On 02/15/2018 04:06 PM, George Herold wrote:> On Thursday, February 15, 2018 at 3:00:33 PM UTC-5, Phil Hobbs wrote: >> On 02/10/2018 05:18 PM, Phil Hobbs wrote: >>> Is horrible. >>> >>> I'm just debugging a nice diode laser controller for one customer and >>> getting ready to do another one for another (much better) customer. It >>> uses a ZXTP25020 PNP with a biggish degeneration resistor and two-pole >>> bypassing of the base to get low noise at high frequency. >>> >>> Turns out the 1/f noise is atrocious. The total noise from 2 Hz on up >>> is only a couple of PPM, but it should be a factor of 10 better than >>> that. With a total base resistance of 1k, the 1/f corner at 40 mA I_C >>> is over 10 kHz. >>> >>> The bias network looks like this: >>> >>> +9V 0----------*--------*-------* >>> | | | >>> | | | >>> | | R >>> | 4.7 | 3.3 R 39 ohm TF >>> | nF | nF R >>> CCC CCC | >>> CCC CCC | >>> | | | / >>> | | |< ZXTP25020 >>> From 0--RRRR--*--RRRR--*---- | >>> Op Amp |\ >>> 499 499 | \ >>> | >>> | >>> --- >>> \ / --> >>> V --> >>> ----- >>> | >>> | >>> GND >>> >>> The emitter resistor can drop up to about 5V. >>> >>> I've got some higher-beta transistors on order (FZT788B), and will >>> reduce the impedance of the bias network, but I was fairly shocked that >>> the 1/f noise was so bad. >>> >>> Cheers >>> >>> Phil Hobbs >>> >> >> <egg-on-face> >> >> Turned out that most of the 1/f noise was due to the HP 50-ohm >> termination I was using as a test load--which turned out to be made of >> cermet--plus the temperature coefficient of the leakage of a 22-uF 50V >> aluminum polymer cap I was using to AC-couple the noise measurement >> amplifier. >> >> I found this out by replacing the laser driver with an HP precision >> power supply (set to 80V) and a 2k wirewound resistor. >> >> The two effects were almost the same size at the lower frequency limit >> of my measurement, so nothing I did changed it much, until I fixed both >> at once. >> >> The 1/f corner is now down around 20 Hz where it belongs, and the box is >> way sub-poissonian outside the op amp bandwidth. >> >> </egg-on-face> > > Eggcellent. (Thanks for sharing.) When looking at noise, I made the same > mistake twice! And only found it when I went back to my notebook.. saying > to myself, "I did this two years ago and it worked.." Big dope slap. > > So what do you use for a coupling cap? And do you guesstimate the 20 Hz > corner.. (since 50 ohms and 22 uF is 1^10-3 sec, ~100 Hz.) > > George h.The noise amp is an LT1028 (1985 date code, PDIP) running noninverting gain of 100. It has a 10 ohm/990 ohm feedback network, and on the noninverting input I have 10k to ground and the aforementioned 22 uF alpo. IIRC JL said that alpos get less leaky after being run for awhile at highish voltage. When I come to build the real test setup for these (assuming we sell any) I'll use a CPH3910 FET buffer running directly into an ADA4898 plus buffer. That way I can use a big resistor and a film cap for the AC coupling, and not have to deal with the 300 kHz noise peak of the LT1028. Might even do an analogue cross-correlation measurement. I really need to make a bunch of amp/filter boards, because I'm continually doing these sorts of measurements. If I got 20 of them made, I could build them into test setups. 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
BJT base current 1/f noise
Started by ●February 10, 2018
Reply by ●February 15, 20182018-02-15
Reply by ●February 15, 20182018-02-15
