JPS5811746B2 - Ultra high frequency transistor amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultra-high frequency band transistor amplifier, and particularly to the structure of the UHF band FET low noise amplifier.

Recently, very high performance G with a gate width of about 1 micron has been developed.
The aAsFET (Field Effect Transistor) has been developed and has low noise characteristics similar to conventional tunnel diode amplifiers at ultra-high frequencies.

Amplifiers with greater output characteristics and intermodulation characteristics than bipolar transistors are being developed.

However, conventional devices have mainly been used for ultra-high frequency bands above the IGHz band, and have not been put to practical use in the UHF band such as the 0.4 to 0.8 GHz band.

The reason for this is that when the input/output impedance of the FET drops to the UHF band, it becomes extremely high, making it difficult to construct a broadband matching circuit.

For example, 1 micron gate GaAsFET (28 to 85,
An example of the input and output impedance at 650MHz for NEC Corporation is 7Ω-j475Ω and 320Ω-j, respectively.
It is 190Ω, which is several times higher than the system line characteristic impedance of 50Ω.

In this case, 50nH (+j200Ω at 650MHz
) large inductor element, IBF (650MHz
-j250Ω) capacitor or several hundred
A wideband amplifier cannot be obtained unless the circuit is constructed using a strip line having a characteristic impedance of about Ω.

Microstrip line circuits used in conventional microwave ICs are high-performance, inexpensive, and highly practical, but because they use substrates with dielectric constants greater than 1, such as alumina and glass Teflon, they are essentially high-impedance circuits. is inappropriate.

Distributed lines also have the disadvantage of being quite large in the UHF band.

On the other hand, if the matching circuit is composed of individual lumped constant elements, the size can be reduced, but mass production is not possible.

In addition, in practice, a coil with an inductance of about 50 nH cannot be used because its resonant frequency is in the UHF band, and especially if the wire is made significantly smaller and thinner in order to raise the resonant frequency, the loss will increase. , the low noise characteristics of the FET are lost.

The purpose of the present invention is to solve the above-mentioned conventional problems and provide a high-performance ultra-high frequency transistor amplifier using lumped constant elements that can be miniaturized without losing the advantages of integrated circuits that are highly mass-producible. be.

According to the present invention, an ultra-high frequency transistor is provided on a dielectric thin plate, and an input circuit connected to the ultra-high frequency transistor by a conductive film lumped constant circuit formed by the dielectric thin plate and a conductive film provided on the dielectric thin plate. A very high frequency transistor amplifier is obtained, which constitutes an output circuit and is characterized in that the dielectric thin plate is supported and short-circuited substantially parallel to a grounded conductive plate at a constant distance.

The present invention will be explained below using drawings showing one embodiment.

FIG. 1 shows a first embodiment of the present invention, in which a is a plan view with the top cover removed, and b is a sectional view taken along line AA''.

FIG. 2 is an equivalent circuit diagram of the input/output circuit of this embodiment.

In Fig. 1, a thickness t is placed on the ground conductor plate 1 at a distance d.
A dielectric thin plate 2 is supported in parallel, a transistor or FET 3 is arranged in the center thereof, and input/output matching circuits are formed in front and behind it.

The ground conductor plate has a case body at its edges, and 21° and 22 to which the input/output connectors 21 and 22 and the top cover 25 are attached are input/output coaxial connectors, whose center conductors 23 and 24 are connected to the circuit and serve as input/output ends. It has become.

The input/output circuit consists of five conductive film inductors 1-L and four conductive film capacitors C1-C4 from the input side, as shown in the equivalent circuit in FIG.

The capacitor C6 is an external capacitor for RF shorting.

The transistor input/output terminals, namely the gate 31 and the drain terminal 32, are connected to the capacitors C2 and C3, and are still connected to the high frequency ground electrode (source electrode in this case) of the transistor.
is fixedly connected to the source electrode 33 and is connected to the source bias terminal 17 and the inductor,
A bias is applied from the drain bias terminal 18 which is continuous from the terminal end.

The ends of the source electrode 33 and the inductor L5 are each grounded at high frequency by an RF short capacitor C5.

In this case, the gate of the FET is DC grounded by the inductor L2 and serves as a bias return path.

Grounding conductive films 11 and 12 are formed on the front and back surfaces of the dielectric thin plate 2, respectively, and are connected through the edge side of the dielectric thin plate 2 as shown in b. It is crimped to the ground conductor plate 1 with 20 fixing screws.

As can be seen from FIG. 1, in this embodiment, the inductors 1 to L5 are made of elongated conductor films, for example 16, on one side of the dielectric thin plate 2.

When the width W of this conductor film is 1rr and the distance t+d from the ground conductor plate is 5 mm, the impedance of this inductor conductor film to the ground is approximately 220Ω, and this length 1
A value of approximately 7 nH per 0 mm is obtained.

