JP3761729B2 - Bias circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a bias circuit, and more particularly to a bias circuit for supplying power for driving a transistor used in a microwave monolithic integrated circuit (MMIC) operating in a microwave or millimeter wave band. is there.
[0002]
[Prior art]
A bias circuit that supplies power to a transistor used in an integrated circuit that operates in a high frequency band such as a microwave or millimeter wave band includes a parasitic reactance component inside the transistor and a reactance component in the bias circuit that supplies power for driving the transistor. May satisfy the resonance condition and cause abnormal oscillation, which may cause the integrated circuit to not operate normally in the microwave / millimeter wave band.
[0003]
As the bias circuit for preventing the abnormal oscillation, for example, as shown in FIGS. 3 and 4 showing the conventional example disclosed in the technical report ED96-182 of the Institute of Electronics, Information and Communication Engineers, a bias for supplying DC power for driving a transistor is used. The circuit prevents the propagation of high-frequency signals in the vicinity of the operating frequency of the high-frequency integrated circuit, so that the tip of the microstrip line 2 is equal to the length of λ / 4 where λ is the wavelength of the propagation signal at the operating frequency of the integrated circuit. In addition, a ground circuit via a MIM (Metal-Insulator-Metal) capacitor 7 and a via hole 5 is added to the power supply terminal of the transistor, and a high-frequency signal in the vicinity of the operating frequency is guided to the ground circuit. Measures are taken to prevent propagation of high-frequency signals to the λ / 4 microstrip line 3 and the DC power supply pad 4 for applying a DC voltage of the bias circuit. There is common.
[0004]
However, the transistor generally has a large gain at a frequency lower than the above operating frequency. Therefore, the parasitic reactance component inside the transistor and the reactance component in the bias circuit that supplies power for driving the transistor satisfy the resonance condition, and are several hundred MHz to several GHz lower than the operating frequency (several tens of GHz). Abnormal oscillation may occur at a relatively low frequency, which may cause the integrated circuit not to operate normally in the microwave / millimeter wave band.
[0005]
In order to guide a transmission signal having a relatively low frequency of several hundred MHz to several GHz to the ground circuit, it is necessary to use a capacitor having a relatively large capacity of about 10 pF or more. Therefore, as shown in FIG. In general, the capacitor 12 is provided independently, and the capacitor 12 and the bias feeding pad 4 of the integrated circuit are connected by means such as a bonding wire 13.
[0006]
[Problems to be solved by the invention]
In the configuration of the conventional bias circuit, in order to prevent abnormal oscillation in a band of about several hundred MHz to several GHz, which is lower than the operating frequency (several tens of GHz) of the MMIC circuit, outside the microwave / millimeter wave band integrated circuit. It is necessary to load a capacitor 12 of about 10 pF or more outside the integrated circuit and to connect the capacitor 12 and the bias feeding pad 4 by means such as a bonding wire. For this reason, the number of manufacturing steps for microwave / millimeter-wave modules configured using a plurality of MMIC chips is increased, and the manufacturing cost of the entire module is necessary for the external capacitors to be loaded and their connection. There has been a problem that the bonding process is increased.
[0007]
The grounding in the microwave / millimeter wave band integrated circuit is generally a method using a via hole. The via hole has a parasitic inductance of about several tens of pH, and this parasitic inductance and the capacitor loaded in the ground circuit resonate. Abnormal oscillation occurs near the resonance frequency, and the microwave / millimeter wave band integrated circuit is normal. There was also a problem that there was a risk of not working.
