Patent Application
20050179484
1. Field of the Invention
The present invention relates to a radio-frequency amplification circuit used for, for example, a transmitter and receiver of radio communication, and a bias voltage supply circuit used for it.
2. Description of the Related Art
About a radio-frequency amplifier used for, for example, satellite communication, ground based microwave communication, mobile communication and so on, in the case that a radio-frequency amplification transistor is composed of an NPN bipolar transistor, a radio-frequency signal is applied to its base (input terminal), and a radio-frequency signal after amplification is outputted from its collector. On this occasion, for realizing high efficiency for a wide range radio-frequency signal level, it is necessary to control a direct current bias voltage supplied to a base of a radio-frequency amplification transistor depending on an input signal level, for that purpose, a bias voltage supply circuit is connected to the base of the radio-frequency amplification transistor.
About such a bias voltage supply circuit, a method of controlling base current of the radio-frequency amplification transistor and deciding electric potential of the input terminal by setting a first NPN bipolar transistor composing a current mirror circuit with a radio-frequency amplification transistor and supplying a constant current to the first NPN bipolar transistor is general.
However, in this method, in the case that input electric power of a radio-frequency signal increases, when base electric potential of the first NPN bipolar transistor composing the current mirror circuit with the radio-frequency amplification transistor fluctuates widely, rectification is generated by a PN junction (diode) between the base and the emitter of the transistor. That is, if a direct current level of the inputted radio-frequency signal fluctuates widely, when the electric potential is at a high level, this diode is powered on and direct current electric potential of the input signal descends. By contraries, when the electric potential of the input signal is at a low level, since the diode is inverse-biased, electric potential descent does not arise. Since time-average is taken by this rectification, the electric potential of the input terminal of the radio-frequency signal descends with the increase of a signal amplitude, as a result, the electric power of a signal outputted from the radio-frequency amplifier is saturated and high power output cannot be obtained.
As the measures, generally, it is known a technique curbing the electric potential fluctuation of the input terminal of the radio-frequency signal by connecting a second NPN bipolar transistor for compensation between a base of a first NPN bipolar transistor mentioned later and a power supply voltage supply line, for compensating fluctuation of the base electric potential of a first NPN bipolar transistor composing a current mirror circuit with a radio-frequency amplification transistor (for example, refer to Kokai (unexamined patent publication) No. H11(1999)-68473).
In
In the radio-frequency amplifier 200 shown in
In the bias circuit 100 shown in
Further, in the bias circuit 100 shown in
In the case that the electric power of the radio-frequency signal inputted to the radio-frequency input terminal 201 increases, the base current Ibe of the radio-frequency amplification transistor Q200 increases and the collector current Ice of the radio-frequency amplification transistor Q200 increases. Simultaneously, the collector current of the second NPN bipolar transistor also increases, wherein this transistor compensates the base electric potential of the current mirror circuit composed of the radio-frequency amplification transistor Q200 and the first NPN bipolar transistor Q100. The transistors Q102 and Q103 operate as a current mirror circuit using a collector current of the second NPN bipolar transistor Q101 as a reference current. Therefore, in the case that size ratio of the radio-frequency amplification transistor Q200 and the first NPN bipolar transistor Q100 is defined as N:1, N times current, that is, current mirror ratio times of the reference current as a collector current of the first NPN bipolar transistor Q100 is applied to the collector of the first NPN bipolar transistor Q100. As a result, even if base electric potential of the radio-frequency amplification transistor Q200 descends, the base current Ibe can be increased automatically so as to compensate the base current.
As described in Kokai (unexamined patent publication) No. H11(1999)-68473, in composition of a bias circuit deciding the base current Ibe by a current flowing in the first NPN bipolar transistor Q100 composing the current mirror circuit with the radio-frequency amplification transistor Q200, descent by compensating the amount of descent of the base potential can be prevented and descent of gain produced by it can be prevented.
