I want to measure the noise of a voltage regulator, probably an LM2941
making 5 volts out. So I need a low noise high gain preamp for a
scope.

Looks like this would work:

https://www.alphalabinc.com/product/lna10/

Any other suggestions?

I could make something, but it's marginal on time/cost and this looks
pretty cool.

Maybe I can bypass the upper feedback resistor to reduce noise, and
massively bypass the output to ground, if all that is atable.

I want 5 volts at a few hundred mA and wideband noise well below 100
uV RMS. I could make my own regulator if I had to, but LM2941 is easy.
This is going to power a bunch of cmos logic, about 20 ns worth total,
and Vcc noise becomes jitter.

I have an old TM500 thing in the dungeon, but I doubt it still works.
I guess I'll dust it off and see.

lørdag den 10. september 2022 kl. 23.34.00 UTC+2 skrev jla...@highlandsniptechnology.com:
> I want to measure the noise of a voltage regulator, probably an LM2941
> making 5 volts out. So I need a low noise high gain preamp for a
> scope.
>
> Looks like this would work:
>
> https://www.alphalabinc.com/product/lna10/
>
> Any other suggestions?
>
> I could make something, but it's marginal on time/cost and this looks
> pretty cool.
>
> Maybe I can bypass the upper feedback resistor to reduce noise, and
> massively bypass the output to ground, if all that is atable.
>
> I want 5 volts at a few hundred mA and wideband noise well below 100
> uV RMS. I could make my own regulator if I had to, but LM2941 is easy.
> This is going to power a bunch of cmos logic, about 20 ns worth total,
> and Vcc noise becomes jitter.

I my math adds up the LM2941 is 150uV typical at 5V, the ancient LM7805 is 40uV

jla...@highlandsniptechnology.com wrote:

====================================
> I want to measure the noise of a voltage regulator, probably an LM2941
> making 5 volts out. So I need a low noise high gain preamp for a
> scope.
>
> Looks like this would work:
>
> https://www.alphalabinc.com/product/lna10/
>
> Any other suggestions?
>
> I could make something, but it's marginal on time/cost and this looks
> pretty cool.
>
> Maybe I can bypass the upper feedback resistor to reduce noise, and
> massively bypass the output to ground, if all that is atable.

** An L/C or even RC filter after the reg will do the job.
Trim the output to make up for any voltage drop.

..... Phil

On Sat, 10 Sep 2022 15:28:03 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

>jla...@highlandsniptechnology.com wrote:
>
>====================================
>> I want to measure the noise of a voltage regulator, probably an LM2941
>> making 5 volts out. So I need a low noise high gain preamp for a
>> scope.
>>
>> Looks like this would work:
>>
>> https://www.alphalabinc.com/product/lna10/
>>
>> Any other suggestions?
>>
>> I could make something, but it's marginal on time/cost and this looks
>> pretty cool.
>>
>> Maybe I can bypass the upper feedback resistor to reduce noise, and
>> massively bypass the output to ground, if all that is atable.
>
>** An L/C or even RC filter after the reg will do the job.
> Trim the output to make up for any voltage drop.
>
>
>.... Phil
>
>

I'd like the noise to be low at low frequencies, down to 1 Hz or less,
so an LC isn't practical. And a load of a few hundred mA makes an RC
impractical too.

On Sat, 10 Sep 2022 14:49:02 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

>lørdag den 10. september 2022 kl. 23.34.00 UTC+2 skrev jla...@highlandsniptechnology.com:
>> I want to measure the noise of a voltage regulator, probably an LM2941
>> making 5 volts out. So I need a low noise high gain preamp for a
>> scope.
>>
>> Looks like this would work:
>>
>> https://www.alphalabinc.com/product/lna10/
>>
>> Any other suggestions?
>>
>> I could make something, but it's marginal on time/cost and this looks
>> pretty cool.
>>
>> Maybe I can bypass the upper feedback resistor to reduce noise, and
>> massively bypass the output to ground, if all that is atable.
>>
>> I want 5 volts at a few hundred mA and wideband noise well below 100
>> uV RMS. I could make my own regulator if I had to, but LM2941 is easy.
>> This is going to power a bunch of cmos logic, about 20 ns worth total,
>> and Vcc noise becomes jitter.
>
>I my math adds up the LM2941 is 150uV typical at 5V, the ancient LM7805 is 40uV

I do want low dropout to minimize dissipation. We'll probably switch
down to +6.25 maybe and then LDO to make a very quiet +5.

This is important so maybe I'll make my own regulator, which would
likely be lower noise than an IC reg.

