Joerg wrote:> Has anyone ever checked the noise performance of logic inverters used as > analog amplifiers?FWIW on one of the projects I compared noise performance of HC gate used as a comparator against real comparator of comparable speed (LM361). For the same conditions, the gate was about 3 times more noisy. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
C-multiplier again
Started by ●May 22, 2010
Reply by ●May 23, 20102010-05-23
Reply by ●May 24, 20102010-05-24
"Tim Williams" <tmoranwms@charter.net> wrote in message news:htco92$nqn$1@news.eternal-september.org...> "Joerg" <invalid@invalid.invalid> wrote in message > news:85u0ihFmddU1@mid.individual.net... >> Since you don't need much current, how about a cheap low-noise non-RR >> opamp such as the LM833 followed by a JFET with its drain tied to the >> input rail? Ok, then you have your transistor back :-) > > Or just cap couple its output to the output rail.Kinda like this. Particularly the right hand part, but maybe the left hand side is handy too. http://myweb.msoe.edu/williamstm/Images/Ripple_Canceller.png The op-amps could be TL072, powered by the output rails (since you said you need bipolar anyway, so there will be a complement of this). Startup could be interesting. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
Reply by ●May 24, 20102010-05-24
On May 23, 9:44=A0pm, Phil Hobbs <pcdhSpamMeSensel...@electrooptical.net> wrote:> Winfield Hill wrote: > > dagmargoodb...@yahoo.com wrote... > >> This shunt filter only needs 200mV headroom: > > >> FIG. 2 > >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 R1 > >> +15V >--+------------------/\/\/\--------+--> Vout 14.8v > >> =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A05 =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.-------+------+--------+ > >> =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 R6 =A0 =A0 =A0==A0|> >> =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0| =A0 =A0 =A0 | =A0 =A0 1k =A0 =A0 =A0==A0|> >> =A0 =A0 =A0 =A0| =A0 =A0 =A0 R3 =A0 =A0 =A0R5 =A0 =A0 =A0| =A0 =A0 =A0=|<' Q3> >> =A0 =A0 =A0 =A0| =A0 =A0 =A02.7M =A0 =A0 10K =A0 =A0 +------| =A0 2n39=06> >> =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|/ Q2 =A0 =A0 ==A0|> >> =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0| =A0 =A0 =A0 +----| =A02n3904 =A0| > >> =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0| =A0 =A0 =A0 | =A0 =A0|>. =A0 =A0 =A0==A0|> >> =A0 =A0 =A0 =A0| =A0 C1 =A0 | =A0 =A0|<' =A0 =A0 =A0 | =A0 =A0 =A0 =A0=|> >> =A0 =A0 =A0 =A0'---||---+----| =A0Q1 =A0 =A0 '--------+ > >> =A0 =A0 =A0 =A0 =A0 10uF =A0 =A0 =A0 |\ 2n3906 =A0 =A0 =A0 =A0 =A0| > >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 ==A0 =A0 =A0R4> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 ==A0 =A0 4.7R> >> =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------+----------------+---- > > > =A0Nice ASCII art. =A0Is fig 2 from your feverish brain? > > > =A0I see your idea, invert the ripple and subtract it out. > > =A0Good. =A0To do that the cancellation amplifier needs to > > =A0be biased class A, so it can work over the entire ripple > > =A0range. =A0It should continuously draw current from the > > =A0supply through R1, and superimpose the inverted ripple > > =A0signal on top of that. =A0 R4 can be trimmed to optimize. > > =A0The new R7 should be sized to handle the p-p ripple. > > > =A0Then John's delicate C-multiplier filter can follower, > > =A0with all the heavy lifting having been done. > > > =A0+15V >--+-----------------/\/\/\--------+--> Vout 14.8v > > =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 5 =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 =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 =A0 R6 =A0 =A0 ==A0 =A0|> > =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0| =A0 =A0 =A0| =A0 =A0 1k =A0 =A0 ==A0 =A0|> > =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 