C-multiplier again
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From: Joerg on 24 May 2010 11:13 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.
From: Joerg on 24 May 2010 11:18 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.
From: Joerg on 24 May 2010 11:19 John Larkin wrote: > 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. > 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.
From: Phil Hobbs on 24 May 2010 14:35 On 5/24/2010 2:12 AM, John Larkin wrote: > 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 > That's limited by the CMR of the op amp, though, which blows the whole thing out of the water--no? That's the point of using the BJT in the first place. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
From: Phil Hobbs on 24 May 2010 14:39
On 5/24/2010 8:09 AM, Mike wrote: > 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 > Like I said, it's basically C_CE/C_BFC. You pick a transistor with reasonable characteristics at frequencies you care about, drive its base from a really really filtered version of V_CC--with a resistor in series to make sure it doesn't oscillate and doesn't blow up if the input or output gets shorted--and put a BFC at the output. If the transistor has 10 pF C_CB and the BFC is 100 uF, that's 140 dB, provided you look after other stuff such as the Early voltage and the ESR of the output cap. Generally if your application needs more than 100 dB of ripple rejection, you have to be pretty careful. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net |