I am looking for an output amplifier for a signal generator

Winfield Hill wrote:
Harry Dellamano wrote...

Winfield Hill wrote ...

... I get a total transistor count of 22.

Very nice Ban and Win. I count 20 transistors with the
current sources added. What have I missed?


Use a better current-source, e.g., Wilson mirror, etc.
Click to expand...
nice piece of hardware , but is not present in your book :)

Mr Hill , many thanks for your work, it's an enourmuos collection of
info on electronic technology ( I have some doubt about the WOM memory
..... )

I think to reserve this design for another application where I probably
need a bit more output voltage and current

but I need some clarification

1) can I use non SMD parts, good old 2n2222 etc. ?

2) can I modifie the feedback network ( 499 - 499 resistor ) or even
consider the circuit as a discrete component OA ?

3) can I parallel some more output transistor ?

at +-25 volt supply can be a very nice beast
 
Winfield Hill wrote:
John Larkin wrote...

Maybe cast an eyeball at THS3062. +-15 supplies, 7000 v/usec, dual,
300 MHz, isolated powerpad. I like to run one section as a gain stage,
then three as pure followers (no overall fb) each with 150 ohms to the
output node. This is TI's fast 30-volt process, one of the few around.
They're rated at 140 mA or something, but really get droopy (and hot!)
if you push them that hard, hence the paralleled sections.


Yes, very nice. John, can you tell us your recommendations for
effectively using TI's PowerPad thermal path in prototype assembly?
Click to expand...
I am bit curious too , the power pad is around 2mm x 2.5 mmm

perhaps I will use a small strip of copper but .....

I the meanwhile I found two interesting chip from texas 'improved AD815'

ths6032
ths6012

so-powerpad too but a bit bigger ....

do the paralleling of op amps is a routine ( with output resistors ) or
not ?
 
mmm wrote...
Winfield Hill wrote:
Harry Dellamano wrote...
Winfield Hill wrote ...

... I get a total transistor count of 22.

Very nice Ban and Win. I count 20 transistors with the
current sources added. What have I missed?

Use a better current-source, e.g., Wilson mirror, etc.

nice piece of hardware , but is not present in your book :)
Click to expand...
See figure 2.48

Mr Hill , many thanks for your work, it's an enourmuos collection
of info on electronic technology ( I have some doubt about the
WOM memory .... )

I think to reserve this design for another application where I
probably need a bit more output voltage and current

but I need some clarification

1) can I use non SMD parts, good old 2n2222 etc. ?

2) can I modifie the feedback network ( 499 - 499 resistor )
or even consider the circuit as a discrete component OA ?

3) can I parallel some more output transistor ?

at +-25 volt supply can be a very nice beast
Click to expand...
Yes.


--
Thanks,
- Win
 
Hello Ken,

The LH0063 IIRC ws even faster. ...
Click to expand...
They are great. But I guess the market for those was too small.

Regards, Joerg

http://www.analogconsultants.com
 
Winfield Hill wrote:
mmm wrote...


Very nice Ban and Win. I count 20 transistors with the
current sources added. What have I missed?

Use a better current-source, e.g., Wilson mirror, etc.

nice piece of hardware , but is not present in your book :)


See figure 2.48
Click to expand...
not the Wilson current mirror .... but the high speed amplifier as a whole.

I was already aware of the presence in the book of the current mirrors
as 'programmable' current source.
 
In article <j9Ave.2423$Uc2.1902@trnddc03>,
Harry Dellamano <harryd@tdsystems.org> wrote:

Something worries me about this circuit. I'm going to add voltages
Modified:
. ---+---+---------------+----+----+----+----- +25
. | | 10mA | | | |
. (I) (I) | | | |
. 20mA | | _ |/ |/ |/ |/
. | +---------U---|----|-----|----| fzt2222a
. | | bead |> |> |> |
. fzt2222a | | | | | |
. ,---)---)----, | | | |
. |/ | \| | .-. .-. .-. .-. 4.7
. +--| | |--+ | | | | | | | |
. | |> | <| | | | | | | | | |
. | '-+-)---' | '-' '-' '-' '-'
.5V 249 | | | | 5V 499 | | | | 50, 6W 10V
. o-/\/\--+ | | +--+-/\/\--+----+----+----+--/\/\---o
. | | | | | | | | |
. | ,-)-+---, | .-. 499 .-. .-. .-. .-. 4.7
. | |< | >| | | | | | | | | | | |
. +--| | |--+ | | | | | | | | | |
. |\ | /| | '-' '-' '-' '-' '-'
. '-)-----)----' | | | | |
. fzt2907a | | gnd | | | | 10V?
. | | 9.3V? _ |< |< |< |
. | +---------U---|----|----|----| fzt2907a
. 20mA | | bead |\ |\ |\ |\
. (I) (I) | | | |
. | | 10mA | | | |
. ---+-----+---------------+----+----+----+---- -25
Click to expand...
It looks to me like the 9.3V on the collector of the PNP transistor would
be forward biasing it. Did I miss something?
--
--
kensmith@rahul.net forging knowledge
 
