JPS6169205A - Crystal oscillation circuit - Google Patents

Abstract

PURPOSE:To attain the assured start of a crystal oscillation circuit with a higher harmonic wave and to maintain the high stability for a long period of time at an optimum oscillation level after the start, by providing a means which switches the circuit constant in order to increase the feedback resistance value in the duration of oscillations and to decrease said resistance value when the oscillation is started. CONSTITUTION:When a power supply is switched on, a signal generating circuit 6 immediately delivers 0 to turn on a switch contact S1 of a switch circuit 5. Then a resistance Rt is connected in parallel to a feedback resistance Rf of an oscillation circuit 3 including an ALS-TTL element 2. Thus the total feedback resistance value is decreased; while the feedback amount of the circuit 3 is increased. As a result, a crystal resonator 1 is intensively oscillated in the 3rd overtone and an output signal having a frequency three times as high as the basic harmonic wave of the oscillator is obtained through an output terminal T via a buffer 4. The output of the circuit 6 is set at 1 after a prescribed period of time during which the stable oscillations of the circuit 3 can be continuous. While the resistance Rt is separated from the circuit 3. Thus the feedback amount is reduced together with reduction of the oscillation intensity. The circuit 3, however, is already oscillated and this oscillation is continued stably in an overtone mode.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a crystal oscillation circuit used in electronic scales and the like that uses a crystal resonator as a pressure-sensitive element of a weight sensor.

(Conventional wave packets and their problems) Crystal resonators are widely used in various fields because they have little temperature dependence and can oscillate at stable frequencies.
It is also used as a pressure-sensitive element in a weight sensor in electronic scales that input signals from a weight sensor and execute various calculation processes.

However, when a crystal oscillator is used as the pressure-sensitive element of the ffEJf sensor of an electronic balance, the frequency change width when weight is applied to the crystal oscillator is very small, so there is a problem that sensitivity and resolution deteriorate. .

For this reason, an attempt has been made to oscillate the oscillation circuit of a single-weight sensor at an apert-7 frequency higher than the third harmonic to improve the sensitivity and resolution of the sensor.

Figure 2 shows an example of a crystal oscillator circuit that oscillates with such a third-order overtone.
The output side of the zero oscillation circuit 3, which connects the 3rd overtone generation resistor Rt to the oscillation circuit 3, which is composed of an ALS-TTLJ element (advanced, low power Schottky TTL element) 2 and feedback resistors R and f. An eight-pass filter 4 for impedance conversion is connected to the output terminal, and a third-order Overton output is obtained from the output terminal. Resistor R1, capacitor ClC2
is connected to prevent parasitic vibration. In addition, ALS-T
TL element 2 is 1 normal low power input, Tokey TTLX
It has superior performance in terms of operating speed, power consumption, etc. compared to other devices.

In a crystal oscillator circuit with such a configuration, a frequency adjustment circuit is not used to generate a resonant frequency, but a feedback resistor with an appropriate constant is used. If selected, the excitation level may become excessive.

There was a problem with the long-term stability (temporal characteristics) of the oscillation circuit.

(Objective of the Invention) The object of the present invention is to solve the problem of such a crystal oscillation circuit, and to configure the circuit to ensure that it starts with harmonics when the power is turned on, and to maintain one oscillation after starting. This improves the long-term stability of a single oscillation circuit by switching the circuit to achieve the optimum excitation level.

(Summary of the invention) t The crystal oscillation circuit of the present invention includes an oscillation circuit using a crystal resonator, and a one-tone generation resistor connected to O7 in order to cause the oscillation circuit to oscillate with harmonics. Means is provided for switching circuit constants so that one resistance is made small and the return resistance is made large when one oscillation is connected.

(Example) An example of the present invention will be described below with reference to the drawings. 1st
The figure shows an example of a crystal oscillation circuit according to the present invention. Circuit elements that are the same as those in the conventional example in FIG. A signal generating circuit 6 is provided which generates a signal for a certain period of time to open the switch contact.

The switch 5 is constituted by an LSI made of a TTL semiconductor element, and when the terminal E is '1', the switch contact SL is off, and when the terminal E is 'O', the switch contact S1 is on.The signal generating circuit 6 is an inverter. The terminal E of the switch 5 is kept at "o" for a predetermined time after power is turned on, and the terminal E of the switch 5 is kept at "o" for a predetermined period of time after the power is turned on.
becomes.

Therefore, when the power is turned on to the oscillation circuit, the signal generation circuit 6 operates for a predetermined time, and the switch contact S of the switch 5,
is on.

Next, the operation of the crystal oscillation circuit according to the present invention will be explained.

When power is applied to the crystal oscillator circuit, the signal generation circuit 6 immediately outputs "0", and the switch contact S1 of the switch 5
Turn on. By this operation, the resistor Rt is connected in parallel to the feedback resistor Rf of the oscillation circuit 3 including the ALS-TTL element 2, so the total feedback resistance value decreases, and the oscillation circuit 3
The amount of feedback increases, and as a result, the crystal oscillator l is strongly excited and oscillates in the third-order overtone mode, and the buffer 4
3 of the fundamental harmonic of the crystal oscillator l from the output terminal T via
An output signal with twice the frequency is obtained.

After a predetermined period of time has elapsed during which the oscillation circuit 3 can continue its oscillation operation stably, the output of the signal generator 6 becomes "1°", the switch contact S1 is turned off, and the resistor Rt is disconnected from the oscillation circuit 3. For this reason, the feedback resistance of the oscillation circuit 3 is only Rf, and the feedback is reduced, resulting in a weakening of the oscillation strength.However, since the oscillation circuit 3 is already in oscillation operation, its operation is stable without stopping. The oscillation operation continues with the third overtone mote.

Note that the switch 5 for switching the feedback amount of the oscillation circuit 3 may be composed of a TTL element as in the embodiment described above, or may be a switch composed of five C-MO elements, or may be composed of a contact switch. You can also.

Further, the signal generating circuit for controlling the switch 5 may also be configured to turn on the switch 5 for a predetermined period of time using, for example, an output signal from a monomulticircuit.

Furthermore, in the above embodiment, the resistor Rt is connected in parallel to the feedback resistor Rf using the switch 5 to reduce the feedback resistance value. If the amount of feedback is increased, the resistor Rt
It is also possible to short-circuit the resistor Rf with the switch 5 and use only the resistor Rf.

(Effects of the Invention) As explained above, the crystal oscillation circuit of the present invention is provided with means for switching the circuit constants at startup and when maintaining the excitation level, so at startup the feedback amount is increased and linear By widening the area, it is possible to stably oscillate with a third-order overtone, and when one oscillation is sustained, the feedback resistance is increased to suppress the excitation level and prevent deterioration of the vibrator. “is obtained.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a crystal oscillation circuit according to the present invention, and FIG. 2 is a circuit diagram of a conventional example. Rf...resistance for feedback, Rt...resistance for generating 3rd overtone, ALS-TTL...advanced,
Low power, Schottky TTL, 3... oscillation circuit,
5... Switch, SI switch contact, 6... Signal generation circuit. Patent applicant: Ishida Koki Seisakusho Co., Ltd.
Agent: Patent attorney Minoru Tsuji (1 other person) Figure 1 Rf

Claims (1)

[Claims] In a crystal oscillation circuit that uses a crystal resonator to oscillate with harmonics, the circuit constants are set such that the feedback resistance value is small when oscillation starts, and the feedback resistance value is large when oscillation continues. A crystal oscillation circuit characterized by being provided with a switching means.