JPH01236802A - Voltage controlled oscillator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] Regarding voltage controlled oscillators used in local oscillation circuits, etc., the purpose of this invention is to realize a voltage controlled oscillator circuit with high stability and a wide variable frequency range. Applying the same control voltage in common to a voltage controlled oscillation circuit that has temperature characteristics and has a characteristic that the frequency increases as the voltage increases, and a voltage controlled oscillator circuit that has the characteristic that the frequency decreases as the voltage increases, The two voltage controlled oscillation circuits are connected in parallel so that the output signals of both voltage controlled oscillation circuits can be mixed by a mixer, and the two voltage controlled oscillation circuits are configured to output a signal having a frequency that is the difference between the two output signals.

[Industrial Application Field] The present invention relates to a voltage controlled oscillator used in local oscillation circuits and the like.

[Prior Art] A phase-locked loop (PLL) synthesizer as shown in FIG. 7 is often used as a highly stable variable frequency oscillator. In the figure, 5 is a voltage-controlled oscillator circuit whose output frequency fo is varied by a DC control voltage, 6 is a frequency divider circuit that can set an arbitrary frequency division ratio n, 7 is a phase comparison circuit, and 8 is a low pass filter.

The phase comparator circuit 7 includes, for example, a crystal oscillator, etc.
a reference signal fr from a highly stable reference oscillator;
A signal fd obtained by dividing the output signal fo from the voltage controlled oscillation circuit 5 by a factor of n in a frequency dividing circuit 6 is input. Here, when the frequencies of the reference signal fr and the signal fd are different, a voltage corresponding to the phase difference is output from the phase comparator circuit 7,
It is filtered by a low-pass filter 8 and becomes a DC control voltage V. Then, the voltage controlled oscillation circuit 5 operates and changes the output signal fo so that the frequency of the signal fd matches the frequency of the reference signal fr. In other words, the frequency division ratio n is set to 6, for example.
If the frequency of the reference signal rr is 10 MHz, the output signal f is set so that the frequency of the signal fd is also 10 MHz.
.

The frequency of is 60M, which is six times the frequency of the reference signal fr.
Hz. Furthermore, this output signal fo is fed back as a signal fd, and in the phase comparator circuit 7, the reference signal f is always
Since it is compared to match r, its stability corresponds to the stability of the reference signal fr.

Further, by changing the frequency division ratio n, an output signal fo of an arbitrary frequency can be obtained.

[Problem to be solved by the invention]

PLL synthesizers are widely used because of their high stability and the ability to obtain arbitrary variable frequencies.
Due to usage requirements, it is desired that the frequency variable range be wider. On the other hand, in order to realize this request, it is necessary to improve the frequency stability in the voltage controlled oscillation circuit 5, which is mainly caused by temperature characteristics. In FIG. 8, when the horizontal axis is the control voltage ■ and the vertical axis is the output signal fo, the characteristics of the voltage controlled oscillator circuit 5 are represented by a straight line ■7 when it is completely stable against temperature changes. . However, when the stability of the voltage controlled oscillator circuit 5 is poor and the frequency of the output signal fo changes due to a change in temperature, the frequency of the output signal fo may have a certain range for the same control voltage ■. become. For example, if the output signals fo at the control voltages v1 and v2 for the characteristic line are fl and f2, respectively, the frequency variable range is flfl (-Sl).

On the other hand, the temperature stability of the voltage controlled oscillator circuit 5 is poor, and if the upper limit frequency of the frequency fluctuation range with respect to temperature changes of the output signal fo at the control voltage v1 is f3, and the lower limit frequency of the frequency fluctuation range at the control voltage v2 is f4, the frequency The variable range of is f4-f3 (=S2), and as is clear from the figure, the variable range of the output signal fo of the voltage controlled oscillation circuit 5 with respect to the control voltage ■ becomes narrow.

Conventionally, as circuit elements in the voltage controlled oscillation circuit 5, a circuit including a crystal or a coil and a capacitor (LC) has been mainly used. Crystals have high stability but have an extremely narrow frequency variable range, and LC circuits have a relatively wide variable range but have poor stability and cannot fully demonstrate their performance.

In recent years, voltage-controlled oscillation circuits using lithium tantalate (LiTaO3) resonators have been developed, and characteristics intermediate between crystal and LC circuits have been confirmed, but the problems have not been completely solved.

