Forums

Cute amplifier - bootstrapped

Started by Unknown January 10, 2013
On Thursday, January 10, 2013 8:44:27 PM UTC-5, Phil Hobbs wrote:
> On 1/10/2013 8:31 PM, bloggs.fredbloggs.fred@gmail.com wrote: >=20 > > On Thursday, January 10, 2013 7:34:26 PM UTC-5, dagmarg...@yahoo.com wr=
ote:
>=20 > >> Adapted from something I saw on the web... >=20 > >> >=20 > >> >=20 > >> >=20 > >> I had to scratch my head until I understood C1: it bootstraps Q1's >=20 > >> >=20 > >> collector load (R2) impedance, turning it effectively into a current >=20 > >> >=20 > >> source. Gain is accordingly greatly increased. G =3D ~220 @ 40KHz. >=20 > >> >=20 > >> >=20 > >> >=20 > >> +3.3V >=20 > >> >=20 > >> --- >=20 > >> >=20 > >> | >=20 > >> >=20 > >> .-------+-------. >=20 > >> >=20 > >> | | >=20 > >> >=20 > >> 5K R1 C1 |/ Q2 >=20 > >> >=20 > >> | 100n .------| 2n5089 >=20 > >> >=20 > >> +---||-|--. |>. >=20 > >> >=20 > >> | | | | >=20 > >> >=20 > >> 15k R2 | '-----+------> >=20 > >> >=20 > >> | | | >=20 > >> >=20 > >> C2 +------' R3 820R >=20 > >> >=20 > >> 10n |/ Q1 | >=20 > >> >=20 > >>> --||-+--| 2n5089 .------+ >=20 > >> >=20 > >> | |>. | | >=20 > >> >=20 > >> | | | R4 470R >=20 > >> >=20 > >> | =3D=3D=3D | | >=20 > >> >=20 > >> | | =3D=3D=3D >=20 > >> >=20 > >> '-----R5------' >=20 > >> >=20 > >> 220k >=20 > >> >=20 > >> >=20 > >> >=20 > >> R3-R4 set the d.c. output level. >=20 > >> >=20 > >> >=20 > >> >=20 > >> Gain is component-sensitive, but the bootstrap is a cute technique. >=20 > >> >=20 > >> That with feedback could stabilize the gain. >=20 > >> >=20 > >> Cheers, >=20 > >> >=20 > >> James Arthur >=20 > > >=20 > > You need to turn that around, it is the emitter follower that is being =
bootstrapped and not the CE. So the CE + CC composite looks like the classi= c very high gain single pole amplifier inside the feedback loop formed by t= he resistor shunt feedback divider, everything is simplified. See the textb= ook write-up here, section 1.17.2:
>=20 > > http://books.google.com/books?id=3D1-jiL0s8y7EC&pg=3DPA78&lpg=3DPA78&dq=
=3Dbootstrapped+emitter+follower&source=3Dbl&ots=3DVm7TxTwrbA&sig=3Dqs8fZul= qYscWBdVuO8TND8jDqI8&hl=3Den&sa=3DX&ei=3DOmnvUMihJ4n49gSmyIHQAw&sqi=3D2&ved= =3D0CC4Q6AEwAA#v=3Donepage&q=3Dbootstrapped%20emitter%20follower&f=3Dfalse
>=20 > > >=20 >=20 >=20 > The output impedance of the follower is probably a few tens of ohms.=20 >=20 > For small signals it doesn't even notice the extra loading on its emitter=
.
>=20 >=20 >=20 > You can bootstrap a follower, in fact you have to if you want the=20 >=20 > bootstrap itself to work properly, but that involves doing something=20 >=20 > with its collector. >=20
Huh? You bootstrap the follower to increase its input impedance, not lower = its output impedance.=20
>=20 >=20 > Cheers >=20 >=20 >=20 > Phil Hobbs >=20 >=20 >=20 > --=20 >=20 > Dr Philip C D Hobbs >=20 > Principal Consultant >=20 > ElectroOptical Innovations LLC >=20 > Optics, Electro-optics, Photonics, Analog Electronics >=20 >=20 >=20 > 160 North State Road #203 >=20 > Briarcliff Manor NY 10510 USA >=20 > +1 845 480 2058 >=20 >=20 >=20 > hobbs at electrooptical dot net >=20 > http://electrooptical.net
On Thu, 10 Jan 2013 17:36:46 -0800 (PST),
bloggs.fredbloggs.fred@gmail.com wrote:

>On Thursday, January 10, 2013 8:08:12 PM UTC-5, John Larkin wrote: >> >> >> https://dl.dropbox.com/u/53724080/Circuits/Current_Sources/Isrc_5.JPG >> >> > >How did that eventually work out?