On Sat, 10 Sep 2022 15:55:47 -0700, jlarkin@highlandsniptechnology.com
wrote:

>On Sat, 10 Sep 2022 14:49:02 -0700 (PDT), Lasse Langwadt Christensen
><langwadt@fonz.dk> wrote:
>
>>lørdag den 10. september 2022 kl. 23.34.00 UTC+2 skrev jla...@highlandsniptechnology.com:
>>> I want to measure the noise of a voltage regulator, probably an LM2941
>>> making 5 volts out. So I need a low noise high gain preamp for a
>>> scope.
>>>
>>> Looks like this would work:
>>>
>>> https://www.alphalabinc.com/product/lna10/
>>>
>>> Any other suggestions?
>>>
>>> I could make something, but it's marginal on time/cost and this looks
>>> pretty cool.
>>>
>>> Maybe I can bypass the upper feedback resistor to reduce noise, and
>>> massively bypass the output to ground, if all that is atable.
>>>
>>> I want 5 volts at a few hundred mA and wideband noise well below 100
>>> uV RMS. I could make my own regulator if I had to, but LM2941 is easy.
>>> This is going to power a bunch of cmos logic, about 20 ns worth total,
>>> and Vcc noise becomes jitter.
>>
>>I my math adds up the LM2941 is 150uV typical at 5V, the ancient LM7805 is 40uV
>
>I do want low dropout to minimize dissipation. We'll probably switch
>down to +6.25 maybe and then LDO to make a very quiet +5.
>
>This is important so maybe I'll make my own regulator, which would
>likely be lower noise than an IC reg.

The classic dodge is a switcher driving a linear regulator, followed
by Phil H's favorite capacitance multiplier, with RC filters all
along.

Joe Gwinn

On Sat, 10 Sep 2022 19:19:24 -0400, Joe Gwinn <joegwinn@comcast.net>
wrote:

>On Sat, 10 Sep 2022 15:55:47 -0700, jlarkin@highlandsniptechnology.com
>wrote:
>
>>On Sat, 10 Sep 2022 14:49:02 -0700 (PDT), Lasse Langwadt Christensen
>><langwadt@fonz.dk> wrote:
>>
>>>lørdag den 10. september 2022 kl. 23.34.00 UTC+2 skrev jla...@highlandsniptechnology.com:
>>>> I want to measure the noise of a voltage regulator, probably an LM2941
>>>> making 5 volts out. So I need a low noise high gain preamp for a
>>>> scope.
>>>>
>>>> Looks like this would work:
>>>>
>>>> https://www.alphalabinc.com/product/lna10/
>>>>
>>>> Any other suggestions?
>>>>
>>>> I could make something, but it's marginal on time/cost and this looks
>>>> pretty cool.
>>>>
>>>> Maybe I can bypass the upper feedback resistor to reduce noise, and
>>>> massively bypass the output to ground, if all that is atable.
>>>>
>>>> I want 5 volts at a few hundred mA and wideband noise well below 100
>>>> uV RMS. I could make my own regulator if I had to, but LM2941 is easy.
>>>> This is going to power a bunch of cmos logic, about 20 ns worth total,
>>>> and Vcc noise becomes jitter.
>>>
>>>I my math adds up the LM2941 is 150uV typical at 5V, the ancient LM7805 is 40uV
>>
>>I do want low dropout to minimize dissipation. We'll probably switch
>>down to +6.25 maybe and then LDO to make a very quiet +5.
>>
>>This is important so maybe I'll make my own regulator, which would
>>likely be lower noise than an IC reg.
>
>The classic dodge is a switcher driving a linear regulator, followed
>by Phil H's favorite capacitance multiplier, with RC filters all
>along.
>
>
>Joe Gwinn

That adds a lot of dissipation.

This looks pretty good. It's actually not bad without R5+C3, kinda
surprising. Using a quiet 3 volt reference helps a lot.

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TEXT 280 456 Left 2 ;OPA197
TEXT 816 408 Left 2 !.tran 50m startup
TEXT 808 296 Left 2 ;T660 5 VOLT LDO
TEXT 824 352 Left 2 ;JL Sep 10 2022
TEXT 560 144 Left 2 ;+5mr

Am 11.09.22 um 00:55 schrieb jlarkin@highlandsniptechnology.com:
> On Sat, 10 Sep 2022 14:49:02 -0700 (PDT), Lasse Langwadt Christensen
> <langwadt@fonz.dk> wrote:
>
>> lørdag den 10. september 2022 kl. 23.34.00 UTC+2 skrev jla...@highlandsniptechnology.com:
>>> I want to measure the noise of a voltage regulator, probably an LM2941
>>> making 5 volts out. So I need a low noise high gain preamp for a
>>> scope.
>>>
>>> Looks like this would work:
>>>
>>> https://www.alphalabinc.com/product/lna10/
>>>
>>> Any other suggestions?
>>>
>>> I could make something, but it's marginal on time/cost and this looks
>>> pretty cool.
>>>
>>> Maybe I can bypass the upper feedback resistor to reduce noise, and
>>> massively bypass the output to ground, if all that is atable.
>>>
>>> I want 5 volts at a few hundred mA and wideband noise well below 100
>>> uV RMS. I could make my own regulator if I had to, but LM2941 is easy.
>>> This is going to power a bunch of cmos logic, about 20 ns worth total,
>>> and Vcc noise becomes jitter.
>>
>> I my math adds up the LM2941 is 150uV typical at 5V, the ancient LM7805 is 40uV
>
> I do want low dropout to minimize dissipation. We'll probably switch
> down to +6.25 maybe and then LDO to make a very quiet +5.
>
> This is important so maybe I'll make my own regulator, which would
> likely be lower noise than an IC reg.

