JPH057112A - Voltage controlled oscillator - Google Patents

Abstract

(57) [Abstract] [Purpose] The present invention relates to a voltage-controlled oscillator used for communication equipment, etc., which compensates for temperature characteristics when a surface acoustic wave resonator is used and has realized low noise and low power consumption.
It is an object of the present invention to provide a voltage controlled oscillator that is low in price, small in size, and has excellent characteristics. [Configuration] A resonance circuit including a frequency expansion coil 2, a surface acoustic wave resonator 3, a variable capacitance diode, etc. is provided as an external circuit of the oscillation active circuit 1, and three temperature compensation capacitors 5, 6, 7 are inserted. Therefore, the temperature characteristic can be compensated. The temperature compensation capacitor 5 also has the effect of increasing the C / N of the oscillator. Furthermore, the active circuit for oscillation 1
By providing the switching circuit 11 in which the bias current can be switched, the optimum bias current according to the frequency with respect to C / N can be made to flow, and low power consumption can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage controlled oscillator mainly used for a frequency synthesizer of a transmitter or a receiver of communication equipment.

[0002]

2. Description of the Related Art In recent years, wireless communication devices have been occupying a narrower band of frequencies and having a larger number of channels from the viewpoint of effective use of frequencies. A voltage controlled oscillator with a variable width is required.

A conventional voltage controlled oscillator will be described below. FIG. 3 shows a conventional voltage controlled oscillator.
(For example, IEICE Transactions vol.2, J65-B (1982) No. 1
Referring to FIG. 3, 1 is an active element circuit part of a Colpitts oscillator circuit, 2 is an inductor for frequency extension, 3 is a surface acoustic wave resonator, 4 is a variable capacitance diode,
Reference numeral 8 is a power supply voltage terminal, 9 is a signal output terminal, and 10 is a frequency control terminal. The operation of the voltage controlled oscillator configured as described above will be described below. In the steady oscillation state, the active element circuit unit 1 can be regarded equivalently as a series circuit of a capacitor and a resistor having a negative value (negative resistance). On the other hand, the surface acoustic wave resonator 3 operates as an inductor, and the series circuit of the surface acoustic wave resonator 3, the frequency extending inductor 2, and the variable capacitance diode 4 also equivalently operates as an inductor. The oscillation frequency is determined by the resonance frequency between the capacitance on the circuit side and the inductance on the resonator side. By controlling the DC voltage applied to the variable capacitance diode 4, the inductance on the resonator side is equivalently changed, and the oscillation frequency can be controlled. Further, since the frequency extension inductor can be regarded as a capacitance having a negative value equivalently, it has a function of equivalently reducing the capacitance value with respect to the control voltage of the variable capacitance diode, and by increasing the frequency extension inductor, The frequency control sensitivity can be improved.

[0004]

However, in the above-mentioned conventional structure, the temperature characteristic of the surface acoustic wave resonator used as the resonator becomes a problem. 36 ° Y-XLi as substrate material
TaO3 is generally used, but when this material is used, the surface acoustic wave resonator has a resonance frequency of -35 ppm / ° C. In addition, since the surface acoustic wave resonator has spurious in the low frequency range of the resonance frequency, if the frequency variable range is wide enough to reach the spurious region, a stable frequency change can be obtained for the control voltage applied to the variable capacitance diode. Absent. For this reason, it cannot be expected that the control sensitivity will be improved by increasing the number of frequency extension inductors. Even if the desired control sensitivity is obtained, it is necessary to increase the control sensitivity by increasing the C of the oscillator.
It becomes a factor that deteriorates / N. For this reason, the voltage controlled oscillator using the surface acoustic wave resonator cannot have a sufficient frequency variable width in consideration of the temperature characteristics. A temperature compensating circuit using a variable capacitance diode or a thermistor, or a digital temperature compensating circuit using a D / A or A / D converter makes the circuit complicated and
It also causes C / N deterioration.

Further, in wireless communication, frequencies are generally different between transmission and reception. The C / N of the oscillator is determined by the bias current of the transistor, the NF of the transistor, the Q value of the resonator, and the like. The minimum transistor bias current required to obtain the desired C / N varies depending on the oscillation frequency. The bias current needs to be set so that C / N can be obtained at a higher frequency, and when the same integrated circuit is used at a low frequency, an extra bias current will flow. Especially transmitted as a monolithic semiconductor integrated circuit,
When it is used for both reception, a means for switching the bias resistance is required to optimally set the bias current.

