JP5019989B2 - High frequency amplifier - Google Patents

Description

  The present invention relates to a configuration of a high-frequency amplifier mainly used in a VHF band, a UHF band, a microwave band, and a millimeter wave band.

  A conventional high frequency amplifier includes a cascode-connected source grounded field effect transistor (hereinafter referred to as “FET”) and a gate grounded FET, a feedback circuit provided between an input terminal and an output terminal of the gate grounded FET, and a source grounded FET. And a transmission line connecting the common-gate FET. In general, it is known that the grounded FET has large output reflection characteristics and poor stability. However, if a feedback circuit composed of a resistor and a capacitor is provided between the input terminal and the output terminal of the grounded FET, the resistance Acts at a predetermined frequency, the gain of the common-gate FET is suppressed, and stability is improved. The frequency for improving the stability is determined by the capacity and the length of the transmission line (see, for example, Non-Patent Document 1).

The other high-frequency amplifier includes a first transistor that amplifies and outputs a high-frequency signal input from a signal input terminal, and a plurality of reactance elements, and an interstage that receives the output signal of the first transistor as an input. A matching circuit and a second transistor that amplifies a high-frequency signal input via the interstage matching circuit and outputs the amplified signal to a signal output terminal. The interstage matching circuit includes an output impedance of the first transistor and a second transistor The impedance matching with the input impedance of the first transistor is performed, and the same bias current as that flowing through the second transistor is supplied to the first transistor.
Then, the output power from the first transistor is input to the second transistor with low loss, and the output or gain is improved. In addition, since the interstage matching circuit is composed of a low-pass filter, there is no circuit element that cuts off the bias, and the bias of the first transistor and the second transistor can be kept common as in the normal cascode connection. (See, for example, Patent Document 1).

JP 2000-229633 A A. Tessmann, 6 others, "A COPANAR 94 GHz LOW-NOISE AMPLIFIER MMIC USING 0.07 μm METAMORPHIC CASCODE HEMTs", 2003 IEEE MTT-S Digest, IEEE, 2003, pp. 1581-1584

  However, in the high-frequency amplifier of Non-Patent Document 1, the constituent circuit specifications are determined only for stability improvement, and the contribution to other characteristics is not mentioned, and the output reflection characteristics are particularly greatly improved. There is a problem of not doing.

  Further, in the high-frequency amplifier of Patent Document 1, the circuit specifications to be configured are determined only for the purpose of improving the output or gain, and the contribution to other characteristics is not mentioned, and the output reflection characteristics are not improved. There's a problem.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a small cascode-connected high-frequency amplifier with improved stability and improved output reflection characteristics.

The high-frequency amplifier according to the present invention is provided in the gate-grounded transistor in a high-frequency amplifier including a grounded-source transistor to which a high-frequency signal is input and a grounded-gate transistor that amplifies and outputs the high-frequency signal amplified by the source-grounded transistor. A feedback circuit, and a matching circuit provided between the common- source transistor and the common-gate transistor, and the matching circuit is configured such that a load when the input side is viewed from the common-gate transistor is connected to a gate of the common-gate transistor. The circuit specifications are determined so that the load becomes a standardized admittance by canceling the inter-source admittance component .

  The effect of the high-frequency amplifier according to the present invention is that a load obtained by viewing the circuit specifications of the matching circuit from the input terminal of the grounded-gate transistor to the input side cancels the gate-source admittance component of the grounded-gate transistor and normalizes the admittance. This means that the output reflection characteristics are improved.

Embodiment 1 FIG.
1 is a configuration diagram of a high-frequency amplifier according to Embodiment 1 of the present invention.
As shown in FIG. 1, the high-frequency amplifier according to the first embodiment of the present invention includes a common gate FET 1, an input terminal 2 of the common gate FET 1, an output terminal 3 of the common gate FET 1, a feedback circuit 4, a common source FET 5, and a common source. An input terminal 6 of the FET 5, an output terminal 7 of the common source FET 5, and a matching circuit 8 are provided.
The feedback circuit 4 is provided between the input terminal 2 and the output terminal 3 of the common-gate FET 1 and includes a resistor.
The matching circuit 8 is provided between the output terminal 7 of the common source FET 5 and the input terminal 2 of the common gate FET 1. The circuit specifications of the matching circuit 8 are set so that a load that cancels the gate-source admittance component of the common-gate FET 1 and becomes a normalized admittance is connected to the input terminal 2 of the common-gate FET 1. The

Next, the operation of the high frequency amplifier according to Embodiment 1 of the present invention will be described.
By providing the feedback circuit 4 between the input terminal 2 and the output terminal 3 of the common-gate FET 1, the gain of the common-gate FET 1 is suppressed at a predetermined frequency. As a result, the stability of the common-gate FET 1 is improved.
Further, the common-gate FET 1 is connected to the common-source FET 5 via the matching circuit 8, and the output reflection characteristics are also improved by setting each circuit specification to a predetermined value.

