JPH1168461A - Piezoelectric oscillation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a highly stable frequency temperature characteristic by providing plural N-th order function generating circuit outputting DC voltage corresponding to a temperature in an optional temperature range so as to constitute a temperature compensation voltage generation circuit. SOLUTION: A voltage controlled crystal oscillator (VCXO) 4 is provided with a cubic function characteristic outputting a specific frequency at a control voltage 2 V at a normal temperature and provided with a maximum value within a temperature range lower than a normal temperature and a minimum value within a temperature range higher than the normal temperature. A temperature sensor 1 provides outputs for plural N-th order function generating circuits 2-1 to 2-n. The circuit 2-1 is provided with a minimum value smaller than +2 V within a temperature range lower than the normal temperature and a maximum value larger than +2 V within a temperature range higher than the normal temperature by setting the normal temperature to be an inflection point temperature as output voltage. The other circuits 2-2 to respectively output the compensation voltage of a proper N-th order function concerning a part in a temperature range where the temperature characteristic of VCXO 4 cannot be compensated sufficiently by the output voltage of the circuit 2-1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric oscillator,
In particular, it relates to a temperature compensated piezoelectric oscillator.

[0002]

2. Description of the Related Art A small crystal oscillator is a key part of a mobile communication device such as a portable telephone which has been increasingly demanded in recent years as a reference frequency source. A crystal oscillator used in such a mobile communication device has stability of an oscillation frequency within an operating temperature range which is one of its important characteristics, that is, a frequency temperature characteristic, usually ± 1 to ± 3 ppm. Stability is required. It is generally known that the frequency characteristics of an AT-cut crystal resonator with respect to a temperature change are approximated by a cubic function, and the frequency-temperature characteristics of a crystal oscillator using this as an oscillation source also depend on those of the crystal resonator. A, which is known to have high frequency stability among quartz oscillators
Even if a T-cut crystal oscillator is used, the frequency temperature characteristics of the crystal oscillator can be adjusted within a temperature range of -40 ° C to + 85 ° C.
It is impossible to keep it within 10 ppm. Because of this,
When used in a mobile communication device, it is common to use a temperature-compensated crystal oscillator (hereinafter referred to as TCXO) provided with a temperature compensation circuit for flattening the frequency-temperature characteristics of the crystal resonator.

As such a TCXO temperature compensation method, an analog indirect temperature compensation method is widely known.
The analog indirect compensation method is a voltage-controlled crystal oscillator (hereinafter referred to as VCXO) having a variable reactance circuit capable of controlling a reactance value such as a variable capacitance diode in an oscillation loop as shown in FIG. And supplies a voltage exhibiting a cubic change derived from a network composed of a resistance element and a thermistor element as shown in FIG. 4B to both ends of the variable reactance circuit. In other words, a cubic function reactance change is given to the temperature change in the oscillation loop, and the frequency temperature characteristic as the crystal oscillation circuit is compensated within a predetermined value.

[0004]

However, in the conventional analog indirect type TCXO, the temperature compensation characteristics of the thermistor elements constituting the temperature compensation voltage generating circuit and the temperature characteristics of the resistance elements and the like cause the following problems. No matter how the temperature compensation voltage generating circuit is adjusted, it is impossible to completely flatten the frequency temperature characteristics of the crystal unit, and in general, a compensation limit value of the frequency temperature characteristics of the analog indirect compensation type TCXO is used. Is within ± 1.0 ppm / about −30 ° C. to + 85 ° C. If a higher stability is required, it is necessary to use a digital type temperature compensation or a constant temperature oven type crystal oscillator. Digital temperature compensation converts ambient temperature information into a digital signal, reads out a control voltage code to be output corresponding to each temperature from a memory device that stores the temperature signal, and sends a voltage control oscillator to the voltage control oscillator based on the control voltage code. It has a compensation circuit configured to generate a control voltage to be supplied. However, since the temperature compensation voltage is changed based on the digitized temperature information, the temperature compensation voltage changes stepwise discontinuously with respect to the change in the ambient temperature. When this temperature compensation voltage is applied to a variable reactance element, a problem of "phase jump" occurs in which the oscillation frequency changes instantaneously with a change in temperature. If a TCXO having such characteristics is used in a mobile communication device, communication will occur. Problems such as interruption of data transmission and transmission of erroneous data. On the other hand, the thermostatic oven crystal oscillator has a highly stable frequency-temperature characteristic and has no frequency “phase jump”, but it is necessary to heat the thermostat to about + 70 ° C. to + 90 ° C. In addition to the drawback that the power consumption is several tens to several hundred times that of TCXO, the crystal oscillator with a thermostat is large and expensive, so it cannot be used for a small and inexpensive mobile communication device. It is.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problem, eliminates "phase jump", and uses a conventional analog indirect compensation type TCXO.
It is an object of the present invention to provide a TCXO which has more stable frequency-temperature characteristics and is easy to downsize.

