JPS641969B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to temperature compensation over a wide temperature range of a crystal oscillator using an AT plate crystal resonator. When creating an oscillator using an AT plate crystal resonator and trying to maintain frequency stability within ±3×10 ^-6 over a wide temperature range of -30 to +70°C, conventionally, a voltage controlled crystal oscillator and a thermistor were used. Generally, a method was adopted in which temperature compensation was performed by combining a temperature-voltage conversion circuit using However, this conventional method requires a highly sensitive voltage variable capacitance diode and a reference voltage generation circuit with excellent temperature stability, making it expensive. Furthermore, the circuit configuration becomes complex, which puts certain limits on miniaturization. There were some shortcomings. On the other hand, Fig. 1 shows a simple temperature compensation circuit conventionally known as a low-temperature section compensation circuit, for example, which is used by inserting it into the TC section of Fig. 11, but this compensation circuit has been made low-cost. Although it is advantageous for miniaturization, it is extremely impossible to uniformly compensate the characteristics of the crystal oscillator over a wide temperature range of -30 to +70°C. The present invention belongs to the temperature compensation circuit of the system shown in FIG. 1, and is intended to eliminate the above-mentioned drawbacks and achieve both miniaturization and cost reduction. The temperature compensation circuit of the present invention is configured as shown in FIG. 2 by connecting two compensation circuits shown in FIG. It is characterized in that the temperature compensation is performed by dividing the temperature compensation circuit into two parts and assigning each part to each part of the compensation circuit. The explanation will be given below using the figures. Conventionally, there are devices that compensate for the temperature characteristics of a crystal oscillator with a configuration similar to the present invention, for example, there is a document (Japanese Patent Publication No. 45-2404), but the content disclosed is that the temperature-frequency characteristics are parabolic. BT changing to
This is to compensate for the temperature of the plate crystal resonator, and therefore the compensation circuit uses two resistive elements (R _P(T) in Figure 2) with opposite resistance-temperature characteristics. The present invention is aimed at temperature compensation of an AT plate crystal resonator exhibiting a cubic curve, and as will be described later, there is a major difference in that the resistance-temperature characteristics of the resistance element R _P(T) are both positive. Figure 3 shows the compensation circuit in Figure 1 converted into an equivalent series circuit.R _S(T) and
C _{S (T)} is an equivalent series resistance and an equivalent series capacitance at temperature T, and are expressed by the following equations (1) and (2), respectively. In other words, the reactance due to capacitors C _P and C _S(T) is expressed as X _P = 1/ωC _P and X _S(T) = 1/
Expressed as ωC _S(T) , R _S(T) = R _P(T) /1+(R _P(T) /X _P ) ² …(1) X _S(T) = X _P /1+(X _P /R _P(T) ) ² ...(2) Thermistor R _P(T) 's reference temperature point is 25°C (ordinary temperature, that is, the reference temperature point of the present invention is approximately ±10°C around 25°C)
) can be selected within the range of
When formulas (1) and (2) are normalized using this as R _P(O) , the following formulas (3) and (4) are obtained. R _S(T) /R _P(O) =β _(T) /1+β _(T) ² /b ² …(3) X _S(T) /X _P =1/1+b ² /β _(T) ² …( 4) However, β _(T) = R _P(T) / R _P(O) b = X _P / R _P(O) . Figure 4 shows the actual numerical calculations performed using equations (3) and (4), with equation (3) shown as a dotted line and equation (4) shown as a solid line. (The horizontal axis β _(T) in Figure 4 is the resistance ratio of the thermistor R _{P (T) at} each temperature, but the resistance value of the thermistor has a negative temperature coefficient, so it is (This corresponds to the fact that the further you go, the lower the temperature becomes.) Now, when we use Figure 4 to consider the temperature compensation effect obtained when the compensation circuits in Figures 2 and 3 are inserted into the oscillation loop (i.e., the TC section in Figure 11), we find that there is no direct relationship with the oscillation frequency. R _S(T) /