Next, circuit specifications of the matching circuit 8 for improving output reflection characteristics will be described.
In general, an equivalent circuit of the common-gate FET 1 without the feedback circuit 4 is represented as shown in FIG. The Y parameter of the common-gate FET 1 includes a gate-source admittance component (hereinafter referred to as “y _gs component”), a drain-source admittance component (hereinafter referred to as “y _ds component”), and a gate-drain interval. The admittance component (hereinafter referred to as “y _gd component”) and the mutual conductance (hereinafter referred to as “gm”) are used to express the equation (1). Here, the capacity of the DC cut shown in FIG. 1 is ignored.
Usually, the y _gs component is the largest, the y _ds component is the next, and the y _dg component is the smallest. Therefore, the y _ds component and the y _dg component can be ignored, and the S parameter is expressed as shown in Equation (2). The

Since the output reflection coefficient of the common-gate FET 1 is 1, which is approximately perfect reflection, it can be seen that the reflection characteristics are very poor.
On the other hand, when the feedback circuit 4 is provided in the grounded gate FET 1 as shown in FIG. 3, the y _ds component between the input terminal 2 and the output terminal 3 of the grounded gate FET 1 cannot be ignored, and only the y _dg component is ignored. The S parameter is expressed as shown in Equation (3). Each element S ₁₁ , S ₁₂ , S ₂₁ , S ₂₂ of the S parameter is expressed by the equations (4), (5), (6), (7).

Here, as shown in FIG. 4, the reflection coefficient of the common-source FET 5 including the matching circuit 8 from the input side of the common-gate FET ₁ is Γ ₁ , and the output reflection coefficient of the cascode FET is Γ ₂₂ .
The reflection coefficient Γ ₂₂ is expressed as in Expression (8) using the S parameter of the common-gate FET 1.

By substituting the S parameter of the common-gate FET 1 expressed by Expression (3) into Expression (8) and obtaining the condition of the reflection coefficient Γ ₁ at which the reflection coefficient Γ ₂₂ becomes 0, Expression (9) is obtained.
Here, when the y _ds component is made sufficiently large, the reflection coefficient Γ ₁ is approximately expressed by Expression (10).

That is, when a load is connected to the input terminal 2 of the common-gate FET ₁ , so that the reflection coefficient Γ ₁ represented by the equation (10) is obtained, the reflection coefficient Γ ₂₂ becomes zero. The load having the reflection coefficient Γ ₁ is a load that cancels the gate-source admittance component of the common-gate FET ₁ and becomes normalized admittance.

  In the high-frequency amplifier according to the first embodiment of the present invention, the load when the circuit specifications of the matching circuit 8 are viewed from the input terminal 2 of the common-gate FET 1 cancels the gate-source admittance component of the common-gate FET 1. As a result, it is determined that the load becomes standardized admittance, so that the output reflection characteristic is improved.

On the other hand, in the circuit configuration in which the common-gate FET 1 without the feedback circuit 4 is connected to the common-source FET 5 via the matching circuit 8, since the y _ds component of the common-gate FET 1 is small, the circuit specifications of the matching circuit 8 can be changed. The effect on the improvement of output reflection characteristics is small.
Further, just providing the feedback circuit 4 to the common gate FET 1 does not improve the output reflection characteristics.

  In addition, the high frequency amplifier according to Embodiment 1 of the present invention does not require a new output matching circuit, and has the effect of reducing the size.

  Although the high-frequency amplifier according to the first embodiment of the present invention is configured using field effect transistors, similar effects can be obtained even when configured using bipolar transistors. When a bipolar transistor is employed, a common emitter transistor is used instead of the common source FET 5 and a common base transistor is used instead of the common gate FET 1.

  Although the transistor bias circuit is not particularly shown, the bias conditions of the common-gate FET 1 and common-source FET 5 may be changed as appropriate. In this case, since the S parameter changes depending on the bias condition, there is an advantage that the degree of freedom in design such as output and reflection characteristics is further improved.

Embodiment 2. FIG.
FIG. 5 is a configuration diagram of a high-frequency amplifier according to Embodiment 2 of the present invention.
The high-frequency amplifier according to the second embodiment of the present invention is different from the high-frequency amplifier according to the first embodiment in that the circuit configurations of the feedback circuit 4 and the matching circuit 8 of the high-frequency amplifier according to the first embodiment are specifically specified. Therefore, the same reference numerals are attached to the same parts, and the description is omitted.
The feedback circuit 4 includes a capacitor 9 and a resistor 10 connected in series.
The matching circuit 8 includes an inductor 11 that connects the input terminal 2 of the common-gate FET 1 and the output terminal 7 of the common-source FET 5, and parallel ground capacitors 12a and 12b that ground both ends of the inductor 11.