On Thu, 15 Feb 2018 16:31:21 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 02/15/2018 04:06 PM, George Herold wrote: >> On Thursday, February 15, 2018 at 3:00:33 PM UTC-5, Phil Hobbs wrote: >>> On 02/10/2018 05:18 PM, Phil Hobbs wrote: >>>> Is horrible. >>>> >>>> I'm just debugging a nice diode laser controller for one customer and >>>> getting ready to do another one for another (much better) customer. It >>>> uses a ZXTP25020 PNP with a biggish degeneration resistor and two-pole >>>> bypassing of the base to get low noise at high frequency. >>>> >>>> Turns out the 1/f noise is atrocious. The total noise from 2 Hz on up >>>> is only a couple of PPM, but it should be a factor of 10 better than >>>> that. With a total base resistance of 1k, the 1/f corner at 40 mA I_C >>>> is over 10 kHz. >>>> >>>> The bias network looks like this: >>>> >>>> +9V 0----------*--------*-------* >>>> | | | >>>> | | | >>>> | | R >>>> | 4.7 | 3.3 R 39 ohm TF >>>> | nF | nF R >>>> CCC CCC | >>>> CCC CCC | >>>> | | | / >>>> | | |< ZXTP25020 >>>> From 0--RRRR--*--RRRR--*---- | >>>> Op Amp |\ >>>> 499 499 | \ >>>> | >>>> | >>>> --- >>>> \ / --> >>>> V --> >>>> ----- >>>> | >>>> | >>>> GND >>>> >>>> The emitter resistor can drop up to about 5V. >>>> >>>> I've got some higher-beta transistors on order (FZT788B), and will >>>> reduce the impedance of the bias network, but I was fairly shocked that >>>> the 1/f noise was so bad. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>>> >>> >>> <egg-on-face> >>> >>> Turned out that most of the 1/f noise was due to the HP 50-ohm >>> termination I was using as a test load--which turned out to be made of >>> cermet--plus the temperature coefficient of the leakage of a 22-uF 50V >>> aluminum polymer cap I was using to AC-couple the noise measurement >>> amplifier. >>> >>> I found this out by replacing the laser driver with an HP precision >>> power supply (set to 80V) and a 2k wirewound resistor. >>> >>> The two effects were almost the same size at the lower frequency limit >>> of my measurement, so nothing I did changed it much, until I fixed both >>> at once. >>> >>> The 1/f corner is now down around 20 Hz where it belongs, and the box is >>> way sub-poissonian outside the op amp bandwidth. >>> >>> </egg-on-face> >> >> Eggcellent. (Thanks for sharing.) When looking at noise, I made the same >> mistake twice! And only found it when I went back to my notebook.. saying >> to myself, "I did this two years ago and it worked.." Big dope slap. >> >> So what do you use for a coupling cap? And do you guesstimate the 20 Hz >> corner.. (since 50 ohms and 22 uF is 1^10-3 sec, ~100 Hz.) >> >> George h. > > >The noise amp is an LT1028 (1985 date code, PDIP) running noninverting >gain of 100. It has a 10 ohm/990 ohm feedback network, and on the >noninverting input I have 10k to ground and the aforementioned 22 uF >alpo. IIRC JL said that alpos get less leaky after being run for awhile >at highish voltage.Alpos? Like the dog food? I like that. I have some leakage measurements, in both directions, if anyone is interested. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●February 15, 20182018-02-15
On Thursday, February 15, 2018 at 4:31:34 PM UTC-5, Phil Hobbs wrote:> On 02/15/2018 04:06 PM, George Herold wrote: > > On Thursday, February 15, 2018 at 3:00:33 PM UTC-5, Phil Hobbs wrote: > >> On 02/10/2018 05:18 PM, Phil Hobbs wrote: > >>> Is horrible. > >>> > >>> I'm just debugging a nice diode laser controller for one customer and > >>> getting ready to do another one for another (much better) customer. It > >>> uses a ZXTP25020 PNP with a biggish degeneration resistor and two-pole > >>> bypassing of the base to get low noise at high frequency. > >>> > >>> Turns out the 1/f noise is atrocious. The total noise from 2 Hz on up > >>> is only a couple of PPM, but it should be a factor of 10 better than > >>> that. With a total base resistance of 1k, the 1/f corner at 40 mA I_C > >>> is over 10 kHz. > >>> > >>> The bias network looks like this: > >>> > >>> +9V 0----------*--------*-------* > >>> | | | > >>> | | | > >>> | | R > >>> | 4.7 | 3.3 R 39 ohm TF > >>> | nF | nF R > >>> CCC CCC | > >>> CCC CCC | > >>> | | | / > >>> | | |< ZXTP25020 > >>> From 0--RRRR--*--RRRR--*---- | > >>> Op Amp |\ > >>> 499 499 | \ > >>> | > >>> | > >>> --- > >>> \ / --> > >>> V --> > >>> ----- > >>> | > >>> | > >>> GND > >>> > >>> The emitter resistor can drop up to about 5V. > >>> > >>> I've got some higher-beta transistors on order (FZT788B), and will > >>> reduce the impedance of the bias network, but I was fairly shocked that > >>> the 1/f noise was so bad. > >>> > >>> Cheers > >>> > >>> Phil Hobbs > >>> > >> > >> <egg-on-face> > >> > >> Turned