JP2911919B2 - High frequency amplifier circuit - Google Patents

Description

The present invention relates to a high-frequency amplifier circuit mounted on a small wireless transmitter such as a portable wireless telephone.

[Conventional technology]

FIG. 3 is a block diagram showing a configuration subsequent to a power amplifier of a conventional wireless transmitter.

A signal in which sound or the like has been modulated at a stage prior to the transmitting unit 31 is
The power is amplified by the amplifier 32 of 31, the isolator 33, the duplexer 3
Via 4, it is emitted as radio waves from an antenna unit 36 having an antenna and a matching circuit.

Using the difference between the transmission frequency and the reception frequency, the duplexer 34 transmits a transmission signal from the transmission unit 31 to the antenna unit 36 and acts as a type of filter that transmits a reception signal from the antenna unit 36 to the reception unit 35. .

Further, the isolator 33 is for preventing the reflected wave generated due to the impedance deviation from being transmitted to the amplifier 32 of the transmission unit 31 when the load of the antenna unit fluctuates due to breakage of the antenna unit 36 or the like. If there is no isolator and this reflected wave enters the amplifier 32, the amplifier 32 becomes unstable, and abnormal oscillation other than the signal frequency may occur.

[Problems to be solved by the invention]

Since wireless devices such as portable telephones are often used outdoors, the antenna portion exposed to the outside is often damaged.

Therefore, in the isolator 33, the antenna section 36 is damaged,
Even if the load fluctuates, in order to prevent the reflected wave from being transmitted to the amplifier 32 and prevent the amplifier 32 from oscillating abnormally,
It was indispensable.

However, there is a problem that the isolator is more expensive than other parts constituting the wireless device and is also larger in size than the other parts, so that it becomes an obstacle in downsizing the wireless device.

Accordingly, an object of the present invention is to prevent an amplifier from oscillating abnormally due to a reflected wave from an antenna unit without using an expensive and large isolator, and to always operate the amplifier stably.

[Means for solving the problem]

In order to achieve the above object, according to the present invention, a series circuit of a resistor and a capacitor for attenuating an input signal including a predetermined frequency to be amplified by the transistor is provided on an input side of a transistor for amplifying an input signal. Bias means including impedance means consisting of: connected to one end of an inductance means that passes a signal other than a predetermined frequency amplified by the transistor to the output side of the transistor, and connected to the other end of the inductance means. Adopts a configuration in which a bias supply terminal for supplying a bias to the transistor and impedance means formed of a series circuit of a resistance element and a capacitance element for attenuating a signal passing through the inductance means are connected.

Note that, as an assumed optimum embodiment, the bias unit is configured to include a plurality of resistance elements and is grounded via a capacitance element, and the bias supply terminal is grounded via a capacitance element. Such a configuration can be adopted.

[Action]

 The principle of the present invention will be described with reference to FIG.

FIG. 1 is a circuit diagram showing a power amplifier circuit of a transmission unit.

In FIG, Q ₀ is a transistor, R1 to R4 is the resistance, C1 -C4 are capacitors, RFC (Radio Frequ
An ency coil is an element in which an inductance is precisely formed by a microstrip line. This microstrip line is formed to have a length equal to or less than a quarter (λ / 4) of a desired transmission frequency wavelength (λ).

The circuit of the present invention is basically composed of three parts: an input side stabilization circuit 1, a transistor Q ₀ , and an output side stabilization circuit 2.

First, the connection relationship of the input-side stabilization circuit 1 and its operation will be described.

The input terminal 3 of the input-side stabilizing circuit 1, the input signal sound or the like is modulated, the input terminal 3 is connected to the gate of the transistor Q _0.

Capacitor C4 is for removing noise on the V _GG, is provided between the V _GG and GND.

The resistance R1~R3 provided between V _GG and GND are determined operating points of the transistors Q ₀ for driving the V _GG resistance-dividing.