However, in this composition of related art, it is only achieved that descent of the base potential is prevented and descent of gain is curbed in the high-power side by descent of the base potential, and it can be achieved to improve a saturation characteristic of the radio-frequency amplification circuit further by shifting a point that gain descends to the further high-power side.
An object of the present invention is to provide newly a radio-frequency amplification circuit having a saturation characteristic more superior than a prior art because descent of electric potential of an input terminal of a radio-frequency signal does not occur because of composition of the circuit and effect more than curb effect of descent of electric potential of the input terminal of the radio-frequency signal obtained by the prior art is obtained, and a bias voltage supply circuit using for it.
A bias voltage supply circuit according to the present invention is a bias voltage supply circuit supplying a direct current bias voltage to an input terminal of a radio-frequency amplification transistor amplifying a radio-frequency signal, having a constant-voltage power supply generating a constant voltage higher than the bias voltage, a rectifier transistor connected between a supply point of a bias voltage connected to an input terminal of the radio-frequency amplification transistor via an element for bias supply and a power supply voltage supply line, wherein a control terminal is kept by a constant voltage that the constant-voltage power source generates, and a constant-current power supply connected between the supply point of the bias voltage and a reference voltage supply line to supply a constant current to the rectifier transistor.
In the present invention, it is preferable that a negative feedback transistor controlled by electric potential of the supply point of the bias voltage and applying negative feedback to the rectifier transistor is connected between the control terminal of the rectifier transistor and a reference voltage supply line.
Specifically, the constant-voltage power supply has two transistors connected diode-connected respectively and series-connected between a control terminal of the transistor for rectification and a reference voltage supply line and a reference current power supply supplying reference current path on a direct current connection of two transistors.
In this case, further specifically, the constant-voltage power supply is composed of a transistor connected with the transistor of a reference voltage supply side in the two series-connected transistors via control terminals commonly and connected between the supply point of the bias voltage and a reference voltage supply line.
A radio frequency amplification circuit according to the present invention has a radio-frequency amplification transistor amplifying a radio-frequency signal, and a bias voltage supply circuit connected to an input terminal of the radio-frequency amplification transistor and supplying a direct current bias voltage to the input terminal, and the bias voltage supply circuit has a constant-voltage power supply generating a constant voltage higher than the bias voltage, a rectifier transistor connected between a supply point of a bias voltage connected to an input terminal of the radio-frequency amplification transistor via an element for bias supply and a power supply voltage supply line, wherein a control terminal is kept by a constant voltage that the constant-voltage power source generates, and a constant-current power supply connected between the supply point of the bias voltage and a reference voltage supply line to supply a constant current to the rectifier transistor.
According to a bias current supply circuit having such a composition (and a radio-frequency amplification circuit including it), in the case that electric power of a radio-frequency signal supplied to an input terminal of a radio-frequency amplification transistor increases and its signal amplitude changes widely via an element for bias supply, the change of the signal amplitude changes electric potential of a bias voltage supply point, that is, a terminal of the reference voltage side of a rectifier transistor. A gate of the rectifier transistor is kept by a voltage lager than a bias voltage generated by the constant-voltage power supply and the rectifier transistor is controlled so that a constant current flows by a constant-current power supply. When electric potential of the terminal of the reference voltage side (the bias voltage supply point) becomes higher, an applied voltage between this reference voltage terminal and a control terminal becomes smaller and a state of the rectifier transistor changes so as to turn off. On the contrary, when electric potential of the bias voltage supply point becomes lower, the applied voltage between the reference voltage terminal and the control terminal of the rectifier transistor becomes larger and the state thereof changes so as to turn on. Therefore, when time-average of this high electric power signal is taken at the time of its inputting, a direct current level of bias voltage rises in comparison with the time of inputting small electric power. Further, when the input electric power becomes higher, rise of this bias voltage reaches a certain limit and the bias voltage descends as a reflection of a saturation characteristic of the transistor. That is, in the present invention, an operation that the bias voltage is raised once at the high electric power side is obtained.
