JPS62220005A - Crystal oscillator - Google Patents

Abstract

PURPOSE:To facilitate the large scale circuit integration without needing a capacitor group as a control element by connecting a capacitor in parallel with a series circuit of resistor groups selected in response to the changeover of a switch and the switch itself. CONSTITUTION:The switch 101 switched in response to a control signal and a resistor group 102 comprising plural resistors selected in response to the changeover of the switch 101 are connected in series. A capacitor 103 is connected in parallel with the series circuit. The series capacitance of a frequency control element is changed by using the switch to select the resistors and the oscillated frequency of the crystal oscillator is controlled in response thereto.

Description

[Detailed Description of the Invention] [Summary] In a crystal oscillator in which a crystal resonator and a frequency control element are connected in series to an oscillation circuit, there is a switch that is switched in accordance with a control signal, and a switch connected in series to the switch. A frequency control element is constituted by a connected resistor group consisting of a plurality of resistors selected in response to switching of the switch, and a capacitor connected in parallel to the series circuit of the switch and the resistor group. Since the values of the resistor and co-capacitor selected by the switch change, the oscillation frequency 26 of the crystal oscillator is stabilized by selecting the resistor of the resistor group according to the control signal.

[Industrial application field]

The present invention relates to a crystal oscillator whose oscillation frequency can be controlled, and more particularly to a crystal oscillator whose oscillation frequency is changed by changing a resistance value and which is suitable for LSI integration.

LS whose oscillation frequency can be controlled by digital control
There is a demand for integrated crystal oscillators.

In this case, it is necessary to use an element that can be easily integrated into an LSI as the frequency control element.

[Conventional technology]

FIG. 4 shows an example of the configuration of a conventional crystal oscillator, and illustrates an original crystal oscillator whose oscillation frequency is stabilized by digital control using a microcomputer. In the figure, 1 is a temperature sensor for detecting the ambient temperature, 2 is an analog-to-digital (A/D) converter that converts the detection signal of temperature sensor 1, which is an analog signal, into a digital signal, and 3 is a control microcomputer. (μCOM), 4 is a switch array controlled by the microcomputer 3, 5 is a capacitor group selectively connected by the switch array 4, 6 is a crystal resonator, and 7 is an oscillation circuit.

In FIG. 4, the switch array 4 always switches any one capacitor in the capacitor group 5 to connect it to the oscillation circuit 7 in series with the crystal resonator 6. As a result, according to the characteristics of the crystal resonator 6, a minute frequency change is caused in the oscillation frequency, which is determined by the value of the capacitor selected from the capacitor group 5. Temperature sensor 1 detects the ambient temperature of the crystal oscillator, and the detected temperature value is sent to A/D converter 2.
The signal is converted into a digital signal and input to the microcomputer 3. In response to the detected temperature digital value, the microcomputer 3 stores the capacitance value that should be connected in series to the crystal oscillator 6 in order to always maintain the oscillation frequency of the crystal oscillator at the specified value, and inputs the capacitance value to the input digital signal. The switch array 4 is controlled accordingly, and a capacitor having the optimum capacitance value for the temperature at that time is selected from the capacitor group 5 and connected to the oscillation circuit 7. In this manner, the crystal oscillator shown in FIG. 4 constitutes a digitally controlled temperature compensated crystal oscillator (DTCXO) whose oscillation frequency is stabilized regardless of temperature changes.

[Problem that the invention seeks to solve]

A digitally controlled temperature-compensated crystal oscillator is particularly suitable as an ultra-small, highly stable crystal oscillator in microcomputer-controlled equipment, and it is therefore desirable that most of the components other than the crystal oscillator can be integrated into an LSI. be done.

However, the conventional crystal oscillator shown in FIG. 4 uses multiple capacitors as frequency control elements. Capacitors are generally difficult to integrate into LSIs, and in particular, it is difficult to precisely adjust their capacitance values.

Therefore, there is a problem in that the crystal oscillator shown in FIG. 4 is not necessarily suitable for constructing an ultra-small, highly stable crystal oscillator integrated into an LSI.

