START540TR STMicroelectronics, START540TR Datasheet - Page 9

• Manufacturer Part Number: START540TR
• Description: RF Bipolar Small Signal NPN High Frequency
• Manufacturer: STMicroelectronics

Specifications of START540TR

• Dc Collector/base Gain Hfe Min: 100
• Mounting Style: SMD/SMT
• Configuration: Single
• Transistor Polarity: NPN
• Collector- Emitter Voltage Vceo Max: 4.5 V
• Emitter- Base Voltage Vebo: 1.5 V
• Continuous Collector Current: 0.04 A
• Power Dissipation: 180 mW
• Maximum Operating Temperature: + 150 C
• Package / Case: SOT-323-4
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The generated low frequency product (f2-f1) modulates the base-emitter and colle ctor-emitter voltages
of the transistor. This modulation causes a base and collector voltages fluctuation that lowers the
linearity of the amplifier.
The base voltage, in fact, determines the quiescent current for the device and the collector voltage
determines the saturation point. In order to reduce this effect a proper bypassing has been implemented
at both c ollector and base. For that reason with the introduction of low frequency decoupling capacitors
C6 (47nF) on the collector and C4 (47nF) on the base improves the IP3 significantly.
The Output IP3 is calculated as follows:
where
present at the amplifier output, and the level of the highest 3rd -order distortion product. The
measured is 74dB.
So we have:
Figure 13: Output IP3 Measurement
IM3 (please refer figure 13) is the difference between one of two equal amplitude test tones
IP3out
=
------------- -
IM 3
2
+
IP3out
Pout
=
=
74
----- -
2
------------- -
IM3
2
+
–
+
13
Pout
=
24dBm
AN1465 - APPLICATION NOTE
9/10
IM3