JPS6118364B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal generation circuit, and particularly to a signal generation circuit using an oscillation circuit that utilizes a piezoelectric material such as a crystal.

In devices such as electronic watches, it is common to use an oscillator with high frequency accuracy using a crystal or ceramic piezoelectric material to obtain a time reference. Figure 1 shows a typical crystal oscillator circuit of n-conductivity type.
Complementary type with MOSFET1 and P conductivity type MOSFET2
It uses a MOS inverter. The number of feedback resistors 3 to determine the operating point of the inverter is usually +M
Use a high value of Ω. A crystal oscillator 4 is provided to define the oscillation frequency, and capacitors 5 and 6
Together with this, they form the feedback circuit of the inverter. In an oscillation circuit with such a configuration, the oscillation frequency is mostly determined by the mechanical dimensions of the crystal resonator 4, so
A highly accurate oscillation frequency can be obtained. However, an oscillation circuit using such a piezoelectric mechanical vibrator (hereinafter referred to as a piezoelectric vibrator) has a power supply voltage (-V).
Typically, the rise of the oscillation waveform during application is very slow. Particularly when the power supply voltage is low, it may take one minute or more after the power supply voltage is applied until a steady oscillation width is obtained. FIG. 2 shows the waveform at the inverter output point 10 at the start of oscillation, and it can be seen that it takes a considerable amount of time to stabilize to a steady state. Although the waveform in FIG. 2 is under very poor conditions, it takes several tens of milliseconds to obtain a predetermined oscillation width even under favorable oscillation conditions. Furthermore, during the period when the predetermined amplitude is not reached, that is, immediately after the start of oscillation, oscillation may start at a very high frequency of the harmonic component of the frequency specific to the crystal, or conversely, at a very difficult frequency independent of the crystal. be. If an oscillation circuit using such a piezoelectric vibrator is built into a device and the output waveform of this oscillator is used as the device's reference clock pulse, the entire device will operate in a very unstable state when the power supply voltage is first applied. Become. In devices such as watches that simply display time using a frequency dividing circuit, there is no particular problem if used after steady oscillation has been achieved, but there has been a trend in recent years to use piezoelectric vibrators in various computers and control devices. A major problem arises when using an oscillator that is Computers have a so-called auto-clear function that automatically sets the entire device to a certain initial state when a power supply voltage is applied. After detecting the application of the power supply voltage, various hardware is initialized and the entire device is set to a certain initial state through certain software processing. In this case, if the electrical characteristics of each part of the hardware are completely uniform, the entire device will start operating at the same time when the oscillation waveform reaches a certain amplitude and frequency, but otherwise it will not work. The problem arises that when a wide range is started and the entire device is ready for operation, it has already been initialized in an incorrect manner.

SUMMARY OF THE INVENTION An object of the present invention is to provide a signal generation circuit that prevents unstable oscillation waveforms when power is applied and allows a device to operate stably.

The signal generation circuit according to the present invention removes the minute amplitude waveform immediately after applying voltage to the oscillation circuit using the history characteristics of the Schmitt circuit so that the output of the oscillation circuit including the piezoelectric vibrator is extracted through the Schmitt circuit. It is characterized in that only waveforms that have reached a certain amplitude are supplied to an arithmetic processing device or the like.

An embodiment of the present invention will be described below with reference to FIGS. 3 to 5.

FIG. 3 is a block diagram showing the configuration of the present invention. Eleven oscillation circuits 11 have the same configuration as in FIG. 1, and the output thereof is connected to the input of the Schmitt circuit 12. The output of the Schmitt circuit 12 is supplied to an arithmetic processing unit 13. Figure 4a shows an example of the configuration of the Schmitts circuit 12 in Figure 3, which includes two resistors.
The history characteristics can be determined by the resistance ratio of RI and Ro. Inverters 16 and 17 connected in series are inverters having a complementary MOS configuration, and a feedback loop is formed via a resistor Ro. Inverter 16
If the input inversion level is 1/2 of the power supply voltage -V, the loop consisting of inverters 16, 17 and the resistor Ro is inverted to the opposite polarity every time the input voltage Vi of the inverter 16 passes -V/2. Vi is a level obtained by resistor division of input Vr and output Vo, and if the output impedance of inverter 17 is sufficiently small, vi = (R _O V _I + RiV _O ) / (R _I +
R _O ). For example, in the case of R _I : R _O = 1:3, in order to invert the output Vo from OV to -V, the input level of -2/3V is required for the input Vi, and the output Vo is inverted from -V to OV. In order to do so, it is necessary to set the input Vr to -1/3V. This situation is shown in FIG. 4b. FIG. 5 shows the operating characteristics of a signal generator having such a configuration. When the power supply voltage -V is applied at _t0 in FIG. 5, the output of the oscillator 11, that is, the input Vr of the Schmitt circuit 12 starts oscillating from an intermediate level with a minute amplitude. The two input levels on the history characteristics of the Schmitt circuit 12 are
When Vi ₁ and Vi ₂ are set, during the period _{t 0} to t ₁ when the oscillation input Vi is between Vr ₁ and Vr ₂ , the output of the Schmitt circuit 12 is not inverted and the oscillation output becomes sufficiently large, and the frequency also becomes normal. A waveform appears at the output Vo of the Schmidt circuit starting from the period t ₁ when it approaches the value of . In this way, by inhibiting the output during the unstable oscillation period immediately after power is applied using the Schmitt circuit 12, only reliable oscillation waveforms are selectively supplied to the processing unit, so that the processing unit can operate correctly even immediately after power is applied. It becomes possible to make it work. In the embodiment of the present invention, the fourth
It goes without saying that the same results can be obtained by using other component circuits that naturally have hysteresis characteristics, such as the Schmitt circuit represented by the circuit shown in FIG. Further, the piezoelectric vibrating body of the oscillation circuit is not limited to crystal, and the circuit configuration is not limited to the embodiments.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a crystal oscillation circuit, FIG. 2 is a diagram showing operating waveforms of the oscillation circuit shown in FIG. 1 immediately after power is applied, and FIG. 3 is a block diagram showing a signal generation circuit according to an embodiment of the present invention. FIG. 4a is a circuit diagram showing an example of a Schmitt circuit, and FIG. 4b is a diagram showing its history characteristics. FIG. 5 is a diagram illustrating the signal output waveform of the embodiment of the present invention. 1, 2...MOSFET, 4...Crystal resonator, 1
1...Oscillation circuit, 12...Schmitt circuit, 13
...Arithmetic processing unit.

Claims (1)

[Claims] 1. The piezoelectric body includes an oscillation circuit that utilizes resonance and a Schmitt circuit having predetermined history characteristics, and the output of the oscillation circuit is taken out as a signal output via the Schmitt circuit, so that when the oscillation of the oscillation circuit starts, A signal generation circuit characterized in that minute amplitude pulses are prevented from appearing in the signal output.