JPH0440702A - Microwave circuit - Google Patents

Abstract

PURPOSE:To prevent the deterioration of the performance and the yield of an MMIC by connecting a diode in parallel to an active element, then supplying the control voltage to the active element and the diode so as to change adversely to each other between the capacity of the active element and that of the diode. CONSTITUTION:A diode 13 which forms an input matching circuit together with a transmission line 2 is connected between an input terminal 10 and a capacity 14 which is short-circuited at a microwave band. Then a bias terminal 15 is provided to apply the control voltage to the anode of the diode 13 in order to secure the matching of impedance. The voltage Va lower than the gate-source voltage Vgs of an FET 1 is applied to the terminal 15. The voltage Vgs is varied so as to change adversely to each other between the capacity of the diode 13 and the input capacity of the FET. Thus it is possible to prevent the deterioration of the gains and the reflection coefficient of an MMIC and to improve the yield of the MMIC.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a microwave circuit, and in particular to an active element for amplifying a microwave signal and for matching the input/output impedance of the active element to the impedance of an adjacent input/output circuit. The present invention relates to a microwave circuit equipped with an impedance matching circuit for.

[Problems to be solved by conventional technology and inventions] In recent years, G.
As the development of field-effect transistors (hereinafter referred to as FETs) and modulation-doped field-effect transistors made of aAs-based and InP-based materials progresses, attempts are being made to monolithically fabricate these transistors, matching circuits, and bias circuits on semiconductor substrates. It is widely practiced in various places. This monolithic IC is called MMIC (Monolithic Mic).
r.

wave Integrated C1rcuit
), and the hybrid microwave integrated circuit (MIC), which has been mainly used for microwaves,
ave Integrated C1rcuit)
It is smaller and more reliable than the . For this reason, UHF
MMICs such as various low-band noise amplifiers, mixers, and oscillators that operate at frequencies ranging from band to millimeter waves have been developed in various places, and are contributing to the miniaturization of microwave transceivers and the like.

In MMIC, active elements (such as FETs and bipolar transistors), microwave lines, and passive elements such as capacitors and resistors are monolithically integrated on a semiconductor substrate. At this time, since the microwave line and capacitor have a large physical size, they can be manufactured with almost no variation if a semiconductor process is used.

However, since active devices such as FETs and bipolar transistors require microfabrication, device characteristics inevitably vary. Specifically, in recent years, gate electrodes of FETs have become finer, and the gate length has been shortened to 0.1 μm. However, it is difficult to manufacture a 0.1 μm gate electrode with good reproducibility, and some variation occurs. Since the drain current of an FET is inversely proportional to the gate length, in an operating state where the drain current is constant, it is necessary to change the gate operating voltage with respect to the gate length.

Also, since gate length and gate capacitance are almost proportional, FE
The input impedance of T will depend on the gate length.

Figure 5 shows a gate summary of 0.1 μm and a gate width of 250 μm.
It is a figure showing the frequency characteristic (1-12GHz) of S parameter of. In the same figure, 50 is the S parameter Sl
The l component, 51, indicates the 822 component of the S parameter. As shown in this frequency characteristic (the input side Sll of the FET is
As a series connection of a resistance component Rin and a capacitance component Cin, the output side S22 has a resistance component Rout and a capacitance component Cou.
It can be expressed as a parallel connection of t. In this FET, Rin is 8Ω and Cin is 0.2pFSRou.
t is 150Ω, Cout is 0.1 pF, and transconductance gm is 60 mS. FIG. 6 shows an equivalent circuit of the above FET.

FIG. 7 is a circuit diagram showing a conventional example of a 12 GHz band MMIC amplifier using the above FET. This MMIC amplifier includes a FETI whose source is grounded, an input terminal 10,
Output terminal 11, input matching circuit 16, and output matching circuit 1
7, a gate bias circuit 18 for applying a bias voltage to the gate of FETI, and a drain voltage application circuit 19 for applying a drain voltage of FET1. The input matching circuit 16 includes an input transmission line 2 connected between the input terminal 10 and the gate of the FETI, and a capacitor 70 connected between the input terminal 10 and GND. Matching circuit 17 includes an output transmission line 3 connected between output terminal 11 and the drain of FETI, and a capacitor 12 connected between output terminal 11 and GND. The gate bias circuit 18 includes a bias terminal 8 for supplying a DC voltage to the gate of the FETI, and a connection between this terminal 8 and GND.
and a choke coil 4 connected between a bias terminal 8 and an input transmission line 2. Further, the drain voltage application circuit 19 includes a bias terminal 9 for supplying a DC voltage to the drain of the FETI, a capacitor 7, and a choke coil 5.