[0006]

According to the present invention, the frequency temperature compensation system is an analog compensation system without "phase jump" of the oscillator frequency with respect to a temperature change. Among them, a thermistor element which cannot be integrated is used. An analog indirect compensation system using a temperature compensation voltage generation circuit having an Nth-order function generation circuit capable of realizing temperature compensation of an oscillator output frequency in an arbitrary temperature range. Further, in order to improve the temperature compensation accuracy, the temperature compensation voltage generation circuit includes a plurality of the N-th order function generation circuits capable of outputting a DC voltage in an arbitrary temperature range. Is applied to a variable reactance element in the oscillation loop of the oscillation circuit to realize a TCXO that achieves frequency temperature compensation.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on embodiments. FIG. 1 is a configuration diagram of a block circuit showing an embodiment of a TCXO using a temperature compensation voltage generation circuit based on the present invention. The TCXO 5 shown in FIG. 1 includes a temperature sensor 1 and a plurality of N-order function generation circuits (2-1, 2-2).
.. 2-n), an adder circuit 3, and a voltage controlled crystal oscillator (VCXO) 4. The output of the temperature sensor 1 is output from a plurality of N-order function generation circuits (2-1). 2-2... 2-n). The output of each of the plurality of N-order function generation circuits (2-1, 2-2,..., 2-n) is input to the control voltage input unit of the VCXO 4 via the addition circuit 3. This constitutes the TCXO 5 shown in FIG. In the example of FIG. 1, the VCXO 4 shown in FIG. 1 is set to output a specific frequency f ₀ when the DC voltage input to the control voltage input unit is +2 V at normal temperature. FIG. 2A shows an example of the frequency-temperature characteristics of the TCXO 5 in a state where the control voltage of the VCXO 4 in FIG. 1 is fixed at +2 V, in which the horizontal axis represents temperature and the vertical axis represents frequency deviation. In other words, it shows a state without the temperature compensation function, and reflects the frequency-temperature characteristics of the crystal unit as it is, and sets a maximum value within a temperature range equal to or lower than normal temperature and a temperature equal to or higher than normal temperature as normal temperature as an inflection point temperature. It exhibits a cubic feature with a local minimum. FIG. 2B shows an example of a frequency control voltage characteristic indicating a change in the oscillation frequency with a change in the control voltage value of the VCXO 4 in FIG. 1 as a control voltage value on the horizontal axis and a frequency deviation on the vertical axis. It can be seen that the frequency of the VCXO4 increases linearly with an increase in the control voltage. FIG. 2C shows an example of a temperature compensation voltage characteristic indicating an output voltage value with respect to the temperature of the Nth-order function generation circuit 2-1 in FIG. 1, in which the horizontal axis represents temperature and the vertical axis represents compensation voltage. The temperature compensation voltage characteristic is a characteristic having a minimum value of +2 V or less in a range lower than room temperature and a maximum value of +2 V or more in a range higher than room temperature, where room temperature is an inflection point temperature.

