JP2002076772A - Crystal oscillator with temperature compensation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a miniaturized temperature compensated oscillator having enhanced noise characteristic with remarkably small in plan shape suitable for surface mounting. SOLUTION: A temperature compensated crystal oscillator is constituted of; a crystal oscillator 5 having a crystal vibrator element 4 and an oscillation circuit excluding the crystal vibration element; a frequency regulation mechanism 16 for regulating oscillation frequency of the above mentioned crystal oscillator; and a temperature compensation circuit 2 having a temperature compensation element including temperature sensitive resistance element of which resistance value varies with temperature so as to flatten the frequency temperature characteristic of the crystal oscillator. A voltage variable capacitance element 3 is inserted in an oscillation closed-loop of the crystal oscillator. At least the temperature compensation circuit, the oscillation circuit excluding the crystal vibration element, and the frequency regulation mechanism are integrated into a signal IC chip. The frequency regulation mechanism is configured with a memory circuit 20, and a frequency regulation voltage generator 19. The oscillation frequency is regulated by applying to the voltage variable capacitance element a frequency regulation voltage generated by the frequency regulation voltage generator based on a signal from the memory circuit.

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 for surface mounting (hereinafter referred to as a temperature-compensated oscillator) using a temperature-sensitive resistance element whose resistance value changes depending on temperature as temperature detecting means. The present invention relates to the above technical field, particularly to a temperature-compensated oscillator suitable for downsizing with good noise characteristics.

[0002]

2. Description of the Related Art Temperature-compensated oscillators are widely used in electronic devices used in dynamic environments, such as mobile radio devices, because they compensate for the oscillation frequency that changes with temperature and stabilize them. Have been. Then, based on the miniaturization of electronic equipment as represented by recent mobile phones, a one-chip IC (LS) in which an oscillation circuit and a temperature compensation circuit are integrated
There is a temperature-compensated oscillator in which I) and a crystal blank are housed in a container and used for surface mounting.

(Example of Prior Art) FIG. 11 is a schematic block circuit diagram of a temperature compensated oscillator for explaining a conventional example. The temperature compensation oscillator includes a voltage control oscillator 1 and a temperature compensation circuit 2. The voltage controlled oscillator 1 has a voltage variable capacitance element 3 inserted in an oscillation closed loop of a crystal oscillator. The crystal oscillator includes an oscillator circuit 5 including a crystal oscillator 4 and a feedback amplifier (not shown) other than the crystal oscillator 4. Then, the frequency temperature characteristic is defined as a cubic curve having a local maximum value on the low temperature side, an inflection point at normal temperature, and a local maximum value on the high temperature side due to the cutting angle of the crystal oscillator (here, AT cut) (No. Curve a in FIG. 12).

The temperature compensating circuit generally includes a cubic function voltage generating circuit 6, a storage circuit 7, and a temperature sensor 8. Briefly, the cubic function voltage generation circuit 6 generates a compensation voltage Vs (T) responsive to the frequency temperature characteristic of the crystal oscillator described above. The compensation voltage Vs (T) is set by, for example, the following equation (1). The coefficients α, β, and γ of the respective orders are determined by temperature compensation data after actually measuring the frequency temperature characteristics of the crystal oscillator. Here, T0 is the inflection point temperature (about 27 ° C.), and T is the ambient temperature. Vs (T) = α (T−T0) 3 + β (T−T0) + γ (1)

[0005] The storage circuit 7 stores temperature compensation data, for example, as a PROM. The temperature compensation data is digitally written from the write terminals a to n including the control terminals. The temperature sensor 8 generates a detection voltage (temperature detection signal) in response to an ambient temperature by using the temperature characteristics of a forward drop voltage in a PN junction region provided inside an IC chip, for example.

In these devices, the compensation voltage Vs (T) depending on the ambient temperature is obtained by the temperature detection signal from the temperature sensor 8.
Is generated and applied to the voltage variable capacitance element 3 of the voltage controlled oscillator 1. The capacitance between terminals of the voltage variable capacitance element 3 changes according to the compensation voltage Vs (T). Therefore, since the series equivalent capacitance (so-called load capacitance) on the circuit side as viewed from the crystal unit 4 changes, the oscillation frequency also changes in response to the temperature (curve B in FIG. 12), and the temperature is eventually compensated. .

