AN10714_1
© NXP B.V. 2010. All rights reserved.
Application note
Rev. 01 — 26 January 2010
3 of 21
NXP Semiconductors
AN10714
Using the BLF574 in the 88 MHz to 108 MHz FM band
1.
Introduction
The BLF574 is a new, 50 V, push-pull transistor using NXP Semiconductors’ 6
th
generation of high voltage LDMOS technology. The two push-pull sections of the device
are completely independent of each other inside the package. The gates of the device are
internally protected by the integrated ElectroStatic Discharge (ESD) diode.
The device is unmatched and is designed for use in applications below 600 MHz where
very high power and efficiency are required. Typical applications are FM/VHF broadcast,
laser or Industrial Scientific and Medical (ISM) applications.
Great care has been taken during the design of the high voltage process to ensure that
the device achieves high ruggedness. This is a critical parameter for successful broadcast
operations. The device can withstand greater than a 10 : 1 VSWR for all phase angles at
full operating power.
Another design goal was to minimize the size of the application circuit. This is important in
that it allows amplifier designers to maximize the power in a given amplifier size. The
design highlighted in this application note achieves over 600 W in the 88 MHz to 108 MHz
band in a space smaller than 50.8 mm
×
101.6 mm (2 ”
×
4 ”). The circuit only needs to be
as wide as the transistor itself, enabling transistor mounting in the final amplifier to be as
close as physically possible while still providing adequate room for the circuit
implementation.
This application note describes the design and the performance of the BLF574 for
Class-B CW and FM type applications in the 88 MHz to 108 MHz frequency band.