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Application Information
MOTOROLA WIRELESS
RF PRODUCT DEVICE DATA
MBC13720
2–11
2
Application Information
The MBC13720 SiGe:C LNA is designed for applications in the 400 MHz to 2.4 GHz range. It has four
different modes; Low IP3, High IP3, Bypass, and Standby. The IC is programmable through the Enable 1
and 2 pins. In Low IP3 mode, the current consumption is optimized. Current consumption is higher in High
IP3 mode to boost the intercept point performance. The gain difference between Low IP3 and High IP3
modes is typically 1.0 dB and typically the Low IP3 mode has a slightly better noise figure performance.
The internal bypass switch is designed for broadband applications. One of the advantages of the
MBC13720 is the simplification of matching network in both bypass and amplifier modes. The bypass
switch is designed such that the changes of input and output return losses between bypass mode and
amplifier mode is minimized. As a result, the mismatch at the LNA input and output is minimized and
therefore, the matching network design is simplified as well.
In the design of the external matching network, conjugate match condition does not necessarily provide the
best noise figure performance. Balancing between noise figure, gain, and intercept point is the major
design consideration. Typical circuits are provided in Figures 2 and 3 for 1.9 GHz, 2.4 GHz and 900 MHz
applications.
In Figure 2, it shows the typical application circuit at 1.9 and 2.4 GHz. The noise figure, input intercept
point, gain, and return losses are optimized. L2 and C2 act as a low frequency trap to improve the input
intercept point. The noise figure measured on this board is 1.4 dB (in Low IP3 mode) at 1.9 GHz, including
the external components, connectors, and PC board. The input third order intercept point is 10 dBm (in
High IP3 mode).
In Figure 3, the typical application circuit at 900 MHz is shown. The input low frequency trap again is used
to maximize the input intercept point. It has moderate IP3 performance and high gain. For higher IP3,
Figure 4 shows the application circuit with feedback network. Capacitive feedback method is used to
reduce the gain and therefore increase the 3rd order input intercept point. The feedback circuit is designed
to provide unconditional stability.
The corresponding PCBs are shown in Figures 5 through 10. Typical characteristics of the application
boards are shown in Table 9.
Figure 2. Typical 1.9 and 2.4 GHz LNA
Application Schematic
RF In
C3
1.0 pF
RF
Out
4
5
6
3
1
2
EN2
C4
4.7 μF
EN1
T2
T3
T1
R1
330
C6 27 pF
T1, T2, T3 = 50
Microstrip Line @ 150 mils
C1 27 pF
C2
4.7 μF
L2
2.7 nH
L1
8.2 nH
Bias
Control
F
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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