JPH0812976B2 - Voltage controlled oscillator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a voltage control type oscillation circuit used in a modulation circuit, a demodulation circuit, a frequency conversion circuit and the like.

(Prior Art) Conventionally, there are various types of voltage-controlled oscillation circuits. Among them, as an example suitable for IC and capable of oscillating at high frequency, there is one described in US Pat. No. 3,963,996.
This is shown in FIG.

Transistors 1 and 2 are oscillating transistors whose emitters are commonly connected to form a differential pair. These transistors 1, 2
A resonance circuit including a capacitor 9 and an inductor 10 is connected between the collectors of the. Also, the transistors 1, 2
The bases of the respective transistors are connected to the bases of the other transistors via the return paths 11 and 12. Further, the common emitter is connected to the current source 7 and the collector of the control transistor 3. The control transistor 3 has the same emitter as the control transistor 4 and forms a differential pair. The common emitters of the transistors 3 and 4 are connected to the current source 6, and the collector of the transistor 4 is connected to the base of the transistor 2.

The oscillator circuit configured as described above includes the transistor 3,
The oscillation frequency is made variable by changing the voltage value applied by the control voltage source 8 connected between the four bases. This conventional circuit is suitable because the output bias is constant even if the applied voltage is changed, and the design is easy when an amplifier circuit or the like is added to the next stage.

(Problems to be Solved by the Invention) However, in the conventional circuit shown in FIG. 5, the variable range of the oscillation frequency is basically determined by the current value of the current source 6. Therefore, when it is necessary to increase the variable range, the current value of the current source 6 must be increased. This leads to an unfavorable situation such as an increase in power consumption and a rise in temperature accompanying it when considering the use of an IC.

Further, when it is desired to improve the linearity of the control characteristic within the desired variable range, the current value of the current source 6 may be increased. However, if this is performed, the above problem similarly occurs and the desired value is increased. The linearity is maintained as it is even outside the variable range of. On the contrary, this is not preferable, and for example, when the conventional circuit is applied to the demodulation circuit, a malfunction occurs in which tuning oscillation occurs at another frequency and erroneous demodulation is performed.

The present invention has been made to eliminate the above-mentioned problems, and provides a voltage-controlled oscillation circuit in which the variable range of the oscillation frequency is wide even with a relatively low current and the linearity of the control characteristic is good. To aim.

[Structure of the Invention] (Means for Solving the Problems) A voltage-controlled oscillation circuit according to the present invention conventionally changes the oscillating frequency by changing the bias current of the oscillating transistor and also between the collector and the base of the oscillating transistor. It controls the voltage.

(Operation) When the collector-base voltage is controlled, the collector-base capacitance of the oscillation transistor changes. Since the capacitance change contributes to changing the oscillation frequency, it is possible to obtain a sufficient oscillation frequency variable range with a smaller current than in the conventional case.

(Embodiment) FIG. 1 shows an embodiment of the present invention. The difference from the conventional circuit is that the control transistor forming a differential pair with the control transistor 3 is a double-collector type transistor 40, and each collector is connected to the bases of the transistors 1 and 2, and in the feedback paths 11 and 12. It is the point that resistors 14 and 15 are inserted in each.

According to this configuration, for example, when the voltage value of the control voltage source 8 is increased to increase the oscillation frequency, the transistor 40
Collector current increases, and the value of the collector-base voltage between the oscillation transistors 1 and 2 increases. As a result, the voltage generated in the resistors 14 and 15, that is, the collector-base voltage of the transistors 1 and 2 increases, and the collector-base capacitance of the transistors 1 and 2 decreases. The oscillating frequency is determined by the resonance circuit composed of the capacitor 9 and the inductor 10. However, the contribution of the collector-base capacitance is substantially large, and the oscillating frequency is increased by reducing the capacitance value. .

Therefore, according to the circuit of the present invention, for example, when the oscillation frequency is increased, the control voltage source 8 is operated to reduce the collector current of the transistor 3 as in the conventional case, and in addition to this, the collector / base of the oscillation transistors 1 and 2 is added. Since the inter-capacitance is reduced, the change in the oscillation frequency can be increased, and a sufficient variable range can be obtained with good linearity even if the current value of the current source 6 is set low.

