So, I had this application requiring really absurd amounts of ripple
rejection--it's a piezo driver in a laser wavelength locker that (for
historical reasons) has to run off a fairly crappy dual isolated 48V
DC-DC converter. The 48V has almost a half volt of ripple at 47 kHz,
and the output noise needed to be in the nanovolts.
As we've discussed here before, ordinary cap multipliers are limited by
Early effect and collector-emitter capacitance. This one is a bit
complicated--14 parts--but according to LTSPICE it provides 180 dB of
ripple rejection from about 40 kHz to above 10 MHz. (In reality it
won't be this good of course.) The interesting thing is that even with
a it drops only about 1.5V, due to daisy-chaining the RC lowpasses--the
second stage is biased from the base of the first stage instead of the
emitter, which saves a diode drop. Adding the second stage requires
only about 350 mV total.
The remaining limitations are due to the combined Early effect of the
transistors--very small, since they form a cascode pair--and all the
interelectrode capacitances in series.
Good medicine for the present problem!
Cheers
Phil Hobbs
Q1 Q2
IN DNLS160 DNLS160 3 OUT
0-----*--- --------- ------RR-*--------0
| \ / \ / |
| \ A \ A |
| --------- --------- |
390 R | | === 47uF alum
R | | | || 1uF X7R
| 390 | 330 330 | |
| | | GND
*--RR---*---RR---*---RR---*----+
| | | | |
| | | | R 91k
=== === === === R
1u | 1u | 1u | 1u | |
| | | | |
GND GND GND GND GND
--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
email: hobbs (atsign) electrooptical (period) net
http://electrooptical.net
Improved capacitance multiplier
Started by ●November 2, 2010
Reply by ●November 2, 20102010-11-02
On Tue, 02 Nov 2010 01:48:59 -0400, Phil Hobbs wrote:> The remaining limitations are due to the combined Early effect of the > transistors--very small, since they form a cascode pair--and all the > interelectrode capacitances in series.Where do you get caps with low enough microphonics for a design like this? (Must be cheap, surface mount, ROHS and in-stock somewhere.) I've tried to design cap multipliers in the past in an attempt to get very low noise voltages, but the microphonics seem to limit the results. Thanks, Allan
Reply by ●November 2, 20102010-11-02
Allan Herriman wrote:> On Tue, 02 Nov 2010 01:48:59 -0400, Phil Hobbs wrote: > >> The remaining limitations are due to the combined Early effect of the >> transistors--very small, since they form a cascode pair--and all the >> interelectrode capacitances in series. > > Where do you get caps with low enough microphonics for a design > like this? (Must be cheap, surface mount, ROHS and in-stock > somewhere.) > > I've tried to design cap multipliers in the past in an attempt to > get very low noise voltages, but the microphonics seem to > limit the results. > > Thanks, > AllanLeaded film caps are the best--if you absolutely can't use them, then I suppose it's a case of "too bad, so sad." Down where board microphonics are a big problem, the PSR of the op amps helps a lot, but not at harmonics of 50 kHz. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 email: hobbs (atsign) electrooptical (period) net http://electrooptical.net
Reply by ●November 2, 20102010-11-02
