JPH11225020A - Vco circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a VCO circuit that enhances the C/N while reserving a wide frequency band. SOLUTION: In this VCO circuit, a resistor 4, an inductor 12, a resonator 13 and a capacitor 7 are connected in series between an input terminal 3 and a base of a transistor(TR) 8 being a component of a resonance circuit, a variable capacitor 6 connects in between grounds and a connecting point between the resistor 4 and the inductor 12, and its output is given to a tank circuit 2. A parallel circuit consisting of a resistor 14, an inductor 15 and a resistor 16 is connected in series between an emitter of the TR 8 and ground.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a VCO circuit, and more particularly to a VCO circuit for communication such as a pager or a portable telephone or a TCO circuit.
The present invention relates to a VCO circuit used for signal processing of a V, VTR, video camera, or the like.

[0002]

2. Description of the Related Art FIG. 5 is an electric circuit diagram showing an example of a conventional VCO. In FIG. 5, the VCO includes a resonance circuit 1 and a tank circuit 2. A control voltage for controlling the oscillation frequency is applied to a control voltage input terminal 3, which is connected to one end of a resonator 5 via a resistor 4, and the other end of the resonator 5 is grounded to a reference potential. You. Resonator 5
Since the capacitance component is small, the varicaps 6 are connected in parallel. The resonance output of the resonator 5 is input to the base of the transistor 8 via the capacitor 7. The transistor 8 is connected to the tank circuit 2 via the capacitor 9 by the output of the resonance circuit 1. The tank circuit 2 includes a transistor 10 receiving the resonance output from the resonance circuit 1 at its base.
And an LC circuit 11 connected between the collector of the transistor 10 and the ground.

[0003]

SUMMARY OF THE INVENTION Resonator 5 shown in FIG.
For example, when a surface acoustic wave element is used, the capacitance component of the surface acoustic wave element is relatively large, and the circuit of FIG. Also,
Since the varicap 6 having a low Q is connected in parallel to the resonator 5, the C / N deteriorates. Further, since the output of the resonance circuit 1 is taken out from the emitter of the transistor 8,
A large output could not be obtained, causing a deterioration in C / N.

Therefore, a main object of the present invention is to provide a VC capable of improving C / N while securing a wide band.
To provide an O-circuit.

[0005]

The invention according to claim 1 is
A VCO circuit using a surface acoustic wave element as a resonator, wherein an input terminal for inputting a control voltage to be applied to the resonator to change the frequency is connected in series between the input terminal and one end of the resonator. A first inductor, a varicap connected between a connection point between the input terminal and the first inductor and a reference potential, and a transistor having the other end of the resonator connected to the base via a capacitor. And a resonance circuit connected between the emitter of the transistor and the reference potential, in which a first resistor, a second resistor, and a parallel circuit of a second inductor are connected in series, and a resonance signal from a varicap is provided. Tank circuit.

[0006]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. In FIG. 1, an inductor 12 and a resonator 13 composed of a surface acoustic wave element are connected in series between the resistor 4 and the capacitor 7 in FIG.
The varicap 6 is connected between the connection point between the resistor 4 and the inductor 12 and the ground. Further, a resonance output is taken from a connection point between the resistor 4 and the inductor 12 and loosely coupled to the tank circuit 2 via the capacitor 9. The tank circuit 2 is configured in the same manner as in the conventional example shown in FIG.

A resistor 14 and an inductor 15 are connected between the emitter of the transistor 8 constituting the emitter follower circuit and the ground.
And the parallel circuit of the resistor 16 are connected in series.

FIG. 2 is a characteristic diagram showing the frequency vs. voltage characteristics of one embodiment of the present invention and a conventional example, and FIG. 3 is a characteristic diagram showing the C / N vs. voltage characteristics similarly. is there.

As shown in FIG. 1, by connecting the resonator 13 composed of a surface acoustic wave element and the inductor 12 in series, as shown in FIG. 2, the variable range of the frequency can be greatly expanded. Also, when the variable range of the frequency is widened, the conflicting C / N characteristics deteriorate, but in one embodiment of the present invention, the resonance circuit 1 and the tank circuit 2 are loosely coupled on the base side, and the transistor 8 of the resonance circuit 1 By connecting one inductor 15 and two resistors 14 and 16 to the emitter side, as shown in FIG. 3, the C / N can be improved as compared with the conventional example.

[0010] As shown in FIG.
An impedance conversion circuit such as a simple emitter follower in which the LC circuit 11 shown in FIG. 1 is omitted may be used.

[0011]

As described above, according to the present invention, the variable range is secured without deteriorating the Q of the resonance system by connecting the resonator in series with the resonance system and further adding an inductor in series. can do. Moreover, the C / N can be improved by taking out the output of the resonance circuit from the varicap side where the output is large and connecting a resistor in parallel with the inductor arranged on the emitter side of the transistor.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram of an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a comparison between a frequency versus voltage characteristic of an embodiment of the present invention and a conventional example.

FIG. 3 is a characteristic diagram showing the C / N versus voltage characteristics of an embodiment of the present invention and a conventional example in comparison.

FIG. 4 is a circuit diagram showing another example of the tank circuit.

FIG. 5 is an electric circuit diagram showing an example of a conventional VCO circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Resonance circuit 2 Tank circuit 3 Input terminal 4, 14, 16 Resistance 6 Varicap 7, 9 Capacitor 8, 10 Transistor 11 LC circuit 12, 15 Inductor 13 Resonator

Claims (1)

[Claims] 1. A V using a surface acoustic wave element as a resonator.
An input terminal to which a control voltage to be applied to the resonator is input in order to change a frequency, a first inductor connected in series between the input terminal and one end of the resonator. A varicap connected between a connection point between the input terminal and the first inductor and a reference potential; a transistor having the other end of the resonator connected to its base via a capacitor; A resonance circuit connected between the emitter and a reference potential, in which a first resistor and a parallel circuit of a second resistor and a second inductor are connected in series, and a tank circuit to which a resonance signal from the varicap is given A VCO circuit comprising: