JPH0441604Y2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Industrial Application Field The present invention relates to a voltage controlled oscillation circuit that is most suitable for an RF converter used in a magnetic recording/reproducing device (VTR) or a video disk. (b) Prior art RF converters (RF modulators) generally used in electronic equipment, such as VTRs or video disks.
A converter called a oscillator is always equipped with a voltage controlled oscillation circuit. In this case, the technology to integrate the constituent elements into integrated circuits (IC) has progressed, and one example is the
The issue is published. Therefore, to explain Fig. 3 of the above-mentioned patent publication, a differential amplifier is composed of Q ₃₁ and Q ₃₂ , a control voltage V _C is applied to the base of the differential amplifier, and a differential pair 3 is connected in two stages.
A method has been proposed in which a phase shift circuit consisting of a resistor 48 and a capacitor 49 is connected to the parallel resonant circuit 46 and the DC blocking capacitor 47 to generate a predetermined oscillation frequency. However, in recent years, the resistor 48 and capacitor 49
Both of these can now be integrated into ICs, and ICs in which the above-mentioned elements constituting the phase shift circuit are installed have begun to be used in VTRs and the like. This is done by applying DC voltages (E ₁ and E ₂ ) from DC power supplies 3 and 4 to the base sides of the first and second transistors 1 and 2, respectively, as shown in Connect the control signal source 5 to
The oscillation unit 6 generates a predetermined oscillation frequency. (c) Problems to be solved by the invention According to the conventional example shown in FIG. 2, the voltages E ₁ and E ₂ are simply
A predetermined bias voltage is obtained from the resistors 7 and 8, and the same voltage is applied to the bases of the first transistor 1 and the second transistor 2.
Although the resistor and capacitor constituting the oscillation unit 6 are constructed so as not to exhibit temperature characteristics, temperature drift in the oscillation frequency due to the temperature coefficient of the IC resistor cannot be avoided, and the oscillation frequency immediately after the power switch is turned on is unavoidable. The temperature drift of
The drift of the oscillation frequency over time has been an obstacle during the adjustment process of a VTR set. This pattern is shown in Figure 3, with the center frequency
For 4.5MHz, from the power switch, especially the IC
This poses a problem as the oscillation frequency decreases due to an increase in the amount of phase shift of the phase shift circuit as the temperature of the resistor increases. (d) Means for solving the problem The present invention first improves the first and second components of the voltage controlled oscillation circuit in order to minimize the temperature drift of the oscillation frequency caused by the temperature characteristics of the above-mentioned components. This configuration includes a base bias circuit applied to the base of the transistor, and a temperature compensation circuit connected to either one of the second transistors. (E) Effect With the configuration of the present invention, the base bias circuit provided on the base side of the second transistor described above is formed by a bias transistor and a voltage dividing circuit, and the voltage setting is optimally obtained and the temperature compensation The circuit can suppress temperature drift in the oscillation frequency. (F) Embodiment To explain the present invention according to the drawings, FIG. 1 shows a voltage controlled oscillation circuit of the present invention, 9 and 10 are first and second transistors, respectively, 11 is an emitter resistor, and 12 and 13 are , 14, 15 are constant current sources, 16,
17 is a bias transistor, 18 is a resistor 1
Voltage divider circuit consisting of 9 and 20, 21 is diode 2
a temperature compensation circuit consisting of 2, 23 and a resistor 24;
Reference numeral 5 denotes an oscillation section including amplification stages 26 and 27, phase shift means 28 and 29, a vector synthesis stage 30, and a resonant circuit 31. To explain the next operation, in the oscillation section 25,
The resonance component generated in the resonant circuit 31 is phase-shifted by +φ and -φ by the phase shift stages 28 and 29, respectively, and the output signal is amplified by the amplifier stages 26 and 27, and then vector-combined by the vector combination stage 30. is added to the resonant circuit 31, and the oscillation frequency in the oscillation section 25 is controlled by the control signal V _C from the control signal source 5. If the currents flowing through the emitters of the first and second transistors 9 and 10 are equal, then the amplifier stage 2
When the amplification factors of 6 and 27 are also equal, the phase of the signal synthesized by the vector synthesis stage 30 becomes zero. Looking at the DC potential at the base of the first transistor 9, a voltage approximately equal to E ₁ -V _BE appears through the bias transistor 16, while the second
Looking at the DC voltage at the base of the transistor 10, the voltage is applied via the bias transistor 17.
