JP3368580B2 - Temperature compensated crystal oscillator - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature-compensated crystal oscillator (hereinafter referred to as a temperature-compensated oscillator) in which the frequency-temperature characteristic of the crystal oscillator is flattened. The present invention relates to a temperature-compensated oscillator in which the sensitivity of a temperature-compensated circuit is enhanced.

[0002]

BACKGROUND OF THE INVENTION A temperature-compensated oscillator has a stable oscillation frequency with respect to temperature, and is therefore particularly used for mobile communication equipment used in a dynamic environment.
One of such devices is a temperature-compensated oscillator using a negative characteristic thermistor (hereinafter referred to as a thermistor) whose resistance value decreases as the temperature rises as a temperature-sensitive resistance element (see Japanese Patent Publication No. 64-1967).

(Example of Prior Art) FIG. 6 is a circuit diagram of a temperature compensation oscillator for explaining a conventional example. The temperature compensation oscillator comprises a crystal oscillator 1 and a temperature compensation circuit 2. The crystal oscillator 1 includes a crystal oscillator 3, a dividing capacitor 4 (ab) that forms a resonance circuit with the crystal oscillator 3, and a feedback amplifier 5 that includes a transistor or the like that maintains the output from the resonance circuit (a so-called Colpitts oscillation circuit). ). The oscillating frequency f0 in such a case largely depends on the series resonance frequency fS0 of the crystal unit 1, and is finally determined by the circuit side series capacitance (load capacitance) CL viewed from the crystal unit 1. . However,
Since the load capacitance is added, the oscillation frequency rises from the series resonance frequency of the crystal unit. Then, in the oscillation region, the oscillation frequency decreases as the load capacitance increases, and increases as the load capacitance decreases. In the figure, VC is a power source, V0 is an output, 6 (ab) is a bias dividing resistor of a transistor, and 7 is a load resistor.

The crystal unit 3 is made of, for example, an AT cut, and has a series resonance frequency f as shown by the curve A in FIG.
S0 has a frequency-temperature characteristic in the form of a cubic curve that increases monotonously with temperature, depending on temperature. Along with this, the frequency-temperature characteristic of the crystal oscillator 1 also becomes a cubic curve shape that increases monotonously with temperature rise depending on the crystal oscillator 3 (curve B in the figure). However, since the load capacitance CL, which has a substantially constant value with respect to the temperature, is connected, the frequency-temperature characteristic of the crystal unit is a curve that is translated substantially upward.
Further, in the figures, both the curves a and b are shown as the deviation Δf at each temperature point with reference to the series resonance frequency fS0 and the oscillation frequency f0 at room temperature of 25 ° C.

The temperature compensating circuit 2 is composed of a high temperature and low temperature compensating circuit 2 (ab) connected in series with the crystal unit 3. Each of the high temperature and low temperature compensation circuits 2 (ab) is composed of a parallel circuit of a thermistor 8 (ab) and a capacitor 9 (ab) and is connected in series. In the parallel circuit, the resistance value of the thermistor 8 (ab) changes depending on the temperature, and thus the resistance component and the reactance component of the impedance between terminals also change depending on the temperature.

In other words, when the parallel circuit of the thermistor 8 (ab) and the capacitor 9 (ab) is converted into an equivalent series circuit, the equivalent series resistance and the equivalent series capacitance change depending on the temperature. Of course, high and low temperature compensation circuit (parallel circuit) 2
Equivalent series capacitances CSa (T), CS which are inter-terminal capacitances of (ab)
If b (T) changes depending on temperature, the load capacitance CL (T) of the entire circuit including the circuit side capacitance CL viewed from the crystal unit 3 also changes. Therefore, the equivalent series capacitance CS (T) of the temperature compensating circuit 2 is set so as to cancel the frequency-temperature characteristic of the crystal oscillator 1.
Can be compensated by changing (see the equivalent diagram of FIG. 8). In the figure, RP (0) a and RP (0) b are room temperature resistance values of the thermistor 8 (ab), and CPa and CPb are capacitors 9.
(Ab) capacity.

