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engineer New Member Offline Posts: 4	Explanation Needed on these topics Jun 16^th, 2011, 12:05am 1) Why both K and B1 are needed for amplifier stability 2) Difference between normal and gummel poon bjt
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buddypoor Community Fellow Offline Posts: 529 Bremen, Germany	Re: Explanation Needed on these topics Reply #1 - Jun 16^th, 2011, 3:44am engineer wrote on Jun 16^th, 2011, 12:05am: 1) Why both K and B1 are needed for amplifier stability Excuse me, but do you really believe that somebody can answer such a "question"? (K could be the Boltzmann constant and B, for example, the magnetic flux density)
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fonseca.ha Junior Member Offline Posts: 28 UK	Re: Explanation Needed on these topics Reply #2 - Jun 16^th, 2011, 6:11am Hello Engineer What do you mean by K and B? H.
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rfcooltools.com

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Re: Explanation Needed on these topics
Reply #3 - Jun 16^th, 2011, 9:15am

Engineer,

The following link depicts the equations for the parameters you are discussing.
http://cp.literature.agilent.com/litweb/pdf/5989-9308EN.pdf

The way I would interpret it is that K can be less than 1 and still be stable so that is where B1 comes into the picture. B1 >0 is similar to |delta|^2 <1 which qualitatively means that the reverse isolation is greater then the forward gain independent of matching. Satisfying B1>1 or |delta|^2 <1 when K<1 implies stability.

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engineer

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Re: Explanation Needed on these topics
Reply #4 - Jun 16^th, 2011, 12:27pm

Hello Folks,

what I mean by K and B1 is

K- Rollet Stability factor

B1 - Auxialary Stability Factor

In almost all books, the say thay for an amplifer to be stable, K>1 and B1 > 0.

I just want to know, why that both quantities are needed. Is K alone not sufficient ? Kindly explain. Also, Can we leave K and consider only B1.

Regards,
Engineer

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rfcooltools.com

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Re: Explanation Needed on these topics
Reply #5 - Jun 16^th, 2011, 7:16pm

Engineer,
Disregard my previous post where I stated that k<1 provided that B1>0 that is not unconditional.

Equations:
B1 = 1+|s11|^2 �|s22|^2 �|Δ|^2

K=(1�|s11|^2 �|s22|^2 +|Δ|^2)/(2|s12 �s21|)

|Δ| = |s11 � s22 � s12 � s21|

if |Δ|>1 then |s11 | could be> 1 and the there are some cases where k>1 and its potentially unstable since the reflected voltage in port1 is greater then the transmitted indicating a negative real impedance. i believe B1 >0 alone is not sufficient. Its clear to me why |Δ|<1 K>1 are stable but it not obvious about K >1 and B>0.

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