I didn't used it, actually. I did use this one https://dl.dropbox.com/u/53724080/Circuits/Current_Sources/TDC_Bootstrap_Ramp.jpg which is simpler but doesn't have adjustable slope. One could include R28 or R36 to add a little 2nd order curvature correction to improve linearity. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
<weird double spaced stuff snipped>

The follower's input impedance is limited by its beta and Early voltage 
at low frequency, and its C_cb at high frequency.  Beta you can't do too 
much about, but Early and C_cb you can fix by bootstrapping its 
collector.  You can't improve the SNR, but you can make the frequency 
response and Zin much prettier.

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510 USA
+1 845 480 2058

hobbs at electrooptical dot net
http://electrooptical.net
On Jan 10, 8:08=A0pm, John Larkin <jlar...@highlandtechnology.com>
wrote:
> On Thu, 10 Jan 2013 16:34:26 -0800 (PST), dagmargoodb...@yahoo.com > wrote: > > > > > > > > > > >Adapted from something I saw on the web... > > >I had to scratch my head until I understood C1: it bootstraps Q1's > >collector load (R2) impedance, turning it effectively into a current > >source. =A0Gain is accordingly greatly increased. G =3D ~220 @ 40KHz. > > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 +3.3V > > =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 5K R1 =A0C1 =A0 =A0 =A0 =A0 |/ =A0Q2 > > =A0 =A0 =A0 =A0 =A0 | 100n .------| =A02n5089 > > =A0 =A0 =A0 =A0 =A0 +---||-|--. =A0 |>. > > =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0| =A0| =A0 =A0 | > > =A0 =A0 =A015k R2 =A0 =A0 =A0| =A0'-----+------> > > =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0| =A0 =A0 =A0 =A0| > > =A0 C2 =A0 =A0 =A0+------' =A0 =A0 =A0 R3 820R > > =A0 10n =A0 |/ Q1 =A0 =A0 =A0 =A0 =A0 =A0 | > >>--||-+--| =A02n5089 =A0.------+ > > =A0 =A0 =A0| =A0|>. =A0 =A0 =A0 =A0| =A0 =A0 =A0| > > =A0 =A0 =A0| =A0 =A0| =A0 =A0 =A0 =A0| =A0 =A0 R4 470R > > =A0 =A0 =A0| =A0 =3D=3D=3D =A0 =A0 =A0 | =A0 =A0 =A0| > > =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =3D=3D=3D > > =A0 =A0 =A0'-----R5------' > > =A0 =A0 =A0 =A0 =A0 220k > > >R3-R4 set the d.c. output level. > > >Gain is component-sensitive, but the bootstrap is a cute technique. > >That with feedback could stabilize the gain. > > Bootstrapping rocks. This thing improves the constant-current-ness of > a linear ramp generator at higher speeds.... > > https://dl.dropbox.com/u/53724080/Circuits/Current_Sources/Isrc_5.JPG
I remember that trick of yours. Fun.
> Phil does some uber-bootstrapped stuff with jfet front ends. He sort > of bootstraps the entire planet, or the entire universe, all around a > BF862.