R _P(O) (dotted curve) can be ignored and X _S(T)
Since only the degree of change in directly changes the oscillation frequency, it is only necessary to pay attention to the solid curve of X _S(T) /X _P. The curve is drawn using b as a parameter, and when you look at it, you can see that X _S(T) / around b=1
Since the X _P curve rises significantly at the position of β _(T) = 1,
It is suitable for temperature compensation around 25℃, and the curve around b=10 is especially suitable for temperature compensation in low temperature areas, and furthermore, b=
It can be seen that the curve around 0.1 is particularly suitable for temperature compensation in high temperature areas. It can also be seen that high and low temperature compensation can be performed simultaneously and independently of each other. The above is the basic principle of temperature compensation of the present invention using the compensation circuit shown in FIG. As already mentioned above, the present invention uses a compensation circuit as shown in FIG. 2, which is constructed by connecting two compensation circuits in FIG. 1 in series. FIG. 5 is an equivalent circuit of the crystal oscillator of the present invention. Y is a symbol of an AT plate crystal resonator, the appended γ is the capacitance ratio of the crystal resonator Y, and C _O is the interelectrode capacitance. Note that in FIG. 5, the portion related to the loop gain, which has no relation to the oscillation frequency, is omitted. If the oscillation frequency of the oscillation circuit shown in FIG. 5 is expressed by dividing the amount of deviation Δ= _−S by _S from the series resonance frequency _S of the crystal resonator, the well-known equation (5) is obtained. Furthermore, in this formula (5),
C _L is the entire series capacitance of the circuit on the compensation circuit side. △ / _S = C _O /2γ (C _O + C _L …(5) Now, in order to perform temperature compensation, it is necessary to change C _L in this equation according to the temperature in a direction that cancels out the temperature characteristics of the crystal resonator. However, the AT used in the present invention
The frequency-temperature characteristics of a plate crystal resonator are shown in Figure 6.
A resonator in which all of the characteristic curves 61 to 64 of the AT plate crystal resonator are within the diagonal lines is suitable. The reason for this is that X _S(T) /
As can be seen from the X _P curve, this is because the reactance changes with negative characteristics with respect to temperature changes (the capacitance value has positive characteristics), and this X _S(T) /
Applying X _P to C _L in equation (5), the temperature compensation of the present invention increases the oscillation frequency in low-temperature areas, and conversely works only in the direction of lowering it in high-temperature areas. . The frequency deviation amount at temperature T is △ _(T) / _S ,
When the load capacity is set as C _L(T) and equation (5) is transformed, C _L(T) = (1/2γ・△ _(T) / _S −1) C _O …(6). Furthermore, let the frequency deviation amount at the reference temperature T _O be △ _(O) / _S = C _O /2γ (C _O + C _L(O) ), and the load capacity at that time be C _{L (O)} , and the deviation amount at the temperature T. The difference between the deviation amount at the reference temperature T _O is called the compensation frequency amount, and if this is set as M _(T) , then M _(T) = △ _(T) / _S - △ _(O) / _S △ _(T) ／ _S ＝M _(T) ＋△ _(O) ／＝M _(T) ＋C _O ／2γ(
C _O +C _L(O) ...(7) The second term on the right side of equation (7) becomes an equation that does not include _S. Next, substituting equation (7) into equation (6), C _L(T) = {C _O +C _L(O) /2γM _(T) (C _O +C _L(O) +C _O -1}
C _O ...(8) This equation (8) is the load capacity (compensation capacity) C _L(T) required to obtain the compensation frequency amount M _(T) at the temperature T.