R3 =A0 =A0 R5 =A0 =A0 =A0| =A0 =A0 =A0=|<' Q3> > =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A02.7M =A0 =A010K =A0 =A0 +------| =A0 2n=4403> > =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|/ Q2 =A0 =A0==A0|> > =A0 =A0 =A0 =A0 =A0| =A0 C1 =A0 | =A0 =A0 =A0+----| =A02n3904 =A0| > > =A0 =A0 =A0 =A0 =A0'---||---+ =A0 =A0 =A0| =A0 =A0|>. =A0 =A0 =A0 =A0| > > =A0 =A0 =A0 =A0 =A0 =A0 10uF =A0| =A0 =A0|<' =A0 =A0 =A0| =A0 =A0 =A0 ==A0|> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 +----| =A0Q1 =A0 =A0'--------+ > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0|\ 2n3906 =A0 =A0 =A0 =A0 =|> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0R7 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 ==A0 =A0 R4> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0TBD 27k =A0 | =A0 =A0 =A0 =A0 =A0 =A0 ==A04.7R> > =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 --+------+---------------+---- > > The Kanner Kap uses an audio power amp to do this, applying a small > amount of positive feedback to multiply the value of a BFC. =A0Works OK, > but it isn't worth paying royalties on. > > Cap multipliers are magic--especially two-pole ones. =A0It's 0.7 volts > well spent IMO. =A0If Early is a worry, use a slower transistor--the > ripple rejection is basically C_CE/C_BFC, with some degradation due to > Early voltage and capacitor ESR.Yep, two-pole--that's the stuff I was fiddling with whilst you guys were posting...(ASCII takes time!) Fig. 3 =3D=3D=3D=3D=3D=3D Q1 Q2 2n3904 2n3904 +15V >--+--------. .----+---. .--+---> +13.3V | \ ^ | \ ^ | R1 ----- R3 ----- | 100R | 100R | | | R2 | | | --- C4 +--/\/\/----+ +------' --- 100uF | 100R | | | C1 --- C2 --- --- C3 | 100uF --- 100uF--- --- 100uF | | | | | =3D=3D=3D =3D=3D=3D =3D=3D=3D =3D=3D=3D GND GND GND GND Output ripple is LT-Spice undetectable. Zout ~=3D 2ohms. Fig. 4 =3D=3D=3D=3D=3D=3D Q1 2n3904 +15V >--+----------------+----. .----+-----> +13.3V | | \ ^ | R1 | ----- | 3.3k | | --- C3 | R2 |/ Q2 | --- 100uF +--/\/\/---+---| 2n3904 | | | 3.3K | |>. | | | | | | =3D=3D=3D C1 --- C2 --- +-------' GND 10uF --- 10uF --- | | | R3 =3D=3D=3D =3D=3D=3D 10k GND GND | =3D=3D=3D GND Buffer Q2 eliminates loading on filter R1C1-R2C2, greatly improving transient response & recovery. The output at Q2(e) is super-clean, but changes in load current modulate Re(Q1) and the drop across it, so output ripple is somewhat worse than the reference. Zout is the same as Fig. 3. Early effect isn't as noticeable as Re, so far. I did a version following Fig. 4 with a one-pole C-mult stage, biased off a divider from Q2(e), and a Sziklai PNP across the whole thing. That means the single-pole stage operates as a cascode and sees no d(Vce) to speak of. 1KHz ripple disappears, and Rout drops to about 0.25 ohms. This version is silly with parts. There needs to be an op amp in there somewhere to greatly simplify things, but it's time for me to turn in. Hopefully these musings will inspire John to continue the fight. -- Cheers, James Arthur
Reply by ●May 24, 20102010-05-24
On Sun, 23 May 2010 21:45:06 -0700 (PDT), dagmargoodboat@yahoo.com wrote:>On May 23, 9:44�pm, Phil Hobbs ><pcdhSpamMeSensel...@electrooptical.net> wrote: >> Winfield Hill wrote: >> > dagmargoodb...@yahoo.com wrote... >> >> This shunt filter only needs 200mV headroom: >> >> >> FIG. 2 >> >> � � � � � � � � � � � � � � R1 >> >> +15V >--+------------------/\/\/\--------+--> Vout 14.8v >> >> � � � �| � � � � � � � � � �5 � � � � � | >> >> � � � �| � � � � � � � � � � � � � � � �| >> >> � � � �| � � � �.