One of the neatest I've seen was a VLF JFET amplifier. It used transformers to bootstrap its input capacitance to nada. James
On Thu, 10 Jan 2013 20:44:27 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 1/10/2013 8:31 PM, bloggs.fredbloggs.fred@gmail.com wrote: >> On Thursday, January 10, 2013 7:34:26 PM UTC-5, dagmarg...@yahoo.com wrote: >>> Adapted from something I saw on the web... >>> >>> >>> >>> I had to scratch my head until I understood C1: it bootstraps Q1's >>> >>> collector load (R2) impedance, turning it effectively into a current >>> >>> source. Gain is accordingly greatly increased. G = ~220 @ 40KHz. >>> >>> >>> >>> +3.3V >>> >>> --- >>> >>> | >>> >>> .-------+-------. >>> >>> | | >>> >>> 5K R1 C1 |/ Q2 >>> >>> | 100n .------| 2n5089 >>> >>> +---||-|--. |>. >>> >>> | | | | >>> >>> 15k R2 | '-----+------> >>> >>> | | | >>> >>> C2 +------' R3 820R >>> >>> 10n |/ Q1 | >>> >>>> --||-+--| 2n5089 .------+ >>> >>> | |>. | | >>> >>> | | | R4 470R >>> >>> | === | | >>> >>> | | === >>> >>> '-----R5------' >>> >>> 220k >>> >>> >>> >>> R3-R4 set the d.c. output level. >>> >>> >>> >>> Gain is component-sensitive, but the bootstrap is a cute technique. >>> >>> That with feedback could stabilize the gain. >>> >>> Cheers, >>> >>> James Arthur >> >> You need to turn that around, it is the emitter follower that is being bootstrapped and not the CE. So the CE + CC composite looks like the classic very high gain single pole amplifier inside the feedback loop formed by the resistor shunt feedback divider, everything is simplified. See the textbook write-up here, section 1.17.2: >> http://books.google.com/books?id=1-jiL0s8y7EC&pg=PA78&lpg=PA78&dq=bootstrapped+emitter+follower&source=bl&ots=Vm7TxTwrbA&sig=qs8fZulqYscWBdVuO8TND8jDqI8&hl=en&sa=X&ei=OmnvUMihJ4n49gSmyIHQAw&sqi=2&ved=0CC4Q6AEwAA#v=onepage&q=bootstrapped%20emitter%20follower&f=false >> > >The output impedance of the follower is probably a few tens of ohms. >For small signals it doesn't even notice the extra loading on its emitter. > >You can bootstrap a follower, in fact you have to if you want the >bootstrap itself to work properly, but that involves doing something >with its collector. > >Cheers > >Phil Hobbs
We bootstrapped a unity-gain 5-volt chopamp to let it follow +-40 volt swings. That was a bear to get working correctly and reliably. The PSRR of the amp was negative (ie, it had gain from power rail to output) at some frequencies. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
On Jan 10, 8:13=A0pm, Phil Hobbs
<pcdhSpamMeSensel...@electrooptical.net> wrote:
> On 1/10/2013 7:34 PM, dagmargoodb...@yahoo.com wrote: > > > > > > > > > > > Adapted from something I saw on the web... > > > I had to scratch my head until I understood C1: it bootstraps Q1's > > collector load (R2) impedance, turning it effectively into a current > > source. =A0Gain is accordingly greatly increased. G =3D ~220 @ 40KHz. > > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 +3.3V > > =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 5K R1 =A0C1 =A0 =A0 =A0 =A0 |/ =A0Q2 > > =A0 =A0 =A0 =A0 =A0 =A0 | 100n .------| =A02n5089 > > =A0 =A0 =A0 =A0 =A0 =A0 +---||-|--. =A0 |>. > > =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0| =A0| =A0 =A0 | > > =A0 =A0 =A0 =A015k R2 =A0 =A0 =A0| =A0'-----+------> > > =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0| =A0 =A0 =A0 =A0| > > =A0 =A0 C2 =A0 =A0 =A0+------' =A0 =A0 =A0 R3 820R > > =A0 =A0 10n =A0 |/ Q1 =A0 =A0 =A0 =A0 =A0 =A0 | > >> --||-+--| =A02n5089 =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 R4 470R > > =A0 =A0 =A0 =A0| =A0 =3D=3D=3D =A0 =A0 =A0 | =A0 =A0 =A0| > > =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =3D=3D=3D > > =A0 =A0 =A0 =A0'-----R5------' > > =A0 =A0 =A0 =A0 =A0 =A0 220k > > > R3-R4 set the d.c. output level. > > > Gain is component-sensitive, but the bootstrap is a cute technique. > > That with feedback could stabilize the gain. > > > Except for the Early effect in Q1.