This is the formula to find. On the other hand, if equation (4) is transformed and expressed as C _S(T) , C _S(T) = (1+b ² /β _(T) ² ) C _P (9). Here, using equations (8) and (9), in order to calculate the compensation circuit conditions of the present invention in the oscillation circuit of FIG. 5, that is, the element values R _{P (T)} and C _P , it is necessary to Simply replace one of the two compensation circuits with a fixed capacitor,
In other words, it is easy to analyze the equivalent circuit in FIG. 7 from the perspective of Ca in FIG. in this case,
As mentioned above, one of the compensation circuits performs calculations by limiting the compensation range to the low-temperature section below room temperature, and the other to the high-temperature section above room temperature. Even if we carefully examine the compensation characteristics of In Figure 7, the relationship between C _S(T) and C _L(T) is calculated as follows: C _L(T) = CaC _S(T) /Ca+C _S(T) ∴C _S(T) = −C _{L(T )} Ca／C _L(T) －Ca …(10) According to equations (8) and (10), the compensation capacitances of the crystal resonator required at temperatures T ₁ and T ₂ are C S (T1) and C _{S (T1)} , respectively.
If C _S(T2) is found, the following equation is established from equation (9). C _S(T1) = (1+b ² /β ₁ ² )C _P …(11) C _S(T2) = (1+b ² /β ₂ ² )C _P …(12) These equations (11) and (12) By solving for C _P and b, the required element values R _{P (O)} and C _P can be obtained as shown in the following equation. ∴C _P =C _S(T2) β ₂ ² -C _S(T1) β ₁ ² /β ₂ ² -β ₁ ² ...(14) ∴R _P(O) =X _C /b=1/ωC _P b (15) Now, using these calculation formulas, we will actually calculate the element values of the compensation circuit required to compensate for curve A shown in FIG. 8. Note that curve A in FIG. 8 is an example of actually measured temperature characteristics of a crystal resonator at a frequency of 12.8 MHz. First, when designing the low-temperature section compensation circuit, we set the temperature to 0℃.
Let T ₁ and temperature -30°C be T ₂ , and the above-mentioned compensation frequency amount M _(T) at T ₁ and T ₂ can be calculated from curve A in FIG. 8 as M ₁ =+4.3×10 ^-6 and M ₂ = +26×10 ^-6 . Assuming that a thermistor with a B constant of 3000 is used in the low-temperature compensation circuit, the resistance ratio β _(T) of the thermistor is determined from Fig. 9 as β ₁ = 2.5 and β ₂ = 9.8, respectively.
(Figure 9 is a graph of the temperature versus resistance ratio of the thermistor). Furthermore, using practical values such as γ = 217 for the crystal oscillator to be compensated and C _O = 4.25PF for C _O , and setting the reference temperature point T _{O =} +25°C, at this time C _L(O) Let C _L(O) = 100PF. Furthermore, the frequency is
Set to 12.8MHz. Table 1 summarizes these numerical values and the calculated element values C _P and R _{P (O)} .
Note that the high temperature compensation circuit is simplified as a fixed capacitor Ca as described above, and is calculated as Ca=101PF. Next, we will design the high temperature section compensation circuit in the same way, but in the case of the high temperature section, the temperature +25℃ is T ₁
If the temperature +70℃ is used as T ₂ , there will be less error in calculations. The reason why T ₁ is made equal to the reference temperature point T _O is that when C _{L ( O)} = 100PF, C _{S (O)} of the low-temperature section compensation circuit is expressed in equation (9) as shown in Table 1. C _P , b and β=1
Substituting and calculating, C _S(O) = 9602PF,
Since C _L(O) ≪C _S(O) , C _L(O) is the value of the high temperature section compensation circuit.
This is because it is mostly determined by C _S(O) . Accordingly
M ₁ =0 Therefore, in this case, β ₁ =1, and as in the design of the low temperature section compensation circuit, M ₂ = -12×10 ^-6 , β ₂
=0.21. The B constant of the thermistor used in the high temperature compensation circuit is set to B=3550〓, and the calculation is performed with Ca=9602PF fixed as the low temperature compensation circuit. Table 1 summarizes these numerical values and calculated results.