Generally, the high temperature compensation circuit 2a has a room temperature resistance value R of the thermistor 8a as shown in FIG. 9 (curve B).
P (0) a is made larger than the reactance XPa (= 1 / ωCPa) due to the capacitance CPa of the capacitor 9a so that the resistance value exponentially decreases as the temperature rises. By doing so, the terminals of the thermistor 8a are opened at room temperature or below, and the equivalent series capacitance CSa (T) at room temperature or below becomes only the capacitance CPa of the capacitor 9a and does not change, so the oscillation frequency also changes. do not do. Further, since the resistance value of the thermistor 8a decreases exponentially at room temperature or higher, the equivalent series capacitance CS (T) gradually increases with the capacitance CPa of the capacitor 9a as a reference (curve B in FIG. 10). Therefore,
Temperature compensation is performed only for high temperature parts above room temperature.

In the low temperature compensation circuit 2b, the room temperature resistance value RP (0) b of the thermistor 9b is made smaller than the reactance XPb (= 1 / ωCPb) due to the capacity CPb of the capacitor 9b, and the terminals of the thermistor are short-circuited at room temperature or higher. (Curve a in FIG. 9). In this way, the equivalent series capacitance CSb (T) does not change at room temperature or higher, simply because a line is added (the equivalent series capacitance is infinite), so that the oscillation frequency does not change. Also, below room temperature, the thermistor 8
Since the resistance value of b increases exponentially, the equivalent series capacitance CSb (T) gradually decreases from infinity to the capacitance CPb of the capacitor 9a. (Curve B in FIG. 10) Therefore, the temperature compensation is performed only for the low temperature portion below the room temperature. From such a thing,
Each compensating circuit 2 (ab) independently shares and compensates for low temperature and high temperature regions, and both are combined to enable temperature compensation over a wide range.

[0009]

(Problems of the prior art) In the temperature-compensated oscillator having the above-mentioned structure, the B constant of the thermistor 8 (ab) and the room temperature resistance values RP (0) a, RP (0) b and the capacitor 9 ( After the capacitance values CPa and CPb of ab) are set by calculation and simulation so that the frequency temperature characteristic of the typical crystal oscillator 1 satisfies the standard (for example, within ± 2 ppm at −30 to 70 ° C.), It is mounted on a circuit board. However, in reality, there are variations in the frequency-temperature characteristics of the individual crystal oscillators 1, particularly due to the cutting angle of the crystal resonator 3. Therefore, although the set values obtained by calculation and simulation are almost the same, there is an error from the actual value. The B constant of the thermistor is determined by the thermistor material, manufacturing method, etc., and represents the slope of the temperature resistance characteristic.

Therefore, conventionally, as shown in FIG. 11, the high temperature compensating circuit 2a is connected in series to the thermistor 8a, and the low temperature compensating circuit 2b is connected in parallel to the adjusting resistor 10 (ab) to form a thermistor resistance network. Had formed. With this configuration, in the high temperature compensating circuit 2a, the adjusting resistor 10a is connected in series to the thermistor 8a, so that the temperature resistance characteristic of the thermistor resistor network is greatly affected on the high temperature side. Therefore,
The equivalent series capacitance CSa (T) can be adjusted especially on the high temperature side with respect to the temperature of the high temperature compensation circuit 2a. Also, the low temperature compensation circuit 2b
Since the adjusting resistor 10b is connected in parallel to the thermistor 8b, the temperature resistance characteristic of the thermistor resistor network is greatly affected on the low temperature side. Therefore, the equivalent series capacitance CSa (T) can be adjusted especially on the low temperature side with respect to the temperature of the low temperature compensation circuit 2b.

Normally, in these adjustments, the adjustment resistor 10 (ab) is replaced so as to satisfy the temperature standard while monitoring the frequency-temperature characteristic. Therefore, the adjustment resistor 10 (ab) can absorb the variation in the frequency-temperature characteristic of each crystal oscillator 1 and obtain the frequency-temperature characteristic within the standard in the high-low temperature region.

(Problems of Prior Art) However, in recent years, there is a strong demand for miniaturization of the crystal oscillator 1, and there is no choice but to make the crystal oscillator (crystal piece) 3 small. However, in this case, the equivalent series capacitance C1 of the crystal unit 3 decreases, and the capacitance ratio γ = C0 / C1 (where C0 is the interelectrode capacitance) increases. Further, the frequency variable amount Δf / of the oscillation frequency f0 from the series resonance frequency fS0 of the crystal unit 3
As is well known, fS0 is expressed by the following equation (1). However, Δf
= F0-fS0.

