JPH05315836A - Temperature compensation type crystal oscillator - Google Patents

Abstract

PURPOSE:To adjust the oscillating frequency by utilizing a drive power supply of the crystal oscillator employing a PEAC element (floating electrode MDS capacitive element). CONSTITUTION:The oscillating frequency is varied by varying a voltage applied to a capacitive electrode of a PEAC element 13 via a 2nd resistor 11 in the crystal oscillator comprising the PEAC element 13, a Colpitz crystal oscillation circuit, a constant voltage source 20 driving an oscillation circuit section and an output circuit. One terminal of the 2nd resistor 11 connects to the drive power supply for the crystal oscillator or other power supply. The frequency is varied by varying the resistance of the 2nd resistor 11 or a voltage of other power supply connected to the 2nd resistor 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage variable capacitance element, more specifically a floating electrode MOS, in a crystal oscillator for generating a reference frequency signal of a device requiring a highly stable frequency such as a portable communication device. The present invention relates to a crystal oscillator whose frequency is adjusted using a capacitive element.

[0002]

2. Description of the Related Art A floating electrode MOS capacitive element (hereinafter referred to as a PEAC element) is used to inject and pour out electrons into a floating electrode by a tunnel current flowing through a thin SiO ₂ film, thereby depleting a depletion layer capacitance formed directly under the electrode. It is a changing element. The number of electrons in the electrode is kept constant unless a sufficient electric field is applied to the electrode so that a tunnel current flows.
The capacitance of the EAC element is kept constant. That is, PEA
The C element can be used as a trimmer capacitor. P
Details of the application of the EAC element to the crystal oscillator are disclosed in the literature, “Development of an electrically frequency-tunable crystal oscillator” (Journal of the Japan Society of Watchmaking, No. 124). Also, PEAC
Since the capacitance of the element changes depending on the bias voltage, the temperature of the crystal resonator can be compensated by using a temperature sensitive element such as a thermistor and changing the bias voltage depending on the ambient temperature.

The details of the application of the temperature-compensated crystal oscillator of the PEAC element are disclosed in Japanese Patent Application No. 61-123896. In order to adjust the output frequency of the crystal oscillator within the required accuracy and so that the user can correct the change thereafter, the crystal oscillator has a frequency adjustment terminal connected to the electron injection terminal of the PEAC element. There is.

[0004]

An electric field of 10 ¹¹ V / m or more is required to pass a tunnel current through the SiO ₂ film. SiO ₂ under the floating electrode of the PEAC element
Since the thickness of the film is 100 Å or more, it is necessary to apply a voltage of 10 V or more to inject and eject electrons. Since the crystal oscillator is generally driven by a voltage of 5 V or less, PEA
Another power source is required to adjust the oscillation frequency by the C element, which is disadvantageous for the user to adjust the frequency.

Further, there is a drawback in that it cannot be practically used in a system which automatically corrects a change in frequency of a crystal oscillator with time based on a highly stable frequency signal of a master station. It is an object of the present invention to solve the above-mentioned drawbacks that are inevitable in a crystal oscillator that uses the PEAC element.

[0006]

The means adopted by the present invention to achieve the above object is to divide a constant voltage by a circuit network composed of a temperature sensitive element and a resistor, and divide the divided voltage through a resistor. In a temperature-compensated crystal oscillator that is applied to a voltage variable capacitance element to compensate for the frequency-temperature characteristic of a crystal resonator, a DC voltage is applied to the voltage variable capacitance element between the voltage variable capacitance element and a second frequency adjustment terminal. A temperature-compensated crystal oscillator, which is provided with a resistance for

[0007]

The present invention is to adjust the oscillation frequency by changing the bias voltage applied to the PEAC element from the outside so as to change the capacitance of the PEAC element.

[0008]

EXAMPLES Next, the present invention will be explained by examples. FIG. 1 shows an embodiment of the present invention. 1 is the V _dd terminal, 2 is the V _ss
Normally + 5V is applied to V _dd at the terminals. 3 is an output terminal,
4 is a first frequency adjustment terminal (hereinafter referred to as FA1 terminal)
Is connected to the current injection / extraction terminal of the PEAC element 13. 5
Is a second frequency adjustment terminal (hereinafter referred to as FA2 terminal), and is connected to the capacitance terminal of the PEAC element through the resistor 11 (R ₅ ). In this embodiment, the oscillator circuit is the inverter 16 (I
₁ ) and a feedback resistor 12 (R _f ) as an inverter amplifier and a crystal oscillator 15 (X) as a Colpitts oscillator circuit. The output of the inverter 16 is added to the buffer inverter 17 (I ₂ ). Inverter 16, 1
7 is driven by a constant voltage source 20 (hereinafter VR) at a constant voltage (for example, 2 V) lower than the power supply voltage V _dd . A signal voltage of the output of the inverter 17 is increased by a level shifter 19 (LS), and an output inverter 18
Added to (I ₃ ).

The final output signal is obtained via the output terminal 3. Reference numeral 21 denotes a metal case that houses the entire crystal oscillation circuit including the crystal oscillator. In this embodiment, the resistor 6 (R
₁ ) 7 (R ₂ ), 8 (R ₃ ) and thermistor 9
The resistor thermistor network consisting of (R _t ) has a potential difference V _dd −
VR is divided and applied to the capacitance terminal of the PEAC element via the resistor 10 (R ₄ ) (the voltage applied to the capacitance terminal of the PEAC element is referred to as bias voltage V _B ). Since the capacitance of the PEAC element decreases as V _B increases, the oscillation frequency increases.

