise amps, still relatively noisy, are slow. The >> LT1028 is below 1 nv/rthz but has issues. > >The AD797 is not significantly noisier or slower, if at all. >I really like the ADA4898-2. > >Depending on how it's measured, a little bit lower ft than the LME, but >more than twice the slew rate, no 300 KHz noise mole hill like LT1028, >and with 2 amplifiers/SO-8 quite a good price, especially if you average >20 devices for _really_ low voltage noise from low impedance sources. > >< http://www.hoffmann-hochfrequenz.de/downloads/lono.pdf > > >and, related: > >< >http://www.hoffmann-hochfrequenz.de/downloads/NoiseMeasurementsOnChemicalBatteries.pdf > > > >< >http://www.hoffmann-hochfrequenz.de/downloads/Noise_Measurements_On_Some_Laboratory_Power_Supplies.pdf > > > >regards, Gerhard >
All the batteries have similar curves, especially at low frequencies. Is there any chance that the presence of DC increased the preamp noise? It wouldn't take much leakage in the input coupling cap to upset the preamp. I assume the preamp is a bunch of paralleled jfets. Some simple tests could discount that possibility. It looks like the Tadiran is the lowest voltage and has the least noise below 1 Hz. -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Thursday, March 12, 2015 at 11:51:22 AM UTC-4, John Larkin wrote:
> On Tue, 10 Mar 2015 17:22:27 +0100, Gerhard Hoffmann wrote: > > >Am 10.03.2015 um 15:57 schrieb John Larkin: > >> On Tue, 10 Mar 2015 08:44:40 -0500, John S <Sophi.2@invalid.org> > >> wrote: > >> > >>> On 3/9/2015 10:36 PM, John Larkin wrote: > >>>> > >>>> > >>>> Has anybody used this one? > >>>> > >>>> http://www.ti.com/product/lme49990 > >>>> > >>>> Sounds too good to be true. > >>> > >>> Note that the GBW is 110MHz on page 1 of the specs :) > >> > >> Yup. The ADI low-noise amps, still relatively noisy, are slow. The > >> LT1028 is below 1 nv/rthz but has issues. > > > >The AD797 is not significantly noisier or slower, if at all. > >I really like the ADA4898-2. > > > >Depending on how it's measured, a little bit lower ft than the LME, but > >more than twice the slew rate, no 300 KHz noise mole hill like LT1028, > >and with 2 amplifiers/SO-8 quite a good price, especially if you average > >20 devices for _really_ low voltage noise from low impedance sources. > > > >< http://www.hoffmann-hochfrequenz.de/downloads/lono.pdf > > > > >and, related: > > > >< > >http://www.hoffmann-hochfrequenz.de/downloads/NoiseMeasurementsOnChemicalBatteries.pdf > > > > > > >< > >http://www.hoffmann-hochfrequenz.de/downloads/Noise_Measurements_On_Some_Laboratory_Power_Supplies.pdf > > > > > > >regards, Gerhard > > > > All the batteries have similar curves, especially at low frequencies. > > Is there any chance that the presence of DC increased the preamp > noise? It wouldn't take much leakage in the input coupling cap to > upset the preamp. I assume the preamp is a bunch of paralleled jfets. > > Some simple tests could discount that possibility. It looks like the > Tadiran is the lowest voltage and has the least noise below 1 Hz. > >
The preamp was massively paralleled ADI op amps (in the previous reference). Cheers, James Arthur
On Thu, 12 Mar 2015 09:00:01 -0700 (PDT), dagmargoodboat@yahoo.com
wrote:

>On Thursday, March 12, 2015 at 11:51:22 AM UTC-4, John Larkin wrote: >> On Tue, 10 Mar 2015 17:22:27 +0100, Gerhard Hoffmann wrote: >> >> >Am 10.03.2015 um 15:57 schrieb John Larkin: >> >> On Tue, 10 Mar 2015 08:44:40 -0500, John S <Sophi.2@invalid.org> >> >> wrote: >> >> >> >>> On 3/9/2015 10:36 PM, John Larkin wrote: >> >>>> >> >>>> >> >>>> Has anybody used this one? >> >>>> >> >>>> http://www.ti.com/product/lme49990 >> >>>> >> >>>> Sounds too good to be true. >> >>> >> >>> Note that the GBW is 110MHz on page 1 of the specs :) >> >> >> >> Yup. The ADI low-noise amps, still relatively noisy, are slow. The >> >> LT1028 is below 1 nv/rthz but has issues. >> > >> >The AD797 is not significantly noisier or slower, if at all. >> >I really like the ADA4898-2. >> > >> >Depending on how it's measured, a little bit lower ft than the LME, but >> >more than twice the slew rate, no 300 KHz noise mole hill like LT1028, >> >and with 2 amplifiers/SO-8 quite a good price, especially if you average >> >20 devices for _really_ low voltage noise from low impedance