JP3450721B2 - Semiconductor device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field effect transistor that performs frequency down conversion of microwaves and millimeter waves.

[0002]

2. Description of the Related Art Conventionally, in order to perform frequency down conversion of microwaves and millimeter waves, as shown in FIG. 14, the drain terminal 3 of a field-effect transistor whose source is grounded has an RF frequency of 1 and a wavelength of a local oscillation wave. An open stub 10 of about / 4 is provided, a stub having a capacitor at the tip is placed, or an RF choke circuit that also has a repeating pattern of 1/4 wavelength is placed to short-circuit the RF frequency or the local oscillation wave at the drain terminal. Designed like
The frequency conversion was performed efficiently. Also,
In order to keep the IF frequency output terminal 13 invisible from the RF frequency band, it was necessary to select the lead line 11 for the IF signal to have a quarter wavelength and also to provide the shunt capacitance 12.

A conventional example is also shown in FIGS. 15, 16 and 17. In either case, since the quarter wavelength line is used as described above, the circuit becomes large.

FIG. 15 shows the open stub 10 of FIG. 14 replaced with a line with a shunted tip.

FIG. 16 shows a structure in which a 1/4 wavelength low impedance line 14 and a 1/4 wavelength high impedance line 15 are replaced by a repeating structure.

FIG. 17 shows the shunt capacitor 12 of FIG. 14 replaced with an open stub 10.

However, these methods tend to narrow the band because the reactance termination condition of the drain terminal is satisfied at a certain specific frequency, and the circuit area is long because a stub or a choke circuit having a long quarter wavelength is used. It was upsized.

However, it is difficult to reduce the chip area required for a microwave / millimeter wave monolithic integrated circuit (MMIC), etc., in particular.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to achieve a circuit area reduction and a wide band in a microwave / millimeter wave frequency down converter.

[0010]

In order to short-circuit the drain terminal of a transistor in a high frequency manner and allow an IF signal to pass through, the drain electrode and the source electrode of the transistor are superposed so as not to be electrically connected. The drain-source capacitance is generated by the
It suffices to prevent the frequency and the local oscillation frequency from leaking. By selecting the electric capacitance so that the IF frequency is not shunted, the transistor itself can have a function as a frequency converter.

Since the RF frequency and the local oscillation frequency are shunted inside the transistor, a wide band can be achieved, and at the same time, a stub having a length of 1/4 wavelength is not required, and the size is reduced.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to examples.

(Embodiment 1) FIG. 1 shows an embodiment of the present invention.

The RF signal and the local oscillation wave input from the gate electrode 1 of the field effect transistor operating as a mixer are generated at a partially overlapping portion of the source electrode 2 and the drain electrode 3 which are grounded at high frequency. It is shunted by the electric capacity and is not output from the drain electrode 3. Since the capacitance is adjusted so as to have a sufficiently large reactance with respect to the generated IF frequency, it is output from the drain electrode 3.

(Embodiment 2) FIG. 2 shows an embodiment of the present invention.

The operating principle is the same as that of the first embodiment, but FIG.
In this case, the shapes of the source electrode 2 and the drain electrode 3 are different. Similarly, although the shapes of the source electrode 2 and the drain electrode 3 are different in FIGS. 3 and 4, the source electrode 2 and the drain electrode 3 are different.
There is no substitute for creating an electric capacity between
The same effect as that of the first embodiment can be obtained.

(Embodiment 3) In FIG. 5, the electric position of the electric capacitance generated between the source electrode 2 and the drain electrode 3 is different. In Example 1 and Example 2, the capacitance was generated at the tip of the gate electrode 1, but in FIG. 5, the drain electrode 3 is covered with the source electrode 2 so as to straddle the gate electrode. However, the RF signal generated at the drain electrode and the local oscillation wave are shunted, and the same effect can be obtained in this case as well.

(Embodiment 4) FIG. 6 shows an embodiment in which the space between the source electrode 2 and the drain electrode 3 is hollow. As shown in FIG. 7, the dielectric 4 is provided between the source electrode 2 and the drain electrode 3. The same effect can be obtained by sandwiching them. Similar effects can be obtained even if the positional relationship between the source electrode 2 and the drain electrode is reversed. Further, the source electrode 2 and the drain electrode 3 are not a single-layer metal film, but a multi-layer film can achieve the same effect.

(Embodiment 5) FIG. 8 shows an embodiment in the case of a T-shaped gate FET. The same effect can be obtained by extending the drain electrode 3 and intersecting it with the source electrode 2.