The capacitor C1 has one end connected to the input terminal 3 via the resistor R2 and the other end connected to GND.

Between the input terminal 3 and GND, because it is connected to the capacitor C1 by the resistor R2, is part of the input signal applied to the transistor Q _0, fled to GND side via this capacitor C1 resistor R2 Go. That is, the input signal is attenuated.

Since the transistor Q ₀ is set so that the gain is maximized at the desired transmission frequency, the signal of the desired transmission frequency among the attenuated input signals is effectively amplified, Of the input signals obtained, the signal of an undesired frequency is hardly amplified.
Therefore, it is possible to effectively remove only noise without significantly lowering a transmission signal of a desired frequency.

Further, the low-frequency components will cause abnormal oscillation of the transistor Q ₀ is the resistance R2, the impedance of a capacitor C1 is visible to a low impedance, the transistors Q ₀ is,
Abnormal oscillation can be prevented.

Next, the connection state and operation of the output-side stabilization circuit 2 will be described.

One end of the output side of the transistor Q ₀ of the output side stabilizing circuit 2 is connected to the GND side, and the other end is connected to the output terminal 4.

The output terminal of the transistor Q ₀ which is connected to the output terminal 4 side is connected to one end of the RFC. The other end of the RFC is connected to GND via the resistors R4 and C2, connected to GND via C3, and directly connected to _VDD . The V _DD, a bias power to the transistor Q ₀ is supplied.

If the high frequency of the signal from the transistor Q ₀ and normal desired is output, the RFC by the capacitor C3 while the GND and short, and since RFC is formed on lambda / 4 of the signal to be desired, desired and The reflected signal is reflected by RFC, and does not flow from the point A shown in the drawing to the GND side.

Therefore, when the transistor Q ₀ is outputting a signal of a frequency that operates stably transmitted, the signal does not flow to the GND side, is output to the output terminal 4.

Then, the transistor Q ₀ is beginning to cause abnormal oscillation,
When a signal with a frequency lower than the desired transmission frequency is output, the RFC is formed at λ / 4 of the desired signal, so other signals pass through without being reflected by the RFC. . The signal passing through this RFC flows to the GND side through the resistor R4 and the capacitor C2 (for example, R4 is a 50Ω resistor).

Therefore, the reflected wave generated due to the damage of the antenna unit, etc.
Be input to the transistor Q _0, the signal other than the transmission frequency is to be removed flows to the GND side, the transistor Q
₀ does not cause abnormal oscillation.

As described above, in the present invention, the input-side stabilizing circuit 1 removes noise of an input signal, and furthermore, the output-side stabilizing circuit 2
In, and to remove low-frequency noise generated when the transistor Q ₀ has caused the abnormal oscillation.

〔Example〕

 An embodiment of the present invention will be described with reference to FIG.

2, the same parts as those in FIG. 1 are given the same numbers.

In the figure, Q1 and Q2 are transistors, R1 to R7 are resistors, C1 to C8 are capacitors, RFC ₁ and RFC ₂ (Ra
A dio frequency coil is an element in which an inductance is precisely formed by a microstrip line.

As shown in FIG. 2, in one embodiment, the circuit shown in FIG. 1 has two stages to increase the gain as a whole.

First, the connection state and operation of the first-stage amplifier circuit will be described.

The input terminal 3 of the input-side stabilizing circuit 1, the input signal sound or the like is modulated, the input terminal 3 is connected to the gate of the transistor Q _1.

Capacitor C4 is for removing noise on the V _GG, is provided between the V _GG and GND.

The resistance R1~R3 provided between V _GG and GND is determined the operating point of the driving transistor Q ₁ with a V _GG resistance-dividing.

The capacitor C1 has one end connected to the input terminal 3 via the resistor R2 and the other end connected to GND.

