JPH02182006A - Fet amplifier - Google Patents

Abstract

PURPOSE:To obtain an excellent matching characteristic over a broad band by providing a series circuit and a parallel circuit to an input matching circuit and an output matching circuit so as to a change in the impedance due to the frequency. CONSTITUTION:A series circuit having a resistor R1 with the same resistance as a resistor Rgs and an inductance L 10 with the same value as Cgs.R<2>gs is provided between a ground terminal and a gate electrode 0 of a FET 1 as an input matching circuit 2 and/or a parallel circuit comprising a conductance G2 equal to a conductance Gds. and an inductance L20 having the same value as a conductance Cds/G<2>ds. is provided in series with the drain D of the FET 1 as an output matching circuit 4, where the resistor Rgs is a gate-source resistor, the Cgs is a gate-source capacitance and connects in series with the resistor Rgs between the gate and source, the conductance Gds is a drain-source conductance and the capacitance Cds is a drainsource capacitance.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is used in the microwave band and millimeter wave band and is composed of FETs (field effect transistors).
It concerns amplifiers.

[Prior art] Figure 4 shows, for example, the Microwave Circuit Analysis and Ambrifer Design (MICROWA
VE CIRCIJIT ANALYSIS AND
AMPLIFIEliDESIGN) J (PREN
TICE-IIALL, INC, published in 1987), Chapter 4-3 Old G11-GAIN AMPLIFI
Fig, 4.3-4 of ERDESIGN (page 139)
(Page 145) is a circuit diagram showing a conventional FET amplifier, in which ■ is a source-grounded FE
T has a gate electrode G, a drain electrode, and a source electrode S. L is an inductance connected to the gate electrode G, C8 is a capacitance connected to the inductance L1, 2 is an input matching circuit composed of an inductance L, and a capacitance C4, and 3 is an input matching circuit 2.
A microwave or millimeter wave signal input terminal is connected to the input terminal, L2 is an inductance connected to the drain electrode,
C2 is the capacitance connected to the drain electrode, 4
is the inductance L! and a capacitance C2, and 5 is an output terminal connected to the output matching circuit 4.

FIG. 5 shows an equivalent circuit of the FETI shown in FIG. 4, where Rgs is a resistance between the gate and source, and Cgs is a capacitance between the gate and source, which are connected in series with Rgs between the gate and the source. Gds is a drain-source conductance, Cds is a drain-source capacitance, and 6 is a current source, which is connected in parallel with Cds and Cds between the drain and source.

FIG. 6 is a Smith chart showing the impedance locus of the source-grounded FETI, where S is the reflection characteristic of the gate electrode G in the frequency range of 2 to 10 GHz, and Sa
t indicates the reflection characteristic in the frequency range of 2 to 20 GHz at the drain electrode.

Next, the operation will be explained. In the FET amplifier shown in FIG. 4, the impedance seen from the gate electrode iG to the FETI and the impedance seen from the input matching circuit 2 from the gate electrode G have a relationship of complex conjugate numbers,
,C, is adjusted.

At the same time, Lx and Ct are adjusted so that the impedance seen from the drain electrode of the FETI and the impedance seen from the drain electrode from the output matching circuit 4 have a relationship of complex conjugate numbers. By adjusting the impedance of the input matching circuit 2 and the output matching circuit 4 in this way, the FETI
By matching this, a large gain can be obtained as an amplifier.

[Problem to be solved by the invention]

Since the conventional FET amplifier is configured as described above, as can be seen from Figure 6, the impedance locus of the FETI changes greatly depending on the frequency, so impedance matching cannot be achieved over a wide band, and therefore a wide band amplifier cannot be obtained. The problem was that it could not be done.

The present invention was made to solve the above-mentioned problems, and aims to provide an FET amplifier that can obtain good matching regardless of frequency and can provide large gain over a wide band.

[Means to solve the problem]

In the FET amplifier according to the present invention, a series circuit of a resistance having the same value as Rgs and an inductance having the same value as Cgs·R''gs is provided between the gate electrode and the ground terminal as a manual matching circuit, and/or As an output matching circuit, a parallel circuit with an inductance having Gds in series with the drain electrode is provided.

[For production]

In the FET amplifier according to the present invention, changes in impedance due to frequency are canceled out by the series circuit and parallel circuit provided in the input matching circuit and the output matching circuit, and good matching characteristics can be obtained over a wide band.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. No. 1,
In FIG. 1, parts substantially corresponding to those in FIG. 4 are designated by the same reference numerals, and explanations thereof will be omitted. R1 is a resistance, LIO is an inductance, and these RL1. are connected in series with each other and provided between the gate electrode and ground, forming an input matching circuit 2.

G2 is conductance, Lzo is inductance, and these Gz and Lz. are connected in parallel with each other and provided between the drain electrode and the output terminal 5, and the output matching circuit 4
It consists of

Next, the operation will be explained. The equivalent circuit of FETI is the fifth
Since it is expressed as shown in the figure, the impedance Zin seen from the input terminal 3 is as follows, assuming each frequency of the input signal is ω.
It is expressed by the following formula.

Rgs+R+ + j (ZJ (LIo-)ω”C
gs In order to obtain a good output VSWR (standing wave ratio) over a wide band, an impedance transformer, which will be described later, is used in an actual FET amplifier. Must be on the axis. In other words, the real part of Zin needs to be a constant and the imaginary part needs to be zero. Therefore, first, the above formula (1)
The real part Re(Z in) and the imaginary part 1 m(Z in)
Divide into. < Rgs-1- for the two denominators of 2(1)
Multiplying by R+) J (Ll (LIO)ω”Cgs, we get
), we get the following formula.

From formulas (4) and (5), R,,L,. The following conditions are required for

R,=Rgs・・・・・・・・・・・・
... (6) Ll. =CgsR"gs...
・・・・・・・・・・・・(7) Equation (6), (7
), the real part Re of Zin is
(Zin) is obtained by substituting equations (6) and (7) into equation (2), Re(Zin) = Rgs ・・・・・・・・・
...... (8), that is, equations (6), (7
) as in R,,L,. If , Zin becomes equal to a constant Rgs that is independent of frequency, and has only the real part.

Similarly, the impedance Zout when looking from the output terminal 5 to the FETI side is calculated from the equivalent circuit shown in Figure 5 using the following formula:
(Zout) and the imaginary part I m (Z out). In formula 01), I m(Zout)
Applying the condition that the term related to ω is zero at −〇, G,
,L.

When calculating, G,=Gds ・・・・・・・・・・・・
02) is obtained. At this time, the real part Re(Zout) of Zout is equal to □. Namely, ds 802), 03) Noyouni (, z.

L2゜ Therefore, it exists on the real axis.

FIG. 2 shows calculated values of the impedance locus for an example of a FET amplifier used in the microwave band. In this case R1=2.5Ω, L+o=0.02 nH.

Gz-3118, Lie-11, 7nH.

It can be seen that the calculated frequency is from 2 GHz to 20 GHz, and both the reflection characteristics SI1+S*1 are independent of frequency and are constant values on the real axis.

When actually used as an amplifier, the reflection characteristics shown in FIG. 2 are insufficient, so an impedance transformer 7.8 is used as shown in FIG. 3. The impedance transformer 7.8 is composed of, for example, an inductance and a capacitance, and its design is easy if the impedance locus does not change with frequency as shown in FIG. The FET amplifier configured as shown in FIG. 3 has excellent characteristics over a very wide band.

In the above embodiment, the input side matching circuit 2 includes R, L,
, G,, L, in the output side matching circuit 4.

Although the above parallel circuit is used, it may be used only for the input side matching circuit 2 or only for the output side matching circuit 4.

〔Effect of the invention〕

As described above, according to the present invention, a series circuit of a resistor having the same value as Rga of the FET and an inductance having the same value as Cgs-R''gs is provided between the gate electrode and the ground terminal as an input matching circuit. By providing a parallel circuit with an inductance having the same value as that directly connected to the drain electrode as an output matching circuit, a constant impedance can be obtained regardless of the frequency, and therefore good matching characteristics can be obtained over a wide band. This has the effect of providing a large gain and facilitating the design of an impedance transformer.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an FET amplifier according to an embodiment of the present invention, FIG. 2 is a Smith chart showing the impedance locus of the FET amplifier shown in FIG. 1, and FIG. 3 is a circuit diagram showing the FET amplifier shown in FIG. 1.
A circuit diagram showing a case where an impedance transformer is provided in an amplifier, Fig. 4 is a circuit diagram showing a conventional FET amplifier, Fig. 5 is an equivalent circuit diagram of an FET, and Fig. 6 is a Smith chart showing an impedance locus of an FET. be. In the figure, 1 is FET, 2 is input matching circuit, 4 is output matching circuit, R4 is resistor, G2 is conductance, L+o
, Lz. is the inductance. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Patent Applicant: Mitsubishi Electric Corporation 1: FET R1 Technology 4 Journal LIOL20: In-T'79th 2nd WJ

Claims (1)

[Claims] A FET consisting of a source-grounded FET, an input matching circuit connected to the gate electrode of this FET, and an output matching circuit connected to the drain electrode of the FET.
In the amplifier, a series circuit of a resistor having a value equal to the gate-source resistance of the FET and an inductance having a value equal to the product of the square of the gate-source resistance and the gate-source capacitance of the FET. an input matching circuit consisting of connecting between the above gate electrode and ground,
and/or a conductance having a value equal to the drain-source conductance of the FET;
The drain-source capacitance of
An FET characterized by using an output matching circuit formed by connecting in series to the drain electrode a parallel circuit with an inductance having a value divided by the source-to-source conductance.
amplifier.