(Embodiment 6) Embodiments 1 to 4 are two-finger FETs, and embodiment 5 is a T-shaped gate.
FIG. 9 shows an embodiment when applied to a comb-shaped multi-finger FET. The drain-source capacitance is obtained by pulling out the central source electrode 2 which is conventionally connected to the air bridge so as to intersect with the drain electrode 3. The drain-source capacitance can also be obtained by drawing out the wide source electrode 2 so as to pass over the gate electrode 1 and the drain electrode 3. Source electrode 2 of this embodiment
In this way, since the width of the electrode can be made large, it is particularly effective in reducing the source inductance of the central source electrode.

(Embodiment 7) FIG.
Although it is an example in the case of a V-shaped gate, by extending the drain electrode 3 in the drawing direction of the drain electrode 3, this is an effective structure particularly when wiring is performed by a coplanar line.

(Embodiment 8) FIG. 11 shows an example of an equivalent circuit of an FET. The 20 regions surrounded by the broken line are the intrinsic components of the FET. The drain-source capacitance 30 is generated inside the transistor by the method described in the first to seventh embodiments. Therefore, the RF signal and LO oscillation wave input from the gate terminal are reactively terminated by the drain-source capacitance 30. As a result, as shown in FIG.
The drain-source capacitance 30 acts as a short circuit for a high frequency such as RF, and opens for a low frequency IF. Since the reactance of the drain-source capacitance 30 is inversely proportional to the frequency, the miraculous movement on the chart becomes slower as the frequency becomes higher on the Smith chart of FIG. That is, drain-source capacitance 3
It can be seen that 0 is a good reactive termination over a wide band.

FIG. 13 shows an embodiment of a wideband down converter. Reference numeral 5 is a coupler, such as a Lange coupler, a merchant balun, a side coupler, or the like, which can obtain wide band characteristics. By combining such a coupler with the FET 7 according to the present invention, it becomes possible to realize a broadband active mixer.

[0024]

According to the present invention, in a microwave / millimeter wave frequency down-converter, it is possible to simultaneously reduce the circuit area and widen the band.

[Brief description of drawings]

FIG. 1 is a top view of a semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a top view of a semiconductor device according to a second embodiment of the present invention.

FIG. 3 is a top view of a semiconductor device that is a second embodiment of the present invention.

FIG. 4 is a top view of a semiconductor device according to a second embodiment of the present invention.

FIG. 5 is a top view of a semiconductor device according to a third embodiment of the present invention.

FIG. 6 is a sectional view of a semiconductor device according to a fourth embodiment of the present invention.

FIG. 7 is a sectional view of a semiconductor device according to a fourth embodiment of the present invention.

FIG. 8 is a sectional view of a semiconductor device according to a fifth embodiment of the present invention.

FIG. 9 is a sectional view of a semiconductor device according to a sixth embodiment of the present invention.

FIG. 10 is a sectional view of a semiconductor device according to a seventh embodiment of the present invention.

FIG. 11 is a circuit diagram for explaining an eighth embodiment of the present invention.

FIG. 12 is a Smith chart for explaining an eighth example of the present invention.

FIG. 13 is a block diagram for explaining a fourth embodiment of the present invention.

FIG. 14 is a top view of a conventional semiconductor device.

FIG. 15 is a top view of a conventional semiconductor device.

FIG. 16 is a top view of a conventional semiconductor device.

FIG. 17 is a top view of a conventional semiconductor device.

[Explanation of symbols]

1 Gate electrode 2 Source electrode 3 drain electrode 4 Dielectric 5 couplers 6a Matching circuit a 6b Matching circuit b 7a FETa according to the present invention 7b FETb according to the present invention 10 1/4 wavelength open stub 11 IF signal lead wire 11 12 shunt capacity 13 IF frequency output terminal 13a IF frequency output terminal a 13b IF frequency output terminal b 14 1/4 wavelength low impedance line 15 1/4 wavelength high impedance line 16 tracks

Claims (2)

(57) [Claims] 1. In a field effect transistor for down-converting the frequency of a high frequency signal, a part of a source electrode and a part of a drain electrode are made to intersect each other so as not to contact each other, and between the source electrode and the drain electrode. A semiconductor device characterized in that a high frequency signal generated at a drain electrode is shunted to a source electrode by generating an electric capacitance, and only an IF signal is taken out from the drain electrode. 2. The semiconductor device according to claim 1, wherein a dielectric is sandwiched between a source electrode and a drain electrode that intersect to generate an electric capacitance.