Between the input terminal 3 and GND, because it is connected to the capacitor C1 by the resistor R2, is part of the input signal applied to the transistor Q _1, fled to GND side via this capacitor C1 resistor R2 Go. That is, the input signal is attenuated.

Transistor Q ₁ is, because it is set such that the gain becomes maximum at the transmission frequency of the desired, among the input signals the damping, but the signal of the transmission frequency to be desired is effectively amplified, and the damping Of the input signals, signals of undesired frequencies are hardly amplified. Therefore, it is possible to effectively remove only noise without significantly lowering a transmission signal of a desired frequency.

Further, the low-frequency components will cause abnormal oscillation of the transistor Q ₁ is, resistor R2, the impedance of a capacitor C1 is visible to a low impedance, the transistor Q ₁ is,
Abnormal oscillation can be prevented.

The output side of the one end of the transistor Q ₁ is connected to the GND side, the other end via a coupling capacitor C8, which is connected to the gate of the transistor Q _2.

The output terminal of the transistor Q ₁ which is connected to the gate of the transistor Q ₂ is connected to one end of the RFC _1. The other end is connected to the GND side via a capacitor C5, and is directly connected to V _DD1 . The V _DD1, the transistor Q ₁ is supplied with a bias.

If the signal to be desired from the transistor Q ₂ is output, in the state of RFC ₁ is GND and the shorted by the capacitor C5, and since RFC ₁ is formed on the lambda / 4 of the signal to be desired, the signal RFC It is reflected at ₁ and does not flow from the point B shown in the figure to the GND side.

Accordingly, the transmission frequency signal of the desired amplified by the transistor Q ₁ is inputted to the gate of the transistor Q _2, does not escape to the GND side. Since RFC ₁ is an inductance element formed by a microstrip line, it can pass DC components well and pass the voltage from V _DD1 to a transistor.
It can be given to Q _1.

Next, the connection state and operation of the second-stage amplifier circuit will be described.

Signal amplified by the transistor to Q ₁ first stage,
Is input to the gate of the transistor Q ₂ of the second stage.

The operations of the resistors R5 to R7 and the capacitors C6 and C7 are exactly the same as the above-described resistors R1 to R3 and the capacitors C4 and C1.

The output side of the one end of the transistor Q ₂ is connected to the GND side,
The other end is connected to the output terminal 4. The output terminal 4 is further connected to the antenna unit. The load impedance of this antenna unit is a low value of, for example, 50Ω.

The output terminal of the transistor Q ₂ to which is connected to the output terminal 4 side is connected to one end of the RFC _2. The other end of RFC ₂ is connected to GND via resistors R4 and C2, connected to GND via C3, and directly connected to _VDD . The V _DD, a bias power to the transistor Q ₂ is supplied.

If the signal of frequency from transistor Q ₂ and a normal desired is output, RFC ₂ by the capacitor C6 in the state GND and short, and since RFC ₂ is formed on the lambda / 4 of the signal to be desired, The signal is reflected by RFC ₂ and does not flow from the point C shown in the drawing to the GND side.

Therefore, when the transistor Q ₂ is outputting a signal of a frequency that operates stably transmitted, the signal does not flow to the GND side, is output to the output terminal 4.

Then, the transistor Q ₂ is beginning to cause abnormal oscillation,
When a signal of a lower frequency than the signal of the desired transmission frequency is output, since RFC ₂ is formed at λ / 4 of the signal of the desired frequency, other signals are not reflected by RFC ₂ Will pass through. The signal that has passed through RFC ₂ flows to the GND side through a resistor R4 and a capacitor C2 (for example, R4 is a 50Ω resistor). In particular, the low-frequency component flows more easily to the GND side because the impedance formed by the resistor R4 and the capacitor C2 appears to be low impedance.

Therefore, the reflected wave generated due to the damage of the antenna unit, etc.
Be input to the transistor Q _2, the signal other than the transmission frequency is to be removed flows to the GND side, the transistor Q
₂ does not cause abnormal oscillation.