I made a cascode version, but that was getting silly. A dual op-amp makes more sense at that point with fewer parts. Talking about silly, a little positive feedback really makes it sing... +3.3V --- | .-------+-------. | | 5K R1 C1 |/ Q2 | 22n .------| 2n5089 +---||-|--. |>. | | | | 15k R2 | '-----+------> | | | C2 +------' R3 820R 10n |/ Q1 |
>--||-+--| 2n5089 .------+
| |>. | | | | | R4 470R | | | | | +---------------' | | | | R6 3r3 | | | | | =3D=3D=3D | | | '-----R5------' 220k G=3D 1050 @ 40KHz. There actually is some negative feedback via R5--that stabilizes the gain a little bit. -- Cheers, James Arthur
On Jan 10, 8:32=A0pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-
Web-Site.com> wrote:
> On Thu, 10 Jan 2013 20:13:12 -0500, Phil Hobbs > > > > > > > > > > <pcdhSpamMeSensel...@electrooptical.net> wrote: > >On 1/10/2013 7:34 PM, dagmargoodb...@yahoo.com wrote: > >> Adapted from something I saw on the web... > > >> I had to scratch my head until I understood C1: it bootstraps Q1's > >> collector load (R2) impedance, turning it effectively into a current > >> source. =A0Gain is accordingly greatly increased. G =3D ~220 @ 40KHz. > > >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 +3.3V > >> =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 5K R1 =A0C1 =A0 =A0 =A0 =A0 |/ =A0Q2 > >> =A0 =A0 =A0 =A0 =A0 =A0 | 100n .------| =A02n5089 > >> =A0 =A0 =A0 =A0 =A0 =A0 +---||-|--. =A0 |>. > >> =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0| =A0| =A0 =A0 | > >> =A0 =A0 =A0 =A015k R2 =A0 =A0 =A0| =A0'-----+------> > >> =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0| =A0 =A0 =A0 =A0| > >> =A0 =A0 C2 =A0 =A0 =A0+------' =A0 =A0 =A0 R3 820R > >> =A0 =A0 10n =A0 |/ Q1 =A0 =A0 =A0 =A0 =A0 =A0 | > >>> --||-+--| =A02n5089 =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 R4 470R > >> =A0 =A0 =A0 =A0| =A0 =3D=3D=3D =A0 =A0 =A0 | =A0 =A0 =A0| > >> =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =3D=3D=3D > >> =A0 =A0 =A0 =A0'-----R5------' > >> =A0 =A0 =A0 =A0 =A0 =A0 220k > > >> R3-R4 set the d.c. output level. > > >> Gain is component-sensitive, but the bootstrap is a cute technique. > >> That with feedback could stabilize the gain. > > >> -- > >> Cheers, > >> James Arthur > > >Except for the Early effect in Q1. > > >Cheers > > >Phil Hobbs > > Except for the shunt-feedback >:-} > > The whole thing is a bit crappy. > > Here's how to do it... > > =A0 =A0 =A0http://www.analog-innovations.com/SED/MC1552-DataSheet.pdf
That's plenty cute--a three-transistor inverting amp, with feedback, then an emitter follower, plus the bias stuff. But is there a bootstrapped collector load in the signal chain? I didn't see it. -- Cheers, James Arthur
On Thursday, January 10, 2013 9:03:23 PM UTC-5, Phil Hobbs wrote:
> <weird double spaced stuff snipped> > > > > The follower's input impedance is limited by its beta and Early voltage > > at low frequency, and its C_cb at high frequency. Beta you can't do too > > much about, but Early and C_cb you can fix by bootstrapping its > > collector. You can't improve the SNR, but you can make the frequency > > response and Zin much prettier. >
Okay, those are fine points, but in this case the designer is trying to eliminate the shunt effect of the emitter follower input bias resistor network, and the bootstrapping succeeds well there.