As a method of dividing the collector current of the control transistor forming a differential pair with the transistor 3, the differential circuit 5 employing the double collector type transistor 40 may be used, or the differential circuit 50 as shown in FIG. Good. That is, the dividing transistors 42 and 43 are prepared, a constant DC voltage 44 is applied to their bases, and the emitters are connected in common to the collector of the controlling transistor 41. In this way, the collector current of the control transistor 41 is divided by the transistors 42 and 43, and
By connecting the collectors of 1,42 to the bases of the oscillation transistors 1,2, the same function as the circuit of FIG. 1 can be exerted. In addition, according to the circuit format of FIG.
A resistor can be connected to each of the emitters of the dividing transistors 42 and 43, so that variation in current division due to variation in the base-emitter voltage of the transistors 42 and 43 can be suppressed.

Further, the resistors 14 and 15 inserted in the feedback paths 11 and 12 can be replaced with diodes. At this time, the voltage generated in the diode is constant with respect to a slight current fluctuation, so that a stable oscillation frequency can be obtained.

Further, in the oscillator circuit shown in FIG. 1, by inserting a resistor in the collector current path of the oscillating transistors 1 and 2, the collector-base voltage of both of these transistors can be widened, and the oscillation frequency It is possible to expand the variable range. The resistor inserted in the collector current path can be replaced with a diode. An example of this is shown in FIG.

The voltage-controlled oscillation circuit shown in FIG. 3 uses a differential circuit 51 of the type shown in FIG. 2 as a control differential circuit, and a plurality of diodes are vertically connected in the collector current paths of the oscillation transistors 1 and 2. Diode series circuits 16 and 17 are respectively inserted. The voltage across the diode has a negative temperature coefficient of about −2 mV / ° C. per diode. Therefore, by using the diode series circuits 16 and 17, it is possible to compensate for a phenomenon in which the oscillation frequency shifts to a higher direction with a temperature rise, and stabilize the oscillation frequency.

The embodiment described so far is an example in which the return paths 11 and 12 are directly connected, and FIG. 4 shows a capacitive feedback type. The main points different from the direct connection type are that capacitors 30 and 31 are inserted in the feedback paths 11 and 12, and a base bias resistor 27 and a base bias resistor 27 are respectively provided between the collector of the control transistor 4 and the bases of the oscillation transistors 1 and 2. 28 is provided, and further, resistors 32 and 33 for midpoint potential are connected in series between the collectors of the oscillation transistors 1 and 2, and a transistor 34 whose base is connected to the midpoint is provided. A resistor 29 is connected between the emitter and the collector of the control transistor 4.

The transistor 34 is for varying the bias applied to the bases of the oscillation transistors 1 and 2, and the collector-base voltage of these transistors 1 and 2 is the resistance 29
It changes depending on the voltage across both ends.

As described above, according to the present invention, the desired variable range can be obtained with good linearity even if the current value of the current source 6 that determines the variable range of the oscillation frequency is set to be relatively low. It is possible to obtain a voltage-controlled oscillator circuit that is extremely practical and suitable for high efficiency.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a voltage controlled oscillator circuit according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing another embodiment of a differential circuit applied to the present invention, FIGS. FIG. 5 is a circuit diagram of another embodiment of the present invention, and FIG. 5 is a configuration diagram of a conventional circuit. 1,2,3,34,40,41,42,43 …… transistor, 8 …… control voltage source, 9,30,31 …… capacitor, 10 …… inductor, 11,12 …… return path, 14, 15 ... resistance.

Claims (2)

[Claims] 1. A first pair of emitters connected in common to form a differential pair.
A second transistor; a resonant circuit connected between the outputs of the first and second transistors; and an output of at least one of the first and second transistors and at least a resistor connected to the input of the other transistor. A variable current means for supplying one output current to the emitters of the first and second transistors and varying the emitter current of the first and second transistors; A voltage-controlled oscillation circuit comprising: a control means for supplying the other output current of the means to the feedback path to control the collector-base voltage of the first and second transistors. 2. A first pair of emitters connected in common to form a differential pair.
A second transistor; a resonance circuit connected between the outputs of the first and second transistors; and an output of at least one transistor of the first and second transistors and a capacitor of the other transistor via a capacitor. A first feedback path connected to the base input; variable current means for supplying one output current to the emitters of the first and second transistors to vary the emitter currents of the first and second transistors; A second feedback path connected from the output midpoint potentials of the first and second transistors to the inputs of the first and second transistors through at least a resistor, and the other output current of the variable current means A voltage control type oscillation circuit comprising: a control means for controlling the collector-base voltage of the first and second transistors by supplying the second feedback path.