JPS6295006A - Traveling-wave type fet amplifier - Google Patents

Abstract

PURPOSE:To raise the cut-off frequency by connecting a gate terminal of each FET and a reactance circuit through a capacitor having a prescribed capacity, and also connecting each gate terminal of each adjacent FET by a resistance of a high resistance. CONSTITUTION:A gate terminal 4 of each FET 3 and a reactance circuit are connected through a capacitor 10 which has been loaded in series to the gate terminal, and also, each gate terminal 4 of each adjacent FET is connected through a resistance 11 of a high resistance. The resistance 11 has a sufficiently higher resistance than the input impedance of the FET, therefore, no influence is exerted on a microwave. Also, a gate bias current of the FET scarcely flows, therefore, a gate bias voltage which has been impressed to a gate bias impressing terminal 12 is impressed as it is to the gate terminal 4 of each FET 3. By loading the capacity 10 of a capacity C, an effective capacity Ce becomes small. That is, by loading the capacitor 10, a cut-off frequency can be raised, and the upper limit value of an available frequency can be raised.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a traveling wave FET amplifier among monolithic broadband amplifiers used in communications, radar, and the like.

[Conventional technology]

Figure 4 shows, for example, y, B, Beyer, etal!
, MK8FEtTDistri-butted Amp
Lifer Design Guidelines
.

“Engineer EKE Trans, Jol, MTT-82, N1
18. PP, H8-15°Mar, 1984, is an equivalent circuit diagram of a conventional traveling wave FIICT amplifier, in which il+ is an input terminal, (2) is an output terminal,
(31 is FET, 141, (5), (61 are the gate terminal and drain terminal of FIICT, respectively.

source terminal, (7a) and (7b) are inductors,
(8a) and (8b) are terminators.

Next, the operation will be explained. The microwave power applied to the input terminal +11 is transferred to each inductor (7a) i terminator (8
a) It propagates in the O direction, but on the way, a part of the above microwave power is supplied to each F K T (31.
The microwave power supplied to lit T (:ll is amplified there, propagates through each inductor (71:+), and reaches the output terminal (2). Here, the inductance Ly/2 of each inductor (7a), each If the inductance Ld/I of the inductor (7b) is set to a predetermined value according to IT' ET +31, good input/output V will be achieved over a wide band.
An amplifier with BWR and flat gain can be obtained.

Next, for the following explanation, the cutoff frequency, which is a factor in determining the upper limit frequency that can be used by such a traveling wave FET amplifier, will be described.

Here, to simplify the explanation, each F K T t31 has the same performance, and the inductance of each inductor (7a) is constant at L2A, and each inductor (7b)
It is assumed that the inductance of is constant at LV2.

The equivalent circuit of FET tel is usually given as shown in FIG. In Fig. 5, when microwave power is applied to the gate terminal (4), the microwave power amplified by the mutual conductance 2m in the FET is transferred to the drain terminal (4).
5), and as a result, what is the amplification effect? In Fig. 5, the gate-drain capacitance CdP is generally very small, so if this metal is approximately ignored, the equivalent circuit in Fig. 4 becomes as shown in Fig. 6 ( As shown in FIG.

Both tal in FIG. 6 and fbl in FIG. 6 are equivalent circuits equivalent to the equal g5 circuit of a distributed constant line with loss. Generally, the characteristic impedance of a distributed constant line does not change with frequency. From this, FETt3
If appropriate inductors (7a), (7b) and terminators (8a), (8b) are used according to 1, good VEIWR characteristics can be achieved over a wide band.

By the way, in a distributed constant line, the equivalent circuit shown in Figure 6 (al, Figure 6 [bl) holds true even in an infinitely small portion, whereas in a traveling waveform PET amplifier, the F Z T
Depending on t3+, a finite inductor (7a), (γb
], which is different from a completely distributed constant line. Figure 6 (a), Figure 6 (bl is also an equivalent circuit equivalent to a lossy low-pass filter.The cut-off frequency fr determines the upper limit of the same wave number that can be used for a low-pass filter. , Figure 6+al, JT is given assuming that R is sufficiently small and can be ignored.

If R1 is sufficiently small and can be ignored, the impedance ZO of the distributed constant line on the gate side in Fig. 6 tal is determined by Cys, L
It is given by the following formula using j' f.

from now becomes.

(From Equation 31, if Zoi is constant, the cutoff frequency becomes larger as Cys becomes smaller. The same thing can be seen in Figure 6 Fbl.
The same can be said of the drain side distributed constant line, and the smaller C(18), the higher the cutoff frequency of the drain side distributed constant line.

By the way, in general, Cgs ) C (18), and this means that C!!s f can be made smaller by the progressive waveform F11fi.
T amplifier cutoff 8 wave number fTfjI: O is important in increasing [Problem to be solved by the invention] In this way, in the conventional traveling waveform FET JI width amplifier, once the PET to be used is determined, its gate source Interval capacity C
There is a problem in that the upper limit of the usable frequency is determined by the cutoff frequency determined by the value θ, and it is not possible to use it at higher frequencies.

The present invention has been made to solve the above-mentioned problems, and its purpose is to increase the cutoff frequency, which is one of the factors that determines the upper limit of the usable frequency of a traveling wave FET amplifier.

[Means to solve all problems]

The traveling waveform FET amplifier according to the present invention connects the gate terminal of each FET and the actance circuit via a capacitor loaded in series with the gate terminal, and
The gate terminals of the ET are connected through a high-resistance resistor.

[Effect]

The traveling waveform FET amplifier according to the present invention can reduce the cutoff frequency by effectively reducing the effective capacitance of the distributed constant line on the gate side of the traveling waveform amplifier by using a capacitor loaded in series with the gate terminal of each PET. Furthermore, by connecting the gate terminals of adjacent F'ETs with a high-resistance resistor, a gate bias voltage can be easily applied without affecting the microwave.

〔Example〕

FIG. 1 is an equivalent circuit diagram of an embodiment of the invention. In Fig. 1, (10) is a capacitor having a predetermined capacity 02;
(11) is a high resistance resistor, and (12) is a gate bias application terminal.

The resistor 11) has a sufficiently high resistance compared to the input impedance of HFKT, so it does not affect microwaves. Also, Fl! : Since the gate bias voltage of T hardly flows, the gate bias voltage applied to the gate bias application terminal Shino is applied as it is to the gate terminal 14+ of each FKT (31).

FIG. 2 is an equivalent circuit on the gate side of FIG. 1 corresponding to FIG. 6 tal. In Figure 2, the resistance (1υ) in Figure 1 is ignored because it is sufficiently large.

The capacitance aS shown in FIG. 2 can be given by the following equation using Cye and C.

From equation 14), by loading a capacitor (101) with a capacity tc, the effective capacity Oe becomes smaller.

The cutoff@wavenumber fTe in the equivalent circuit of FIG. 2 is obtained by substituting O,=z in place of Cya in equation (3).

That is, by loading the capacitor (+a+f) in FIG. 1, the cutoff frequency can be increased and the upper limit of usable frequency can be increased.

In addition, although the case where an inductor of a lumped constant circuit element is used as a reactance circuit has been described above, the present invention is not limited to this, and as shown in FIG. 3, a microstrip line f13) is used as a reactance circuit. It's okay.

〔Effect of the invention〕

As described above, according to this invention, Fl! : By loading a capacitor in series to the gate terminal of T, the traveling waveform F
It is possible to increase the wave number between cutoffs of the distributed constant line on the gate side of the KT amplifier, and as a result, there is an effect that the entire usable upper limit frequency can be increased. Also, the adjacent FE
What is the effect of easily applying gate bias by connecting the gate terminal of T with a high resistance resistor?

[Brief explanation of drawings]

FIG. 1 is an equivalent circuit diagram of a traveling waveform PET amplifier according to one embodiment of the present invention, FIG. 2 is an equivalent circuit diagram on the gate side of FIG. 1, and FIG. 8 is a traveling waveform FET according to another embodiment of the present invention.
Figure 4 is an equivalent circuit diagram of the conventional traveling wave FET amplifier, Figure 5 is an equivalent circuit diagram of FFXT, Figure 6 (al and Figure 6 ib+ are the gate side and gate side of Figure 4, respectively). This is an equivalent circuit diagram on the drain side. (3) is FKT, +41 is the gate terminal, (5)
is a drain terminal, (7a), (7b) n inductor; 1101 is a capacitor. (Ill tI'i resistance. In the figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] A traveling waveform FE formed by connecting the gate terminals of adjacent FETs and the drain electrodes of the adjacent FETs with a reactance circuit having a predetermined inductance.
The T amplifier is characterized in that the gate terminal of each of the FETs and the reactance circuit are connected via a capacitor having a predetermined capacity, and the gate terminals of adjacent FETs are connected with a high-resistance resistor. The traveling waveform F
ET amplifier.