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1983-10-04
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57 lines
FREQ S21 S12
in GHz MAG ANGLE MAG ANGLE
0.01 1.488 177.91 0.011 88.33
0.02 1.487 175.82 0.022 86.68
0.03 1.485 173.73 0.034 85.03
0.04 1.481 171.65 0.045 83.38
0.05 1.477 169.58 0.056 81.74
0.06 1.472 167.52 0.067 80.11
0.07 1.466 165.47 0.077 78.49
0.08 1.46 163.43 0.088 76.88
0.09 1.452 161.41 0.098 75.29
0.1 1.444 159.41 0.109 73.72
We may now save these S-parameters on disk, in a file
that we shall call J309. This data set is to be used in the
next two examples.
d. FEEDBACK AMPLIFIER
Looking at the stability analysis of our modelled device,
we find that it is marginally stable:
FREQ INPUT STABILITY CIRCLES
in GHz DIST ANGLE RADIUS I/O K
0.01 1.15 31.53 0.56 O 0.01
0.02 1.5 51.79 1.11 O 0.02
0.03 1.91 63.72 1.6 O 0.02
0.04 2.3 71.33 2.05 O 0.03
0.05 2.65 76.67 2.42 O 0.04
0.06 2.95 80.72 2.73 O 0.05
0.07 3.18 83.97 2.97 O 0.05
0.08 3.36 86.7 3.15 O 0.06
0.09 3.49 89.08 3.28 O 0.07
0.1 3.57 91.19 3.36 O 0.08
The three columns after the frequency describe the loca-
tion and size of the stability circle. The fifth column, with
the I's and O's, indicates whether the region of stability is
inside (I) or outside (O) this circle. The last column is the
Linville stability factor. If this last value is greater than
or equal to 1.0, then the device is unconditionally stable.
If it is between 1.0 and 0.0, then the device is conditionally
stable. If it is between 0.0 and -1.0, then the device is
conditionally unstable. If it is less than or equal to -1.0,
then the device is unconditionally unstable. In our example,
the stability factor is just slightly greater than 0.0, indi-
cating a condition of marginal stability when the device is
terminated with 50 ohms.
To correct this, we need to minimize S12, the reverse
transmission coefficient. This is commonly done through neu-
tralization (or unilateralization), which can be accomplished
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