Therefore, when the capacitance ratio γ increases with the miniaturization, the frequency variable amount Δf of the crystal unit 3 is increased.
/ FS0 decreases. From this, it can be said that the detection sensitivity of the thermistor resistance network by the adjustment resistor 10 (ab) becomes small on the high temperature side (for example, 70 ° C.) and the low temperature side (for example, −30 ° C.) where a large amount of frequency change is required. However, there was a problem that temperature compensation could not be performed. Further, in the above-mentioned configuration, since the adjusting resistor 10 (ab) is required, there is a problem that the number of elements is increased to raise the cost and the miniaturization of the temperature compensation oscillator is hindered.

(Object of the Invention) It is an object of the present invention to provide a temperature-compensated oscillator in which the number of elements is reduced by eliminating the adjustment resistor, the cost is reduced, the size is further reduced, and the temperature can be compensated. To aim.

[0015]

[Means for Solving the Problems] (Points of Interest) In the present invention,
Since a thermistor resistance network is formed by adding an adjustment resistor to the thermistor, we have focused on the point that the amount of change in resistance value with respect to temperature change decreases and the detection sensitivity decreases, compared to the temperature resistance characteristic of the thermistor.

(Solution) The basic solution is to adjust the frequency-temperature characteristic by changing the reference resistance value of the temperature-sensitive resistance element at the reference temperature.

[0017]

In the present invention, the reference resistance value at the reference temperature of the temperature sensitive resistance element is directly changed to adjust the frequency temperature characteristic, so that the detection sensitivity of the temperature sensitive resistance element is prevented from being lowered and the temperature compensation is performed. It is possible. Moreover, the adjustment resistor is not required. An embodiment of the present invention will be described below.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram of a temperature compensation oscillator for explaining an embodiment of the present invention. The same parts as those of the prior art example are given the same numbers to simplify the description. The temperature-compensated oscillator is a crystal oscillator 1 including an AT-cut crystal resonator 3, a dividing capacitor 4 (ab), and an oscillation circuit element such as a feedback amplifier 5, a thermistor 8 (ab), and a capacitor 9 (ab) as described above. High and low temperature compensation circuit 2 (a
It consists of a temperature compensating circuit 2 in which b) is connected in series (see the previous figure). In this embodiment, the thermistor 8 (ab) of the high temperature / low temperature compensation circuit 2 (ab) is, for example, 200
Thermistor material 11 (a having a B constant of 0 to 4000)
b) is directly printed and formed on the circuit board 12 on which oscillator circuit elements (not shown) are arranged. Thermistor material 11
(Ab) is made of metal oxide or the like, and the circuit board 12 is made of ceramics which facilitates printing.

In such a device, as described above, the room temperature resistance value RP0 of the thermistor 8 (ab) and the capacitance value of the capacitor 9 (ab) in the high temperature and low temperature compensation circuit 2 (ab) are first calculated by simulation and the like. CPa, CPb
Is set. Next, the capacitor 9 (a
b) is attached, and the thermistor material 11 (ab) having room temperature resistance values RP0a 'and RP0b' which are smaller than the set values RP0a and RP0b is printed and formed on the circuit board 12. Then, the notch 13 is provided in the thermistor material 11 (ab) by, for example, a laser, and the room temperature resistance values RP0a 'and RP0b' are adjusted by changing them from a small value to a large value. In this case, while monitoring the frequency-temperature characteristic of the crystal oscillator 1, for example, the frequency deviation Δf at five temperature points centered at room temperature
The notch 13 is provided while measuring / f. Then, the adjustment ends when the frequency-temperature characteristic satisfies the temperature standard.

With such a configuration, the B constant is set to a constant value and the room temperature resistance values RP0a and RP0b of the thermistor 8 (ab) are set.
Is changed from a small value to a large value, the temperature resistance characteristic of the thermistor 8a in the high temperature compensating circuit 2a changes more greatly in the vicinity of room temperature than in the high temperature range. Also, the low temperature compensation circuit 2
The temperature resistance characteristic of the thermistor 8b at b changes more greatly in the low temperature region than near room temperature. The resistance value of the thermistor is expressed by the following equation (2). Therefore, the room temperature resistance value RP0
Is the coefficient of the exponential function, and the larger the coefficient is, the larger the amount of change in the resistance value on the low temperature side is on the high temperature side. RP (T) = RP0 · eB (1 / T-1 / T0) “However, index after B” ··· (2)

Therefore, in such a configuration, since the temperature resistance characteristic of the thermistor 8 (ab) changes, the equivalent series capacitance C of the high temperature and low temperature compensation circuit 2 (ab) changes accordingly.
Frequency temperature characteristics can be corrected by controlling Sa (T) and CSb (T). Then, for example, in the high temperature compensation circuit 2a, the B constant and the room temperature resistance value RP0a are set to the same value, and the conventional adjustment resistor 10
Compared with the case of a, the temperature resistance characteristic becomes the curves a and b of FIG. Similarly, comparing the cases of the low temperature compensation circuit 2b, the results are c and d. Curves a and c are for the present embodiment, and curves b and d are for the conventional case.

