JPS58146113A - Fet amplifier - Google Patents

Abstract

PURPOSE:To match an external impedance and a impedance at the terminal of amplifier, by opening one end of a strip conductor connected to the terminal and connecting one end of a strip conductor placed in parallel to the specified terminal of the amplifier and the other end to a resistor and a capacitor for termination. CONSTITUTION:One end of a strip conductor 18 connected to a power supply is opened. One end of a strip conductor 19 in parallel with the conductor 18 is connected to an input terminal 2 of an FET amplifier 1, and the other end is terminated with a resistor 11 and a capacitor 12. Since the capacitance of the capacitor 12 is selected for the reactance so as to be almost zero at microwave band, the strip conductors 18, 19, a dielectric base 8 and a ground conductor 9 form a coupling line 20. This coupling line is a band pass filter and arbitrary characteristic impedance is selected by selecting the width and length of the strip conductors 18, 19 and the interval between the strip conductors suitably.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microwave band FET amplifier in which an FIT input/output matching circuit is constructed of microstrips.

Here, to simplify the explanation, we will use a FET with a stability coefficient of 1 or less in the low frequency band and 1 or more in the microwave band.
The figure shows the case where i is used.

Figure 1(a) is a front view of a conventional FET amplifier;
b) is the equivalent circuit in the microwave band of Fig. 1 (1).

FIG. 1 (() is an equivalent circuit in a low frequency band of FIG. 1 (,).

In Fig. 1(a), (1) is a FET, and +21 is a gate terminal.

(3) is the source terminal, (4) is the drain terminal, (5+
, (61° (7) is the IJ tube conductor, (8) is the electroconductor board, (9) is the ground conductor, (ilm is the bias terminal, Qll is the resistor, and is the capacitor.

FET (ll's gate terminal (2) and strip conductor +
One end of 51, the drain terminal (4) and the strip conductor (6
), one end of the source terminal (3) and the ground conductor (9) are connected by soldering or the like. ) IJ tube conductor (
One end of 7) is connected to the IJ tube conductor (5), the other end is connected to the bias terminal α [W:], and between the bias terminal OG and the ground conductor (9), there is a resistor 01 and a capacitor (2). are connected in parallel. Another strip conductor (7
) is connected to the IJ tube conductor (6)K.

The other end is connected to the ground conductor (9
)K connected. The bias terminal is a terminal for applying a proper bias voltage to the FET.

Connected to DC power supply. Furthermore, the strip conductor (5
1 and +61 are connected to a power source and a load, respectively.

The equivalent circuit of Figure 1 (,) in the microwave band is shown in Figure 1 (b).
).

In this figure, the reference symbol is an input matching circuit, α4 is an output matching circuit, and α9 is a bias line. The input matching circuit αJ has the function of matching the power supply impedance and the input impedance of the FIT (11), and is composed of a microstrip consisting of a strip conductor (5j, a dielectric substrate (8), and a ground conductor (9)). In addition, the output matching circuit α4 has the function of matching the load impedance and the output impedance of the FET (1), and the output matching circuit α4 has the function of matching the load impedance and the output impedance of the FET (1).
It is composed of a microstrip consisting of a dielectric substrate (8) and a ground conductor (9). Further, the bias line structure is composed of a microstrip consisting of a strip conductor (7), a dielectric substrate (8) and a ground conductor (9), and the length of the bias line α9 is selected to be a wavelength of n.

The capacitance and actance of capacitor 04 are selected so that el is zero in the microwave band, and the impedance when looking at the bias line Q51 (III) from the gate terminal (2) and drain terminal (4) of FIT (1) is approximately Therefore, the microwave incident from the power supply passes through the input matching circuit (131) and is amplified by the FET (11).

Furthermore, it is supplied to the load through an output matching circuit (141't-).