Further, other N-order function generating circuits (2-
2, 2-3 ... 2-n) is not output or 0
It is assumed that the output is V. 1 when the temperature compensation voltage shown in FIG. 2C is input to the control voltage input section of the VCXO 4 in FIG. 1 having the characteristics of FIGS. 2A and 2B.
The frequency temperature characteristic of CXO5 cannot be sufficiently canceled in the temperature range A 'to A and B' to B and C 'to C shown in FIG. 2D, which is the analog indirect compensation in the prior art. It corresponds to the compensation limit state in the method. FIG. 2
In order to make the frequency-temperature characteristics shown in FIG. 2D more stable, the frequency characteristics of the temperature ranges A 'to A and B' to B and C 'to C shown in FIG. The correction compensation voltage as shown in FIG. 3 (e) may be input to the control voltage input section of the VCXO4. Note that the characteristic of FIG.
It can be obtained from (b) and FIG. 2 (d). The correction compensation voltage as shown in FIG. 3 (e) can be expressed by a plurality of functional expressions. In this example, the temperature ranges A ′ to A are set to facilitate understanding of the effects of the present invention. As a quadratic correction compensation voltage, the temperature ranges B 'to B are cubic correction compensation voltages, and the temperature ranges C' to C are linear function correction compensation voltages. The correction voltages in the three temperature ranges are output from different N-order function generation circuits, respectively, and FIG. 3F shows the output from the temperature range A ′ in FIG. 2D output from the N-order function generation circuit 2-2. FIG. 3 (g) shows the compensation compensation voltage of A, and FIG. 3 (g) shows the compensation compensation voltage of the temperature range B ′ to B in FIG. 2 (d) output from the N-order function generation circuit 2-3. ) Is the N-order function generation circuit 2
-4 from the temperature range C ′ in FIG.
Is the correction compensation voltage.

The N-order function generating circuit (2-2, 2-3,
2-4) is added to the compensation voltage output from the N-order function generation circuit 2-1 by the addition circuit 3 shown in FIG. 1, and then the VCXO shown in FIG.
By inputting the voltage to the control voltage input unit of FIG. 4, the frequency temperature characteristic of the TCXO 5 shown in FIG. 1 is highly stable (for example, within ± 0.5 ppm / −30 ° C. to + 85%) as shown in FIG.
° C). In the embodiment according to the present invention, an AT-cut quartz oscillator is used as the oscillator piezoelectric element. However, the present invention is not limited to this, and the output of the N-order function generating circuit shown in FIG. 1 is not limited to a cubic function. By adjusting using any function, the present invention can be applied to various piezoelectric elements.

[0010]

The temperature-compensated piezoelectric oscillator having the temperature-compensated voltage generating circuit according to the present invention is of an analog compensation type, so that there is no "phase jump" generated by a digital method. Since it is composed of a plurality of N-order function generation circuits capable of outputting a DC voltage in an arbitrary temperature range, it realizes a more stable frequency-temperature characteristic as compared with a temperature-compensated piezoelectric oscillator using a conventional technique. It is possible. Further, the temperature compensation voltage generating circuit according to the present invention does not use a thermistor element, so that it is easy to integrate and further downsize the oscillator.

[0011]

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a TCXO according to the present invention.

FIG. 2A shows oscillator frequency temperature characteristics before compensation. FIG. 2B shows frequency control voltage characteristics of VCXO. FIG. 2C shows compensation voltage of N-order function generation circuit 2-1. d) ··· Shows TCXO frequency temperature characteristics

FIG. 3 (e) ··· Compensation compensation voltage (f) ··· Compensation compensation voltage by Nth order function generation circuit 2-2 (g) ··· Compensation compensation voltage by Nth order function generation circuit 2-3 (h) · • Correction compensation voltage by N-order function generation circuit 2-4 (i) • Frequency temperature characteristic of TCXO according to the present invention

4A shows a block diagram of a conventional analog indirect type temperature-compensated oscillator. FIG. 4B shows an example of a compensation voltage generating circuit.

[Explanation of symbols]

1. Temperature sensor 2. Voltage generation circuit block (2-1, 2-2, 2-3 ... 2-n) Nth order function generation circuit 3. Addition circuit 4. Voltage controlled crystal oscillator (VCXO) R1, R2, R3: resistance element THR1, THR2: thermistor element

Claims (2)

[Claims] A voltage-controlled oscillation circuit for supplying a predetermined compensation voltage to the voltage-controlled oscillation circuit in accordance with a temperature change; In a temperature-compensated oscillator in which a change in frequency is suppressed, the voltage generation circuit includes a plurality of Nth-order function voltage generation circuits and an adding means for adding the outputs of the Nth-order function voltage generation circuits. Type oscillator. 2. The temperature-compensated oscillator according to claim 1, wherein at least one of the Nth-order function voltage generation circuits constituting said voltage generation circuit is a third-order function generation circuit.