On Nov 1, 10:48 pm, Phil Hobbs <pcdhSpamMeSensel...@electrooptical.net> wrote:> So, I had this application requiring really absurd amounts of ripple > rejection--it's a piezo driver in a laser wavelength locker that (for > historical reasons) has to run off a fairly crappy dual isolated 48V > DC-DC converter. The 48V has almost a half volt of ripple at 47 kHz, > and the output noise needed to be in the nanovolts.Would 4 x 12V rechargable batteries do (?). I could explain further unless that option has been eliminated. Regards Ken> As we've discussed here before, ordinary cap multipliers are limited by > Early effect and collector-emitter capacitance. This one is a bit > complicated--14 parts--but according to LTSPICE it provides 180 dB of > ripple rejection from about 40 kHz to above 10 MHz. (In reality it > won't be this good of course.) The interesting thing is that even with > a it drops only about 1.5V, due to daisy-chaining the RC lowpasses--the > second stage is biased from the base of the first stage instead of the > emitter, which saves a diode drop. Adding the second stage requires > only about 350 mV total. > > The remaining limitations are due to the combined Early effect of the > transistors--very small, since they form a cascode pair--and all the > interelectrode capacitances in series. > > Good medicine for the present problem! > > Cheers > > Phil Hobbs > > Q1 Q2 > > IN DNLS160 DNLS160 3 OUT > > 0-----*--- --------- ------RR-*--------0 > | \ / \ / | > | \ A \ A | > | --------- --------- | > 390 R | | === 47uF alum > R | | | || 1uF X7R > | 390 | 330 330 | | > | | | GND > *--RR---*---RR---*---RR---*----+ > | | | | | > | | | | R 91k > === === === === R > 1u | 1u | 1u | 1u | | > | | | | | > GND GND GND GND GND > > -- > Dr Philip C D Hobbs > Principal > ElectroOptical Innovations > 55 Orchard Rd > Briarcliff Manor NY 10510 > 845-480-2058 > > email: hobbs (atsign) electrooptical (period) nethttp://electrooptical.net
Reply by ●November 2, 20102010-11-02
Ken S. Tucker wrote:> On Nov 1, 10:48 pm, Phil Hobbs > <pcdhSpamMeSensel...@electrooptical.net> wrote: >> So, I had this application requiring really absurd amounts of ripple >> rejection--it's a piezo driver in a laser wavelength locker that (for >> historical reasons) has to run off a fairly crappy dual isolated 48V >> DC-DC converter. The 48V has almost a half volt of ripple at 47 kHz, >> and the output noise needed to be in the nanovolts. > > Would 4 x 12V rechargable batteries do (?). > I could explain further unless that option has been eliminated. > Regards > Ken > >> As we've discussed here before, ordinary cap multipliers are limited by >> Early effect and collector-emitter capacitance. This one is a bit >> complicated--14 parts--but according to LTSPICE it provides 180 dB of >> ripple rejection from about 40 kHz to above 10 MHz. (In reality it >> won't be this good of course.) The interesting thing is that even with >> a it drops only about 1.5V, due to daisy-chaining the RC lowpasses--the >> second stage is biased from the base of the first stage instead of the >> emitter, which saves a diode drop. Adding the second stage requires >> only about 350 mV total. >> >> The remaining limitations are due to the combined Early effect of the >> transistors--very small, since they form a cascode pair--and all the >> interelectrode capacitances in series. >> >> Good medicine for the present problem! >> >> Cheers >> >> Phil Hobbs >> >> Q1 Q2 >> >> IN DNLS160 DNLS160 3 OUT >> >> 0-----*--- --------- ------RR-*--------0 >> | \ / \ / | >> | \ A \ A | >> | --------- --------- | >> 390 R | | === 47uF alum >> R | | | || 1uF X7R >> | 390 | 330 330 | | >> | | | GND >> *--RR---*---RR---*---RR---*----+ >> | | | | | >> | | | | R 91k >> === === === === R >> 1u | 1u | 1u | 1u | | >> | | | | | >> GND GND GND GND GND >>Batteries aren't a good solution for this, because the data runs are very long, and they'd have to be charged up every so often, and maintained, and they're a lot larger and more expensive as well. The cap multiplier will fit in a board space the size of a nickel very comfortably. (Other parts of the system do use batteries, mainly because of pickup.) Other EMI paths are probably going to dominate here as well, but once the conduction via the supply is gone, we can nail those too. Low noise sensor design is always an onion problem. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 email: hobbs (atsign) electrooptical (period) net http://electrooptical.net
Reply by ●November 2, 20102010-11-02
On Nov 2, 8:12=A0am, Phil Hobbs <pcdhSpamMeSensel...@electrooptical.net> wrote:> Ken S. Tucker wrote: > > On Nov 1, 10:48 pm, Phil Hobbs > > <pcdhSpamMeSensel...@electrooptical.net> =A0wrote: > >> So, I had this application requiring really absurd amounts of ripple > >> rejection--it's a piezo driver in a laser wavelength locker that (for > >> historical reasons) has to run off a fairly crappy dual isolated 48V > >> DC-DC converter. =A0The 48V has almost a half volt of ripple at 47 kHz=,> >> and the output noise needed to be in the nanovolts. > > > Would =A04 x 12V rechargable batteries do (?). > > I could explain further unless that option has been eliminated. > > Regards > > Ken > > >> As we've discussed here before, ordinary cap multipliers are limited b=y> >> Early effect and collector-emitter capacitance. =A0This one is a bit > >> complicated--14 parts--but according to LTSPICE it provides 180 dB of > >> ripple rejection from about 40 =A0kHz to above 10 MHz. =A0(In reality =it> >> won't be this good of course.) =A0The interesting thing is that even w=ith> >> a it drops only about 1.5V, due to daisy-chaining the RC lowpasses--th=e> >> second stage is biased from the base of the first stage instead of the > >> emitter, which saves a diode drop. =A0Adding the second stage requires > >> only about 350 mV total. > > >> The remaining limitations are due to the combined Early effect of the > >> transistors--very small, since they form a cascode pair--and all the > >> interelectrode capacitances in series. > > >> Good medicine for the present problem! > > >> Cheers > > >> Phil Hobbs > > >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Q1 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Q2 > > >> IN =A0 =A0 =A0 =A0DNLS160 =A0 =A0 =A0 =A0 =A0 =A0DNLS160 =A0 =A0 =A0 3==A0 =A0 =A0 =A0 =A0OUT> > >> 0-----*--- =A0 =A0 =A0 =A0 --------- =A0 =A0 =A0 =A0 ------RR-*-------=-0> >> =A0 =A0 =A0 =A0 | =A0 \ =A0 =A0 =A0 / =A0 =A0 =A0 =A0 \ =A0 =A0 =A0 / ==A0 =A0 =A0 =A0 |> >> =A0 =A0 =A0 =A0 | =A0 =A0\ =A0 =A0 A =A0 =A0 =A0 =A0 =A0 \ =A0 =A0 A ==A0 =A0 =A0 =A0 =A0|> >> =A0 =A0 =A0 =A0 | =A0 --------- =A0 =A0 =A0 =A0 --------- =A0 =A0 =A0 ==A0 |> >> =A0 =A0390 =A0R =A0 =A0 =A0 | =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 ==A0 =A0 =A0 =A0 =A0=3D=3D=3D =A047uF alum> >> =A0 =A0 =A0 =A0 R =A0 =A0 =A0 | =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 ==A0 =A0 =A0 =A0 =A0 | =A0 || 1uF X7R> >> =A0 =A0 =A0 =A0 | =A0390 =A0| =A0330 =A0 =A0 =A0330 =A0 | =A0 =A0 =A0 ==A0 =A0 =A0 |> >> =A0 =A0 =A0 =A0 | =A0 =A0 =A0 | =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 ==A0 =A0 =A0 =A0 =A0GND> >> =A0 =A0 =A0 =A0 *--RR---*---RR---*---RR---*----+ > >> =A0 =A0 =A0 =A0 | =A0 =A0 =A0 | =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0| =A0 ==A0|> >> =A0 =A0 =A0 =A0 | =A0 =A0 =A0 | =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0| =A0 ==A0R 91k> >> =A0 =A0 =A0 =A0=3D=3D=3D =A0 =A0 =3D=3D=3D =A0 =A0 =A0=3D=3D=3D =A0 ==A0 =A0=3D=3D=3D =A0 R> >> =A0 =A0 =A01u | =A0 =A01u | =A0 =A0 1u | =A0 =A0 1u | =A0 =A0| > >> =A0 =A0 =A0 =A0 | =A0 =A0 =A0 | =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0| =A0 ==A0|> >> =A0 =A0 =A0 =A0GND =A0 =A0 GND =A0 =A0 =A0GND =A0 =A0 =A0GND =A0GND > > Batteries aren't a good solution for this, because the data runs are > very long, and they'd have to be charged up every so often, and > maintained, and they're a lot larger and more expensive as well. =A0The > cap multiplier will fit in a board space the size of a nickel very > comfortably. =A0(Other parts of the system do use batteries, mainly > because of pickup.) > > Other EMI paths are probably going to dominate here as well, but once > the conduction via the supply is gone, we can nail those too. =A0Low nois=e> sensor design is always an onion problem. > > Cheers > > Phil Hobbs > > -- > Dr Philip C D Hobbs > Principal > ElectroOptical Innovations > 55 Orchard Rd > Briarcliff Manor NY 10510845-480-2058begin_of_the_skype_highlighting=A0==A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0845-480-2058=A0=A0=A0=A0=A0=A0end_of= _the_skype_highlighting> > email: hobbs (atsign) electrooptical (period) nethttp://electrooptical.ne=t- Hide quoted text -> > - Show quoted text -Here is a circuit that uses a single darlington stage: http://sound.westhost.com/project15.htm Tom
Reply by ●November 2, 20102010-11-02
On Nov 2, 10:11 am, 2G <soar2mor...@yahoo.com> wrote:> On Nov 2, 8:12 am, Phil Hobbs <pcdhSpamMeSensel...@electrooptical.net> > wrote: > > > > > Ken S. Tucker wrote: > > > On Nov 1, 10:48 pm, Phil Hobbs > > > <pcdhSpamMeSensel...@electrooptical.net> wrote: > > >> So, I had this application requiring really absurd amounts of ripple > > >> rejection--it's a piezo driver in a laser wavelength locker that (for > > >> historical reasons) has to run off a fairly crappy dual isolated 48V > > >> DC-DC converter. The 48V has almost a half volt of ripple at 47 kHz, > > >> and the output noise needed to be in the nanovolts. > > > > Would 4 x 12V rechargable batteries do (?). > > > I could explain further unless that option has been eliminated. > > > Regards > > > Ken > > > >> As we've discussed here before, ordinary cap multipliers are limited by > > >> Early effect and collector-emitter capacitance. This one is a bit > > >> complicated--14 parts--but according to LTSPICE it provides 180 dB of > > >> ripple rejection from about 40 kHz to above 10 MHz. (In reality it > > >> won't be this good of course.) The interesting thing is that even with > > >> a it drops only about 1.5V, due to daisy-chaining the RC lowpasses--the > > >> second stage is biased from the base of the first stage instead of the > > >> emitter, which saves a diode drop. Adding the second stage requires > > >> only about 350 mV total. > > > >> The remaining limitations are due to the combined Early effect of the > > >> transistors--very small, since they form a cascode pair--and all the > > >> interelectrode capacitances in series. > > > >> Good medicine for the present problem! > > > >> Cheers > > > >> Phil Hobbs > > > >> Q1 Q2 > > > >> IN DNLS160 DNLS160 3 OUT > > > >> 0-----*--- --------- ------RR-*--------0 > > >> | \ / \ / | > > >> | \ A \ A | > > >> | --------- --------- | > > >> 390 R | | === 47uF alum > > >> R | | | || 1uF X7R > > >> | 390 | 330 330 | | > > >> | | | GND > > >> *--RR---*---RR---*---RR---*----+ > > >> | | | | | > > >> | | | | R 91k > > >> === === === === R > > >> 1u | 1u | 1u | 1u | | > > >> | | | | | > > >> GND GND GND GND GND > > > Batteries aren't a good solution for this, because the data runs are > > very long, and they'd have to be charged up every so often, and > > maintained, and they're a lot larger and more expensive as well. The > > cap multiplier will fit in a board space the size of a nickel very > > comfortably. (Other parts of the system do use batteries, mainly > > because of pickup.) > > > Other EMI paths are probably going to dominate here as well, but once > > the conduction via the supply is gone, we can nail those too. Low noise > > sensor design is always an onion problem. > > > Cheers > > > Phil Hobbs > > > -- > > Dr Philip C D Hobbs > > Principal > > ElectroOptical Innovations > > 55 Orchard Rd > > Briarcliff Manor NY 10510845-480-2058begin_of_the_skype_highlighting 845-480-2058 end_of_the_skype_highlighting > > > email: hobbs (atsign) electrooptical (period) nethttp://electrooptical.net-Hide quoted text - > > > - Show quoted text - > > Here is a circuit that uses a single darlington stage: > > http://sound.westhost.com/project15.htm > > TomWe'll need to know the rapidity of the load variation in watt units, then design a V-regulator to meet the nanovolt spec. Personally, I think the cap amplifier is a primitive approach, instead I'd go for a fast feed-back V-reg. My background is designing voltages standard for labs, so I'm quite interested in this discussion. Regards Ken
Reply by ●November 2, 20102010-11-02
Ken S. Tucker wrote:> On Nov 2, 10:11 am, 2G<soar2mor...@yahoo.com> wrote: >> On Nov 2, 8:12 am, Phil Hobbs<pcdhSpamMeSensel...@electrooptical.net> >> wrote: >> >> >> >>> Ken S. Tucker wrote: >>>> On Nov 1, 10:48 pm, Phil Hobbs >>>> <pcdhSpamMeSensel...@electrooptical.net> wrote: >>>>> So, I had this application requiring really absurd amounts of ripple >>>>> rejection--it's a piezo driver in a laser wavelength locker that (for >>>>> historical reasons) has to run off a fairly crappy dual isolated 48V >>>>> DC-DC converter. The 48V has almost a half volt of ripple at 47 kHz, >>>>> and the output noise needed to be in the nanovolts. >> >>>> Would 4 x 12V rechargable batteries do (?). >>>> I could explain further unless that option has been eliminated. >>>> Regards >>>> Ken >> >>>>> As we've discussed here before, ordinary cap multipliers are limited by >>>>> Early effect and collector-emitter capacitance. This one is a bit >>>>> complicated--14 parts--but according to LTSPICE it provides 180 dB of >>>>> ripple rejection from about 40 kHz to above 10 MHz. (In reality it >>>>> won't be this good of course.) The interesting thing is that even with >>>>> a it drops only about 1.5V, due to daisy-chaining the RC lowpasses--the >>>>> second stage is biased from the base of the first stage instead of the >>>>> emitter, which saves a diode drop. Adding the second stage requires >>>>> only about 350 mV total. >> >>>>> The remaining limitations are due to the combined Early effect of the >>>>> transistors--very small, since they form a cascode pair--and all the >>>>> interelectrode capacitances in series. >> >>>>> Good medicine for the present problem! >> >>>>> Cheers >> >>>>> Phil Hobbs >> >>>>> Q1 Q2 >> >>>>> IN DNLS160 DNLS160 3 OUT >> >>>>> 0-----*--- --------- ------RR-*--------0 >>>>> | \ / \ / | >>>>> | \ A \ A | >>>>> | --------- --------- | >>>>> 390 R | | === 47uF alum >>>>> R | | | || 1uF X7R >>>>> | 390 | 330 330 | | >>>>> | | | GND >>>>> *--RR---*---RR---*---RR---*----+ >>>>> | | | | | >>>>> | | | | R 