I did not measure the LM2941, but the Lm2940 is about the worst
choice possible.
It would require real work to be better than a LT3042. Its main
drawback is the small load current because of the tiny package.

<
https://www.flickr.com/photos/137684711@N07/24070698809/in/album-72157662535945536/
>
0 dB is 1nV/rtHz.

In the LT3042 data sheet is a a circuit with an external NPN
to take the heat. It measures about the same as the 3042 alone.
The noise peak climbs to 100 KHz but does not grow in size.

Adding more output C increases peaking. Cset may be increased
at the cost of larger startup time. Cset=100u can make sense and
lowers the 1/f corner to a few Hz. It is not really 1/f but
1/f**2 or 3. More than 100u seems not to help.

<
https://www.flickr.com/photos/137684711@N07/24070698809/in/album-72157662535945536/
>

Some empty boardlets are left over. 1.5A@5V from a 6.6V raw
source is ok. The transistor costs a diode drop vs. bare 3042.

The worse-than-1/f did haunt the preamp I used in 2016 when the
spectra were taken. It was a much too small input cap. That must
be much larger than needed for f-3dB to be able to short
the thermal bias-r noise of the amplifier through the low
impedance DUT. The DUT _must_ be low impedance or the 220pV/rtHz
of the preamp is not useful. (20*ADA4898 in parallel summed up)
A 4700uF wet slug tantalum is about right, but that opens
another can of worms.

Even board layout counts. Above 500 KHz, voltage noise of the
amplifier did increase. on flickr, there is a picture showing
the routing with a felt pen. I suspected the tantalum, but it
wasn't the culprit as shown by a mesh of wires.

But I forgot about the shorted tantalum when I tried to measure
the noise of some Li ion batteries next week. That ended the
life of the preamp in a cruel way. Post mortem Pic is on
Flickr, more to the right.

I have a new amplifier with 16 * CPH3910 FETs, only 320nV/rtHz
instead of 220. But much less noise current, which helps for
cross correlation with 2 amplifiers. The Agilent 89441A can
do that. 2 b published in october.

cheers
Gerhard

Am 11.09.22 um 05:01 schrieb Gerhard Hoffmann:

I did not get the url right.
<
https://www.flickr.com/photos/137684711@N07/52349011053/in/dateposted-public/
>

Gerhard

On Sun, 11 Sep 2022 05:01:34 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:

>Am 11.09.22 um 00:55 schrieb jlarkin@highlandsniptechnology.com:
>> On Sat, 10 Sep 2022 14:49:02 -0700 (PDT), Lasse Langwadt Christensen
>> <langwadt@fonz.dk> wrote:
>>
>>> lørdag den 10. september 2022 kl. 23.34.00 UTC+2 skrev jla...@highlandsniptechnology.com:
>>>> I want to measure the noise of a voltage regulator, probably an LM2941
>>>> making 5 volts out. So I need a low noise high gain preamp for a
>>>> scope.
>>>>
>>>> Looks like this would work:
>>>>
>>>> https://www.alphalabinc.com/product/lna10/
>>>>
>>>> Any other suggestions?
>>>>
>>>> I could make something, but it's marginal on time/cost and this looks
>>>> pretty cool.
>>>>
>>>> Maybe I can bypass the upper feedback resistor to reduce noise, and
>>>> massively bypass the output to ground, if all that is atable.
>>>>
>>>> I want 5 volts at a few hundred mA and wideband noise well below 100
>>>> uV RMS. I could make my own regulator if I had to, but LM2941 is easy.
>>>> This is going to power a bunch of cmos logic, about 20 ns worth total,
>>>> and Vcc noise becomes jitter.
>>>
>>> I my math adds up the LM2941 is 150uV typical at 5V, the ancient LM7805 is 40uV
>>
>> I do want low dropout to minimize dissipation. We'll probably switch
>> down to +6.25 maybe and then LDO to make a very quiet +5.
>>
>> This is important so maybe I'll make my own regulator, which would
>> likely be lower noise than an IC reg.
>
>I did not measure the LM2941, but the Lm2940 is about the worst
>choice possible.
>It would require real work to be better than a LT3042. Its main
>drawback is the small load current because of the tiny package.
>
><
>https://www.flickr.com/photos/137684711@N07/24070698809/in/album-72157662535945536/
> >
>0 dB is 1nV/rtHz.
>
>In the LT3042 data sheet is a a circuit with an external NPN
>to take the heat. It measures about the same as the 3042 alone.
>The noise peak climbs to 100 KHz but does not grow in size.
>
>Adding more output C increases peaking. Cset may be increased
>at the cost of larger startup time. Cset=100u can make sense and
>lowers the 1/f corner to a few Hz. It is not really 1/f but
>1/f**2 or 3. More than 100u seems not to help.
>
><
>https://www.flickr.com/photos/137684711@N07/24070698809/in/album-72157662535945536/
> >
>
>Some empty boardlets are left over. 1.5A@5V from a 6.6V raw
>source is ok. The transistor costs a diode drop vs. bare 3042.

