JPH11298246A - Temperature compensated oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature compensated oscillator with which the followup ability of an oscillation frequency with respect to changes in a control voltage is improved and the direction of changes in the oscillation frequency can be easily changed corresponding to changes in the control voltage. SOLUTION: The proposed oscillator consists of an N type semiconductor substrate 55, an insulating film 59 formed on the substrate 55 and a conductive film 61 formed on the film 59, wherein as a second conductive area, a high- density P type area 53 is provided on the N substrate 55, in contact with an area 57 covered with the conductive film 61 inside the 55 so as to supply a small amount of carriers at high speed on a condition for forming an inverted layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to frequency adjustment of a temperature compensated oscillator.

[0002]

2. Description of the Related Art A crystal oscillator using a crystal oscillator has a higher frequency stability than other oscillators. Fluctuations in the oscillation frequency due to temperature characteristics pose a problem. In order to solve this problem, a so-called temperature-compensated oscillator that compensates for the temperature characteristics of a crystal resonator is widely used.

The temperature compensation of the temperature compensated oscillator will be described with reference to FIG. The temperature detection circuit 71 outputs a voltage depending on the temperature to the control voltage generation circuit 73. The control voltage generation circuit 73 receives the voltage from the temperature detection circuit 71, amplifies the voltage,
Alternatively, the output voltage is output to the frequency adjustment circuit 75 after performing inversion amplification processing. The frequency adjustment circuit 75 controls the oscillation frequency of the crystal oscillation circuit 77 according to the input voltage.

When the oscillation frequency of the crystal oscillation circuit 77 fluctuates due to a temperature change, the fluctuation is compensated for as follows. The control voltage generation circuit 73 includes a temperature detection circuit 71
, And the frequency adjustment circuit 75 controls the oscillation frequency of the crystal oscillation circuit 77 to output a voltage to the frequency adjustment circuit 75 that can offset the variation of the oscillation frequency due to the temperature.

[0005] In this manner, the crystal oscillation circuit 77 can oscillate at a constant frequency irrespective of a temperature change, and temperature compensation is performed.

As the frequency adjusting circuit 75, an element such as a varicap diode or an MIS type variable capacitance capacitor whose capacitance changes by application of a DC voltage is used. Compared to a varicap diode utilizing the voltage dependence of the PN junction capacitance of a semiconductor, a MIS type variable capacitor can obtain a large capacitance change in a lower voltage and a narrow voltage range. The oscillation frequency adjustment width of the oscillator can be widened.
Since it can be mounted on an OS type integrated circuit, it can be easily integrated on a one-chip type temperature compensation circuit.

[0007] As shown in FIG. 7, the MIS type variable capacitor has a structure composed of an N-type semiconductor substrate 91, an insulating film 89 formed thereon, a conductive film 87 and a dense N-type region 83. The dark N-type region 83 functions to draw out the conductive film-insulating film-the semiconductor-side electrode of the semiconductor capacitor.

When the voltage at the terminal 85 connected to the conductive film 87 is increased from the voltage value Va to the voltage value Vb, the capacitance value increases as shown in FIG. At the voltage value Va, holes are induced on the surface 93 of the region of the semiconductor substrate 91 covered with the conductive film 87 as shown in FIG.
Is formed, and a depletion layer 94 is formed below it. As the voltage increases, the thickness of the depletion layer 94 gradually decreases.

The capacitance of the MIS type variable capacitance capacitor is a series combined capacitance of a capacitor having the insulating film 89 interposed therebetween and a capacitor having the depletion layer 94 interposed therebetween. Accordingly, when the thickness of the depletion layer 94 is reduced and the capacitance of the capacitor sandwiching the depletion layer 94 is increased, the capacitance value of the MIS type variable capacitor increases with an increase in voltage as described above.

When the voltage reaches the voltage value Vb, the depletion layer 94 disappears, and electrons are induced on the surface 93 to form an accumulation layer 95, as shown in FIG. In the voltage value Vb, the depletion layer 9
Since 4 disappears, the capacitance value of the MIS type variable capacitance capacitor becomes equal to the capacitance value of the capacitor formed with the insulating film 89 interposed therebetween, and becomes constant at a voltage higher than that.

[0011]

However, the MIS
The type variable capacitance capacitor has poor followability of the capacitance change with respect to the voltage change. If the voltage of the terminal 85 is instantaneously changed from the voltage value Vb to the voltage value Va, the change in the capacitance value cannot be followed, and after the voltage changes. , The capacitance value changes slowly. Therefore, when used in the frequency control circuit of the oscillation circuit of the temperature-compensated oscillator, the change in the oscillation frequency is delayed with respect to the change in the control voltage. There is a problem of becoming.

