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Details, datasheet, quote on part number:NCO8701
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APPLICATION NOTE
A wideband 30 W push-pull amplifier with two MOS transistors BLF244 (VDS = 28 V); range 25 - 110 MHz
NCO8701
Philips Semiconductors
A wideband 30 W push-pull amplifier with two MOS Application Note transistors BLF244 (VDS = 28 V); range 25 - 110 MHz NCO8701
CONTENTS 1 2 2.1 2.2 2.3 2.4 3 3.1 3.2 3.3 3.4 4 4.1 4.2 5 6 6.1 6.2 6.3 6.4 7 8 INTRODUCTION AMPLIFIER DESIGN General Powergain, input- and output impedance Output matching section Input matching section TRANSFORMER DESIGN General Design of the output transformer Design of the input transformer The tapped choke (T2) AMPLIFIER CONSTRUCTION Printed circuit board and component layout Heatsink AMPLIFIER ALIGNMENT AMPLIFIER PERFORMANCE General Performance at constant output power Performance at constant input power Performance at constant frequency CONCLUSIONS REFERENCES
1998 Mar 23
2
Philips Semiconductors
A wideband 30 W push-pull amplifier with two MOS transistors BLF244 (VDS = 28 V); range 25 - 110 MHz
1 INTRODUCTION
Application Note NCO8701
A wideband push-pull power amplifier has been developed for the frequency range 25-110 MHz. The design is based on the BLF244, a silicon N-channel enhancement mode vertical D-MOS transistor designed for large-signal amplifier applications in the VHF range. This device can deliver 15 W output power at 175 MHz when operated from a 28 V supply. The transistor has a 4-lead flange envelope with a ceramic cap (SOT123). The objective was to design and construct a 30 W wideband amplifier with high gain and efficiency and low input VSWR and second order distortion. With respect to gain and efficiency a reasonable flatness was desired. The push-pull design is employed because of its low second order distortion. The design and practical realization of this amplifier are described in the following chapters. 2 2.1 AMPLIFIER DESIGN General
The schematic set up of the amplifier is depicted in Fig.1.
handbook, full pagewidth
BLF244 RF INPUT MATCHING + GAIN EQUALIZATION NETWORK BLF244
1:1 50
RF OUTPUT MATCHING NETWORK
1:1 50
MGH988
Fig.1
Two 1 : 1 balance to unbalance transformers are applied; one for splitting the single-ended input source into two out of phase sources driving the transistor-inputs, the other for adding the outputs from the transistors. Transmission line transformers are employed because of there excellent broadband response. These transformers consist of a twisted-wire-pair transmission line wound on a ferrite toroid. At the input side a special matching network is applied to obtain a low VSWR and compensation for variation in gain with frequency. The matching network at the output side provides the transistors with the optimum load for an output power of 30 W at VDS = 28 V. 2.2 Powergain, input- and output impedance
The design has been started by determining powergain, input impedance and output impedance of the transistor for the frequency range 25-110 MHz. First the output impedance was determined. For HF and VHF the optimum load resistance RL can be calculated with reasonable accuracy with the formula:
1998 Mar 23
3
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