JPH0631992B2 - Sounding drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a tone generation driving circuit.

[Prior Art] For example, a configuration as shown in FIG. 4 is used as a sound generation drive circuit in an alarm timepiece. In the figure, the attack pulse of FIG. 5A is supplied to the terminal a, the transistor 6 becomes conductive, and the capacitor 4 is charged. When this attack pulse stops, capacitor 4
Since the charged electric charge of is discharged through the resistor 5, the voltage of the terminal b changes as shown in FIG. 2B. On the other hand, the acoustic signal of FIG. 5C is supplied to the terminal c. By this pulse, the switching circuits 2a and 2b are alternately turned on, whereby an acoustic signal whose amplitude is modulated as shown in FIG. 5D is generated at the terminal d, and the output transistor 1 is generated as shown in FIG. 5E. A current flows and the sounding body 7 is driven.

[Problems to be Solved] For example, the envelope of voice requires a time constant of 0.1 seconds to 3 seconds.
Moreover, in order to realize a small circuit space, the capacitor 4 is usually a ceramic type of 0.1 μF or less,
At this time, the resistor 5 needs to have a high resistance of 1 to 30 MΩ, which makes it difficult to integrate the resistor 5 in the IC.

Further, since the output transistor 1 usually has a threshold voltage of 0.5 to 1 v, when the voltage at the terminal b becomes equal to or lower than the threshold voltage V _TH as shown in FIG. 5B, the output current of the output transistor 1 in the conventional device described above. Is Fig. 5E
As described above, there is a drawback in that the sound generated from the sounding body 7 is also interrupted.

It is an object of the present invention to provide a small-area sound generation drive circuit that generates a drive signal that attenuates the sound from the sounding body with an optimum envelope.

[Means for Solving the Problems] The present invention relates to a charging / discharging circuit which includes at least a capacitor and is charged by the arrival of an attack pulse, an output transistor for driving a sounding unit, and a charging voltage of the capacitor by an acoustic signal. And a switching circuit for supplying the output transistor to the output transistor. The time constant of the charging / discharging circuit is optimized by connecting the discharge control transistor that is switched by the pulse in parallel with the capacitor in the charging / discharging circuit by eliminating the interruption of the sound. A discharge control transistor that is switched, A series circuit composed of a sub-capacitor having a smaller capacity than that of the above-mentioned capacitor is connected in parallel to the above-mentioned capacitor, and a switching circuit which is switched by the pulse at a timing opposite to that of the discharge control transistor is connected in parallel to the above-mentioned sub-capacitor. As a result, the area of the circuit can be reduced.

[Embodiment] Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, 1 to 7 are the same as those in FIG.
Reference numeral 8 is a diode-connected transistor having substantially the same size as the output transistor 1 and the same threshold value, and 9 is a discharge control transistor for controlling the discharge time of the capacitor 4.

Next, the operation will be described with reference to FIG. The discharge control transistor 9 is for adjusting the discharge time (envelope waveform) by the capacitor 4 and the resistor 5, and its operation will be described later. First, the transistor 8 is made to have substantially the same size as the output transistor 1 in the same step, and its forward voltage drop is designed to be the same voltage as the threshold voltage V _TH of the output transistor 1. Therefore, the voltage at the terminal b due to the discharge of the capacitor 4 becomes as shown in FIG. 2B, and does not _fall below the threshold voltage V _TH of the output transistor 1. Therefore,
The amplitude-modulated acoustic signal generated at the terminal d is smoothly attenuated as shown in FIG. 2D, and a sound with a lingering sound can be generated without sudden interruption as in the conventional case.

Next, the operation of controlling the envelope waveform by the discharge control transistor 9 will be described. A pulse is supplied to the input terminal e of the discharge control transistor 9, switching is performed by this pulse, and the capacitor 4 is discharged only when the discharge control transistor 9 is on. Therefore, by adjusting the duty of the pulse from the input terminal e, the discharge time of the capacitor 4, that is, the envelope waveform of FIG. 2B can be arbitrarily controlled,
The length of the afterglow can be adjusted. In other words, the time constant can be adjusted by the duty of the pulse, such that the apparent time constant can be increased without increasing the area of the capacitor 4 or the resistor 5.

Next, a second embodiment of the present invention will be described with reference to the drawings.

FIG. 3 shows the envelope waveform adjustment using a capacitor instead of the resistor 5 in FIG. 1. In FIG. 3, 1 to 9 are the same as those in FIG. 1 and 10 is a capacitor. Sub-capacitor with smaller capacity than 4, 11 is "1"
Is a switching circuit that turns on when is input.

Next, the operation will be described. The discharge control transistor 9 and the switching circuit 11 are alternately switched by the clock signal supplied to the input terminal e. Therefore, when the input terminal e is “0” and the discharge control transistor 9 is on, the current discharged from the capacitor 4 is charged in the sub-capacitor 10, and then the input terminal e becomes “1”, and the switching circuit When 11 is turned on, the sub capacitor 10
Discharges. Therefore, the discharge time of the capacitor 4,
That is, the envelope waveform is controlled by the frequency of the lock signal supplied to the input terminal e.

By the above operation, the output current of the output transistor 1 is
Similar to the case of the first embodiment, it becomes as shown in FIG. 2E.

[Effect] According to the present invention, since the acoustic signal supplied to the output transistor does not become lower than the threshold voltage, the sound from the sounding body is not interrupted on the way as in the conventional case, and the optimum reverberation is accompanied. It can generate high quality sound. Also, since the discharge time of the capacitor can be controlled by the discharge control transistor or sub capacitor, the time constant can be increased without increasing the capacitor or resistance of the charging / discharging circuit, and the time constant can be adjusted by the pulse duty or frequency. The circuit area can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an electric circuit diagram showing a first embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the operation of FIG. 1, and FIG. FIG. 5 is an electric circuit diagram showing the second embodiment, FIG. 4 is an electric circuit diagram showing a conventional example, and FIG. 5 is a waveform diagram for explaining the operation of FIG. A ... Charge / discharge circuit 1 ... Output transistor 2a, 2b, 11 ... Switching circuit 8 ... Transistor 9 ... Discharge control transistor 10 ... Sub capacitor

Claims (3)

[Claims] 1. A charging / discharging circuit which includes at least a capacitor and is charged by the arrival of an attack pulse, an output transistor for driving a sounding means, and a switching which supplies a charging voltage of the capacitor to the output transistor by an acoustic signal. And a diode-connected transistor having the same threshold value as the output transistor is provided in parallel with the capacitor in the charge / discharge circuit. 2. The sound generation drive circuit according to claim 1, wherein a discharge control transistor switched by a pulse is connected in parallel to the capacitor in the charge / discharge circuit. 3. The tone driving circuit according to claim 1, wherein a series circuit including a discharge control transistor switched by a pulse and a sub-capacitor having a smaller capacity than the capacitor is connected in parallel to the capacitor, and the pulse is generated. A sound generation drive circuit characterized in that a switching circuit that is switched at a timing opposite to that of the discharge control transistor is connected in parallel to the sub capacitor.