out that most of the 1/f noise was due to the HP 50-ohm > >> termination I was using as a test load--which turned out to be made of > >> cermet--plus the temperature coefficient of the leakage of a 22-uF 50V > >> aluminum polymer cap I was using to AC-couple the noise measurement > >> amplifier. > >> > >> I found this out by replacing the laser driver with an HP precision > >> power supply (set to 80V) and a 2k wirewound resistor. > >> > >> The two effects were almost the same size at the lower frequency limit > >> of my measurement, so nothing I did changed it much, until I fixed both > >> at once. > >> > >> The 1/f corner is now down around 20 Hz where it belongs, and the box is > >> way sub-poissonian outside the op amp bandwidth. > >> > >> </egg-on-face> > > > > Eggcellent. (Thanks for sharing.) When looking at noise, I made the same > > mistake twice! And only found it when I went back to my notebook.. saying > > to myself, "I did this two years ago and it worked.." Big dope slap. > > > > So what do you use for a coupling cap? And do you guesstimate the 20 Hz > > corner.. (since 50 ohms and 22 uF is 1^10-3 sec, ~100 Hz.) > > > > George h. > > > The noise amp is an LT1028 (1985 date code, PDIP) running noninverting > gain of 100. It has a 10 ohm/990 ohm feedback network, and on the > noninverting input I have 10k to ground and the aforementioned 22 uF > alpo. IIRC JL said that alpos get less leaky after being run for awhile > at highish voltage.Of course, sorry I wasn't thinking clearly. We've got bag fulls of 10 uF panasonic film caps I use for such stuff.> > When I come to build the real test setup for these (assuming we sell > any) I'll use a CPH3910 FET buffer running directly into an ADA4898 plus > buffer. That way I can use a big resistor and a film cap for the AC > coupling, and not have to deal with the 300 kHz noise peak of the > LT1028. Might even do an analogue cross-correlation measurement.Oh I've always wanted to do that, I don't really have anything useful to look at.> > I really need to make a bunch of amp/filter boards, because I'm > continually doing these sorts of measurements. If I got 20 of them > made, I could build them into test setups.I'm always hacking up old pcb's for the next project. I've got a drawer full of 'not quite right' pcb's. (I'm the opposite of JL, each board may take several spins.) George H.> > 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 15, 20182018-02-15
On 02/15/2018 08:37 PM, John Larkin wrote:> On Thu, 15 Feb 2018 16:31:21 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 02/15/2018 04:06 PM, George Herold wrote: >>> On Thursday, February 15, 2018 at 3:00:33 PM UTC-5, Phil Hobbs wrote: >>>> On 02/10/2018 05:18 PM, Phil Hobbs wrote: >>>>> Is horrible. >>>>> >>>>> I'm just debugging a nice diode laser controller for one customer and >>>>> getting ready to do another one for another (much better) customer. It >>>>> uses a ZXTP25020 PNP with a biggish degeneration resistor and two-pole >>>>> bypassing of the base to get low noise at high frequency. >>>>> >>>>> Turns out the 1/f noise is atrocious. The total noise from 2 Hz on up >>>>> is only a couple of PPM, but it should be a factor of 10 better than >>>>> that. With a total base resistance of 1k, the 1/f corner at 40 mA I_C >>>>> is over 10 kHz. >>>>> >>>>> The bias network looks like this: >>>>> >>>>> +9V 0----------*--------*-------* >>>>> | | | >>>>> | | | >>>>> | | R >>>>> | 4.7 | 3.3 R 39 ohm TF >>>>> | nF | nF R >>>>> CCC CCC | >>>>> CCC CCC | >>>>> | | | / >>>>> | | |< ZXTP25020 >>>>> From 0--RRRR--*--RRRR--*---- | >>>>> Op Amp |\ >>>>> 499 499 | \ >>>>> | >>>>> | >>>>> --- >>>>> \ / --> >>>>> V --> >>>>> ----- >>>>> | >>>>> | >>>>> GND >>>>> >>>>> The emitter resistor can drop up to about 5V. >>>>> >>>>> I've got some higher-beta transistors on order (FZT788B), and will >>>>> reduce the impedance of the bias network, but I was fairly shocked that >>>>> the 1/f noise was so bad. >>>>> >>>>> Cheers >>>>> >>>>> Phil Hobbs >>>>> >>>> >>>> <egg-on-face> >>>> >>>> Turned out that most of the 1/f noise was