I think I'll make my own LDO with an opamp and an n-fet. By the time I
have a dpak fet and some giant caps, the opamp and a few passives add
not much more board area.

If I use a good 3 volt reference (which I'll have) I expect much less
low frequency noise than using the 1.25v bandgap and feedback point of
a regulator.

None of that stuff will be on the same die as the big hot pass
transistor.

I'll prowl the dungeon and see if I have a AM503 amplifier, and see if
it still works, to measure the LDO noise. Or maybe just trust Spice.

Joe Gwinn wrote:
> On Sat, 10 Sep 2022 15:55:47 -0700, jlarkin@highlandsniptechnology.com
> wrote:
>
>> On Sat, 10 Sep 2022 14:49:02 -0700 (PDT), Lasse Langwadt Christensen
>> <langwadt@fonz.dk> wrote:
>>
>>> lørdag den 10. september 2022 kl. 23.34.00 UTC+2 skrev jla...@highlandsniptechnology.com:
>>>> I want to measure the noise of a voltage regulator, probably an LM2941
>>>> making 5 volts out. So I need a low noise high gain preamp for a
>>>> scope.
>>>>
>>>> Looks like this would work:
>>>>
>>>> https://www.alphalabinc.com/product/lna10/
>>>>
>>>> Any other suggestions?
>>>>
>>>> I could make something, but it's marginal on time/cost and this looks
>>>> pretty cool.
>>>>
>>>> Maybe I can bypass the upper feedback resistor to reduce noise, and
>>>> massively bypass the output to ground, if all that is atable.
>>>>
>>>> I want 5 volts at a few hundred mA and wideband noise well below 100
>>>> uV RMS. I could make my own regulator if I had to, but LM2941 is easy.
>>>> This is going to power a bunch of cmos logic, about 20 ns worth total,
>>>> and Vcc noise becomes jitter.
>>>
>>> I my math adds up the LM2941 is 150uV typical at 5V, the ancient LM7805 is 40uV
>>
>> I do want low dropout to minimize dissipation. We'll probably switch
>> down to +6.25 maybe and then LDO to make a very quiet +5.
>>
>> This is important so maybe I'll make my own regulator, which would
>> likely be lower noise than an IC reg.
>
> The classic dodge is a switcher driving a linear regulator, followed
> by Phil H's favorite capacitance multiplier, with RC filters all
> along.
>
>
> Joe Gwinn
>

One trick I sometimes use is to let the regulator worry about the DC and
the load regulation, and then apply an AC-coupled op amp loop to null
out the noise.

That way, the AC-coupling goes on the high-Z end (the op amp input), so
you can have any corner frequency you like. (If it's very very slow,
you'll want to restrict the output swing of the amp to prevent the rail
going out of spec.)

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

On Sat, 10 Sep 2022 16:23:41 -0700, jlarkin@highlandsniptechnology.com
wrote:

>On Sat, 10 Sep 2022 19:19:24 -0400, Joe Gwinn <joegwinn@comcast.net>
>wrote:
>
>>On Sat, 10 Sep 2022 15:55:47 -0700, jlarkin@highlandsniptechnology.com
>>wrote:
>>
>>>On Sat, 10 Sep 2022 14:49:02 -0700 (PDT), Lasse Langwadt Christensen
>>><langwadt@fonz.dk> wrote:
>>>
>>>>lørdag den 10. september 2022 kl. 23.34.00 UTC+2 skrev jla...@highlandsniptechnology.com:
>>>>> I want to measure the noise of a voltage regulator, probably an LM2941
>>>>> making 5 volts out. So I need a low noise high gain preamp for a
>>>>> scope.
>>>>>
>>>>> Looks like this would work:
>>>>>
>>>>> https://www.alphalabinc.com/product/lna10/
>>>>>
>>>>> Any other suggestions?
>>>>>
>>>>> I could make something, but it's marginal on time/cost and this looks
>>>>> pretty cool.
>>>>>
>>>>> Maybe I can bypass the upper feedback resistor to reduce noise, and
>>>>> massively bypass the output to ground, if all that is atable.
>>>>>
>>>>> I want 5 volts at a few hundred mA and wideband noise well below 100
>>>>> uV RMS. I could make my own regulator if I had to, but LM2941 is easy.
>>>>> This is going to power a bunch of cmos logic, about 20 ns worth total,
>>>>> and Vcc noise becomes jitter.
>>>>
>>>>I my math adds up the LM2941 is 150uV typical at 5V, the ancient LM7805 is 40uV
>>>
>>>I do want low dropout to minimize dissipation. We'll probably switch
>>>down to +6.25 maybe and then LDO to make a very quiet +5.
>>>
>>>This is important so maybe I'll make my own regulator, which would
>>>likely be lower noise than an IC reg.
>>
>>The classic dodge is a switcher driving a linear regulator, followed
>>by Phil H's favorite capacitance multiplier, with RC filters all
>>along.
>>
>>
>>Joe Gwinn
>
>That adds a lot of dissipation.

That's the reason to start with a switcher - most of the voltage drop
is there.

