JP2001267845A - Voltage controlled oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage controlled oscillator suited to a monolithic integrated circuit and having a wide frequency variation range independently of a temperature change. SOLUTION: A positive feedback circuit is formed between the base and emitter of a transistor(TR) (10), at least one of controllable power supplies (14, 16) for applying potential to the base or emitter of the TR (10) is provided, a power supply (15) for supplying potential to the collector of the TR (10) is provided, and a resistor (8) is connected between the base of the TR (10) and a power supply terminal for controlling base potential. The emitter of the TR (10) is connected to a power supply terminal for applying potential to the emitter by using at least one of an inductor and a transmission line, an output terminal (1) for obtaining an oscillation output from the TR (10) is formed and a capacitor (30) is connected between the base and collector of the TR (10).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a local oscillator and a frequency synthesizer used for a radio device in a microwave to millimeter wave band. As an application example, ETC ( E
lectircal T oll C ollecting), wireless LAN, FWA (F ix
ed W ireless A ccess) Wireless terminal / device or the like for the oscillator is an essential high-frequency circuit.

[0002]

2. Description of the Related Art A local oscillator is one of the essential element circuits in a microwave / millimeter-wave radio device, and is monolithic for the purpose of miniaturization, economy and high functionality of the radio device.
Research on ICs (monolithic microwave / millimeter-wave integrated circuits: MMICs) is under way. Phase locked loop (PLL)
Since the local oscillator uses a crystal oscillator output as a reference signal, it has features such as high frequency stability and the ability to reduce phase noise near the carrier, and has been widely used as an effective configuration method of local oscillators. . The PLL local oscillator basically consists of a voltage-controlled oscillator, a frequency divider and a phase comparator.The voltage-controlled oscillator affects the characteristics of the PLL local oscillator, so it has high frequency stability, high output level, wide frequency range and Low phase noise characteristics are desired. In particular, in recent years, various frequency bands, flexibly corresponding software radio by changing software against modulation scheme and data format (e.g., Digital cellular PDC (P ersonal D igital C ellular in Japan in Phone), in Europe GSM (G lobal S ystem for M obile communication
s), switching IS-95 in the US with software 1
Research is being promoted)
An oscillator having a wide frequency variable range that can support various frequency bands is indispensable.

FIG. 4 shows a first conventional voltage controlled oscillator. 110 is a FET oscillation device (F ield E ffect T ransistor) , terminal 151 of the varactor diode 150 of the voltage-controlled variable capacitance element through the inductor 120 with the gate terminal 111 of the FET110 is grounded through the inductor 121 Connected to. Terminal 152 of varactor diode 150
Is connected to the control voltage input terminal 114 through the resistor 140 and is grounded through the capacitor 130. The source terminal 113 is connected to an inductor 122 and a capacitor 131. The inductor 122 is directly grounded via a resistor 141, and the drain terminal 112 is connected to the inductor
3 and connected to the drain voltage supply terminal 115, and the output terminal through the inductor 124 and the output capacitance element 133.
Connected to 100. The terminal 115 is connected to the capacitor 132
Through the ground, and the inductors 123 and 124 and the capacitors 132 and 133 form an output matching circuit. The above terminal
When a drain voltage is applied to 115, the gate of the FET 110 exhibits a capacitive negative impedance, so that the gate terminal
By connecting a variable inductance to 111, a voltage controlled oscillator is configured. In the prior art, the variable inductance is the varactor diode 150 and the inductor 1
20 has been realized. Further, the varactor diode 120 connects the drain and the source of the FET, and controls the sum of the gate-source capacitance C _gs and the gate-drain capacitance C _gd with respect to the control voltage, thereby forming a voltage-controlled variable capacitance element. Therefore, it is possible to form an integrated circuit on a semiconductor substrate and realize an economical circuit with good reproducibility.

[0004] However, in the first conventional voltage controlled oscillator, a varactor is used to obtain a variable reactance. However, when the varactor is realized by a monolithic microwave integrated circuit (MMIC) integrated on a semiconductor substrate, a gate and a varactor are required. Source-to-source capacity
Since C _gs can be changed only about 1: 2, it is difficult to further expand the frequency tuning range.