A technical object of the present invention is to solve these problems of conventional voltage controlled oscillation circuits and to realize a voltage controlled oscillation circuit that is highly stable and has a wide variable frequency range.

[Means for Solving the Problems] FIG. 1 is a block diagram illustrating the basic principle of a voltage controlled oscillator according to the present invention. (2) and 2 are voltage controlled oscillation circuits, which have the same temperature characteristics. The voltage controlled oscillation circuit 1 has a characteristic that the frequency increases as the voltage increases, and the voltage controlled oscillator circuit 2 has a frequency characteristic that the frequency decreases as the voltage increases. Then, the same control voltage Vfc is commonly applied to both type pressure controlled oscillation circuits 1.2, and the output signals f1 and f of both type pressure controlled oscillation circuits 1.2 are
The voltage controlled oscillation circuits 1 and 2 are connected in parallel so that the voltage controlled oscillation circuits 1 and 2 can be mixed by the mixer 3, and output a signal having a frequency that is the difference between the Okayama power signals f1 and f2.

[Operation] In FIG. 1, the control voltage V of the voltage controlled oscillation circuit 1 is now
The characteristic of the output signal f1 with respect to fc is assumed to have a positive slope as shown in FIG. On the other hand, common control voltage Vf
The control voltage V of the voltage controlled oscillation circuit 2 controlled by c
It is assumed that the characteristic of the output signal f2 with respect to fc has a negative characteristic as shown in FIG. The hundred output signals f1 and T2 are mixed in mixer 3 and the difference frequency (fl-T
2) is selected, high frequency components are further removed by the low pass filter 4, and the result is output as an output signal f3. This relationship is shown in FIG.

For example, when the control voltage Vfc is T3, the frequency of the output signal f1 is 15.0 MHz, and the frequency of the output signal f2 is 10.0 MI (z), the output signal f3 is the difference of 5
Become Ml1z. Furthermore, by changing the control voltage Vfc, T4
When the frequency of the output signal fl is 15.15MH2
, the frequency of the output signal f2 is 9.9MHz, the difference between these, the output signal f3, is 5.25M! (It becomes z.

That is, by changing the control voltage Vfc from T3 to T4, a frequency change of 0.25 M11z can be obtained. This means that when considering a single voltage controlled oscillation circuit 1 or 2, the same control voltage Vfc
0.15 for voltage controlled oscillator circuit 1
Mtlz frequency change, and voltage controlled oscillation circuit 2
In contrast to the case where only a 0.1 MHz frequency change was obtained, a significant expansion of the frequency change was achieved.

Regarding the stability of the frequency of the output signal f3 with respect to temperature changes, as shown in FIG. 5, if the horizontal axis is the temperature and the vertical axis is the frequency change Δf with respect to the temperature at a certain control voltage Vo, then The frequency change Δf of the double pressure controlled oscillator circuit 1.2 at the temperature to is zero. In general, if the same circuit configuration is adopted, is there a voltage control? The temperature characteristics of the 111 oscillation circuit 1.2 show a similar tendency. If the temperature coefficient of the double pressure controlled oscillation circuit 1.2 is negative, the frequency will decrease as the temperature rises, as shown in FIG. However, both types of pressure controlled oscillator circuits 1.2 each have their own unique coefficients, and the temperature characteristic of voltage controlled oscillation circuit 1 is T1, and the temperature characteristic of voltage controlled oscillation circuit 2 is T2.
, T2. The double pressure controlled oscillator circuit 1.2 generates output signals f1 and T with respect to the control voltage Vfc.
Since the direction in which the frequency of 2 changes is opposite, the temperature characteristic of the output signal f3 obtained from the difference between the output signal f1 and T2 is as follows.
It is expressed as T3 which is the difference between both temperature characteristics T1 and T2.

This means that originally a single voltage controlled oscillation circuit 1 or 2
, the temperature characteristic has a large value as shown by T1 or T2, but the output signal f3 is obtained by combining the output signals f1 and T2 of the two voltage controlled oscillator circuits 1.2. By doing so, as shown by the broken line T3, the frequency change with respect to temperature change is significantly reduced.