due to the HP 50-ohm >>>> termination I was using as a test load--which turned out to be made of >>>> cermet--plus the temperature coefficient of the leakage of a 22-uF 50V >>>> aluminum polymer cap I was using to AC-couple the noise measurement >>>> amplifier. >>>> >>>> I found this out by replacing the laser driver with an HP precision >>>> power supply (set to 80V) and a 2k wirewound resistor. >>>> >>>> The two effects were almost the same size at the lower frequency limit >>>> of my measurement, so nothing I did changed it much, until I fixed both >>>> at once. >>>> >>>> The 1/f corner is now down around 20 Hz where it belongs, and the box is >>>> way sub-poissonian outside the op amp bandwidth. >>>> >>>> </egg-on-face> >>> >>> Eggcellent. (Thanks for sharing.) When looking at noise, I made the same >>> mistake twice! And only found it when I went back to my notebook.. saying >>> to myself, "I did this two years ago and it worked.." Big dope slap. >>> >>> So what do you use for a coupling cap? And do you guesstimate the 20 Hz >>> corner.. (since 50 ohms and 22 uF is 1^10-3 sec, ~100 Hz.) >>> >>> George h. >> >> >> The noise amp is an LT1028 (1985 date code, PDIP) running noninverting >> gain of 100. It has a 10 ohm/990 ohm feedback network, and on the >> noninverting input I have 10k to ground and the aforementioned 22 uF >> alpo. IIRC JL said that alpos get less leaky after being run for awhile >> at highish voltage. > > Alpos? Like the dog food? I like that.99-44/100% pure dog food, or something like that. ;)> > I have some leakage measurements, in both directions, if anyone is > interested.I saved the ones you posted earlier, but any other data are welcome! 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 16, 20182018-02-16
On Friday, February 16, 2018 at 8:31:34 AM UTC+11, Phil Hobbs wrote:> On 02/15/2018 04:06 PM, George Herold wrote: > > On Thursday, February 15, 2018 at 3:00:33 PM UTC-5, Phil Hobbs wrote: > >> On 02/10/2018 05:18 PM, Phil Hobbs wrote: > >>> Is horrible. > >>> > >>> I'm just debugging a nice diode laser controller for one customer and > >>> getting ready to do another one for another (much better) customer. It > >>> uses a ZXTP25020 PNP with a biggish degeneration resistor and two-pole > >>> bypassing of the base to get low noise at high frequency. > >>> > >>> Turns out the 1/f noise is atrocious. The total noise from 2 Hz on up > >>> is only a couple of PPM, but it should be a factor of 10 better than > >>> that. With a total base resistance of 1k, the 1/f corner at 40 mA I_C > >>> is over 10 kHz. > >>> > >>> The bias network looks like this: > >>> > >>> +9V 0----------*--------*-------* > >>> | | | > >>> | | | > >>> | | R > >>> | 4.7 | 3.3 R 39 ohm TF > >>> | nF | nF R > >>> CCC CCC | > >>> CCC CCC | > >>> | | | / > >>> | | |< ZXTP25020 > >>> From 0--RRRR--*--RRRR--*---- | > >>> Op Amp |\ > >>> 499 499 | \ > >>> | > >>> | > >>> --- > >>> \ / --> > >>> V --> > >>> ----- > >>> | > >>> | > >>> GND > >>> > >>> The emitter resistor can drop up to about 5V. > >>> > >>> I've got some higher-beta transistors on order (FZT788B), and will > >>> reduce the impedance of the bias network, but I was fairly shocked that > >>> the 1/f noise was so bad. > >>> > >>> Cheers > >>> > >>> Phil Hobbs > >>> > >> > >> <egg-on-face> > >> > >> Turned out that most of the 1/f noise was due to the HP 50-ohm > >> termination I was using as a test load--which turned out to be made of > >> cermet--plus the temperature coefficient of the leakage of a 22-uF 50V > >> aluminum polymer cap I was using to AC-couple the noise measurement > >> amplifier. > >> > >> I found this out by replacing the laser driver with an HP precision > >> power supply (set to 80V) and a 2k wirewound resistor. > >> > >> The two effects were almost the same size at the lower frequency limit > >> of my measurement, so nothing I did changed it much, until I fixed both > >> at once. > >> > >> The 1/f corner is now down around 20 Hz where it belongs, and the box is > >> way sub-poissonian outside the op amp bandwidth. > >> > >> </egg-on-face> > > > > Eggcellent. (Thanks for sharing.) When looking at noise, I made the same > > mistake twice! And only found it when I went back to my notebook.. saying > > to myself, "I did this two years ago and it worked.." Big dope slap. > > > > So what do you use for a coupling cap? And do you guesstimate the 20 Hz > > corner.. (since 50 ohms and 22 uF is 1^10-3 sec, ~100 Hz.) > > > > George h. > > > The noise amp is an LT1028 (1985 date code, PDIP) running noninverting > gain of 100.