Amplifiers – With semiconductor amplifying device – Including field effect transistor
Patent
1987-05-21
1989-07-11
Mullins, James B.
Amplifiers
With semiconductor amplifying device
Including field effect transistor
307319, 330 54, 330286, 330297, H03F 360
Patent
active
048475688
ABSTRACT:
In order to supply a d.c. bias to the drain electrodes of MESFETS (1-4) in a distributed amplifier operating in the 500 MHz to 20 GHz or above, a d.c. source (15) is connected to the drain line (5,9,11,14) via a feed component (16) which comprises a ferrite bead (17) having an axial aperture (18). A coil (19) comprising, for example, four turns of 20 micron gold wire is wound on the bead in toroidal fashion. The bead may be of the kind which is used for low-frequency interference suppression or for encircling the emitter lead-out wire of a bipolar transistor operating in the lower megahertz range. At these relatively low frequencies in the conventional use of the bead, the bead material will exhibit low magnetic losses and high permeability. However, in the present invention, due to the microwave signal in the coil, the bead operates over a frequency band which is many times higher than its normal operating band. At these high frequencies the bead material exhibits quite large losses. The feed component acts, as far as the microwave signal is concerned, as though it is a relatively large resistor, which isolates the low impedance of the d.c. source from the microwave signal path in the drain line. As far as the bias supply is concerned, the d.c. resistance of the coil is negligible, so that there is virtually no d.c. power dissipated in the feed component. The feed component can be used for other applications where a high resistance at microwave frequencies is required, together with substantially zero d.c. resistance.
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IEEE Transactions on Microwave Theory and Techniques, vol. MT-32, No. 3, 3/84, pp. 268-373, "MESFET Distributed Amplifier Design Guidelines".
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Mullins James B.
National Research Development Corporation
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