JPS6015037B2 - crystal clock - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a quartz watch that is compensated for temperature-induced changes in rate.

An object of the present invention is to improve the time accuracy of a crystal clock.

The time standard for crystal clocks currently in use is 150.
×Cut type crystal units are often used.

As is well known, the temperature characteristic of the vibration frequency of this crystal resonator has a parabolic characteristic with respect to temperature, which has the disadvantage that the rate of the clock changes depending on the temperature. One method of eliminating this drawback, that is, compensating for the temperature characteristics, is to perform correction using a logic circuit using a temperature detection oscillator, as described below. However, this method has the disadvantage that the rate of the clock changes due to fluctuations in the power supply voltage.
The present invention obviates this drawback. FIG. 1 is a system diagram of a conventional temperature compensated crystal clock. In the figure 1
is a crystal oscillator, 2 is a frequency divider, 3 is a time display, 4 is a temperature detection oscillator, 5 is a difference frequency generator, and 6 is a square calculator. If a bent crystal resonator of 150× cut type is used as the resonator of the crystal oscillator, the oscillation frequency f of the crystal oscillator can be expressed as follows. f=b{11a(t-to)2} However, t is the temperature of the watch, the inflection point temperature of the oscillation frequency of the crystal oscillator, and is usually selected to be around 25o0.

a is a quadratic coefficient of approximately 3.5×10-8, and b is an oscillation frequency at the inflection point temperature. The output of the crystal oscillator is frequency-downgraded by a frequency divider to produce a normally one-second signal output that is applied to a time display. If this continues, the rate of the clock will change depending on the temperature, as is clear from the previous equation. Therefore, the difference frequency between the output frequency from the middle stage of the frequency divider and the temperature detection oscillator frequency is obtained by a difference frequency generator, squared by a square calculator, and added to the frequency divider input and added to the crystal oscillator oscillation frequency. In other words, if the oscillation frequency of the temperature detection oscillator changes linearly with respect to temperature, the rate of change is appropriate, and it matches the intermediate output frequency of the frequency divider at the inflection point temperature, then a in the previous equation is involved. The term is eliminated, allowing the clock to maintain a constant rate regardless of temperature. The output from the middle stage of the frequency divider to the square calculator in the figure determines the basic time for square calculation, and the oscillation frequency of the temperature detection oscillator is referenced only during this time. As described above, although this example is an excellent method in principle, it has major drawbacks in practice.

The biggest drawback is that CR oscillators or LC oscillators are usually used as temperature detection oscillators, but these have much worse voltage characteristics than crystal oscillators. When the frequency is corrected, the corrected frequency is largely influenced by voltage driving according to the voltage characteristics of the temperature detection oscillator. In particular, when using a hand display mechanism as a time display, a hand drive motor is used as a converter, and because a large current flows momentarily through this motor every second, the battery voltage is intermittently reduced. This results in a large decrease in the temperature detection oscillator's oscillation frequency, and the oscillation frequency of the temperature detection oscillator also changes significantly. For this reason, the amount of compensation for the temperature characteristics of the crystal oscillator also fluctuates, making it impossible to obtain a highly accurate timepiece. The amount of this fluctuation, in other words, the amount of decrease in battery voltage, varies greatly depending on factors such as remaining battery capacity and ambient temperature, and it is impossible to adjust the amount of compensation in anticipation of these factors. The present invention makes it possible to stably compensate for the temperature characteristics of the crystal oscillator by stabilizing the power supply voltage of the temperature detection oscillator, and also allows the constant voltage power supply to operate only during the period in which the oscillation frequency of the temperature detection oscillator is referenced. This suppresses the increase in current consumption.

FIG. 2 is a system diagram of a specific example of the quartz watch of the present invention.

In the figure, 7 is a crystal oscillator, 8 is a cylinder divider, 9 is a time display, 1 is a temperature detection oscillator, 11 is a difference frequency generator,
12 is a square calculator, and 13 is a constant voltage circuit. Although the general operation is the same as the example shown in FIG. 1, there are major differences in the following points. That is, in this example, the output from the frequency divider that is synthesized inside the frequency divider is added to the square calculator to determine the basic time for square calculation, and the constant voltage circuit is operated intermittently. The output is coupled to a temperature detection oscillator. FIG. 3 is an example of a constant voltage circuit used in the present invention.

The illustrated circuit is an example constructed of a CMOS circuit, and the voltage supplied from the voltage input terminal 14 is output from the voltage output terminal 16 in accordance with the control voltage of the control terminal 15. That is, when the control voltage is at a low potential, the output voltage is made constant, so the temperature detection oscillator connected thereto oscillates stably with respect to the environment other than the temperature of the watch. The value of this constant voltage can be changed by changing the threshold values of transistors 17 and 18. On the other hand, when the control voltage is at a high potential, no current flows through the circuit of FIG. 3, and no voltage appears at the output. Therefore, since the temperature detection oscillator is operated intermittently according to the output of the constant voltage circuit, power consumption can be reduced. With the above configuration, the present invention has the following effects.

1. The temperature detection accuracy of the temperature detection oscillator is improved without being affected by the power consumption of the time indicator, the remaining battery capacity, etc., and the time accuracy of the clock is improved.

2. Constant voltage circuits, which generally have poor power efficiency, can be used for only the necessary time.
That is, since the temperature detection oscillator is operated only when its oscillation frequency is referenced, the increase in current consumption can be suppressed to a low value.

As described above, the present invention is a crystal clock that performs temperature compensation using the oscillation frequency of a temperature detection oscillator, in which the oscillator is operated via a constant voltage circuit only during the period when the oscillation frequency of the temperature detection oscillator is referenced. This will be useful for the practical application of high-precision, low-power consumption clocks.

[Brief explanation of the drawing]

Figure 1 is a system diagram of a secondary temperature-compensated quartz clock, Figure 2
The figure is a system diagram of a specific example of the present invention, and FIG. 3 is an example of a constant voltage circuit used in the present invention. 7... Crystal oscillator, 13... Constant voltage circuit, 10... Temperature detection oscillator, 12...
- Square calculator. Boo diagram Bu 2 diagram O 3 diagram

Claims (1)

[Claims] 1. In a crystal clock consisting of a crystal oscillator, a frequency dividing circuit, and a time display device, a temperature detection oscillator, means for compensating the temperature characteristics of the crystal oscillator using the oscillation frequency of the temperature detection oscillator, and for driving the temperature detection oscillator. The constant voltage circuit has a voltage input terminal, a control terminal, and a voltage output terminal that outputs a constant voltage according to the voltage of the control terminal, and the temperature detection oscillator is connected to the control terminal intermittently. A crystal clock, characterized in that an output signal of the frequency dividing circuit is inputted to drive the clock.