AN1941 Freescale Semiconductor / Motorola, AN1941 Datasheet - Page 5

• Manufacturer Part Number: AN1941
• Description: Modeling Thermal Effects in RF LDMOS Transistors
• Manufacturer: Freescale Semiconductor / Motorola

2. Enter the label for the thermal port.
3. Click on the port labeled “T” on the DUT.
4. The thermal port has been labeled.
5. ADS then calculates T
NOTE: For better viewing on the Web of Step 4 graphic and Figure 5, click on link for larger versions of graphics.
MOTOROLA SEMICONDUCTOR APPLICATION INFORMATION
equation:
T
(flange)
(flange)
= θ
JC
using the following
Figure 5. Root and MET Model IV Curves Superimposed
* P
Freescale Semiconductor, Inc.
DISS
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Go to: www.freescale.com
The data sheet value for this will be used if the user sets
R
CONCLUSION
characteristics. The data from this multivariate plot can be
used in an RF simulation in conjunction with other RF
characteristics, such as drain efficiency, to create a more
accurate expression for V
temperature compensation circuit.
model and the MET model at 25°C and illustrates the potential
for error between the two models. As shown, the models tend
to agree with each other at lower V
the models tend to deviate at more practical levels of
drain–source currents and voltages. A typical bias condition
for the MRF19125 is V
1100 mA. The Root model shows that the required gate
voltage is approximately 3.79 V, whereas the MET model
more accurately shows the required gate voltage to be 3.71 V.
Although the difference of only 80 mV between the two models
may seem insignificant, it would account for a difference of
600 mA in I
the model types in more advanced RF simulations in ADS.
These topics are beyond the scope of this application note and
will be discussed in subsequent ADS user application notes.
TH
The thermal resistance, θ
Figure 4 shows the overall T
Figure 5 shows the superimposed IV curves of the Root
There are advantages and disadvantages for using each of
To access all Motorola RF LDMOS Model libraries, go to:
= –1.
http://www.motorola.com/rf/models
DQ
at this drain voltage.
DS
GS
= 26 V with a quiescent current of
JC
. This would be equivalent to a
, is predefined by ADS as R
DS
FLANGE
and lower I
, I
DS
DQ
AN1941
. However,
and V
5
TH
GS
.