sources. >> > >> >< http://www.hoffmann-hochfrequenz.de/downloads/lono.pdf > >> > >> >and, related: >> > >> >< >> >http://www.hoffmann-hochfrequenz.de/downloads/NoiseMeasurementsOnChemicalBatteries.pdf >> > > >> > >> >< >> >http://www.hoffmann-hochfrequenz.de/downloads/Noise_Measurements_On_Some_Laboratory_Power_Supplies.pdf >> > > >> > >> >regards, Gerhard >> > >> >> All the batteries have similar curves, especially at low frequencies. >> >> Is there any chance that the presence of DC increased the preamp >> noise? It wouldn't take much leakage in the input coupling cap to >> upset the preamp. I assume the preamp is a bunch of paralleled jfets. >> >> Some simple tests could discount that possibility. It looks like the >> Tadiran is the lowest voltage and has the least noise below 1 Hz. >> >> > >The preamp was massively paralleled ADI op amps (in the previous reference). > >Cheers, >James Arthur
OK, but there must be a biggish DC blocking cap. [1] One easy test: connect 4 batteries in series adding, nom 6 volts, measure noise. Then connect them series opposing, nom 0 volts, repeat. That assumes the noise is uncorrelated between cells. That's not true for thermal effects, and batteries have relatively huge TCs. So mummify them in bubble wrap an see if that changes anything. [1] leakage in capacitors is non-metallic, so the electron ordering effect of metallic conductors is not present. So maybe capacitor leakage has shot noise. -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Thursday, March 12, 2015 at 12:35:55 PM UTC-4, John Larkin wrote:
> On Thu, 12 Mar 2015 09:00:01 -0700 (PDT), dagmargoodboat@yahoo.com > wrote: > > >On Thursday, March 12, 2015 at 11:51:22 AM UTC-4, John Larkin wrote: > >> On Tue, 10 Mar 2015 17:22:27 +0100, Gerhard Hoffmann wrote: > >> > >> >Am 10.03.2015 um 15:57 schrieb John Larkin: > >> >> On Tue, 10 Mar 2015 08:44:40 -0500, John S <Sophi.2@invalid.org> > >> >> wrote: > >> >> > >> >>> On 3/9/2015 10:36 PM, John Larkin wrote: > >> >>>> > >> >>>> > >> >>>> Has anybody used this one? > >> >>>> > >> >>>> http://www.ti.com/product/lme49990 > >> >>>> > >> >>>> Sounds too good to be true. > >> >>> > >> >>> Note that the GBW is 110MHz on page 1 of the specs :) > >> >> > >> >> Yup. The ADI low-noise amps, still relatively noisy, are slow. The > >> >> LT1028 is below 1 nv/rthz but has issues. > >> > > >> >The AD797 is not significantly noisier or slower, if at all. > >> >I really like the ADA4898-2. > >> > > >> >Depending on how it's measured, a little bit lower ft than the LME, but > >> >more than twice the slew rate, no 300 KHz noise mole hill like LT1028, > >> >and with 2 amplifiers/SO-8 quite a good price, especially if you average > >> >20 devices for _really_ low voltage noise from low impedance sources. > >> > > >> >< http://www.hoffmann-hochfrequenz.de/downloads/lono.pdf > > >> > > >> >and, related: > >> > > >> >< > >> >http://www.hoffmann-hochfrequenz.de/downloads/NoiseMeasurementsOnChemicalBatteries.pdf > >> > > > >> > > >> >< > >> >http://www.hoffmann-hochfrequenz.de/downloads/Noise_Measurements_On_Some_Laboratory_Power_Supplies.pdf > >> > > > >> > > >> >regards, Gerhard > >> > > >> > >> All the batteries have similar curves, especially at low frequencies. > >> > >> Is there any chance that the presence of DC increased the preamp > >> noise? It wouldn't take much leakage in the input coupling cap to > >> upset the preamp. I assume the preamp is a bunch of paralleled jfets. > >> > >> Some simple tests could discount that possibility. It looks like the > >> Tadiran is the lowest voltage and has the least noise below 1 Hz. > >> > >> > > > >The preamp was massively paralleled ADI op amps (in the previous reference). > > > >Cheers, > >James Arthur > > OK, but there must be a biggish DC blocking cap. [1] > > One easy test: connect 4 batteries in series adding, nom 6 volts, > measure noise. Then connect them series opposing, nom 0 volts, repeat. > > That assumes the noise is uncorrelated between cells. That's not true > for thermal effects, and batteries have relatively huge TCs. So > mummify them in bubble wrap an see if that changes anything. > > [1] leakage in capacitors is non-metallic, so the electron ordering > effect of metallic conductors is not present. So maybe capacitor > leakage has shot noise.
