JPH04129308A - High frequency amplifier - Google Patents

Abstract

PURPOSE:To allow a strip line to absorb a reflecting wave by forming a parallel resonance circuit with an inductive strip line and a capacitive element in a bias circuit. CONSTITUTION:A high frequency capacitor C7 and a high frequency coil L10 form a parallel resonance circuit, and a high frequency capacitor C8 and a high frequency coil L30 form a parallel resonance circuit. The resonance frequency is made coincident with a center frequency of a high frequency signal, is passed through without loss and the length of the coils L10, L30 is decreased more than the lambda/4 of the high frequency signal to be amplified. Thus, small size and light weight configuration are attained. Furthermore, since the resonance circuit comprising the capacitor C7 and the coil L10 (the capacitor C8 and the coil L30) forms a low pass filter, harmonic frequencies (f2, f3...) of the high frequency signal to be amplified other than the fundamental wave f0 are eliminated and a gate bias circuit 4 and a drain bias circuit 5 also act like harmonic wave elimination.

Description

[Detailed Description of the Invention] [Summary] Regarding the improvement of a high frequency amplifier suitable for mobile phones, etc., the object is to provide a high frequency amplifier that has a simple configuration, reduces the occupied area, and can eliminate harmonics. A high frequency amplifier comprising: a high frequency amplification transistor having a matching circuit connected to an input end and an output end, respectively; and a bias circuit supplying a bias voltage to the high frequency transistor, the bias circuit being connected to the transistor. The device is configured to include an inductive stripline and a capacitive element that forms a parallel resonant circuit together with the inductive stripline.

[Industrial application field]

The present invention relates to improvements in high frequency amplifiers suitable for mobile telephones and the like.

In recent years, so-called mobile phones have become popular as portable telephones. The basic functions required of a mobile phone are to be small and lightweight, have high operational efficiency, and
The point is that harmonics do not occur. Mobile phones have a built-in high-frequency amplifier to amplify the transmitted signal, but currently many use hybrid ICs, and micro ICs (MIC or MIC).
MIC) development is required. A problem that exists in high frequency amplifiers in reducing their size and weight is reducing the area of the bias circuit of the high frequency amplifier.

[Conventional technology]

FIG. 3 shows an example of a conventional high frequency amplifier. This figure 3 shows a unit for one stage of high frequency amplifier (Si+BStage
). As the high frequency amplification transistor, a GAFET (hereinafter referred to as transistor 2) capable of highly efficient operation is used. transistor 2
Input matching circuit 1 and coupling capacitor C1 are connected to the gate of
An input terminal IN is connected to the transistor 2 via a matching circuit 3 and a coupling capacitor C2, and an output terminal OUT is connected to the drain of the transistor 2 via a matching circuit 3 and a coupling capacitor C2, and its source is grounded. A gate bias circuit 4 for supplying a DC bias voltage for operating the transistor 2 is connected to the gate of the transistor 2, and a drain bias circuit 5 is connected to the drain for the same purpose.

The gate bias circuit 4 includes a high frequency coil L1 connected to a line l connected to the gate of the transistor 2, and an AC grounding capacitor C1 for grounding the high frequency coil L1 at high frequencies to maintain stable operation of the transistor 2 in the low frequency range. It has a resistor R1 (50Ω) for AC grounding, a high frequency coil L2, and a capacitor C1 for AC grounding, and supplies a negative bias voltage Bl.

The drain bias circuit 5 includes a high frequency coil L1 connected to the drain of the transistor 2.A capacitor C1 for AC grounding is used to ground the high frequency coil L3 at high frequencies.In order to obtain stable operation of the output matching circuit 3 in the low frequency region. resistance (50Ω), and AC grounding capacitor C1
It has a high frequency coil L and has a high bias voltage vB2
supply. High frequency coil L4 is gate bias circuit 4
Unlike the high frequency coil L2, it is directly connected to the high frequency coil L3 without using the resistor R2.