Ken Smith wrote...
Winfield Hill wrote: [ circuit snipped ]

Something worries me about this circuit. I'm going to add voltages
Modified:

. ---+---+---------------+----+----+----+----- +25
. | | 10mA | | | |
. (I) (I) | | | |
. 20mA | | _ |/ |/ |/ |/
. | +---------U---|----|-----|----| fzt2222a
. | | bead |> |> |> |
. fzt2222a | | | | | |
. ,---)---)----, | | | |
. |/ | \| | .-. .-. .-. .-. 4.7
. +--| | |--+ | | | | | | | |
. | |> | <| | | | | | | | | |
. | '-+-)---' | +5V '-' '-' '-' '-'
. 249 | | | | 499 | | | | 50, 6W
. o-/\/\--+ | | +--+-/\/\--+----+----+----+--/\/\---o
. +5V | | | | | | | | | +10V
. | ,-)-+---, | .-. 499 .-. .-. .-. .-. 4.7
. | |< | >| | | | | | | | | | | |
. +--| | |--+ | | | | | | | | | |
. |\ | /| | '-' '-' '-' '-' '-'
. '-)-----)----' | | | | |
. fzt2907a | | gnd | | | | +10V?
. | | +9.3V? _ |< |< |< |
. | +---------U---|----|----|----| fzt2907a
. 20mA | | bead |\ |\ |\ |\
. (I) (I) | | | |
. | | 10mA | | | |
. ---+-----+---------------+----+----+----+---- -25

It looks to me like the 9.3V on the collector of the PNP transistor
would be forward biasing it. Did I miss something?
Click to expand...
Which PNP are you referring to, the input PNP long-tail differential
pair? It's base would be at +5V. Oops! That doesn't work at all!


--
Thanks,
- Win
 
mmm wrote...
Winfield Hill wrote:
mmm wrote...

Very nice Ban and Win. I count 20 transistors with the
current sources added. What have I missed?

Use a better current-source, e.g., Wilson mirror, etc.

nice piece of hardware , but is not present in your book :)

See figure 2.48

not the Wilson current mirror .... but the high speed amplifier
as a whole. I was already aware of the presence in the book of
the current mirrors as 'programmable' current source.
Click to expand...
Well, they make the best current sources. I get 20 transistors,
unless one wants to add two more for reliable performance, then
it's 22 transistors total. Not so many in the IC world, nor in
our new SMT machine-assembly "parts-are-free" world, either.


--
Thanks,
- Win
 
John Larkin wrote...
Winfield Hill wrote:

John Larkin wrote...

Maybe cast an eyeball at THS3062. +-15 supplies, 7000 v/usec, dual,
300 MHz, isolated powerpad. I like to run one section as a gain stage,
then three as pure followers (no overall fb) each with 150 ohms to the
output node. This is TI's fast 30-volt process, one of the few around.
They're rated at 140 mA or something, but really get droopy (and hot!)
if you push them that hard, hence the paralleled sections.

Yes, very nice. John, can you tell us your recommendations for
effectively using TI's PowerPad thermal path in prototype assembly?

You really need a pc board to test parts like this. Given that, a
copper island under the chip, peppered with thermal vias to the ground
plane (if a multilayer) and also to a 'thermal antenna' pad on the
flip side. It doesn't take a lot of copper to cut the theta of an SO-8
by a factor of 3 or so.
Click to expand...
Can you give us a typical R-theta for the setup you describe above?


--
Thanks,
- Win
 
On 28 Jun 2005 04:07:48 -0700, Winfield Hill
<Winfield_member@newsguy.com> wrote:

John Larkin wrote...

Winfield Hill wrote:

John Larkin wrote...

