JPH02220509A - Impedance matching circuit - Google Patents

Abstract

PURPOSE:To reduce the cost with a decreased occupied area of an inductor by providing a resonance circuit and designing the circuit inductance to be small and the inductive reactance to be large. CONSTITUTION:An inductance 23 and a capacitance 25 are connected in parallel to form a resonance circuit. One terminal of the resonance circuit connects to a drain D of a FET 21 being a component of a common source amplifier and the other terminal connects to an external circuit 24. Moreover, the resonance angular frequency omega0 of the resonance circuit is expressed as omega0(L.C)<1/2>, where L is the inductance and C is the capacitance. The angular frequency omegawith respect to the frequency (f) at which the impedance matching is to be taken between the output side of the FET 21 and an external circuit 24 is smaller than the resonance frequency omega0 by omega. Since the inductive reactance is increased with a smaller omega, the inductance is selected small to decrease the occupied area thereby reducing the cost.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an amplifier in an ultra-high frequency band integrated circuit.

This invention relates to an impedance matching circuit such as an oscillator 1 frequency conversion circuit.

Integrated circuits such as amplifiers used in ultra-high frequency bands (for example, microwave bands) are fabricated using field-effect transistors (FETs) on semiconductor substrates such as GaAs.

It is constructed by integrating resistors, capacitors, inductors, etc.

In order to reduce the cost of such integrated circuits, it is desired to integrate as many circuits as possible on one semiconductor substrate.

[Conventional technology]

Amplifiers using FETs generally have high output and input impedances and large capacitive reactances.

For example, the output impedance at 8GHz, 1207, and 15G old of the source common amplifier using FET shown in FIG.
They are expressed as B and C.

In an amplifier circuit using such an FET, as shown in FIG. 4, by connecting an inductor 53 having a large inductance value to the drain (D) of the FET 51, the output impedance of the FET 51 and the external circuit 5 can be adjusted.
4 (for example, 50Ω as a characteristic impedance).

In order to realize the inductor 53 having such a large inductance value on an integrated circuit, a spiral inductor as shown in FIG. 6 is used.

[Problem to be solved by the invention]

By the way, in the conventional method described above, an inductor having a large inductance value is required as an impedance matching circuit. For this purpose, it is necessary to increase the number of turns of the spiral inductor, which poses a problem in that the area occupied by the spiral inductor on the semiconductor substrate increases.

For example, a spiral inductor with an inductance of 5 nH has a size of about 300 um square, and this large inductor occupies most of the area of an integrated circuit. Therefore, the number of circuits that can be integrated on one semiconductor substrate is Because of their small number, such integrated circuits have become expensive.

The present invention was created in view of these points, and an object of the present invention is to provide an impedance matching circuit that reduces the area occupied by an inductor on an integrated circuit.

[Means to solve the problem]

In order to achieve the above object, the present invention provides an impedance matching circuit that includes a resonant circuit consisting of an inductor and a capacitor connected in parallel and performs impedance matching between circuits connected at both ends. is configured to have a resonant frequency higher than the operating frequency.

[For production]

By setting the resonant frequency of a resonant circuit consisting of an inductor and a capacitor higher than the operating frequency, this resonant circuit has a large inductive reactance at the operating frequency.

In the present invention, a large inductive reactance can be obtained using an inductor having a small inductance value.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 shows the configuration of an impedance matching circuit in an embodiment of the present invention.

In FIG. 1, an inductor 23 and a capacitor 25 are connected in parallel to form a resonant circuit. One end of this resonant circuit is FET21, which constitutes a source-grounded amplifier.
The other end is connected to the drain (D) of the external circuit 2.
Connected to 4.

The reactance X at a predetermined angular frequency ω of the resonant circuit formed by the inductor 23 and capacitor 25 is expressed by the formula (1
).

jX-... (1) 1 / jωL + jωC However, L is the inductance of the inductor 23.

C is the capacitance of the capacitor 25.

Also, the resonant angular frequency ω of the resonant circuit. is expressed as in equation (2) using inductance L and capacitance C.

ω. -1/ (LC)"" ... (2)
Here, the angular frequency ω corresponding to the operating frequency f (hereinafter referred to as operating frequency ω) is the above-mentioned resonance angular frequency ω, as shown in equation (3). The angular frequency is set to be Δω lower than . This operating frequency f is the frequency at which the FET 21 performs the amplification operation, that is, the frequency between the output side of the FET 21 and the external circuit 2.
This is the frequency at which impedance matching should be achieved between the two.