FIG. 1(c) is an equivalent circuit in a low frequency band of FIG. 1(&). In this figure, Oe is the power supply impedance, αη
is the load impedance. strip conductor t5+,
+61. (In the low frequency band where the length of 71 is sufficiently small compared to the wavelength and the reactance of the capacitor circle is sufficiently large compared to the value of resistor at+, FIT can be expressed as a power supply impedance α6) and a resistor Qll connected in parallel. Also, the impedance viewed from the drain terminal (4) on the load side can be expressed as a load αη.

The reflection coefficient Pout viewed from the drain terminal (4) of FET (11) to the FET side is given by equation (1).

Here, 511e 81□, S2□, S2□ are FIT +
1) S parameter, Pa is the reflection coefficient when looking at the power supply side from the gate terminal (2) of FIT (11).

For stable operation in low frequency band, Pout and load impedance a'? ), it is necessary to choose the relationship appropriately. FE
T (11-8 Parameter, power supply impedance Q6
1 and the load impedance αη is the PET used (1
), depending on power supply and load. In such a case,
By using an appropriate resistance aυ, it is possible to obtain P out that is stable with respect to the load impedance αη.

Power source impedance is typically 50Ω. However, FET
A waveguide may be connected to the input side of the amplifier, or in the case of a multi-stage amplifier, another FET amplifier may be connected. In these cases, the source impedance must be 50Ω.
(P- differs depending on what is connected to the input side of the FET amplifier.For this reason, in the past, in order to make the FET amplifier stable in the low frequency band, the resistance a was set according to the Pll.
I selected and used t+'i.

In this way, it is necessary to select the resistor 011 gold according to the impedance of the waveguide connected to the input side of the FET amplifier and the impedance of other FET amplifiers, and the disadvantage is that the selection of the resistor αB and the selection of 0υ becomes very troublesome. was there. f
So, for a certain power source impedance 0 (to), the resistance α1
Even if I selected 1, oscillation sometimes occurred when other power supply impedances were selected.

In order to eliminate these drawbacks, the present invention uses an input matching circuit for an αT amplifier consisting of an IJ tube conductor with one end open, a dielectric substrate, a ground conductor, and an IJ tube conductor whose one end is terminated with a resistor and a capacitor. The following is an example using a coupled line.

The drawings will be explained in detail.

Fig. 2(,) is a front view of an embodiment of the FET amplifier of the present invention, Fig. 2(b) is an equivalent circuit in the microwave band of Fig. 2(a), and Fig. 2(c) is the equivalent circuit of Fig. 2(a) in the microwave band. This is the equivalent circuit of (,) at low frequency.

In FIG. 2(,), CIL is a strip conductor. One end of the strip conductor U-hinoki is connected to a power source, and the other end is open. Moreover, one end of the strip conductor α9 is connected to the gate terminal (2) of FjET (11),
A bias terminal is connected to the other end, and a resistor (Ill) and a capacitor (2) are connected in parallel between the bias terminal head and the ground conductor (9). 2) are arranged in parallel with each other at a predetermined interval.

The equivalent circuit of Jin's FET amplifier in the microwave band is shown in FIG. 2(b). In this figure, (a) is a coupled line. Since the capacitance of the capacitor (2) is selected so that the reactance becomes zero at tl in the microwave band, the strip conductor (2).

A coupled line head can be formed with the dielectric substrate (8) and the ground conductor (9).

This coupled line (A) exhibits band-pass filter characteristics and can be adjusted arbitrarily by selecting the width and length of the strip conductor (IIJ) and the spacing between the strip conductors (2) and (to) to appropriate dimensions. By choosing the length of the coupled line head to correspond to the wavelength, it can be regarded as a 1/4 wavelength transmission line with a certain characteristic impedance near the center frequency.

Therefore, the coupling line (4) can be used as an input matching circuit (131) that matches the input impedance of the FET fil and the power supply impedance.