According to a bias voltage supply circuit and a radio-frequency amplification circuit using it, as mentioned above, as an operation that a bias voltage is raised once at the high electric power side is obtained, as the result, an effect shifting a point that gain descends to a high electric power side can be obtained. As the result, by the present invention, it can be realized that a radio-frequency amplification circuit having superior linearity and a saturation characteristic that high input electric power can be realized.
These and other objects and features of the present invention will become clearer from the following description of the preferred embodiments given with reference to the accompanying drawings, in which:
Preferred embodiments of the present invention will be described with reference to the accompanying drawings that the case of using a bipolar transistor as a transistor is defined as an example. Note that, in the present invention, it is possible to use a MOS transistor as a transistor, in that case, by displacing an NPN bipolar transistor with a MOS transistor in the drawings below and displacing “base” with “gate”, “emitter” with “supply” and “collector” with “drain”, it is possible to apply the present invention in a similar way.
In use of electric power amplification of radio communication, it is composed of multistage usually, however, in this
A radio-frequency amplification circuit 1A shown in
In such composition, a radio-frequency signal inputted from the input terminal Ti is outputted from the output terminal To after amplifying by the radio-frequency amplification transistor TR1 and impedance-matching.
A bias voltage supply circuit 2A has four NPN bipolar transistors TR2, TR3, TR4 and TR5, two capacitors C1 and C2, a reference electric current supply 5 and an inductor L1.
An example of a “constant-voltage power supply” is composed of the transistors TR2 and TR3 and the reference current power supply 5. Further, the transistor TR4 composes an example of a “rectifier transistor” and the transistor TR5 composes an example of a “constant-current power supply”. Note that, in
The reference current power supply 5, the transistors TR3 and TR2 composing the constant-voltage power supply is series-connected between the electric supply voltage Vdd and a reference voltage Vss. About the transistors TR2 and TR3, a base and a collector are connected respectively, that is, each transistor is diode-connected. A connection point of the base and the collector of the transistor TR3 (hereinafter referred to as a node ND2) is an output of this constant-voltage power supply and the constant-voltage power supply has a function to keep electric potential of this node ND2 constant in response to a current flowing through the reference current power supply 5. Hereinafter, electric potential of the node ND2 is defined as Vb1.
A base of the rectifier transistor TR4 is connected to the node ND2. A collector of the rectifier transistor TR4 is connected to a supply line of an electric supply voltage Vdd2 and its emitter is connected to the node ND1 that is a supply point of the bias voltage Vbb. The capacitor C2 is connected between the base (node ND2) of the rectifier transistor TR4 and the reference voltage Vss, as the result, oscillation of that rectifier transistor is prevented and stabilization of electric potential of the node ND2 is achieved.
The transistor TR5 connected between the node ND1 and the reference voltage Vss has a function as a constant-current power supply for flowing a constant current through the rectifier transistor TR4, about that point, it may be replaced with a constant-current power supply circuit or a resistor having other composition and so on. Here, a base of the transistor TR5 is connected to a diode-connected base of the transistor TR2. Further, the capacitor C1 is connected between the node ND1 and the reference voltage Vss, therefore the node ND1 is AC grounded.
Next, an operation of such a circuit composition will be explained.
In the bias voltage supply circuit 2A according to the present embodiment, a transistor composing a current mirror circuit with a radio-frequency amplification transistor (for example, Q100 in
Diode-connected two transistors TR2 and TR3 generate basic voltage Vb1 for giving the bias voltage Vbb of the base of the radio-frequency amplification transistor TR1 at the node ND2 via the rectifier transistor TR4. That is, when a base bias current of an NPN bipolar transistor level current is flowed by the reference current power supply 5, electric potential Vb1 of the node ND2 becomes about the twice voltage of the bias voltage of the base Vbb when a radio-frequency signal is not inputted to the radio-frequency amplification transistor TR1. This electric potential Vb1 of the node ND2 can be fine-tuned by a current given from the reference current power supply 5.