Further, the voltage of the terminal 85 is changed to a voltage value Vb.
When the voltage of the MIS-type variable capacitor changes in the direction of the voltage Va, the direction of the capacitance change with respect to the voltage change is one-way. There is also a problem that it is difficult to change the direction.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to improve the followability of the oscillation frequency to the change of the control voltage, and to change the direction of the change of the oscillation frequency to the change of the control voltage. Is to provide a temperature-compensated oscillator that is easy to use.

[0014]

In order to achieve the above object, a temperature compensated oscillator according to the present invention comprises a temperature detecting circuit, a control voltage generating circuit, a frequency adjusting circuit, and an oscillating circuit. The adjusting circuit has an MIS type variable capacitor, inputs the output voltage of the control voltage generation circuit to the MIS type variable capacitor, and adjusts the oscillation frequency of the oscillation circuit. A conductive semiconductor, an insulating film formed on the first conductive semiconductor,
A conductive film formed of a conductive film formed on the insulating film, an insulating film, and a semiconductor capacitor structure. The first conductive type semiconductor is in contact with a region covered with the conductive film of the first conductive type semiconductor. Is provided with a second conductivity type region.

[Operation] The MIS type variable capacitor is
When a voltage that forms an inversion layer on the semiconductor surface is applied, there is no portion for supplying minority carriers, and it takes time for the minority carrier concentration to reach a thermal equilibrium state. Until this minority carrier concentration reaches thermal equilibrium,
The thickness of the depletion layer changes, and the capacitance of the MIS variable capacitor also changes. This is the reason why the MIS type variable capacitance capacitor has poor followability of the capacitance change to the voltage change.

If the semiconductor constituting the MIS type variable capacitance capacitor is provided with a region of the opposite conductivity type which acts to supply minority carriers, the minority carrier concentration reaches a thermal equilibrium state at a very high speed. The ability of the capacitance to follow the change can be greatly improved. If a semiconductor of the MIS type variable capacitance capacitor is provided with a region of the opposite conductivity type that acts to supply minority carriers, the accumulation layer is formed and then the accumulation layer disappears to form an inversion layer. Until this time, the capacitance of the MIS type variable capacitor decreases with respect to the voltage, but after the inversion layer is formed, the direction of the capacitance change is reversed and the capacitance increases.

For this reason, in the MIS type variable capacitor having a structure in which an area for supplying a minority carrier is provided,
Unlike the conventional MIS type variable capacitance capacitor,
Not only the portion of the capacitance change until the accumulation layer disappears and the inversion layer is formed, but also the portion of the capacitance change after the inversion layer is formed can be used for adjusting the oscillation frequency.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments for implementing a temperature compensated oscillator according to the present invention will be described below with reference to the drawings. FIG. 1 is a block circuit diagram of a temperature compensated oscillator according to an embodiment of the present invention.

[Description of Configuration: FIG. 1] As shown in FIG.
In the temperature compensated oscillator according to the present invention, the temperature detection circuit 1
1, a control voltage generation circuit 13, and a frequency adjustment circuit 15
, An oscillation circuit 17 and an external control voltage input terminal 12. The frequency adjustment circuit 15 includes MIS type variable capacitance capacitors 31 and 35. The oscillation circuit 17 includes a crystal oscillator 37, an inverter 41, and a feedback resistance element 39.

The temperature detection circuit 11 and the external control voltage input terminal 12 are connected to a control voltage generation circuit 13, and the control voltage generation circuit 13 is connected to the frequency adjustment circuit 15 via the resistance elements 25 and 27, and the MIS type variable Capacitors 31, 35
Are connected to both ends of the crystal oscillator 37 of the oscillation circuit 17, and the other electrode 65 is grounded.

[Description of Structure: FIG. 2] FIG. 2 shows the structure of the MIS type variable capacitance capacitors 31 and 35. As shown in FIG. 2, the MIS type variable capacitors 31 and 35 are
Conductive film-insulating film-semiconductor capacitor composed of an N-type semiconductor substrate 55, which is a conductive type semiconductor, an insulating film 59 formed on the N-type semiconductor substrate 55, and a conductive film 61 formed on the insulating film 59 The N-type semiconductor substrate 5 has a structure and is in contact with a region 57 covered with the conductive film 61 of the N-type semiconductor substrate 55.
5, a dark P-type region 53 as a second conductivity type region is provided;
The N-type region 5 is in contact with the region 57 and is
1 is provided.

[Explanation of Operation: FIGS. 1, 2 and 3]
And FIG. 4 and FIG. 5] Next, the operation of the temperature compensated oscillator according to the embodiment of the present invention will be described with reference to FIG. 1, FIG. 2, FIG. 3, FIG. FIG.
In FIG. 4 and FIG. 4, the same components as those in FIG. 1 and FIG.

