JPH07106852A - Temperature compensated crystal oscillation circuit - Google Patents

Abstract

PURPOSE:To obtain the temperature compensation circuit of a crystal oscillation circuit able to be integrated with simple configuration. CONSTITUTION:A trimmer capacitor 12 and capacitors C11, C12 are connected in series with one terminal of a crystal oscillator 11, and transistors (TRs) 3, 4 are connected in parallel with the capacitors C11, C12. Then a controller 21 turns on/off the TRs 3, 4 based on a temperature detected by a semiconductor temperature sensor 25 arranged in the vicinity of the crystal oscillator 11 and a combined reactance of the capacitors C11, C12 is changed to cancel a change in the reactance due to the temperature of the crystal oscillator 11.

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 circuit used in a wireless communication terminal.

[0002]

2. Description of the Related Art A crystal oscillator is used as a reference oscillator of a wireless communication device, but the reactance component of the crystal oscillator changes with temperature. Therefore, the crystal oscillating circuit is provided with a temperature compensating circuit that corrects the temperature change of the oscillation frequency.

FIG. 5 is a circuit diagram of a conventional temperature-compensated crystal oscillation circuit. In the figure, a trimmer capacitor 12 is connected to one end of a crystal oscillator 11, and a plurality of chip thermistors 13 having negative temperature characteristics of reactance components and a plurality of temperature compensating capacitors having positive characteristics are connected to the other end of the trimmer capacitor 12. C1 is connected in series. The plurality of chip thermos 13 and the plurality of temperature compensating capacitors C1 constitute a temperature compensating circuit 14 for canceling the change in the reactance component of the crystal unit 11. Further, the trimmer capacitor 12, the chip thermistor 13, and the capacitor C1 form a load circuit 15 of the crystal oscillation circuit.

The trimmer capacitor 12 is an adjusting capacitor for setting the oscillation frequency of the crystal oscillation circuit at a desired oscillation frequency at room temperature. Crystal oscillator 11
The other end of the transistor TR1 via the capacitor C2
Of the resistor R1 having one end connected to the DC power source V and the other end of the resistor R2 having one end grounded. This resistance R1, R
2 supplies a predetermined bias voltage to the base of the transistor TR1. The collector of the transistor TR1 is connected to the DC power supply V, the capacitor C3 is connected between the collector and the emitter, and the capacitor C4 is connected between the base and the emitter. The transistor TR1, the capacitors C3, C4, etc. constitute a Colpitts oscillator circuit 16.

The emitter of the transistor TR1 is connected to the base of the transistor TR2 via a coupling capacitor C6. The base of the transistor TR1 has the other end of a resistor R4 having one end connected to the power supply V and the other end having a grounded resistor. The other end of R5 is connected. A bias voltage determined by the voltage division ratio of the resistors R4 and R5 is supplied to the base of the transistor TR2. The collector of the transistor TR2 is the coil L
1 is connected to a DC power source V, and the emitter is connected to the other end of a resistor R6 whose one end is grounded. The collector output of the transistor TR2 is output to the outside via the coupling capacitor C9. The buffer amplifier circuit 17 includes the transistor TR2 and the coil L1.
Are configured. The capacitors C5 and C7 are power supply bypass capacitors.

Now, the maximum value on the high temperature side of the frequency change value Δf / F of the oscillation frequency of the crystal oscillation circuit before temperature compensation is f
_MAX (value based on the frequency change value at the reference temperature T _REF in FIG. 6, the same applies below), maximum value f _MIN on the low temperature side
And The upper diagram of FIG. 6 shows the temperature characteristic of the frequency change value of the oscillation frequency of the crystal oscillation circuit, and the lower diagram shows the temperature characteristic of the reactance component of the temperature compensation circuit 14.

The temperature compensating circuit 14 is the crystal unit 1
It has the inverse characteristic of the change characteristic of the reactance component depending on the temperature of 1, and the reactance decreases as the temperature rises. As shown in FIG. 6, in the temperature characteristic of the temperature compensation circuit 14, the reactance value becomes the maximum value I _H at the temperature T _L on the low temperature side of the temperature compensation range of the crystal unit and the reactance value at the temperature T _H on the high temperature side. It has the characteristic of being the minimum value I _L.

As a result, the temperature characteristic of the frequency change value of the oscillation frequency of the crystal oscillation circuit 14 is corrected from the characteristic shown by the broken line in FIG. 6 to the characteristic shown by the solid line in the figure. That, f _MAX the maximum value of the high temperature side from f _MAX frequency change value ', and the low temperature side maximum value f _MIN from f _MIN of' next, the frequency change with temperature becomes smaller.

[0009]

However, since the above-mentioned temperature compensating circuit 14 requires a plurality of chip thermistors, the mounting area becomes large and it is difficult to miniaturize the circuit. Further, since a thermistor having a negative temperature characteristic and a capacitor having a positive temperature characteristic cannot be formed inside the IC, the temperature compensating circuit cannot be integrated into an IC, and mobile wireless communication in which miniaturization of the circuit is required. It was not suitable for machines.

An object of the present invention is to provide a temperature compensation circuit for a crystal oscillation circuit which has a simple structure and can be integrated into an IC.

[0011]

A temperature-compensated crystal oscillation circuit according to the present invention comprises a crystal oscillator, a variable reactance element, and
A plurality of capacitors connected in series to the variable reactance element, a plurality of switching elements connected in parallel to the plurality of capacitors, a semiconductor temperature sensor, and a plurality of switching elements turned on based on the output voltage of the semiconductor temperature sensor, And a control circuit for turning it off.

[0012]

In the present invention, the control circuit turns the switching element on and off based on the temperature detected by the semiconductor temperature sensor, and changes the combined reactance of the plurality of capacitors so as to cancel the change in the reactance due to the temperature of the crystal unit. I am letting you. Therefore, the temperature compensating circuit that stabilizes the oscillation frequency of the crystal oscillating circuit can be composed of a semiconductor temperature sensor, a capacitor, a transistor, and the like that can be integrated into an IC, so that the temperature compensating circuit of the temperature compensating crystal oscillating circuit can be downsized.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit configuration diagram of a temperature-compensated crystal oscillation circuit according to an embodiment of the present invention. In the following description, the same parts as those of the conventional oscillator circuit of FIG. 5 are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 1, a trimmer capacitor 12 is connected to one end of a crystal oscillator 11, capacitors C11 and C12 are connected in series with the trimmer capacitor 12, and the other end of the capacitor C12 is grounded. The trimmer capacitor 12 and the capacitors C11 and C12 form a load circuit 22 of a crystal oscillation circuit.

The collector of the transistor TR3 is connected to the connection point between the capacitor 11 and the trimmer capacitor 12, and the emitter thereof is grounded. The collector of the transistor TR4 is connected to the connection point between the capacitors C11 and C12, and the emitter thereof is grounded.

A signal Data1 is supplied to the base of the transistor TR3 from the terminal 21a of the controller 21 via the coil L2 and the resistor R11, and the transistor TR4.
A signal Data2 is supplied from the terminal 21b of the controller 21 via the coil L3 and the resistor R12 to the base of the.

The signal Da output from the controller 22
When ta1 is "1", the transistor TR3 is turned on, the capacitors C11 and C12 are grounded, and the signal Dat
When a2 is "1", the transistor TR4 is turned on and only the capacitor C12 is grounded.

The Colpitts oscillation circuit 16 described above is connected to the other end of the crystal oscillator 11. The output signal of the Colpitts oscillator circuit 16 is amplified by the buffer amplifier circuit 17 and output to the outside.

A semiconductor temperature sensor 23 is arranged near the crystal unit 11, and the semiconductor temperature sensor 23 is arranged.
Changes almost the same temperature as the crystal oscillator 11, and outputs the base-emitter voltage V _BE according to the detected temperature. The output voltage V _BE of the semiconductor temperature sensor 23 is amplified by the buffer amplifier circuit 24 and then output to the V _BE output terminal 21 c of the controller 21.

The controller 21 is a semiconductor temperature sensor 2
3 is a circuit that outputs signals Data1 and Data2 that turn on and off the transistors TR3 and TR4 in accordance with the output voltage of No. 3.