Note that when the FETI shown in FIG. 5 is used in this circuit, the circuit constants are set as follows.

Input transmission line 2: characteristic impedance 50Ω, electrical length 67 degrees (electrical length θ=1/λ·π, where L is the physical length of the line and λ is the wavelength within the line.

Input circuit 70: 1.0 pF Output transmission line 3: Characteristic impedance 50Ω, electrical length 95 degrees Output side capacitance 12: 0.35 pF When the circuit constants are set as described above, the gain of the MMIC amplifier at 12 GHz is 18. 8 dB, and the input/output reflection coefficient is approximately 0.

However, as mentioned above, the gate length varies, and as a result, the input capacitance Cin varies from 0°18 to 0.2 within the wafer plane.
Assuming that it is distributed in the range of 29F, Sl at 12GHz
l will vary. Figure 4 shows this variation. Regarding Fig. 4, points A, B, and C are each C1n
=0.22,0°20.corresponds to 0.18pF. Also, A-, BC= (white circles) are A, B, respectively.
The complex conjugate impedance at point C is shown.

Even though S11 varies as shown in FIG. 4, the matching circuit in the MMIC is set based on point B, so a problem arises in that matching loss increases as S11 deviates from point B.

In the circuit of FIG. 7, Cin of FETI is 0°18.
MM I when it varies from 0.20.0.22pF
Table 1 shows the calculation results of the gain of C and the input reflection coefficient. Note that here, in order to simplify the discussion, only Cin is changed, and the other equivalent circuit constants are kept constant. Further, the input reflection coefficient is the reflection coefficient when the FETI is viewed from the terminal in FIG.

Table 1 As described above, since the microwave characteristics of the MMIC vary due to variations in the gate length, the matching circuit of the MMIC must be adjusted according to the variations in the microwave characteristics after the MMIC is fabricated.

However, in order to adjust the matching circuit after manufacturing the MMIC, it is necessary to change the length and width of the input transmission line 2 and the output transmission line, and to change the capacitance 12.70, which is impossible.

This has been a cause of deteriorating the performance and yield of MMIC.

The present invention has been made in view of the above problem, and even if there are variations in active elements, especially variations in microwave characteristics, MM
It is an object of the present invention to provide a microwave circuit that can prevent deterioration in IC performance and yield.

"Means for Solving the Problems" A microwave circuit according to the present invention for achieving the above object includes an active element for amplifying a microwave input signal, and an adjacent input/output circuit that changes the input/output impedance of the active element. An impedance matching circuit or a microwave circuit formed on a substrate for matching the impedance of the active element, the impedance matching circuit comprising: an input transmission line for transmitting a microwave input signal to the active element; a power transmission line for transmitting a microwave output signal from the active element; a diode connected in parallel to the active element to correct a change in the capacitance of the active element; a capacitance of the active element and a capacitance of the diode; and control voltage supply means for supplying a control voltage to the active element and the diode such that the voltages change inversely to each other.

[Function] According to the present invention having the above configuration, since the diode is connected in parallel with the active element, when the control voltage of the diode is changed, the capacitance of the diode and the active element is changed.
At the same time, the current in the active element also changes. The capacitance increases and decreases in an inverse relationship between the diode and the active element, so if the capacitance of the active element is smaller than the desired value, adjusting the control voltage higher will increase the diode's capacitance, causing the opposite effect. If the capacitance of the active element is larger than the desired value, the capacitance of the diode is reduced by adjusting the control voltage to a smaller value.This allows impedance matching to be performed in a self-aligned manner against variations in the capacitance of the active element. becomes possible.

[Example code] Hereinafter, the present invention will be explained in detail by giving examples.