The coefficient (constant term) γ in equation (1) controls the oscillation frequency at normal temperature (strictly, the inflection point temperature). In the figure, reference numeral 9 is a high-frequency blocking resistor, Vcc is a power supply, Vo
ut is an oscillation output.

In such a temperature-compensated oscillator, the voltage-controlled oscillator 1 except for the crystal oscillator 4 and the temperature-compensating circuit 2 are integrated on an IC chip 10 indicated by a chain line. Therefore, the temperature compensated oscillator is basically composed of the crystal oscillator 4 and the IC
The chip 10 has two elements. Thereby, a significant size reduction can be achieved.

Generally, one end of a crystal piece 4a forming the crystal unit 4 is fixed (held) by a conductive adhesive 12 to the bottom surface of one concave portion of a surface mount container 11 made of a laminated ceramic, and is subjected to, for example, seam welding. The cover 13 is joined and hermetically sealed. Then, the IC chip 10 is face-down bonded to the bottom of the other concave portion by ultrasonic thermocompression bonding (FIG. 13). Alternatively, the IC chip 10 is held on the bottom surface of the concave portion of the surface mount container 11 and the crystal blank 4a is held and sealed in a stepped manner (FIG. 14).

Reference numeral 14 in the figure denotes a metal ring for seam welding, and reference numeral 15 denotes a filler for protection. A large-capacity capacitor, such as a bypass capacitor between the power supply and the ground, which is difficult to make into an IC, is accommodated as necessary.

[0011]

[Problems to be Solved by the Invention]
However, in the temperature compensated oscillator having the above configuration, the temperature characteristic of the forward drop voltage in the PN junction region provided inside the IC chip as described above is used as the temperature detecting means of the temperature compensation circuit. That is, the temperature detection signal is formed by using the temperature characteristic with a small voltage change with respect to the temperature.
Therefore, the noise component generated inside the IC chip becomes relatively large with respect to the detection signal, and the noise characteristics are degraded. In addition, there is a problem that current consumption increases because a weak detection signal is amplified and controlled.

(Object of the Invention) It is an object of the present invention to provide a small temperature-compensated oscillator which is excellent in noise characteristics and has a small planar outer shape, especially for surface mounting.

[0013]

According to the present invention, a temperature-sensitive resistance element employed in an existing temperature compensating circuit, for example, a thermistor having a negative temperature coefficient is used as temperature detecting means. That is, attention is paid to the point that the oscillation frequency is adjusted by the constant term γ of the cubic function voltage generation circuit.

(Solution) According to the present invention, there is provided an oscillation circuit including a voltage variable capacitance element inserted into an oscillation closed loop of a crystal oscillator, and excluding at least a temperature compensation circuit including a temperature sensing element and a crystal resonator, and a frequency adjustment mechanism. Are integrated on an IC chip. The frequency adjustment mechanism is formed from a storage circuit and a frequency adjustment voltage generation circuit, and the oscillation frequency is adjusted by applying a frequency adjustment voltage from the frequency adjustment voltage generation circuit based on a signal from the storage circuit to the voltage variable capacitance element. This is defined as a first solution (claim 1).

[0015] Further, the crystal piece forming the crystal resonator and the first
A second solution is that the IC chip of the solution is housed in a surface mount container, and a temperature compensation circuit (temperature compensation element) is arranged in a cutout provided on the back surface of the surface mount container. .

[0016]

In the present invention, a temperature-sensitive resistor is used as the temperature detecting means of the temperature compensating circuit as before, so that the level of the temperature detecting signal is relatively increased with respect to the internal noise of the IC chip. In addition, since the frequency adjustment mechanism is integrated in the IC chip, a capacitor for adjustment is not required (first example).
Solution).

Further, since the temperature compensating element is arranged in the notch provided on the back surface of the surface mount container, the planar outer shape can be reduced (second solution). Hereinafter, embodiments of the present invention will be described by taking two different compensation systems (claims 2 and 3) as examples.

