JPH02168705A - Voltage controlled oscillating circuit - Google Patents

Abstract

PURPOSE:To obtain the variable range of sufficient oscillating frequencies by means of a small current by changing the oscillating frequencies with changing the bias current of an oscillating transistor(TR), and controlling the voltage between collector bases of the oscillating TR. CONSTITUTION:A control TR forming a differential pair with a control TR3 is made into a TR40 in a double collector shape, respective collectors are connected to the bases of TRs 1 and 2, and resistances 14 and 15 are inserted to feedback paths 11 and 12. In such a constitution, when the voltage value of a controlled voltage source 8 is increase, for example, in order to increase the oscillating frequencies, the collector current of the TR40 is increased, and the voltage value between the collector bases of the both oscillating TRs 1 and 2 is increased. Thus, the base voltage between the respective TRs 1 and 2 is increased, and the capacity value of the collector bases is decreased. The oscillating frequencies are determined by a resonance circuit consisting of a capacitor 9 and an inductor 10, in addition the contribution of the capacity between the collector bases is large, and by decreasing the capacity value, the oscillating frequencies is increased.

Description

[Detailed description of the invention] This invention relates to voltage-controlled oscillation circuits used in switching circuits, etc.

(Prior Art) There have been various types of voltage controlled oscillator circuits. Among them, one example that is suitable for IC implementation and capable of oscillating at high frequencies is the one described in US Patent No. 3,963.99fi. This is shown in FIG.

The transistors 12 are oscillation transistors whose emitters are commonly connected and form a differential pair. These transistors 1, 2
A resonant circuit consisting of a capacitor 9 and an inductor 10 is connected between the collectors of the . Further, the transistor 1
, 2 is connected to the base of the other transistor via a feedback path 11.12. Furthermore, the common emitter is connected to the current source 7 and to the collector of the control transistor 3. Control transistor 3
Similarly, the control l transistor 4 and the emitter are common, and these form a differential pair. The common emitters of transistors 3 and 4 are connected to a current source 6 and transistor 4
The collector of is connected to the base of the transistor 2.

The oscillation circuit configured as described above includes transistors 3,
The oscillation frequency is made variable by changing the voltage value applied by a control voltage source 8 connected between the bases of 4. In this conventional circuit, the output bias remains constant even when the applied voltage is changed, which is not preferable when adding an amplifier circuit etc. to the next stage.For example, when applying the conventional circuit to a demodulation circuit, it is difficult to This causes malfunctions such as oscillation tuned to the frequency and erroneous demodulation.However, voltage control, which has a wide variable range of oscillation frequency even at relatively low currents, and has good linearity of control characteristics, is not ideal as shown in Figure 5. In the conventional circuit, the variable range of the oscillation frequency is basically determined by the current value of the current source 6. Therefore, if it is necessary to increase the variable range, the current value of the current source 6 must be increased. This is an IC
Considering this, an undesirable situation arises in that power consumption increases and the temperature rises accordingly.

Also, if you want to improve the linearity of the control characteristics within the desired variable range, you should just increase the current value of the current source 6. If you do this, the above problem will occur as well, and the desired Even outside the variable range, linearity is maintained as is. This changes the bias current of the oscillation transistor to change the oscillation frequency and also controls the collector-base voltage of the oscillation transistor.

(Function) 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 variable range of the oscillation frequency even with a smaller current than in the past.

The difference between the oscillation frequency and the high oscillation frequency due to the decrease in the capacitance value 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 base of the transistor 12. Resistors 14.
This is the point where 15 was inserted.

According to this configuration, for example, when the voltage value of the control voltage source 8 is increased in order to increase the oscillation frequency, the transistor 40
The collector current of oscillation transistors 1 and 2 increases, and the value of the collector-base voltage between both oscillation transistors 1 and 2 increases. As a result, the voltage generated at the resistor 14, 15, that is, the base voltage of each transistor 1.2 increases, and the value of the collector-base capacitance of each transistor 1, 2 decreases.

