High frequency amplifier

An emitter of a transistor (1) for high frequency amplification and a cathode of a diode (5) for generating reference voltage are grounded via an inductance (20). Anode electric potential of the diode (5) decreases with increase in output power of the transistor (1) and thus the operation of the transistor (1) is limited. Since the diode is an on linear element, it is possible to quickly limit the operation of the transistor (1) in response to an increase in output current, thereby preventing a breakdown caused by overcurrent.

FIELD OF THE INVENTION

The present invention relates to a high frequency amplifier using a high frequency transistor.

BACKGROUND OF THE INVENTION

In amplifiers used for radio communication of mobile telephones and so on, generally two or three compound semiconductor transistors for high frequency amplification are connected in multiple stages. In recent years, hetero bipolar transistors are mainly used as compound semiconductor transistors in consideration of a single positive power supply operation and so on.

When a current driving bipolar transistor is used for an amplifier having an output power of about 1 to 3 W for mobile telephone terminals, a bias circuit is generally used. The bias circuit includes, in addition to a bipolar transistor for high frequency amplification, another bipolar transistor which supplies a bias to the base of the transistor by means of an emitter follower. (see Japanese Patent Laid-Open No. 2003-273660).

Further, methods using a directional coupler and a detector circuit are generally used to detect an output power of an amplifier and control the bias voltage of the amplifier according to the output power.

FIG. 20shows an example of a conventional high frequency amplifier.

A high frequency input signal is inputted from a high frequency power input terminal17to the base of a bipolar transistor1for high frequency amplification (hereinafter, referred to as a transistor1), is outputted from the collector thereof, and is outputted from a high frequency power output terminal18.

A bias is supplied from a voltage source13to the collector of the transistor1via a collector power supply circuit12such as a λ/4 wavelength line. Base bias is supplied from a voltage source14to the base of the transistor1by means of an emitter follower of a bipolar transistor2for bias supply. The bias current of the transistor1is adjusted according to the voltage of the voltage source14and a resistor7. A resistor8suppresses excessive base current of the transistor1.

Reference numeral15denotes a voltage source for supplying the collector bias of the bipolar transistor2for bias supply.

FIG. 21shows that the output power and temperature dependence of the high frequency amplifier shown inFIG. 20are improved by using the diode5for generating the reference voltage. To be specific, the base electric potential of the bipolar transistor2for bias supply is so adjusted by an operational amplifier3as to be equal to a voltage generated in the diode5for generating the reference voltage. The transistor2supplies base bias to the transistor1by means of the emitter follower and the diode5has been biased by a constant current source4. The bias current of the transistor1is adjusted by the constant current source4.

FIG. 22shows an example of a high frequency amplifier having the function of adjusting the bias of a high frequency transistor according to an output power. A high frequency signal is inputted from a high frequency power input terminal17. An output from a high frequency amplifier61passes through a directional coupler64and is outputted from a high frequency power output terminal18. The output is partially inputted to a detector circuit65by the directional coupler64. The output voltage of a control power supply circuit66is controlled for a desired characteristic according to the output level of the detector circuit65. The voltage is supplied to a base or gate voltage supply terminal62and a collector or drain voltage supply terminal63of the high frequency amplifier61.

However, in the case of the high frequency amplifier using the conventional bipolar transistor, when the output load of the high frequency amplifier fluctuates, the bipolar transistor for high frequency amplification rapidly increases in collector current and thus a breakdown may occur in the transistor.

Generally, a breakdown is prevented by the following methods:1) A resistor is provided in the collector or emitter of a high frequency transistor.2) A resistor is provided in the base of a high frequency transistor.3) The size of a high frequency transistor is increased to have a higher allowable current.4) The output power of a high frequency amplifier is detected and a bias voltage is controlled so as to prevent the occurrence of a breakdown in the high frequency amplifier at high output power.

However, in 1), power added efficiency is seriously reduced by a resistance loss in the high-power amplifier. In 3), power gain and power added efficiency decrease because the high frequency transistor increases in size. Further, a semiconductor chip increases in size.

Although method 2) is most commonly used, a voltage drop in the resistor is proportionate to a base current and thus a resistance value enough to prevent a breakdown in the event of fluctuations in output load degrades a characteristic in an actually used area. Method 4) requires a directional coupler and a detector circuit, so that a characteristic is degraded by a loss in the directional coupler and the detector circuit and the high frequency amplifier increases in size.

As described above, in the conventional art, when the collector current of an amplifier increases due to fluctuations in the output load of the amplifier, a breakdown may occur in a transistor. In order to prevent a breakdown, the high frequency characteristic of the amplifier degrades and the size of the amplifier increases.

It is an object of the present invention to provide a high frequency amplifier which can prevent a breakdown in a transistor without degrading the high frequency characteristic of the high frequency amplifier.

DISCLOSURE OF THE INVENTION

A high frequency amplifier according to the first aspect of the present invention, in which a high frequency input signal is applied between the ground and an input circuit of a transistor for high frequency amplification and a high frequency output signal is outputted from one end of an output circuit of the transistor for high frequency amplification, wherein the other end of the output circuit is connected to the ground via a sensor element serving as a load resistance component at the frequency of the high frequency input signal, and a terminal voltage of the sensor element is fed back to the input of a bias voltage regulator circuit of the input circuit via a nonlinear element to limit the operations of the output circuit.

A high frequency amplifier according to the second aspect of the present invention, in which an input circuit of a first transistor for high frequency amplification and an input circuit of a second transistor for high frequency amplification are connected in parallel, a high frequency input signal is applied between the ground and the input circuits of the first and second transistors for high frequency amplification, and a high frequency output signal is outputted from one end of an output circuit in each of the first and second transistors for high frequency amplification, the output circuits being connected in parallel, wherein out of the first and second transistors for high frequency amplification, the other end of the output circuit of the first transistor for high frequency amplification is grounded, the other end of the output circuit of the second transistor for high frequency amplification is connected to the ground via a sensor element serving as a load resistance component at the frequency of the high frequency input signal, and a terminal voltage of the sensor element is fed back to the input of a bias voltage regulator circuit of the input circuit in each of the first and second transistors for high frequency amplification via a nonlinear element to limit the operations of the output circuits.

A high frequency amplifier according to the third aspect of the present invention, in claim1or2, wherein the sensor element is an inductance or resistor or a series circuit of an inductance and a resistor.

A high frequency amplifier according to the fourth aspect of the present invention, wherein according to the first aspect or the second aspect, the nonlinear element for feeding back the terminal voltage of the sensor element to the input of the bias voltage regulator circuit is a diode biased in the forward direction, and one end of the diode is grounded via a capacitor.

A high frequency amplifier according to the fifth aspect of the present invention, in which a high frequency input signal is applied between the ground and an input circuit of a transistor for high frequency amplification and a high frequency output signal is outputted from one end of an output circuit of the transistor for high frequency amplification, wherein the other end of the output circuit is connected to the ground via a sensor element serving as a load resistance component at the frequency of the high frequency input signal, a terminal voltage of the sensor element is fed back to the input of a bias voltage regulator circuit of the input circuit via a nonlinear element to limit the operations of the output circuit, the sensor element is constituted of an inductance or resistor or a series circuit of an inductance and a resistor, the nonlinear element for feeding back the terminal voltage of the sensor element to the input of the bias voltage regulator circuit is a diode biased in the forward direction, and one end of the diode is grounded via a capacitor.

A high frequency amplifier according to the sixth aspect of the present invention, in which an input circuit of a first transistor for high frequency amplification and an input circuit of a second transistor for high frequency amplification are connected in parallel, a high frequency input signal is applied between the ground and the input circuits of the first and second transistors for high frequency amplification, and a high frequency output signal is outputted from one end of an output circuit in each of the first and second transistors for high frequency amplification, the output circuits being connected in parallel, wherein out of the first and second transistors for high frequency amplification, the other end of the output circuit of the first transistor for high frequency amplification is grounded, the other end of the output circuit of the second transistor for high frequency amplification is connected to the ground via a sensor element serving as a load resistance component at the frequency of the high frequency input signal, a terminal voltage of the sensor element is fed back to the input of a bias voltage regulator circuit of the input circuit in each of the first and second transistors for high frequency amplification via a nonlinear element to limit the operations of the output circuits, the sensor element is constituted of an inductance or resistor or a series circuit of an inductance and a resistor, the nonlinear element for feeding back the terminal voltage of the sensor element to the input of the bias voltage regulator circuit is a diode biased in the forward direction, and one end of the diode is grounded via a capacitor.

A high frequency amplifier according to the seventh aspect of the present invention, wherein according to the first aspect or the second aspect, the nonlinear element for feeding back the terminal voltage of the sensor element to the input of the bias voltage regulator circuit is a first diode biased in the forward direction, a second diode biased in the forward direction with the grounded cathode is provided in addition to the first diode, and the terminal voltage is fed back to the input of the bias voltage regulator circuit of the input circuit according to an electric potential difference between the anode electric potential of the first diode and the anode electric potential of the second diode to limit the operations of the output circuit.