[0008]
Accordingly, an object of the present invention is to prevent abnormal oscillation in an operating frequency band of an integrated circuit, in particular, an integrated circuit for microwave / millimeter wave band and a frequency band lower than the operating frequency band, and abnormal oscillation outside the integrated circuit. It is an object of the present invention to provide a bias circuit for an integrated circuit that does not require the provision of a capacitor for preventing this.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, a bias circuit that supplies a DC power supply for driving a transistor is a short stub having a length equal to one-fourth of the wavelength of a propagation signal in the operating frequency band of a monolithic integrated circuit. A first ground circuit in which a series circuit composed of a first MIM capacitor and a first via hole is connected between the front end and the first via hole; and the first MIM capacitor and a bias feeding pad. A microstrip line having a length equal to one-fourth of the wavelength of the propagation signal formed therebetween, and a first via between the vicinity of the connection point between the microstrip line and the bias feed pad and the second via hole. A second ground circuit is formed by connecting a series circuit of a thin film resistor and a second MIM capacitor.
[0010]
According to a preferred embodiment of the present invention, the operating frequency of the MMIC circuit is set to several tens of GHz, and in order to prevent abnormal oscillation in a low frequency range of several hundred MHz to several GHz, the first thin film resistor is 50Ω, The first MIM capacitor is about 10 to 50 pF.
[0011]
Further, in order to prevent abnormal oscillation at an intermediate frequency between the operating frequency of the MMIC circuit and the frequency of several hundred MHz to several GHz, a thin film resistor is provided between the tip of the short stub and the first via hole. Is connected to a series circuit formed of a third MIM capacitor, and a third grounding circuit is configured to ground the intermediate frequency to the substrate together with the first via hole.
[0012]
According to the present invention, it is possible to prevent abnormal oscillation in a wide frequency band from the vicinity of DC to the operating frequency of the millimeter wave band. Furthermore, since the first, second and third ground circuits are all formed in the MMIC circuit, no external capacitor is required.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
1 and 2 are a circuit diagram of an embodiment of a bias circuit according to the present invention and a layout plan view of circuit elements on the MMIC of the bias circuit, respectively.
[0014]
An MMIC such as an oscillation circuit (not shown) is connected to the gate terminal G of the field effect transistor 1, a bias circuit for applying a DC voltage is connected to the drain terminal D, and the source terminal S is grounded. The transistor 1 constitutes an amplifier circuit. The bias circuit includes a short stub constituted by a microstrip line 2 having a length of λ / 4, and a tip of the microstrip line 2 where λ is a wavelength of a specific frequency (referred to as an operating frequency) component of an input signal. And a MIM capacitor 7 connected between the via hole 5 and a microstrip line 3 having a length of λ / 4 connected between the tip of the short stub (microstrip line) 2 and the DC power supply pad 4. The series circuit of the thin film resistor 11 and the MIM capacitor 9 connected between the vicinity of the DC power supply pad 4 and the via hole 6, and the thin film resistor 10 connected between the tip of the short stub 2 and the via hole 5 It has a series circuit of capacitive MIM capacitors 8.
[0015]
In the circuit configured as described above, the portion of the MIM capacitor 7 connected between the tip of the short stub 2 and the via hole 5 and the λ / 4 connected between the tip of the short stub 2 and the DC power supply pad 4. The length of the portion with the microstrip line 3 is the same as the conventionally known bias circuit shown in FIGS. 3 and 4, and when the bias circuit side is viewed from the connection point D that is the feeding point of the transistor 1, The impedance is open at the operating frequency of the MMIC circuit, and the transmission signal in the operating frequency band does not propagate to the bias circuit.
[0016]
A series circuit portion of the thin film resistor 11 and the MIM capacitor 9 connected between the vicinity of the DC power supply pad 4 and the via hole 6 transmits a transmission signal in a low frequency band of about several hundred MHz to several GHz or less. 4 is configured to prevent the propagation to 4. The series circuit portion of the thin film resistor 10 and the electrostatic capacitance MIM capacitor 8 connected between the tip of the short stub 2 and the via hole 5 transmits a transmission signal in an intermediate frequency band between the operating frequency and the low frequency band. A ground circuit for preventing propagation to the DC power supply pad 4 is configured.