[0018]

FIG. 1 is a schematic block circuit diagram of a temperature compensated oscillator for explaining a first embodiment of the present invention. The same parts as those in the prior art are denoted by the same reference numerals, and description thereof will be simplified or omitted. The temperature-compensated oscillator comprises a voltage-controlled oscillator 1, a temperature compensation circuit 2, and a frequency adjustment mechanism 16. The voltage controlled oscillator 1 is formed by inserting the voltage variable capacitance element 3 in the oscillation closed loop of the crystal oscillator as described above. The temperature compensating circuit 2 is composed of a temperature-sensitive resistance network composed of temperature-sensitive resistance elements. Here, the temperature-sensitive resistance element is a thermistor having a negative temperature coefficient whose resistance value decreases with increasing temperature.

As shown in FIG. 2, in this example, the temperature-sensitive resistor network responds to the frequency-temperature characteristic of the crystal oscillator, and includes a low-temperature portion below a maximum value and a medium-temperature portion including a normal temperature between a maximum value and a minimum value. , And three thermistors 17 (abc) whose resistance values change in response to a high-temperature portion having a maximum value or more. And
Generates the aforementioned compensation voltage Vs (T) responsive to the ambient temperature,
This is applied to the voltage variable capacitance element 3. Reference numeral 18 denotes a high-temperature compensation adjusting resistor for adjusting a compensation voltage on the high-temperature side.

The frequency adjusting mechanism 16 comprises a frequency adjusting voltage generating circuit 19 and a storage circuit 20. The frequency adjustment voltage generation circuit 16 applies an adjustment voltage to the voltage variable capacitance element 3 according to a signal from the storage circuit 20, and adjusts the oscillation frequency. The storage circuit 20 writes the frequency adjustment data for determining the constant term γ in the above-described equation (1) into the write terminals a to n including the control terminals.
And is stored and retained.

In such a case, the temperature compensating circuit 2 in addition to the quartz oscillator 4 is constituted by discrete components. Then, as indicated by a dashed line, the voltage control oscillator 1 and the frequency adjustment mechanism section 16 excluding the temperature compensation circuit 2 and the crystal oscillator 4 are integrated on the IC chip 10. Then, for example, the following structure is adopted.

That is, as shown in FIG. 3, the IC chip 10 is face-down bonded by, for example, ultrasonic thermocompression bonding to the bottom surface of the concave portion of the surface mount container 11, and one end of the crystal blank 4 a is electrically conductive adhesive 12. Sticks to the step. Then, the notches 21 (a
b) 3 composed of chip elements forming the temperature compensation circuit 2
One thermistor 17 (abc) and high temperature compensation adjustment resistor 1
8 is arranged. Here, each thermistor 17 (abc)
Are connected in series and in parallel to each other, and individual sensitivity adjustment resistors for adjusting the respective temperature resistance characteristics are not used, and a thermistor 17 (a) having a preset normal temperature resistance value and a B constant is used.
Select bc).

The surface mount container 11 is made of a laminated ceramic as described above. In this example, the upper frame 11a, the middle frame 11b forming a step on both ends, and the notches 21 (a) on both sides.
The bottom wall 11c is formed into a three-layer structure having an E-shape having b) (FIG. 4). The notch 21 (ab) extends below the step from both ends, and mounting electrodes (not shown) are formed on the four corner back surfaces and side surfaces of the bottom wall. FIG. 5 is an external view of the surface mount container excluding the metal ring.

With such a configuration, the temperature compensation circuit 2
Since the thermistor 17 is used as a temperature detecting means for
As compared with the case where the forward drop voltage of the PN junction is used, the resistance change (detection voltage) with respect to temperature can be increased. Therefore, noise (internal noise) generated inside the IC chip 10 is relatively reduced. From this, the noise characteristics of the temperature compensated oscillator can be improved. Further, since it is not necessary to use the detection voltage (temperature detection signal) as it is to amplify it, current consumption can be suppressed.

The frequency adjusting mechanism 16 is connected to the IC chip 1
After the temperature compensation oscillator is assembled, the oscillation frequency is adjusted independently of the temperature compensation circuit 2 by a write signal after the temperature compensation oscillator is assembled. Therefore, size reduction is promoted as compared with the case where a capacitor for frequency adjustment is used. In comparison with the case where the oscillation frequency is also adjusted only by the compensation voltage Vs (T) from the temperature compensation circuit 2 without using a capacitor, the design of the temperature compensation circuit 2 (selection of each element value) is facilitated. .