-------+------+--------+ >> >> � � � �| � � � �| � � � | � � �| � � � �| >> >> � � � �| � � � �| � � � | � � R6 � � � �| >> >> � � � �| � � � �| � � � | � � 1k � � � �| >> >> � � � �| � � � R3 � � �R5 � � �| � � �|<' Q3 >> >> � � � �| � � �2.7M � � 10K � � +------| � 2n3906 >> >> � � � �| � � � �| � � � | � � �| � � �|\ >> >> � � � �| � � � �| � � � | � �|/ Q2 � � �| >> >> � � � �| � � � �| � � � +----| �2n3904 �| >> >> � � � �| � � � �| � � � | � �|>. � � � �| >> >> � � � �| � C1 � | � �|<' � � � | � � � �| >> >> � � � �'---||---+----| �Q1 � � '--------+ >> >> � � � � � 10uF � � � |\ 2n3906 � � � � �| >> >> � � � � � � � � � � � �| � � � � � � � �R4 >> >> � � � � � � � � � � � �| � � � � � � � 4.7R >> >> � � � � � � � � � � � �| � � � � � � � �| >> >> � � � � � � � � �------+----------------+---- >> >> > �Nice ASCII art. �Is fig 2 from your feverish brain? >> >> > �I see your idea, invert the ripple and subtract it out. >> > �Good. �To do that the cancellation amplifier needs to >> > �be biased class A, so it can work over the entire ripple >> > �range. �It should continuously draw current from the >> > �supply through R1, and superimpose the inverted ripple >> > �signal on top of that. � R4 can be trimmed to optimize. >> > �The new R7 should be sized to handle the p-p ripple. >> >> > �Then John's delicate C-multiplier filter can follower, >> > �with all the heavy lifting having been done. >> >> > �+15V >--+-----------------/\/\/\--------+--> Vout 14.8v >> > � � � � �| � � � � � � � � � 5 � � � � � | >> > � � � � �| � � � � � � � � � � � � � � � | >> > � � � � �| � � � �.------+------+--------+ >> > � � � � �| � � � �| � � �| � � �| � � � �| >> > � � � � �| � � � �| � � �| � � R6 � � � �| >> > � � � � �| � � � �| � � �| � � 1k � � � �| >> > � � � � �| � � � R3 � � R5 � � �| � � �|<' Q3 >> > � � � � �| � � �2.7M � �10K � � +------| � 2n4403 >> > � � � � �| � � � �| � � �| � � �| � � �|\ >> > � � � � �| � � � �| � � �| � �|/ Q2 � � �| >> > � � � � �| � C1 � | � � �+----| �2n3904 �| >> > � � � � �'---||---+ � � �| � �|>. � � � �| >> > � � � � � � 10uF �| � �|<' � � �| � � � �| >> > � � � � � � � � � +----| �Q1 � �'--------+ >> > � � � � � � � � � | � �|\ 2n3906 � � � � | >> > � � � � � � � � �R7 � � �| � � � � � � � R4 >> > � � � � � � � �TBD 27k � | � � � � � � �4.7R >> > � � � � � � � � � | � � �| � � � � � � � | >> > � � � � � � � � --+------+---------------+---- >> >> The Kanner Kap uses an audio power amp to do this, applying a small >> amount of positive feedback to multiply the value of a BFC. �Works OK, >> but it isn't worth paying royalties on. >> >> Cap multipliers are magic--especially two-pole ones. �It's 0.7 volts >> well spent IMO. �If Early is a worry, use a slower transistor--the >> ripple rejection is basically C_CE/C_BFC, with some degradation due to >> Early voltage and capacitor ESR. > > >Yep, two-pole--that's the stuff I was fiddling with whilst you guys >were posting...(ASCII takes time!) > >Fig. 3 >====== > Q1 Q2 > 2n3904 2n3904 >+15V >--+--------. .----+---. .--+---> +13.3V > | \ ^ | \ ^ | > R1 ----- R3 ----- | > 100R | 100R | | > | R2 | | | --- C4 > +--/\/\/----+ +------' --- 100uF > | 100R | | | > C1 --- C2 --- --- C3 | > 100uF --- 100uF--- --- 100uF | > | | | | > === === === === > GND GND GND GND > > >Output ripple is LT-Spice undetectable. Zout ~= 2ohms. > > >Fig. 4 >====== Q1 > 2n3904 >+15V >--+----------------+----. .----+-----> +13.3V > | | \ ^ | > R1 | ----- | > 3.3k | | --- C3 > | R2 |/ Q2 | --- 100uF > +--/\/\/---+---| 2n3904 | | > | 3.3K | |>. | | > | | | | === > C1 --- C2 --- +-------' GND > 10uF --- 10uF --- | > | | R3 > === === 10k > GND GND | > === > GND > >Buffer Q2 eliminates loading on filter R1C1-R2C2, greatly improving >transient response & recovery. > >The output at Q2(e) is super-clean, but changes in load current >modulate Re(Q1) and the drop across it, so output ripple is somewhat >worse than the reference. Zout is the same as Fig. 3. > >Early effect isn't as noticeable as Re, so far. > >I did a version following Fig. 4 with a one-pole C-mult stage, biased >off a divider from Q2(e), and a Sziklai PNP across the whole thing. >That means the single-pole stage operates as a cascode and sees no >d(Vce) to speak of. 1KHz ripple