As is clear from this comparison, in the case of this embodiment (curves a and c), the room temperature resistance values RP0a and RP0b are adjusted, so that the detection sensitivity based on the B constant of the thermistor is maintained. On the other hand, the high temperature compensation circuit 2 in the conventional example
In the case of the thermistor resistance network of a (curve B), since the adjusting resistor 10a is connected in series, the resistance value is increased not only at room temperature resistance value RP0a but also at a high temperature region, so that the detection sensitivity is lowered. Further, in the case of the thermistor resistance network in the low temperature compensation circuit 2b (curve D), since the adjusting resistor 10b is connected in parallel, not only the room temperature resistance value RP0b but also the resistance value is reduced not only in the low temperature region but also in the detection sensitivity. The detection sensitivity here means the amount of change in the resistance value with respect to temperature, and is, for example, the ratio RP (T) / RP0 of the resistance value RP (T) at the temperature T to the room temperature resistance value RP0.

Therefore, in the conventional case, the adjusting resistor 10
When the room temperature resistance values RP0a and RP0b are controlled by (ab), the detection sensitivity decreases as described above and the resistance change decreases, and the equivalent series capacitances CSa (T) and CSb (T) also change at room temperature. It becomes smaller in the high temperature range and the low temperature range. Therefore, when the capacity ratio γ becomes large, the high / low temperature range (-3
Temperature compensation at 0 ° C. and 70 ° C.) becomes impossible. On the other hand, in the present embodiment, since the room temperature resistance values RP0a and RP0b of the thermistor 8 (ab) are directly adjusted, the resistance change is increased while maintaining the detection sensitivity of the thermistor and the equivalent series capacitance CSa (T). , CSb (T) also increase in the high temperature region and the low temperature region relative to the room temperature. Therefore, the crystal unit 3
Even when the size is small and the capacity ratio γ is large, a sufficient amount of frequency change is obtained and temperature compensation in a high and low temperature range is possible. Further, along with this, since the adjustment resistor 10 (ab) is not required and each compensation circuit 2 (ab) is only the thermistor 8 (ab) and the capacitor 9 (ab), miniaturization can be promoted.

[0024]

[Other Matters] In the above embodiment, the temperature compensating circuit including the thermistor 8 (ab) and the capacitor 9 (ab) has been described as an example, but as shown in FIG. It can also be applied to the thermistor resistor network of the temperature compensating circuit 15 for compensating the load temperature by applying the compensation voltage VS to the voltage variable capacitance element 14 and temperature compensating the frequency temperature characteristic. In the figure, VC is a constant voltage source, 16 is a high frequency element resistance, and 18 and 19 are resistors for overall adjustment.

That is, in the conventional temperature compensating circuit 15 shown in FIG. 3, the low temperature portion TL and the normal temperature portion TM of the frequency temperature characteristic are shown.
Among the thermistors 16 (abc) for low temperature, room temperature, and high temperature, which respond to the high temperature portion TH, particularly the thermistor 16 (ab) for low temperature and room temperature, respectively, the adjusting resistor 17 is provided.
(Ab) was connected to adjust its temperature resistance characteristic.
The frequency-temperature characteristic of interest in this case is an AT-cut cubic curve having a maximum value on the low temperature side, an inflection point at room temperature, and a minimum value on the high temperature side, as shown in FIG. As described above, if the present invention is applied, the detection resistance can be increased by removing the adjustment resistor 17 (ab) as shown in FIG. 5, and miniaturization is promoted.

Although the thermistor material 11 (ab) is formed on the circuit board 12 on which the oscillation circuit element is arranged, for example, it is formed on a thermistor board (not shown) which is separate from the circuit board, and this is formed on the circuit board. May be installed. In this case, even if the cut 13 is too deep and an adjustment error occurs, only the thermistor substrate needs to be discarded, which is rational (economical).