FIG. 5 shows a second conventional voltage controlled oscillator which solves the above-mentioned problem disclosed in US Pat. No. 5,973,575. In the figure, reference numeral 210 denotes a transistor which is an oscillation element, and a base terminal 211 of the transistor 210 is connected to a base voltage control terminal 214 serving as a first control terminal via a resistor 208, and via a transmission line 202. Capacitor 203
And grounded. The emitter terminal 213 is connected to the transmission line 204 and the capacitor 205,
205 is grounded, the line 204 is grounded via a capacitor 207, and connected to an emitter voltage control terminal 216 serving as a second control terminal via an inductor 206.
Here, a positive feedback circuit is formed between the base and the emitter as viewed from the transistor 210. The collector terminal 212 of the transistor 210 is connected to a transmission line 220, and the transmission line 220 is connected to an output terminal via a capacitor 223.
It is connected to a capacitor 200 via a transmission line 221 and is grounded. Here, the collector voltage supply terminal 215 is connected to a connection point between the transmission line 221 and the capacitor 222. Collector voltage supply terminal 21
When a collector voltage is applied to 5, the base of the transistor 210 presents a capacitive negative impedance. Therefore, an oscillator is configured by connecting the transmission line 202 to the base terminal 211. Here, the base terminal 2 of the transistor 210
The input impedance looking at the output load side from 11 is described in the literature (K.
Kamogawa, K. Nishikawa, C. Yamaguchi, M. Hirano, I.
Toyoda, and T. Tokumitsu, “Wide-Tuning Range Si B
ipolar VCO's Based on Three-Dimensional MMIC Techn
ology, ”IEEE Transactions on Microwave Theory and
Techniques, vol.45, no.12, pp.2436-2443, December
From 1997), it is expressed by the following equation.

[0006]

(Equation 1)

Note that g _be is the conductance between the base and the emitter (the reciprocal of the resistance R _be between the base and the emitter), C _{bc is the} capacitance between the base and the collector, R _{b is the} base resistance, and g _m is the mutual conductance. Yes, Z _L (= R _L + jX _L ) is the load impedance connected to the collector. From the above formula, transistor 21
0 base when emitter resistor R _BE is changed, the base is negative impedance of the variable capacitive, than this oscillation frequency is changed, the voltage controlled oscillator is constituted. Between the base and emitter of the transistor 210 resistance _R be Habe over the pin w 21
It can be controlled by a base current depending on the voltage between 1 and the emitter terminal 213. As a method of controlling the base current, there are a method of controlling the voltages supplied from the base voltage control terminal 214 and the emitter voltage control terminal 216 simultaneously, and a method of fixing one of them and controlling the other.

As described above, in the second conventional voltage controlled oscillator, since the capacitive reactance can be changed at a large ratio by controlling the base current with the control voltage, the voltage controlled oscillator is very different from the one using a varactor. Wide frequency tuning is possible. Further, since the voltage-controlled oscillator is constituted by one transistor, the structure is simple and economical, and when monolithic, the yield can be improved more than twice as much as the conventional one. In addition, the phase noise of the voltage controlled oscillator is 1 / f noise of the oscillation element, and the oscillation element and the variable reactance element
Is caused by up-conversion near the oscillation frequency due to the mixing effect due to the nonlinearity of
This circuit realizes a variable inductance by the varistor characteristic in the transistor of the oscillation element, and can remove a non-linear factor other than the oscillation element as compared with the conventional circuit, so that an oscillator with low phase noise can be realized. In general, the oscillation frequency changes sharply because the base current of a transistor increases exponentially with respect to the base-emitter voltage, but the insertion of the resistor 208 causes a voltage drop due to the current flowing through the resistor 208. It is possible to gradually change the voltage applied to the base terminal by utilizing the above, so that a voltage-controlled oscillator having excellent controllability can be realized.

However, since the base-collector capacitance of the transistor changes with respect to the external temperature, in the conventional voltage controlled oscillator, the instability of the oscillation frequency with respect to the temperature change has been a problem.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to realize a voltage controlled oscillator suitable for a monolithic integrated circuit and having a wide frequency variable range regardless of a temperature change.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, a feature of the present invention is to form a positive feedback circuit between a base and an emitter of a transistor, and to control the potential of the base or the emitter of the transistor. A power supply for supplying a potential to the collector of the transistor; a resistor connected between a base of the transistor and a power supply terminal for controlling a base potential; a potential connected to the emitter and the emitter of the transistor; Are connected using at least one of an inductor and a transmission line, an output terminal for taking out an oscillation output of the transistor is provided, and a voltage at which a capacitor is connected between a base and a collector of the transistor is provided. In the controlled oscillator.