On 1/10/2013 9:34 PM, bloggs.fredbloggs.fred@gmail.com wrote:
> On Thursday, January 10, 2013 9:03:23 PM UTC-5, Phil Hobbs wrote: >> <weird double spaced stuff snipped> >> >> >> >> The follower's input impedance is limited by its beta and Early voltage >> >> at low frequency, and its C_cb at high frequency. Beta you can't do too >> >> much about, but Early and C_cb you can fix by bootstrapping its >> >> collector. You can't improve the SNR, but you can make the frequency >> >> response and Zin much prettier. >> > > Okay, those are fine points, but in this case the designer is trying to eliminate the shunt effect of the emitter follower input bias resistor network, and the bootstrapping succeeds well there. >
That's sort of a strange way to look at it. The common-emitter stage wouldn't do much without those resistors, so I'd identify them as the collector load of the first stage rather than an input network for the second stage. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 USA +1 845 480 2058 hobbs at electrooptical dot net http://electrooptical.net
On Thu, 10 Jan 2013 18:20:19 -0800 (PST), dagmargoodboat@yahoo.com wrote:

>On Jan 10, 8:32&#2013266080;pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My- >Web-Site.com> wrote: >> On Thu, 10 Jan 2013 20:13:12 -0500, Phil Hobbs >> >> >> >> >> >> >> >> >> >> <pcdhSpamMeSensel...@electrooptical.net> wrote: >> >On 1/10/2013 7:34 PM, dagmargoodb...@yahoo.com wrote: >> >> Adapted from something I saw on the web... >> >> >> I had to scratch my head until I understood C1: it bootstraps Q1's >> >> collector load (R2) impedance, turning it effectively into a current >> >> source. &#2013266080;Gain is accordingly greatly increased. G = ~220 @ 40KHz. >> >> >> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; +3.3V >> >> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080;--- >> >> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; | >> >> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; .-------+-------. >> >> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; | >> >> &#2013266080; &#2013266080; &#2013266080; &#2013266080; 5K R1 &#2013266080;C1 &#2013266080; &#2013266080; &#2013266080; &#2013266080; |/ &#2013266080;Q2 >> >> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; | 100n .------| &#2013266080;2n5089 >> >> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; +---||-|--. &#2013266080; |>. >> >> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080;| &#2013266080;| &#2013266080; &#2013266080; | >> >> &#2013266080; &#2013266080; &#2013266080; &#2013266080;15k R2 &#2013266080; &#2013266080; &#2013266080;| &#2013266080;'-----+------> >> >> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080;| &#2013266080; &#2013266080; &#2013266080; &#2013266080;| >> >> &#2013266080; &#2013266080; C2 &#2013266080; &#2013266080; &#2013266080;+------' &#2013266080; &#2013266080; &#2013266080; R3 820R >> >> &#2013266080; &#2013266080; 10n &#2013266080; |/ Q1 &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; | >> >>> --||-+--| &#2013266080;2n5089 &#2013266080;.------+ >> >> &#2013266080; &#2013266080; &#2013266080; &#2013266080;| &#2013266080;|>. &#2013266080; &#2013266080; &#2013266080; &#2013266080;| &#2013266080; &#2013266080; &#2013266080;| >> >> &#2013266080; &#2013266080; &#2013266080; &#2013266080;| &#2013266080; &#2013266080;| &#2013266080; &#2013266080; &#2013266080; &#2013266080;| &#2013266080; &#2013266080; R4 470R >> >> &#2013266080; &#2013266080; &#2013266080; &#2013266080;| &#2013266080; === &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; &#2013266080;| >> >> &#2013266080; &#2013266080; &#2013266080; &#2013266080;| &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; | &#2013266080; &#2013266080; === >> >> &#2013266080; &#2013266080; &#2013266080; &#2013266080;'-----R5------' >> >> &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; &#2013266080; 220k >> >> >> R3-R4 set the d.c. output level. >> >> >> Gain is component-sensitive, but the bootstrap is a cute technique. >> >> That with feedback could stabilize the gain. >> >> >> -- >> >> Cheers, >> >> James Arthur >> >> >Except for the Early effect in Q1. >> >> >Cheers >> >> >Phil Hobbs >> >> Except for the shunt-feedback >:-} >> >> The whole thing is a bit crappy. >> >> Here's how to do it... >> >> &#2013266080; &#2013266080; &#2013266080;http://www.analog-innovations.com/SED/MC1552-DataSheet.pdf > >That's plenty cute--a three-transistor inverting amp, with feedback, >then an emitter follower, plus the bias stuff. But is there a >bootstrapped collector load in the signal chain? I didn't see it.
Not to thread-drift or anything (who, me?) but similar toplogies are, if possible, even more ancient than JT. This is the once-famous "GE circuit", widely used for phono and tape preamps. https://dl.dropbox.com/u/53724080/Circuits/GEcircuit.jpg I wouldn't be surprised if there were a tube ancestor. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators