JPH03101523A - High frequency amplifier circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a high frequency amplification circuit installed in a small radio transmitter such as a portable radio telephone. The purpose is to prevent abnormal oscillation of the amplifier by not transmitting the signal to the input terminal (3), the output terminal (4), the first power supply (GND), and the second power supply. (vDD) and a third power supply (Vcc,), an input end is connected to the input terminal (3), one end of the output end is connected to the output terminal (4), and the other end of the output end is connected to the output terminal (4). 1st
A transistor (Q0) connected to the power supply (GND) of impedance means (R2, C1) provided between the input terminal (3) and the first power source (GND) and attenuating the signal input from the input terminal (3); , the frequency signal amplified by the transistor (Q0) is output to the output terminal (
4), and one end is connected to the output terminal of the transistor (Q0) connected to the output terminal (4) so that signals other than the frequency concerned are passed to the first power supply (GND) side. A high frequency amplification circuit is created by the connected inductance means (RFC), the impedance means (R4, C2) and capacitance (C3) connected to the other end of the inductance means (RFC), and the second power supply (v0). Configure.

[Industrial application field]

TECHNICAL FIELD The present invention relates to a high frequency amplification circuit installed in a small radio transmitter such as a portable radio telephone.

[Conventional technology]

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

The signal modulated with audio or the like before the transmitting section 31 is power amplified by the amplifier 32 of the transmitting section 31, and then sent to the isolator 33.
Via the duplexer 34, the signal is emitted as a radio wave from an antenna section 36 including an antenna and a matching circuit.

The duplexer 34 utilizes the difference between the transmitting frequency and the receiving frequency to transmit the transmitted signal from the transmitting section 31 to the antenna section 36, and functions as a kind of filter that transmits the received signal from the antenna section 36 to the receiving section 35. .

Further, the isolator 33 is provided to prevent reflected waves generated due to impedance deviation from being transmitted to the amplifier 32 of the transmitting section 31 when the load on the antenna section changes due to damage to the antenna section 36 or the like.

If there is no isolator and this reflected wave enters the amplifier 32, the amplifier 32 will become unstable and may cause abnormal oscillation at frequencies other than the signal frequency.

[Problem to be solved by the invention]

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

Therefore, even if the antenna section 36 is damaged and its load fluctuates, the isolator 33 is indispensable in order to prevent reflected waves from being transmitted to the amplifier 32 and to prevent the amplifier 32 from abnormally oscillating. Ta.

However, since the isolator is more expensive than other parts constituting the radio, and its size is also larger than other parts, there is a problem in that it becomes an obstacle to downsizing the radio.

Therefore, it is an object of the present invention to prevent the amplifier from abnormally oscillating due to reflected waves from the antenna section and to always operate the amplifier stably without using an expensive and large isolator.

[Means to solve the problem]

In order to achieve the above object, the present invention provides an input terminal (3), an output terminal (4), and a first power supply (G
ND), second power supply (VDD), and third power supply (VCC)
and an input end is connected to the input terminal (3), one end of the output end is connected to the output terminal (4), and the other end of the output end is connected to the first
a transistor (Q0) connected to the power supply (GND) of impedance means (R2, CI) provided between the input terminal (3) and the first power source (GND) and for attenuating the signal input from the input terminal (3); and the transistor. The signal at the frequency amplified by (Q0) is output to the output terminal (4), and the signal at a frequency other than the frequency is passed through the output terminal (4) to the first power supply (GND) side.
an inductance means (RFC), one end of which is connected to the output end of the transistor (Q,), and an impedance means (R4, C2) and a capacitor (R4, C2) connected to the other end of the inductance means (RFC). C3) and the second power supply (VDD) constitute a high frequency amplification circuit.

[Effect]

The present invention will be explained in detail using FIG.

FIG. 1 is a circuit diagram showing a power amplification circuit of a transmitter.

In the figure, Qo is a transistor, R1-R4 are resistors, 01-C4 are capacitors, and RF C
(Radio Frequency Co11
) is an element whose inductance is precisely formed by a microstrip line. This microstrip line is formed to have a length equal to or less than one-fourth (λ/4) of the wavelength (λ) of the desired transmission frequency.

The circuit of the present invention basically consists of an input side stabilizing circuit 1° transistor Q0. The output side stabilization circuit 2 is composed of three parts.

First, the connection relationship and operation of the input side stabilizing circuit 1 will be explained.

A signal modulated with audio or the like is input to an input terminal 3 of the input side stabilizing circuit 1, and this input terminal 3 is connected to the gate of a transistor Q.

Capacitor C4 removes noise on VGG, and is provided between VGli and GND.

Further, resistors R1 to R3 provided between VGG and GND divide VGG into resistive voltages to determine the operating point for driving the transistor Qo.

One end of the capacitor C1 is connected to the input terminal 3 via the resistor R2, and the other end is connected to GND.

A capacitor CI and a resistor R are connected between input terminal 3 and GND.
2, a part of the input signal applied to the transistor Q0 escapes to the GND side via the capacitor C1 and resistor R2. In other words, the input signal is attenuated.

Since the transistor Q0 is set so that the gain is maximized at the desired transmission frequency, the signal at the desired transmission frequency among the attenuated input signals is effectively amplified, but the attenuated signal at the desired transmission frequency is effectively amplified. Of the input signals, signals with undesired frequencies are rarely amplified.

Therefore, only the noise can be effectively removed without significantly lowering the transmission signal of the desired frequency.

In addition, the low frequency component that causes abnormal oscillation of transistor Q0 is caused by the impedance of resistor R2 and capacitor C1 appearing to be low impedance.
, can prevent abnormal oscillation.

Next, the connection state and operation of the output side stabilizing circuit 2 will be explained.

One end of the output side of the transistor Qa 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 end of the transistor Q0 connected to the output terminal 4 side is connected to one end of the RFC. The other end of RFC is connected to GND via resistors R4 and 02, and also to GND via C, 3, and directly to VDI. With this VDD, transistor Q0
Bias power is supplied to the

When a normal desired high frequency signal is output from transistor Q0, RFC is connected to GN by capacitor C3.
Since it is shorted to D and RFC is formed at λ/4 of the desired signal, the desired signal is RFC
Therefore, it does not flow from point A shown in the figure to the GND side.

Therefore, when the transistor Q0 operates stably and outputs a signal at the frequency to be transmitted, the signal does not flow to the GND side but is output to the output terminal 4.

Next, transistor Q0 begins to cause abnormal oscillation,
If a signal with a lower frequency than the desired transmission frequency is output, the RFC is formed at λ/4 of the desired signal, so other signals will pass through without being reflected by the RFC. . The signal that has passed through the RFC flows to the GND side through a resistor R4 and a capacitor C2 (for example, R4 is a 50Ω resistor).

Therefore, even if reflected waves caused by damage to the antenna section are input to transistor Q, signals at frequencies other than those to be transmitted will flow to the GND side and be removed, so transistor Q0 will not cause abnormal oscillation. do not have.

As described above, in the present invention, the input side stabilization circuit 1 removes noise from the input signal, and the output side stabilization circuit 2 removes noise from the input signal.
Low frequency noise generated when transistor Q0 causes abnormal oscillation is removed.

〔Example〕

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

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

In the figure, Ql and Q2 are transistors, and R1-R7
is a resistor, 01 to C8 are capacitors, and RFC
, and RF C1 (Radio Frequency
Co11) is an element whose inductance is precisely formed by a microstrip line.

As shown in FIG. 2, in one embodiment, the circuit shown in FIG. 1 is made into two stages to increase the overall gain.

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

A signal modulated with audio or the like is input to an input terminal 3 of the input side stabilizing circuit 1, and this input terminal 3 is connected to the gate of a transistor Q.

Capacitor C4 removes noise on VGG, and is provided between Vaa and GND.

Further, resistors R1 to R3 provided between VGG and GND divide VGG into resistive voltages to determine the operating point for driving the transistor Q.

One end of the capacitor C1 is connected to the input terminal 3 via the resistor R2, and the other end is connected to GND.

A capacitor CI and a resistor R are connected between input terminal 3 and GND.
2, a part of the input signal applied to the transistor Q escapes to the GND side via the capacitor C1 and resistor R2. In other words, the input signal is attenuated.

Since the transistor Q1 is set so that the gain is maximized at the desired transmission frequency, the signal at the desired transmission frequency among the attenuated input signals is effectively amplified; Among the signals, signals at undesired frequencies are rarely amplified. Therefore, only the noise can be effectively removed without significantly lowering the transmission signal of the desired frequency.

In addition, the low frequency component that causes abnormal oscillation of transistor Q is caused by the impedance of resistor R2 and capacitor C1 appearing to be low impedance.
, can prevent abnormal oscillation.

One end of the output side of the transistor Q is connected to the GND side, and the other end is connected to the gate of the transistor Q2 via a coupling capacitor C8.

The output terminal of transistor Q, which is connected to the gate of transistor Q2, is connected to one end of RFC.

The other end is connected to the GND side via a capacitor C5 and directly to vII. This VDI)l
Therefore, transistor Q is supplied with a bias.

Transistor Q! When a desired signal is output from the capacitor C5, the RF Ct is shorted to GND and RFC is formed at λ/4 of the desired signal, so the signal is reflected by RFC. Therefore, it does not flow from point B shown in the figure to the GND side.

Therefore, the signal of the desired transmission frequency amplified by transistor Q is input to the gate of transistor Q2, and does not escape to the GND side. Incidentally, since RFC is an inductance element formed by a microstrip line, direct current can pass through it well, and the voltage from Vt1DI can be applied to transistor Q.

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

The signal amplified by the first stage transistor Q is
Second stage transistor Q! input into the gate.

The functions of the resistors R5 to R7 and capacitors C6 and C7 are exactly the same as those of the resistors R1 to R3 and capacitors C4 and CI described above.

One end of the output side of the transistor Q2 is connected to the GND side, and the other end is connected to the output terminal 4. The output terminal 4 is further connected to an antenna section.

The load impedance of this antenna section is as low as 50Ω, for example.

The output end of the transistor Q connected to the output terminal 4 side is connected to one end of the RFC. And RFC,
The other end is connected to GND through resistors R4 and 02, and also connected to GND through C3, and directly connected to VDD.
It is connected to the. With this vo, transistor Q!
Bias power is supplied to the

When a normal desired frequency signal is output from transistor Q2, RFCt becomes G due to capacitor C6.
Since it is shorted to ND and RFC is formed at λ/4 of the desired signal, the signal is RFC!
Therefore, it does not flow toward the GND side from the 0 point shown in the figure.

Therefore, when the transistor Q2 operates stably and outputs a signal at the frequency to be transmitted, the signal does not flow to the GND side but is output to the output terminal 4.

Next, transistor Qz begins to cause abnormal oscillation,
If a signal with a lower frequency than the signal with the desired transmission frequency is output, RFCz is λ/4 of the signal with the desired frequency.
The other signals are RFC! It will pass through without being reflected. The signal that has passed through this RFC is connected to a resistor R4 and a capacitor C2 (for example, R
4 is a 50Ω resistor) and flows to the GND side. especially,
For low frequency components, the impedance made up of resistor R4 and capacitor C2 appears to be low impedance, so the GN is more
It easily flows to the D side.

Therefore, the reflected waves caused by damage to the antenna section, etc., are transmitted to the transistor Q! Even if the signal is input to the transmitter, signals other than the frequency to be transmitted flow to the GND side and are removed, so that the transistor Q2 does not cause abnormal oscillation.

As described above, in one embodiment of the present invention, the transistor Q2
If it operates stably and outputs a signal at the frequency to be transmitted, the signal does not flow to the GND side and is output to the output terminal 4.

Further, even if a reflected wave caused by damage to the antenna section or the like is input to the transistor Q2, the transistor Q2 will not cause abnormal oscillation.

In other words, on the input side of transistor Q, the low frequency noise of the input signal is passed to the GND side to stabilize the operation of transistor Q, and furthermore, on the output side of transistor Q2, if transistor Q2 causes abnormal oscillation. It removes low frequency noise.

Note that in one embodiment, amplification is performed in two stages using two transistors, but in order to obtain the desired overall gain, it is recommended to set the gain of the first stage higher than the gain of the second stage. is effective.

The reason is as described below.

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

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

In the second stage, the input signal is released to the GND side using the capacitor C6 and the resistor R6, and the input signal is attenuated. This effectively reduces the noise without reducing the gain of the desired signal. You can remove it.

Specifically, in the circuit shown in Fig. 2, the values of the resistors R2 and R6 between the input terminal and the capacitors C1 and C6 connected to GND are adjusted so that, for example, the resistor R2 is 300Ω and the resistor R6 is 160Ω. It can be achieved by doing this.

Furthermore, by being able to set the value of resistor R6 in the second stage input section to a small value, the antenna section has a low impedance (
For example, the transistor Q
The second operation can be stabilized.

Further, at this time, the value of the power supply VDDI + "DD2 biasing the transistors Q, , Q, may be changed as appropriate.

The present invention has been described above with reference to one embodiment, and FETs are used as transistors in the drawings, but bipolar transistors may also be used.

In addition, in one embodiment, the number of stages of the amplifier was explained as two stages, but
It is also possible to have multiple stages.

〔effect〕

As explained above, according to the present invention, it is possible to prevent abnormal oscillation of the amplifier due to reflected waves from the antenna section without using an isolator.

Therefore, since an isolator, which is an expensive and large component, is not used, this greatly contributes to lower cost and smaller size of radio equipment.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram explaining the present invention in detail, FIG. 2 is a circuit diagram explaining an embodiment of the present invention, and FIG. 3 is a block diagram showing the configuration of a conventional radio device. be. Q0~Q2......Transistor R0~R1
·········resistance

Claims (1)

[Claims] An input terminal (3), an output terminal (4), a first power source (GND), a second power source (V_D_D), and a third power source (V_G_G), and the input terminal is the input terminal. (3), one end of the output terminal is connected to the output terminal (4), and the other end of the output terminal is connected to the first output terminal (4).
Transistor (Q_0) connected to the power supply (GND) of
and the third power source (V_G_G) and the first power source (GND)
a bias means provided between the input terminal (3) and the first power supply (GND) and supplying a bias to the transistor (Q_0); The impedance means (R2, C1) that attenuates the input signal and the signal of the frequency amplified by the transistor (Q_0) are output to the output terminal (4), and signals other than the frequency are output to the first terminal. Connect the output terminal (4) so that it passes to the power supply (GND) side.
An inductance means (RFC) whose one end is connected to the output terminal of the transistor (Q_0) connected to the transistor (Q_0), and an impedance means (R4, C2) and a capacitor (C3) connected to the other end of the inductance means (RFC). ) and the second power supply (V_D_D).