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Design >> RF Design >> Explanation Needed on these topics
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Message started by engineer on Jun 16^th, 2011, 12:05am

Title: Explanation Needed on these topics
Post by engineer on 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

Title: Re: Explanation Needed on these topics
Post by buddypoor on 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)

Title: Re: Explanation Needed on these topics
Post by fonseca.ha on Jun 16^th, 2011, 6:11am

Hello Engineer
What do you mean by K and B?
H.

Title: Re: Explanation Needed on these topics
Post by rfcooltools.com on 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.

http://rfcooltools.com

Title: Re: Explanation Needed on these topics
Post by engineer on 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

Title: Re: Explanation Needed on these topics
Post by rfcooltools.com on 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.

http://rfcooltools.com