disappears, and Rout drops to about >0.25 ohms. > >This version is silly with parts. There needs to be an op amp in >there somewhere to greatly simplify things, but it's time for me to >turn in. Hopefully these musings will inspire John to continue the >fight.This is what I have so far: ftp://jjlarkin.lmi.net/P14_reg.gif The wall wart is prefiltered by a C-L-C filter that should buy me about 40 dB at the switcher frequency. Then this thing should be good for maybe 100 more. Then I have some more RCs before the photodiodes and a couple of other critical things. This regulates to 13.4 to allow some headroom here and there. The LM8261 has about 10 nv/rthz noise, which is a whole nother story. John
Reply by ●May 24, 20102010-05-24
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:> Cap multipliers are magic--especially two-pole ones. It's 0.7 volts > well spent IMO. If Early is a worry, use a slower transistor--the > ripple rejection is basically C_CE/C_BFC, with some degradation due to > Early voltage and capacitor ESR. > > Cheers > > Phil HobbsPhil, you mentioned earlier being able to reach 140 db in one stage: http://groups.google.com/group/sci.electronics.design/msg/143f77519fed66e8 That's a ratio of 10 million to one. How do you do it? Thanks, Mike
Reply by ●May 24, 20102010-05-24
Vladimir Vassilevsky wrote:> > > Joerg wrote: > > >> Has anyone ever checked the noise performance of logic inverters used >> as analog amplifiers? > > FWIW on one of the projects I compared noise performance of HC gate used > as a comparator against real comparator of comparable speed (LM361). For > the same conditions, the gate was about 3 times more noisy. >Oh, thanks, then I guess inverters don't look so good in this domain. No free lunch there :-) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Reply by ●May 24, 20102010-05-24
Joerg wrote: [...]> Since you don't need much current, how about a cheap low-noise non-RR > opamp such as the LM833 followed by a JFET with its drain tied to the > input rail? Ok, then you have your transistor back :-) >P.S.: N-channel depletion mode devices may be more practical here, less hairy during start-up and shutdown because of the +/-20V abs max on the gate and intrinsic diode. BSS159 etc. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Reply by ●May 24, 20102010-05-24
John Larkin wrote:> On Sun, 23 May 2010 21:45:06 -0700 (PDT), dagmargoodboat@yahoo.com > wrote: > >> On May 23, 9:44 pm, Phil Hobbs >> <pcdhSpamMeSensel...@electrooptical.net> wrote: >>> Winfield Hill wrote: >>>> dagmargoodb...@yahoo.com wrote... >>>>> This shunt filter only needs 200mV headroom: >>>>> FIG. 2 >>>>> R1 >>>>> +15V >--+------------------/\/\/\--------+--> Vout 14.8v >>>>> | 5 | >>>>> | | >>>>> | .-------+------+--------+ >>>>> | | | | | >>>>> | | | R6 | >>>>> | | | 1k | >>>>> | R3 R5 | |<' Q3 >>>>> | 2.7M 10K +------| 2n3906 >>>>> | | | | |\ >>>>> | | | |/ Q2 | >>>>> | | +----| 2n3904 | >>>>> | | | |>. | >>>>> | C1 | |<' | | >>>>> '---||---+----| Q1 '--------+ >>>>> 10uF |\ 2n3906 | >>>>> | R4 >>>>> | 4.7R >>>>> | | >>>>> ------+----------------+---- >>>> Nice ASCII art. Is fig 2 from your feverish brain? >>>> I see your idea, invert the ripple and subtract it out. >>>> Good. To do that the cancellation amplifier needs to >>>> be biased class A, so it can work over the entire ripple >>>> range. It should continuously draw current from the >>>> supply through R1, and superimpose the inverted ripple >>>> signal on top of that. R4 can be trimmed to optimize. >>>> The new R7 should be sized to handle the p-p ripple. >>>> Then John's delicate C-multiplier filter can follower, >>>> with all the heavy lifting having been done. >>>> +15V >--+-----------------/\/\/\--------+--> Vout 14.8v >>>> | 5 | >>>> | | >>>> | .