In the embodiment shown in FIG. 1, a capacitor is inserted between the base terminal and the collector terminal in parallel with the base-collector capacitance of the transistor. Seems to be connected between collectors. Therefore, when the capacitor connected between the base terminal and the collector terminal is sufficiently larger than the capacitance between the base and the collector of the transistor, the change in the capacitance between the base and the collector due to the temperature change can be ignored. As a result, a voltage controlled oscillator having high frequency stability with respect to temperature can be realized.

In the embodiment shown in FIG. 2, since the load on the output side is directly connected to the emitter terminal via a capacitor, the load on the output side can act as a load for generating negative resistance. As a result, the oscillation condition can be determined in consideration of the load on the output side in advance, so that the impedance matching circuit on the output side becomes unnecessary. That is, FIG.
In the embodiment, in addition to the effects of the embodiment of FIG. 1, the impedance matching circuit can be eliminated to greatly reduce the size of the circuit and improve the reflection characteristics on the output side.

Further, in the third embodiment, the emitter of the transistor is short-circuited by the inductor or the transmission line,
Since the potential of the emitter can always be set to 0 V, the emitter voltage control terminal can be omitted, and the circuit configuration can be simplified.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] FIG. 1 shows a first embodiment of a voltage controlled oscillator according to the present invention.

In FIG. 1, reference numeral 10 denotes a transistor which is an oscillation element, and a base terminal 11 of the transistor 10 has a resistor 8
Is connected to the base voltage control terminal 14 serving as a first control terminal via the transmission line 2 and to the capacitor 3 via the transmission line 2 and is grounded. Further, the emitter terminal 13 is connected to the transmission line 4 and the capacitor 5, the capacitor 5 is grounded, and the line 4 is grounded via the capacitor 7, and becomes the second control terminal via the inductor 6. Connected to voltage control terminal 16. Here, a positive feedback circuit is formed between the base and the emitter as viewed from the transistor 10. The collector terminal 12 of the transistor 10 is connected to a transmission line 20, and the transmission line 20 is connected to the output terminal 1 via a capacitor 23.
It is connected to a capacitor 22 via a transmission line 21 and is grounded. Here, the collector voltage supply terminal 15 is connected to the transmission line
It is connected to the connection point of 21 and capacitor 22. The base terminal 11 and the collector terminal 12 of the transistor 10 are connected via a capacitor 30. When a collector voltage is applied to the collector voltage supply terminal 15, the base of the transistor 10 exhibits a capacitive negative impedance, so that the transmission line 2 is connected to the base terminal 11 to form an oscillator. Also, the base voltage control terminal 14
And the base current flowing through the transistor 10 can be controlled by the voltage supplied from the emitter voltage control terminal 16. Functions as a varistor which depends on the base-emitter resistance R _{b e} Habe over scan current of the transistor 10, to operate equivalently as a variable capacitance in a positive feedback circuit, the base becomes negative impedance of the variable capacitive, Thus, the oscillation frequency changes, and a voltage controlled oscillator is formed. As a method of controlling the base current, there are a method of controlling the voltage supplied from the base voltage control terminal 14 and the voltage supplied from the emitter voltage control terminal 16 simultaneously, and a method of fixing one of them and controlling the other.

As described above, in the first embodiment of the present invention,
In parallel with the base-collector capacitance C _bc in a transistor and the capacitor 30 is inserted between the base and collector terminals, is equivalently connected between the capacitance of the sum of both C _BC Gabe over scan collector It will be like. Therefore, the input impedance when the output load side is viewed from the base terminal 11 of the transistor 10 is expressed as follows.

[0019]

(Equation 2)