This is to prevent the bias voltage vB2 from dropping due to the resistor R.

In the above configuration, the high frequency signal (e.g. 800 to 900 MHz) input to the input terminal IN is connected to the coupling capacitor C.
Through impedance matching of the input matching circuit 1, the signal is transmitted to the transistor 2 via I without causing any reflection. Transistor 2 has a voltage of 1v+■ given by gate bias circuit 4 and drain bias circuit 5.
It performs an amplifying action at the operating point determined by B11 B2 , and is outputted from the output terminal OUT via the output matching circuit 3 and the coupling capacitor C2.

[Problem to be solved by the invention]

The problem with the above conventional high frequency amplifier is that the area occupied by the high frequency coils L and B2 in the gate bias circuit 4 and drain bias circuit 5 becomes an obstacle to converting the high frequency amplifier into a micro IC.

That is, as shown in FIG.
900MHz) 1/4 wavelength (hereinafter referred to as λ/4)
It is formed by a strip line with a length of . This λ/4 strip line of the high frequency coil L1 occupies a large area on the MIC board, and becomes a major obstacle in reducing the size and weight.

In order to solve this problem, it is conceivable to use double substrates and sandwich the high frequency coil L between the side substrates, but this would be difficult to manufacture and would be expensive. This also applies to the high frequency coil L3.

On the other hand, when transmitting a high frequency signal, the occurrence of harmonics other than the fundamental wave (second, third, . . . nth harmonics) causes communication failures, so it is necessary to suppress or eliminate them. Conventionally, it was necessary to add a harmonics removal circuit in addition to the high-frequency amplifier, and the presence of such a harmonics removal circuit (for example, a low-pass filter) was also a problem in achieving compactness, light weight, and high efficiency.

SUMMARY OF THE INVENTION An object of the present invention is to provide a high frequency amplifier that has a simple configuration, can reduce the occupied area, and can eliminate harmonics.

[Means to solve the problem]

In order to solve the above problems, the present invention provides a high frequency amplification transistor (2) having a matching circuit (1, 3) connected to its input end and output end, respectively, and the high frequency transistor (2).
), a high frequency amplifier having a bias circuit (4, 5) that supplies a bias voltage to the bias circuit (4, 5);
4, 5) is an inductive strip line (Llo
, L) and this inductive stripline (Ll[l'
A capacitive element (Lao) that constitutes a parallel resonant circuit together with
C, C, 6, 7).

[Effect]

According to the invention, inductive strip lines (L1oSL3o) and capacitive elements (C,
Since a parallel resonant circuit is formed with C8, 7, 8), the effect equivalent to the conventional λ/4 strip line, that is, the absorption effect of the reflected wave in the transistor (2), is reduced to λ/4.
It is possible to use strip lines (L, L) with a length of 4 or less.As a result, the area occupied by the bias circuit (4, 5) can be reduced.In addition, this resonant circuit ,
It acts as a low-pass filter in the signal transmission path, and therefore, by setting the cutoff frequency in correspondence with the fundamental wave of the high-frequency signal to be amplified, the harmonic component can be removed. No need to add any circuit. This point also contributes to reduction in size and weight.

〔Example〕

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

First Embodiment FIG. 1 shows a first embodiment of the present invention. In FIG. 1, the same parts as in FIG. 3 are given the same reference numerals and will be described below.

The feature of this first embodiment is that a high frequency capacitor C is connected to the line 11 and grounded, and a high frequency capacitor C8 is connected to the line 12 and grounded. High frequency capacitor C1 and high frequency coil 1° constitute a parallel resonant circuit, and similarly high frequency capacitor C1 and high frequency coil 3o constitute a parallel resonant circuit. By making the resonance frequency coincide with the center frequency of the high-frequency signal to be amplified, the high-frequency signal to be amplified can be passed through without loss, and as a result, the high-frequency coil LL can be amplified by λ of the high-frequency signal to the power of lOゝ30. It is possible to make it shorter than /4. The ability to shorten this strip line means that the MIC
This will help reduce the area occupied on the substrate, that is, make it smaller and lighter. Further, each resonant circuit formed by the high frequency capacitor C and the high frequency coil 10' is connected to the line 1.
Since 12 low-pass filters are configured on the signal transmission path,
High-frequency harmonics (f, f...) other than the fundamental wave (fo) of the high-frequency signal to be amplified can be removed, and the gate bias circuit 4 and drain bias circuit 5 can also perform a harmonics removal function. It becomes possible.

