JP2564387Y2 - 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 which enables a temperature-compensated range of an AT-cut crystal resonator having a large characteristic curve variation.

[0002]

2. Description of the Related Art For an AT-cut crystal unit,
As shown in FIG. 4, an amplifier 42 is connected to one end of an AT-cut crystal oscillator 41, and a capacitor and a negative temperature characteristic are connected to the other end as a temperature-compensated crystal oscillator capable of temperature compensation from a low-temperature region to a high-temperature region. A temperature-compensated crystal oscillator in which a low-temperature region compensating circuit 43 and a high-temperature region compensating circuit 44, which are connected in parallel with a thermistor, is already known (see Japanese Patent Publication No. 64-1969).

As a result, a crystal oscillator capable of performing stable temperature compensation in a wide temperature range from a low temperature region to a high temperature region is achieved.

[0004]

2. Description of the Related Art However, the above-described crystal resonator which can be temperature-compensated by the temperature-compensated crystal oscillator has its natural frequency-temperature characteristic with respect to a reference point O as shown by V, W and X in FIG. The characteristic exists only in the first quadrant and the third quadrant, that is, the characteristic is limited to the crystal oscillator having the characteristic of the monotonically increasing cubic curve. For example, the maximum value and the minimum value of the cubic curve are in the second quadrant or the third quadrant. 4
The characteristics Y and Z in the quadrant were regarded as the quartz oscillators not to be compensated.

For this reason, in order to obtain a quartz oscillator having the above-described monotonically increasing cubic curve characteristic, a quartz oscillator cut at a special angle from a quartz substrate is used. There was a problem.

The present invention has been devised in view of the above-mentioned problem, and has as its object that the maximum value and the minimum value of the frequency-temperature characteristic curve of the cubic function are in the second quadrant or the fourth quadrant. This is a temperature-compensated crystal oscillator that can perform temperature compensation in a wide temperature range from a low temperature range to a high temperature range even in a general crystal resonator.

[0007]

Concrete means for solving the problems The concrete means proposed by the present invention for solving the above-mentioned problems is that the horizontal axis represents the temperature, the vertical axis represents the frequency, the reference temperature and the reference temperature. An amplifier is provided at one end of an AT-cut crystal resonator having a cubic curve characteristic in which a maximum value and a minimum value of a frequency temperature characteristic are in a second quadrant and a fourth quadrant with respect to coordinates having a frequency as an origin. A third rotation in which the local maximum value and the local minimum value become the third quadrant and the first quadrant, respectively, by being rotated counterclockwise around the origin of the tertiary characteristic curve of the crystal resonator in series with the other end of the crystal resonator. Temperature compensating capacitor that corrects to have the curve characteristic of, a low-temperature region compensating circuit in which a capacitor and a thermistor having a negative temperature characteristic are connected in parallel, and a capacitor and a thermistor having a negative temperature characteristic are connected in parallel. High-temperature region compensation circuit connected to The is a temperature compensated crystal oscillator, characterized in that the respective connections.

[0008]

According to the temperature compensated crystal oscillator having the above configuration,
The slope of the natural frequency-temperature characteristic curve of the crystal unit is corrected to a monotonically increasing cubic curve by a temperature compensation capacitor connected to the other end of the crystal unit. The temperature compensation circuit in which the low-temperature region compensation circuit and the high-temperature region compensation circuit are connected in series to the crystal unit having the monotonically increasing frequency-temperature characteristic and the temperature compensation capacitor is performed.

As a result, even in the case of a crystal unit which could not be temperature-compensated in a wide temperature range in the past, temperature compensation can be easily performed, and it is not necessary to cut the crystal substrate at a special angle. Its practicality is extremely large.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a temperature compensated crystal oscillator according to the present invention. FIG. 1 is a circuit diagram of a temperature compensated crystal oscillator.

In FIG. 1, reference numeral 1 denotes an AT-cut crystal resonator, reference numeral 2 denotes an amplifier circuit, reference numeral 3 denotes a temperature compensation capacitor, reference numeral 4 denotes a low-temperature region compensation circuit, and reference numeral 5 denotes a high-temperature region compensation circuit.