Here, C _BC = C _bc + C _c (C _c : capacitor 30
Capacity value). The capacitance value of the capacitor 30 is sufficiently larger than the to database collector capacity C _bc transistor, the capacitance C _bc between the base and the collector with the temperature change be varied, the capacitance C _BC scarcely changes , Equation (2)
Does not change. Therefore, the first aspect of the present invention
In this embodiment, it is possible to suppress the fluctuation of the oscillation frequency due to the temperature change, and it is possible to realize a voltage control oscillator having high stability. Also, transistor 10
Since the base-emitter resistance is not affected by the capacitor 30, a very wide frequency tuning range can be realized similarly to the second conventional voltage controlled oscillator. Further, since the voltage-controlled oscillator is constituted by one transistor, the structure is simple and economical. Also, the phase noise of the voltage controlled oscillator is generated by the up-conversion of the 1 / f noise of the oscillation element to the vicinity of the oscillation frequency due to the mixing effect due to the nonlinearity of the oscillation element or the variable reactance element (conventionally, a varactor diode, etc.) However, in the first embodiment of the present invention, since no transistor is used other than the oscillation element, a voltage controlled oscillator having better phase noise characteristics than the conventional one can be realized. further,
When a bipolar transistor having excellent 1 / f noise characteristics is used, the phase noise can be further reduced. In general, the oscillation frequency changes sharply because the base current of the transistor increases exponentially with respect to the base-emitter voltage. However, when the resistor 8 is inserted, the voltage drop due to the current flowing through the resistor 8 is reduced. It is possible to gradually change the voltage applied to the base terminal by utilizing the above, so that a voltage-controlled oscillator having excellent controllability can be realized. In the first embodiment of the present invention, the same effect can be obtained by using a transmission line instead of the inductor 6. The same applies to the case where an inductor is used instead of the transmission line 2 and the transmission line 4.

[Second Embodiment] FIG. 2 shows a second embodiment of the voltage-controlled oscillator according to the present invention. 2, the same components as those in FIG. 1 are denoted by the same reference numerals.

In FIG. 2, reference numeral 10 denotes a transistor which is an oscillation element, and a base terminal 11 of the transistor 10 has a resistor 8
Is connected to the base voltage control terminal 14 serving as a first control terminal via the transmission line 2 and to the capacitor 3 via the transmission line 2 and is grounded. Further, the emitter terminal 13 is connected to the transmission line 4 and the capacitor 5, the capacitor 5 is grounded, and the line 4 is grounded via the capacitor 7, and becomes the second control terminal via the inductor 6. Connected to voltage control terminal 16. Further, the emitter terminal 13 is connected to the output terminal 1 through the capacitor 9. Here, a positive feedback circuit is formed between the base and the emitter as viewed from the transistor 10. Further, the collector terminal 12 of the transistor 10 is connected to a collector voltage supply terminal 15 via an inductor 24, and is also connected to a capacitor 25, which is grounded. Also, the base terminal 11 and the collector terminal of the transistor 10
12 are connected via a capacitor 30. When a collector voltage is applied to the collector voltage supply terminal 15,
Since the base of the transistor 10 exhibits a capacitive negative impedance, an oscillator is configured by connecting the transmission line 2 to the base terminal 11. Further, the base current flowing through the transistor 10 can be controlled by the voltages supplied from the base voltage control terminal 14 and the emitter voltage control terminal 16.
Functions as a varistor which depends on the base-emitter resistance R _BE Habe over scan current of the transistor 10, to operate equivalently as a variable capacitance in a positive feedback circuit, the base becomes negative impedance of the variable capacitive, this The oscillation frequency further changes, and a voltage controlled oscillator is formed. As a method of controlling the base current, there are a method of controlling the voltage supplied from the base voltage control terminal 14 and the voltage supplied from the emitter voltage control terminal 16 simultaneously, and a method of fixing one of them and controlling the other.

According to the above-described second embodiment, the same effects as in the first embodiment of the present invention can be obtained. Further, since the load of the output terminal 1 (for example, 50 [Ω]) is directly connected to the emitter terminal 13 via the capacitor 9, the load of the output terminal 1 is designed as a load for generating a negative resistance. Can be incorporated into Therefore, since the oscillation condition can be determined in consideration of the load on the output side in advance, the reflection coefficient from the load on the output terminal 1 can be improved, and the impedance matching circuit on the output side becomes unnecessary. Further, since the impedance matching circuit can be omitted, the circuit can be significantly reduced in size. The same effect is obtained even when a lossless circuit including an inductor, a transmission line, a capacitor, and the like is inserted between the emitter terminal 13 and the capacitor 9.

Third Embodiment FIG. 3 shows a third embodiment of the voltage controlled oscillator according to the present invention. 3, the same components as those in FIG. 1 are denoted by the same reference numerals.