Maybe cast an eyeball at THS3062. +-15 supplies, 7000 v/usec, dual,
300 MHz, isolated powerpad. I like to run one section as a gain stage,
then three as pure followers (no overall fb) each with 150 ohms to the
output node. This is TI's fast 30-volt process, one of the few around.
They're rated at 140 mA or something, but really get droopy (and hot!)
if you push them that hard, hence the paralleled sections.

Yes, very nice. John, can you tell us your recommendations for
effectively using TI's PowerPad thermal path in prototype assembly?

You really need a pc board to test parts like this. Given that, a
copper island under the chip, peppered with thermal vias to the ground
plane (if a multilayer) and also to a 'thermal antenna' pad on the
flip side. It doesn't take a lot of copper to cut the theta of an SO-8
by a factor of 3 or so.

Can you give us a typical R-theta for the setup you describe above?
Click to expand...
Nope.

John
 
In article <d9qclr0g0n@drn.newsguy.com>,
Winfield Hill <Winfield_member@newsguy.com> wrote:

How about we remove the gain of 2:

. ---+---+---------------+----+----+----+----- +25
. | | 10mA | | | |
. (I) (I) | | | |
. 20mA | | _ |/ |/ |/ |/
. | +---------U---|----|-----|----| fzt2222a
. | | bead |> |> |> |
. fzt2222a | | | | | |
. ,---)---)----, | | | |
. |/ | \| | .-. .-. .-. .-. 4.7
. +--| | |--+ | | | | | | | |
. | |> | <| | | | | | | | | |
. | '-+-)---' | +10V '-' '-' '-' '-'
. | | | | | | | | 50, 6W
. o-------+ | | +----------+----+----+----+--/\/\---o
. +10V | | | | | | | | +10V
. | ,-)-+---, | .-. .-. .-. .-. 4.7
. | |< | >| | | | | | | | | |
. +--| | |--+ | | | | | | | |
. |\ | /| | '-' '-' '-' '-'
. '-)-----)----' | | | |
. fzt2907a | | | | | | +10V?
. | | +9.3V? _ |< |< |< |
. | +---------U---|----|----|----| fzt2907a
. 20mA | | bead |\ |\ |\ |\
. (I) (I) | | | |
. | | 10mA | | | |
. ---+-----+---------------+----+----+----+---- -25
Click to expand...
Now the PNP still has a reverse bias on its collector but I'm still
worried about it a bit. Many bipolars have a "dynamic saturation" effect
where they slow down as the collector voltage gets down below about 2V. I
don't off hand know to what degree XXX2907s have this effect.

How about:
Vcc Vcc Vcc
! ! !
\ \ /
/ / \
\ \ /
/ / \
! ! !
V ! !
--- ! !
! !/ e !/ e
+-------!----------!------ .... repeat as needed
! !\ !\
!/ !
in-! !
!\ e !
! ! ........
+--- +---------+------- Out
! ! ! . !
\ \ ! . /
/ / ! . \ 50R
\ \ ! . /
/ / ! . \
! ! ! . !
gnd Vee ! . Gnd
! .
----- Mirror line -----------
--
--
kensmith@rahul.net forging knowledge
 
On Sun, 26 Jun 2005 15:50:39 GMT, "Harry Dellamano"
<harryd@tdsystems.org> wrote:

"Winfield Hill" <hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote in
message news:d9mbss011al@drn.newsguy.com...

It'd be more interesting if the amplifier were spec'd for +/-10V
matched-impedance output into a 50-ohm load. We'd set it up for
a gain of 2x, with +/-20V output and at least +/-25V supplies.

. ---+---+---------------+----+----+----+----- +25
. | | 10mA | | | |
. (I) (I) | | | |
. 20mA | | _ |/ |/ |/ |/
. | +---------U---|----|-----|----| fzt2222a
. | | bead |> |> |> |
. fzt2222a | | | | | |
. ,---)---)----, | | | |
. |/ | \| | .-. .-. .-. .-. 4.7
. +--| | |--+ | | | | | | | |
. | |> | <| | | | | | | | | |
. | '-+-)---' | '-' '-' '-' '-'
. 249 | | | | 499 | | | | 50, 6W
. o-/\/\--+ | | +--+-/\/\--+----+----+----+--/\/\---o
. | | | | | | | | |
. | ,-)-+---, | .-. 499 .-. .-. .-. .-. 4.7
. | |< | >| | | | | | | | | | | |
. +--| | |--+ | | | | | | | | | |
. |\ | /| | '-' '-' '-' '-' '-'
. '-)-----)----' | | | | |
. fzt2907a | | gnd | | | |
. | | _ |< |< |< |
. | +---------U---|----|----|----| fzt2907a
. 20mA | | bead |\ |\ |\ |\
. (I) (I) | | | |
. | | 10mA | | | |
. ---+-----+---------------+----+----+----+---- -25