The quartz resonator 1 has electrodes formed on a quartz side cut in the AT direction from a rough quartz crystal and has a fundamental frequency of 1 MHz to 30 MHz.

The amplifier circuit 2, which is connected to one end of the crystal resonator 1, the transistor Tr, a capacitor C _1, C _2, C _3, and a resistor R ₁ to R _4. That amplifies the oscillation of the amplifier circuit 2, crystal oscillator 1, the capacitor C _1, C ₂ of the amplifier circuit 2, which forms one of the input and output capacitor components of the crystal oscillator 1 in Colpitts oscillation circuit.

The temperature compensating capacitor 3 is a crystal oscillator 1
Is connected to the other end of the crystal oscillator 1 and has a natural frequency −
The temperature characteristic is corrected to a frequency-temperature characteristic having a predetermined slope. If the temperature coefficient and the capacitance of the temperature compensating capacitor 3 are appropriately set in accordance with the natural frequency-temperature characteristics of the crystal unit 1, the frequency-temperature characteristics in which the crystal unit 1 and the temperature compensating capacitor 3 are connected in series are obtained. Can be corrected to a monotonically increasing cubic curve passing through only the first and third quadrants with respect to the reference point.

The low temperature region compensation circuit 4 is configured by connecting a capacitor C ₄ , a negative characteristic thermistor Th ₁ and a variable resistor R ₅ in parallel. By the low temperature region compensation circuit 4,
Low temperature region of the crystal unit 1 and the temperature compensating capacitor 3;
For example, it functions to correct the slope of the frequency-temperature characteristic of 20 ° C. or less. That is, the characteristic is monotonically increased in the third quadrant of FIG.

The high temperature region compensation circuit 5 is configured by connecting a capacitor C ₅ and a negative characteristic thermistor Th ₂ in parallel. The high-temperature region compensation circuit 5 functions to correct the inclination of the frequency-temperature characteristics of the crystal resonator 1 and the temperature compensating capacitor 3 in the high-temperature region, for example, 20 ° C. or more. That is, the flattening is performed by decreasing the inclination of the monotonous increase existing in the first quadrant of FIG.

According to the above-described temperature-compensated crystal oscillator, first, the cubic curve of the natural frequency-temperature characteristic of the crystal unit 1 is corrected to a monotonically increasing cubic curve by the temperature compensating capacitor 3. In this step, compensation for the low-temperature region and compensation for the high-temperature region are performed. That is, in the characteristic diagram of FIG. 2, characteristics such as characteristics Y and Z are converted into characteristics V, W and X, and in this state, compensation is performed from a low temperature region to a high temperature region.

Next, the setting of the temperature compensating capacitor 3 for correcting the crystal oscillator 1 to apparently monotonically increasing frequency-temperature characteristics will be described.

First, as a setting procedure, a series resonance frequency fs, an equivalent parallel capacitance C _O , and an equivalent parallel capacitance C ₁ of an equivalent circuit of the crystal unit ₁ are obtained. The coefficient a of the cubic term of the cubic equation approximated from the frequency-temperature characteristic of the crystal unit 1, the coefficient b of the second order term, the coefficient c of the first order term, and the reference temperature T _O are obtained. The load capacitance C _L0 of the crystal unit 1 at the reference temperature T _O is determined. As frequency variation with temperature of the crystal resonator 1 becomes zero, obtaining the predetermined temperature characteristic of the load capacitance C _L of the temperature compensating capacitor 3. The temperature, load capacity, and slope at which the characteristic has the minimum and maximum points are determined. At a reference temperature T _O , a series circuit of a capacitor having a temperature coefficient kc with a capacitance value of C _T0 and a capacitor having a capacitance value of C _A with a temperature coefficient of zero has a capacitance value and a temperature gradient at a temperature determined by: Are equal, the capacitance value C _T0 and the temperature coefficient k
Determine c. For a new load capacitance C _L obtained by subtracting the temperature characteristic from the desired value of the previous load capacitance C _L.

