11
Hints and Troubleshooting
Oscillation
Unconditional stability of the MGA-85563 is dependent
on having very good grounding. Inadequate device
grounding or poor PCB layout techniques could cause
the device to be potentially unstable.
Even though a design may be unconditionally stable (K >
1 and B1 > 0) over its full frequency range, other possibil-
ities exist that may cause an amplier circuit to oscillate.
One thing to check is feedback in bias circuits. It is impor-
tant to capacitively bypass the connections to active bias
circuits to ensure stable operation. In multistage circuits,
feedback through bias lines can also lead to oscillation.
Components of insucient quality for the frequency
range of the amplier can sometimes lead to instabil-
ity. Also, component values that are chosen to be much
higher in value than is appropriate for the application
can present a problem. In both of these cases, the com-
ponents may have reactive parasitics that make their im-
pedances very dierent than expected. Chip capacitors
may have excessive inductance, or chip inductors can
exhibit resonances at unexpected frequencies.
A Note on Supply Line Bypassing
Multiple bypass capacitors are normally used through-
out the power distribution within a wireless system.
Consideration should be given to potential resonances
formed by the combination of these capacitors and the
inductance of the DC distribution lines. The addition of
a small value resistor in the bias supply line between
bypass capacitors will often de-Q the bias circuit and
eliminate resonance eects.
Statistical Parameters
Several categories of parameters appear within this data
sheet. Parameters may be described with values that are
either “minimum or maximum,” “typical,” or “standard
deviations.”
The values for parameters are based on comprehensive
product characterization data, in which automated mea-
surements are made on of a minimum of 500 parts taken
from three non-consecutive process lots of semiconduc-
tor wafers. The data derived from product characteriza-
tion tends to be normally distributed, e.g., ts the stan-
dard bell curve.
Parameters considered to be the most important to
system performance are bounded by minimum or
maximum values. For the MGA-85563, these parame-
ters are: Gain (Gtest), Noise Figure (NFtest), and Device
Current (Id). Each of the guaranteed parameters is 100%
tested as part of the manufacturing process.
Values for most of the parameters in the table of Electri-
cal Specications that are described by typical data are
the mathematical mean (μ), of the normal distribution
taken from the characterization data. For parameters
where measurements or mathematical averaging may
not be practical, such as S-parameters or Noise Param-
eters and the performance curves, the data represents a
nominal part taken from the center of the characteriza-
tion distribution. Typical values are intended to be used
as a basis for electrical design.
To assist designers in optimizing not only the immedi-
ate amplier circuit using the MGA-85563, but to also
evaluate and optimize trade-os that aect a complete
wireless system, the standard deviation (σ) is provided
for many of the Electrical Specications parameters (at
25°C) in addition to the mean. The standard deviation is
a measure of the variability about the mean. It will be re-
called that a normal distribution is completely described
by the mean and standard deviation.
Standard statistics tables or calculations provide the
probability of a parameter falling between any two
values, usually symmetrically located about the mean.
Referring to Figure 24 for example, the probability of a
parameter being between ±1V is 68.3%; between ±2V is
95.4%; and between ±3V is 99.7%.
68%
95%
99%
Parameter Value
Mean (μ)
(typical)
-3σ-2σ-1σ+1σ+2σ+3σ
Figure 24. Normal Distribution.
Phase Reference Planes
The positions of the reference planes used to specify S-
parameters and Noise Parameters for the MGA-85563 are
shown in Figure 25. As seen in the illustration, the refer-
ence planes are located at the point where the package
leads contact the test circuit.
REFERENCE
PLANES
TEST CIRCUIT
Figure 25. Phase Reference Planes.