OPAMP trouble

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

Reply to
jw
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+

resistor

and

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

Reply to
Ingvar Esk

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

Reply to
John Larkin

Thanks for the help.

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

--jw

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datasheet

Reply to
jw

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

Reply to
John Larkin

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

Reply to
jw

you'll be lucky to find any op-amp thjat works that fast.

yes, try a broadband amplifier chip instead, you may need a few in series for that gain.

Bye. Jasen

Reply to
Jasen Betts

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

Reply to
jw

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