JP2000223971A - Self-bias circuit and arranging method of self-bias circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a self-bias circuit to be stably operated from a low frequency to a high frequency. SOLUTION: This circuit is provided in an IC, provided with a FET 3, a pad 2 for grounding and a self-bias capacitor 1 provided between a source 3a of the FET 3 and the pad 2 for grounding and used in a micro wave band and a millimeter wave band. The self bias capacitor 1 is also provided outside an area between the source 3a of the FET 3 and the pad 2 for grounding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a self-bias circuit used in a microwave band and a millimeter wave band.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional example of a self-biasing circuit used at a high frequency such as a millimeter wave band. In this conventional example, since the operating frequency is limited to a high frequency, stabilization is achieved only at a high operating frequency. Therefore, the capacitance value of the self-biasing capacitor 100 may be small, and the width W of the capacitor 100 is set short.

FIG. 6 shows a conventional example of a self-biasing circuit used at a low frequency such as a microwave band. In this conventional example, since the operating frequency is limited to a low frequency, stabilization is achieved only at a low operating frequency. Therefore, the area of the self-biasing capacitor 110 may be increased, and the capacitor length L is set to be long.

[0004]

However, these prior arts have the following problems. In the circuit of FIG.
Operation may become unstable at low frequencies. FIG. 5 shows an example of a simulation result of the circuit of FIG. In this example, the length L and the width W of the self-biasing capacitor 100 are shown.
Are the simulation results when L = 30 μm and W = 100 μm, respectively, from 10 GHz to 20 G
In Hz, the K factor (indicator of the stability of operation, which is unstable when K is 1 or less, indicates that it is stable when K is 1 or more) is 1 or less, and is unstable. I understand. This is the self-biasing capacitor 1
The reason is that the capacity value of 00 is small.

In the circuit shown in FIG. 6, the operation may become unstable at a high frequency. FIG. 7 shows an example of a simulation result of the circuit of FIG. In this example, the length L and the width W of the self-biasing capacitor 110 are respectively set to L = 10.
This is a simulation result when 0 μm and W = 200 μm. From 60 GHz to 80 GHz, the K factor is 1 or less, and it is apparent that the K factor is unstable. This is because the length L of the self-biasing capacitor 110 is long. That is, in the related art, it was not possible to cover from a low frequency to a high frequency with one circuit.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides a self-biasing circuit that operates stably from a low frequency to a high frequency.

[0007]

According to a first aspect of the present invention, there is provided a micro-circuit comprising a FET, a ground pad, and a self-biasing capacitor provided between the source of the FET and the ground pad. In a self-biasing circuit provided in an IC for use in a wave band and a millimeter wave band, the self-biasing capacitor is provided outside a region between a source of the FET and a ground pad. It is a self-biasing circuit that is a feature. The invention according to claim 2 is the self-biasing circuit according to claim 1, wherein the self-biasing capacitor is provided in an L-shaped region adjacent to the ground pad.

According to a third aspect of the present invention, there is provided a microwave band and a millimeter wave band having an FET, a ground pad, and a self-biasing capacitor provided between the source of the FET and the ground pad. A self-biasing circuit provided in an IC, wherein the self-biasing capacitor is also provided outside a region between a source of the FET and a ground pad. This is the arrangement method.

[0009]

FIG. 1 shows the configuration of a first embodiment of the present invention. The self-biasing capacitor 1 is arranged so as to surround the ground pad 2 (via hole or flip chip ground pad). The length of the self-biasing capacitor 1 is L and the width is W. FET3
The source 3a is arranged as close as possible to the self-biasing capacitor 1. Gate 3 of FET3
b is grounded via the gate bias resistor 4.
3c is the drain of FET3.

Next, the operation of this embodiment will be described. FE
Since the source 3a of T3 is arranged as close as possible to the self-biasing capacitor 1, the length L of the self-biasing capacitor 1 is set between the source 3a of the FET 3 and the ground pad 2. About the distance of At high frequencies in the millimeter-wave band, the shorter the length L, the better the stability of the self-bias circuit. On the other hand, at low frequencies below the microwave band, the area (L
× W) is greater, the stability of the self-bias circuit is better.