The 60V Vcbo rating of the fzt2222a and fzt2907a would suffice.
One could run the input-pair current sources at 20mA and the
collector sources at 10mA, to insure enough available current
to drive the output emitter-follower transistors at full load.
The 20mA current sources could be made from two BJTs, so I get
a total transistor count of 22. The PCB would run rather hot.

Hmm, what does spice tell us about this circuit's performance?
You can use 2n2222 and 2n2907 models, they're the same dies.


--
Thanks,
- Win

Very nice Ban and Win. I count 20 transistors with the current sources
added. What have I missed? Please don't answer, "everything since the third
grade".
Regards,
Harry
Click to expand...
This is the kind of circuit we refer to as "component rich."

John
 
On Tue, 28 Jun 2005 08:03:49 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Sun, 26 Jun 2005 15:50:39 GMT, "Harry Dellamano"
harryd@tdsystems.org> wrote:


"Winfield Hill" <hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote in
message news:d9mbss011al@drn.newsguy.com...

It'd be more interesting if the amplifier were spec'd for +/-10V
matched-impedance output into a 50-ohm load. We'd set it up for
a gain of 2x, with +/-20V output and at least +/-25V supplies.

. ---+---+---------------+----+----+----+----- +25
. | | 10mA | | | |
. (I) (I) | | | |
. 20mA | | _ |/ |/ |/ |/
. | +---------U---|----|-----|----| fzt2222a
. | | bead |> |> |> |
. fzt2222a | | | | | |
. ,---)---)----, | | | |
. |/ | \| | .-. .-. .-. .-. 4.7
. +--| | |--+ | | | | | | | |
. | |> | <| | | | | | | | | |
. | '-+-)---' | '-' '-' '-' '-'
. 249 | | | | 499 | | | | 50, 6W
. o-/\/\--+ | | +--+-/\/\--+----+----+----+--/\/\---o
. | | | | | | | | |
. | ,-)-+---, | .-. 499 .-. .-. .-. .-. 4.7
. | |< | >| | | | | | | | | | | |
. +--| | |--+ | | | | | | | | | |
. |\ | /| | '-' '-' '-' '-' '-'
. '-)-----)----' | | | | |
. fzt2907a | | gnd | | | |
. | | _ |< |< |< |
. | +---------U---|----|----|----| fzt2907a
. 20mA | | bead |\ |\ |\ |\
. (I) (I) | | | |
. | | 10mA | | | |
. ---+-----+---------------+----+----+----+---- -25

The 60V Vcbo rating of the fzt2222a and fzt2907a would suffice.
One could run the input-pair current sources at 20mA and the
collector sources at 10mA, to insure enough available current
to drive the output emitter-follower transistors at full load.
The 20mA current sources could be made from two BJTs, so I get
a total transistor count of 22. The PCB would run rather hot.

Hmm, what does spice tell us about this circuit's performance?
You can use 2n2222 and 2n2907 models, they're the same dies.


--
Thanks,
- Win

Very nice Ban and Win. I count 20 transistors with the current sources
added. What have I missed? Please don't answer, "everything since the third
grade".
Regards,
Harry




This is the kind of circuit we refer to as "component rich."

John
Click to expand...
Seems pretty SPARSE to me ;-)

The PORTION of a WiFi chip that I'm currently working on (just the
limiting/log RSSI IF strip) has....

PMOS 6
NMOS 54
NPN 296 (SiGe)
R 288
C 318

Counts in the 20's are simply farts in a strong breeze ;-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
 
On Tue, 28 Jun 2005 08:24:58 -0700, Jim Thompson
<thegreatone@example.com> wrote:

On Tue, 28 Jun 2005 08:03:49 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Sun, 26 Jun 2005 15:50:39 GMT, "Harry Dellamano"
harryd@tdsystems.org> wrote:


"Winfield Hill" <hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote in
message news:d9mbss011al@drn.newsguy.com...