The rectifier transistor TR4 operates as a so-called common collector type amplifier and the bias voltage Vbb descended by a voltage between the base and the emitter of the rectifier transistor is outputted to the radio-frequency amplification transistor TR1. At this time, the transistor TR5 operates as a constant-current power supply. The transistor TR5 draws a portion of current outputted from the emitter of the rectifier transistor TR4 and flows it to the reference electric potential Vss.
The capacitor C1 is implemented for reducing a radio-frequency signal component that could not be blocked by the inductor L1. However, as mentioned later, if the radio-frequency signal component is removed off, the present invention cannot demonstrate the effect, therefore it is necessary to implement elements having a value suitable as the capacitor C1 and the inductor L1. Note that, in the case that a radio-frequency component suppression ability of the inductor L1 is enough, the capacitor C1 may be omitted. Further, the capacitor C2 for preventing oscillation can be omitted in the case that electric potential Vb1 of the node ND2 is in stable.
In the case that there is no radio-frequency signal inputted from the input terminal Ti or the case that an input voltage of a radio-frequency signal is low and its amplitude is comparatively small, since a current drive ability of the transistor TR5 as a constant-current power supply overcomes electric potential fluctuation of the node ND1 and flows constant current to the rectifier transistor TR4, the bias voltage Vbb emerged at the node ND1 does not change.
When input electric power of a radio-frequency signal increases and its amplitude becomes comparatively large, a radio-frequency signal component attenuated by the inductor L1 and the capacitor C1 changes electric potential of the node ND1. Therefore, electric potential of the emitter of the transistor TR4 and the collector of the transistor TR5 becomes large and small with time. Since the collector of the transistor TR5 has high impedance, that operation is hardly affected by this radio-frequency signal component.
On the contrary, the rectifier transistor TR4 changes its electric potential with the following behavior by a phase state of the radio-frequency signal applied to the emitter.
First, when an emitter voltage of the rectifier transistor TR4 swings positively widely, a voltage between the base and the emitter of the transistor TR4 becomes small, the transistor TR4 becomes an off state and a collector current is temporally interrupted.
Further, when an emitter voltage of the rectifier transistor TR4 swings negatively widely, a voltage between the base and the emitter of the transistor TR4 becomes large, the transistor changes to an on state deeply and a large current is flowed between the collector and the emitter.
Although these two states are repeated by time change of the radio-frequency signal presenting at the node ND1, since a current flowing in the rectifier transistor TR4 becomes exponentially large for its voltage between the base and the emitter, a rectification operation such that current larger than time of no signal as the time average is performed. As the result, a DC level of the bias voltage Vbb supplied to the base of the radio-frequency amplification transistor TR1 increases by growing input electric power and amplitude of the radio-frequency signal component.
Further, when electric power of an inputted radio-frequency signal is enlarged, rise of this bias voltage Vbb reaches a pole by regulated by saturation characteristic of the bipolar transistor and so on, and after that it changes to a decrease.
In
In
On the contrary, as a comparative example, a characteristic in the case of setting a transistor composing a current mirror circuit with a radio-frequency amplification transistor is shown in
In a circuit of the comparative example shown in
The points that a radio-frequency amplification circuit 1B shown in
In the present embodiment, by replacing the inductor L1 with the resistor R1, an advantage of the other point of view that area occupied by the bias supply element can be reduced can be obtained.
A large point that a radio-frequency amplification circuit 1C shown in
When the voltage Vbb of the node ND1 is raised, electric potential of the base terminal of the negative feedback transistor TR6 connected to the node ND1 via the resistor R3 is raised. Then, a current flowing between the collector and the emitter of the negative feedback transistor TR6 increases. At this time, a portion of a current from a reference current power supply that should flow to the two diode-connected transistors TR2 and Tr3 is drawn by the transistor TR6, so the electric potential Vb1 of the node ND1 descends. Therefore, applied voltage between the base and the emitter of the rectifier transistor TR4 descends for that and a point that the bias voltage Vbb is reduced or raised is shifted.
