A 300w Mosfet Linear Amplifier For 50 Mhz

 In an earlier article, the author described a 50 MHz 125V
250W class C Amplifier using the ARF448A/B high voltage
MOSFET devices.
1
  This paper now describes an improved
version of that Amplifier which is capable of class AB linear
operation. The design changes required and the procedures
involved are explained and demonstrated.  A complete
description of the Amplifier and its construction are
presented as well as the measured performance.
INTRODUCTION
High voltage, high Power MOSFETs have been shown to
be very capable RF Power Amplifiers
2
  The metal gate
architecture of the ARF series of devices from Advanced
Power Technology has raised the frequency limits for this
type of device to 100 MHz.  The APT448A/B is typical of
the series.  It has a 68000 square mil die with a breakdown
voltage rating, BVdss, of 450V.  The device is packaged in
the inexpensive TO-247 plastic package and is available in
common source symmetric pairs.  Like all MOSFETs the
gate threshold voltage, Vth,  has a negative temperature
coefficient.  This makes operation as a linear amplifier
difficult to impossible.
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50MHz Amplifier Schematic
50MHz Amplifier Schematic



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