91k >>>>> === === === === R >>>>> 1u | 1u | 1u | 1u | | >>>>> | | | | | >>>>> GND GND GND GND GND >> >>> Batteries aren't a good solution for this, because the data runs are >>> very long, and they'd have to be charged up every so often, and >>> maintained, and they're a lot larger and more expensive as well. The >>> cap multiplier will fit in a board space the size of a nickel very >>> comfortably. (Other parts of the system do use batteries, mainly >>> because of pickup.) >> >>> Other EMI paths are probably going to dominate here as well, but once >>> the conduction via the supply is gone, we can nail those too. Low noise >>> sensor design is always an onion problem. >> >>> Cheers >> >>> Phil Hobbs >> >>> -- >>> Dr Philip C D Hobbs >>> Principal >>> ElectroOptical Innovations >>> 55 Orchard Rd >>> Briarcliff Manor NY 10510845-480-2058begin_of_the_skype_highlighting 845-480-2058 end_of_the_skype_highlighting >> >>> email: hobbs (atsign) electrooptical (period) nethttp://electrooptical.net-Hide quoted text - >> >>> - Show quoted text - >> >> Here is a circuit that uses a single darlington stage: >> >> http://sound.westhost.com/project15.htm >> >> Tom > > We'll need to know the rapidity of the load variation in watt units, > then design a V-regulator to meet the nanovolt spec. > Personally, I think the cap amplifier is a primitive approach, instead > I'd go for a fast feed-back V-reg. > My background is designing voltages standard for labs, so I'm quite > interested in this discussion. > Regards > KenFood and sex are pretty primitive too, but still widely popular. ;) I'm not very interested in the exact output voltage, because it's driving a bunch of op amps, and their PSR is effectively infinite at low frequencies. It's the SMPS ripple that's the problem, one that rears its ugly head in essentially every ultrasensitive measurement system. If you actually possess a regulator design that will produce 1-nanovolt noise output with 1 V of ripple on the input, I'd love to see it. BTW by getting rid of the output resistor and putting a 12 ohm/47 uF lowpass section in the collector of Q1, you can get the same rejection with lower impedance and lower voltage drop. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 email: hobbs (atsign) electrooptical (period) net http://electrooptical.net
Reply by ●November 2, 20102010-11-02
On Nov 2, 1:48=A0am, Phil Hobbs <pcdhSpamMeSensel...@electrooptical.net> wrote:> So, I had this application requiring really absurd amounts of ripple > rejection--it's a piezo driver in a laser wavelength locker that (for > historical reasons) has to run off a fairly crappy dual isolated 48V > DC-DC converter. =A0The 48V has almost a half volt of ripple at 47 kHz, > and the output noise needed to be in the nanovolts. > > As we've discussed here before, ordinary cap multipliers are limited by > Early effect and collector-emitter capacitance. =A0This one is a bit > complicated--14 parts--but according to LTSPICE it provides 180 dB of > ripple rejection from about 40 =A0kHz to above 10 MHz. =A0(In reality it > won't be this good of course.) =A0The interesting thing is that even with > a it drops only about 1.5V, due to daisy-chaining the RC lowpasses--the > second stage is biased from the base of the first stage instead of the > emitter, which saves a diode drop. =A0Adding the second stage requires > only about 350 mV total. > > The remaining limitations are due to the combined Early effect of the > transistors--very small, since they form a cascode pair--and all the > interelectrode