The present invention solves the above-mentioned problems of the prior art. A simple circuit structure using an inexpensive component called a temperature compensating capacitor as an external component allows a temperature change without degrading C / N. To provide an inexpensive voltage controlled oscillator having a stable frequency variable width, and to switch the bias current built in the semiconductor integrated circuit so that an optimum bias current can flow with respect to C / N over a wider frequency range. The purpose is to reduce the power consumption of the circuit by the switching circuit.

[0007]

To achieve this object, a voltage controlled oscillator according to the present invention employs a Colpitts type oscillating circuit of a collector grounded type, an oscillating transistor, a feedback capacitor, a bias resistor, an emitter follower for output. Is provided inside the semiconductor integrated circuit, a first temperature compensating capacitor is inserted between the base of the oscillation transistor and the ground as an external circuit of the semiconductor integrated circuit, and a resonance loop forms a second temperature from the base of the oscillation transistor. A compensation capacitor, a frequency expansion inductor, a surface acoustic wave resonator, and a cathode of a variable capacitance diode are connected in series, the anode is grounded, and a third temperature compensation capacitor is connected in parallel with the variable capacitance diode. As a configuration that controls the oscillation frequency by applying a voltage to the cathode of the That. The temperature compensation capacitor is 3
Two out of two is fine. Further, the bias current of the oscillation transistor can be switched by opening or grounding the terminal provided outside the semiconductor integrated circuit, and the switching circuit is connected in parallel with the emitter resistance of the oscillation transistor. It has the function of switching the bias current depending on the frequency band.

[0008]

With this configuration, when the surface acoustic wave resonator or the inductor is used as the resonator, the oscillation frequency has a negative temperature characteristic, while the negative temperature characteristic of the temperature compensation capacitor causes the oscillation frequency to change. It is compensated in the direction of the positive temperature characteristic. Moreover, since only an inexpensive temperature compensation capacitor is used, it is possible to inexpensively configure a voltage controlled oscillator having a stable frequency variable width in consideration of temperature characteristics. Further, the temperature compensation capacitor inserted between the base and collector of the oscillation transistor also has a function of suppressing the influence of the capacitance between the collector and base of the transistor, which causes deterioration of C / N, and can improve C / N. . Further, by switching the bias current with an external terminal, when the frequency of transmission and reception is switched and used, C /
With respect to N, the bias current can be used with an optimum bias current, and low power consumption can be achieved.

[0009]

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a circuit configuration diagram of a voltage controlled oscillator circuit according to a first embodiment of the present invention. In FIG. 1, 1 is an active circuit for oscillation, 2 is an extension inductor for expanding a variable frequency range, 3 is a surface acoustic wave resonator, 4 is a variable capacitance diode, 5, 6 and 7 are temperature compensation capacitors, 8 Is a power supply terminal, 9 is an output terminal,
Reference numeral 10 is a frequency control terminal, 11 is a bias current switching circuit, and 12 is an external terminal for switching the bias current. The oscillation active circuit 1 is configured as a semiconductor integrated circuit,
Reference numeral 101 is an oscillation transistor, 102 is a transistor of an output emitter follower circuit, and 103 is a first emitter resistor. FIG. 2 is a detailed circuit configuration diagram of the bias current switching circuit portion of the voltage controlled oscillator circuit according to the first embodiment of the present invention. In FIG. 2, 111 and 112
Is a switching transistor, and 113 is a second emitter resistance.

The operation of the voltage-controlled oscillator configured as described above will be described below. First, the oscillation active circuit 1 has a Colpitts type configuration, and the output is taken out from the emitter follower circuit. Further, a temperature compensating capacitor 6, a frequency expanding inductor 2 and a surface acoustic wave resonator 3 are connected in series from the base of the oscillation transistor 101, and a variable capacitance diode 4 is further connected. The oscillation frequency can be controlled by controlling the bias voltage of the variable capacitance diode.

Further, the bias current switching circuit 11 is
When the external terminal 12 is open, the transistor 111 is in the conductive state and the transistor 112 is in the non-conductive state, and the emitter resistance of the oscillation transistor can be regarded as only the emitter resistance 1. On the other hand, when the external terminal 12 is grounded, the transistor 112 becomes conductive and the emitter resistance can be regarded as a parallel circuit of the emitter resistance 1 and the emitter resistance 2, so that the bias current flowing through the transistor can be switched.