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

Referring to the figure, the difference between the microwave circuit of this embodiment and the microwave circuit of FIG. A diode 13 for configuring the circuit is connected, and a bias terminal 15 for applying a control voltage for impedance matching is connected to the anode of the diode 13.

The diode 13 has an n-type semiconductor and a metal (for example, A
A material having a Schottky barrier with Ti) is used. Here, the carrier concentration of the n-type semiconductor is 3X1017
At about am-3, the Schottky electrode area is about 1000 μm
Set it to 2. A Schottky electrode of the diode 13 is connected to the bias terminal 15, and one ohmic electrode is connected to the transmission line 2.

The bias terminal 15 is connected to the gate-source voltage V of the FET 1 (usually 0 to -IV in the case of MESFET (7)).
Va in this embodiment, in which a voltage V8 lower than ) is applied, is set to -1.5V.

By configuring the input matching circuit as described above,
The bias voltage va is equal to the gate-source voltage V1. Since the diode 13 is lowered, by changing ■,
The capacitance of the FET and the input capacitance of the FET change in opposite ways.

Note that even when using a diode other than a diode using an n-type semiconductor and a metal Schottky barrier, connect the diode so that the increase and decrease in capacitance of the active element and the diode are opposite, and set the control voltage Va. .

The above embodiment will be described in further detail with reference to the voltage/capacitance characteristic diagram of the diode shown in FIG.

The reflection coefficient (S11) when looking at the FET from D in Figure 1 is:
When Rin=8Ω and C1n=0.2pF, point B in FIG. 4 is obtained as described above. The characteristic impedance of the transmission line 2 to match this Sll is 50Ω and the electrical length is 6
7 degrees, the capacity of the diode is 1. It is OpF. At this time, the reflection coefficient when looking at the diode side from D is point B in Figure 4.
−, and complex conjugate matching is achieved. however,
The gate length of FET1 varies, and Cin is 0.18 to 0.
．． becomes 22pF, and the gate-source voltage at that time is V,
,i! Assuming that the voltages are -0.5 to -0.7V, respectively, S11 varies within the range of points A to C in FIG. However, in this embodiment, since the diode 13 is used in this impedance matching circuit, the capacitance of the diode 13 changes as shown in FIG. 3 as Vl changes. That is, due to variations in the gate length of FET1, 1. Ga-
When the voltage changes from 0.5V to -0.7V, the capacitance of the diode 13 at that time becomes about 0.8 to 1.3 pF, as shown by the characteristic curve 31 in FIG. Therefore, when v is -0,5, -〇,6, -0.7V, the reflection coefficient when looking at the diode side from D in Figure 1 is point Al in Figure 4.
, Bl, C1 (X mark).

Also, points A'', B-, CItV,, in Fig. 4 are -0°5
, -0. 6. -0. It is the reflection coefficient that gives the complex conjugate impedance of FET S11 at 7V.

In the conventional example shown in FIG. 7, the reflection coefficient when looking to the left from node D' is always as follows even if Cin (Vt,) of the FET changes:
Since it is at point B, Cin is 0.18pF (V, , =-
0, TV) +::, then points B' and C in Figure 4
' distance causes matching loss, and Cin is 0.22pF.
(Vgs=-o, 5V), the distance between points B- and A' in FIG. 4 becomes a matching loss.

However, in this example, when C1n=0.18pF, the fourth
The distance between points C1 and C- in the figure is the matching loss, and C1n=0
．． At 22 pF, the distance between point A1 and point A' in FIG. 4 results in a matching loss, so the matching loss is smaller than in the conventional example. Table 2 provides a concrete comparison of the above. In addition,
The input reflection coefficient is from terminal 10 to F in Figures 1 and 7.
This is a look at the ET side. Furthermore, although the values of the FET parameters except Cin are fixed, there is no significant difference in the relative values of the gain and input reflection coefficient between the conventional example and this embodiment.

Table 2 (a) Table 2 (b) As is clear from the above table, this example has better gain and input reflection coefficient than the conventional example, demonstrating the effect of reducing matching loss using diode 13. There is. Therefore, if the capacitance of the diode 13 of the matching circuit is appropriately selected,
The diode 13 absorbs variations in the gate capacitance of the FET, serves to prevent deterioration of the gain and reflection coefficient of the MMIC, and improves the yield of the MMIC.

