C-multiplier again
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From: Vladimir Vassilevsky on 23 May 2010 22:59 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
From: Tim Williams on 23 May 2010 23:21 "Tim Williams" <tmoranwms(a)charter.net> wrote in message news:htco92$nqn$1(a)news.eternal-september.org... > "Joerg" <invalid(a)invalid.invalid> wrote in message > news:85u0ihFmddU1(a)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
From: dagmargoodboat on 24 May 2010 00:45 On May 23, 9:44 pm, Phil Hobbs <pcdhSpamMeSensel...(a)electrooptical.net> wrote: > Winfield Hill wrote: > > dagmargoodb...(a)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. -- Cheers, James Arthur
From: John Larkin on 24 May 2010 02:12 On Sun, 23 May 2010 21:45:06 -0700 (PDT), dagmargoodboat(a)yahoo.com wrote: >On May 23, 9:44�pm, Phil Hobbs ><pcdhSpamMeSensel...(a)electrooptical.net> wrote: >> Winfield Hill wrote: >> > dagmargoodb...(a)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
From: Mike on 24 May 2010 08:09
Phil Hobbs <pcdhSpamMeSenseless(a)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 Hobbs Phil, 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 |