In the surface acoustic wave resonator, the resonance frequency changes depending on the temperature characteristic of the substrate. As an example, 36 ° Y-X
When a LiTaO3 substrate is used, it has a temperature characteristic of -35 ppm / ° C. When the center frequency of oscillation is 400 MHz, it is 840k with respect to temperature change from -10 to 50 ° C.
It becomes the change width of Hz. On the other hand, in the surface acoustic wave resonator, the control frequency range cannot be increased because the spurious region exists in the low range of the resonance frequency. Further, if the sensitivity is increased too much, it may cause deterioration of the C / N value. UJ type capacitors with a temperature coefficient of -750ppm / ° C were used as the temperature compensation capacitors inserted in the three places, and the capacitance value was selected appropriately to reduce the temperature change of the oscillation frequency.
It can be suppressed to 10 ppm / ° C. or less. Further, since it is a temperature compensation circuit using only passive elements, there is almost no deterioration in C / N. Further, among the temperature compensation capacitors, the one inserted between the base and the ground also serves to reduce the influence of the capacitance existing between the base and collector of the transistor, which causes the deterioration of C / N.

Further, in order to obtain a sufficient C / N, a bias current corresponding to the oscillating frequency must be passed through the transistor. By having a bias current switching function, one kind of semiconductor integrated circuit can oscillate with a minimum required bias current for C / N in both the frequency band of transmission and reception of wireless communication.

Although three temperature compensating capacitors are used in the embodiment of the present invention, a temperature compensating effect can be obtained by combining two of them. Further, the resonator is not limited to the surface acoustic wave resonator, and the same effect can be obtained even for a resonator having an oscillation frequency with a negative temperature characteristic. The bias current switching means is the NPN transistor 2
It is not limited to the stage switching circuit.

[0015]

As described above, according to the present invention, when the surface acoustic wave resonator is used as the resonator in the semiconductor integrated circuit except the resonance circuit portion of the voltage controlled oscillator, the temperature of the oscillation frequency becomes a problem. By inserting an inexpensive temperature compensation capacitor into two to three places of the circuit, the temperature compensation can be performed and the C / N of the oscillator can be improved.
Further, by having a function for switching the bias current by opening or grounding a terminal provided outside the semiconductor integrated circuit, an optimum bias current can flow in the frequency band to be used, and voltage control with low noise can be performed. The effect is great in achieving low power consumption, small size, and low price of the oscillator.

[Brief description of drawings]

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

FIG. 2 is a detailed circuit diagram of an embodiment of a bias current switching circuit in the voltage controlled oscillator of the present invention.

FIG. 3 is a conventional example of the voltage controlled oscillator of the present invention.

[Explanation of symbols]

1 Active oscillator circuit 2 Inductor for frequency extension 3 Surface acoustic wave resonator 4 Variable capacitance diode 5 Temperature compensation capacitor 6 Temperature compensation capacitor 7 Temperature compensation capacitor 11 Bias current switching circuit

Continued front page    (72) Inventor Makoto Hasegawa             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Masahiro Mimura             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Takayuki Shimazu             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electronics             Industry Co., Ltd.

Claims (3)

[Claims] 1. A collector of a Colpitts oscillator circuit is grounded by a first bypass capacitor to form a collector-grounded system, a first feedback capacitor is connected between a base and an emitter of the transistor, and a resistance element is used. Supply a base bias to the ground, and connect a second feedback capacitor, an emitter resistance to the ground, and an emitter follower for output between the emitter of the transistor and the ground,
All the above circuit elements are configured inside the semiconductor integrated circuit,
As an external circuit from the base of the transistor of the semiconductor integrated circuit, an inductor, a resonator, and a resistor are connected in series to the base, and the anode is grounded between a point between the resonator and the resistor and ground. A capacitance diode is provided, and a first connecting point on the connecting line connecting the base and the inductor to ground, a first connecting point to the inductor, and a first connecting line connecting the diode to the resistor.
A voltage controlled oscillator, characterized in that at least two of three points between a point and ground are provided with temperature compensating capacitors, and a voltage is applied to the cathode of the variable capacitance diode through a resistor to control the oscillation frequency. 2. A circuit in which a switching circuit and a resistor are connected in series is connected in parallel with the emitter resistance of the transistor by switching a bias current of the transistor by opening or grounding a terminal provided outside the semiconductor integrated circuit. The voltage controlled oscillator according to claim 1, wherein 3. The voltage controlled oscillator according to claim 1, wherein a surface acoustic wave resonator is used as the resonator.