AN4003 Datasheet, PDF (1/6 Pages) Fairchild Semiconductor – PC POWER SUPPLY DESIGN WITH KA3511

Application Note
AN4003
Closed Loop Control Maximizes
MAPM-030400-010C00 and MAPM-030400-060C00 Module Performance
Rev. 1
I. Introduction
The MAPM-030400-010C00 and MAPM-030400-060C00 RF amplifier modules work together to form the basic
building block of a 30 MHz to 400 MHz amplifier that can supply over 60 W of output power. With the addition
of a few components, gain flatness over frequency and temperature can be maximized over its entire frequency
range to create a compact amplifier suitable for digital, AM and FM applications.
II. Description of the Amplifiers and Open Loop Performance
The MAPM-030400-010C00 Pre Amplifier is designed for a fixed 13 dBm input power. The ALC pin is then
used to adjust the RF power level from 0 W to over 10 W with a 0 V to 10 V control voltage. The module itself
consists of two stages of RF amplification. The first stage is push-pull cascode that can supply about 2 W. A
gain-equalization network is included between the stages. The final stage of the preamp is a conventional
Class AB silicon bipolar RF power amplifier with transformer-based matching. ALC is accomplished by setting
the current through the cascode chain as well as the bias current in the Class AB stage. This module is con-
tained in a compact aluminum housing.
The MAPM-030400-060C00 Power Amp consists of a single stage DMOS transistor with broadband coaxial
transformer-based matching. It is in a copper housing for maximum heat transfer.
When both modules are cascaded with a 1.75 dB pad between them, the power transfer curves look like Figure
1. The RF output power at a fixed 4.0 V ALC voltage ranges from 10 W to 94 W – a variation of 9.7 dB. The
saturated RF output power ranges from 73 W to over 100 W.
Pout Vs ALC by Frequency
120
60 MHz 90 MHz
Pre-amp driving power amp
1.75 dB isolation between Amps
100
Vcc = 27 V
225 MHz 175 MHz
250 MHz
Pin = 13 dBm
80
30 MHz
60
40
20
0
0
2
4
6
8
ALC (Volts)
400 MHz
300 MHz
350MHz
400 MHz
350 MHz
300 MHz
250 MHz
175 MHz
125 MHz
90 MHz
60 MHz
30 MHz
10
12
Figure 1. Varying ALC voltages results in gain variation. Closed-loop control can improve gain
flatness over frequency and temperature.
1
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