It'd be more interesting if the amplifier were spec'd for +/-10V
matched-impedance output into a 50-ohm load. We'd set it up for
a gain of 2x, with +/-20V output and at least +/-25V supplies.

. ---+---+---------------+----+----+----+----- +25
. | | 10mA | | | |
. (I) (I) | | | |
. 20mA | | _ |/ |/ |/ |/
. | +---------U---|----|-----|----| fzt2222a
. | | bead |> |> |> |
. fzt2222a | | | | | |
. ,---)---)----, | | | |
. |/ | \| | .-. .-. .-. .-. 4.7
. +--| | |--+ | | | | | | | |
. | |> | <| | | | | | | | | |
. | '-+-)---' | '-' '-' '-' '-'
. 249 | | | | 499 | | | | 50, 6W
. o-/\/\--+ | | +--+-/\/\--+----+----+----+--/\/\---o
. | | | | | | | | |
. | ,-)-+---, | .-. 499 .-. .-. .-. .-. 4.7
. | |< | >| | | | | | | | | | | |
. +--| | |--+ | | | | | | | | | |
. |\ | /| | '-' '-' '-' '-' '-'
. '-)-----)----' | | | | |
. fzt2907a | | gnd | | | |
. | | _ |< |< |< |
. | +---------U---|----|----|----| fzt2907a
. 20mA | | bead |\ |\ |\ |\
. (I) (I) | | | |
. | | 10mA | | | |
. ---+-----+---------------+----+----+----+---- -25

The 60V Vcbo rating of the fzt2222a and fzt2907a would suffice.
One could run the input-pair current sources at 20mA and the
collector sources at 10mA, to insure enough available current
to drive the output emitter-follower transistors at full load.
The 20mA current sources could be made from two BJTs, so I get
a total transistor count of 22. The PCB would run rather hot.

Hmm, what does spice tell us about this circuit's performance?
You can use 2n2222 and 2n2907 models, they're the same dies.


--
Thanks,
- Win

Very nice Ban and Win. I count 20 transistors with the current sources
added. What have I missed? Please don't answer, "everything since the third
grade".
Regards,
Harry




This is the kind of circuit we refer to as "component rich."

John

Seems pretty SPARSE to me ;-)

The PORTION of a WiFi chip that I'm currently working on (just the
limiting/log RSSI IF strip) has....

PMOS 6
NMOS 54
NPN 296 (SiGe)
R 288
C 318

Counts in the 20's are simply farts in a strong breeze ;-)

...Jim Thompson
Click to expand...
Sometimes an IC datasheet will include a component count. It's amazing
to see (it's getting hard to type, with two new kittens walking on my
keyboard. The Brat named them Ajax and Comet) numbers like "278
equivalent transistors" for an opamp or a simple logic part.

That's one reason that discrete circuit design (ie, not IC) is a dying
art: most of the time, it makes more sense to buy ICs than to design
with a bunch of discretes. So us circuit designers have to move up the
abstraction stack, buy lots of cheap chips, and combine them into more
complex stuff. I'm doing small PCBs that would have been racks full of
stuff a few years ago. A few exceptions remain: high power, high
speed, high voltage, RF.

Simple = elegant.

John
 
On Tue, 28 Jun 2005 08:48:24 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 28 Jun 2005 08:24:58 -0700, Jim Thompson
thegreatone@example.com> wrote:

On Tue, 28 Jun 2005 08:03:49 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

[snip]

This is the kind of circuit we refer to as "component rich."

John

Seems pretty SPARSE to me ;-)

The PORTION of a WiFi chip that I'm currently working on (just the
limiting/log RSSI IF strip) has....

PMOS 6
NMOS 54
NPN 296 (SiGe)
R 288
C 318

Counts in the 20's are simply farts in a strong breeze ;-)

...Jim Thompson

Sometimes an IC datasheet will include a component count. It's amazing
to see (it's getting hard to type, with two new kittens walking on my
keyboard. The Brat named them Ajax and Comet) numbers like "278
equivalent transistors" for an opamp or a simple logic part.

That's one reason that discrete circuit design (ie, not IC) is a dying
art: most of the time, it makes more sense to buy ICs than to design
with a bunch of discretes. So us circuit designers have to move up the
abstraction stack, buy lots of cheap chips, and combine them into more
complex stuff. I'm doing small PCBs that would have been racks full of
stuff a few years ago. A few exceptions remain: high power, high
speed, high voltage, RF.

