JP2785831B2 - Voltage controlled oscillator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] A voltage controlled oscillator used in a PLL circuit or the like has a high C / N ratio, a wide frequency variable width, stabilizes the temperature characteristics of an output frequency, and uses the output frequency as a source. A first voltage-controlled oscillator having a frequency change with respect to a predetermined temperature change, wherein the frequency change with respect to the predetermined temperature change is three times larger than that of the first oscillator. A second voltage-controlled oscillator having a lower output frequency than the output frequency of the first oscillator, and an output signal of the first and second oscillators being mixed to form a first voltage-controlled oscillator and a second voltage-controlled oscillator. And a means for outputting a frequency obtained by adding the frequency of the first voltage controlled oscillator to the frequency of the difference between the voltage controlled oscillators or a harmonic thereof.

[Industrial Application Field] The present invention relates to a voltage controlled oscillator used for a PLL circuit or the like.

[Conventional technology]

In recent years, magnetic disk devices, optical disk devices, etc.
Data readout devices for industrial / consumer equipment such as DAT, or wireless communication devices have a high C / N ratio (corresponding to the difference between the signal peak value and noise), a wide frequency variable width, and temperature-frequency characteristics. There is a demand for a stable voltage controlled oscillator.

By the way, LC oscillations and multivibrators have been used as voltage-controlled oscillators with a wide frequency variable width.
It was a step forward in terms of N ratio. The voltage controlled oscillator using crystal oscillation has a good C / N ratio and stable temperature characteristics of the output frequency, but lacks a variable frequency range. Although in recent years have been developed to a voltage controlled oscillator using LiTaO ₃ vibrator fill meantime, stable temperature of the frequency variable width and crystal oscillator par of the LC oscillation par -
Frequency characteristics could not be obtained.

To solve this problem, a voltage-controlled oscillator as shown in FIG. 5 has been proposed. That is, the fifth
In the figure, VC04 and VC05 are voltage controlled oscillators controlled by a control voltage Vc, and have temperature-frequency characteristics as shown in FIG. 6 as VC04 and VC05, respectively. Further, in FIG. 5, a mixer MIX3 mixes each output signal from the oscillators VC04 and VC05, and then mixes the low-pass filter LPF2.
As a result, the mixdown signal (having the frequency of the difference between the output signal frequencies) is extracted as the output signal OUT.

With this configuration, the temperature-frequency characteristic of the output signal OUT corresponding to the mixdown signal is, as shown in FIG. 6, the temperature-frequency characteristic of the two source oscillators VC04 and VC05. A flat (ie, stable) characteristic corresponding to the difference is obtained.

Further, by setting the voltage-frequency characteristics of each of the voltage-controlled oscillators VC04 and VC05 to predetermined characteristics (for example, reversing the slope of the voltage-frequency characteristics of each of the oscillators), the output signal corresponding to the difference frequency is obtained. The OUT frequency variable width can also be expanded.

As described above, according to the voltage-controlled oscillator shown in FIG. 5, the use of the LiTaO ₃ resonator as the oscillating element maintains a good C / N ratio, increases the frequency variable width, and increases the temperature-frequency characteristic. Can be stabilized.

[Problems to be solved by the invention]

However, in the device shown in FIG.
As described above, since the frequency of the difference between the output frequencies of the two source oscillators is taken out, the output signal generated
There is a disadvantage that the frequency of OUT becomes low, and therefore, the usability is deteriorated particularly when used for a wireless device or the like.

The present invention has been made to solve such a problem, and as described above, by using a LiTaO ₃ vibrator, C /
The output frequency is made equal to or higher than that of the source oscillator while taking advantage of the features that the N ratio is high, the frequency variable width is wide, and the temperature characteristics of the output frequency are stable. .