Second Embodiment FIG. 2 shows a second embodiment of the present invention. This example is
Distributed constant circuit 6 in place of high frequency capacitors C9 and C8
, discloses an example in which distributed constant circuits 7 are connected to lines 11 and 12, respectively.

The distributed constant circuit 6 and the distributed constant circuit 7 are ultimately circuits consisting of a combination of inductance and capacitance, and by setting the circuit constants, a resonant circuit and a low-pass 10' 30 filter can be configured including the high frequency coil LL. Similar to the first embodiment,
It is possible to reduce the area occupied by the strip lines of the gate bias circuit 4 and drain bias circuit 5 including the high-frequency coils L 1 and L 2 and to eliminate harmonics.

Note that the distributed constant circuit 6 and the distributed constant circuit 7 may be lumped constant circuits.

〔Effect of the invention〕

As described above, according to the present invention, the area occupied by the bias circuit can be reduced by connecting the capacitive strip line constituting the resonant circuit with the inductive strip line for absorbing reflected waves in the bias circuit. It becomes possible to remove harmonics and achieve the desired purpose.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a first embodiment of the present invention, Fig. 2 is a circuit diagram showing a second embodiment of the invention, Fig. 3 is a circuit diagram showing a conventional high frequency amplifier, and Fig. 4 is a circuit diagram showing a conventional high frequency amplifier. It is an explanatory diagram of the problem. 1... Input matching circuit 2... Transistor 3... Output matching circuit 4... Gate bias circuit 5... Drain bias circuit 6... Distributed constant circuit 7... Distributed constant circuit c, ...Coupling capacitor C2...Coupling capacitor C3...AC grounding capacitor C4...AC grounding capacitor C5...AC grounding capacitor C6...AC grounding capacitor C7...High frequency capacitor C8... ... High frequency capacitor Ll ... High frequency coil L2 ... High frequency coil L3 ... High frequency coil L4 ... High frequency coil L5 ... High frequency coil LL ... High frequency coil 10ゝ 30 1 Sl ... Line R1 ...Resistor R2...Resistor ■B1...Bias voltage ■B2...Bias voltage IN...Input terminal OUT...Output terminal

Claims (1)

[Claims] 1. Matching circuits (1, 3) at the input end and the output end, respectively.
A high frequency amplifier comprising: a high frequency amplification transistor (2) connected to a high frequency amplification transistor (2); and a bias circuit (4, 5) that supplies a bias voltage to the high frequency transistor (2), the bias circuit (4, 5) Transistor (2
) connected to the inductive stripline (L_1_0,
L_3_0) and this inductive stripline (L_1
A high-frequency amplifier characterized by comprising: capacitive elements (C_7, C_8, 6, 7) that constitute a parallel resonant circuit together with C_0, L_3_0). 2. In the high frequency amplifier according to claim 1, the inductive strip line is connected to high frequency coils (L_1_0, L_3_0
). 3. In the high frequency amplifier according to claim 1 or 2, the capacitive element is a high frequency grounded capacitor (C_7
, C_8). 4. The high frequency amplifier according to claim 1 or 2, wherein the capacitive element includes a strip line (6, 7). 5. The high frequency amplifier according to claim 1 or 2, wherein the capacitive strip line includes a distributed constant circuit. 6. The high frequency amplifier according to claim 1, wherein the resonant circuit has a reduced pass filter characteristic.