ω=ω. −Δω (ω.〉〉Δω)... (3) Resonant circuit resistance X at such operating frequency ω
is expressed as equation (4) by transforming equation (1) using equations (2) and (3).

As can be seen from equation (4), the reactance X becomes a large inductive reactance when Δω is small.

For example, ω. /Δω=10, the reactance of the resonant circuit at the operating frequency ω corresponds to an inductance value approximately five times the inductance of the inductor 23. Therefore, when the inductance L0 is required to match the capacitive reactance of the above-mentioned FE, T21, matching can be performed using the inductor 23 having an inductance of 1/5 L6.

At this time, the capacitance C of the capacitor 25 is calculated by the formula (
2).

Thus, the resonant angular frequency ω is higher than the operating frequency ω by Δω. A large inductive reactance can be achieved at the operating frequency ω by a resonant circuit having ω.

Thereby, the impedance on the output side of the FET 21 and the impedance of the external circuit 24 (for example, 50Ω as a characteristic impedance) can be matched using an inductor having a small inductance value.

FIG. 2 shows a configuration example of a cascode amplifier to which an impedance matching circuit according to an embodiment of the present invention is applied.

In the figure, 31 and 32 are FETs 33 and 3
6 is an inductor, 34 and 35 are resistors.

37 is a capacitor, 38 is an input terminal, and 39 is an external circuit.

As shown in the figure, FET 3 constitutes a common gate amplifier.
The drain (D) of 2 is connected to the inductor 36 and capacitor 3.
It is connected to an external circuit 39 via a resonant circuit consisting of 7 and 7.

FIG. 3(a) shows the characteristics when impedance matching is performed using an inductor having an inductance of 3.3 nH instead of the resonant circuit connected to the cascode amplifier shown in FIG.

In the figure, the horizontal axis shows frequency (G) (z), and the vertical axis shows gain (dB).

Further, FIG. 3(b) shows the characteristics of the cascode amplifier shown in FIG. 2.

Here, the resonant circuit connected to the cascode amplifier consists of an inductor 3 with an inductance of 1.68 nH.
6 and a capacitor 37 having a capacitance of 0.05PF.

In this way, the output of the cascode amplifier shown in FIG. It becomes possible to achieve impedance matching between the side and the external circuit 39.

This allows the area occupied by the inductor in the integrated circuit to be significantly reduced.

On the other hand, the capacitance (0.05pF) as mentioned above
Since a capacitor having 37 can be integrated using a relatively small area on a semiconductor substrate, the area increased by adding this capacitor 37 to an integrated circuit is small, and the area occupied by the inductor is reduced. is much larger.

In the embodiment of the present invention described above, the resonance angular frequency ω higher than the operating frequency ω by Δω is provided on the output side of the amplifier using the FET. We considered the case of impedance matching between the output side of this amplifier and the external circuit by connecting a parallel resonant circuit with It may be something you take.

Furthermore, the present invention is not limited to amplifiers, and can be applied to impedance matching circuits on the input and output sides of active circuits such as oscillator 1 frequency conversion circuits.

〔Effect of the invention〕

As described above, according to the present invention, an impedance matching circuit having a large inductive reactance can be configured using an inductor having a small inductance value. This makes it possible to reduce the area occupied by the inductor, thereby making it possible to reduce the area of the integrated circuit and provide a low-cost ultra-high frequency band integrated circuit.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an impedance matching circuit according to an embodiment of the present invention, FIG. 2 is a diagram showing the configuration of a cascode amplifier to which the impedance matching circuit according to an embodiment of the present invention is applied, and FIG. 3 is a diagram showing the characteristics of the cascode amplifier. 4 is a block diagram of an amplifier using an FET, FIG. 5 is an explanatory diagram of the output impedance of an amplifier using an FET, and FIG. 6 is a diagram showing an example of a spiral inductor. In the figure, 21.31 and 32.51 are field effect transistors (FE
T), 23.33, 36.53 are inductors, 24.39.5
4 is an external circuit, 25.37 is a capacitor, 34.35 is a resistor, and 38 is an input terminal. Figure Kuniyoshiki (GHH) Ice control ((Otsu G)-1, Ri

Claims (1)

[Claims] (1) In an impedance matching circuit that includes a resonant circuit consisting of an inductor and a capacitor connected in parallel and performs impedance matching between the circuits connected at both ends, the resonant circuit has a resonant frequency higher than the operating frequency. Features an impedance matching circuit.