A high frequency amplifier according to the eighth aspect of the present invention, in which a high frequency input signal is applied between the ground and an input circuit of a transistor for high frequency amplification and a high frequency output signal is outputted from one end of an output circuit of the transistor for high frequency amplification, wherein the other end of the output circuit is connected to the ground via a sensor element serving as a load resistance component at the frequency of the high frequency input signal, a terminal voltage of the sensor element is fed back to the input of a bias voltage regulator circuit of the input circuit via a nonlinear element to limit the operations of the output circuit, the sensor element is constituted of an inductance or resistor or a series circuit of an inductance and a resistor, the nonlinear element for feeding back the terminal voltage of the sensor element to the input of the bias voltage regulator circuit is a first diode biased in the forward direction, a second diode biased in the forward direction with the grounded cathode is provided in addition to the first diode, and the terminal voltage is fed back to the input of the bias voltage regulator circuit of the input circuit according to an electric potential difference between the anode electric potential of the first diode and the anode electric potential of the second diode to limit the operations of the output circuit.

A high frequency amplifier according to the ninth aspect of the present invention, in which an input circuit of a first transistor for high frequency amplification and an input circuit of a second transistor for high frequency amplification are connected in parallel, a high frequency input signal is applied between the ground and the input circuits of the first and second transistors for high frequency amplification, and a high frequency output signal is outputted from one end of an output circuit in each of the first and second transistors for high frequency amplification, the output circuits being connected in parallel, wherein out of the first and second transistors for high frequency amplification, the other end of the output circuit of the first transistor for high frequency amplification is grounded, the other end of the output circuit of the second transistor for high frequency amplification is connected to the ground via a sensor element serving as a load resistance component at the frequency of the high frequency input signal, a terminal voltage of the sensor element is fed back to the input of a bias voltage regulator circuit of the input circuit in each of the first and second transistors for high frequency amplification via a nonlinear element to limit the operations of the output circuits, the sensor element is constituted of an inductance or resistor or a series circuit of an inductance and a resistor, the nonlinear element for feeding back the terminal voltage of the sensor element to the input of the bias voltage regulator circuit is a first diode biased in the forward direction, a second diode biased in the forward direction with the grounded cathode is provided in addition to the first diode, and the terminal voltage is fed back to the input of the bias voltage regulator circuit of the input circuit according to an electric potential difference between the anode electric potential of the first diode and the anode electric potential of the second diode to limit the operations of the output circuits.

A high frequency amplifier according to the tenth aspect of the present invention, wherein according to the first aspect or the second aspect, the nonlinear element for feeding back the terminal voltage of the sensor element to the input of the bias voltage regulator circuit is a diode biased in the forward direction, and the diode generates the reference voltage of the bias circuit for biasing the input circuit of the transistor for high frequency amplification.

A high frequency amplifier according to the eleventh aspect of the present invention, in which a high frequency input signal is applied between the ground and an input circuit of a transistor for high frequency amplification and a high frequency output signal is outputted from one end of an output circuit of the transistor for high frequency amplification, wherein the other end of the output circuit is connected to the ground via a sensor element serving as a load resistance component at the frequency of the high frequency input signal, a terminal voltage of the sensor element is fed back to the input of a bias voltage regulator circuit of the input circuit via a nonlinear element to limit the operations of the output circuit, the sensor element is constituted of an inductance or resistor or a series circuit of an inductance and a resistor, the nonlinear element for feeding back the terminal voltage of the sensor element to the input of the bias voltage regulator circuit is a diode biased in the forward direction, and the diode generates the reference voltage of the bias circuit for biasing the input circuit of the transistor for high frequency amplification.

A high frequency amplifier according to the twelfth aspect of the present invention, in which an input circuit of a first transistor for high frequency amplification and an input circuit of a second transistor for high frequency amplification are connected in parallel, a high frequency input signal is applied between the ground and the input circuits of the first and second transistors for high frequency amplification, and a high frequency output signal is outputted from one end of an output circuit in each of the first and second transistors for high frequency amplification, the output circuits being connected in parallel, wherein out of the first and second transistors for high frequency amplification, the other end of the output circuit of the first transistor for high frequency amplification is grounded, the other end of the output circuit of the second transistor for high frequency amplification is connected to the ground via a sensor element serving as a load resistance component at the frequency of the high frequency input signal, a terminal voltage of the sensor element is fed back to the input of a bias voltage regulator circuit of the input circuit in each of the first and second transistors for high frequency amplification via a nonlinear element to limit the operations of the output circuits, the sensor element is constituted of an inductance or resistor or a series circuit of an inductance and a resistor, the nonlinear element for feeding back the terminal voltage of the sensor element to the input of the bias voltage regulator circuit is a diode biased in the forward direction, and the diode generates the reference voltage of the bias circuit for biasing the input circuit of the transistor for high frequency amplification.

A high frequency amplifier according to the thirteenth aspect of the present invention, wherein according to the first aspect or the second aspect, the nonlinear element for feeding back the terminal voltage of the sensor element to the input of the bias voltage regulator circuit is a diode biased in the forward direction, and the diode is constituted of a series connection of two or more diodes or a junction diode between the base and emitter of a bipolar transistor.

A high frequency amplifier according to the fourteenth aspect of the present invention, in which a high frequency input signal is applied between the ground and an input circuit of a transistor for high frequency amplification and a high frequency output signal is outputted from one end of an output circuit of the transistor for high frequency amplification, wherein the other end of the output circuit is connected to the ground via a sensor element serving as a load resistance component at the frequency of the high frequency input signal, a terminal voltage of the sensor element is fed back to the input of a bias voltage regulator circuit of the input circuit via a nonlinear element to limit the operations of the output circuit, the sensor element is constituted of an inductance or resistor or a series circuit of an inductance and a resistor, the nonlinear element for feeding back the terminal voltage of the sensor element to the input of the bias voltage regulator circuit is a diode biased in the forward direction, and the diode is constituted of a series connection of two or more diodes or a junction diode between the base and emitter of a bipolar transistor.

A high frequency amplifier according to the fifteenth aspect of the present invention, in which an input circuit of a first transistor for high frequency amplification and an input circuit of a second transistor for high frequency amplification are connected in parallel, a high frequency input signal is applied between the ground and the input circuits of the first and second transistors for high frequency amplification, and a high frequency output signal is outputted from one end of an output circuit in each of the first and second transistors for high frequency amplification, the output circuits being connected in parallel, wherein out of the first and second transistors for high frequency amplification, the other end of the output circuit of the first transistor for high frequency amplification is grounded, the other end of the output circuit of the second transistor for high frequency amplification is connected to the ground via a sensor element serving as a load resistance component at the frequency of the high frequency input signal, a terminal voltage of the sensor element is fed back to the input of a bias voltage regulator circuit of the input circuit in each of the first and second transistors for high frequency amplification via a nonlinear element to limit the operations of the output circuits, the sensor element is constituted of an inductance or resistor or a series circuit of an inductance and a resistor, the nonlinear element for feeding back the terminal voltage of the sensor element to the input of the bias voltage regulator circuit is a diode biased in the forward direction, and the diode is constituted of a series connection of two or more diodes or a junction diode between the base and emitter of a bipolar transistor.

A high frequency amplifier according to the sixteenth aspect of the present invention includes high frequency amplifier circuits connected in multiple stages, the circuit applying a high frequency input signal between the ground and an input circuit of a transistor for high frequency amplification and outputting a high frequency output signal from one end of an output circuit of the transistor for high frequency amplification, wherein out of the high frequency amplifier circuits, the other end of the output circuit of a specific high frequency amplifier circuit is grounded via a sensor element serving as a load resistance component at the frequency of the high frequency input signal, and a terminal voltage of the sensor element is fed back to the input of a bias voltage regulator circuit in an input circuit of the other high frequency amplifier circuit to limit the operations of the output circuit.

According to the present invention, a high frequency voltage generated in a sensor element between the ground and the output circuit of a transistor for high frequency amplification is fed back to an input bias circuit. Thus, when overcurrent flows through the transistor, it is possible to quickly reduce an input voltage, thereby preventing a breakdown caused by overcurrent in the transistor without degrading the high frequency characteristic of an amplifier.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1shows a conceptual diagram showing a high frequency amplifier of the present invention.

A high frequency input signal is inputted from a high frequency power input terminal17and is supplied to an input circuit between a base and an emitter of a bipolar transistor1for high frequency amplification.

The output circuit of the bipolar transistor1for high frequency amplification is configured between a collector and the emitter. An amplified high frequency signal is outputted from the collector serving as one end of the output circuit and outputted from a high frequency power output terminal18. An input matching circuit9and an output matching circuit11are similar to those of the conventional example. An input bias voltage is applied from a control power supply circuit66, which acts as a bias voltage regulator circuit, to the base of the transistor1via a resistor7. A voltage is applied from the control power supply circuit66to the collector of the transistor1via a collector power supply circuit12such as a λ/4 wavelength line.

The emitter of the transistor1is grounded via an inductance20which is a sensor element acting as a load resistance component at the frequency of the high frequency input signal. The terminal voltage of an inductance20is fed back to the input of the bias voltage regulator circuit of the transistor1via a diode5as a nonlinear element for generating the reference voltage, so that the operations of the transistor1are limited. Reference numeral4denotes a constant current source circuit.

Referring to the operation explanatory drawings ofFIGS. 2 to 5, the following will describe the operation principle ofFIG. 1.

FIG. 2is a circuit diagram in which the inductance20is used as a sensor element. An amplified collector current passes through the emitter in response to a high frequency signal inputted from the base of the transistor1, and an emitter current having an almost equal high frequency amplitude is generated across the inductance20.

The emitter of the transistor1and the cathode of the diode5, which has been biased in the forward direction by the constant current source4, are connected to each other and grounded via the inductance20, resulting in an electric potential difference having a high frequency amplitude across the diode5. At this point, due to a capacitance to the ground on the anode of the diode5and the nonlinearity of the diode, a voltage amplitude decreases in such a way that the anode electric potential of the diode5is clipped by the threshold voltage of the diode5. The time waveform of a voltage generated across the diode5and a direct-current component are shown inFIGS. 3A and 3B. A direct-current electric potential difference across the diode decreases at high power. The direct-current electric potential difference across the inductance20is 0. That is, as shown inFIG. 4, the anode of the diode5decreases in electric potential as the transistor1increases in output power, and the electric potential is rapidly reduced by the nonlinearity of the diode as the output power increases.

The constant current source4is used as the bias of the diode in the present embodiment. Also a constant voltage source can enable similar operations by substituting voltage for current. It is needless to say that the same effect can be obtained in an unideal state where the constant current source4has an internal resistor4aas shown inFIG. 5Aor a voltage source13has an internal resistor13aas shown inFIG. 5B.

In this way, the emitter of the transistor1and the cathode of the diode5for generating the reference voltage are grounded via the inductance20in the high frequency amplifier ofFIG. 1. Thus, as shown inFIG. 2, the anode of the diode5decreases in electric potential as the output power of the transistor1increases. The bias state of the transistor1can be controlled through the resistor7and the collector power supply circuit12such as a λ/4 wavelength line according to the output power level by the control power supply circuit66, which outputs a desired voltage while using the anode electric potential of the diode5as a control signal.

More specifically,FIG. 6shows the high frequency amplifier ofFIG. 1in use for an actual circuit.

A high frequency input signal is inputted from the high frequency power input terminal17to the base of the transistor1, is outputted from the collector thereof, and is outputted from the high frequency power output terminal18. A bias is supplied by the voltage source13to the collector of the transistor1through the collector power supply circuit12such as a λ/4 wavelength line. The base voltage of a bipolar transistor2for bias supply is adjusted by an operational amplifier circuit3in such a way that the base voltage of the bipolar transistor1for high frequency amplification is equal to a voltage generated in the diode5for generating the reference voltage. The transistor2supplies base bias to the transistor1by means of an emitter follower and the diode5has been biased by the constant current source4. The bias current of the bipolar transistor1for high frequency amplification is adjusted by the constant current source4. The resistor7suppresses excessive base current of the bipolar transistor1for high frequency amplification. The resistor7may be omitted in the present embodiment.

Reference numeral14denotes a voltage source for supplying the collector bias of the bipolar transistor2for bias supply. Reference numeral17denotes the high frequency power input terminal and reference numeral18denotes the high frequency power output terminal. The emitter of the transistor1and the cathode of the diode5for generating the reference voltage are grounded via the inductance20. Thus, as shown inFIG. 2, the anode of the diode5decreases in electric potential as the output power of the transistor1increases.

The base electric potential of the bipolar transistor2for bias supply is outputted by the operational amplifier circuit3and is adjusted in such a way that the base electric potential of the transistor1and the anode electric potential of the diode5are equal to each other, so that the operations of the transistor1are limited.

Since the diode of a nonlinear element is used, it is possible to quickly limit the operations of the transistor1in response to an increased collector current.

FIG. 7shows simulation results on comparisons of voltage fluctuations on the base terminal of a high frequency amplifier transistor between the conventional base resistor and the present embodiment. In the present embodiment, a base voltage rapidly decreases at high power, and the base voltage is forcibly interrupted and thus no breakdown occurs when the collector current is rapidly increased by fluctuations in the output load of the amplifier.

As described above, the present embodiment makes it possible to readily control a base voltage rapidly increasing according to an increased collector current of the transistor for high frequency amplification and improve resistance to breakdown in the high frequency amplifier.

FIG. 8shows the main part of a high frequency amplifier according to (Embodiment 2) of the present invention. Other configurations are similar to those of (Embodiment 1).