[0017]
According to a specific embodiment of the present invention, the operating frequency is 60 GHz, and the parasitic inductance components of the via holes 5 and 6 are about 30 pH (usually 10 to 50 pH), so that the thin film resistors 10 and 11 are both 50Ω, The capacitance of the MIM capacitors 8 and 9 was configured to be about 10 pF.
[0018]
Note that the values of the MIM capacitors 8 and 9 are determined by the operating frequency and the parasitic inductance components of the via holes 5 and 6. However, in a normal MMIC, the capacitance is desirably about 10 pF. Further, when the via hole has a large inductance component, the capacitance of the MIM capacitor 9 is set so that a transmission signal in a low frequency band of about several hundred MHz to several GHz or less is not propagated to the DC power supply pad 4. Need to be set to an appropriate size.
[0019]
As described above, in this embodiment, a transmission signal having a frequency between the operating frequency band of the MMIC and a low frequency band of about several hundred MHz is propagated to the DC power supply pad 4 and causes abnormal oscillation. It provides a means to prevent.
[0020]
5 and 6 are diagrams for explaining the transmission characteristics of the bias circuit of the above embodiment. FIG. 5 shows the transmission characteristics of the transmission signal to the DC power supply pad 4 when the bias circuit side is viewed from the connection point between the bias circuit and the main line, that is, the drain terminal D of the transistor 1. The horizontal axis represents frequencies in the range from 0 to 100 GHz, and the vertical axis represents pass characteristics in the range from -50 dB to 0 dB. The smaller the numerical value, that is, the larger the negative value, the smaller the passing amount of the transmission signal from the connection point between the bias circuit and the main line to the DC pad.
[0021]
In the figure, curves a, b, and c respectively show the above-mentioned embodiment, the above-described embodiment except the series circuit portion of the thin film resistor 11 and the capacitance MIM capacitor 9, and all the ground circuits from the above-mentioned embodiment. The characteristics of the excluded circuit are shown. In the characteristic c, the resonance condition is satisfied near the operating frequency of 60 GHz, and abnormal oscillation is likely to occur. In the case of providing only the ground circuit composed of the MIM capacitor 8 having the capacitance of about 1 pF of the 50Ω thin film resistor 10 of FIG. 1 of the characteristic b, the resonance characteristic around 60 GHz is slightly improved. Further, like the bias circuit of the above-described embodiment of the characteristic a, a ground circuit composed of a 50Ω thin film resistor 10 and an MIM capacitor 8 of about 1 pF, a 50Ω thin film resistor 11, and an MIM capacitor 9 having a capacitance of about 10 pF, In the case of having both of the ground circuits composed of the via holes 6, the pass characteristics are further improved, and the frequency at which abnormal oscillation occurs does not exist in the range of 0 to 100 GHz.
[0022]
FIG. 6 is an enlarged view of the pass characteristics in the low frequency band of 1 GHz or less in FIG. In the above embodiment, by providing the ground circuit composed of the 50Ω thin film resistor 11, the MIM capacitor 9 having a capacitance of about 10 pF, and the via hole 6, the pass characteristic is greatly improved, and the low frequency band close to direct current is obtained. It can be seen that the risk of abnormal oscillation is reduced.
[0023]
As mentioned above, although one Example of this invention was described, this invention is not limited to the said Example. As shown in FIG. 7, the ground circuit may be directly connected to the DC power supply pad 4. The 50Ω thin film resistor 11, the MIM capacitor 9, and the via hole 6 do not need to be arranged on a straight line. Depending on the arrangement state of each circuit element in the MMIC circuit, the 50Ω thin film resistor 11, the MIM capacitor 9, the via Even if the holes 6 are arranged in an L shape, the effects expected in the present invention are not affected at all.