Moreover, the high frequency propagation wavelength on such a conductor film inductor supported in the air is almost equal to the propagation wavelength in the air, so for example, an inductor of 40nH and approximately 40mm in length is 65
It is less than 1/1o of the 0 MHz wavelength of about 490 mm, and is considered to be almost a lumped constant.

Further, if the width is about 1rr, the Q value will also be about 1000.

On the other hand, the conductive film capacitors C1 to C4 in the matching circuit have a simple structure in which a dielectric thin plate 2 is sandwiched between them.For example, in the case of C1, a rectangular conductive film 13.15 is formed on the surface of the dielectric thin plate.
Two capacitors connected in series are formed between the conductor film 14 on the opposite back surface.

If you use a high-frequency printed circuit board that uses a dielectric thin plate such as Teflon glass, you will get the lumped constants mentioned above.

C can be obtained at a very low cost and easily by simply patterning a conductor film.

In the case of Teflon glass, the dielectric constant is about 2.6, so if this thickness 1=0.8 mm, a 1 pF capacitor can be easily obtained by etching a conductor pattern of about 34 mm2.

Since a high impedance circuit requires only a very small capacitance, the conductor film capacitor with the above-mentioned simple structure is suitable.

The Q value of the UHF band is also expected to be several thousand or more.

As described above, according to the present invention, a very inexpensive material such as a high frequency printed board is used, and the high impedance circuit required for a UHF (UHF) transistor amplifier has very high performance.
And it can be obtained as a small lumped constant.

Moreover, the manufacturing method is suitable for mass production, and inexpensive amplifiers can be obtained.

Furthermore, since it is easy to obtain through holes using printed board technology, it is also possible to achieve even higher performance as in the second embodiment shown in FIG.

FIG. 3 is a diagram showing a part of the second embodiment, in which a is a single-plate ceramic capacitor as the RF shorting capacitor C5, a transistor 3 is mounted on it, and the whole is connected to a grounding conductor on the back side through a through hole 50. It is fixed on the source electrode 33 connected to the membrane 12.

3' is the ground terminal of the transistor. Furthermore, in this case, a grounding support conductor 1' is used to support the dielectric thin plate 2 in the center and to short-circuit the grounding conductor film 12 directly to the grounding conductor plate.

Such a through-hole structure enables RF grounding with less unnecessary inductance in the grounding portion.

Further, as shown in FIG. 5B, if the through hole 50 is used, the conductor film inductor 19 can be formed in a spiral shape and connected to the conductor film lead 19' on the other side, and the conductor film inductor can be made smaller.

In this case, if a capacitor in series with the inductor is required, the through hole shown in the figure can be eliminated.

As the dielectric thin plate, in addition to the above-mentioned Teflon glass, Teflon alone, polyolefin, etc. high frequency printed boards, for lower frequencies, ordinary printed boards such as epoxy, melamine, polyester, phenol resin, etc. may be used, and quartz, alumina ceramic, etc. Inorganic dielectric materials such as

Although these have a large dielectric constant, this does not pose much of a problem when they are supported in the air as in the present application.

The conductor film is a copper film in the case of printed boards, but a gold plating coating is required if necessary.
Chromium-gold, titanium-platinum-gold films, etc. are used.

Although this application is primarily aimed at UHF band low-noise FET amplification, it goes without saying that the principles of this application can also be applied to UHF band bipolar transistor amplifiers or UHF SHFS amplifiers that require very high impedance input/output circuits.

[Brief explanation of drawings]

FIG. 1a is a plan view showing the first embodiment with the L lid removed, FIG. 1b is a cross-sectional view along AA', and FIG. 2 is an equivalent circuit diagram thereof. In the figure, 1 is a ground conductor plate, 2 is a dielectric thin plate, 3 is a transistor, L1 to L are conductor film inductors, and 01 to C
4 is a conductive film capacitor, C5 is an RF short capacitor 21, 22 is an input/output connector, 12° 13 is a grounding conductive film, 20 is a set screw, 17 is a source bias terminal, 1
8 is a drain bias terminal, and 25 is an upper lid. FIG. 3 is a partial sectional view a and a partial plan view showing the second embodiment, in which 1' indicates a grounding support conductor, and 50 indicates a through hole.

Claims (1)

[Claims] 1. An ultra-high frequency transistor is provided on a dielectric thin plate, and an input/output matching circuit is connected to the ultra-high frequency transistor by a conductive film lumped constant circuit formed by the dielectric thin plate and a conductive film provided on the dielectric thin plate. 1. An ultra-high frequency transistor amplifier characterized in that the thin dielectric plate is supported and short-circuited in parallel with a ground conductive plate at a constant distance.