I was interested in the coupling caps. In his first paper (about the preamp ) He first used 16 10uF X7R ceramics (50V 1206), (160 uF and 10k ohm), he then switched to mylar.. but too big so went back to the ceramics. I've got noise problems of my own at the moment. I was testing some new mirrors in a Fabry-perot cavity and discovered that our diode laser is noisy. Grumble... I think it's current noise.. at least there is all this "new" interference peaks on the spectrum. Here's a slow scan through the F-P transmission. https://www.dropbox.com/sh/1dzk4zwo44cw0m0/AACwTtJik_847xD42xYclsKVa?dl=0 The first two are the noisy laser controller, (TEK00, TEK01) the last two the old demo version. The width is only a few MHz, so just building shake gives me a bit of jitter on the spectrum. George H.
> > -- > > John Larkin Highland Technology, Inc > picosecond timing laser drivers and controllers > > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.com
On 03/12/2015 01:34 PM, George Herold wrote:
> On Thursday, March 12, 2015 at 12:35:55 PM UTC-4, John Larkin wrote: >> On Thu, 12 Mar 2015 09:00:01 -0700 (PDT), dagmargoodboat@yahoo.com >> wrote: >> >>> On Thursday, March 12, 2015 at 11:51:22 AM UTC-4, John Larkin wrote: >>>> On Tue, 10 Mar 2015 17:22:27 +0100, Gerhard Hoffmann wrote: >>>> >>>>> Am 10.03.2015 um 15:57 schrieb John Larkin: >>>>>> On Tue, 10 Mar 2015 08:44:40 -0500, John S <Sophi.2@invalid.org> >>>>>> wrote: >>>>>> >>>>>>> On 3/9/2015 10:36 PM, John Larkin wrote: >>>>>>>> >>>>>>>> >>>>>>>> Has anybody used this one? >>>>>>>> >>>>>>>> http://www.ti.com/product/lme49990 >>>>>>>> >>>>>>>> Sounds too good to be true. >>>>>>> >>>>>>> Note that the GBW is 110MHz on page 1 of the specs :) >>>>>> >>>>>> Yup. The ADI low-noise amps, still relatively noisy, are slow. The >>>>>> LT1028 is below 1 nv/rthz but has issues. >>>>> >>>>> The AD797 is not significantly noisier or slower, if at all. >>>>> I really like the ADA4898-2. >>>>> >>>>> Depending on how it's measured, a little bit lower ft than the LME, but >>>>> more than twice the slew rate, no 300 KHz noise mole hill like LT1028, >>>>> and with 2 amplifiers/SO-8 quite a good price, especially if you average >>>>> 20 devices for _really_ low voltage noise from low impedance sources. >>>>> >>>>> < http://www.hoffmann-hochfrequenz.de/downloads/lono.pdf > >>>>> >>>>> and, related: >>>>> >>>>> < >>>>> http://www.hoffmann-hochfrequenz.de/downloads/NoiseMeasurementsOnChemicalBatteries.pdf >>>>>> >>>>> >>>>> < >>>>> http://www.hoffmann-hochfrequenz.de/downloads/Noise_Measurements_On_Some_Laboratory_Power_Supplies.pdf >>>>>> >>>>> >>>>> regards, Gerhard >>>>> >>>> >>>> All the batteries have similar curves, especially at low frequencies. >>>> >>>> Is there any chance that the presence of DC increased the preamp >>>> noise? It wouldn't take much leakage in the input coupling cap to >>>> upset the preamp. I assume the preamp is a bunch of paralleled jfets. >>>> >>>> Some simple tests could discount that possibility. It looks like the >>>> Tadiran is the lowest voltage and has the least noise below 1 Hz. >>>> >>>> >>> >>> The preamp was massively paralleled ADI op amps (in the previous reference). >>> >>> Cheers, >>> James Arthur >> >> OK, but there must be a biggish DC blocking cap. [1] >> >> One easy test: connect 4 batteries in series