As shown in FIG. 1, the temperature detecting circuit 11 detects the temperature of the oscillating circuit 17 and outputs a temperature-dependent voltage to the control voltage generating circuit 13. Control voltage generation circuit 13
Inputs the voltage from the temperature detection circuit 11 and inputs the output voltage to the frequency adjustment circuit 15 via the resistance elements 25 and 27.

The control voltage generation circuit 13 inputs an external control voltage from the external control voltage input terminal 12 and inputs the output voltage to the frequency adjustment circuit 15 via the resistance elements 25 and 27. The resistance elements 25 and 27 are connected to the control voltage generation circuit 13
This is to prevent the MIS type variable capacitors 31 and 35 constituting the frequency adjustment circuit 15 from being capacitively affected.

From the control voltage generation circuit 13 to the resistance element 25,
27, the output voltage of the control voltage generating circuit 13 input to the frequency adjusting circuit 15 is applied to the terminals 63 and 64 of the MIS type variable capacitors 31 and 35, and the MIS type variable capacitor 31 described below is applied. , 35, the oscillation circuit 1 depends on the relationship between the applied voltage and the change in capacitance.
7 is controlled.

The operation of the MIS type variable capacitors 31 and 35 will be described. As shown in FIG. 3, the deep N-type region 51 has a function of drawing out the conductive film, the insulating film, and the semiconductor-side electrode of the semiconductor capacitor, and is electrically connected to the deep P-type region 53. Terminal 65 is a dark N-type region 51
The terminals 63 are connected to the conductive film 61, respectively.

The voltage between the terminal 65 and the terminal 63 is set to a voltage value V
As the voltage is increased from 1 to the voltage value V4, the capacitance value of the MIS type variable capacitor changes as shown in FIG.

In the voltage value V1, as shown in FIG.
Holes, which are minority carriers, are induced on the surface 58 of the substrate 7 to form an inversion layer 56, and a depletion layer 54 is formed below the inversion layer 56. Until the voltage between the terminal 65 and the terminal 63 reaches the voltage value V2, the hole concentration of the inversion layer 56 is high, and
6 is equivalent to a conductive electrode, and the dark P-type region 53
Plays the role of extracting the electrodes of the inversion layer 56, so that the capacitance value of the MIS variable capacitance capacitor is equal to the capacitance value of the capacitor formed with the insulating film 59 interposed therebetween, and the capacitance value is constant.

The voltage between the terminal 65 and the terminal 63 is a voltage value V
2, the hole concentration of the inversion layer 56 decreases, and the inversion layer 56 deviates from a state in which it is equivalent to a conductive electrode. , And a capacitor composed in series with the depletion layer 54 interposed therebetween, and the series combined capacitance value sharply decreases, and the capacitance value becomes minimum at the voltage value V3.

The voltage between the terminal 65 and the terminal 63 is a voltage value V
As the height increases from 3, the thickness of the depletion layer 54 gradually decreases. In this state, the capacitance value of the MIS type variable capacitance capacitor is different from that of the capacitor formed with the insulating film 59 interposed therebetween.
This is a series combined capacitance value of the capacitors formed with the depletion layer 54 interposed therebetween. Therefore, when the thickness of the depletion layer 54 decreases and the capacitance value of the capacitor sandwiching the depletion layer 54 increases, the capacitance value of the MIS variable capacitance capacitor also increases. The capacitance value increases.

When the voltage between the terminals 65 and 63 reaches the voltage value V4, the depletion layer 54 disappears, and electrons are induced on the surface 58 to form the accumulation layer 60 as shown in FIG. The capacitance value of the variable capacitor is determined by the insulating film 59.
, And becomes equal to the capacitance value of the capacitor formed between them, and the capacitance value becomes constant at a voltage equal to or higher than the voltage value V4.

The voltage between the terminal 65 and the terminal 63 is set to a voltage value V
When the voltage is instantaneously changed from 4 to the voltage value V3, the accumulation layer 60 existing on the surface 58 disappears, and the inversion layer 56 and the depletion layer 54 are formed as shown in FIG.

At this time, the deep P-type region 53 supplies holes to the inversion layer 56, and the hole concentration of the inversion layer 56 reaches a thermal equilibrium state very quickly. As a result, the thickness of the depletion layer 54 quickly reaches a constant value, and the capacitance value of the MIS type variable capacitor changes following the voltage change between the terminals 65 and 63 without delay.

This operation is exactly the same when the voltage between the terminals 65 and 63 is instantaneously changed from the voltage value V4 to any lower voltage value.