In this example, the thermistor 17 (ab) in which element values (normal temperature resistance value and B constant) are set in advance.
Since c) is used, individual sensitivity adjustment resistors are not required. Therefore, the temperature compensating circuit can be composed of four thermistors 17 (abc) and the high-temperature compensating adjusting resistor 18 responding to the low temperature, the medium temperature and the high temperature, and minimize the number of temperature compensating elements of the temperature compensating circuit.

For these reasons, the temperature compensation element can be arranged in the notch 21 (ab) provided on the back surface side of the surface mount container 11, and the planar outer shape can be particularly reduced. Further, in this example, the notch 21 (ab) is formed in the bottom wall 1 located below the step.
Since it is provided at both ends of 1c, the height dimension can be maintained as small as the conventional example without increasing the number of ceramic layers.

[0028]

FIG. 6 is a schematic block circuit diagram of a temperature compensated oscillator for explaining a second embodiment of the present invention. The description of the same parts as in the first embodiment is omitted. That is, the first embodiment shows an example in which the compensation voltage Vs (T) is applied to the voltage controlled oscillator 1 (the voltage variable capacitance element 3) and the temperature is compensated in a so-called indirect method as in the conventional example. In the second embodiment, an example is shown in which a so-called direct method is used, which comprises a parallel circuit of a thermistor and a capacitor, and uses a change in capacitance between terminals (equivalent series capacitance) of the parallel circuit.

The temperature-compensated oscillator comprises the voltage-controlled oscillator 1, the temperature-compensating circuit 2, and the frequency adjusting mechanism 16 as described above. The temperature compensation circuit 2 and the crystal unit 4 are discrete components, and the voltage control oscillator 1 and the frequency adjustment mechanism unit 16 excluding at least the temperature compensation circuit 2 and the crystal unit 4
Are integrated on an IC chip.

The temperature compensation circuit 2 is connected in series with the crystal oscillator 4 and inserted into the oscillation closed loop of the voltage controlled oscillator 1. Here, as shown in FIG. 7, the high temperature compensating circuit 23H and the low temperature compensating circuit 23L each composed of a parallel circuit of the thermistors 17H and 17L and capacitors 22H and 22L are connected in series. The frequency temperature characteristic of the crystal unit 4 (crystal oscillator) is selected as a monotonically increasing cubic curve having an inflection point near room temperature. The high-temperature and low-temperature compensation circuits independently compensate for the frequency-temperature characteristics in the high-temperature and low-temperature regions with respect to the normal temperature.

That is, the high-temperature compensation circuit 23H lowers the oscillation frequency as indicated by the arrow A because the resistance value of the thermistor 17H decreases as the temperature rises and the inter-terminal capacitance increases. Further, the low-temperature compensation circuit 23L acts to increase the oscillation frequency as indicated by the arrow B because the resistance value of the thermistor 17L increases and the inter-terminal capacitance decreases as the temperature decreases. Therefore, the frequency-temperature characteristics of the crystal oscillator are flatly compensated. The normal temperature resistance value of the thermistor 17H is high, and the resistance value of the thermistor 17L is low, so that each operation is independent.

In these devices, the IC chip 10 is fixed to the bottom surface of the concave portion of the surface mount container 11 as described above, and the crystal blank 4a is held on the step. Then, the thermistors 17H and 17L and the capacitors 22H and 22L of the high-temperature and low-temperature compensation circuit are arranged in a pair in the notch 21 (ab) on the back surface. As the thermistors 17H and 17L, elements having preset element values are selected as described above, and the sensitivity adjustment resistors are not used.

With such a configuration, since the thermistor 17 is used as the temperature detecting means as in the first embodiment, the resistance change with respect to the temperature is increased, and the noise generated inside the IC chip 10 is relatively reduced. However, the noise characteristics of the temperature-compensated oscillator can be improved to reduce the current consumption.

The frequency adjustment mechanism 16 is connected to the IC chip 1
0, and the oscillation frequency is adjusted by the write signal. Therefore, for example, a capacitor for frequency adjustment connected to the temperature compensation circuit is not required, and the miniaturization is promoted.