Simple = elegant.

John
Click to expand...
I've been at IC design for so long, ~43 years now, that I have trouble
doing cost-efficient discrete designs... I tend to use too many
components... of course everything works textbook since, in my world,
there are NO tweaks allowed.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
 
Hello John,

That's one reason that discrete circuit design (ie, not IC) is a dying
art: most of the time, it makes more sense to buy ICs than to design
with a bunch of discretes. So us circuit designers have to move up the
abstraction stack, buy lots of cheap chips, and combine them into more
complex stuff. I'm doing small PCBs that would have been racks full of
stuff a few years ago. A few exceptions remain: high power, high
speed, high voltage, RF.
Click to expand...
Not always. It is amazing how much of the mundane stuff is still done in
discrete. I was looking whether the time had come, after 10 years or so,
to move one of the designs I had done for a client to a uC or maybe an
ASIC. So I asked them what the current cost per board was. The answer
blew me away. Maybe I'll look at the circuit again in another ten years.

Simple = elegant.
Click to expand...
Sometimes it is "cheap = better than elegant" ;-)

Regards, Joerg

http://www.analogconsultants.com
 
On 28 Jun 2005 04:07:48 -0700, Winfield Hill
<Winfield_member@newsguy.com> wrote:

John Larkin wrote...

Winfield Hill wrote:

John Larkin wrote...

Maybe cast an eyeball at THS3062. +-15 supplies, 7000 v/usec, dual,
300 MHz, isolated powerpad. I like to run one section as a gain stage,
then three as pure followers (no overall fb) each with 150 ohms to the
output node. This is TI's fast 30-volt process, one of the few around.
They're rated at 140 mA or something, but really get droopy (and hot!)
if you push them that hard, hence the paralleled sections.

Yes, very nice. John, can you tell us your recommendations for
effectively using TI's PowerPad thermal path in prototype assembly?

You really need a pc board to test parts like this. Given that, a
copper island under the chip, peppered with thermal vias to the ground
plane (if a multilayer) and also to a 'thermal antenna' pad on the
flip side. It doesn't take a lot of copper to cut the theta of an SO-8
by a factor of 3 or so.

Can you give us a typical R-theta for the setup you describe above?
Click to expand...

Take a look at the board in a.b.s.e. It has two GigaLogic chips and
two GaAs distributed amps, all power-padded and heatsunk. Ghastly.

John
 
Ban wrote...
Jim Thompson wrote:
Ban wrote...
Here is a discrete O/P stage, you can parallel more transistors. I
also have a gain stage somewhere, but do not remember the file name.
:-(

+---+-----------+----+-----
| | | |
| | | |
current sources (I) (I) | |
| | _ |/ |/
| +------U-------| BF720
| | bead |> |
| | | |
| | | |
o +---)---)----+ | |
| |/ | \| | .-. .-.
+-| | |- + | | | |
| |> | <| | | | | |
| +-+-)---+ | '-' '-'
| | | BF720 | | |
| | | | | |
| | | +------+----+-o
| | | BF721 | | |
| +-)-+---+ | .-. .-.
| |< | >| | | | | |
+-| | |- + | | | |
|\ | /| | '-' '-'
+-)-----)----+ | |
| | | |
| | _ |< |
| +------U-------| BF721
| | bead |\ |\
current sources (I) (I) | |
| | | |
| | | |
+-----+-----------+----+----

What subtlety am I missing that keeps it from having big rail-to-rail
current draw?

Maybe the subtlety is the feedback connection between O/P and bases
of the long tailed pairs? The current into the output transistors
will regulate by itself. We do never saturate or starve the first
stage, it's a buffer, not an amplifier. Whatever current is not used
in the first stage will flow into the output transistors, it is not
controlled by a fixed bias voltage. The right current source has
10mA, half of the left one. These 10mA are consumed by the input
transistor, so there is nothing left for the power stage.
Click to expand...
Nope, not so simple Ban. Small offsets in the input pair can easily
create say 10% current imbalance, and the resulting 1mA drive will be
magnified by the output transistor's beta, possibly leading to >100mA
of class-A rail-rail current. If each side's feedback was returned
from one of its output transistor's emitters, before the equalizing
resistor, the class-A current problem could be mitigated. But what
you really want is a way to predetermine and control the quiescent
bias current, which ideally for a high-speed amp should not be zero.
This can be done by adding current sources and resistors at the input.