But dissipation be damned - we want low noise.

>This looks pretty good. It's actually not bad without R5+C3, kinda
>surprising. Using a quiet 3 volt reference helps a lot.

Interesting, but I won't get to this SPICE for a while.

Joe Gwinn

>
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>

On Sat, 10 Sep 2022 14:33:49 -0700, jlarkin@highlandsniptechnology.com
wrote:

>I want to measure the noise of a voltage regulator, probably an LM2941
>making 5 volts out. So I need a low noise high gain preamp for a
>scope.
>
>Looks like this would work:
>
>https://www.alphalabinc.com/product/lna10/
>
>Any other suggestions?
>
>I could make something, but it's marginal on time/cost and this looks
>pretty cool.
>
>Maybe I can bypass the upper feedback resistor to reduce noise, and
>massively bypass the output to ground, if all that is atable.
>
>I want 5 volts at a few hundred mA and wideband noise well below 100
>uV RMS. I could make my own regulator if I had to, but LM2941 is easy.
>This is going to power a bunch of cmos logic, about 20 ns worth total,
>and Vcc noise becomes jitter.
>
>I have an old TM500 thing in the dungeon, but I doubt it still works.
>I guess I'll dust it off and see.

Be sure to make your noise measurements in-situ.

The environment can influence the regulator's performance.

Low noise linears react to simple board rotation.

RL

On Sat, 10 Sep 2022 14:33:49 -0700, jlarkin@highlandsniptechnology.com
wrote:

>I want to measure the noise of a voltage regulator, probably an LM2941
>making 5 volts out. So I need a low noise high gain preamp for a
>scope.
>
>Looks like this would work:
>
>https://www.alphalabinc.com/product/lna10/
>
>Any other suggestions?
>
>I could make something, but it's marginal on time/cost and this looks
>pretty cool.
>
>Maybe I can bypass the upper feedback resistor to reduce noise, and
>massively bypass the output to ground, if all that is atable.
>
>I want 5 volts at a few hundred mA and wideband noise well below 100
>uV RMS. I could make my own regulator if I had to, but LM2941 is easy.
>This is going to power a bunch of cmos logic, about 20 ns worth total,
>and Vcc noise becomes jitter.
>
>I have an old TM500 thing in the dungeon, but I doubt it still works.
>I guess I'll dust it off and see.

It may not be too critical - almost any low noise, battery operated
AC-coupled amplifier will give a good indication of relative noise
levels, in an iterative process.

You'll want to see a good margin on your actual requirements, then
recheck in the physical application.

I used to use a simple BPO two-transistor version of the 'liniac',
with increased decoupling capacitors, running off a PP9 battery.
It used to take some 10s of seconds to DC-stabilize after turn-on.
Switched gains of x10, x100.

RL

On Sun, 11 Sep 2022 11:11:05 -0400, Joe Gwinn <joegwinn@comcast.net>
wrote:

>On Sat, 10 Sep 2022 16:23:41 -0700, jlarkin@highlandsniptechnology.com
>wrote:
>
>>On Sat, 10 Sep 2022 19:19:24 -0400, Joe Gwinn <joegwinn@comcast.net>
>>wrote:
>>
>>>On Sat, 10 Sep 2022 15:55:47 -0700, jlarkin@highlandsniptechnology.com
>>>wrote:
>>>
>>>>On Sat, 10 Sep 2022 14:49:02 -0700 (PDT), Lasse Langwadt Christensen
>>>><langwadt@fonz.dk> wrote:
>>>>
>>>>>lørdag den 10. september 2022 kl. 23.34.00 UTC+2 skrev jla...@highlandsniptechnology.com:
>>>>>> I want to measure the noise of a voltage regulator, probably an LM2941
>>>>>> making 5 volts out. So I need a low noise high gain preamp for a
>>>>>> scope.
>>>>>>
>>>>>> Looks like this would work:
>>>>>>
>>>>>> https://www.alphalabinc.com/product/lna10/
>>>>>>
>>>>>> Any other suggestions?
>>>>>>
>>>>>> I could make something, but it's marginal on time/cost and this looks
>>>>>> pretty cool.
>>>>>>
>>>>>> Maybe I can bypass the upper feedback resistor to reduce noise, and
>>>>>> massively bypass the output to ground, if all that is atable.
>>>>>>
>>>>>> I want 5 volts at a few hundred mA and wideband noise well below 100
>>>>>> uV RMS. I could make my own regulator if I had to, but LM2941 is easy.
>>>>>> This is going to power a bunch of cmos logic, about 20 ns worth total,
>>>>>> and Vcc noise becomes jitter.
>>>>>
>>>>>I my math adds up the LM2941 is 150uV typical at 5V, the ancient LM7805 is 40uV
>>>>
>>>>I do want low dropout to minimize dissipation. We'll probably switch
>>>>down to +6.25 maybe and then LDO to make a very quiet +5.
>>>>
>>>>This is important so maybe I'll make my own regulator, which would
>>>>likely be lower noise than an IC reg.
>>>
>>>The classic dodge is a switcher driving a linear regulator, followed
>>>by Phil H's favorite capacitance multiplier, with RC filters all
>>>along.
>>>
>>>
>>>Joe Gwinn
>>
>>That adds a lot of dissipation.
>
>That's the reason to start with a switcher - most of the voltage drop
>is there.
>
>But dissipation be damned - we want low noise.
>
>
>>This looks pretty good. It's actually not bad without R5+C3, kinda
>>surprising. Using a quiet 3 volt reference helps a lot.
>
>Interesting, but I won't get to this SPICE for a while.
>
>
>Joe Gwinn
>
>

This is better. The mosfet was basically ohmic, but an NPN still acts
like a follower.