InFIG. 8, a resistor70is used as a sensor element. Operation principles will be discussed below.

An amplified corrector current is outputted in response to a high frequency signal inputted from the base of a transistor1. An emitter current having an almost equal high frequency amplitude is generated across the resistor70. When the direct-current components of the emitter current increase according to an increase in output power, the voltage generated across the resistor70also increases. A diode5is biased by a constant current source4and a constant voltage is generated across the diode5. Thus, the anode electric potential of the diode5is the sum of the voltage across the diode5and the voltage across the resistor70. That is, as shown inFIG. 9, the anode electric potential of the diode5increases with the output power of the transistor1. When a resistance value is large and the diode has nonlinearity due to high frequency amplification discussed in (Embodiment 1), the anode electric potential decreases at high power. However, the amplifier cannot have high power due to a resistance loss on the emitter.

According to the present embodiment, it is possible to achieve a high frequency amplifier which controls the bias current of a high frequency transistor in the high frequency amplifier according to an output power, for example, a high frequency amplifier having a continuous bias current control function, by which the bias current of the transistor is reduced to have smaller current consumption at low output power and the bias current of the transistor is increased to have higher output at high output power.

The constant current source is used as the bias of the diode in the present embodiment. Also a constant voltage source can enable similar operations by substituting voltage for current. Needless to say, the same effect can be obtained even when the power supply is not ideal as shown inFIG. 5Aor5B of (Embodiment 1).

FIG. 10shows the main part of a high frequency amplifier according to (Embodiment 3) of the present invention. Other configurations are similar to those of (Embodiment 1).

InFIG. 10, a series circuit of a resistor70and an inductance20is used as a sensor element. Operation principles will be discussed below.

An amplified corrector current is outputted in response to a high frequency input signal inputted from the base of a transistor1. An emitter current having an almost equal high frequency amplitude is generated across the series circuit of the resistor70and the inductance20. When the high frequency amplitude and direct-current components of the emitter current increase according to an increase in output power, as discussed in (Embodiment 1) and (Embodiment 2), the anode electric potential of the diode5at low output power increases with output due to the effect of the resistor70, whereas the anode electric potential at high power decreases with increase in output due to the capacitance of the anode to the ground and the nonlinear effect of the diode.FIG. 11shows the characteristic.

According to the present embodiment, it is possible to achieve a high frequency amplifier which controls the bias current of a high frequency transistor in the high frequency amplifier according to an output power as discussed in (Embodiment 2). For example, it is possible to achieve high resistance to breakdown at high power as discussed in (Embodiment 1), in a high frequency amplifier having a continuous bias current control function by which the bias current of the transistor is reduced to have smaller current consumption at low output power and the bias current of the transistor is increased to have higher output at high output power.

The constant current source is used as the bias of the diode in the present embodiment. Also a constant voltage source can enable similar operations by substituting voltage for current. Needless to say, the same effect can be obtained even when the power supply is not ideal as shown inFIG. 5Aor5B of (Embodiment 1).

FIG. 12shows a high frequency amplifier of (Embodiment 4).FIG. 13shows them a in part thereof. Constituent elements with the same actions as (Embodiment 1) will be indicated by the same reference numerals.

The bases of transistors1and67for high frequency amplification are connected to each other and the collectors thereof are also connected to each other. The emitter of the transistor1is grounded, and the emitter of the transistor67and the cathode of a diode5having been biased in the forward direction by a constant current source4are grounded via an inductance20.

The characteristic of a high frequency amplifier is degraded by excessive resistance or inductance between the ground and the emitter or source of a high frequency transistor used for the high frequency amplifier. The present embodiment has an advantage that the transistor1for main amplification has a large emitter area and the transistor67for sub amplification and output power detection has a small emitter area, so that output power can be detected without degrading the characteristic of the high frequency amplifier. The same effect can be obtained by using a resistor or a series circuit of a resistor and an inductance instead of the inductance of the present embodiment.

A constant current source4is used as the bias of the diode5in the present embodiment. Also a constant voltage source can enable similar operations by substituting voltage for current. Needless to say, the same effect can be obtained even when the power supply is not ideal as shown inFIG. 5Aor5B of (Embodiment 1).

FIG. 12shows an actual circuit using the configuration ofFIG. 13. A series circuit of a resistor70and the inductance20is used as a sensor element. As described above, the transistor1for main amplification has a large emitter area and the transistor67for sub amplification and output power detection has a small emitter area. The emitter of the transistor1is grounded, and the emitter of the transistor67and the cathode of the diode5having been biased in the forward direction by the constant current source4are grounded via the series circuit of the resistor70and the inductance20.

A high frequency input signal is inputted from a high frequency power input terminal17to the bases of the transistors1and67, is outputted from the connected collectors, and is outputted from a high frequency power output terminal18. An input matching circuit9and an output matching circuit11are similar to those of the conventional example.

A bias is supplied by a voltage source13to the collector of the bipolar transistor1for high frequency amplification through a collector power supply circuit12such as a λ/4 wavelength line.

The base voltage of a bipolar transistor2for bias supply is supplied by the diode5for generating the reference voltage. The transistor2supplies the base bias to the two transistors1and67by means of an emitter follower and the diode5has been biased by the constant current source4. The bias current of the two transistors1and67is adjusted by the constant current source4. A resistor8suppresses excessive base current of the transistor1. The resistor8may be omitted in the present embodiment.

Reference numeral14denotes a voltage source for supplying a collector bias to the bipolar transistor2for bias supply. Reference numeral17denotes the high frequency power input terminal and reference numeral18denotes the high frequency power output terminal. The emitter of the transistor67and the cathode of the diode5for generating the reference voltage are grounded via the series circuit of the resistor70and the inductance20. Thus, as discussed in (Embodiment 3), the anode electric potential of the diode5increases with the output power of the transistor1and the electric potential decreases at high power. The anode electric potential of the diode5determines the base electric potential of the bipolar transistor2for bias supply. Thus, it is possible to achieve high resistance to breakdown at high power as (Embodiment 1) in a high frequency amplifier having a continuous bias current control function discussed in (Embodiment 2), in which the bias current of the transistor is reduced to have smaller current consumption at low output power, and the bias current of the transistor is increased to have higher output at high output power. In addition, the output power of the high frequency amplifier is detected by the transistor67having a small emitter size and the characteristic of the high frequency amplifier is determined by the transistor1, so that a preferred high frequency characteristic can be obtained without being affected by the inductance or the resistor.

FIG. 14shows the operation principles of (Embodiment 5) of the present invention. Other configurations are similar to those of the foregoing embodiments.

An amplified collector current is outputted in response to a high frequency input signal inputted from the base of a bipolar transistor1for high frequency amplification. The emitter of the transistor1and the cathode of a diode5having been biased in the forward direction by a constant current source4are connected to each other and are grounded via an inductance20. The anode of the diode5is grounded via a capacitor68.

In (Embodiment 5), a parasitic component generated by the structure of the diode is used for a capacitance between the ground and the anode of the diode5.FIG. 15shows the time waveform of an anode electric potential and changes of a direct-current component when the diode is changed in capacitance to the ground. InFIG. 15, the capacitor for grounding the anode has values of 0.1 pf (anode DC electric potential of 1.0 V at 5 dB gain compression), 1 pf (anode DC electric potential of 0.44 V at 5 dB gain compression), and 5 pf (anode DC electric potential of 0.30 V at 5 dB gain compression). The high frequency amplitude of the anode electric potential decreases with increase in the value of the capacitor for grounding the anode, thereby reducing the anode electric potential more effectively than (Embodiment 1). Another advantage is that the anode electric potential corresponding to the output power can be obtained by the direct-current component. The same effect can be obtained by using a resistor or a series circuit of a resistor and an inductance instead of the inductance of the present embodiment.

The constant current source is used as the bias of the diode5in the present embodiment. Also a constant voltage source can enable similar operations by substituting voltage for current. Needless to say, the same effect can be obtained even when the power supply is not ideal as shown inFIG. 5Aor5B of (Embodiment 1).

FIG. 16shows a high frequency amplifier according to (Embodiment 6) of the present invention. Constituent elements with the same actions as (Embodiment 1) will be indicated by the same reference numerals.

A high frequency input signal is inputted from a high frequency power input terminal17to the base of a bipolar transistor1for high frequency amplification, is outputted from the collector thereof, and is outputted from a high frequency power output terminal18. An input matching circuit9and an output matching circuit11are similar to those of the conventional example.

The emitter of the transistor1and the cathode of a diode5for generating the reference voltage are grounded via an inductance20.

A subtraction is performed by an operational amplifier3on the anode electric potential of the diode5and the anode electric potential of a second diode69which has been biased in the forward direction by a second constant current source71. The cathode of the second diode69is grounded. The bias state of the bipolar transistor for high frequency amplification is controlled through a resistor7and a collector power supply circuit12such as a λ/4 wavelength line according to the output power level by a control power supply circuit66, which outputs a desired voltage while using the output of the operational amplifier3as a control signal.