Although the thermistor 8 (ab) is adjusted by laser after the thermistor material 11 (ab) is formed by printing on the circuit board, the room temperature resistance values RP0a and RP0b of the thermistor 8 (ab) obtained by simulation are shown. A plurality of thermistors may be prepared in advance as the center, and these may be replaced as adjusting parts so as to satisfy the frequency temperature characteristics within the standard. The room temperature resistance value R of the thermistor 8
P0 can be varied depending on the size of the thermistor material and the electrode. Although the temperature sensitive resistance element has been described as a thermistor, it can be basically applied to a temperature sensitive resistance element having a positive temperature characteristic, that is, a so-called posistor.

As described above, the present embodiment can be freely changed as required. In short, the frequency temperature characteristic based on the element value obtained by simulation or the like is corrected by adjusting the room temperature resistance value of the thermistor. However, the temperature-compensated oscillator in which the adjusting resistor is removed thereby basically belongs to the technical scope of the present invention. Note that, for example, the compensating circuit including only the thermistor and the capacitor in the embodiment is publicly known for explaining the principle, but the present invention provides a means for adjusting the frequency temperature characteristic in such a thing.

[0029]

According to the present invention, since the room temperature resistance value at the reference temperature of the temperature sensitive resistance element is changed to correct the frequency temperature characteristic, the adjustment resistor is not required, the number of elements is reduced, the cost is reduced, and It is possible to provide a temperature-compensated oscillator that is downsized and is capable of temperature compensation.

[Brief description of drawings]

FIG. 1 is a partial view of a temperature compensation oscillator for explaining an embodiment of the present invention.

FIG. 2 is a temperature resistance characteristic diagram of the thermistor for explaining the function and effect of the present invention.

FIG. 3 is a circuit diagram of a conventional example for explaining another embodiment of the present invention.

FIG. 4 is a frequency-temperature characteristic diagram for explaining another embodiment of the present invention.

FIG. 5 is a temperature compensation circuit diagram for explaining another embodiment of the present invention.

FIG. 6 is a circuit diagram of a temperature compensation oscillator for explaining a conventional example.

FIG. 7 is a frequency-temperature characteristic diagram illustrating a conventional example.

FIG. 8 is an equivalent circuit diagram of a temperature compensation oscillator for explaining a conventional example.

FIG. 9 is a temperature resistance characteristic diagram of a thermistor for explaining a conventional example.

FIG. 10 is a characteristic diagram of an equivalent series capacitance for explaining a conventional example.

FIG. 11 is a temperature compensation circuit diagram illustrating a conventional example.

[Simple explanation of symbols]

1 crystal oscillator, 2, 15 temperature compensation circuit, 3 crystal oscillator, 4, 9 capacitor, 5 feedback amplifier, 6, 7, 1
0, 17, 18, 19 resistance, 8, 16 thermistor,
11 thermistor material, 12 circuit board, 13 notch, 14 voltage variable capacitance element,

Continuation of the front page (56) Reference JP 56-68002 (JP, A) JP 5-251932 (JP, A) JP 9-223929 (JP, A) JP 60-201705 (JP , A) Actual Kaihei 5-15520 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) H03B 5/32 H03B 5/04

Claims (4)

(57) [Claims] 1. A by changing the load capacitance of the crystal oscillator based on a change in resistance value with respect to temperature of the temperature-sensitive resistance element, a temperature compensated crystal oscillator compensates for the frequency-temperature characteristic of the crystal oscillator, the temperature sensitive resistor element No temperature sensitive resistance material
It is formed on the edge substrate and cuts into the temperature sensitive resistance material.
A temperature-compensated crystal oscillator characterized by being provided and directly adjusting a reference resistance value at a reference temperature. 2. The temperature-compensated crystal oscillator according to claim 1, wherein the insulating plate is a circuit board on which an oscillation circuit including a crystal oscillator is arranged. 3. The temperature-compensated crystal oscillator according to claim 1 , further comprising a temperature-compensated circuit which is connected in series with the crystal unit and is composed of a parallel circuit of the temperature-sensitive resistance element and a reactance element. A temperature-compensated crystal oscillator that controls the equivalent series reactance of the parallel circuit based on the change of the resistance value with respect to the temperature of the element to change the load capacitance of the crystal resonator to compensate the frequency-temperature characteristic of the crystal oscillator. 4. The temperature-compensated crystal oscillator according to claim 1 , further comprising a temperature compensation circuit including the temperature-sensitive resistance element, wherein the compensation voltage from the temperature-compensation circuit is based on a change in the resistance value of the temperature-sensitive resistance element. Is applied to a voltage variable capacitance element connected to a crystal oscillator to change the load capacitance of the crystal oscillator to compensate the frequency temperature characteristic of the crystal oscillator.