In this way, a normal FE that does not have very wide-band characteristics
In the T111 width amplifier, the desired amplification characteristics can be achieved even if the coupled line (2) is used as a matching circuit.

FIG. 2(c) is an equivalent circuit in a low frequency band. Figure 2 (
Since the coupled line (4)) shown in b) has a sufficiently large characteristic impedance in the low frequency band, the impedance seen from the gate terminal (2) of FET (11) to the power supply side is only the resistance circle, and Ps is the power supply impedance. Regardless, it is determined only by the resistance (111. Therefore, an appropriate resistance α
By selecting D, it is possible to achieve stability in the low frequency band regardless of the power supply impedance.

As mentioned above, even if something with arbitrary impedance is connected to the input side of the PV amplifier, the impedance seen from the gate terminal (2) of FET (11) to the power supply side is only the normal pressure resistance αl. There is an advantage that it is not necessary to select the resistance αυ according to the impedance of the waveguide connected to the input side of the FET amplifier and other FET amplifiers as in the conventional case, and a very stable FET amplifier can be obtained.

Figures 3 and 4 show another embodiment of the present invention, in which the resistor Qυ and capacitor are through-holes C, which are through-hole plated or bonded. Ground conductor 1 through υ
9) Ic! It is also possible to continue.

Although the case where the coupled line is used in the input matching circuit has been described above, the present invention is not limited to this, and may be used in the output matching circuit, and in the case of a multi-stage amplifier, it may be used between stages. Furthermore, although the case where the coupled line is constructed of microstrips has been described, the present invention does not change even if the coupled line is constructed of strip lines.

As described above, according to the present invention, one end of a strip conductor is left open, and one end of another strip conductor provided parallel to the IJ tube conductor at a predetermined interval is terminated with a resistor and a capacitor. Coupled line i By using it as a matching circuit for FET amplifiers, desired amplification characteristics can be obtained in the microwave band, and the FET is stable in the low frequency band.
You can get an amplifier. Moreover, there is no need to add a resistor according to the impedance of the waveguide or other FET amplifier connected to the input side of the FET amplifier as in the conventional case, and the design becomes very simple.

[Brief explanation of the drawing]

FIG. 1 (tortoise) is a front view of a conventional FET amplifier, and FIG. 1 (b) is an equivalent circuit diagram in the microwave band of FIG. 1 (凇). FIG. 1(c) is an equivalent circuit diagram in a low frequency band of FIG. 1(,). Fig. 2(,) is a front view of the FF/T amplifier of the present invention, Fig. 2(b) is an equivalent circuit diagram of Fig. 2(&) in the microwave band, and Fig. 2(e) is the FF/T amplifier of the present invention. The equivalent circuit diagram in the low frequency band shown in (-), and FIGS. 3 and 4 are front views of other embodiments of the FBT amplifier of the present invention. In the figure, (1) is FIT, +21 is gate terminal,
(3) is the source terminal, (4) is the drain terminal, (51
, (61, (71 is Su) IJ tube conductor, (8) is dielectric substrate, (9) is ground conductor, (10 is bias terminal, 0
1J is a resistor, 021 is a capacitor, αQ is an input matching circuit, and α gradient is an output matching circuit. (15) is the bias line, [1 is the power supply impedance. u'71 is the load impedance, (2), 4 strips, (21 is the coupled line, @ is the through hole. In Figure 9, the same or equivalent parts are indicated with the same symbol. Agent Shin Kuzuno - Figure 2 of 1ryJ ((1) Figure 2 (υ) Figure 2 (C) @ Figure 3 Figure 4

Claims (1)

[Claims] In a microwave band FICT amplifier consisting of a matching circuit composed of microstrips and an FET, an IJ tube conductor with one end open is provided on a dielectric substrate, and is provided parallel to the strip conductor at a predetermined distance. A PG amplifier characterized in that one end of the other strip conductor is terminated with a resistor and a capacitor, and the other end is connected to a predetermined terminal of the FIT.