[0024]
The ground circuit including the thin film resistor 10 and the MIM capacitor 8 can be realized by providing a via hole independently, but in order to reduce the circuit area of the MMIC, the via hole 5 used for grounding the short stub 2 is grounded. It is desirable to use a circuit. The capacitance of the MIM capacitor 8 has a magnitude of about 1 pF. This is an example when the parasitic inductance component of the via hole 5 is about 30 pH, and when the inductance component has a different magnitude. Therefore, it is necessary to set the capacitance of the MIM capacitor 8 to an appropriate size so that a transmission signal in a low frequency band of about 30 GHz or less does not propagate to the DC power supply pad 4.
[0025]
【The invention's effect】
As described above, in the bias circuit of the millimeter wave band MMIC, a transmission signal having a frequency in the frequency band of several hundred MHz to several GHz and the operating frequency band of the MMIC propagates to the DC power supply pad 4 to cause abnormal oscillation. Can be prevented. Further, by providing two ground circuits, it is possible to reduce the propagation of the high-frequency signal to the bias circuit over a wide band from the vicinity of DC to immediately below the operating frequency of the MMIC. This solves the problem of resonance between the MIM capacitor in the bias circuit and the inductance component of the via hole.
[0026]
In addition, it is not necessary to provide a chip capacitor or the like outside the MMIC for the purpose of preventing this resonance, and there is an effect that the number of manufacturing steps and the manufacturing cost of the module using the microwave / millimeter wave band MMIC are reduced.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an embodiment of a bias circuit according to the present invention.
FIG. 2 is a partial plan view of an MMIC constituting a circuit diagram of an embodiment of a bias circuit according to the present invention.
FIG. 3 is a circuit diagram of a bias circuit in a conventional microwave / millimeter wave MMIC.
FIG. 4 is a plan view of an MMIC of a bias circuit in a conventional microwave / millimeter wave MMIC.
FIG. 5 is a characteristic diagram for explaining pass characteristics indicating the degree of leakage of a high-frequency signal to the bias circuit in the circuit diagram of one embodiment of the bias circuit according to the present invention.
6 is a partially enlarged view of the pass characteristic of FIG.
FIG. 7 is a partial plan view of an MMIC constituting a circuit diagram of another embodiment of the bias circuit according to the present invention.
[Explanation of symbols]
1: transistor,
2: 1/4 wavelength microstrip line,
3: 1/4 wavelength microstrip line,
4: Pad for bias feeding,
5, 6: Via hole,
7, 8, 9: MIM capacitor,
10, 11: Thin film resistor,
12: External capacitor
13: Bonding wire.

Claims (1)

A bias circuit for supplying power for driving a transistor formed in a monolithic integrated circuit operating in a microwave / millimeter wave band ,
A short stub having one end connected to the voltage supply terminal of the transistor and the other end connected to the first MIM capacitor and having a length equal to a quarter of the wavelength of the propagation signal in the operating frequency band of the monolithic integrated circuit; A first grounding circuit in a series circuit comprising the first MIM capacitor and the first via hole;
A microstrip line having a length equal to a quarter of the wavelength connecting the bias feeding pad and the other end of the short stub;
A first thin film resistor, a second MIM capacitor, and a second via hole are connected in series between the connection point between the microstrip line and the bias power supply pad and the ground, and a frequency component lower than the frequency of the operating frequency band. Between the other end of the short stub and the first MIM capacitor, the second thin film resistor and the third MIM capacitor, and lower than the frequency of the operating frequency band. And a third grounding circuit in which the third MIM capacitor is grounded via the first via hole for a second series circuit for short-circuiting a frequency component higher than the frequency of the frequency component,
The capacitances of the first, second, and third MIM capacitors are in the vicinity of the operating frequency of the MMIC, about several hundred MHz or less , depending on the magnitude of the parasitic inductance component of the first and second via holes, respectively. The bias circuit is set to a value capable of preventing a transmission signal in a low frequency band and a frequency band near the middle of the two frequency bands from propagating to the DC voltage supply pad .

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