In this example, the thermistor 17H,
17L does not use a sensitivity adjusting resistor, and therefore has a minimum number of elements (see Japanese Patent Application Laid-Open No. 11-284436). From these facts, the notch 2 provided on the back side of the surface mount container 11
The temperature compensating element can be arranged in 1 (ab), and the planar outer shape can be particularly reduced.

[0036]

Others In each of the above embodiments, the thermistor 17 is a chip element. However, a thermistor base material may be formed by printing between electrodes on a thin plate. In this case, the normal temperature resistance value may be adjusted by cutting off the thermistor base material (see Japanese Patent Application Laid-Open No. H11-284436). Notch 1
A space for 6 (ab) and a sensitivity adjusting resistor may be connected if necessary.

The notches 21 (ab) are provided at both ends in the longitudinal direction of the bottom wall 11c, but the intermediate frames 1 (ab) are provided on both sides in the width direction.
It may be provided in a range not exceeding the frame width of 1b (not shown).
Further, for example, a lower frame may be provided on a flat bottom wall to form a concave portion, and a temperature compensating element such as a thermistor 17 (abc) including a sensitivity adjusting resistor may be arranged (FIG. 9). The thermistor base material 24 (abc) and the sensitivity adjustment resistor 25 (ab
c) The thin plate 26 formed by printing may be arranged to widen the adjustment range of the thermistor 17. However, since the number of layers increases and the height increases, the above embodiment is more advantageous.

The IC chip 10 has a temperature compensation circuit 2
In addition, the voltage controlled oscillator 1 and the frequency adjustment mechanism section 16 except for the crystal resonator 4 are integrated, but the voltage variable capacitance element 3 of the voltage controlled oscillator 1 is separated (discrete) and disposed on the bottom of the concave portion of the surface mount oscillator 11. You may. In this way, the voltage variable capacitance element 3 can be easily changed, and the degree of freedom in selecting the voltage-capacity characteristics of the voltage variable capacitance element 3 can be increased.

On the contrary, for example, an AFC (Automatic Frequency Control) mechanism is integrated in the IC chip 10 and the AF
The C voltage may be applied to the voltage variable capacitance element 3. The integration of these into the IC chip 10 can be selected as needed without departing from the spirit of the present invention.

The bottom wall 11c of the surface mount container 11 is
A plurality of layers may be provided according to the height dimension of the chip element arranged in the cutout 21. This is because the thickness of the ceramic sheet before firing is limited. Further, when the notch 21 approaches the inner end of the step, the strength of the joint surface may be reduced, and a crack or the like may occur. In this case, for example, the bottom wall 11c may be divided into upper and lower layers, the upper layer may be a flat plate, and the lower layer may have an E-shape. However, the upper layer is made as thin as possible (for example, 1/3 or less) with respect to the lower layer to suppress the height dimension.

Although the cover of the surface mount container 11 is seam-welded, it may be sealed with resin or glass.
Although the temperature-sensitive resistance element is a thermistor having a negative temperature coefficient, it may be a positive thermistor having a positive temperature coefficient. Further, the high-temperature compensation adjusting resistor 18 in the first embodiment is used.
Can be omitted according to the frequency temperature characteristics of the crystal oscillator.

In the first embodiment, the temperature-sensitive resistor network is formed of three thermistors corresponding to the three regions of a low-temperature portion, a medium-temperature portion and a high-temperature portion. For example, the thermistor may be divided into two regions of a low-temperature portion and a high-temperature portion in accordance with the frequency temperature characteristics and the specification temperature, and may be formed of two thermistors corresponding thereto.

[0043]

According to the present invention, a voltage variable capacitance element is inserted into an oscillation closed loop of a crystal oscillator, and an oscillation circuit and a frequency adjustment mechanism excluding at least a temperature compensation circuit comprising a temperature sensitive element and a crystal resonator are provided. It is integrated on an IC chip. The frequency adjustment mechanism is formed from a storage circuit and a frequency adjustment voltage generation circuit, and the oscillation frequency is adjusted by applying a frequency adjustment voltage from the frequency adjustment voltage generation circuit based on a signal from the storage circuit to the voltage variable capacitance element. I do. Also,
The crystal chip and the IC chip that form the crystal unit are housed in a surface mount container, and a temperature compensation circuit (temperature compensating element) is arranged in the cutout provided on the back surface of the surface mount container. It is possible to provide a small temperature-compensated oscillator for surface mounting, particularly with a small planar outer shape.

[Brief description of the drawings]

FIG. 1 is a schematic block circuit diagram of a temperature compensated oscillator (indirect method) for explaining a first embodiment of the present invention.

FIG. 2 is a diagram of a temperature compensation circuit (compensation voltage generation circuit) for explaining an embodiment of the present invention.

FIG. 3 is a structural sectional view of a temperature compensated oscillator applied to one embodiment of the present invention.

FIG. 4 is an exploded view of a surface mount container applied to one embodiment of the present invention.

FIG. 5 is an external view of a surface mount container applied to one embodiment of the present invention.

FIG. 6 is a schematic block circuit diagram of a temperature-compensated oscillator (direct method) illustrating a second embodiment of the present invention.

FIG. 7 is a circuit diagram of a temperature compensation circuit for explaining a second embodiment of the present invention.

FIG. 8 is a frequency temperature characteristic diagram of the crystal oscillator applied to the second embodiment of the present invention.

FIG. 9 is another structural sectional view of the temperature compensated oscillator applied to each embodiment of the present invention.

FIG. 10 is a diagram of a thermistor showing another example applied to, for example, the first embodiment of the present invention.

FIG. 11 is a schematic block circuit diagram of a temperature compensated oscillator illustrating a conventional example.

FIG. 12 is a frequency temperature characteristic diagram of a crystal oscillator illustrating a conventional example.

FIG. 13 is a structural sectional view of a temperature-compensated oscillator explaining a conventional example.

FIG. 14 is a structural sectional view of a temperature-compensated oscillator explaining a conventional example.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 voltage controlled oscillator, 2 temperature compensation circuit, 3 voltage variable capacitance element, 4 crystal oscillator, 9 high frequency blocking resistance, 10
IC chip, 11 surface mount container, 12 conductive adhesive, 13 cover, 14 metal ring, 15 filler,
16 frequency adjustment mechanism section, 17 thermistor, 18 high temperature compensation adjustment resistor, 21 notch, 22 capacitor, 23
Compensation circuit, 24 thermistor base material, 25 sensitivity adjustment resistor, 26 thin plate.

Claims (4)

[Claims] 1. A crystal oscillator comprising a crystal oscillator and an oscillation circuit other than the crystal oscillator, a frequency adjustment mechanism for adjusting the oscillation frequency of the crystal oscillator, and a temperature-sensitive resistance element whose resistance value changes in response to temperature. A temperature compensating element comprising a temperature compensating element including a temperature compensating circuit for flattening the frequency-temperature characteristic of the crystal oscillator, wherein a voltage variable capacitance element is inserted into an oscillation closed loop of the crystal oscillator, and at least the temperature compensating circuit is provided. An oscillation circuit and a frequency adjustment mechanism excluding a crystal oscillator and a frequency adjustment mechanism are integrated on an IC chip, the frequency adjustment mechanism is formed from a storage circuit and a frequency adjustment voltage generation circuit, and the frequency adjustment mechanism is based on a signal from the storage circuit. Temperature-compensated water, wherein an oscillation frequency is adjusted by applying a frequency adjustment voltage from a frequency adjustment voltage generation circuit to the voltage variable capacitance element. Oscillator. 2. The temperature compensating circuit comprises a temperature-sensitive resistance network mainly including the temperature-sensitive resistance element, and generates a compensation voltage applied to the voltage variable capacitance element to flatten frequency-temperature characteristics of the crystal oscillator. 2. The temperature compensated crystal oscillator according to claim 1, wherein: 3. The temperature compensating circuit comprises a parallel circuit of the temperature-sensitive resistance element and a capacitor inserted in an oscillation closed loop of the crystal oscillator, and changes a capacitance between terminals of the parallel circuit in response to temperature. 2. The temperature compensated crystal oscillator according to claim 1, wherein a frequency temperature characteristic of the crystal oscillator is flattened. 4. The device according to claim 1, wherein the crystal piece forming the crystal unit and the IC chip are accommodated in a surface mounting container, a notch is provided on a back surface of the surface mounting container, and the temperature is provided in the notch. A temperature-compensated oscillator comprising a compensation element.