That is, in the circuit composition shown in
Note that, the control of a degree of a rise of such a bias voltage Vbb and its rising point can be performed also by changing each of an element parameter value of the inductor L1 and the capacitor C1 and controlling largeness of a radio-frequency signal component leaked to the node ND1. However, there is a limit by such a change of the element parameters and disadvantages on the cost and so on might be large when changing the element parameters because of the area penalty and the restriction on the process. Particularly, when enlarging the inductor L1, not only the occupied area becomes large, but the characteristic obtained when enlarging the area might become a limit. Further, when enlarging the capacitor C1 the occupied area also becomes large, when adopting a capacitor which occupied area is small there is a disadvantage that the structure becomes complex and the process cost is raised.
In the present embodiment, for example, in the case only control of the element parameters of the inductor L1 and the capacitor C1 is not enough like this, by compensating that with an operation of the negative feedback transistor, the degree of freedom of the control of an electric characteristic for input electric power of the bias voltage Vbb becomes high. As the result, realization of a radio-frequency amplification circuit that obtains a desired characteristic more easily with suppressing a disadvantage on the cost can be realized.
Further, setting the negative feedback transistor TR6 contributes the stabilization of the bias voltage for the fluctuation of the electric supply voltage.
In detail, since the radio-frequency amplification transistor TR1 has very high impedance ideally□when the electric supply voltage Vdd1 fluctuates a base current and a collector current do not change. However, practically, realization of such an ideal transistor is difficult because of restriction of process and size and so on. Therefore, consideration by the fluctuation of the electric supply is required.
When by the fluctuation of the electric supply voltage the base current of the radio-frequency amplification transistor TR1 changes widely, the collector current of the transistor TR4 fluctuates and the voltage between the base and the emitter Vbe also changes. When the electric supply voltage is raised, the base current of the transistor TR1 becomes small, the current between the base and the emitter Ibe of the transistor TR6 becomes small, a state of the transistor TR6 turn to power-off and a current component drawn by the transistor TR6 decreases. Therefore, since the base electric potential Vb1 of the rectifier transistor TR4 is raised, the transistor TR4 becomes a state to turn to power-on more easily, as the result, the bias voltage Vbb becomes large and operates to enlarge the base current of the transistor TR1. On the contrary, when the base current of the transistor TR1 becomes large by the electric power fluctuation, by tracing the above mentioned opposite process, it operates to reduce the base current.
As mentioned above, in the present embodiment, an effect to control a bias voltage fluctuation by an electric supply voltage fluctuation can be obtained.
Next, in the above the first to the third embodiment, the bias voltage Vbb is raised once, however, an effect that it gives to a gain characteristic will be explained.
A quality of a saturation characteristic of electric power is decided whether a linear region is wide and whether a point that saturation begins corresponds to high input electric power. Although there are many methods of judging this quality of the characteristic, for radio-frequency electric power amplifier generally, the quality of electric saturation characteristic is judged by measuring so-called P1 dB (1 dB gain compression power-point). The P1 dB is defined as the input (or output) electric power when the gain descends by 1 dB from the linear region in raising the input electric power.
As shown in
Note that, in a judgment of the quality of electric power saturation, the same result can be obtained by methods other than the above mentioned method comparing the P1 dB.
As mentioned above, it is proved that with a bias electric power supply circuit of the present invention, the P1 dB of a radio-frequency electric power circuit is improved and linearity of an electric power saturation characteristic is improved.
Note that the present invention is not limited to the above embodiments and includes modifications within the scope of the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| P2004-037969 | Feb 2004 | JP | national |