<snip> I got thanked once for suggesting that someone replace an LT1028 with an AD797, which does seem to be a better behaved part. It's a long time ago - about twenty years - so I can't remember exactly why it was better in the application, or what the application was. Element14 (Newark) still seems to stock it, and while it's not cheap - around $10 - it's not prohibitively expensive. Apparently it is made with the their advanced complementary bipolar process (whatever that is) which offers decent PNP transistors. -- Bill Sloman, Sydney
Reply by ●February 16, 20182018-02-16
On Thu, 15 Feb 2018 13:43:35 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:>On Thu, 15 Feb 2018 15:00:26 -0500, Phil Hobbs ><pcdhSpamMeSenseless@electrooptical.net> wrote: > >>On 02/10/2018 05:18 PM, Phil Hobbs wrote: >>> Is horrible. >>> >>> I'm just debugging a nice diode laser controller for one customer and >>> getting ready to do another one for another (much better) customer. It >>> uses a ZXTP25020 PNP with a biggish degeneration resistor and two-pole >>> bypassing of the base to get low noise at high frequency. >>> >>> Turns out the 1/f noise is atrocious. The total noise from 2 Hz on up >>> is only a couple of PPM, but it should be a factor of 10 better than >>> that. With a total base resistance of 1k, the 1/f corner at 40 mA I_C >>> is over 10 kHz. >>> >>> The bias network looks like this: >>> >>> +9V 0----------*--------*-------* >>> | | | >>> | | | >>> | | R >>> | 4.7 | 3.3 R 39 ohm TF >>> | nF | nF R >>> CCC CCC | >>> CCC CCC | >>> | | | / >>> | | |< ZXTP25020 >>> From 0--RRRR--*--RRRR--*---- | >>> Op Amp |\ >>> 499 499 | \ >>> | >>> | >>> --- >>> \ / --> >>> V --> >>> ----- >>> | >>> | >>> GND >>> >>> The emitter resistor can drop up to about 5V. >>> >>> I've got some higher-beta transistors on order (FZT788B), and will >>> reduce the impedance of the bias network, but I was fairly shocked that >>> the 1/f noise was so bad. >>> >>> Cheers >>> >>> Phil Hobbs >>> >> >><egg-on-face> >> >>Turned out that most of the 1/f noise was due to the HP 50-ohm >>termination I was using as a test load--which turned out to be made of >>cermet--plus the temperature coefficient of the leakage of a 22-uF 50V >>aluminum polymer cap I was using to AC-couple the noise measurement >>amplifier. >> >>I found this out by replacing the laser driver with an HP precision >>power supply (set to 80V) and a 2k wirewound resistor. >> >>The two effects were almost the same size at the lower frequency limit >>of my measurement, so nothing I did changed it much, until I fixed both >>at once. >> >>The 1/f corner is now down around 20 Hz where it belongs, and the box is >>way sub-poissonian outside the op amp bandwidth. >> >></egg-on-face> >> >>Cheers >> >>Phil Hobbs > >You should have caught that long ago when I asked if you had run a >noise vs device parameter simulation in LTspice ?>:-} > > ...Jim ThompsonAs done this way... <http://www.analog-innovations.com/SED/PSpice_Noise_Calculation.pdf> Note that the individual contributions from each noise source, resistor, device noise, whatever, are tabulated in the .OUT file, where it'd be a piece-a-cake to spot the extra noise... had you included the termination in your simulation in the first place ;-) Oooooops! LTspice doesn't have a .OUT file!! Nor does it have a .NET file. Sonofa gun! Wonder why that may be? Maybe to hide the idealized components Mikey replaces your real components with to enhance simulation speed? But Hey!!! LTspice is FREE ;-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | It's what you learn, after you know it all, that counts.