  In the high-frequency amplifier according to the second embodiment of the present invention, the inductance of the inductor 11 and the capacitances of the parallel grounded capacitors 12a and 12b are the load of the gate grounded FET1 as viewed from the input terminal 2 of the gate grounded FET1. Since it is determined to cancel the admittance component between the gate and the source so that the load becomes standardized admittance, the output reflection characteristic is improved.

  Further, in the millimeter wave band or the like, the impedance when the source grounded FET 5 side is viewed from the output terminal 7 of the source grounded FET 5 is inductive, and the gate grounded FET 1 side provided with the feedback circuit 4 is viewed from the input terminal 2 of the gate grounded FET 1. The impedance is higher than the impedance seen from the source grounded FET 5 side. Therefore, impedance matching is possible with the parallel-grounded capacitors 12a and 12b having a small capacity, and the circuit size can be reduced.

Embodiment 3 FIG.
6 is a block diagram of a high frequency amplifier according to Embodiment 3 of the present invention.
In the high frequency amplifier according to the second embodiment of the present invention, the source of the common source FET 5, the parallel grounded capacitor 12a, the gate of the common gate FET 1, and the parallel grounded capacitor 12b are grounded to different grounds, respectively. In the high frequency amplifier according to the third embodiment, the source of the common-source FET 5 and the parallel grounded capacitor 12a are grounded to the same ground, and the gate of the common-gate FET1 and the parallel grounded capacitor 12b are grounded to the same ground. . The rest of the configuration is the same as that of the high-frequency amplifier according to the second embodiment.

  In the high-frequency amplifier according to the third embodiment of the present invention, the inductance of the inductor 11 and the capacitances of the parallel grounded capacitors 12a and 12b are the loads of the gate grounded FET1 as viewed from the input terminal 2 and the load of the gate grounded FET1. Since it is determined to cancel the admittance component between the gate and the source so that the load becomes standardized admittance, the output reflection characteristic is improved.

  Further, as described above, since the parallel ground capacitors 12a and 12b can have a small capacitance, they can be disposed close to the gate ground FET 1 and the source ground FET 5, and the ground to which the parallel ground capacitor 12b is grounded and the gate of the gate ground FET 1 are grounded. The ground to which the parallel grounding capacitor 12a is grounded and the ground to which the source of the common source FET 5 is grounded can be shared. For this reason, the number of ground patterns can be reduced, and the circuit size can be further reduced.

  In the high-frequency amplifier according to the third embodiment of the present invention, the ground to which the parallel grounded capacitor 12b is grounded and the ground to which the gate of the gate grounded FET1 is grounded, and the ground to which the parallel grounded capacitor 12a is grounded and the source grounded FET5 Although the ground to which the source of each is grounded is shared, only one of them may be shared.

1 is a configuration diagram of a high-frequency amplifier according to Embodiment 1 of the present invention. It is an equivalent circuit of a gate grounded field effect transistor. It is an equivalent circuit of a grounded-gate field effect transistor provided with a feedback circuit. It is the equivalent circuit which showed the reflection coefficient in the gate grounded field effect transistor provided with the feedback circuit. It is a block diagram of the high frequency amplifier which concerns on Embodiment 2 of this invention. It is a block diagram of the high frequency amplifier which concerns on Embodiment 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Grounded gate FET, 2 (Terminal grounded FET) input terminal, 3 (Gated grounded FET) output terminal, 4 Feedback circuit, 5 Source grounded FET, 6 (Source grounded FET) Input terminal, 7 (Source grounded FET) ) Output terminal, 8 matching circuit, 9 capacitor, 10 resistor, 11 inductor, 12a, 12b parallel grounded capacitor, Γ ₁ reflection coefficient, Γ ₂₂ reflection coefficient.

Claims (3)

In a high frequency amplifier including a grounded source transistor to which a high frequency signal is input and a grounded gate transistor for amplifying and outputting the high frequency signal amplified by the grounded source transistor,
A feedback circuit provided in the gate-grounded transistor;
A matching circuit provided between the source grounded transistor and the gate grounded transistor ,
The above-mentioned matching circuit has circuit specifications determined so that the load seen from the grounded gate transistor becomes the standardized admittance by canceling the gate-source admittance component of the grounded gate transistor. A high-frequency amplifier characterized by that . The feedback circuit is composed of a resistor and a capacitor,
2. The high-frequency amplifier according to claim 1, wherein the matching circuit includes a transmission line and two parallel grounding capacitors that ground both ends of the transmission line. On one of the parallel ground capacitors and the same ground gates of the gate-grounded transistor, or, according to claim 2, characterized in that the source of the other of the parallel ground capacitor and the source-grounded transistor is grounded to the same ground High frequency amplifier.

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