No comp on the opamp is weird but seems to work. I'd better breadboard
this.

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John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:

> This is better. The mosfet was basically ohmic, but an NPN still acts
> like a follower.
>
> No comp on the opamp is weird but seems to work. I'd better breadboard
> this.

Not bad. -189dB to 10 Hz, then rises to about -100 dB.
Noise is ~7.5nV/root(Hz) with a slight hump around 10.5 KHz, then falls off
to 1nV/root(Hz) at 100 KHz.

No need for a fancy NPN. A 2N3055 is fine at these low frequencies.

https://tinyurl.com/438bb8a7

Are you going to be able to measure noise?

--
MRM

On Mon, 12 Sep 2022 09:11:45 -0000 (UTC), Mike Monett VE3BTI
<spamme@not.com> wrote:

>John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:
>
>> This is better. The mosfet was basically ohmic, but an NPN still acts
>> like a follower.
>>
>> No comp on the opamp is weird but seems to work. I'd better breadboard
>> this.
>
>Not bad. -189dB to 10 Hz, then rises to about -100 dB.

Much better than the mosfet version. At low drop, a fet is basically a
couple-of-ohms resistor from the unreg input to the output.

>
>Noise is ~7.5nV/root(Hz) with a slight hump around 10.5 KHz, then falls off
>to 1nV/root(Hz) at 100 KHz.
>
>No need for a fancy NPN. A 2N3055 is fine at these low frequencies.
>
>https://tinyurl.com/438bb8a7

I want a surfacemount high-beta NPN. It's impressive how many
different fets we have in stock and how few classic bipolar
transistors.

We do have FZT692 in SOT-223. It looks perfect for this regulator.
Beta is 500 min (!) at 2v and 100 mA. Its Early voltage must be
insane.

>
>Are you going to be able to measure noise?

I will, somehow. I'm especially concerned about low frequency, 1/f,
noise, which will modulate my prop delays. LDOs aren't usually
specified for 1/f but opamps are. Putting the voltage ref on the power
chip, apologies to Bob Widlar, isn't always the best idea.

On Mon, 12 Sep 2022 07:12:23 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:

>On Mon, 12 Sep 2022 09:11:45 -0000 (UTC), Mike Monett VE3BTI
><spamme@not.com> wrote:
>
>>John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:
>>
>>> This is better. The mosfet was basically ohmic, but an NPN still acts
>>> like a follower.
>>>
>>> No comp on the opamp is weird but seems to work. I'd better breadboard
>>> this.
>>
>>Not bad. -189dB to 10 Hz, then rises to about -100 dB.
>
>
>Much better than the mosfet version. At low drop, a fet is basically a
>couple-of-ohms resistor from the unreg input to the output.
>
>>
>>Noise is ~7.5nV/root(Hz) with a slight hump around 10.5 KHz, then falls off
>>to 1nV/root(Hz) at 100 KHz.
>>
>>No need for a fancy NPN. A 2N3055 is fine at these low frequencies.
>>
>>https://tinyurl.com/438bb8a7
>
>
>I want a surfacemount high-beta NPN. It's impressive how many
>different fets we have in stock and how few classic bipolar
>transistors.
>
>We do have FZT692 in SOT-223. It looks perfect for this regulator.
>Beta is 500 min (!) at 2v and 100 mA. Its Early voltage must be
>insane.
>
>>
>>Are you going to be able to measure noise?
>
>I will, somehow. I'm especially concerned about low frequency, 1/f,
>noise, which will modulate my prop delays. LDOs aren't usually
>specified for 1/f but opamps are. Putting the voltage ref on the power
>chip, apologies to Bob Widlar, isn't always the best idea.
>

It's interesting that nobody seems to make a voltage reg that accepts
an external reference. Some ADCs and DACs have an internal ref with
external over-ride capability.

One can drive the ADJ pin of a 317 type from an opamp, basically use
it as a power amp.

You can stack LM1117s to get 1.25, 2.5... volt steps, like an FPGA
might want.