The oscillation frequency is determined by the resonant circuit constituted by the capacitor 9 and the inductor IO, but substantially the collector-base capacitance has a large contribution, and when increasing the frequency, the control voltage source 8 must be operated. As in the conventional case, the collector current of the transistor 3 is reduced, and in addition, the capacitance between the collector and base of the oscillation transistor 1゜2 is reduced, so the change in the oscillation frequency can be increased, and the current source 6 is Even if the current value is set low, a sufficient variable range can be obtained with good linearity.

In addition, as a method of dividing the collector current of the control transistor forming a differential pair with the transistor 3, in addition to using the differential circuit 5 that employs a double collector type transistor 40, it is also possible to use a differential circuit 50 as shown in FIG. Good too. That is, dividing transistors 42 and 43 are prepared, a constant DC voltage 44 is applied to their bases, and their emitters are commonly connected to the collector of the control transistor 41. In this way, the collector current of the control transistor 41 is divided by the transistors 42 and 48,
Each transistor 41. ．． By connecting the collector of 42 to the base of the oscillation transistor 12, the same function as the circuit shown in FIG. 1 can be achieved. In addition, the second
According to the circuit format shown in the figure, the dividing transistor 42.43
A resistor can be connected to each emitter of the transistors 42 and 43, thereby suppressing variations in current division due to variations in the voltages between the bases and emitters of the transistors 42 and 43.

Also, return route 1.1. , 12, a resistor 14.
15 can also be replaced with a diode. At this time, since the voltage generated by the diode remains constant despite slight current fluctuations, a stable oscillation frequency can be obtained.

Furthermore, in the oscillation circuit shown in Fig. 1, by inserting a resistor into the collector current path of the oscillation transistors 1 and 2, it is possible to widen the voltage between the collector and base of both of these transistors, and the oscillation frequency of the -layer can be increased. It is possible to expand the variable range of. Further, 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 oscillator circuit shown in FIG. 3 uses a differential circuit 51 of the type shown in FIG. Circuits 16 and 17 are inserted respectively. The voltage across each diode is approximately -2mV per diode.
It has a negative temperature coefficient of /'C. Therefore, by using the diode series circuits 16 and 17, it is possible to compensate for the phenomenon in which the oscillation frequency shifts toward higher levels as the temperature rises, and to stabilize the oscillation frequency.

The embodiments described so far are examples in which the feedback paths 11 and 12 are of the direct connection type, but FIG. 4 shows a capacitive feedback type. The main difference from the direct connection type is that capacitors 3o and 31 are inserted in the feedback path 11 and 12, and in order to divide the collector current of the control transistor 4, between the collector and the bases of the oscillation transistors 1 and 2. A base bias resistor 27, 28 is provided respectively, and a midpoint potential resistor 32, 33 is connected in series between the collectors of the oscillation transistor 1.2, and the base of the transistor 34 is connected to the midpoint of the resistor 32, 33. and this transistor 34
A resistor 29 is connected between the emitter of the control transistor 4 and the collector of the control transistor 4.

The transistor 84 shown in No. 1 makes the bias applied to the base of the oscillation transistor 1゜2 variable, and the voltage between the collector and base of these transistors 1 and 2 changes depending on the voltage across the resistor 29. It is a diagram.

1, 2. 3.34, 40.41, 42.43...
Transistor, 8... Control voltage source, 9.30.3
1... Capacitor, 10... Inductor, 11.
12... Return path, 14, 1.5... Resistance.

Claims (1)

[Claims] A first and second transistor whose emitters are commonly connected to form a differential pair, a resonant circuit connected between each output of the first and second transistors, and at least one of the first and second transistors. a feedback path connecting the output of one transistor to the input of the other transistor;
variable current means for varying the emitter currents of the first and second transistors connected to the emitters of the transistors;
A voltage controlled oscillation circuit comprising: control means for controlling collector-base voltages of the first and second transistors between the feedback paths.