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Details, datasheet, quote on part number:NCO8705
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APPLICATION NOTE
A linear amplifier (1.6 - 28 MHz) for 8 W PEP in class-A with the BLF175
NCO8705
Philips Semiconductors
A linear amplifier (1.6 - 28 MHz) for 8 W PEP in class-A with the BLF175
CONTENTS 1 2 3 4 4.1 4.2 4.2.1 4.2.2 4.3 4.4 4.5 5 6 6.1 6.2 7 7.1 7.2 7.3 8 9 9.1 SUMMARY INTRODUCTION GENERAL CONSIDERATIONS DESIGN OF THE AMPLIFIER Circuit description Design procedure Powergain Cut-off frequency Calculation Output matching Input matching AMPLIFIER ALIGNMENT AMPLIFIER CONSTRUCTION Construction notes Heatsink AMPLIFIER PERFORMANCE General Performance at constant output power Performance at constant frequency CONCLUSION REFERENCE CIRCUIT DIAGRAM OF THE WIDEBAND LINEAR AMPLIFIER
Application Note NCO8705
1998 Mar 23
2
Philips Semiconductors
A linear amplifier (1.6 - 28 MHz) for 8 W PEP in class-A with the BLF175
1 SUMMARY
Application Note NCO8705
In this report a description is given of a wideband linear amplifier intended for driver applications in SSB transmitters for the frequency range 1.6 to 28 MHz. It employs a MOS-transistor BLF175 suited for a supply voltage of 50 V. The transistor is adjusted in class-A with a quiescent drain current of 800 mA. The main properties at Po = 8 W PEP are: Powergain: 28.3 - 28.6 dB IMD (d3): -41 dB IMD (d5): -60 dB Input return loss: -26 dB. 2 INTRODUCTION
The amplifier that will be discussed in this report concerns a wideband linear amplifier, designed for driver applications is SSB transmitters in the HF band. This design is based on the RF power MOS-transistor BLF175 which is primarily designed for communication purposes in the HF-band. This device can deliver 8 W PEP in class-A at an IMD (d3) < -40 dB, when operated from a supply voltage of 50 V. It is encapsulated in a SOT123 four-lead flange type with a ceramic cap. 3 GENERAL CONSIDERATIONS
One of the most important factors to be considered in the design of driver stages for SSB transmitters is intermodulation distortion. The major cause for intermodulation distortion is the non-linear transfer characteristic of the transistor. A generally accepted IM distortion figure is < -40 dB. To achieve this, driver stages must be operated in class-A. One of the properties of a class-A amplifier is its low efficiency, which for pre-drivers is of less importance. The amplifier must have a flat gain response, within a few tenths of a dB. Its response should preferably be superiour to that of the final amplifier of a SSB transmitter. The input return loss versus frequency must be low because, it will possibly form the load of a pre-driver. 4 4.1 DESIGN OF THE AMPLIFIER Circuit description
Figure 1 shows the basic circuit of this broadband amplifier. Negative feedback combined with parallel input compensation has been applied to obtain flat gain and low input return loss.
handbook, full pagewidth
RF
L 4÷1 50 input C 50 output
Rgs
MGM367
Fig.1 Basic circuit of the wideband amplifier.
1998 Mar 23
3
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