In this embodiment, as the temperature rises, the resistance value of the thermistor 9 decreases and the V applied to the PEAC element decreases.
_B becomes smaller and tries to lower the oscillation frequency. Therefore, if the frequency temperature characteristic of the crystal unit 15 is positive, this is compensated by the oscillation frequency temperature characteristic of the circuit, and as a result, the frequency temperature characteristic is improved. FIG. 2 shows an example of actual use of the present invention. A voltage E ₀ (for example, 5 V) is applied between the terminals 1 and 2. A load impedance 23 is connected between the terminals 2 and 3. A voltage E ₁ ( ₁₃ V or higher) is applied between the terminals 4 and 1 via the switch 25. Switch 2
The frequency is changed by turning 5 on (the frequency is increased in this embodiment). Next, the variable resistor 26 (R ₆ ) is connected between the terminals 5 and 1. By increasing or decreasing the value of R ₆ , the bias voltage V _B of the PEAC element can be changed and the oscillation frequency can be changed.

FIG. 3 shows another practical use example of the present invention. A voltage E ₂ is applied between the terminals 5 and 2. The oscillation frequency can be changed by changing E ₂ (in the case of the present embodiment, the oscillation frequency decreases when E ₂ is increased).
FIG. 4 is a diagram showing the frequency variable characteristic of the present embodiment. In FIG. 1, terminal 5 is connected to terminal 1 and the value of R ₅ is 39
Centering on 0 kΩ ± 80 kΩ (R ₅ = 310 to 470 k
Ω) shows the change in oscillation frequency when changed. In order to obtain a constant oscillation frequency temperature characteristic by compensating the variation in the frequency temperature characteristic of the crystal unit 15, various values of resistances R ₁ , R ₂ and R ₃ forming the resistance thermistor network are selected. In this embodiment, R ₁ is in the range of 13 kΩ to 91 kΩ. Therefore, if R ₅ = 390 ± 80 kΩ, then +2.5 to + 3.5 × 10 ⁻⁶ , −3.5 to −4.5.
A variable width of × 10 ^-6 can be obtained. This is an amount sufficient to accommodate the aging of the crystal oscillator. Specifically, R ₅ = 300 kΩ and a variable resistor of 200 kΩ may be used as R ₆ .

Next, FIG. 5 is a conventional circuit diagram for explaining the present invention. The second frequency adjustment terminal (FA2) 5 is connected to the PEA via the resistor 11 ′ (R ₅ ) and the resistor 10 (R ₄ ).
It is connected to the capacitance terminal of the C element 13. FIG. 6 is a diagram showing frequency variable characteristics of the circuit of FIG. Since the resistor 11 'is connected directly to the resistor thermistor network, frequency variable amount of R ₅ is greatly affected by the R _1. For example, R ₁ =
In the case of 13 kΩ, ΔR = −50 kΩ changes −2 × 10 ⁻⁶ , whereas in the case of R ₁ = 91 kΩ, −10 × 10 ⁻⁶ also changes. This is very inconvenient because it is not possible to recommend an appropriate value to the user.

As described above, the resistor 11 'for frequency adjustment is used.
It can be seen that (R ₅ ) should be directly connected to the capacitive electrode of the PEAC element. FIG. 7 shows another embodiment of the present invention. Variable capacitance diode 1 as temperature compensation element
3'is a conventional trimmer capacitor 13 "used as a frequency adjusting element. The operating principle is the same as that of the embodiment of FIG.

[0014]

As described above, according to the present invention, by connecting the frequency adjusting resistor directly to the capacitive electrode of the PEAC element, the frequency with a small variation in the variable width depending on the resistance value of the temperature compensating thermistor network. A variable characteristic can be obtained, which makes it easier for a user to set a condition for correcting a frequency change due to a change with time of the crystal oscillator.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an example of use of the present invention.

FIG. 3 is a circuit diagram showing another example of use of the present invention.

FIG. 4 is a diagram showing frequency variable characteristics according to an embodiment of the present invention.

FIG. 5 is a conventional circuit diagram for explaining the present invention.

FIG. 6 is a diagram showing frequency variable characteristics of the circuit of FIG.

FIG. 7 is a circuit diagram showing another embodiment of the present invention.

[Explanation of symbols]

 1, 2, 3, 4, 5 Terminals 6, 7, 8, 12 Resistance 9 Thermistor 10 First resistance 11 Second resistance 13 PEAC element 13 'Variable capacitance diode 14 Capacitor 15 Crystal oscillator 16, 17, 18 Inverter 19 Level Shifter 20 Constant Voltage Power Supply 21 Case 22, 24, 27 Power Supply 23 Load 25 Switch 26 Variable Resistor

Claims (1)

[Claims] 1. A constant voltage is divided by a circuit network including a temperature sensitive element and a resistor, and the divided voltage is applied to a voltage variable capacitance element via a first resistor to compensate for the frequency temperature characteristic of a crystal oscillator. In the temperature-compensated crystal oscillator described above, a second resistor for applying a DC voltage to the voltage variable capacitance element is connected to a connection point between the voltage variable capacitance element and the first resistor. Temperature compensated crystal oscillator.