[Table] Using the element values obtained as above, −30 to
The M _(T) obtained in the temperature range of +80°C is summarized in Table 2, and the results of compensating for the high and low temperature parts of curve A in Figure 8 using these compensation circuits as in the present invention are shown in the curve in the same figure. It was written as B.

[Table] As shown in curve B in Figure 8, the compensation method according to the present invention improves the frequency-temperature characteristics of the AT plate crystal resonator by ±1.5× over a wide temperature range of -30 to +80°C.
Has the ability to compensate below 10 ^-6 . This is a temperature compensation effect that cannot be achieved by the compensation circuit shown in FIG. 1 alone. The feature of the present invention is that by connecting two independent compensation circuits in series and directly connecting them to the crystal resonator, a temperature compensation effect can be obtained in both the low temperature section and the high temperature section. It is in. The design condition for making the high and low temperature compensation operate independently of each other is that the ratio of the reactance of the parallel capacitor to the resistance value of the thermistor at room temperature, that is, b in equation (13), is b>6, and b<0.1 in the high temperature section compensation circuit. The reason is X _S(T) / in Figure 4.
Explaining this using the curves b = 0.1 and b = 7 of the X _P curve, when b = 0.1, there is little change in the reactor in the low temperature section, and when b = 7, there is little change in the reactor in the high temperature section, so they do not affect each other's oscillation frequency. It is. This becomes even clearer when looking at M _(T) in the low temperature and high temperature sections of Table 2. Next, a method for adjusting the sensitivity of the compensation circuit will be explained. In the compensation circuit of the present invention shown in Fig. 2, the γ and _CO of the crystal resonator may change due to manufacturing variations, and the temperature characteristics may vary depending on the cut angle of the diaphragm, as shown in Fig. 6. , it is necessary to select R _P and C _P individually and design a compensation circuit each time, and this is not suitable for the production of crystal oscillators, which require a particularly low price. To compensate for this, in order to adjust the sensitivity of the thermistor, an adjustment resistor is inserted in parallel with the thermistor in the low-temperature compensation circuit, and an adjustment resistor is inserted in series with the thermistor in the high-temperature compensation circuit. do. FIG. 10 shows a compensation circuit in which the resistor is inserted. It is well known that the equivalent resistance of a semiconductor device such as a variable resistor or a PIN diode can be substituted for these adjustment resistors. By inserting such an adjusting resistor, it is possible to make a large sensitivity adjustment at low or high temperatures, while having almost no effect near room temperature. The reason why the method of inserting the sensitivity adjustment resistor is different in the low-temperature section and the high-temperature section can be explained using the X _S(T) /X _S curve in Figure 4. By inserting it, b increases and the sensitivity decreases, but since the reactance is saturated above room temperature, there is little change in frequency. On the other hand, in the high temperature section (b = 0.1 curve), by inserting a resistor in series with the thermistor, b
This is because the reactance is saturated at temperatures below room temperature, so there is little change in frequency, although the sensitivity decreases. It is extremely useful industrially to be able to independently adjust the sensitivity of the thermistor at low and high temperatures. Now, C _S(T) of the low-temperature part compensation circuit (part L) and the high-temperature part compensation circuit (part H) in Figure 10.
If we calculate each in the same way as we derived equation (9), we obtain equations (16) and (17). C _S(T) = {1+(a+β _(T) ² )/β _(T) ²・b ² /a ² }C _P
…(16) C _S(T) = {1+b ² /(a+β _(T) ² )}C _P …(17) However, R _C /R _P(O) = a. Therefore, b and which are appropriately designed and selected in advance
Any desired C _S(T) by using C _P and adding R _C to it
The value of a to obtain is obtained from equations (16) and (17), respectively. becomes. Within the range that satisfies the conditions of C _S(T) C _P and a>0, the value of R _C for sensitivity adjustment is determined by equation (18) in the low temperature section and equation (19) in the high temperature section. It turns out. The practical way to use this R _C is to substitute a variable resistor for this R _C and adjust the variable resistor so that the oscillation frequency at a temperature T ₂ matches the oscillation frequency at a reference temperature T _O. It's both reliable and easy. In Table 3, the amount of compensation frequency M _(T) when R _C is added to the compensation circuit designed previously (Table 1) is listed for each of the above-mentioned a values. When looking at M _(T) in Table 3, it can be seen that the sensitivity is greatly adjusted in the low temperature section (or high temperature section) by the adjustment resistor inserted in parallel or series with the thermistor, and that the sensitivity is greatly adjusted at +25℃.
It can be seen that this effect hardly appears in the high temperature area above (or the low temperature area below +25°C).