On Mon, 12 Sep 2022 08:14:47 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:

>On Mon, 12 Sep 2022 07:12:23 -0700, John Larkin
><jlarkin@highlandSNIPMEtechnology.com> wrote:
>
>>On Mon, 12 Sep 2022 09:11:45 -0000 (UTC), Mike Monett VE3BTI
>><spamme@not.com> wrote:
>>
>>>John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:
>>>
>>>> This is better. The mosfet was basically ohmic, but an NPN still acts
>>>> like a follower.
>>>>
>>>> No comp on the opamp is weird but seems to work. I'd better breadboard
>>>> this.
>>>
>>>Not bad. -189dB to 10 Hz, then rises to about -100 dB.
>>
>>
>>Much better than the mosfet version. At low drop, a fet is basically a
>>couple-of-ohms resistor from the unreg input to the output.
>>
>>>
>>>Noise is ~7.5nV/root(Hz) with a slight hump around 10.5 KHz, then falls off
>>>to 1nV/root(Hz) at 100 KHz.
>>>
>>>No need for a fancy NPN. A 2N3055 is fine at these low frequencies.
>>>
>>>https://tinyurl.com/438bb8a7
>>
>>
>>I want a surfacemount high-beta NPN. It's impressive how many
>>different fets we have in stock and how few classic bipolar
>>transistors.
>>
>>We do have FZT692 in SOT-223. It looks perfect for this regulator.
>>Beta is 500 min (!) at 2v and 100 mA. Its Early voltage must be
>>insane.
>>
>>>
>>>Are you going to be able to measure noise?
>>
>>I will, somehow. I'm especially concerned about low frequency, 1/f,
>>noise, which will modulate my prop delays. LDOs aren't usually
>>specified for 1/f but opamps are. Putting the voltage ref on the power
>>chip, apologies to Bob Widlar, isn't always the best idea.
>>
>
>It's interesting that nobody seems to make a voltage reg that accepts
>an external reference. Some ADCs and DACs have an internal ref with
>external over-ride capability.
>
>One can drive the ADJ pin of a 317 type from an opamp, basically use
>it as a power amp.

I've seen exactly this done to power LNAs, after a switched that did
the bulk of the voltage dropping.

Joe Gwinn

>You can stack LM1117s to get 1.25, 2.5... volt steps, like an FPGA
>might want.

mandag den 12. september 2022 kl. 17.15.05 UTC+2 skrev John Larkin:
> On Mon, 12 Sep 2022 07:12:23 -0700, John Larkin
> <jla...@highlandSNIPMEtechnology.com> wrote:
>
> >On Mon, 12 Sep 2022 09:11:45 -0000 (UTC), Mike Monett VE3BTI
> ><spa...@not.com> wrote:
> >
> >>John Larkin <jla...@highlandSNIPMEtechnology.com> wrote:
> >>
> >>> This is better. The mosfet was basically ohmic, but an NPN still acts
> >>> like a follower.
> >>>
> >>> No comp on the opamp is weird but seems to work. I'd better breadboard
> >>> this.
> >>
> >>Not bad. -189dB to 10 Hz, then rises to about -100 dB.
> >
> >
> >Much better than the mosfet version. At low drop, a fet is basically a
> >couple-of-ohms resistor from the unreg input to the output.
> >
> >>
> >>Noise is ~7.5nV/root(Hz) with a slight hump around 10.5 KHz, then falls off
> >>to 1nV/root(Hz) at 100 KHz.
> >>
> >>No need for a fancy NPN. A 2N3055 is fine at these low frequencies.
> >>
> >>https://tinyurl.com/438bb8a7
> >
> >
> >I want a surfacemount high-beta NPN. It's impressive how many
> >different fets we have in stock and how few classic bipolar
> >transistors.
> >
> >We do have FZT692 in SOT-223. It looks perfect for this regulator.
> >Beta is 500 min (!) at 2v and 100 mA. Its Early voltage must be
> >insane.
> >
> >>
> >>Are you going to be able to measure noise?
> >
> >I will, somehow. I'm especially concerned about low frequency, 1/f,
> >noise, which will modulate my prop delays. LDOs aren't usually
> >specified for 1/f but opamps are. Putting the voltage ref on the power
> >chip, apologies to Bob Widlar, isn't always the best idea.
> >
> It's interesting that nobody seems to make a voltage reg that accepts
> an external reference.

LM723 ?

On Monday, September 12, 2022 at 7:12:37 AM UTC-7, John Larkin wrote:
> On Mon, 12 Sep 2022 09:11:45 -0000 (UTC), Mike Monett VE3BTI
> <spa...@not.com> wrote:
>
> >John Larkin <jla...@highlandSNIPMEtechnology.com> wrote:
> >
> >> This is better. The mosfet was basically ohmic, but an NPN still acts
> >> like a follower.
> >>
> >> No comp on the opamp is weird but seems to work. I'd better breadboard
> >> this.
> >
> >Not bad. -189dB to 10 Hz, then rises to about -100 dB.
> Much better than the mosfet version. At low drop, a fet is basically a
> couple-of-ohms resistor from the unreg input to the output.

I'd say, rather, that a FET needs more slew rate from the driving op amp
than a bipolar transistor. dV/dt is a limited resource when considering
broad bandwidth types of noise. Miller capacitance in the transistor
will partly compensate the op amp...