------+------+--------+ >>>> | | | | | >>>> | | | R6 | >>>> | | | 1k | >>>> | R3 R5 | |<' Q3 >>>> | 2.7M 10K +------| 2n4403 >>>> | | | | |\ >>>> | | | |/ Q2 | >>>> | C1 | +----| 2n3904 | >>>> '---||---+ | |>. | >>>> 10uF | |<' | | >>>> +----| Q1 '--------+ >>>> | |\ 2n3906 | >>>> R7 | R4 >>>> TBD 27k | 4.7R >>>> | | | >>>> --+------+---------------+---- >>> The Kanner Kap uses an audio power amp to do this, applying a small >>> amount of positive feedback to multiply the value of a BFC. Works OK, >>> but it isn't worth paying royalties on. >>> >>> Cap multipliers are magic--especially two-pole ones. It's 0.7 volts >>> well spent IMO. If Early is a worry, use a slower transistor--the >>> ripple rejection is basically C_CE/C_BFC, with some degradation due to >>> Early voltage and capacitor ESR. >> >> Yep, two-pole--that's the stuff I was fiddling with whilst you guys >> were posting...(ASCII takes time!) >> >> Fig. 3 >> ====== >> Q1 Q2 >> 2n3904 2n3904 >> +15V >--+--------. .----+---. .--+---> +13.3V >> | \ ^ | \ ^ | >> R1 ----- R3 ----- | >> 100R | 100R | | >> | R2 | | | --- C4 >> +--/\/\/----+ +------' --- 100uF >> | 100R | | | >> C1 --- C2 --- --- C3 | >> 100uF --- 100uF--- --- 100uF | >> | | | | >> === === === === >> GND GND GND GND >> >> >> Output ripple is LT-Spice undetectable. Zout ~= 2ohms. >> >> >> Fig. 4 >> ====== Q1 >> 2n3904 >> +15V >--+----------------+----. .----+-----> +13.3V >> | | \ ^ | >> R1 | ----- | >> 3.3k | | --- C3 >> | R2 |/ Q2 | --- 100uF >> +--/\/\/---+---| 2n3904 | | >> | 3.3K | |>. | | >> | | | | === >> C1 --- C2 --- +-------' GND >> 10uF --- 10uF --- | >> | | R3 >> === === 10k >> GND GND | >> === >> GND >> >> Buffer Q2 eliminates loading on filter R1C1-R2C2, greatly improving >> transient response & recovery. >> >> The output at Q2(e) is super-clean, but changes in load current >> modulate Re(Q1) and the drop across it, so output ripple is somewhat >> worse than the reference. Zout is the same as Fig. 3. >> >> Early effect isn't as noticeable as Re, so far. >> >> I did a version following Fig. 4 with a one-pole C-mult stage, biased >> off a divider from Q2(e), and a Sziklai PNP across the whole thing. >> That means the single-pole stage operates as a cascode and sees no >> d(Vce) to speak of. 1KHz ripple disappears, and Rout drops to about >> 0.25 ohms. >> >> This version is silly with parts. There needs to be an op amp in >> there somewhere to greatly simplify things, but it's time for me to >> turn in. Hopefully these musings will inspire John to continue the >> fight. > > > This is what I have so far: > > ftp://jjlarkin.lmi.net/P14_reg.gif > > The wall wart is prefiltered by a C-L-C filter that should buy me > about 40 dB at the switcher frequency. Then this thing should be good > for maybe 100 more. Then I have some more RCs before the photodiodes > and a couple of other critical things. > > This regulates to 13.4 to allow some headroom here and there. > > The LM8261 has about 10 nv/rthz noise, which is a whole nother story. >Try a low noise audio opamp and a depletion mode n-channel. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Reply by ●May 24, 20102010-05-24
On Mon, 24 May 2010 08:19:40 -0700, Joerg <invalid@invalid.invalid> wrote:>John Larkin wrote: >> On Sun, 23 May 2010 21:45:06 -0700 (PDT), dagmargoodboat@yahoo.com >> wrote: >> >>> On May 23, 9:44 pm, Phil Hobbs >>> <pcdhSpamMeSensel...@electrooptical.net> wrote: >>>> Winfield Hill wrote: >>>>> dagmargoodb...@yahoo.com wrote... >>>>>> This shunt filter only needs 200mV headroom: >>>>>> FIG. 2 >>>>>> R1 >>>>>> +15V >--+------------------/\/\/\--------+--> Vout 14.8v >>>>>> | 5 | >>>>>> | | >>>>>> | .