What is difference between K factor and Mu Factor

stability factor mu

Hi, i have been looking into LNA design in ADS and have come across a design which calculates the K Factor along with B1 parameter and also the Mu factor.
The statement is that K>1 and B1>0 for stability, Mu>1 for stability.

What exactly is the difference between K factor and the Mu factor, when should i use one over the other? Although the resulting calculations (when tabulated in ADS) are very close to being exact, i am just curious as to when and why you would choose one over the other.

Thanks,
Chris.

mu stability factor

Hi

When working with k factor, it is important that it is larger then 1. However, the acctual value is not telling anything. You can not say that an amplifier with k=3 is "more stable" then amplifier with k=1.1. On the other hand, mu factor can tell you that, the higher it is , more far from oscillations the amplifer is.

Hope this helps

flyhigh

To follow up:

As noted K>1 says stability but give no hint at how far outside the smith chart the stability circles are. Similarly if you get K<1 it doesn't give you much insight as to what to do, or where to do it.

On the other hand Mu and Muprime have direct relation and give great insight.

Mu is the distance from the center of the Smith Chart to nearest point of instability on the INPUT stability circles. Muprime is the same, but for the OUTPUT stability circles. Hence a mu or muprime of 1 means that a stability circle just brushes the edge of the smith chart.

Here's the real cool thing about plotting both Mu and Muprime that blows K-Factor stability analysis out of the water:

Lets say you get a Mu of 0.9, a Muprime of 0.2, and a K of 0.5.

The large Mu says you only have to do a little work at the INPUT to stabilize the circuit, and the small Muprime says that fixing it at the output is near futile (counter intuitive at first). If you then go plot the stability circles at the offending frequency (or range of frequencies) you can immediately see if adding series resistance, shunt resistance, or both is the correct path. Stability circles on the left indicates the need for series resisance, while stability circles on the right indicates shunt resistance. Stability circles on the top or bottom are best solves with both a series and shunt resistance.

Hi,
I'm currently designing a UWB patch antenna using CST MWS. I got all the results i want such as S11,radiation pattern etc. The line impedance of my antenna also got 50 ohms. But what is confusing me is the smith chart not all 50 ohms at my desired frequency (3.1 - 10.6 GHz). Is smith chart still important since i already got 50 ohms at line impedance? And what would happen to the fabricated antenna if the smith chart not 50 ohms?