Reply by ●February 16, 20182018-02-16
>"Jim Thompson" wrote in message >news:ah7e8d52k2205n6laj6i3iqo0kmacpnd1c@4ax.com...As done this way... <http://www.analog-innovations.com/SED/PSpice_Noise_Calculation.pdf>>Note that the individual contributions from each noise source, >resistor, device noise, whatever, are tabulated in the .OUT file, >where it'd be a piece-a-cake to spot the extra noise... had you >included the termination in your simulation in the first place ;-)>Oooooops! LTspice doesn't have a .OUT file!! Nor does it have a .NET >file. Sonofa gun!I have a noise report in SS where I order the noise of each component and state its % to the total. -- Kevin Aylward http://www.anasoft.co.uk - SuperSpice http://www.kevinaylward.co.uk/ee/index.html
Reply by ●February 16, 20182018-02-16
On Fri, 16 Feb 2018 20:21:00 -0000, "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> wrote:>>"Jim Thompson" wrote in message >>news:ah7e8d52k2205n6laj6i3iqo0kmacpnd1c@4ax.com... > > >As done this way... > ><http://www.analog-innovations.com/SED/PSpice_Noise_Calculation.pdf> > >>Note that the individual contributions from each noise source, >>resistor, device noise, whatever, are tabulated in the .OUT file, >>where it'd be a piece-a-cake to spot the extra noise... had you >>included the termination in your simulation in the first place ;-) > >>Oooooops! LTspice doesn't have a .OUT file!! Nor does it have a .NET >>file. Sonofa gun! > >I have a noise report in SS where I order the noise of each component and >state its % to the total. > >-- Kevin Aylward >http://www.anasoft.co.uk - SuperSpice >http://www.kevinaylward.co.uk/ee/index.html"%" would be nice... would make the noise report quicker to scan for "culprits". What always surprises me, no matter how many times I've done it, is the "culprit" is something _other_ than anticipated ;-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | It's what you learn, after you know it all, that counts.