As described above, the MIS variable capacitance capacitors 31 and 35 constituting the frequency adjustment circuit 15 of the temperature compensated oscillator according to the present invention do not change their capacitance even if the applied voltage changes rapidly. Instantly follow the change,
No delay in the frequency change response occurs in the temperature compensated oscillator. This effect is remarkable when the external control voltage that changes at a high speed is input from the external control voltage input terminal 12 to the control voltage generation circuit 13 to control the oscillation frequency of the oscillation circuit 17.

The voltage change range from V2 to V3 in the above description is a so-called minority carrier generation voltage range, and the voltage change range from V3 to V4 is a so-called majority carrier generation voltage range. The capacitance change directions with respect to the voltage change direction in each voltage range are opposite to each other, and the capacitance change in any voltage range can be used for controlling the oscillation frequency of the oscillation circuit 17.

In the description of the above embodiment, an N-type semiconductor substrate is taken as an example of the first conductivity type semiconductor.
P provided on a N-type semiconductor substrate or an N-type semiconductor substrate
A similar effect can be obtained by using a type region or an N type region provided on a P type semiconductor substrate.

[0038]

As described above, according to the present invention, the MIS-type variable capacitor constituting the frequency adjustment circuit of the temperature-compensated oscillator has a conduction type region serving as a minority carrier supply source. For this reason, since the capacitance change with respect to the voltage change applied to the MIS type variable capacitance capacitor instantaneously follows, the response delay in the frequency control of the temperature compensated oscillator is eliminated, and the oscillation frequency tracking performance of the temperature compensated oscillator is eliminated. Obstacles can be eliminated.

Further, the capacitance change in any of the minority carrier generation voltage range and the majority carrier generation voltage range can be used for controlling the frequency of the oscillation circuit. The direction of change can be easily changed.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing a temperature compensated oscillator according to an embodiment of the present invention.

FIG. 2 is a structural diagram showing a MIS variable capacitance capacitor of the temperature compensated oscillator according to the embodiment of the present invention.

FIG. 3 is a structural diagram showing an MIS type variable capacitor for explaining the operation of the temperature compensated oscillator according to the embodiment of the present invention.

FIG. 4 is a structural diagram showing a MIS type variable capacitor for explaining the operation of the temperature compensated oscillator according to the embodiment of the present invention.

FIG. 5 is a graph showing the relationship between the voltage and the capacitance of the MIS variable capacitor of the temperature compensated oscillator according to the embodiment of the present invention.

FIG. 6 is a block circuit diagram showing a temperature-compensated oscillator in a conventional example.

FIG. 7 is a structural view showing a conventional MIS type variable capacitance capacitor.

FIG. 8 is a structural diagram showing a MIS type variable capacitor in a conventional example.

FIG. 9 is a graph showing the relationship between the voltage and the capacitance of a conventional MIS variable capacitor.

[Explanation of symbols]

 Reference Signs List 11 temperature detection circuit 13 control voltage generation circuit 15 frequency adjustment circuit 17 oscillation circuit 53 second conductivity type region 55 first conductivity type semiconductor 57 region covered with conductive film of first conductivity type semiconductor 59 insulating film 61 conductive film

Claims (6)

[Claims] A temperature detection circuit, a control voltage generation circuit,
A frequency adjustment circuit and an oscillation circuit are provided. The frequency adjustment circuit has an MIS type variable capacitance capacitor. The output voltage of the control voltage generation circuit is input to the MIS type variable capacitance capacitor to adjust the oscillation frequency of the oscillation circuit. The MIS type variable capacitor is a conductive film-insulating film composed of a first conductive type semiconductor, an insulating film formed on the first conductive type semiconductor, and a conductive film formed on the insulating film. −
Having a semiconductor capacitor structure, in contact with a region covered with a conductive film of a first conductive type semiconductor,
A temperature compensated oscillator characterized in that a second conductivity type region is provided in a first conductivity type semiconductor. 2. The semiconductor device according to claim 1, wherein the semiconductor of the first conductivity type and the region of the second conductivity type are electrically connected to each other. Temperature compensated oscillator. 3. The semiconductor device according to claim 1, wherein the first conductive type semiconductor according to claim 1 or 2 is a P-type region provided on an N-type semiconductor substrate. Characteristic temperature compensated oscillator. 4. The semiconductor device according to claim 1, wherein the first conductive type semiconductor according to claim 1 or 2 is an N-type region provided on a P-type semiconductor substrate. Characteristic temperature compensated oscillator. 5. The temperature-compensated oscillator according to claim 1, wherein the capacitance is varied by applying a voltage in a majority carrier generation voltage range. 6. The temperature-compensated oscillator according to claim 1, wherein the capacitance is varied by applying a voltage in a minority carrier generation voltage range.