capacitances in series. > > Good medicine for the present problem! > > Cheers > > Phil Hobbs > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 Q1 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Q2 > > IN =A0 =A0 =A0 =A0DNLS160 =A0 =A0 =A0 =A0 =A0 =A0DNLS160 =A0 =A0 =A0 3 ==A0 =A0 =A0 =A0 =A0OUT> > 0-----*--- =A0 =A0 =A0 =A0 --------- =A0 =A0 =A0 =A0 ------RR-*--------0 > =A0 =A0 =A0 =A0| =A0 \ =A0 =A0 =A0 / =A0 =A0 =A0 =A0 \ =A0 =A0 =A0 / =A0 ==A0 =A0 =A0 |> =A0 =A0 =A0 =A0| =A0 =A0\ =A0 =A0 A =A0 =A0 =A0 =A0 =A0 \ =A0 =A0 A =A0 ==A0 =A0 =A0 =A0|> =A0 =A0 =A0 =A0| =A0 --------- =A0 =A0 =A0 =A0 --------- =A0 =A0 =A0 =A0 =|> =A0 390 =A0R =A0 =A0 =A0 | =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 ==A0 =A0 =A0=3D=3D=3D =A047uF alum> =A0 =A0 =A0 =A0R =A0 =A0 =A0 | =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 ==A0 =A0 =A0 =A0 | =A0 || 1uF X7R> =A0 =A0 =A0 =A0| =A0390 =A0| =A0330 =A0 =A0 =A0330 =A0 | =A0 =A0 =A0 =A0 ==A0 =A0 |> =A0 =A0 =A0 =A0| =A0 =A0 =A0 | =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 ==A0 =A0 =A0 =A0GND> =A0 =A0 =A0 =A0*--RR---*---RR---*---RR---*----+ > =A0 =A0 =A0 =A0| =A0 =A0 =A0 | =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0| =A0 =A0| > =A0 =A0 =A0 =A0| =A0 =A0 =A0 | =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0| =A0 =A0R=91k> =A0 =A0 =A0 =3D=3D=3D =A0 =A0 =3D=3D=3D =A0 =A0 =A0=3D=3D=3D =A0 =A0 =A0==3D=3D=3D =A0 R> =A0 =A0 1u | =A0 =A01u | =A0 =A0 1u | =A0 =A0 1u | =A0 =A0| > =A0 =A0 =A0 =A0| =A0 =A0 =A0 | =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0| =A0 =A0| > =A0 =A0 =A0 GND =A0 =A0 GND =A0 =A0 =A0GND =A0 =A0 =A0GND =A0GND > > -- > Dr Philip C D Hobbs > Principal > ElectroOptical Innovations > 55 Orchard Rd > Briarcliff Manor NY 10510 > 845-480-2058 > > email: hobbs (atsign) electrooptical (period) nethttp://electrooptical.ne=t Fun, I would have first tried taking the drive for the base of Q2 from the collector of Q1, rather than the long string of RC's. Did you perchance try it that way also? And was it worse? George H.
Reply by ●November 2, 20102010-11-02
On Nov 2, 12:03 pm, Phil Hobbs <pcdhSpamMeSensel...@electrooptical.net> wrote:> Ken S. Tucker wrote: > > On Nov 2, 10:11 am, 2G<soar2mor...@yahoo.com> wrote: > >> On Nov 2, 8:12 am, Phil Hobbs<pcdhSpamMeSensel...@electrooptical.net> > >> wrote: > > >>> Ken S. Tucker wrote: > >>>> On Nov 1, 10:48 pm, Phil Hobbs > >>>> <pcdhSpamMeSensel...@electrooptical.net> wrote: > >>>>> So, I had this application requiring really absurd amounts of ripple > >>>>> rejection--it's a piezo driver in a laser wavelength locker that (for > >>>>> historical reasons) has to run off a fairly crappy dual isolated 48V > >>>>> DC-DC converter. The 48V has almost a half volt of ripple at 47 kHz, > >>>>> and the output noise needed to be in the nanovolts. > > >>>> Would 4 x 12V rechargable batteries do (?). > >>>> I could explain further unless that option has been eliminated. > >>>> Regards > >>>> Ken > > >>>>> As we've discussed here before, ordinary cap multipliers are limited by > >>>>> Early effect and collector-emitter capacitance. This one is a bit > >>>>> complicated--14 parts--but according to LTSPICE it provides 180 dB of > >>>>> ripple rejection from about 40 kHz to above 10 MHz. (In reality it > >>>>> won't be this good of course.) The interesting thing is that even with > >>>>> a it drops only about 1.5V, due to daisy-chaining the RC lowpasses--the > >>>>> second stage is biased from the base of the first stage instead of the > >>>>> emitter, which saves