| Author |
Message |
Jeff
Guest
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 Posted:
Thu Sep 22, 2005 12:35 am Post subject:
Buffer Amp IC suggestions plse |
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Hi,
Ive been trying to locate a suitable unity gain buffer amplifier IC that can
drive a 50 load.
Application is to buffer a VCO output at 5Mhz.
Needs to be 8pin DIP and operate on a single-ended supply.
I had found what I wanted in the CLC109, but cant seem to find a supplier.
Any suggestions greatly appreciated regarding type and supplier that is user
friendly to international countries.
JEFF
ZL3JK
New Zealand
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Winfield Hill
Guest
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| Posted:
Thu Sep 22, 2005 12:35 am Post subject:
Re: Buffer Amp IC suggestions plse |
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Jeff wrote...
| Quote: |
Ive been trying to locate a suitable unity gain buffer amplifier
IC that can drive a 50 load.
Application is to buffer a VCO output at 5Mhz.
Needs to be 8pin DIP
|
LTC's LT1206 comes in TO220, miniDIP and soic packages,
and Digi-Key has them in stock for $6.25 each...
http://rocky.digikey.com/WebLib/Linear%20Tech/Web%20Data/LT1206.pdf
http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=329191
| Quote: | and operate on a single-ended supply.
|
Oops, +/-5V supply. What's your signal voltage? And did
you want your output to have a 50-ohm source impedance?
--
Thanks,
- Win |
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Jeff
Guest
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| Posted:
Thu Sep 22, 2005 12:35 am Post subject:
Re: Buffer Amp IC suggestions plse |
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Needs to drive into 50 ohms. input level approx 150mV at 5Mhz
"Winfield Hill" <Winfield_member@newsguy.com> wrote in message
news:dgsmk501sr9@drn.newsguy.com...
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John Popelish
Guest
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| Posted:
Thu Sep 22, 2005 12:35 am Post subject:
Re: Buffer Amp IC suggestions plse |
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Jeff wrote:
| Quote: | Hi,
Ive been trying to locate a suitable unity gain buffer amplifier IC that can
drive a 50 load.
Application is to buffer a VCO output at 5Mhz.
Needs to be 8pin DIP and operate on a single-ended supply.
I had found what I wanted in the CLC109, but cant seem to find a supplier.
Any suggestions greatly appreciated regarding type and supplier that is user
friendly to international countries.
JEFF
ZL3JK
New Zealand
An AD817 can deliver +-50 mA and has a gain bandwidth product of 50 MHz. |
http://www.analog.com/UploadedFiles/Data_Sheets/289066266ad817.pdf
<4$ from Digikey.
Good for either a gain 1 buffer or a gain 2 with series 50 ohm
resistor, 50 ohm source. |
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Winfield Hill
Guest
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| Posted:
Thu Sep 22, 2005 5:37 am Post subject:
Re: Buffer Amp IC suggestions plse |
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Jeff wrote...
Unless you source with 50 ohms (2x signal plus 50-ohm resistor),
and terminate with 50-ohms, the issue becomes how much cable
capacitance? Either the load looks resistive (100 ohms in the
former case) or capacitive.
--
Thanks,
- Win |
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Jeff
Guest
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| Posted:
Thu Sep 22, 2005 7:03 am Post subject:
Re: Buffer Amp IC suggestions plse |
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Thanks. The AD817 looks good, and I can source it locally from Australia.
Thanks all for your help.
JEFF
"John Popelish" <jpopelish@rica.net> wrote in message
news:CYedna5XIIWNdKzeRVn-rA@adelphia.com...
| Quote: | Jeff wrote:
Hi,
Ive been trying to locate a suitable unity gain buffer amplifier IC that
can
drive a 50 load.
Application is to buffer a VCO output at 5Mhz.
Needs to be 8pin DIP and operate on a single-ended supply.
I had found what I wanted in the CLC109, but cant seem to find a
supplier.
Any suggestions greatly appreciated regarding type and supplier that is
user
friendly to international countries.
JEFF
ZL3JK
New Zealand
An AD817 can deliver +-50 mA and has a gain bandwidth product of 50 MHz.
http://www.analog.com/UploadedFiles/Data_Sheets/289066266ad817.pdf
4$ from Digikey.
Good for either a gain 1 buffer or a gain 2 with series 50 ohm
resistor, 50 ohm source. |
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Mac
Guest
|
| Posted:
Thu Sep 22, 2005 8:35 am Post subject:
Re: Buffer Amp IC suggestions plse |
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|
On Thu, 22 Sep 2005 09:14:55 +1200, Jeff wrote:
| Quote: | Hi,
Ive been trying to locate a suitable unity gain buffer amplifier IC that can
drive a 50 load.
Application is to buffer a VCO output at 5Mhz.
Needs to be 8pin DIP and operate on a single-ended supply.
I had found what I wanted in the CLC109, but cant seem to find a supplier.
Any suggestions greatly appreciated regarding type and supplier that is user
friendly to international countries.
