How much phase shift is necessary between stages before "a shitload of amps 
in parallel" is called "distributed amplifier"?  And what is the role of 
that phase shift, what does it actually accomplish?  Like, why not put a 
bunch of amps in a circle and feed their outputs radially towards the center 
and skip the phase shift BS?

Tim

-- 
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms 

Tim Williams wrote:
> How much phase shift is necessary between stages before "a shitload of amps 
> in parallel" is called "distributed amplifier"?  And what is the role of 
> that phase shift, what does it actually accomplish?  Like, why not put a 
> bunch of amps in a circle and feed their outputs radially towards the center 
> and skip the phase shift BS?
> 
> Tim
> 
Phase shift is not the objective, it's the consequence.
Each amplifier has some input impedance.
If you drive them all in parallel, you get LOW impedance.
If you make them elements of a distributed transmission line,
you make the whole thing easier to drive.  Ditto on the output.

On Sat, 9 Jan 2010 23:29:22 -0600, "Tim Williams"
<t...@charter.net> wrote:

>How much phase shift is necessary between stages before "a shitload of amps 
>in parallel" is called "distributed amplifier"?  And what is the role of 
>that phase shift, what does it actually accomplish?  Like, why not put a 
>bunch of amps in a circle and feed their outputs radially towards the center 
>and skip the phase shift BS?
>
>Tim

A distributed amp forms a transmission line from inductors (or
t-coils) and a bunch of grid/gate capacitances, and another
transmission line from inductors and the plate/drain capacitances.
Such a transmission line can be very long and keep a fairly constant
bandwidth. 

This structure allows you to put the tranconductances of all the gain
things in parallel without the capacitances being in parallel, so GBW
goes up. Putting tubes or fets directly in parallel increases
transconductance and capacitance together, so GBW doesn't get better.

A more fundamental concept is that a transmission line charges a lot
of capacitance, but only one bit at a time, by spreading out the
charging in time. A distributed amp trades time delay for GBW.

ftp://jjlarkin.lmi.net/DistAmp.JPG

The really fast e/o modulator drivers, DC to 20 or maybe 40 GHz, are
GaAs integrated distributed amps.

http://www.hittite.com/products/view.html/view/HMC465LP5

John

On Sat, 9 Jan 2010 23:29:22 -0600, "Tim Williams"
<t...@charter.net> wrote:

>How much phase shift is necessary between stages before "a shitload of amps 
>in parallel" is called "distributed amplifier"?  And what is the role of 
>that phase shift, what does it actually accomplish?  Like, why not put a 
>bunch of amps in a circle and feed their outputs radially towards the center 
>and skip the phase shift BS?

As already pointed out, the input and output capacitances would be in
parallel. The failure of a single component could take down the whole
system.

A similar way to avoid this kind of problems is to use the Wilkinson
power divider to split the input signal into several paths to be
amplified and combining them back again with an other Wilkinson power
divider. This has been often used to combine a large number of medium
power transmitter modules to produce similar power levels than a big
transmitter tube. 

The failure of a single module only drops the total output power with
that amount, but it does not affect the operation of the other
modules.

On Jan 10, 6:29=A0am, "Tim Williams" <tmoran...@charter.net> wrote:
> How much phase shift is necessary between stages before "a shitload of am=
ps
> in parallel" is called "distributed amplifier"? =A0And what is the role o=
f
> that phase shift, what does it actually accomplish? =A0Like, why not put =
a
> bunch of amps in a circle and feed their outputs radially towards the cen=
ter
> and skip the phase shift BS?

It's the Percival distributed amplifer - he patented it back in 1936
when he was working on the EMI televison project

http://en.wikipedia.org/wiki/Distributed_amplifier

Blumlein produced a lot more patents, but Percival managed to survive
the war, and was stiil working at EMI Central Research in West London
when I worked there from 1976 to 1979.

I know about his distributed amplifier before I went to work there,
and pleased when I got to meet him, when he grilled me about some work
that I was doing. Sadly the answers I gave him weren't the ones that
he wanted to hear.