The reason will be described below. The capacitance of the self-biasing capacitor 1 is Cx, the equivalent inductance corresponding to the size of the electrode of the self-biasing capacitor 1 (the equivalent inductance from the source 3a of the FET 3 to the ground pad 2) is Lx, and Assuming that the equivalent inductance is Ly, the following admittance is inserted between the source 3a of the FET 3 and the ground point (ground). 1 / (jωCx) + jωLx + jωLy Here, at a high frequency in the millimeter wave band, 1 / (jω
Cx) is close to 0, so that jωLx + jωLy = jω (Lx + L)
The admittance of y) can be seen. At high frequencies in the millimeter wave band, the FET 3 operates more stably when the inductance added to the source 3a of the FET 3 is as small as possible. Since the Lx is proportional to the length L of the self-biasing capacitor 1, the stability of the self-biasing circuit is improved as the length L is shorter at a high frequency in the millimeter wave band.

On the other hand, at low frequencies below the microwave band, since jωLx + jωLy is close to 0, FE
Between the source 3a of T3 and the ground point, 1 / (jωC
The admittance of x) can be seen. Admittance 1 added to source 3a of FET 3 as Cx increases
Since / (jωCx) becomes small, the FET operates stably. Cx is the area L × W of the self-biasing capacitor 1
At low frequencies below the microwave band, the greater the area L × W of the self-biasing capacitor 1, the better the stability of the self-biasing circuit.

Therefore, in order to stably operate the self-biasing circuit from a low frequency to a high frequency, the length L of the self-biasing capacitor 1 may be reduced and the width W may be increased. Here, in order to make the self-biasing capacitor 1 not look like a stub at a high frequency in the millimeter wave band while increasing W, the grounding pad 2 is formed so that the self-biasing capacitor 1 can be well grounded. A self-biasing capacitor 1 is arranged so as to surround it.

FIG. 2 shows a simulation of the self-biasing circuit.
Shows the results of the Here, the K factor is an index indicating stability, and is unstable when it is 1 or less, and is stable when it is 1 or more. FIG.
Is a case where the length L of the self-biasing capacitor 1 is 30 μm and the width W is 200 μm. The following simulation parameters are used. Gate width of FET3 =
200 μm, the capacitor value of the self-biasing capacitor 1 is about 3.0 pF at 100 μm □, the size of the ground pad 2 is 100 μm □, and its equivalent inductance is 10 μm.
The pH was set. The gate bias resistance 4 (the resistance between the gate 3b of the FET 3 and the ground) was 45Ω. It can be seen from the graph of FIG. 2 that a stable self-bias circuit is obtained in a wide frequency band from 100 MHz to 100 GHz.

The dimensions of L and W of the self-biasing capacitor 1 suitable for the present invention differ depending on the gate width of the FET 3 and the equivalent inductance of the ground pad 2, but L is preferably 50 μm or less and W is preferably 150 μm or more. . The distance between the source 3a of the FET 3 and the self-biasing capacitor 1 is preferably 10 μm or less.

FIG. 3 shows a second embodiment of the present invention. At a high frequency, a stable operation can be obtained by making the capacitor length L1 of the self-biasing capacitor 10 equal to L in FIG. 1, and at a low frequency, the capacitor area (L1 × W1 + L2 × W2) is reduced. By making the same as L × W, stable operation can be obtained.

[0017]

According to the present invention, since the self-biasing circuit itself can be stabilized in a wide frequency band, the MMIC
In the case where the present circuit is configured in multiple stages by a (microwave monolithic integrated circuit), it is not necessary to separately provide a stabilizing circuit. Therefore, the circuit configuration can be simplified and the chip size can be reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is a graph showing a simulation result of the first embodiment.

FIG. 3 is a configuration diagram of a second embodiment of the present invention.

FIG. 4 is a configuration diagram of a first conventional example.

FIG. 5 is a graph showing a simulation result of the first conventional example.

FIG. 6 is a configuration diagram of a second conventional example.

FIG. 7 is a graph showing a simulation result of a second conventional example.

[Explanation of symbols]

 1, 10, 100, 110 Self-biasing capacitor 2 Ground pad 3 FET 3a Source 3b Gate 3c Drain 4 Gate bias resistance

Claims (3)

[Claims] 1. An integrated circuit for use in a microwave band and a millimeter wave band, comprising: an FET; a ground pad; and a self-biasing capacitor provided between a source of the FET and a ground pad. In the provided self-bias circuit, the self-bias capacitor is provided outside a region between a source of the FET and a ground pad. 2. The self-biasing circuit according to claim 1, wherein the self-biasing capacitor is provided in an L-shaped region adjacent to the ground pad. 3. An integrated circuit for use in a microwave band and a millimeter wave band, comprising: an FET; a ground pad; and a self-biasing capacitor provided between a source of the FET and a ground pad. In the provided self-biasing circuit, the self-biasing capacitor is provided outside a region between a source of the FET and a ground pad.