1. Home
  2. Electronics Design
  3. NOISE FIGURE OF A BIPOLAR TRANSISTOR
  4. Page 3

NOISE FIGURE OF A BIPOLAR TRANSISTOR

effect, and end up with a resistor that has less than 4KTR noise. Assuming the amplifier you use for the Miller effect is ultra-low-noise. This could buy you

3db in the limit, assuming you used this resistor as a termination. Don't know how practical this really is.

with less than 2 nv/root-hz, I think. Some of those parts have probably gone obsolete.

Good idea. My fave at the moment is that PNP-wraparound-BF862 follower running into the - input of an ADA4898 or 4899 (a 500 MHz, +-5V part). But that has about sqrt(2) times more voltage noise and doesn't have the good drift of a LT1028. That's often a good trade for 1 pA input bias current.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 USA 
+1 845 480 2058 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs
Loading thread data ...

ity,

ctivity

The Wiedemann-Franz law, yes. But it doesn't apply if you have superconductors available. They conduct electricity but not heat. Or more accurately: the electron-mediated heat conductivity freezes out, but phonon-mediated remains.

But it still is tough...

Regards, Mikko

Reply to
Mr Stonebeach

conductivity

But you'd still be transferring k(T_hot-T_cold) per hertz just via I**2*R, even with superconducting wires, right?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

tivity,

nductivity

Yes, exactly, you would. The cooling effect via the Nyquist mechanism would be there, and the effect would not get counteracted by the heat backconduction. As John argued, with non-superconductors any temperature difference (due to the Nyquist mechanism) would tend to equilibrate via ordinary heat conduction.

My colleaques one floor up have actually been experimenting with related effects.

Regards, Mikko

Reply to
Mr Stonebeach

conductivity

Thermal conductivity of superconducting Nb is not so bad. About 0.25* RRR at 4.2K. Of course you can make the "wires" extremely thin since the currents are very low.

Reply to
Spehro Pefhany

noise figure .My question is how exactly a noise figure of a single bip[olar transistor is defined measured .

And you are responding to this scammer WHY?

?-(

Reply to
josephkk

At 4.2K Nb is still quite close to its transition temperature. Normal electrons (which do carry heat, as per two-fluid model) freeze away exponentially when the temperature is lowered below the transition. At half-Tc the normal electron fraction still contributes significantly on the heat conductivity.

Regards, Mikko

Reply to
Mr Stonebeach

On 12/02/13 21.09, Tim Wescott wrote: ...

Hi Tim

Do you mean the Norton amplifier?:

Lossless Feedback Amplifiers: Theory and Advanced Techniques:

formatting link
"... Perhaps the single most significant development in high dynamic range amplifiers has been that of the lossless feedback amplifier. Conceived and patented by David Norton and Allen Podell of Adams-Russell (2), this to- pology is often referred to as a Norton amplifier, and sometimes as noiseless feedback. ..."

/Glenn

Reply to
Glenn

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.