[Means for solving the problem]

FIG. 1 is a block diagram showing the basic configuration of the present invention, in which VC01 and VC02 are voltage controlled oscillators controlled by a control voltage Vc, respectively. As shown as VC02, the frequency change of the VC02 with respect to a predetermined temperature change is smaller than three times the frequency change of the VC01, for example, 2 times.
It is to be doubled. Then, the output signals of the two oscillators are mixed by a mixer MIX1 and further passed through a band-pass filter BPF, whereby a combined output signal of the output signals (the output frequency of the first oscillator, the first oscillator and the second oscillator, Signal that sums the output frequency of the difference
Is taken out as the output signal OUT.

That is, a first voltage-controlled oscillator having a frequency change with respect to a predetermined temperature change, a frequency change with respect to the predetermined temperature change being larger than the first oscillator and smaller than three times, and being higher than the output frequency of the first oscillator. A second voltage-controlled oscillator having a low output frequency, and mixing the output signals of the first and second oscillators to generate a first voltage equal to the difference frequency between the first voltage-controlled oscillator and the second voltage-controlled oscillator. A means for outputting a frequency obtained by adding the frequencies of the control oscillators or a harmonic thereof is provided.

Here, the reason why the frequency change of the second voltage controlled oscillator with respect to a predetermined temperature change is set to be larger than the frequency change of the first voltage controlled oscillator and smaller than three times will be described.

In the present invention, the frequency variation Δ
fo [Hz / ° C] is given by Δfo = | Δf1 + (Δf1−Δf2) | (Δf1 <Δf2 <3 · Δf1 [Hz / ° C]). According to the relationship of Δf1 <Δf2 <3 · Δf1, if the relationship is a · Δf1 = Δf2 (1 <a <3), the frequency variation Δfo is Δfo = | Δf1 + (Δf1−Δf2) | = | Δf1 + ( Δf1−a · Δf1) | = | 2 · Δf1−a · Δf1 |, and if a = 2, Δfo = | 2 · Δf1−a · Δf1) | = | 2 · Δf1−a · Δf1 | = 0 Becomes

Further, if a = 1.3, Δfo = | 2 · Δf1−1.3 · Δf1) | = | 0.7 · Δf1 |, which indicates that the temperature characteristic is improved with respect to Δf1.
If a = 2.6, this is the same as Δfo = | −0.6 · Δf1 |.

However, when a falls below 1 or exceeds 3, (a
= 3.3) Δfo = | 2 · Δf1−3.3 · Δf1) | = | −1.3 · Δf1 | Therefore, in the present invention, as described above, it is important that 1 <a <3.

The voltage-frequency characteristics of the oscillators VC01 and VC02 have opposite slopes, as shown as VC01 and VC02 in FIG. 4, respectively.

(Operation)

With the above-described configuration, for example, the temperature-frequency characteristic of the oscillator VC01 is now assumed to be -100 Hz / ° C, while the temperature-frequency characteristic of the oscillator VC02 is −200H / ° C.
Assuming z / ° C., the output frequency difference between VC01 and VC02 increases by −100 Hz each time the temperature rises by 1 ° C. Thus, as described above, by mixing the output signals of the two oscillators and then extracting the combined output signal,
Even if the output signal of the oscillator VC01 has a temperature-frequency characteristic of -100 Hz / ° C, the difference between the temperature-frequency characteristics of the oscillators VC01 and VC02 is -100 Hz / ° C. As shown in FIG. 3, the change in the temperature-frequency characteristic cancels out, and the temperature-frequency characteristic of the combined output signal becomes 0 Hz / ° C. (that is, a flat and stable characteristic).

Further, as described above, the voltage-frequency characteristics of the oscillators VC01 and VC02 are set to have opposite slopes as shown in FIG. 4 (that is, the output frequency of VC01 is made proportional to the control voltage, while By making the output frequency of VC02 inversely proportional to the control voltage), the frequency variable width of the above-mentioned band is changed by the source oscillators VC01 and VC01.
It is expanded from the frequency variable width of VC02 (that is, for example, 2
Doubled).