In FIG. 3, reference numeral 10 denotes a transistor which is an oscillation element, and a base terminal 11 of the transistor 10 has a resistor 8
Is connected to a base voltage control terminal 14 serving as a first control terminal, and is connected to a capacitor 3 via a transmission line 2, and the capacitor 3 is grounded. The emitter terminal 13 is connected to the transmission line 4 and the capacitor 5. The transmission line 4 and the capacitor 5 are both grounded, and a positive feedback circuit is formed between the base and the emitter as viewed from the transistor 10. Further, the collector terminal 12 of the transistor 10 is connected to the transmission line 20, and the transmission line 20 is connected to the output terminal 1 via the capacitor 23, and is connected to the capacitor 22 via the transmission line 21, and is grounded. ing. Here, the collector voltage supply terminal 15 is connected to the transmission line 21.
And the connection point of the capacitor 22. The base terminal 11 and the collector terminal 12 of the transistor 10 are connected via a capacitor 30. When a collector voltage is applied to the collector voltage supply terminal 15, the base of the transistor 10 exhibits a capacitive negative impedance, so that the transmission line 2 is connected to the base terminal 11 to form an oscillator. Also, the base voltage control terminal 14
The base current flowing through the transistor 10 can be controlled by the voltage supplied from the transistor. Functions as a varistor which depends on the base-emitter resistance R _BE Habe over scan current of the transistor 10, to operate equivalently as a variable capacitance in a positive feedback circuit, the base becomes negative impedance of the variable capacitive, this The oscillation frequency further changes, and a voltage controlled oscillator is formed.

According to the third embodiment, the same effects as those of the first embodiment of the present invention can be obtained,
The ten emitters are short-circuited in a DC manner by the transmission line 4 and the potential of the emitter can be uniquely set to 0 V, so that the emitter voltage control terminal can be omitted. Therefore, a voltage controlled oscillator having a simple circuit configuration can be realized.

[0027]

As described above, according to the present invention, there is provided a voltage controlled oscillator that operates stably irrespective of a change in the base-collector capacitance of a transistor due to an external temperature.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a voltage controlled oscillator according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a voltage controlled oscillator according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram of a voltage controlled oscillator according to a third embodiment of the present invention.

FIG. 4 is a circuit diagram of a first conventional voltage controlled oscillator.

FIG. 5 is a circuit diagram of a second conventional voltage controlled oscillator.

[Explanation of symbols]

 1 Output terminal 2, 4, 20, 21 Transmission line 3, 5, 7, 9, 23, 25, 30 Capacitor 6, 24 Inductor 8 Resistance 10 Transistor 11 Base terminal 12 Collector terminal 13 Emitter terminal 14 Base voltage control terminal 15 Collector Voltage control terminal 16 Emitter voltage control terminal 100 Output terminal 110 FET 111 Gate terminal 112 Drain terminal 113 Source terminal 114 Control voltage input terminal 115 Drain voltage supply terminal 120, 121, 122, 123, 124 Inductor 130, 131, 132, 133 Capacitor 140, 141, 208 Resistance 150 Varactor diode 151, 152 Terminal 200 Output terminal 202, 204, 220, 221 Transmission line 203, 205, 207, 209, 223, 225, 230 Capacitor 206, 224 Inductor 210 Transistor 211 Base terminal 212 Collector Terminal 213 Emitter terminal 214 Base voltage control terminal 215 Collector voltage control terminal 216 Collector voltage control terminal

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masao Nakagawa 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo F-term in Nippon Telegraph and Telephone Corporation (reference) 5J081 AA02 AA11 BB01 BB06 BB10 CC07 CC17 CC30 DD03 DD24 DD29 EE02 EE03 EE09 GG02 KK02 KK08 KK22 LL02 MM02

Claims (4)

[Claims] 1. A power supply for forming a positive feedback circuit between a base and an emitter of a transistor, comprising at least one controllable power supply for applying a potential to the base or the emitter of the transistor, and supplying a potential to a collector of the transistor. A resistor is connected between a base of the transistor and a power supply terminal for controlling a base potential, and at least one of an inductor and a transmission line is used between an emitter of the transistor and a power supply terminal for applying a potential to the emitter. A voltage controlled oscillator having an output terminal for taking out an oscillation output of the transistor, wherein a capacitor is connected between a base and a collector of the transistor. 2. The voltage controlled oscillator according to claim 1, wherein an emitter of said transistor is grounded via at least one of an inductor and a transmission line. 3. The voltage controlled oscillator according to claim 1, wherein the output terminal is connected to a collector of the transistor via an impedance matching circuit. 4. The voltage controlled oscillator according to claim 1, wherein said output terminal is connected to an emitter of said transistor via a capacitor.