JEFF
ZL3JK
New Zealand
|
What you want is a video buffer or video op-amp. Linear Technologies,
National Semiconductor, and Analog Devices are among the many companies
that make such things.
Note that some of these devices get a bit squirrelly if they see a
capacitive load. So I recommend that you do something like this: (use
courier or other constant-width font for ASCII art schematic)
|\ 50
in--|+\__+____/\/\____/> to 50 Ohm load
+--|-/ |
| |/ |
| |
+--/\/\-+
| Rf
\
/Ra
\
/
|
-----
GND
Rf and Ra would be the same value. Use a value recommended by the
datasheet, or 1k if the datasheet doesn't recommend a specific value.
Follow any other suggestions in the datasheet as well. For example, they
may suggest a small capacitor directly from the op-amp output to inverting
input.
You probably want to terminate the input with a 50 Ohm resistor, too, but
I don't know, so I'll leave it out.
It sounds like you may need AC-coupling, so you can put blocking
capacitors on the input and/or output. Oh, if you put a blocking cap on
the input, be sure to also provide a DC (resistive) path to GND or to the
mid-rail point if you are going single-supply.
Just chose a capacitor big enough so that 1/(2*pi*R*C) is much lower than
5 MHz, your signal of interest. (R in this case is 50 Ohms) There is no
problem putting a capacitor like this in the signal path: Since it looks
like a short circuit at higher frequencies, it does not capacitively load
the amp at frequencies where the amp might be unstable. Also, the series
50 Ohm resistor keeps the overall impedance resistive.
HTH
--Mac |
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Mac
Guest
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Fred Bloggs
Guest
|
| Posted:
Thu Sep 22, 2005 4:35 pm Post subject:
Re: Buffer Amp IC suggestions plse |
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Winfield Hill wrote:
Well- why not your super-duper 74HCU04 linear amp or whatever it was?-
is that available in Tiny Logic? |
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Winfield Hill
Guest
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| Posted:
Thu Sep 22, 2005 4:35 pm Post subject:
Re: Buffer Amp IC suggestions plse |
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Mac wrote...
Ouch, a 30mA supply current!
--
Thanks,
- Win |
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Jeff
Guest
|
| Posted:
Fri Sep 23, 2005 12:35 am Post subject:
Re: Buffer Amp IC suggestions plse |
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|
Thanks for those ideas. I was considering putting a low pass filter after
the amp. The 2 shunt caps work out to be 560pF each.
JEFF
"Mac" <foo@bar.net> wrote in message
news:pan.2005.09.22.04.44.20.615469@bar.net...
| Quote: | On Thu, 22 Sep 2005 09:14:55 +1200, Jeff wrote:
Hi,
Ive been trying to locate a suitable unity gain buffer amplifier IC that
can
drive a 50 load.
Application is to buffer a VCO output at 5Mhz.
Needs to be 8pin DIP and operate on a single-ended supply.
I had found what I wanted in the CLC109, but cant seem to find a
supplier.
Any suggestions greatly appreciated regarding type and supplier that is
user
friendly to international countries.
JEFF
ZL3JK
New Zealand
What you want is a video buffer or video op-amp. Linear Technologies,
National Semiconductor, and Analog Devices are among the many companies
that make such things.
Note that some of these devices get a bit squirrelly if they see a
capacitive load. So I recommend that you do something like this: (use
courier or other constant-width font for ASCII art schematic)
|\ 50
in--|+\__+____/\/\____/> to 50 Ohm load
+--|-/ |
| |/ |
| |
+--/\/\-+
| Rf
\
/Ra
\
/
|
-----
GND
Rf and Ra would be the same value. Use a value recommended by the
datasheet, or 1k if the datasheet doesn't recommend a specific value.
Follow any other suggestions in the datasheet as well. For example, they
may suggest a small capacitor directly from the op-amp output to inverting
input.
You probably want to terminate the input with a 50 Ohm resistor, too, but
I don't know, so I'll leave it out.
It sounds like you may need AC-coupling, so you can put blocking
capacitors on the input and/or output. Oh, if you put a blocking cap on
the input, be sure to also provide a DC (resistive) path to GND or to the
mid-rail point if you are going single-supply.
Just chose a capacitor big enough so that 1/(2*pi*R*C) is much lower than
5 MHz, your signal of interest. (R in this case is 50 Ohms) There is no
problem putting a capacitor like this in the signal path: Since it looks
like a short circuit at higher frequencies, it does not capacitively load
the amp at frequencies where the amp might be unstable. Also, the series
50 Ohm resistor keeps the overall impedance resistive.
HTH
--Mac
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Ross Herbert
Guest
|
| Posted:
Fri Sep 23, 2005 3:09 pm Post subject:
Re: Buffer Amp IC suggestions plse |
|
|
On Thu, 22 Sep 2005 09:14:55 +1200, "Jeff"
<jeff_164@NOSPAMhotmail.com> wrote:
| Quote: | Hi,
Ive been trying to locate a suitable unity gain buffer amplifier IC that can
drive a 50 load.
