JPH0276304A - Crystal oscillation circuit - Google Patents

Abstract

PURPOSE:To decrease the temperature coefficient of the oscillated frequency to the utmost by making the oscillated frequency of a crystal oscillation circuit nearly constant with respect to ambient temperature change. CONSTITUTION:A diode 1 is placed in the vicinity of a crystal oscillator 7 and the temperature of the crystal oscillator 7 is measured by the temperature of the diode 1 while supposing that the ambient temperature of the diode 1 is the same as that of the crystal oscillator 7. That is, since the forward resistance of the diode 1 varies with its temperature, a constant current is supplied to the diode 1 from a constant current circuit 2, the forward voltage drop is inputted to an A/D converter 3 to convert the voltage into a digital signal, then the digital output of the A/D converter 3 is a function of temperature. That is, when the ambient temperature is changed while keeping the connection of the input and output of a conversion circuit 4 all open, the output of the A/D converter 3 is changed and the oscillated frequency of the crystal oscillation circuit is changed, and the switching state of switching elements S01-S1n is changed. The changed switching state and an output signal of the A/D converter 3 at that time are related to each other through the internal connection of the conversion circuit 4. Thus, the oscillated frequency is made nearly constant independently of the temperature change.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a crystal oscillation circuit, and particularly to correction of the temperature coefficient of its oscillation frequency.

[Prior Art] FIG. 2 is a connection diagram showing a conventional circuit, in which 5 is an inverter, 6 is a resistor, 7 is a crystal oscillator, and 8 and 9 are capacitors. The inverter 5 has an amplification effect,
Oscillation occurs due to anti-coupling from its output terminal to its input terminal. This oscillation frequency is approximately equal to the unique resonant frequency of the crystal oscillator 7, and the temperature coefficient of the resonant frequency directly becomes the temperature coefficient of the oscillation frequency.

Figure 3 shows the frequency deviation Δf of the oscillation frequency f of the crystal oscillation circuit.
FIG. 3 is a diagram showing the relationship between /f and ambient temperature° C., with different curves indicating characteristics of different crystal oscillators.

[Problems to be Solved by the Invention] As described above, the conventional circuit has a problem in that the oscillation frequency changes depending on the temperature.

The object of the present invention is to solve the above-mentioned problems of the conventional circuit and to obtain a crystal oscillation circuit in which the temperature coefficient of the oscillation frequency is made as small as possible.

[Means for Solving the Problems] In the present invention, the temperature coefficient of the crystal oscillation circuit is compensated for by changing the capacitance of a capacitor loaded in parallel with the crystal oscillator according to the temperature. Figure 4 shows load capacity and oscillation frequency deviation Δf
2 is a diagram showing the relationship between /f, and different curves show characteristics for different crystal oscillators.

The capacitance of the load capacitor may be changed so as to give the same amount of change in the opposite direction as the change in Δf/f due to temperature. In this invention, the temperature in this case is measured by the forward voltage drop of a diode through which a constant current flows.

[Function] Measure the frequency-temperature characteristics of the crystal oscillator to be used and its load capacitance-frequency characteristics in advance, and change the load capacitor so that the temperature characteristics of the oscillation frequency can be compensated within the operating temperature range. .

[Examples] Examples of the present invention will be described below with reference to the drawings. 1st
The figure is a connection diagram showing one embodiment of the present invention. In Figure 1, the same symbols as in Figure 2 indicate the same or corresponding parts, 1 is a diode, 2 is a constant current circuit, and 3 is an analog-to-digital converter (hereinafter referred to as (abbreviated as A/D), COI, CO2, C
on, C1l, C12, and C1n are capacitors, respectively.
SOL, S02, Son, Sll, S12. Each Sln is a switching element.

The diode 1 is placed near the crystal oscillator 7, and the temperature of the crystal oscillator 7 is measured by the diode 1 assuming that the ambient temperature is the same. In other words, since the forward resistance of diode 1 changes depending on its temperature, a constant current is passed through diode 1 from constant current circuit 2, and the forward voltage drop is input to A/D B and converted into a digital signal. When converted to a signal, the digital number at the output of A/D 3 represents a function of temperature. Therefore, when determining the diode to be used, A/D
The temperature at that time can be determined from the output of step 3.

On the other hand, when the crystal oscillator 7 to be used is determined, it is known which curve in FIGS. 3 and 4 the Δf/f changes. The amount by which the load capacitor should be changed in order to give a change of -Δf/f to the change in Δf/f corresponding to the output of A/D3 can be determined from FIGS. 3 and 4. Since it is known which of the switching elements S01 to Sin should be controlled to open or close in order to give that change, there is It is decided what kind of response should be taken. The internal connections of the conversion circuit 4 may be made according to this determination.

When the crystal oscillator 7 used is changed, the characteristics shown in FIGS. 3 and 4 change, so the internal connections of the conversion circuit 4 may be changed in accordance with this change.

In order to experimentally determine the internal connections of the conversion circuit 4, it may be carried out, for example, in the following order. That is, the conversion circuit 4
If the ambient temperature changes while all connections between the input and output of the A/D3 are off, the output of the A/D3 will change and the oscillation frequency of the crystal oscillator circuit will change, but switching is performed to minimize this frequency change. The open/close states of elements 801 to Sin are changed. This changed opening/closing state and the A/
It is only necessary to associate the output signal of D3 with the internal connection of the conversion circuit 4.

In this way, the oscillation frequency can be kept approximately constant regardless of temperature changes.

[Effects of the Invention] As described above, according to the present invention, the oscillation frequency of the crystal oscillation circuit can be kept almost constant despite changes in ambient temperature.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram showing an embodiment of the present invention, FIG. 2 is a connection diagram showing a conventional circuit, and FIG. 3 is a diagram showing the relationship between the frequency deviation of the oscillation frequency of a crystal oscillation circuit and the ambient temperature. FIG. 4 is a diagram showing the relationship between frequency deviation of oscillation frequency and load capacity. 1... Diode, 2... Constant current circuit, 3... A
/D, 4... Conversion circuit, 5... Inverter, 6...
・Resistance, 7...Crystal oscillator, C01, CO2, COm
, C11, C12, C1n...capacitor, SQL,
SO2, SOm, S11, S12. Sin...Switching element. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] A constant current circuit that flows a predetermined constant current in the forward direction through the diode, an analog-digital converter that inputs the voltage between the electrodes of the diode and converts it into a digital signal, and an output of the analog-digital converter. an oscillation circuit configured by connecting a parallel circuit of a crystal oscillator and a resistor between the input terminal of the inverter and its output terminal, and an input terminal of the above-mentioned inverter. and a plurality of capacitors each inserted between the output terminal and the ground potential, a plurality of switching elements each connected between the plurality of capacitors and the ground potential, and opening/closing of the plurality of switching elements. A crystal oscillation circuit comprising: means for controlling according to the control signal output from the conversion circuit.