Generally, the oscillation frequency of a crystal oscillator is expressed by the following equation (1).

[0021]

(Equation 1)

The temperature characteristic of the crystal unit is represented by the series resonance frequency fs _(T) , and it is assumed that C _O and C ₁ are invariant with respect to temperature. In general, the frequency-temperature characteristics of an AT-cut quartz resonator are approximated by a cubic curve (cubic equation e), so that the series resonance frequency fs _(T) of the ambient temperature T is equal to the reference temperature T
If it is _O , it is expressed by equation (2). Note that fs ₍₀₎ is the resonance frequency at the reference temperature T _O.

[0023]

(Equation 2)

[0024]

(Equation 3)

Here, a, b and c are proportional constants.

By substituting (2) for (1), the following (4)
It becomes an expression.

[0027]

(Equation 4)

Next, the desired temperature characteristics of the load capacity will be considered.

[0029] In (4), at ambient temperature _{T = T O, fs (T} ) = f (0), because it is e = 0, f ₍₀₎ is expressed by equation (5).

[0030]

(Equation 5)

Even if the ambient temperature T fluctuates, there is no frequency temperature change. That is, C is such that fs _(T) = f ₍₀₎ is constant.
If L _(T) is changed, the temperature compensation of the crystal unit is ideally performed. The load capacitance CL _(T) temperature characteristic value at this time is a desired value to be obtained. When the calculation is performed as Expression (4) = Expression (5), Expression (6) is obtained.

[0032]

(Equation 6)

Differentiating equation (6) with temperature T gives equation (7).

[0034]

(Equation 7)

The extreme value (maximum value or minimum value) of the equation (7) is obtained. When the equation (2) is differentiated twice by T and calculated as an extreme value, the equation (9) is obtained.

[0036]

(Equation 8)

[0037]

(Equation 9)

In equation (9), T is set to zero and T is set to T '.
Asking.

[0039]

(Equation 10)

Here, T 'indicates a temperature at which the rate of change of the frequency with respect to the temperature becomes maximum or minimum.

By substituting this T 'into the differential equation of T in equation (3), _eXN is expressed by equation (11).

[0042]

[Equation 11]

Next, equation (10) is substituted into equations (6) and (7) to calculate the load capacitance CL _{(T ')} and its slope dCL _(T') / dT at the extreme temperature. .

[0044]

(Equation 12)

[0045]

(Equation 13)

[0046] That is, in the load capacitance CL _O becomes crystal oscillator at a reference temperature T _O, to zero the temperature variation of the frequency,
The load capacity as shown in the equation (6) is required, and the extreme value of the temperature change rate is the equation (13), and the temperature is (10)
At T ′ in the equation, the capacitance value is given by equation (12).

Next, the inclination correction by the temperature compensating capacitor 3 will be described.

The temperature coefficient of the temperature compensating capacitor 3 is Kc
Then, the temperature characteristic CT _(T) becomes the equation (14).

[0049]

[Equation 14]

Here, the temperature compensating capacitor 3 is a capacitor having a temperature coefficient Kc and a fixed capacitor C having a temperature coefficient of zero.
Considering the series circuit of A, and considering the total capacitance as the load capacitance CL _(T) of the crystal unit 1, the expression (15) is obtained.

[0051]

(Equation 15)

Further, the equation (15) is differentiated by T.

[0053]

(Equation 16)

The previously obtained equation (10) is replaced by (15), (1)
6) Substitute in equation.

[0055]

[Equation 17]

[0056]

(Equation 18)

M ₁ , M _{2 in} equations (12) and (13) and (1
7) Kc and CT ₍₀₎ are obtained by setting equation (18) to be equal.

[0058]

[Equation 19]

[0059]

(Equation 20)

The equation (19) is substituted into the equation (20).

[0061]

(Equation 21)

The equation (19) is substituted into the equation (21).

[0063]

(Equation 22)

The equation (19) is substituted into the equation (22).