-------+------+--------+ >>>>>> | | | | | >>>>>> | | | R6 | >>>>>> | | | 1k | >>>>>> | R3 R5 | |<' Q3 >>>>>> | 2.7M 10K +------| 2n3906 >>>>>> | | | | |\ >>>>>> | | | |/ Q2 | >>>>>> | | +----| 2n3904 | >>>>>> | | | |>. | >>>>>> | C1 | |<' | | >>>>>> '---||---+----| Q1 '--------+ >>>>>> 10uF |\ 2n3906 | >>>>>> | R4 >>>>>> | 4.7R >>>>>> | | >>>>>> ------+----------------+---- >>>>> Nice ASCII art. Is fig 2 from your feverish brain? >>>>> I see your idea, invert the ripple and subtract it out. >>>>> Good. To do that the cancellation amplifier needs to >>>>> be biased class A, so it can work over the entire ripple >>>>> range. It should continuously draw current from the >>>>> supply through R1, and superimpose the inverted ripple >>>>> signal on top of that. R4 can be trimmed to optimize. >>>>> The new R7 should be sized to handle the p-p ripple. >>>>> Then John's delicate C-multiplier filter can follower, >>>>> with all the heavy lifting having been done. >>>>> +15V >--+-----------------/\/\/\--------+--> Vout 14.8v >>>>> | 5 | >>>>> | | >>>>> | .------+------+--------+ >>>>> | | | | | >>>>> | | | R6 | >>>>> | | | 1k | >>>>> | R3 R5 | |<' Q3 >>>>> | 2.7M 10K +------| 2n4403 >>>>> | | | | |\ >>>>> | | | |/ Q2 | >>>>> | C1 | +----| 2n3904 | >>>>> '---||---+ | |>. | >>>>> 10uF | |<' | | >>>>> +----| Q1 '--------+ >>>>> | |\ 2n3906 | >>>>> R7 | R4 >>>>> TBD 27k | 4.7R >>>>> | | | >>>>> --+------+---------------+---- >>>> The Kanner Kap uses an audio power amp to do this, applying a small >>>> amount of positive feedback to multiply the value of a BFC. Works OK, >>>> but it isn't worth paying royalties on. >>>> >>>> Cap multipliers are magic--especially two-pole ones. It's 0.7 volts >>>> well spent IMO. If Early is a worry, use a slower transistor--the >>>> ripple rejection is basically C_CE/C_BFC, with some degradation due to >>>> Early voltage and capacitor ESR. >>> >>> Yep, two-pole--that's the stuff I was fiddling with whilst you guys >>> were posting...(ASCII takes time!) >>> >>> Fig. 3 >>> ====== >>> Q1 Q2 >>> 2n3904 2n3904 >>> +15V >--+--------. .----+---. .--+---> +13.3V >>> | \ ^ | \ ^ | >>> R1 ----- R3 ----- | >>> 100R | 100R | | >>> | R2 | | | --- C4 >>> +--/\/\/----+ +------' --- 100uF >>> | 100R | | | >>> C1 --- C2 --- --- C3 | >>> 100uF --- 100uF--- --- 100uF | >>> | | | | >>> === === === === >>> GND GND GND GND >>> >>> >>> Output ripple is LT-Spice undetectable. Zout ~= 2ohms. >>> >>> >>> Fig. 4 >>> ====== Q1 >>> 2n3904 >>> +15V >--+----------------+----. .----+-----> +13.3V >>> | | \ ^ | >>> R1 | ----- | >>> 3.3k | | --- C3 >>> | R2 |/ Q2 | --- 100uF >>> +--/\/\/---+---| 2n3904 | | >>> | 3.3K | |>. | | >>> | | | | === >>> C1 --- C2 --- +-------' GND >>> 10uF --- 10uF --- | >>> | | R3 >>> === === 10k >>> GND GND | >>> === >>> GND >>> >>> Buffer Q2 eliminates loading on filter R1C1-R2C2, greatly improving >>> transient response & recovery. >>> >>> The output at Q2(e) is super-clean, but changes in load current >>> modulate Re(Q1) and the drop across it, so output ripple is somewhat >>> worse than the reference. Zout is the same as Fig. 3. >>> >>> Early effect isn't as noticeable as Re, so far. >>> >>> I did a version following Fig. 4 with a one-pole C-mult stage, biased >>> off a divider from Q2(e), and a Sziklai PNP across the whole thing. >>> That means the single-pole stage operates as a cascode and sees no >>> d(Vce) to speak of. 1KHz ripple disappears, and Rout drops to about >>> 0.25 ohms. >>> >>> This version is silly with parts. There needs to be an op amp in >>> there somewhere to greatly simplify things, but it's time for me to >>> turn in. Hopefully these musings will inspire John to continue the >>> fight. >> >> >> This is what I have so far: >> >> ftp://jjlarkin.lmi.net/P14_reg.gif >> >> The wall wart is prefiltered by a C-L-C filter that should buy me >> about 40 dB at the switcher frequency. Then this thing should be good >> for maybe 100 more. Then I have some more RCs before the photodiodes >> and a couple of other critical things. >> >> This regulates to 13.4 to allow some headroom here and there. >> >> The LM8261 has about 10 nv/rthz noise, which is a whole nother story. >> > >Try a low noise audio opamp and a depletion mode n-channel.Well, I can't spend the rest