JPS60254805A - Voltage-controlled oscillation circuit - Google Patents

Abstract

PURPOSE:To improve temperature characteristics over the entire range of oscillation frequency by setting the temperature coefficient of a variable constant current source which varies the oscillation frequency to a specific value different from the temperature coefficient of a constant current source. CONSTITUTION:The bases of transistors (TR)1 and 2 are connected to the collectors of TRs 2 and 1, so a parallel resonance circuit 11 oscillates at a roughly determined frequency. The resonance frequency of this formed VCO is varied by controlling the current flowing through the variable constant current source 8. Then, the temperature coefficient of the variable constant current source 8 is set to the specific value which is different from the temperature coefficient of the constant current source 7 and determined by the temperature coefficient of the total current of both constant current sources 7 and 8 and the variable frequency range of the VCO. Consequently, temperature characteristics at both terminals of the variable range of the oscillation frequency cancel each other and the temperature characteristics are improved over the entire range of the oscillation frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a voltage controlled oscillator circuit (hereinafter referred to as VCO) used in a high frequency circuit such as a television receiver. [Prior Art] In general, vCO is indispensable, especially for PLL circuits, and there are various forms, but it is used in the TV IF band (30 to 60
The type shown in FIG. 1 is often used for VCOs in integrated circuits used in MHz). In the figure, 1.2 is the first . The second transistor 5.6 is a coil and a capacitor connected between the collectors of both transistors 1 and 2, and both constitute a parallel resonant circuit 11. 3.4
are connected between the collector of the transistor 1.2 and the power supply terminal 10, respectively. A second resistor, 7, is a constant current source connected between the common emitter of transistors 1 and 2 and the ground, 8 is a variable resistor connected in parallel with the constant current source 7, and capable of varying the current value according to the control terminal 9 voltage. It is a constant current source.

Next, the operation will be explained. Since the bases of transistors 1 and 2 are connected to the collectors of transistors 2 and 1, respectively, they perform positive feedback operation, and generally the coil 5
．． It oscillates at a resonant frequency determined by capacitor 6. The oscillation frequency can be controlled by varying the sink current from the emitter of transistor 1.2. In reality, the oscillation frequency can be varied by varying the sink current and varying the collector-base capacitance in the saturation region of transistors 1 and 2. The constant current source 7 sucks a constant current 1, and the variable constant current source 8 draws a constant current 1 according to the voltage applied to the control terminal 9.
The sinking current can be varied from O to I2.

In general, increasing the sink current increases the collector-base capacitance of transistors 1 and 2, lowering the oscillation frequency, but since the collector-base capacitance has a positive temperature coefficient with respect to temperature, conventional voltage control In the oscillation circuit, the oscillation frequency is corrected by giving the constant current sources 7 and 8 the same negative temperature characteristic so that the temperature characteristic disappears at the center of the variable region. However, in this conventional circuit, if the variable range of the oscillation frequency is widened, the temperature coefficient of the collector-base capacitance changes due to the bias current of the constant current source, so there is a drawback that the temperature characteristics deteriorate at the edge of the variable range. Ta.

[Summary of the invention]

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and in a VCO, the temperature coefficient of the variable constant current source for varying the oscillation frequency is different from the temperature coefficient of the constant current source. By setting the temperature coefficient of the total current of the defined current sources to a predetermined value set by the variable frequency range of the VCO, a voltage controlled oscillation circuit is provided that can reduce the temperature characteristics over the entire variable range of the oscillation frequency. This is what we intend to provide.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. The voltage controlled oscillation circuit according to an embodiment of the present invention has a circuit configuration similar to that shown in FIG. 1 showing the conventional circuit, but the variable constant current source 8 has a predetermined temperature coefficient different from that of the constant current source 7 It is something that has.

FIG. 2 shows the total current that must be passed through the constant current source 7.8 in order to oscillate each constant frequency of [0, [1, and I2] versus temperature. In the figure, frequencies f1 to f2 are the variable frequency range of the voltage controlled oscillation circuit, with fl being the highest frequency and I2 being the lowest. Therefore, I1 is the current of the constant current source 7, and I2 is the maximum current of the variable constant current source 8.

Generally, increasing the total current of the defined current sources 7.8 also increases the temperature coefficient of the oscillation frequency. In the integrated circuit ■CO, if the sink current 11 of the constant current source 7 is 1 mA and the maximum current 12 of the variable constant current source 8 is 1 mA, for example, the total current of the constant current sources 7 and 8 is II (this If the current of the variable constant current source 8 is O), the temperature coefficient of the total current is 13,400 ppm, and when 11+12, the temperature coefficient of the total current is 138 ooppm. Temperature coefficient of 7 is 13400pp
m, whereas the temperature coefficient of the variable constant current source 8 (which is constant regardless of the constant current value of the variable constant current source 8) is = +3800 (I 1 + 12) -34
00I 1) /I2 ppm, the temperature characteristics at both ends of the oscillation frequency variable range, that is, fl and I2, can be canceled, and the temperature characteristics can be corrected almost at any position within the variable range. It is something that can be done.

In the above example, the sink current 11. When I2 is both 1 mA, the temperature coefficient of the variable constant current source 8 is -4200 ppm. In order to achieve different temperature coefficients with this constant current source 7.8, it is only necessary to select the type of diffused resistor in the integrated circuit, or to utilize the change in VBH of the diode due to the current density, which is relatively easy to achieve. It is.

When configuring a PLL circuit using the VCO according to this embodiment configured as described above and performing video detection on a television,
Even if the IF multiplied signal frequency deviates from the regular center frequency, the PLL circuit will not become unlocked due to a change in temperature.

In the above embodiment, a case has been described in which a VCO is used in a video detection circuit, but the present invention can also be applied to a local oscillation circuit used for frequency conversion, and the same effects as in the above embodiment can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, in a VCO, the temperature coefficient of the variable constant current source for varying the oscillation frequency is set to the temperature coefficient of the total current of the defined current source, which is different from the temperature coefficient of the constant current source; By setting the value to a predetermined value determined by the variable frequency range of the VCO, the temperature characteristics at both ends of the variable frequency range of the oscillation frequency are canceled, and it is possible to configure a CO with good temperature characteristics at any oscillation frequency. .

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a voltage controlled oscillator circuit according to a conventional example and an embodiment of the present invention, and FIG. 2 is a diagram showing the temperature characteristics of the sink current of the circuit of FIG. 1. 1.2... 1st. Second transistor, 3.4...
1st. Second resistor, 5, 6... Coil, capacitor 1
DESCRIPTION OF SYMBOLS 1... Parallel resonant circuit, 7, 8... Constant current source, variable constant current source, 9... Control terminal, 10... Power supply terminal. Agent Masuo Oiwa Figure 1 n 511→

Claims (1)

[Claims] (1) The first type in which the bases are connected to each other's collectors and the emitters are commonly connected. a second transistor; a first transistor connected between the collector of each transistor and the power supply terminal; a second resistor, a parallel resonant circuit connected between the collector of the picture transistor, a constant current source connected between the common emitter of both transistors and ground, and a constant current source connected in parallel with the constant current source. 1. A voltage controlled oscillator circuit comprising: a variable constant current source having a predetermined temperature coefficient different from that of the source and capable of varying a current value according to a control voltage.