The capacitors C11 and C12, the transistors TR3 and TR4, the semiconductor temperature sensor 23, the controller 21 and the like constitute a temperature compensating circuit 25. As shown in FIG. 2, the semiconductor temperature sensor 23 has a characteristic that the output voltage V _BE decreases as the temperature rises.
The voltage value A is output when a, and the voltage value B is output when the temperature is Tb. The controller 21 is a semiconductor temperature sensor 23.
In the temperature range C (see FIG. 2) in which the output voltage of V is larger than the voltage value A, as shown in FIG. 3, Data1 = 0, Data1
In the temperature range D in which the signal of 2 = 0 is output and the output voltage of the semiconductor temperature sensor 23 is less than the voltage value A and is equal to or more than the voltage value B, D
The signals of data1 = 0 and Data = 1 are output. Also,
In the temperature range E in which the output voltage of the semiconductor temperature sensor 23 is smaller than the voltage value B, Data1 = 1 as shown in FIG.
Is output.

The operation of the temperature compensation circuit shown in FIG. 1 will be described. First, in the temperature range C (when the temperature is equal to or lower than Ta) where the output voltage of the semiconductor temperature sensor 23 is equal to or higher than the voltage value A,
The controller 21 outputs the signals Data1 = 0 and Data2 = 0 to the bases of the transistors TR3 and TR4, and the transistors TR3 and TR4 are turned off. In this case, the temperature compensating circuit 25 is a circuit in which the capacitor C11 and the capacitor C12 are connected in series, and the reactance component thereof has the maximum value I _H.

Further, the temperature range D (temperature T in which the output voltage of the semiconductor temperature sensor 23 is lower than the voltage value A and higher than the voltage value B).
In the range from a to temperature Tb), the controller 21
Outputs a signal of Data1 = 0 and Data2 = 1, the transistor TR3 is turned off, the transistor TR4 is turned on, and both ends of the capacitor C12 are grounded. In this case, the temperature compensation circuit 25 is a circuit to which only the capacitor C11 is connected, and the reactance component thereof has the intermediate value I _M.

Further, in the temperature range E (when the temperature is equal to or higher than the temperature Tb) in which the output voltage of the semiconductor temperature sensor 23 is smaller than the voltage value B, the controller 21 outputs Data1 = 1, D.
A signal of ata2 = 0 is output, the transistor TR3 is turned on, and the capacitors C11 and C12 are grounded.
In this case, the reactance component of the temperature compensation circuit 25 becomes substantially zero I _L.

Therefore, in the temperature ranges C, D and E, the oscillation frequency is determined by the reactance component represented by the following equation. Note that I ₁ is the reactance component of C11, I
₂ is the reactance component of C12, and I _T is the reactance component of the trimmer capacitor C12.

The reactance I _C of the load circuit 22 in the temperature range C can be expressed by the following equation. I _C = (I _H + I _T ) / (I _H · _IT ) = (I ₁ + I ₂ + I ₁ · I ₂ · _IT ) / [(I ₁ + I ₂ ) _IT ] (1) Similarly, the temperature The reactance I _{D in the} range D can be expressed by the following equation.

I _D = (I _M + I _T ) / (I _M · I _T ) = (I ₁ + I _T ) / (I ₁ · I _T ) (2) Further, the reactance I _{E in the} temperature range _E is expressed by the following equation. Can be expressed as

_IE = _IL + _IT = _IT (3) Therefore, the capacities of the capacitors C11, C12 and the trimmer capacitor 12 should be set so as to satisfy the above equations (1), (2) and (3). Then, the reactance of the temperature compensation circuit 25 changes in the direction of canceling the change of the reactance of the crystal unit 11, and the temperature compensation of the oscillation frequency becomes possible.

Here, the frequency change value Δf / F on the high temperature side (the side where the oscillation frequency increases) before correction of the crystal oscillation circuit
The maximum value of _fMAX (value based on the frequency change value at the reference temperature T _REF ), and the change value of the oscillation frequency is ± within the temperature range E above the temperature Tb on the high temperature side where the temperature compensation is started.
In order to fall within the range of X _H PPM, the following formula needs to hold.

(F _MAX −X _H ) / 2 = X _H (4) Therefore, similarly to X _H = f _MAX / 3, the maximum frequency change value before compensation on the low temperature side (side where the oscillation frequency becomes low). values and f _MIN, at a temperature Ta following temperatures C on the low temperature side to start the temperature compensation, in order to change values of the oscillation frequency is in the range of ± X _L PPM needs the following expression holds.