FIG. 2 is a circuit diagram showing another embodiment of the present invention. The difference from the embodiment shown in FIG.
The lower part 21 is connected to the output transmission line 3, and the lower parts 20 and 21 also serve as a bias circuit for the FET 1. In this embodiment, the diode 13 is connected in parallel with the FETI without the input/output transmission line 2.3. Therefore, when the gate operating voltage V□ changes,
If the capacitance of the diode is selected to compensate for the change in the input capacitance of the FETI, there will be almost no change in the capacitance at point E in FIG. 2, so there is no need to adjust the matching circuit.

Furthermore, since the absolute value of the capacitance change of the FETI is small, the area of the diode 13 for correcting it can also be small. Further, since the capacitance changes of FET1 and diode 13 occur in the same phase unlike in FIG. 1, even when a large signal is input from input terminal 10, diode 13 can correct the capacitance of FETI. Therefore, the microwave circuit shown in FIG. 2 can be applied to large amplitude power supply.

Note that although the present invention has been explained with a focus on the input capacitance of the FET in FIGS. The diode is not limited to one using a Schottky junction of an n-type semiconductor and a metal, and a pn junction diode or the like can also be used. Also,
Similar effects can be obtained when the present invention is applied not only to MMICs but also to hybrid integrated circuits.

[Effects of the Invention] As explained above, according to the present invention, variations in the capacitance of the active element can be corrected by the diode connected in parallel to the active element and the control voltage applied to the diode and the active element. As a result, the performance and yield of MMIC can be improved. In addition, even if the bias point of the active element changes, the matching loss is reduced by the diode correcting the capacitance, so it can be used not only in small signal amplifiers but also in a wide range of microwave circuits such as large signal amplifiers and voltage-controlled variable gain amplifiers. The effect is that it can be applied to

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of an MMIC amplifier showing one embodiment of the present invention, Fig. 2 is a circuit diagram of an MMIC amplifier showing another embodiment of the invention, and Fig. 3 is a diagram showing voltage/capacitance characteristics of a diode. , Fig. 4 shows the relationship between Sl and FET input capacitance
Figure 5 shows the frequency characteristics of S11 and S22 of the FET, Figure 6 shows the equivalent circuit diagram of the FET, and Figure 7 shows a conventional example of an MMIC amplifier. It is a circuit diagram. In the figure, 1 is an FET, 2 is an input transmission line, 3 is an output transmission line, 13 is a diode, and 15 is a control voltage application terminal. L1 Diagram 2 Ward 3 Spoon Chi 4 Trouble 6 Diagram ■ Procedural Amendment 1, Display of Case 1990 Patent Application No. 148933 2, Title of Invention Microwave Circuit 3, Person Making Amendment Relationship with Case Patent applicant address: 22-22 Nagaike-cho, Abeno-ku, Osaka City Name:
(504) Sharp Corporation Representative Haruo Tsuji 4, Agent address: 2-1-29 Minamimorimachi, Kita-ku, Osaka Sumitomo Bank Minamimorimachi Building Phone: Osaka (06) 361-2021 Ke0
Name Patent Attorney (6474) Kube Fukami 5, date of amendment order voluntary amendment 6, column 7 for detailed explanation of the invention subject to amendment, contents of amendment (1) Correct "noise amplifier" to "low noise amplifier". (2) Delete "z" on page 11, line 20 of the specification. (3) In the second line of page 12 of the specification, "in Figure 1" was replaced with "
Correct it to the point in Figure 1. that's all

Claims (1)

[Claims] An active element for amplifying a microwave input signal and an impedance matching circuit for matching the input/output impedance of the active element to the impedance of an adjacent input/output circuit are formed on a substrate. A microwave circuit, the impedance matching circuit comprising: an input transmission line for transmitting a microwave input signal to the active element; an output transmission line for transmitting a microwave output signal from the active element; a diode connected in parallel to the active element to correct a capacitance change of the active element, and supplying a control voltage to the active element and the diode so that the capacitance of the active element and the capacitance of the diode change oppositely to each other; and control voltage supply means for.