of my career working on this circuit! It would be interesting to power an opamp from the output; then there's no PSRR problem. A depletion fet would add enough offset so the thing (might) start up and work. But the fet would be acting almost resistive at low voltage, so the PSRR thing returns with a vengence. A bipolar PNP, with constant-current base drive (like Tim's circuit) is interesting, but still has Early feedthrough. A strategicly placed resistor could null out most of that. An RRO opamp, like in my circuit, incorporates the error amp and the PNP, all in one SOT23. The guys who designed it cared about PSRR and had a zillion transistors to work with. Any attempt to add regulation to a noise filter circuit must inject the noise of the regulator device into the loop; in my case, it's the 10 nv per of the LM8261. The loop comp parts can be tweaked to trade off noise injection versus transient load regulation. I *could* spend the rest of my career on this. Maybe I'll toss another 120 uF polymer cap after the first inductor, and move on with my life. If I keep changing this board, The Brat will take up patricide. John
Reply by ●May 24, 20102010-05-24
John Larkin wrote:> On Mon, 24 May 2010 08:19:40 -0700, Joerg <invalid@invalid.invalid> > wrote: > >> John Larkin wrote: >>> On Sun, 23 May 2010 21:45:06 -0700 (PDT), dagmargoodboat@yahoo.com >>> wrote: >>> >>>> On May 23, 9:44 pm, Phil Hobbs >>>> <pcdhSpamMeSensel...@electrooptical.net> wrote: >>>>> Winfield Hill wrote: >>>>>> dagmargoodb...@yahoo.com wrote... >>>>>>> This shunt filter only needs 200mV headroom: >>>>>>> FIG. 2 >>>>>>> R1 >>>>>>> +15V >--+------------------/\/\/\--------+--> Vout 14.8v >>>>>>> | 5 | >>>>>>> | | >>>>>>> | .-------+------+--------+ >>>>>>> | | | | | >>>>>>> | | | R6 | >>>>>>> | | | 1k | >>>>>>> | R3 R5 | |<' Q3 >>>>>>> | 2.7M 10K +------| 2n3906 >>>>>>> | | | | |\ >>>>>>> | | | |/ Q2 | >>>>>>> | | +----| 2n3904 | >>>>>>> | | | |>. | >>>>>>> | C1 | |<' | | >>>>>>> '---||---+----| Q1 '--------+ >>>>>>> 10uF |\ 2n3906 | >>>>>>> | R4 >>>>>>> | 4.7R >>>>>>> | | >>>>>>> ------+----------------+---- >>>>>> Nice ASCII art. Is fig 2 from your feverish brain? >>>>>> I see your idea, invert the ripple and subtract it out. >>>>>> Good. To do that the cancellation amplifier needs to >>>>>> be biased class A, so it can work over the entire ripple >>>>>> range. It should continuously draw current from the >>>>>> supply through R1, and superimpose the inverted ripple >>>>>> signal on top of that. R4 can be trimmed to optimize. >>>>>> The new R7 should be sized to handle the p-p ripple. >>>>>> Then John's delicate C-multiplier filter can follower, >>>>>> with all the heavy lifting having been done. >>>>>> +15V >--+-----------------/\/\/\--------+--> Vout 14.8v >>>>>> | 5 | >>>>>> | | >>>>>> | .------+------+--------+ >>>>>> | | | | | >>>>>> | | | R6 | >>>>>> | | | 1k | >>>>>> | R3 R5 | |<' Q3 >>>>>> | 2.7M 10K +------| 2n4403 >>>>>> | | | | |\ >>>>>> | | | |/ Q2 | >>>>>> | C1 | +----| 2n3904 | >>>>>> '---||---+ | |>. | >>>>>> 10uF | |<' | | >>>>>> +----| Q1 '--------+ >>>>>> | |\ 2n3906 | >>>>>> R7 | R4 >>>>>> TBD 27k | 4.7R >>>>>> | | | >>>>>> --+------+---------------+---- >>>>> The Kanner Kap uses an audio power amp to do this, applying a small >>>>> amount of positive feedback to multiply the value of a BFC. Works OK, >>>>> but it isn't worth paying royalties on. >>>>> >>>>> Cap multipliers are magic--especially two-pole ones. It's 0.7 volts >>>>> well spent IMO. If Early is a worry, use a slower transistor--the >>>>> ripple rejection is basically C_CE/C_BFC, with some degradation due to >>>>> Early voltage and capacitor ESR. >>>> Yep, two-pole--that's the stuff I was fiddling with whilst you guys >>>> were posting...(ASCII takes time!) >>>> >>>> Fig. 3 >>>> ====== >>>> Q1 Q2 >>>> 2n3904 2n3904 >>>> +15V >--+--------. .----+---. .