(F _MIN −X _L ) / 2 = X _L (5) Therefore, X _L = f _MIN / 3 Therefore, the frequency change value f _MAX on the high temperature side is the change value f on the low temperature side.
_With a crystal unit 11 with temperature characteristics larger than _MIN , maximum ±
The temperature compensation can be performed up to the range of X _H PPM, and the crystal oscillator 11 having the temperature characteristic in which the frequency change value f _MIN on the low temperature side is larger than the conversion value f _MAX on the high temperature side can perform the temperature compensation up to the range of ± X _L PPM. It will be possible.

FIG. 4 shows a frequency change value Δ of the crystal oscillation circuit when temperature compensation is applied by the temperature compensation circuit 25 of the embodiment.
The temperature characteristics of f / F and the reactance of the temperature compensation circuit 25 are shown.

Here, the semiconductor temperature sensor 23 detects the temperature T at which the frequency change value Δf / F corresponds to −f _MIN / 3PPM.
It is assumed that the voltage A is output at a and the voltage B is output at the temperature Tb at which Δf / F corresponds to + f _MAX / 3PPM (see FIG. 2).

As the ambient temperature decreases, the compensation temperature Ta on the low temperature side
When the temperature reaches, the reactance of the temperature compensation circuit 25 changes from I _M to the maximum value I _H as described above. As a result, the temperature change of the reactance of the crystal unit 11 is canceled out, and the frequency change value Δf / after temperature compensation at the temperature Ta is cancelled.
F changes from -f _MIN / 3 to + f _MIN / 3. Then, until the temperature Ta ′ at which the frequency change value Δf / F becomes f _{MIN in} the temperature characteristic before correction (the characteristic indicated by the broken line in FIG. 4), Δf
/ F is corrected in the range of ± f _MIN / 3.

The ambient temperature rises and the compensation temperature Tb on the high temperature side
Reactance of the temperature compensation circuit 25 changes from I _M to I _L. As a result, the temperature change of the reactance of the crystal unit 11 is canceled out, and the frequency change value Δf / F after temperature compensation at the temperature Tb changes from + f _MAX / 3 to −f _MAX / 3. The frequency change value Δf / F is f in the temperature characteristic before correction (the characteristic shown by the broken line in FIG. 4).
Δf / F is corrected to a range of ± f _MAX / 3 up to the temperature Tb ′ at which _MAX is reached.

As described above, in this embodiment, the temperature compensating circuit includes the semiconductor temperature sensor 23 and the capacitors C11 and C1.
2 and transistors such as transistors TR3 and TR4 that can be integrated into an IC, the temperature compensation circuit can be miniaturized. In particular, it is suitable for mobile wireless terminals and the like that are required to be downsized.

In the above-mentioned embodiment, the two capacitors C11 and C12 and the two transistors TR3 and TR are used.
Although 4 is used to switch the reactance of the temperature compensation circuit in three temperature ranges C, D, and E, the reactance may be changed in a more detailed temperature range by increasing the number of capacitors and transistors. Further, a variable inductance or the like may be used instead of the trimmer capacitor for adjusting the oscillation frequency.

[0038]

According to the present invention, since it is not necessary to use a plurality of chip thermistors or the like in the temperature compensation circuit, the circuit can be downsized. Also, a transistor that can be integrated into an IC,
Since the temperature compensating circuit can be configured with a semiconductor temperature sensor, a capacitor, etc., the circuit can be further downsized, and it is particularly suitable as a temperature compensating circuit for a mobile wireless device, which requires miniaturization.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a temperature-compensated crystal oscillation circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing a temperature characteristic of an output voltage of a semiconductor temperature sensor.

FIG. 3 is a diagram showing a relationship between temperature and Data1 and Data2.

FIG. 4 is a diagram showing a frequency change value of an oscillation frequency and a temperature characteristic of reactance of a temperature compensation circuit.

FIG. 5 is a circuit configuration diagram of a conventional temperature compensation oscillation circuit.

FIG. 6 is a diagram showing a frequency change value of an oscillation frequency in a conventional oscillation circuit and a temperature characteristic of reactance of a temperature compensation circuit.

[Explanation of symbols]

 11 crystal oscillator 12 trimmer capacitor C11, C12 capacitor 21 controller 23 semiconductor temperature sensor

Claims (1)

[Claims] 1. A crystal oscillator, a variable reactance element, a plurality of capacitors connected in series to the variable reactance element, a plurality of switching elements connected in parallel to the plurality of capacitors, and a semiconductor temperature sensor. And a control circuit for turning on and off the plurality of switching elements based on an output voltage of the semiconductor temperature sensor.