adding, nom 6 volts, >> measure noise. Then connect them series opposing, nom 0 volts, repeat. >> >> That assumes the noise is uncorrelated between cells. That's not true >> for thermal effects, and batteries have relatively huge TCs. So >> mummify them in bubble wrap an see if that changes anything. >> >> [1] leakage in capacitors is non-metallic, so the electron ordering >> effect of metallic conductors is not present. So maybe capacitor >> leakage has shot noise. > > > I was interested in the coupling caps. In his first paper (about the preamp > ) He first used 16 10uF X7R ceramics (50V 1206), (160 uF and 10k ohm), he then switched to mylar.. but too big so went back to the ceramics. > > I've got noise problems of my own at the moment. I was testing some new mirrors in a Fabry-perot cavity and discovered that our diode laser is noisy. Grumble... I think it's current noise.. at least there is all this "new" interference peaks on the spectrum. > > Here's a slow scan through the F-P transmission. > https://www.dropbox.com/sh/1dzk4zwo44cw0m0/AACwTtJik_847xD42xYclsKVa?dl=0 > > The first two are the noisy laser controller, (TEK00, TEK01) the last two the old demo version. The width is only a few MHz, so just building shake gives me a bit of jitter on the spectrum. > > George H.
What's the span? Looks like mode hopping to me--you wouldn't have those sharp jaggies if it were FM noise--the sidebands would have at least the same width as the carrier. Small differences in the temperature and bias current can change that. Wolfgang's Laserblog <https://hololaser.wordpress.com> has a bunch of interesting plots of noise vs T and I. 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
On Thursday, March 12, 2015 at 2:11:52 PM UTC-4, Phil Hobbs wrote:
> On 03/12/2015 01:34 PM, George Herold wrote: > > On Thursday, March 12, 2015 at 12:35:55 PM UTC-4, John Larkin wrote: > >> On Thu, 12 Mar 2015 09:00:01 -0700 (PDT), dagmargoodboat@yahoo.com > >> wrote: > >> > >>> On Thursday, March 12, 2015 at 11:51:22 AM UTC-4, John Larkin wrote: > >>>> On Tue, 10 Mar 2015 17:22:27 +0100, Gerhard Hoffmann wrote: > >>>> > >>>>> Am 10.03.2015 um 15:57 schrieb John Larkin: > >>>>>> On Tue, 10 Mar 2015 08:44:40 -0500, John S <Sophi.2@invalid.org> > >>>>>> wrote: > >>>>>> > >>>>>>> On 3/9/2015 10:36 PM, John Larkin wrote: > >>>>>>>> > >>>>>>>> > >>>>>>>> Has anybody used this one? > >>>>>>>> > >>>>>>>> http://www.ti.com/product/lme49990 > >>>>>>>> > >>>>>>>> Sounds too good to be true. > >>>>>>> > >>>>>>> Note that the GBW is 110MHz on page 1 of the specs :) > >>>>>> > >>>>>> Yup. The ADI low-noise amps, still relatively noisy, are slow. The > >>>>>> LT1028 is below 1 nv/rthz but has issues. > >>>>> > >>>>> The AD797 is not significantly noisier or slower, if at all. > >>>>> I really like the ADA4898-2. > >>>>> > >>>>> Depending on how it's measured, a little bit lower ft than the LME, but > >>>>> more than twice the slew rate, no 300 KHz noise mole hill like LT1028, > >>>>> and with 2 amplifiers/SO-8 quite a good price, especially if you average > >>>>> 20 devices for _really_ low voltage noise from low impedance sources. > >>>>> > >>>>> < http://www.hoffmann-hochfrequenz.de/downloads/lono.pdf > > >>>>> > >>>>> and, related: > >>>>> > >>>>> < > >>>>> http://www.hoffmann-hochfrequenz.de/downloads/NoiseMeasurementsOnChemicalBatteries.pdf > >>>>>> > >>>>> > >>>>> < > >>>>> http://www.hoffmann-hochfrequenz.de/downloads/Noise_Measurements_On_Some_Laboratory_Power_Supplies.pdf > >>>>>> > >>>>> > >>>>> regards, Gerhard > >>>>> > >>>> > >>>> All the batteries have similar curves, especially at low frequencies. > >>>> > >>>> Is there any chance that the presence of DC increased the preamp > >>>> noise? It wouldn't take much leakage in the input coupling cap to > >>>> upset the preamp. I assume the preamp is a bunch of paralleled jfets. > >>>> > >>>> Some simple tests could discount that possibility. It looks like the > >>>> Tadiran is the lowest voltage and has the least noise below 1 Hz. > >>>> > >>>> > >>> > >>> The preamp was massively paralleled ADI op amps (in the previous reference). > >>> > >>> Cheers, > >>> James Arthur > >> > >> OK, but there must be a biggish DC blocking cap. [1] > >> > >> One easy test: connect 4 batteries in series adding, nom 6 volts, > >> measure noise. Then connect them series opposing, nom 0 volts, repeat. > >> > >> That assumes the noise is uncorrelated between cells. That's not true > >> for thermal effects, and batteries have relatively huge TCs. So > >> mummify them in bubble wrap an see if that changes anything. > >> > >> [1] leakage in capacitors is non-metallic, so the electron ordering > >> effect of metallic conductors is not present. So maybe capacitor > >> leakage has shot noise. > > > > > > I was interested in the coupling caps. In his first paper (about the preamp > > ) He first used 16 10uF X7R ceramics (50V 1206), (160 uF and 10k ohm), he then switched to mylar.. but too big so went back to the ceramics. > > > > I've got noise problems of my own at the moment. I was testing some new mirrors in a Fabry-perot cavity and discovered that our diode laser is noisy. Grumble... I think it's current noise.. at least there is all this "new" interference peaks on the spectrum. > > > > Here's a slow scan through the F-P transmission. > > https://www.dropbox.com/sh/1dzk4zwo44cw0m0/AACwTtJik_847xD42xYclsKVa?dl=0 > > > > The first two are the noisy laser controller, (TEK00, TEK01) the last two the old demo version. The width is only a few MHz, so just building shake gives me a bit of jitter on the spectrum. > > > > George H. > > What's the span? > > Looks like mode hopping to me--you wouldn't have those sharp jaggies if > it were FM noise--the sidebands would have at least the same width as > the carrier. Small differences in the temperature and bias current can > change that.
Hi Phil, I don't think it's mode hopping... it would be much worse. I can get feedback from the F-P cavity, but I monitor the transmission through an Rb cell and that spectrum stays clean. It's a confocal F-P cavity, FSR = 385 MHz, (20 cm radius), with a finesse of 100 - 150 or so.. depending on how well I set the mirror position. So the width of the transmission peak is 3-4 MHz. It looks to be current noise..interference from somewhere. (Well I see current noise from the noisy unit and not the other.) Though I want to make sure of that before I start drilling down. I also wonder about noise on piezo drive signal... Grumble, one good way to ruin my day. My bigger concern is that there are other "bad" units out there that we'll have to recall... but I'm getting ahead of myself. George H.
> Wolfgang's Laserblog <https://hololaser.wordpress.com> has a bunch of > interesting plots of noise vs T and I. > > 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
On 03/12/2015 02:43 PM, George Herold wrote:
> On Thursday, March 12, 2015 at 2:11:52 PM UTC-4, Phil Hobbs wrote: >> On 03/12/2015 01:34 PM, George Herold wrote: >>> On Thursday, March 12, 2015 at 12:35:55 PM UTC-4, John Larkin wrote: >>>> On Thu, 12 Mar 2015 09:00:01 -0700 (PDT), dagmargoodboat@yahoo.com >>>> wrote: >>>> >>>>> On Thursday, March 12, 2015 at 11:51:22 AM UTC-4, John Larkin wrote: >>>>>> On Tue, 10 Mar 2015 17:22:27 +0100, Gerhard Hoffmann wrote: >>>>>> >>>>>>> Am 10.03.2015 um 15:57 schrieb John Larkin: >>>>>>>> On Tue, 10 Mar 2015 08:44:40 -0500, John S <Sophi.2@invalid.org> >>>>>>>> wrote: >>>>>>>> >>>>>>>>> On 3/9/2015 10:36 PM, John Larkin wrote: >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> Has anybody used this one? >>>>>>>>>> >>>>>>>>>> http://www.ti.com/product/lme49990 >>>>>>>>>> >>>>>>>>>> Sounds too good to be true. >>>>>>>>> >>>>>>>>> Note that the GBW is 110MHz on page 1 of the specs :) >>>>>>>> >>>>>>>> Yup. The ADI low-noise amps, still relatively noisy, are slow. The >>>>>>>> LT1028 is below 1 nv/rthz but has issues. >>>>>>> >>>>>>> The AD797 is not significantly noisier or slower, if at all. >>>>>>> I really like the ADA4898-2. >>>>>>> >>>>>>> Depending on how it's measured, a little bit lower ft than the LME, but >>>>>>> more than twice the slew rate, no 300 KHz noise mole hill like LT1028, >>>>>>> and with 2 amplifiers/SO-8 quite a good price, especially if you average >>>>>>> 20 devices for _really_ low voltage noise from low impedance sources. >>>>>>> >>>>>>> < http://www.hoffmann-hochfrequenz.de/downloads/lono.pdf > >>>>>>> >>>>>>> and, related: >>>>>>> >>>>>>> < >>>>>>> http://www.hoffmann-hochfrequenz.de/downloads/NoiseMeasurementsOnChemicalBatteries.pdf >>>>>>>> >>>>>>> >>>>>>> < >>>>>>> http://www.hoffmann-hochfrequenz.de/downloads/Noise_Measurements_On_Some_Laboratory_Power_Supplies.pdf >>>>>>>> >>>>>>> >>>>>>> regards, Gerhard >>>>>>> >>>>>> >>>>>> All the batteries have similar curves, especially at low frequencies.. >>>>>> >>>>>> Is there any chance that the presence of DC increased the preamp >>>>>> noise? It wouldn't take much leakage in the input coupling cap to >>>>>> upset the preamp. I assume the preamp is a bunch of paralleled jfets.. >>>>>> >>>>>> Some simple tests could discount that possibility. It looks like the >>>>>> Tadiran is the lowest voltage and has the least noise below 1 Hz. >>>>>> >>>>>> >>>>> >>>>> The preamp was massively paralleled ADI op amps (in the previous reference). >>>>> >>>>> Cheers, >>>>> James Arthur >>>> >>>> OK, but there must be a biggish DC blocking cap. [1] >>>> >>>> One easy test: connect 4 batteries in series adding, nom 6 volts, >>>> measure noise. Then connect them series opposing, nom 0 volts, repeat. >>>> >>>> That assumes the noise is uncorrelated between cells. That's not true >>>> for thermal effects, and batteries have relatively huge TCs. So >>>> mummify them in bubble wrap an see if that changes anything. >>>> >>>> [1] leakage in capacitors is non-metallic, so the electron ordering >>>> effect of metallic conductors is not present. So maybe capacitor >>>> leakage has shot noise. >>> >>> >>> I was interested in the coupling caps. In his first paper (about the preamp >>> ) He first used 16 10uF X7R ceramics (50V 1206), (160 uF and 10k ohm), he then switched to mylar.. but too big so went back to the ceramics. >>> >>> I've got noise problems of my own at the moment. I was testing some new mirrors in a Fabry-perot cavity and discovered that our diode laser is noisy. Grumble... I think it's current noise.. at least there is all this "new" interference peaks on the spectrum. >>> >>> Here's a slow scan through the F-P transmission. >>> https://www.dropbox.com/sh/1dzk4zwo44cw0m0/AACwTtJik_847xD42xYclsKVa?dl=0 >>> >>> The first two are the noisy laser controller, (TEK00, TEK01) the last two the old demo version. The width is only a few MHz, so just building shake gives me a bit of jitter on the spectrum. >>> >>> George H. >> >> What's the span? >> >> Looks like mode hopping to me--you wouldn't have those sharp jaggies if >> it were FM noise--the sidebands would have at least the same width as >> the carrier. Small differences in the temperature and bias current can >> change that. > > Hi Phil, I don't think it's mode hopping... it would be much worse. > I can get feedback from the F-P cavity, but I monitor the transmission through an Rb cell and that spectrum stays clean. > > It's a confocal F-P cavity, FSR = 385 MHz, (20 cm radius), with a finesse of 100 - 150 or so.. depending on how well I set the mirror position. > > So the width of the transmission peak is 3-4 MHz. > > It looks to be current noise..interference from somewhere. > (Well I see current noise from the noisy unit and not the other.) > Though I want to make sure of that before I start drilling down. > I also wonder about noise on piezo drive signal... > Grumble, one good way to ruin my day. > My bigger concern is that there are other "bad" units out there that > we'll have to recall... but I'm getting ahead of myself. > > George H.