a diode drop. Adding the second stage requires > >>>>> only about 350 mV total. > > >>>>> The remaining limitations are due to the combined Early effect of the > >>>>> transistors--very small, since they form a cascode pair--and all the > >>>>> interelectrode capacitances in series. > > >>>>> Good medicine for the present problem! > > >>>>> Cheers > > >>>>> Phil Hobbs > > >>>>> Q1 Q2 > > >>>>> IN DNLS160 DNLS160 3 OUT > > >>>>> 0-----*--- --------- ------RR-*--------0 > >>>>> | \ / \ / | > >>>>> | \ A \ A | > >>>>> | --------- --------- | > >>>>> 390 R | | === 47uF alum > >>>>> R | | | || 1uF X7R > >>>>> | 390 | 330 330 | | > >>>>> | | | GND > >>>>> *--RR---*---RR---*---RR---*----+ > >>>>> | | | | | > >>>>> | | | | R 91k > >>>>> === === === === R > >>>>> 1u | 1u | 1u | 1u | | > >>>>> | | | | | > >>>>> GND GND GND GND GND > > >>> Batteries aren't a good solution for this, because the data runs are > >>> very long, and they'd have to be charged up every so often, and > >>> maintained, and they're a lot larger and more expensive as well. The > >>> cap multiplier will fit in a board space the size of a nickel very > >>> comfortably. (Other parts of the system do use batteries, mainly > >>> because of pickup.) > > >>> Other EMI paths are probably going to dominate here as well, but once > >>> the conduction via the supply is gone, we can nail those too. Low noise > >>> sensor design is always an onion problem. > > >>> Cheers > > >>> Phil Hobbs > > >>> -- > >>> Dr Philip C D Hobbs > >>> Principal > >>> ElectroOptical Innovations > >>> 55 Orchard Rd > >>> Briarcliff Manor NY 10510845-480-2058begin_of_the_skype_highlighting 845-480-2058 end_of_the_skype_highlighting > > >>> email: hobbs (atsign) electrooptical (period) nethttp://electrooptical.net-Hidequoted text - > > >>> - Show quoted text - > > >> Here is a circuit that uses a single darlington stage: > > >>http://sound.westhost.com/project15.htm > > >> Tom > > > We'll need to know the rapidity of the load variation in watt units, > > then design a V-regulator to meet the nanovolt spec. > > Personally, I think the cap amplifier is a primitive approach, instead > > I'd go for a fast feed-back V-reg. > > My background is designing voltages standard for labs, so I'm quite > > interested in this discussion. > > Regards > > Ken > > Food and sex are pretty primitive too, but still widely popular. ;) > > I'm not very interested in the exact output voltage, because it's > driving a bunch of op amps, and their PSR is effectively infinite at low > frequencies. It's the SMPS ripple that's the problem, one that rears > its ugly head in essentially every ultrasensitive measurement system.It's a good thing to solve.> If you actually possess a regulator design that will produce 1-nanovolt > noise output with 1 V of ripple on the input, I'd love to see it.To start : (a nano is 10^-9), so we'll need at least 10^10 control, within the tolerance braces. Likely need staged 2x OP-amps for that, or 5x Darlington. Supposing we build that regulator, how would we measure it, to ascertain we're in specs? (shooting for 1 part in 10^10).> BTW by getting rid of the output resistor and putting a 12 ohm/47 uF > lowpass section in the collector of Q1, you can get the same rejection > with lower impedance and lower voltage drop.Yeah that's a course filter, gotta look at math, the number above are the spec.> Cheers> > Phil Hobbs > > -- > Dr Philip C D Hobbs > Principal > ElectroOptical Innovations > 55 Orchard Rd > Briarcliff Manor NY 10510 > 845-480-2058Cheers Ken S. Tucker