[0065]

(Equation 23)

By using a temperature compensating capacitor having a capacitance value equal to or smaller than CT ₍₀₎ given by the equation (22) and having a temperature coefficient equal to Kc given by the equation (23), Between the capacitor and the temperature compensating capacitor 3-
The cubic curve of the frequency characteristic increases monotonically, and the reference temperature T _O
Is the origin, and a curve passes through the first quadrant and the third quadrant.

As described above, after the temperature-frequency characteristic of the crystal unit 1 is corrected to a temperature-frequency characteristic curve passing through the first quadrant and the third quadrant by connecting the temperature compensating capacitor 3, the Japanese Patent Publication No. 64-1969 is disclosed. The temperature is compensated by the method disclosed in (1). For example, the characteristics of a crystal resonator. Series resonance frequency: 16.587 MHz. Equivalent series capacitance: 15.7 fF. Equivalent series capacitance: 4 pF. Third-order curve of frequency-temperature characteristics: a = 1.049 × 10 ⁻¹⁰ b = −5.43 × 10 ⁻¹⁰ c = −3.031 × 10 ⁻⁷ Reference temperature T _O = 25 Capacitance value 33.331 pF as compensation capacitor Temperature coefficient Kc = −1848.94 PPM / ° C. Thermistor reference resistance 7 as low temperature region temperature compensation circuit 4 The temperature compensation of the crystal oscillator was performed with the thermistor reference resistance 957.532Ω as the thermistor reference resistance 957.532Ω as the high temperature region temperature compensating circuit 5 and with the parallel characteristic 99.5266 pF as the high temperature region temperature compensation circuit 5.

FIG. 3 shows the result.

In the figure, a line S represents frequency-temperature characteristics after compensation, and a line T represents frequency-temperature characteristics before compensation.
Line U is the compensation value.

As is apparent from the line T in FIG. 3, even if the crystal unit has frequency-temperature characteristics passing through the second and fourth quadrants with the reference temperature of 25 ° C. as the origin, the line S
As described above, after the temperature compensation, compensation can be performed within a variation of ± 1 PPM in a temperature range of −30 to + 75 ° C.

As described above, according to the present invention, there is provided a crystal resonator having a frequency-temperature characteristic that passes through the second and fourth quadrants with reference to the reference temperature at which temperature compensation has conventionally been difficult. However, by appropriately setting the characteristics of the temperature compensating capacitor 3, the temperature can be easily compensated, and even with the ordinary crystal resonator 1, the temperature can be compensated over a wide temperature range.

[0072]

As described above, according to the present invention, a temperature-compensated crystal oscillator capable of performing temperature compensation in a wide temperature range from a low temperature region to a high temperature region even in a general crystal resonator.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a temperature compensated oscillation circuit according to the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a temperature and a frequency of a crystal resonator.

FIG. 3 is a characteristic diagram showing a degree of compensation by the temperature compensated oscillation circuit of the present invention.

FIG. 4 is a circuit diagram of a conventional temperature compensated oscillation circuit.

[Explanation of symbols]

 1, 41 crystal oscillator 2, 42 amplifying circuit 3 capacitor for temperature compensation 4, 43 low-temperature region compensation circuit 5, 44 high-temperature region compensation circuit

Claims (1)

(57) [Scope of request for utility model registration] The temperature is represented on the horizontal axis, the frequency on the vertical axis, and the reference temperature.
Degrees and the frequency at the reference temperature as the origin.
On the other hand, the maximum value and the minimum value of the frequency temperature characteristic are in the second quadrant,
An amplifier is provided at one end of an AT-cut crystal resonator having a third-order curve characteristic serving as a fourth quadrant, and the origin of a third-order characteristic curve of the crystal resonator is serially connected to the other end of the crystal resonator. A temperature compensating capacitor which is rotated left to the center to correct the local maximum value and the local minimum value so as to have a cubic curve characteristic of a third quadrant and a first quadrant, respectively; a capacitor and a thermistor having a negative temperature characteristic; Temperature-compensated crystal oscillator characterized in that a low-temperature region compensation circuit is connected in parallel with a capacitor, and a high-temperature region compensation circuit is connected in parallel with a capacitor and a thermistor having a negative temperature characteristic. .