You need to look at the driving impedance before you declare one
technology "quieter" than another. That is, you have voltage noise and
current noise. For low driving impedance, bipolar will be quieter since
current noise will not be significant, plus a bipolar will have lower
thermal noise. For high impedance, JFET may be a better solution.
Opamps are around 1nv/rootHz these days. That isn't all that easy to
achieve discretely.
Noise is proportional to the square root of the bandwidth, so less is
more. But that is broadband noise. I'm not sure about phase noise.
On 2/28/2012 10:41 AM, Bill Fuqua wrote:
Discrete amplifiers are always less noisy than integrated amplifiers.
If you want really low noise design a one with JFETs and Bipolar
transistors.
I am trying to understand the contribution to phase noise by the opamps.
Perhaps the "threshold" is shifting and amplifier is being driven to
saturation?
I am new to this group but have had lots of RF experience and weak signal
detection experience.
73
Bill wa4lav
Date: Tue, 28 Feb 2012 07:34:09 -0500
From: Bob Camp <[email protected]>
Hi
Very cool. How much power can you run through the device? Put another
way, if you drive it with +13 dbm do all the numbers get 5 db better?
I doubt very many of us will be worrying about weather it's below -153
at 10 Hz or not?
Bob
On Feb 28, 2012, at 5:42 AM, Bruce Griffiths wrote:
> The attached plot indicates the phase noise performance obtainable
with a wideband FET (OPA653) input opamp.
> With a 10MHz +9dBm input, the phase noise floor is around -163dBc/Hz
at 1kHz offset and around -154dBc/Hz at 10Hz offset.
> A quieter test source would be useful particularly for offsets below
10Hz.
>
> Bruce
> <OPA653PN2.gif>_______________________________________________
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William L. Fuqua III P.E.
Sr. Electrical Engineer
CP 177 Chemistry Physics Building
Department of Physics and Astronomy
University of Kentucky
Lexington,KY 40506-0055
Phone: 1-859-257-4155
e-mail: [email protected]
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