As described above, in one embodiment of the present invention, the transistor Q ₂
Operates stably and outputs a signal of a frequency to be transmitted, the signal does not flow to the GND side, but is output to the output terminal 4.

Further, the reflected wave caused by damage of the antenna unit, be input to the transistor Q _2, the transistor Q ₂ is not such to cause abnormal oscillation.

That is, the input side of the transistor Q _1, to stabilize the operation of the transistor Q ₁ low-frequency noise of the input signal by passing the GND side, further, at the output side of the transistor Q _2, the transistor Q ₂ has caused the abnormal oscillation The low frequency noise that occurs is removed.

In one embodiment, amplification is performed in two stages using two transistors. However, in order to obtain a desired gain as a whole, the gain of the first stage should be set higher than the gain of the second stage. Is effective. The reason is as follows.

As described above, since the transistor of one embodiment is set so that the gain is maximized at a desired transmission frequency, signal components of other frequencies are hardly amplified.

Therefore, in the first stage, the gain is sufficiently increased to amplify both the signal of the desired transmission frequency and the signal of the noise component.

And in the second stage, by the capacitor C6 and the resistor R6,
By letting the input signal escape to the GND side and attenuating the input signal, it is possible to effectively remove only noise without significantly lowering the gain of the desired signal.

Specifically, for example, in the circuit of FIG.
This can be realized by adjusting the values of the resistors R2 and R6 between the input terminal and the capacitors C1 and C6 connected to the GND, such as 300Ω and the resistor R6 to 160Ω.

Further, since the value of the resistor R6 in the input portion of the second stage can be set small, the impedance can be close to the low impedance (for example, 50Ω) of the antenna portion, and the transistor Q ₂
Operation can be stabilized.

At this time, the power supply V biasing the transistors Q ₁ and Q ₂
The values of _DD1 and _VDD2 may be changed as appropriate.

Although the present invention has been described with reference to one embodiment, and an FET is used as a transistor in the drawings, a bipolar type may be used.

Further, in the embodiment, the number of stages of the amplifier is described as two, but may be further increased.

〔effect〕

As described above, according to the present invention, it is possible to prevent an amplifier from abnormally oscillating due to a reflected wave from an antenna unit without using an isolator.

Therefore, since an isolator which is expensive and is a large part is not used, it greatly contributes to cost reduction and miniaturization of the wireless device.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating the principle of the present invention, FIG. 2 is a circuit diagram illustrating an embodiment of the present invention, and FIG. 3 is a block diagram illustrating a configuration of a conventional radio. is there. Q _{0 to} Q ₂ … Transistors R _{1 to} R ₇ … Resistors C _{1 to} C ₈ … Capacitors

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Naoyuki Sekine 1000 Kasashi Ahara, Showa-cho, Nakakoma-gun, Yamanashi Prefecture Fujitsu Yamanashi Electronics Co., Ltd. (56) References JP-A-62-298207 (JP, A) JP-A-2 -107010 (JP, A)

Claims (3)

(57) [Claims] An input means for inputting a transistor for amplifying an input signal includes impedance means comprising a series circuit of a resistance element and a capacitance element for attenuating an input signal including a predetermined frequency to be amplified by the transistor. Bias means is connected, one end of an inductance means that passes a signal other than a predetermined frequency amplified by the transistor is connected to the output side of the transistor, and a bias is applied to the transistor at the other end of the inductance means. A high-frequency amplifier circuit, comprising: a bias supply terminal for supplying; and an impedance unit comprising a series circuit of a resistance element and a capacitance element for attenuating a signal passing through the inductance means. 2. The high-frequency amplifier circuit according to claim 1, wherein said bias means includes a plurality of resistance elements and is grounded via a capacitance element. 3. The high-frequency amplifier circuit according to claim 2, wherein said bias supply terminal is grounded via a capacitance element.