〔Example〕

Next, examples will be used to explain how the voltage controlled oscillator according to the present invention is actually implemented. FIG. 6 is a circuit diagram showing an embodiment of the voltage controlled oscillator according to the present invention, with broken lines 91
The part surrounded by 9 corresponds to the voltage controlled oscillation circuit 1 in FIG. 1, and the part surrounded by the broken line 92 corresponds to the voltage controlled oscillation circuit 2. Each circuit forms a Colpitts oscillation circuit, but the varicap 11 is controlled by a common control voltage Vfc.
．． By changing the capacitance of 12, the oscillation frequency is changed. The capacitance of the varicaps 11 and 12 decreases as the voltage applied across them increases.The control voltage Vfc is applied to both ends of the varicap 11 in the voltage controlled oscillation circuit 91 via the resistor 13. When the control voltage Vfc is increased, the capacitance of the varicap 11 is decreased and the frequency of the output signal f1 is increased.

Further, regarding the voltage controlled oscillation circuit 92, the Haricap 1
The voltage applied to 2 varies from the power supply voltage Vcc to the control voltage Vfc.
Therefore, when the control voltage Vfc is increased, the voltage applied to the haricap 12 is decreased.

Therefore, the capacitance of the haricap 12 increases and the frequency of the output signal "2" decreases.

The part surrounded by a broken line 10 corresponds to the mixer 3 in FIG. 1, and a resonance circuit formed by a coil 14 and a capacitor 15 selects the frequency of the difference between the output signals f1 and T2.

The part surrounded by the broken line 16 corresponds to the low-pass filter 4, and has a cutoff frequency (=1
It is possible to attenuate frequencies higher than ÷2πνL C,') and output an output signal f3 having a frequency that is the difference between the output signals f1 and f2.

〔Effect of the invention〕

As described above, according to the present invention, the voltage controlled oscillation circuit 1 having the characteristic that the frequency increases as the voltage increases and the voltage controlled oscillating circuit 2 having the characteristic that the frequency decreases as the voltage increases are connected in parallel. , the same control voltage Vfc is applied in common, and the output signals fL and f2 of both types of pressure controlled oscillation circuits 1.2 are mixed by a mixer 3 to output a signal f3 having a frequency that is the difference between the Okayama power bonds f1 and f2. By configuring
It has become possible to significantly increase the variable frequency range. Furthermore, it is possible to ensure temperature characteristics corresponding to the difference in temperature characteristics between the two types of pressure-controlled oscillator circuits 1.2, making it possible to greatly improve stability. This means, for example, variable width +1%, stability ±500 ppm, and variable width -1%, stability ±50 ppm.
If a voltage controlled oscillator according to the present invention is constructed by combining two voltage controlled oscillator circuits of 0 ppm, it is possible to realize a voltage controlled oscillator with a variable width of 2% and a stability of ±250 ppm.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the basic principle of the voltage controlled oscillator according to the present invention, Figures 2 and 3 are frequency characteristic diagrams of each voltage controlled oscillator circuit, Figure 4 is a diagram showing each output signal, and Figure 5. 6 is a diagram showing the temperature characteristics of the voltage controlled oscillator circuit, FIG. 6 is a circuit diagram showing an embodiment of the voltage controlled oscillator according to the present invention, and FIG.
FIG. 8 is a diagram showing the LL synthesizer, and FIG. 8 is a diagram showing the frequency variable characteristics of the voltage controlled oscillation circuit. In the figure, 1.9L2.92 is a voltage controlled oscillation circuit, 3
4 is a mixer, 4 is a low-pass filter, and 11.12 is a varicap. Patent Applicant Fujitsu Limited Sub-Agent Patent Attorney Yasushi Fukushima Wensuiben Sun Moon Mumu Genbu Dai Cao Diagram CO I Frequency Diagonal Column Diagram 2 CO2 Zhou Liquid Number Sho Chu Diagram 3 Output Signal q Hold/Pressure Figure 4 Temperature @ Frustration 5th diagram (Voltage cable of #0.) Part Guhi Sakata Figure 7 Zone d formula E @ 1 di = 1 variant) i Figure 8

Claims (1)

[Claims] For a voltage controlled oscillation circuit (1) which has the same temperature characteristics and has a characteristic that the frequency increases as the voltage increases, and a voltage controlled oscillator circuit (2) that has the characteristic that the frequency decreases as the voltage increases, By applying the same control voltage in common, the output signals (f1), (
Two voltage controlled oscillation circuits (1) and (2) are connected in parallel so that f2) can be mixed by a mixer (3), and a signal with a frequency that is the difference between both output signals (f1) and (f2) is generated. A voltage controlled oscillator characterized in that it is configured to output.