[Means for solving problems]

In order to solve the problems of the prior art, the crystal oscillator of the present invention has a crystal oscillator in which a crystal resonator and a frequency control element are connected in series to an oscillation circuit, and the principle shown in FIG. It is equipped with each means shown in the basic structure.

101 is a switch, and switching is performed according to a control signal.

Reference numeral 102 denotes a resistor group, which is connected in series to the switch (101) and includes a plurality of resistors selected in response to switching of the switch (101).

A capacitor 103 is connected in parallel to a series circuit of a switch (101) and a resistor group (102).

[Effect]

The oscillation frequency of the crystal oscillator shown in FIG. 1 is determined according to the characteristics of the crystal oscillator, mainly depending on the capacitance value of the frequency control element. The capacitor (103) and the switch (101) cause the resistor group (102) to change the series capacitance value in the frequency control element isometrically, thereby controlling the oscillation frequency of the crystal oscillator in accordance with the control signal.

〔Example〕

FIG. 2 shows one embodiment of the present invention.
The same parts as in the conventional example shown in the figures are indicated by the same numbers, and their operations are also similar. 8 is a resistor group switched by the switch array 4, and 9 is a capacitor.

If we assume that the parallel circuit of capacitance and resistance is shown in Fig. 3(a), its equivalent circuit will be as shown in Fig. 3(b), where the respective capacitances c and c' and resistances R and R' in both
As is well known, there is the following relationship between them.

(1), (From the relationship of Equation 27, the oscillation frequency can be controlled by changing the series capacitance value of the crystal resonator 6 isometrically by switching the resistance in the resistor group 8 in the circuit shown in Fig. 2. I understand that.

It is easy to implement a resistor into an LSI, and its value can also be easily adjusted precisely. In the crystal oscillator shown in FIG. 2, the capacitor 9 is the only capacitive element, and the variable element is the resistor group 8, so that a compact highly stable crystal oscillator that can be integrated into an LSI can be easily realized.

The resistors constituting the resistor group 8 in the switch array 4 may be connected in such a way that each switch element is selected in sequence to select the corresponding resistance, or each switch element is connected in parallel in order to select each resistance in sequence. They may be connected in parallel.

In the crystal oscillator shown in FIG. 2, the switch array 4 can be constructed using ordinary transistor switches, but it may also be constructed using C-MOS switches. When the switch array 4 is composed of C-MOS switches, the on-resistance of the C-MOS switches can be used as each resistance in the resistor group 8, and therefore the resistor group 8 can be omitted. , which is further advantageous in making it into an LSI.

〔Effect of the invention〕

As explained above, according to the crystal oscillator of the present invention, a group of capacitors is not required as a control element when frequency control is performed by changing the frequency control element of the crystal oscillator in stages based on temperature control, etc. , it is easy to implement a compact, highly stable crystal oscillator that can be easily integrated into an LSI,
It is particularly suitable as a digitally controlled temperature compensated crystal oscillator.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the basic configuration of the present invention, FIG. 2 is a diagram showing the configuration of an embodiment of the present invention, FIG. 3 is a diagram explaining conversion between a series circuit and a parallel circuit, and FIG. 1 is a diagram showing a configuration example of a conventional crystal oscillator. 1...Temperature sensor 2...Analog-digital (A/D) converter 3...
・Microcomputer (μCOM) 4...Switch array 5...Capacitor group 6...Crystal resonator 7...Oscillation circuit 8...Resistor group 9...Capacitor

Claims (2)

[Claims] (1) In a crystal oscillator in which a crystal resonator and a frequency control element are connected in series to an oscillation circuit, the frequency control element includes: a switch (101) that is switched according to a control signal; ) connected in series with a resistor group (102) consisting of a plurality of resistors selected in response to switching of the switch (101); A crystal oscillator comprising: a capacitor (103) connected to a capacitor (103); (2) The crystal oscillator according to claim 1, wherein the switch (101) and the resistor group (102) are comprised of a plurality of C-MOS switches that are turned on in response to a control signal.