【table】

[Table] Finally, stabilization of the output level of the device of the present invention will be explained. FIG. 11 is a specific circuit diagram of the present invention. If the resistor _R3 is shorted, this circuit becomes a curved collector-grounded Colpitts circuit. When taking out the oscillation output from the emitter of the transistor TR through the capacitor _C4 and from the output terminal OUTB as conventionally done in this circuit, the change in the series resistance value R _S(T) of the compensation circuit described above is directly This is not preferable because it affects the oscillation level. The R _S(T) value is calculated under the conditions of the element values listed in Table 1.
Table 4 shows the results calculated using equation (1) in the temperature range of -30 to +80°C. When looking at the overall R _S(T) value shown in Table 4, at -30°C, it is 1.32 times that at +25°C, +80
℃, it is 2.85 times that at +25℃, and therefore the output level fluctuates greatly as shown by curve B in FIG.

[Table] However, as a solution to this problem, as shown in Figure 11, a resistor _R3 is placed and the oscillation output is connected to the output terminal from the collector of the transistor TR via the capacitor _C5 .
When taking out the signal from OUT A, there is almost no fluctuation in the output level due to the change in R _{S (T)} mentioned above, and the output level becomes extremely stable as shown by curve A in FIG. 12. This is because the output in this case utilizes the saturation effect of the collector output when the base of the transistor is overloaded. (It is believed that the base input in the oscillation circuit of FIG. 11 during steady oscillation is an excessive input.) As described above, this invention uses an AT board with an extremely simple circuit configuration. This invention has the feature of extremely strongly improving the frequency-temperature characteristics of a crystal oscillator, over a wide temperature range of -30 to +80°C, and its effects are remarkable, making it an extremely useful invention industrially. In addition, as mentioned above, the variable resistor R _C of the present invention
This can be constructed from semiconductor resistance elements such as diodes and transistors. At this time, the resistance value of those resistive elements is the DC current value (to be passed between the base and emitter of the diode or transistor) or the value of the direct current (to be applied to the gate of the FET).
It can be changed by the DC voltage value.
(Using a PIN type diode achieves good results). Controlling the compensation of the frequency-temperature characteristics of a crystal oscillator using such direct current and voltage is of interest because it suggests the possibility of adding indirect temperature compensation.

[Brief explanation of drawings]

FIG. 1 shows a temperature compensation circuit conventionally known for compensating for low-temperature parts, and FIG. 2 shows a temperature compensation circuit of the present invention.
Figure 3 is a circuit equivalently converted into a series version of Figure 1.
The figure is a graph that calculated R _S(T) and X _S(T) in Figure 3, and
The figure is an equivalent circuit diagram of the oscillation circuit of the present invention, and Figure 6 is
A graph of temperature characteristics depending on the cutting angle of an AT plate crystal resonator, Fig. 7 is an equivalent circuit for designing a compensation circuit, Fig. 8 is a graph showing the temperature characteristics of a crystal resonator and characteristics after compensation, Fig. 9 is a graph showing the temperature characteristics of the thermistor, Fig. 10 is a compensation circuit in which a compensation sensitivity adjustment resistor is inserted, Fig. 11 is a specific circuit diagram when the present invention is implemented, and Fig. 12 is the temperature characteristics of the oscillation output. A graph of actual measurements is shown. Y...Crystal resonator, R _P(T) ...Thermistor (and its resistance value), C _P ...Capacitor, R _C ...Variable resistor, C _L
...Load capacity.

Claims (1)

[Claims] 1. In a crystal oscillator including an AT plate crystal oscillator and an amplifier, the crystal oscillator is connected in series to the crystal oscillator, both of which are composed of a parallel circuit of a capacitor and a thermistor having negative temperature characteristics. Two temperature compensation circuits, one for low-temperature part compensation and one for high-temperature part compensation, are connected and inserted in series, and the temperature is the ratio of the capacitor value to the equivalent series capacitance value of the compensation circuit. In the low-temperature compensation circuit, the amount of change is small at temperatures above room temperature, but increases at low temperatures, and in the high-temperature compensation circuit, the amount of change is small at temperatures below room temperature, but at high temperatures. A temperature compensated crystal oscillator, characterized in that the values of the capacitor and thermistor are set such that the values of the capacitor and thermistor become larger. 2. By selecting the ratio of the reactance of the capacitor of the temperature compensation circuit and the resistance value of the thermistor at room temperature to 6 or more in the low temperature compensation circuit and 0.1 or less in the high temperature compensation circuit, 2. The temperature compensated crystal oscillator according to claim 1, wherein the temperature compensated crystal oscillator is set so that the change in reactance of the other temperature compensation circuit is substantially constant in the compensation region. 3 For adjusting the compensation sensitivity of the temperature compensation circuit,
2. A temperature compensated crystal oscillator according to claim 1, wherein a resistor is inserted in parallel to the thermistor in the low temperature compensation circuit, and a resistor is inserted in series with the thermistor in the high temperature compensation circuit. 4. A temperature compensated crystal oscillator according to claim 3, wherein the resistor is a variable resistor. 5. The temperature-compensated crystal oscillator according to claim 3, wherein the resistor is a semiconductor resistance element whose equivalent resistance value changes with direct current or direct current voltage. 6. The temperature compensated crystal oscillator according to claim 5, wherein the semiconductor resistance element is a diode. 7. The temperature compensated crystal oscillator according to claim 5, wherein the semiconductor resistance element is a transistor. 8. A patent characterized in that, in a crystal oscillator that uses a transistor as the amplifier and whose collector is equivalently grounded, a resistor is inserted between the collector and the ground, and the oscillation output is derived from the collector. A temperature compensated crystal oscillator according to any one of claims 1 to 7.