A voltage approximately equal to E ₂ −V _BE appears. In the above equation, V _BE is the voltage between the base and emitter of each transistor, and E ₁ <E _2. However, since current flows to the temperature compensation circuit 21, the voltage drop due to the base resistor 32 of the second transistor 10 I _B R _B
occurs, and the base potential of the second transistor 10 becomes
E ₂ −V _BE −I _B R _B. (I _B indicates the current flowing through the base resistor 32, and R _B indicates the resistance value of the resistor 32.) The temperature compensation operation will be explained using the vector diagrams shown in FIGS. 4a, b, and c. A case not affected by temperature is shown in Figure 4a. The vector 30 is the output of the vector synthesis stage 30 in FIG.
is the output of the phase shift means 28, vector 29 is the output of the phase shift means 29, vector 26 is the output of the amplification means 26, and vector 27 is the output of the amplification means 27.
shows the output of Assume that the temperature rises in the state shown in FIG. 4a and the amount of phase shift of the phase shift means 28 and 29 is delayed. At this time, the phase shift delay amounts Δθ of the phase shift means 28 and 29 are equal to each other, and the change thereof is θ ₁ =θ−Δθ, θ ₂
=-θ+Δθ. Therefore, vector 26 and
27 is phase-shifted, and the resultant vector lags behind the original phase as shown in FIG. 4b. At this time, in the temperature compensation circuit 21 of FIG. 1, as the temperature rises, the voltage V _D across the diodes 22 and 23 decreases, and the current I _B increases. Then, according to the above equation, the base voltage of the second transistor 10 decreases, and its collector current decreases. On the other hand, the collector current of the first transistor 9 increases by the amount of the decrease. Therefore,
The gain of the amplifying means 26 becomes large, and the gain of the amplifying means 27 becomes small. Then, the vector 26 in Figure 4b
is large, vector 27 is small, and the composite vector after the change returns to its original phase as shown in FIG. 4c. Therefore, according to the circuit of FIG. 1, it is possible to perform temperature compensation. If the base potentials of the first and second transistors 9 and 10 are set equal, the temperature inside the set increases as the power switch is turned on.
The temperature compensation circuit 21 works to offset the drift of the oscillation frequency because the forward voltage V _f of the diodes 22 and 23 has a negative temperature coefficient. (g) Effects of the invention According to the invention, a predetermined voltage can be applied from a DC power supply through a voltage divider circuit to a bias transistor.
In addition to the second transistor that constitutes the voltage controlled oscillator circuit and to which the reference voltage is applied, a temperature compensation circuit is connected to the second transistor. This can be minimized, and in particular, problems in the adjustment process during assembly can be eliminated.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the voltage controlled oscillation circuit of the present invention, Fig. 2 is a circuit diagram showing a conventional voltage controlled oscillation circuit, Fig. 3 is a characteristic diagram showing the temperature drift of the center frequency, Fig. 4 a, b and c are vector diagrams for explaining FIG. 1; Explanation of main figure numbers, 5... Control signal source, 9... First transistor, 10... Second transistor, 16, 17... Bias transistor, 2
1... Temperature compensation circuit, 22, 23... Diode, 25... Oscillation section.

Claims (1)

[Scope of utility model registration request] a resonant circuit, a first phase shift circuit that shifts the phase of the output signal of the resonant circuit by θ degrees, a second phase shift circuit that shifts the phase of the output signal of the resonant circuit by -θ degrees, and the first phase shift circuit of the first phase shift circuit. a first amplifier that amplifies the output signal; and a first amplifier that amplifies the output signal;
A voltage controlled oscillator circuit comprising: a second amplifier that amplifies the output signal of the phase shift circuit; and a vector synthesis circuit that performs vector synthesis of the output signals of the first and second amplifiers and applies the synthesized signal to the resonant circuit. , a differential amplifier comprising first and second transistors whose emitters are commonly connected, the collector of the first transistor being connected to the first amplifier, and the collector of the second transistor being connected to the second amplifier; a voltage divider circuit that generates a first DC voltage applied to the base of the first transistor and a second DC voltage greater than the first DC voltage applied to the base of the second transistor; and a control signal for adjusting the oscillation frequency. a control signal source that applies the voltage to the base of the first transistor, and a temperature compensation circuit that includes a series circuit of a diode and a resistor and applies a temperature compensation voltage created by dividing the second DC voltage to the base of the second transistor. A voltage controlled oscillation circuit characterized in that the oscillation frequency is stabilized.