Reply by ●February 16, 20182018-02-16
On 02/16/2018 01:19 PM, Jim Thompson wrote:> On Thu, 15 Feb 2018 13:43:35 -0700, Jim Thompson > <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: > >> On Thu, 15 Feb 2018 15:00:26 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 02/10/2018 05:18 PM, Phil Hobbs wrote: >>>> Is horrible. >>>> >>>> I'm just debugging a nice diode laser controller for one customer and >>>> getting ready to do another one for another (much better) customer. It >>>> uses a ZXTP25020 PNP with a biggish degeneration resistor and two-pole >>>> bypassing of the base to get low noise at high frequency. >>>> >>>> Turns out the 1/f noise is atrocious. The total noise from 2 Hz on up >>>> is only a couple of PPM, but it should be a factor of 10 better than >>>> that. With a total base resistance of 1k, the 1/f corner at 40 mA I_C >>>> is over 10 kHz. >>>> >>>> The bias network looks like this: >>>> >>>> +9V 0----------*--------*-------* >>>> | | | >>>> | | | >>>> | | R >>>> | 4.7 | 3.3 R 39 ohm TF >>>> | nF | nF R >>>> CCC CCC | >>>> CCC CCC | >>>> | | | / >>>> | | |< ZXTP25020 >>>> From 0--RRRR--*--RRRR--*---- | >>>> Op Amp |\ >>>> 499 499 | \ >>>> | >>>> | >>>> --- >>>> \ / --> >>>> V --> >>>> ----- >>>> | >>>> | >>>> GND >>>> >>>> The emitter resistor can drop up to about 5V. >>>> >>>> I've got some higher-beta transistors on order (FZT788B), and will >>>> reduce the impedance of the bias network, but I was fairly shocked that >>>> the 1/f noise was so bad. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>>> >>> >>> <egg-on-face> >>> >>> Turned out that most of the 1/f noise was due to the HP 50-ohm >>> termination I was using as a test load--which turned out to be made of >>> cermet--plus the temperature coefficient of the leakage of a 22-uF 50V >>> aluminum polymer cap I was using to AC-couple the noise measurement >>> amplifier. >>> >>> I found this out by replacing the laser driver with an HP precision >>> power supply (set to 80V) and a 2k wirewound resistor. >>> >>> The two effects were almost the same size at the lower frequency limit >>> of my measurement, so nothing I did changed it much, until I fixed both >>> at once. >>> >>> The 1/f corner is now down around 20 Hz where it belongs, and the box is >>> way sub-poissonian outside the op amp bandwidth. >>> >>> </egg-on-face> >>> >>> Cheers >>> >>> Phil Hobbs >> >> You should have caught that long ago when I asked if you had run a >> noise vs device parameter simulation in LTspice ?>:-} >> >> ...Jim Thompson > > As done this way... > > <http://www.analog-innovations.com/SED/PSpice_Noise_Calculation.pdf> > > Note that the individual contributions from each noise source, > resistor, device noise, whatever, are tabulated in the .OUT file, > where it'd be a piece-a-cake to spot the extra noise... had you > included the termination in your simulation in the first place ;-) > > Oooooops! LTspice doesn't have a .OUT file!! Nor does it have a .NET > file. Sonofa gun!It does have netfiles, and stuff you print gets put in the log file. But none of that works if the model doesn't include the noise correctly. For instance, the ADA4898 model from AD overestimates the 1/f noise by some orders of magnitude, which is irritating. The 4899 model is much more realistic, but that one is ten times as fast and only runs on +-5V. And in the present case, I would have needed a correct model of the random 30-year-old HP termination I was initially using as the load. ;) 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 17, 20182018-02-17
-----Original Message----- From: Jim Thompson Sent: Friday, February 16, 2018 9:00 PM Newsgroups: sci.electronics.design Subject: Re: BJT base current 1/f noise On Fri, 16 Feb 2018 20:21:00 -0000, "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> wrote:>>"Jim Thompson" wrote in message >>news:ah7e8d52k2205n6laj6i3iqo0kmacpnd1c@4ax.com... > > >As done this way... > ><http://www.analog-innovations.com/SED/PSpice_Noise_Calculation.pdf> > >>>Note that the individual contributions from each noise source, >>>resistor, device noise, whatever, are tabulated in the .OUT file, >>>where it'd be a piece-a-cake to spot the extra noise... had you >>>included the termination in your simulation in the first place ;-) > >>Oooooops! LTspice doesn't have a .OUT file!! Nor does it have a .NET >>>file. Sonofa gun! > >>I have a noise report in SS where I order the noise of each component and >>state its % to the total.>"%" would be nice... would make the noise report quicker to scan for >"culprits".>What always surprises me, no matter how many times I've done it, is >the "culprit" is something _other_ than anticipated ;-)Oscillator phase noise is somewhat bizarre. It acts like FM capture effect. You can have a noise plot, find and eliminate a dominant noise noise, yet still have the "improved" topology have an essentially overlaid new phase plot. A new noise source just pops up as the dominant, and the noise don't change. Kevin Aylward http://www.anasoft.co.uk - SuperSpice http://www.kevinaylward.co.uk/ee/index.html