As described in (Embodiment 1), the anode electric potential of the diode5decreases with increase in the output power of the bipolar transistor1for high frequency amplification. By calculating a difference from the second diode69by means of the operational amplifier3, it is possible to generate a control signal set at 0 in the absence of output power at positive and negative polarities.

The same effect can be obtained by using a resistor or a series circuit of a resistor and an inductance instead of the inductance20of the present embodiment.

The constant current source is used as the bias of the diode in the present embodiment. Also a constant voltage source can enable similar operations by substituting voltage for current. Needless to say, the same effect can be obtained even when the power supply is not ideal as shown inFIG. 5Aor5B of (Embodiment 1).

(Embodiment 6) can be readily applied to other embodiments.

FIG. 17shows a high frequency amplifier of a two-stage configuration according to (Embodiment 7) of the present invention. A high frequency input signal is inputted from a high frequency power input terminal17to the base of a transistor67via an input matching circuit9. An amplified signal is inputted to the base of the transistor1via an interstage matching circuit10and is outputted from a high frequency power output terminal18via an output matching circuit11.

A bias is supplied by voltage sources13and15respectively to the collector of the transistor1and the collector of the transistor67through a collector power supply circuit12such as a λ/4 wavelength line.

As shown inFIG. 18, a base bias supply circuit19for the transistors1and67is constituted of a bipolar transistor2for bias supply that supplies base bias by means of an emitter follower, a constant current source4, a diode5for generating the reference voltage, an operational amplifier circuit3, and a voltage source14.

Resistors7and8suppress excessive base current of the transistors1and67. The resistors7and8may be omitted in the present embodiment.

The emitter of the transistor67for the first-stage amplification and the cathode of the diode5for generating the reference voltage in the bias circuit ofFIG. 18are grounded via an inductance20. The bias circuit supplies a bias to the base of the transistor67. As discussed in (Embodiment 1), the base electric potential of the transistor67decreases with increase in the output power of the second bipolar transistor67for high frequency amplification, thereby preventing a breakdown at excessive power.

In the present embodiment, the operations of the transistor67in the first stage are limited to prevent a breakdown of the transistor1for outputting high power in the last stage.

Further, by performing bias control on the relationship between input power and output power of the transistor in the first stage, the present embodiment is applicable to a linear amplifier capable of correcting amplitude distortion of the transistor in the last stage.

FIG. 19shows a high frequency amplifier according to (Embodiment 8) of the present invention.

The high frequency amplifier has a two-stage configuration of bipolar transistors67and1for high frequency amplification. A high frequency input signal is inputted from a high frequency power input terminal17to the base of the transistor67via an input matching circuit9. An amplified signal is inputted to the base of the transistor1via an interstage matching circuit10and is outputted from a high frequency power output terminal18via an output matching circuit11.

Bias supply to the collector of the transistor1and the collector of the transistor67and a base bias supply circuit for the transistors1and67are similar to those ofFIG. 17of (Embodiment 7). Resistors7and8suppress excessive base current of the transistors1and67. The resistors7and8may be omitted in the present embodiment.

The emitter of the transistor1for the last-stage amplification and the cathode of the diode5for generating the reference voltage in the bias circuit ofFIG. 18are grounded via an inductance20. The bias circuit supplies a bias to the base of the transistor67in the first stage. As discussed in (Embodiment 1), the base voltage of the transistor67decreases with increase in the output power of the transistor1, thereby preventing a breakdown at excessive power. In the present embodiment, the output power of the transistor1in the last stage is detected and the operations of the transistor67in the first stage are limited to prevent a breakdown of the transistor1for outputting high power in the last stage.

Further, by performing bias control on the relationship between input power and output power of the transistor in the first stage, the present embodiment is also applicable to a linear amplifier capable of correcting amplitude distortion of the transistor in the last stage.

The foregoing embodiments discussed examples where the transistors for high frequency amplification are bipolar. The same effect can be obtained by using a field-effect transistor. In the case of the field-effect transistor for high frequency amplification, an input circuit is formed between the gate and source of the transistor, an output circuit is formed between the drain and source of the transistor, and the sensor element is interposed between the ground and the source.

In the foregoing embodiments, the diode5is used as a nonlinear element. To be specific, the diode5is constituted of a series connection of two or more diodes or a junction diode between the base and emitter of a bipolar transistor. The same effect can be obtained by using other nonlinear elements instead of the diode.

The high frequency amplifier of the present invention can quickly reduce the bias voltage of an input circuit when overcurrent flows through a transistor for high frequency amplification. Thus, it is possible to prevent a breakdown caused by overcurrent of the transistor for high frequency amplification without degrading the high frequency characteristic of the amplifier. Hence, the present invention is useful for radio communication of a mobile telephone or the like.