.. ---+---+-----------+----+-----
.. | | | |
.. 10mA 5mA | |
.. | | _ |/ |/
.. | +------U-------| fzt2222a
.. | | | bead |> |>
.. 1mA | | | |
.. | ,---)---)----+------+ | quiescent
.. | |/ | \| | | | Iq = 10mA
.. +--| | |--' | |
.. | |> | <| 10 10
.. 100 '-+-)---' 1W 1W
.. | | | fzt2222a | |
.. o---+ | | (matched) +----+---o
.. | | | fzt2907a | |
.. 100 ,-)-+---, 10 10
.. | |< | >| 1W 1W
.. +--| | |--, | |
.. | |\ | /| | | |
.. | '-)-----)----+------+ |
.. 1mA | | | |
.. | | | _ |< |<
.. | +------U-------| fzt2907a
.. | | bead |\ |\
.. 10mA 5mA | |
.. | | | |
.. ---+-----+-----------+----+----


--
Thanks,
- Win
 
On Sun, 26 Jun 2005 10:15:08 GMT, "Ban" <bansuri@web.de> wrote:

mmm wrote:
I trying to build a signal generator with 20 Vpp open circuit , 10Vpp
on 50 Ohm output and frequency range up to 10MHz , so I need at least
30MHz bandwith ( don't blame me if you think is a bit low !! )

I have found almost suitable parts in Analog Device AD815 or Texas
BUF634 plus high speep Op Amp.

Now I am looking for alternative implementation of output stage

An discrete or Op Amp + discrete output stage solution will be very
good if they have a small component count and if the components are
easy to find.

Here is a discrete O/P stage, you can parallel more transistors. I also have
a gain stage somewhere, but do not remember the file name. :-(

+---+-----------+----+-----
| | | |
| | | |
current sources (I) (I) | |
| | _ |/ |/
| +------U-------| BF720
| | bead |> |
| | | |
| | | |
o +---)---)----+ | |
| |/ | \| | .-. .-.
+-| | |- + | | | |
| |> | <| | | | | |
| +-+-)---+ | '-' '-'
| | | BF720 | | |
| | | | | |
| | | +------+----+-o
| | | BF721 | | |
| +-)-+---+ | .-. .-.
| |< | >| | | | | |
+-| | |- + | | | |
|\ | /| | '-' '-'
+-)-----)----+ | |
| | | |
| | _ |< |
| +------U-------| BF721
| | bead |\ |\
current sources (I) (I) | |
| | | |
| | | |
+-----+-----------+----+----
(created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de)
view\fixed font


thanks in advance
Click to expand...
What subtlety am I missing that keeps it from having big rail-to-rail
current draw?

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
 
Jim Thompson wrote:
Here is a discrete O/P stage, you can parallel more transistors. I
also have a gain stage somewhere, but do not remember the file name.
:-(

+---+-----------+----+-----
| | | |
| | | |
current sources (I) (I) | |
| | _ |/ |/
| +------U-------| BF720
| | bead |> |
| | | |
| | | |
o +---)---)----+ | |
| |/ | \| | .-. .-.
+-| | |- + | | | |
| |> | <| | | | | |
| +-+-)---+ | '-' '-'
| | | BF720 | | |
| | | | | |
| | | +------+----+-o
| | | BF721 | | |
| +-)-+---+ | .-. .-.
| |< | >| | | | | |
+-| | |- + | | | |
|\ | /| | '-' '-'
+-)-----)----+ | |
| | | |
| | _ |< |
| +------U-------| BF721
| | bead |\ |\
current sources (I) (I) | |
| | | |
| | | |
+-----+-----------+----+----
(created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de)
view\fixed font



What subtlety am I missing that keeps it from having big rail-to-rail
current draw?
Click to expand...
Maybe the subtlety is the feedback connection between O/P and bases of the
long tailed pairs? The current into the output transistors will regulate by
itself. We do never saturate or starve the first stage, it's a buffer, not
an amplifier. Whatever current is not used in the first stage will flow into
the output transistors, it is not controlled by a fixed bias voltage. The
right current source has 10mA, half of the left one. These 10mA are consumed
by the input transistor, so there is nothing left for the power stage.

...Jim Thompson
Click to expand...
--
ciao Ban
Bordighera, Italy
 
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