Am 11.09.22 um 05:30 schrieb jlarkin@highlandsniptechnology.com:
> On Sun, 11 Sep 2022 05:01:34 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
> wrote:
>
>> Am 11.09.22 um 00:55 schrieb jlarkin@highlandsniptechnology.com:
>>> On Sat, 10 Sep 2022 14:49:02 -0700 (PDT), Lasse Langwadt Christensen
>>> <langwadt@fonz.dk> wrote:
>>>
>>>> lørdag den 10. september 2022 kl. 23.34.00 UTC+2 skrev jla...@highlandsniptechnology.com:
>>>>> I want to measure the noise of a voltage regulator, probably an LM2941
>>>>> making 5 volts out. So I need a low noise high gain preamp for a
>>>>> scope.
>>>>>
>>>>> Looks like this would work:
>>>>>
>>>>> https://www.alphalabinc.com/product/lna10/
>>>>>
>>>>> Any other suggestions?
>>>>>
>>>>> I could make something, but it's marginal on time/cost and this looks
>>>>> pretty cool.
>>>>>
>>>>> Maybe I can bypass the upper feedback resistor to reduce noise, and
>>>>> massively bypass the output to ground, if all that is atable.
>>>>>
>>>>> I want 5 volts at a few hundred mA and wideband noise well below 100
>>>>> uV RMS. I could make my own regulator if I had to, but LM2941 is easy.
>>>>> This is going to power a bunch of cmos logic, about 20 ns worth total,
>>>>> and Vcc noise becomes jitter.
>>>>
>>>> I my math adds up the LM2941 is 150uV typical at 5V, the ancient LM7805 is 40uV
>>>
>>> I do want low dropout to minimize dissipation. We'll probably switch
>>> down to +6.25 maybe and then LDO to make a very quiet +5.
>>>
>>> This is important so maybe I'll make my own regulator, which would
>>> likely be lower noise than an IC reg.
>>
>> I did not measure the LM2941, but the Lm2940 is about the worst
>> choice possible.
>> It would require real work to be better than a LT3042. Its main
>> drawback is the small load current because of the tiny package.
>>
>> <
>> https://www.flickr.com/photos/137684711@N07/24070698809/in/album-72157662535945536/
>> >
>> 0 dB is 1nV/rtHz.
>>
>> In the LT3042 data sheet is a a circuit with an external NPN
>> to take the heat. It measures about the same as the 3042 alone.
>> The noise peak climbs to 100 KHz but does not grow in size.
>>
>> Adding more output C increases peaking. Cset may be increased
>> at the cost of larger startup time. Cset=100u can make sense and
>> lowers the 1/f corner to a few Hz. It is not really 1/f but
>> 1/f**2 or 3. More than 100u seems not to help.
>>
>> <
>> https://www.flickr.com/photos/137684711@N07/24070698809/in/album-72157662535945536/
>> >
>>
>> Some empty boardlets are left over. 1.5A@5V from a 6.6V raw
>> source is ok. The transistor costs a diode drop vs. bare 3042.
>
> I think I'll make my own LDO with an opamp and an n-fet. By the time I
> have a dpak fet and some giant caps, the opamp and a few passives add
> not much more board area.
>
> If I use a good 3 volt reference (which I'll have) I expect much less
> low frequency noise than using the 1.25v bandgap and feedback point of
> a regulator.

LT3042 uses a precision current source to develop the output voltage
over a resistor. That is easily filtered.

They even have a proposal of using a post-filtered LT6555
reference with the *1 output stage of the LT3042.

>
> None of that stuff will be on the same die as the big hot pass
> transistor.

Like their external cheap D44H10 NPN

> I'll prowl the dungeon and see if I have a AM503 amplifier, and see if
> it still works, to measure the LDO noise. Or maybe just trust Spice.

You can trust spice, but you cannot trust the models.
Few have 1/f noise, or even correct data.
Many transistor models have been made with the Orcad parts
program. You recognize them since all have the same RBB.

Gerhard

Am 11.09.22 um 05:30 schrieb jlarkin@highlandsniptechnology.com:

> I'll prowl the dungeon and see if I have a AM503 amplifier, and see if
> it still works, to measure the LDO noise. Or maybe just trust Spice.

The current probe amplifier?

On Tue, 13 Sep 2022 04:33:57 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:

>Am 11.09.22 um 05:30 schrieb jlarkin@highlandsniptechnology.com:
>
>> I'll prowl the dungeon and see if I have a AM503 amplifier, and see if
>> it still works, to measure the LDO noise. Or maybe just trust Spice.
>
>The current probe amplifier?
>
>
>

No, sorry, Am502.

https://w140.com/tekwiki/wiki/TM500_and_TM5000_plug-ins#/media/File:Tek_am502_1.jpg

John Larkin <jlarkin@highlandSNIPMEtechnology.com> wrote:

> No, sorry, Am502.
>
> https://w140.com/tekwiki/wiki/TM500_and_TM5000_plug-ins#/media/File:Tek_a
> m502_1.jpg

That is a very nice variable bandwidth amplifier. It would be nice to have a
HP 3400A true RMS voltmeter, 10 Hz to 10 MHz to convert the p-p readings to
true rms. That way, you could get consistent readings to compare with various
datasheets. Or just use a scope if it has true rms conversion.

--
MRM