OPAMP trouble

J

jw

Guest
Hi,

My opamp looks like it isn't amplifying and I need some help. I have a
MCP606 opamp in a DIP package.

I am inputting a very fast (almost 1GHz) sine wave into this OPAMP on the +
input, but this is a very low voltage signal usually between 10 to 30
millivolts.

Then want to amplify this signal at least 1000-fold, so I connected the
output to the - input with a 1000 ohm resistor and further, a 1 ohm resistor
connecting this same - input to ground, to get the desired amplification.

But when I connect the Oscope to the output of the OPAMP, it does not show
any amplification of the input signal.

In fact, the magniture of the output is still in the 10-30 MV range - the
same as the input.

I forgot to mention that I have also connected a 0.01 F cap between GND and
Vdd, as recommended.

Can anone tell me why this is not amplifying? Is the signal too fast for
this amp?

--thx, jw
 
"jw" <letron_2000no__spam@yahoo.com> wrote in message
news:VecOe.3554$Z87.2230@newssvr14.news.prodigy.com...
Hi,

My opamp looks like it isn't amplifying and I need some help. I have a
MCP606 opamp in a DIP package.

I am inputting a very fast (almost 1GHz) sine wave into this OPAMP on the
+
input, but this is a very low voltage signal usually between 10 to 30
millivolts.

Then want to amplify this signal at least 1000-fold, so I connected the
output to the - input with a 1000 ohm resistor and further, a 1 ohm
resistor
connecting this same - input to ground, to get the desired amplification.

But when I connect the Oscope to the output of the OPAMP, it does not show
any amplification of the input signal.

In fact, the magniture of the output is still in the 10-30 MV range - the
same as the input.

I forgot to mention that I have also connected a 0.01 F cap between GND
and
Vdd, as recommended.

Can anone tell me why this is not amplifying? Is the signal too fast for
this amp?

--thx, jw
Click to expand...
You are far beyond what the OPamp can deliver. If you look at the datasheet
its gain*bandwidth=155kHz. That means that at 155kHz you don't have more
that 1 time amplification. (At 15kHz you can have 10 times.)

BR
Ingvar
 
Thanks for the help.

Does anyone know an opamp that can operate at these high speeds?

--jw

"Ingvar Esk" <ingvar.esk@ericsson.com> wrote in message
news:dec6k2$r3c$1@news.al.sw.ericsson.se...
"jw" <letron_2000no__spam@yahoo.com> wrote in message
news:VecOe.3554$Z87.2230@newssvr14.news.prodigy.com...
Hi,

My opamp looks like it isn't amplifying and I need some help. I have a
MCP606 opamp in a DIP package.

I am inputting a very fast (almost 1GHz) sine wave into this OPAMP on
the
+
input, but this is a very low voltage signal usually between 10 to 30
millivolts.

Then want to amplify this signal at least 1000-fold, so I connected the
output to the - input with a 1000 ohm resistor and further, a 1 ohm
resistor
connecting this same - input to ground, to get the desired
amplification.

But when I connect the Oscope to the output of the OPAMP, it does not
show
any amplification of the input signal.

In fact, the magniture of the output is still in the 10-30 MV range -
the
same as the input.

I forgot to mention that I have also connected a 0.01 F cap between GND
and
Vdd, as recommended.

Can anone tell me why this is not amplifying? Is the signal too fast
for
this amp?

--thx, jw



You are far beyond what the OPamp can deliver. If you look at the
datasheet
its gain*bandwidth=155kHz. That means that at 155kHz you don't have more
that 1 time amplification. (At 15kHz you can have 10 times.)

BR
Ingvar
Click to expand...
 
On Tue, 23 Aug 2005 03:00:21 GMT, "jw" <letron_2000no__spam@yahoo.com>
wrote:

Thanks for the help.

Does anyone know an opamp that can operate at these high speeds?

--jw
Click to expand...
Are you sure you need this much gain at 1 GHz?

Your spec of 30 mv in and a gain above 1000 implies over 30 volts out.
That's very serious power at this sort of frequency.

And anything with that much gain at a GHz will need very serious
shielding between the input and output to keep from oscillating; so
much so that any single gain stage, if it existed (and it doesn't)
would oscillate like a bandit.

Only a few opamps will give a gain of over 1 at 1 GHz, and then not
much over 1. InGaAs MMICS are usually used for gain up here, maybe 20
dB or so (10:1 voltage) per stage.

What's this for?

John
 
Oh - here it looks like I would need, say, a gain of 30-fold, so this would
give me output of about 1 V or so, from the amplifier.

I am using this to amplify a signal I am receiving on an antenna, as an
experiment for learning about wireless circuits, no more than that.

--jw

Your spec of 30 mv in and a gain above 1000 implies over 30 volts out.
That's very serious power at this sort of frequency.

What's this for?

John
Click to expand...
 
On Wed, 24 Aug 2005 03:02:15 GMT, "jw" <letron_2000no__spam@yahoo.com>
wrote:

Oh - here it looks like I would need, say, a gain of 30-fold, so this would
give me output of about 1 V or so, from the amplifier.

I am using this to amplify a signal I am receiving on an antenna, as an
experiment for learning about wireless circuits, no more than that.

--jw
Click to expand...
Maybe look at the Mini-Circuits ERA-series of mmic amps. They have
gains to 10:1 or so at mucho GHz, and they're cheap and easy to use.
To play with these, read the appnotes carefully. Breadboard by
soldering everything flat and low on an piece of unetched copperclad
PCB material.

At these speeds, everything must be zero length, if not shorter, and
the input must be far away from the output... obviously an interesting
tradeoff.

John
 
In article <VecOe.3554$Z87.2230@newssvr14.news.prodigy.com>, jw wrote:
Hi,

My opamp looks like it isn't amplifying and I need some help. I have a
MCP606 opamp in a DIP package.

I am inputting a very fast (almost 1GHz) sine wave into this OPAMP on the +
input, but this is a very low voltage signal usually between 10 to 30
millivolts.
Click to expand...
you'll be lucky to find any op-amp thjat works that fast.

Then want to amplify this signal at least 1000-fold,

Can anone tell me why this is not amplifying? Is the signal too fast for
this amp?
Click to expand...
yes, try a broadband amplifier chip instead, you may need a few in series
for that gain.

Bye.
Jasen
 
Thanks for these suggestions - I'm learning a lot already. --jw
 
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