--+---> +13.3V >>>> | \ ^ | \ ^ | >>>> R1 ----- R3 ----- | >>>> 100R | 100R | | >>>> | R2 | | | --- C4 >>>> +--/\/\/----+ +------' --- 100uF >>>> | 100R | | | >>>> C1 --- C2 --- --- C3 | >>>> 100uF --- 100uF--- --- 100uF | >>>> | | | | >>>> === === === === >>>> GND GND GND GND >>>> >>>> >>>> Output ripple is LT-Spice undetectable. Zout ~= 2ohms. >>>> >>>> >>>> Fig. 4 >>>> ====== Q1 >>>> 2n3904 >>>> +15V >--+----------------+----. .----+-----> +13.3V >>>> | | \ ^ | >>>> R1 | ----- | >>>> 3.3k | | --- C3 >>>> | R2 |/ Q2 | --- 100uF >>>> +--/\/\/---+---| 2n3904 | | >>>> | 3.3K | |>. | | >>>> | | | | === >>>> C1 --- C2 --- +-------' GND >>>> 10uF --- 10uF --- | >>>> | | R3 >>>> === === 10k >>>> GND GND | >>>> === >>>> GND >>>> >>>> Buffer Q2 eliminates loading on filter R1C1-R2C2, greatly improving >>>> transient response & recovery. >>>> >>>> The output at Q2(e) is super-clean, but changes in load current >>>> modulate Re(Q1) and the drop across it, so output ripple is somewhat >>>> worse than the reference. Zout is the same as Fig. 3. >>>> >>>> Early effect isn't as noticeable as Re, so far. >>>> >>>> I did a version following Fig. 4 with a one-pole C-mult stage, biased >>>> off a divider from Q2(e), and a Sziklai PNP across the whole thing. >>>> That means the single-pole stage operates as a cascode and sees no >>>> d(Vce) to speak of. 1KHz ripple disappears, and Rout drops to about >>>> 0.25 ohms. >>>> >>>> This version is silly with parts. There needs to be an op amp in >>>> there somewhere to greatly simplify things, but it's time for me to >>>> turn in. Hopefully these musings will inspire John to continue the >>>> fight. >>> >>> This is what I have so far: >>> >>> ftp://jjlarkin.lmi.net/P14_reg.gif >>> >>> The wall wart is prefiltered by a C-L-C filter that should buy me >>> about 40 dB at the switcher frequency. Then this thing should be good >>> for maybe 100 more. Then I have some more RCs before the photodiodes >>> and a couple of other critical things. >>> >>> This regulates to 13.4 to allow some headroom here and there. >>> >>> The LM8261 has about 10 nv/rthz noise, which is a whole nother story. >>> >> Try a low noise audio opamp and a depletion mode n-channel. > > Well, I can't spend the rest of my career working on this circuit! >Yup, saw the thread too late, when you mentioned "Gerbers due on Monday".> It would be interesting to power an opamp from the output; then > there's no PSRR problem. A depletion fet would add enough offset so > the thing (might) start up and work. But the fet would be acting > almost resistive at low voltage, so the PSRR thing returns with a > vengence. > > A bipolar PNP, with constant-current base drive (like Tim's circuit) > is interesting, but still has Early feedthrough. A strategicly placed > resistor could null out most of that. > > An RRO opamp, like in my circuit, incorporates the error amp and the > PNP, all in one SOT23. The guys who designed it cared about PSRR and > had a zillion transistors to work with. > > Any attempt to add regulation to a noise filter circuit must inject > the noise of the regulator device into the loop; in my case, it's the > 10 nv per of the LM8261. The loop comp parts can be tweaked to trade > off noise injection versus transient load regulation. > > I *could* spend the rest of my career on this. Maybe I'll toss another > 120 uF polymer cap after the first inductor, and move on with my life. >If it works and is good enough, time to let it go. If not you could add a simple one-transistor cap multiplier into the positive supply of the opamp. Three parts, all tiny.> If I keep changing this board, The Brat will take up patricide. >Aha, I thought that it's the brat pushing you on this project :-) I think my dad would have had a hissy fit if I'd ever done that. He occasionally said "You electrical guys, you don't have a lot of patience, do ya?" -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