--
Bill Sloman, Nijmegen

On a sunny day (Sat, 09 Jan 2010 21:55:13 -0800) it happened John Larkin
<j...@highNOTlandTHIStechnologyPART.com> wrote in
<l...@4ax.com>:

>On Sat, 9 Jan 2010 23:29:22 -0600, "Tim Williams"
><t...@charter.net> wrote:
>
>>How much phase shift is necessary between stages before "a shitload of amps 
>>in parallel" is called "distributed amplifier"?  And what is the role of 
>>that phase shift, what does it actually accomplish?  Like, why not put a 
>>bunch of amps in a circle and feed their outputs radially towards the center 
>>and skip the phase shift BS?
>>
>>Tim
>
>A distributed amp forms a transmission line from inductors (or
>t-coils) and a bunch of grid/gate capacitances, and another
>transmission line from inductors and the plate/drain capacitances.
>Such a transmission line can be very long and keep a fairly constant
>bandwidth. 
>
>This structure allows you to put the tranconductances of all the gain
>things in parallel without the capacitances being in parallel, so GBW
>goes up. Putting tubes or fets directly in parallel increases
>transconductance and capacitance together, so GBW doesn't get better.
>
>A more fundamental concept is that a transmission line charges a lot
>of capacitance, but only one bit at a time, by spreading out the
>charging in time. A distributed amp trades time delay for GBW.
>
>ftp://jjlarkin.lmi.net/DistAmp.JPG
>
>The really fast e/o modulator drivers, DC to 20 or maybe 40 GHz, are
>GaAs integrated distributed amps.
>
>http://www.hittite.com/products/view.html/view/HMC465LP5

WOW!
But 238 $ for RoHS...
Good to know it exists though.

>John
>
>

On a sunny day (Sun, 10 Jan 2010 00:01:51 -0800 (PST)) it happened Bill Sloman
<b...@ieee.org> wrote in
<d...@k17g2000yqh.googlegroups.com>:

>On Jan 10, 6:29 am, "Tim Williams" <tmoran...@charter.net> wrote:
>> How much phase shift is necessary between stages before "a shitload of am=
>ps
>> in parallel" is called "distributed amplifier"?  And what is the role o=
>f
>> that phase shift, what does it actually accomplish?  Like, why not put =
>a
>> bunch of amps in a circle and feed their outputs radially towards the cen=
>ter
>> and skip the phase shift BS?
>
>It's the Percival distributed amplifer - he patented it back in 1936
>when he was working on the EMI televison project
>
>http://en.wikipedia.org/wiki/Distributed_amplifier
>
>Blumlein produced a lot more patents, but Percival managed to survive
>the war, and was stiil working at EMI Central Research in West London
>when I worked there from 1976 to 1979.
>
>I know about his distributed amplifier before I went to work there,
>and pleased when I got to meet him, when he grilled me about some work
>that I was doing. Sadly the answers I gave him weren't the ones that
>he wanted to hear.

So he did not believe in global warming either, so what.

John Larkin wrote:
> On Sat, 9 Jan 2010 23:29:22 -0600, "Tim Williams"
> <t...@charter.net> wrote:
> 
> 
>>How much phase shift is necessary between stages before "a shitload of amps 
>>in parallel" is called "distributed amplifier"?  And what is the role of 
>>that phase shift, what does it actually accomplish?  Like, why not put a 
>>bunch of amps in a circle and feed their outputs radially towards the center 
>>and skip the phase shift BS?

> A distributed amp forms a transmission line from inductors (or
> t-coils) and a bunch of grid/gate capacitances, and another
> transmission line from inductors and the plate/drain capacitances.
> Such a transmission line can be very long and keep a fairly constant
> bandwidth. 
> 
> This structure allows you to put the tranconductances of all the gain
> things in parallel without the capacitances being in parallel, so GBW
> goes up. Putting tubes or fets directly in parallel increases
> transconductance and capacitance together, so GBW doesn't get better.

It could be difficult to match the operating conditions for devices 
connected in parallel; parallel is also prone to parasitic differential 
mode oscillations.