Moreover, by taking out the combined output signal as described above as the output signal OUT, the frequency of the output signal can be at least equal to or higher than the output frequency of the source oscillator.

〔Example〕

As described above, the frequency change of the second oscillator VC02 with respect to a predetermined temperature change needs to be larger than the frequency change of the first oscillator VC01 and smaller than three times at all temperatures.

FIG. 2 shows an embodiment for constructing such an oscillator VC02, in which a local oscillator OSC, a voltage controlled oscillator VC03,
The oscillator VC02 is constituted by the mixer MIX2 and the low-pass filter LPF1.

Here, for example, the output frequency of the first oscillator VC01 is
50 MHz, the output frequency of the above voltage controlled oscillator VC03
100 megahertz (for example, temperature 25 ° C, control voltage 2.5V
). By doing so, the oscillator used for the oscillator VC03 is changed to the oscillator VC01.
(The LiTaO ₃ single crystal is used in each case), and the output frequency of the oscillator VC03 is twice as high as that of the oscillator VC01 as described above. However, the frequency change with respect to the predetermined temperature change is also doubled, and the temperature-frequency characteristic shown as VC02 in FIG. 3 can be easily realized.

Next, the output signal of the oscillator VC03 is mixed with the output signal of, for example, a 70 MHz local oscillator (using a crystal or the like) OSC (the frequency change with respect to a temperature change is negligible) in the mixer MIX2. Through the filter LPF1, the frequency of the difference between the output frequencies of the oscillators VC03 and OSC (ie, 30 MHz) is obtained.

Next, the output frequency of the first voltage controlled oscillator VC01 (50
Megahertz) and an output frequency (30 megahertz) extracted from the low-pass filter LPF1 are mixed by a mixer MIX1 and further passed through a band-pass filter BFP, whereby the combined output signal (in this case, 70 megahertz is obtained. “50+ (50−30) = 70 MHz”.)
As an output signal OUT.

If the output signal of the oscillator VC03 is obtained by multiplying the frequency of the output signal of the oscillator VC01 by using a frequency, a common voltage-controlled oscillator VC01 is used.
The output signal of VC03 can also be obtained.

〔The invention's effect〕

According to the present invention, by utilizing the conventional voltage controlled oscillator, the C / N ratio is high, the frequency variable width is wide,
The temperature characteristic of the output frequency is stable, and the output frequency can be equal to or higher than that of the source oscillator, and can be used over a wide range of industrial fields including wireless devices.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of the present invention, FIG. 2 is a block diagram showing one embodiment of the present invention, and FIG. 3 shows a temperature-frequency characteristic of the device shown in FIG. FIG. 4, FIG. 4 is a diagram showing voltage-frequency characteristics of the device shown in FIG. 1, FIG. 5 is a block diagram showing an example of the prior art, and FIG. 6 is a device shown in FIG. FIG. 4 is a diagram showing temperature-frequency characteristics of FIG. (Explanation of symbols) VC01 to VC05: voltage-controlled oscillator, OSC: local oscillator, MIX1 to MIX3: mixer, LPF1 to LPF2: low-pass filter, BPF: band-pass filter.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H03L 1/02 H03B 21/00

Claims (2)

(57) [Claims] A first voltage-controlled oscillator having a frequency change with respect to a predetermined temperature change; a frequency change with respect to the predetermined temperature change being larger than the first voltage-controlled oscillator and smaller than three times, and A second voltage controlled oscillator having an output frequency lower than an output frequency of the voltage controlled oscillator;
And the output signal of the second voltage-controlled oscillator is mixed, and the frequency of the first voltage-controlled oscillator is added to the frequency of the difference between the first voltage-controlled oscillator and the second voltage-controlled oscillator. And a means for outputting a frequency or a harmonic thereof. 2. The second voltage-controlled oscillator has a voltage-frequency characteristic opposite to that of the first voltage-controlled oscillator.
The voltage controlled oscillator according to claim 1.