Hmm. Yes, ordinary mode hopping would make it a lot wider than 3 MHz, that's for sure, but those spiky things can't be ordinary noise sidebands, because genuine sidebands couldn't be narrower than the main line. I suppose it could be acquiring and then losing self-lock on the cavity, which can happen pretty fast. What does the AM noise look like? Does the shape change when you change scan speed? 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
On Thursday, March 12, 2015 at 2:50:56 PM UTC-4, Phil Hobbs wrote:
> On 03/12/2015 02:43 PM, George Herold wrote:
<big snip>
> >>> I was interested in the coupling caps. In his first paper (about the preamp > >>> ) He first used 16 10uF X7R ceramics (50V 1206), (160 uF and 10k ohm), he then switched to mylar.. but too big so went back to the ceramics. > >>> > >>> I've got noise problems of my own at the moment. I was testing some new mirrors in a Fabry-perot cavity and discovered that our diode laser is noisy. Grumble... I think it's current noise.. at least there is all this "new" interference peaks on the spectrum. > >>> > >>> Here's a slow scan through the F-P transmission. > >>> https://www.dropbox.com/sh/1dzk4zwo44cw0m0/AACwTtJik_847xD42xYclsKVa?dl=0 > >>> > >>> The first two are the noisy laser controller, (TEK00, TEK01) the last two the old demo version. The width is only a few MHz, so just building shake gives me a bit of jitter on the spectrum. > >>> > >>> George H. > >> > >> What's the span? > >> > >> Looks like mode hopping to me--you wouldn't have those sharp jaggies if > >> it were FM noise--the sidebands would have at least the same width as > >> the carrier. Small differences in the temperature and bias current can > >> change that. > > > > Hi Phil, I don't think it's mode hopping... it would be much worse. > > I can get feedback from the F-P cavity, but I monitor the transmission through an Rb cell and that spectrum stays clean. > > > > It's a confocal F-P cavity, FSR = 385 MHz, (20 cm radius), with a finesse of 100 - 150 or so.. depending on how well I set the mirror position. > > > > So the width of the transmission peak is 3-4 MHz. > > > > It looks to be current noise..interference from somewhere. > > (Well I see current noise from the noisy unit and not the other.) > > Though I want to make sure of that before I start drilling down. > > I also wonder about noise on piezo drive signal... > > Grumble, one good way to ruin my day. > > My bigger concern is that there are other "bad" units out there that > > we'll have to recall... but I'm getting ahead of myself. > > > > George H. > > Hmm. Yes, ordinary mode hopping would make it a lot wider than 3 MHz, > that's for sure, but those spiky things can't be ordinary noise > sidebands, because genuine sidebands couldn't be narrower than the main > line. > > I suppose it could be acquiring and then losing self-lock on the cavity, > which can happen pretty fast. What does the AM noise look like? Does > the shape change when you change scan speed?
There is no lock on the cavity (F-P or diode laser). The F-P is not scanable, just some mirrors in a tube. We scan the laser through the FP cavity modes. If I scan the laser faster all the spikey things just happen on a faster time scale.. I only see a few in a pass through one FP mode. It's not like there is excess broad band noise, but more like 1/f or increased interference, pickup. Anyway first I've got to eliminate the piezo electronics as the noise source. George H.
> > 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
Diode lasers have a strong tendency to lock to any stray reflection--almost like a phase-conjugate mirror with gain. You can make unintentional ECDLs really easily unless you have a whole lot of attenuation or a couple of stages of isolation. 

Cheers

Phil Hobbs