Application is to buffer a VCO output at 5Mhz.
Needs to be 8pin DIP and operate on a single-ended supply.
I had found what I wanted in the CLC109, but cant seem to find a supplier.
Any suggestions greatly appreciated regarding type and supplier that is user
friendly to international countries.
JEFF
ZL3JK
New Zealand
|
Here's a dual op-amp in 8 pin DIP which should do what you want
http://www.analog.com/UploadedFiles/Data_Sheets/242276322AD8397_0.pdf |
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johan aeq
Guest
|
| Posted:
Fri Sep 23, 2005 10:09 pm Post subject:
Re: Buffer Amp IC suggestions plse |
|
|
Try a SL560
"Jeff" <jeff_164@NOSPAMhotmail.com> schreef in bericht
news:k3kYe.13434$iM2.1134628@news.xtra.co.nz...
| Quote: | Hi,
Ive been trying to locate a suitable unity gain buffer amplifier IC that
can
drive a 50 load.
Application is to buffer a VCO output at 5Mhz.
Needs to be 8pin DIP and operate on a single-ended supply.
I had found what I wanted in the CLC109, but cant seem to find a supplier.
Any suggestions greatly appreciated regarding type and supplier that is
user
friendly to international countries.
JEFF
ZL3JK
New Zealand
|
|
|
| Back to top |
|
|
Chris Jones
Guest
|
| Posted:
Sat Oct 01, 2005 12:35 am Post subject:
Re: Buffer Amp IC suggestions plse |
|
|
Winfield Hill wrote:
| Quote: | Jeff wrote...
Needs to drive into 50 ohms. input level approx 150mV at 5Mhz
Winfield Hill wrote ...
Jeff wrote...
Ive been trying to locate a suitable unity gain buffer amplifier
IC that can drive a 50 load.
Application is to buffer a VCO output at 5Mhz.
Needs to be 8pin DIP
LTC's LT1206 comes in TO220, miniDIP and soic packages,
and Digi-Key has them in stock for $6.25 each...
http://rocky.digikey.com/WebLib/Linear%20Tech/Web%20Data/LT1206.pdf
http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=329191
and operate on a single-ended supply.
Oops, +/-5V supply. What's your signal voltage? And did
you want your output to have a 50-ohm source impedance?
Unless you source with 50 ohms (2x signal plus 50-ohm resistor),
and terminate with 50-ohms, the issue becomes how much cable
capacitance? Either the load looks resistive (100 ohms in the
former case) or capacitive.
I would say it depends on the cable you choose. If there is a 50 Ohm load |
and you connect it to your buffer amplifier with 50 Ohm coaxial cable, then
the buffer amplifier will see a 50 Ohm resistive load, not capacitive at
all.
It is probably still wise to use the gain-of-two amplifier and 50 Ohm source
resistor in case the load happens to be a poor match. If you really don't
need this feature then I would be tempted to use an emitter follower with
just one transistor. (Do they make transistors in DIP-8 packages?)
Chris |
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Winfield Hill
Guest
|
| Posted:
Sat Oct 01, 2005 6:47 am Post subject:
Re: Buffer Amp IC suggestions plse |
|
|
Chris Jones wrote...
| Quote: | Winfield Hill wrote:
Jeff wrote...
Needs to drive into 50 ohms. input level approx 150mV at 5Mhz
Winfield Hill wrote ...
Jeff wrote...
Ive been trying to locate a suitable unity gain buffer amplifier
IC that can drive a 50 load. Application is to buffer a VCO
output at 5Mhz. Needs to be 8pin DIP
LTC's LT1206 comes in TO220, miniDIP and soic packages,
and operate on a single-ended supply.
Oops, +/-5V supply. What's your signal voltage? And did
you want your output to have a 50-ohm source impedance?
Unless you source with 50 ohms (2x signal plus 50-ohm resistor),
and terminate with 50-ohms, the issue becomes how much cable
capacitance? Either the load looks resistive (100 ohms in the
former case) or capacitive.
I would say it depends on the cable you choose. If there is a 50 Ohm
load and you connect it to your buffer amplifier with 50 Ohm coaxial
cable, then the buffer amplifier will see a 50 Ohm resistive load,
not capacitive at all.
It is probably still wise to use the gain-of-two amplifier and 50 Ohm
source resistor in case the load happens to be a poor match. If you
really don't need this feature then I would be tempted to use an
emitter follower with just one transistor. (Do they make transistors
in DIP-8 packages?)
|
I agree, if the load has no capacitance, source terminating with
50-ohms eliminates the cable-capacitance issue, and the driver only
sees a 100-ohm load at high frequencies, above those where the open-
end reflection has time to return. Although the input to the cable
is attenuated by 2x (hence the 2x gain you suggested), the end of
the cable gets the 2x back due to the open circuit, so a gain-of-two
amplifier shouldn't be needed. Just the 50-ohm sourcing resistor,
after the emitter follower.
--
Thanks,
- Win |
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