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Cute amplifier - bootstrapped

Started by Unknown January 10, 2013
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
On Thu, 10 Jan 2013 16:34:26 -0800 (PST), dagmargoodboat@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.
Commonly done in class-B output stages to get closer to rail-to-rail behavior. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On Jan 10, 7:36=A0pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-
Web-Site.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. > > Commonly done in class-B output stages to get closer to rail-to-rail > behavior.
That's another advantage. -- Cheers, James Arthur
On Thu, 10 Jan 2013 16:34:26 -0800 (PST), dagmargoodboat@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.
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 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. -- 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 1/10/2013 7:34 PM, dagmargoodboat@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 >
Except for the Early effect in Q1. 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 1/10/2013 8:08 PM, John Larkin wrote:
> On Thu, 10 Jan 2013 16:34:26 -0800 (PST), dagmargoodboat@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. > > 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 > > 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. > >
Bootstraps are fun. I'm doing one right now for a surface voltage tool for a semiconductor equipment maker. Even with vaguely realistic strays, SPICE says that the bootstrap gain is between 0.9995 and 0.9998 over the frequency band of interest. I actually get to build this one, so we'll see. Doesn't fix the noise due to the bootstrapped capacitance differentiating the BF862's voltage noise, but since that's about 0.8 nV in 1 Hz, going lower is hard unless the external capacitance is large. My best ones so far use series-shunt feedback around the BF862, to get a lower source impedance without increasing the noise, and then bootstrap the whole works. You can also put the bootstrap inside the series-shunt loop, which has some minor noise advantage (since the bootstrap device's noise is inside the loop) but makes the compensation really squirrelly at high frequency. 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 Thursday, January 10, 2013 7:34:26 PM UTC-5, dagmarg...@yahoo.com wrote:
> Adapted from something I saw on the web... >=20 >=20 >=20 > I had to scratch my head until I understood C1: it bootstraps Q1's >=20 > collector load (R2) impedance, turning it effectively into a current >=20 > source. Gain is accordingly greatly increased. G =3D ~220 @ 40KHz. >=20 >=20 >=20 > +3.3V >=20 > --- >=20 > | >=20 > .-------+-------. >=20 > | | >=20 > 5K R1 C1 |/ Q2 >=20 > | 100n .------| 2n5089 >=20 > +---||-|--. |>. >=20 > | | | | >=20 > 15k R2 | '-----+------> >=20 > | | | >=20 > C2 +------' R3 820R >=20 > 10n |/ Q1 | >=20 > >--||-+--| 2n5089 .------+ >=20 > | |>. | | >=20 > | | | R4 470R >=20 > | =3D=3D=3D | | >=20 > | | =3D=3D=3D >=20 > '-----R5------' >=20 > 220k >=20 >=20 >=20 > R3-R4 set the d.c. output level. >=20 >=20 >=20 > Gain is component-sensitive, but the bootstrap is a cute technique. >=20 > That with feedback could stabilize the gain. >=20 >=20 >=20 > -- >=20 > Cheers, >=20 > James Arthur
You need to turn that around, it is the emitter follower that is being boot= strapped and not the CE. So the CE + CC composite looks like the classic ve= ry high gain single pole amplifier inside the feedback loop formed by the r= esistor shunt feedback divider, everything is simplified. See the textbook = write-up here, section 1.17.2: http://books.google.com/books?id=3D1-jiL0s8y7EC&pg=3DPA78&lpg=3DPA78&dq=3Db= ootstrapped+emitter+follower&source=3Dbl&ots=3DVm7TxTwrbA&sig=3Dqs8fZulqYsc= WBdVuO8TND8jDqI8&hl=3Den&sa=3DX&ei=3DOmnvUMihJ4n49gSmyIHQAw&sqi=3D2&ved=3D0= CC4Q6AEwAA#v=3Donepage&q=3Dbootstrapped%20emitter%20follower&f=3Dfalse
On Thu, 10 Jan 2013 20:13:12 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 1/10/2013 7:34 PM, dagmargoodboat@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 >> > >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... http://www.analog-innovations.com/SED/MC1552-DataSheet.pdf Or broken out for analysis, from a previous post... http://www.analog-innovations.com/SED/MC1552LookAlike.pdf ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
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?
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 -- 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