JPS642448Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a monosic transistor amplifier that exhibits low VSWR characteristics for power loads with a plurality of characteristic impedances.

A conventional monosic FET amplifier having a negative feedback circuit consisting of a resistor and a DC blocking capacitor between a gate electrode and a drain electrode will be explained as an example.

Figure 1 shows a monolith with a conventional feedback circuit.
FIG. 2 is a structural diagram of a FET amplifier. In Figure 1, 1
is a semiconductor substrate such as GaAs or Si, 2 is a FET
3 is the gate electrode of FET, 4 is the source electrode of
The drain electrode of the FET, 5 is a dielectric forming a thin film capacitor, 6 is a resistor, and 7 is a metal film.

FIG. 2 is an equivalent circuit diagram of FIG. 1.

In the figure, Rf is the resistance value of resistor 6, and Rs is the FET source resistance. gm is the FET transconductance, Cf
is the capacitance of the thin film capacitor according to 5, Cgs is the gate-source capacitance, and Vgs is the voltage applied to the gate-source capacitance terminal. Compatible with 4 electrodes. When Cf is large and Cgs is small and can be ignored, the S parameters S ₁₁ and S ₂₂ of the amplifier are given by the following equations.

S ₁₁ = S ₂₂ = Rf (1 + gmRs) - gmZo ² / (Rf + 2Zo) (1
+gmRs) +gmZo ² (1) Here, Zo is the characteristic impedance of the input/output port.

From equation (1), it can be seen that Rf exists such that S ₁₁ =S ₂₂ =0.

In this way, by inserting a resistor having a resistance value such that S ₁₁ =S ₂₂ =0 as described above is inserted between the drain electrode and the gate electrode, an amplifier with good broadband input/output VSWR characteristics can be obtained.

As shown in equation (1), the optimal resistance value Rf to obtain broadband characteristics is a function of the characteristic impedance of the input/output port, and different values of Rf are required to match different characteristic impedances.

However, with conventional monolithic amplifiers that have a negative feedback circuit consisting of a resistor and a DC blocking capacitor between the gate electrode and drain electrode, it is possible to achieve good input/output VSWR characteristics only for a certain characteristic impedance. but,
For characteristic impedances different from this, there was a drawback in that a new monosonic amplifier having a resistor with a different resistance value had to be manufactured.

In order to eliminate these conventional drawbacks, this invention provides a metal film (hereinafter referred to as an air bridge) on the substrate with a space between the metal films connected to both terminals of the resistor of the feedback circuit, and connects the air bridge as necessary. By disconnecting the amplifier, a monosonic amplifier exhibiting low VSWR characteristics for a plurality of characteristic impedances is obtained.The drawings will be described in detail below.

FIG. 3 is a structural diagram of one embodiment of a monolithic transistor amplifier according to this invention. In FIG. 3, 8 is a resistor a, 9 is a resistor b, and 10 is an air bridge.

FIG. 4 is an equivalent circuit diagram of FIG. 3. Resistance Rfa
is the resistance of resistor a8, and resistance Rfb is the resistance of resistors b and 9. The air bridge 10 short-circuits both ends of the resistors b and 9.

The resistance Rf between the metal film 7 and the drain electrode 4 is equal to Ra when the air bridge short-circuits both ends of the resistors b and 9. When the air bridge is mechanically cut, the resistance Rf between the metal film 7 and the drain electrode becomes equal to Ra+Rb.

Therefore, if the resistors Ra and Rb are set so that low VSWR can be obtained for different Zo according to equation (1) above, the input/output ports can be easily connected by simply disconnecting the air bridge as necessary. The characteristic impedance Zo can be selected.

Note that the above description has been made for the case where one air bridge is added to one resistor, but this invention is not limited to this, and can be applied to cases where one air bridge is added to multiple resistors, or when multiple air bridges are added to one resistor. May be used when adding an air bridge.

In the monolithic transistor amplifier according to this invention, a metal film is provided on the substrate with a space between the metal films connected to both terminals of the resistor of the feedback circuit, and by cutting this metal film as necessary, multiple The advantage is that low VSWR characteristics can be obtained compared to the characteristic impedance of .

[Brief explanation of the drawing]

Figure 1 shows a monolithic circuit with a conventional feedback circuit.
A structural diagram of a FET amplifier, Fig. 2 is an equivalent circuit diagram of Fig. 1, Fig. 3 is a structural diagram of an embodiment of a monolithic transistor amplifier according to this invention, and Fig. 4 is an equivalent circuit diagram of the one shown in Fig. 3. It is. In the figure, 1 is a semiconductor substrate such as GaAs or Si, 2 is a source electrode of FET, 3 is a gate electrode of FET, 4 is a drain electrode of FET, 5 is a dielectric forming a thin film capacitor, 6 is a resistor, 7 is a metal film, 8 is a resistor a, 9 is a resistor b, and 10 is an air bridge. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

Claims (1)

[Scope of utility model registration request] In a monolithic transistor amplifier having a resistor, electricity is transmitted through a space on the substrate between a metal film connected to one end of the resistor formed on the substrate and a metal film connected to the other end of the resistor. A monolithic transistor amplifier characterized by having a metal film that is a conductor.