> A more fundamental concept is that a transmission line charges a lot
> of capacitance, but only one bit at a time, by spreading out the
> charging in time. A distributed amp trades time delay for GBW.
> 
> ftp://jjlarkin.lmi.net/DistAmp.JPG
> 
> The really fast e/o modulator drivers, DC to 20 or maybe 40 GHz, are
> GaAs integrated distributed amps.
> 
> http://www.hittite.com/products/view.html/view/HMC465LP5

Long while ago, I worked with the distributed RF power amps using tubes. 
Somewhat 1.5kW of linear power from 30 to 100 MHz without tunning.
The problem with it is different operating conditions for every active 
device: while going forward, the input wave gets weaker, and the output 
wave gets stronger. This results in lower power efficiency and gain. 
Each device can be used with different matching, and/or the line 
impeadances could be made variable; however it makes the amp complicated 
and narrows down the GBW.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

On Jan 10, 2:25=A0pm, Jan Panteltje <pNaonStpealm...@yahoo.com> wrote:
> On a sunny day (Sun, 10 Jan 2010 00:01:51 -0800 (PST)) it happened Bill S=
loman
> <bill.slo...@ieee.org> wrote in
> <d802f538-3334-4bd4-9216-672343dd1...@k17g2000yqh.googlegroups.com>:
>
>
>
>
>
> >On Jan 10, 6:29=A0am, "Tim Williams" <tmoran...@charter.net> wrote:
> >> How much phase shift is necessary between stages before "a shitload of=
 am=3D
> >ps
> >> in parallel" is called "distributed amplifier"? =A0And what is the rol=
e o=3D
> >f
> >> that phase shift, what does it actually accomplish? =A0Like, why not p=
ut =3D
> >a
> >> bunch of amps in a circle and feed their outputs radially towards the =
cen=3D
> >ter
> >> and skip the phase shift BS?
>
> >It's the Percival distributed amplifer - he patented it back in 1936
> >when he was working on the EMI televison project
>
> >http://en.wikipedia.org/wiki/Distributed_amplifier
>
> >Blumlein produced a lot more patents, but Percival managed to survive
> >the war, and was stiil working at EMI Central Research in West London
> >when I worked there from 1976 to 1979.
>
> >I know about his distributed amplifier before I went to work there,
> >and pleased when I got to meet him, when he grilled me about some work
> >that I was doing. Sadly the answers I gave him weren't the ones that
> >he wanted to hear.
>
> So he did not believe in global warming either, so what.

Back in 1978, global warming wasn't a topic of any direct interest to
EMI Central Research and we certainly didn't discuss it.

And I don't recall him being sceptical about what I told him (whateer
it was) - he had hoped that the situation was different from the one I
laid out, but he hadn't had any strong expectations either way.

--
Bill Sloman, Nijmegen

On Jan 9, 9:29=A0pm, "Tim Williams" <tmoran...@charter.net> wrote:
> How much phase shift is necessary between stages before "a shitload of am=
ps
> in parallel" is called "distributed amplifier"? =A0And what is the role o=
f
> that phase shift, what does it actually accomplish? =A0Like, why not put =
a
> bunch of amps in a circle and feed their outputs radially towards the cen=
ter
> and skip the phase shift BS?

As you go from one amplifier to the next, there is a delay in the
output side
of things.  You need to match this on the input side.  A cute device
that I
have long wanted to make just for the fun is a distributed parametric
amplifier
like this:



-------+--------+-------A Repeat
       !        !
      =3D=3D=3D       V
       ^       =3D=3D=3D
       !        !
 ------++---------------C
        !       !
 --------------++-------D
        !      !
        V     =3D=3D=3D
       =3D=3D=3D     ^
        !      !
--------+------+--------B


The AB line is carrying the signal and the CD line is carrying the
pump.
At each point along the cable some of the pump energy is converted to
the "sum" energy.  Because the signal is a lot less than the pump or
the
sum, less of it goes towards making the sum.  When you get to the far
end
the pump and the input signal are mostly gone and only the "sum"
signal
is used.  A nice thing about such devices is that they are extremely
low
noise because there is no interaction with heat of the devices and no
electrons are working alone.

The trick would be making the speed of the lines work out right so
that
the adding is always exactly in phase in the forward direction.