JPS6329371A - Deciding circuit for kind of appearance signal - Google Patents

Abstract

PURPOSE:To attain automatic decision of the kind of appearance signal by providing a comparator circuit forming a discharge path for a capacitor and a voltage detection circuit detecting the appearance of one AC signal in a capacitor. CONSTITUTION:The holding voltage of a capacitor 9 charged from a positive power supply via a resistor 10 rises only for a period an output of a NOR gate 8 rises at a high level as shown in voltage waveform (g) as the charging is progressed and descends as the discharge is progressed in other period. When the magneto-optic signal is fed to an input terminal 1, the holding voltage of the capacitor 9 is kept at nearly 0V, a high level signal representing the appearance of the magneto-optic signal is outputted to an output terminal 12 from an inverter 11 and the signal is fed to an automatic switching circuit. On the other hand, no magneto-optic signal is fed to the input terminal 1 and a CD signal is fed to an input terminal 2, then a low level signal representing the appearance of the CD signal is outputted to the output terminal 12 from the inverter 11. Thus, the kind of appearance signal is decided automatically.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a circuit for determining the type of appearing signal used in optical recording/reproducing devices and the like.

BACKGROUND OF THE INVENTION Recently, with the practical use of magneto-optical recording/reproducing devices that utilize the magneto-optical effect, attempts have been made to make them compatible with optical recording/reproducing devices such as compact discs using the conventional pure optical system.

In the reproduction system of this dual-purpose device, an optical head and a differential amplifier circuit immediately following it are installed separately for each type of optical reproduction method and reproduction level, and a demodulation section at the subsequent stage is installed separately for each type. The idea is to make the device more versatile and economical by sharing it.

In such a dual-use reproduction system, a switching circuit is required between the two types of front-stage parts and the common demodulation part to change the circuit connection depending on which method is being used for reproduction. . Conventionally, it has been considered that the operation of such a switching circuit relies on the manual operation of the full operator of this device.

Problems to be Solved by the Invention The above-mentioned conventional switching systems rely on manual operations by the device user, which poses the problem of not only complicating operations but also prone to erroneous operations.

DESCRIPTION OF THE INVENTION A circuit for determining the type of appearing signal of the present invention which solves the problems of the prior art described above uses a capacitor charged from a power source via a resistor, an AC signal on one side, and a DC component of the AC signal on the other side. A comparison circuit that forms a discharge path in the capacitor when the former is large or small, and one of the AC signals appears when the voltage of the capacitor becomes above or below a predetermined value. By including a voltage detection circuit that detects this, the type of the appearing signal is automatically determined.

Hereinafter, the operation of the present invention will be explained in detail together with examples.

Embodiment FIG. 1 is a block diagram showing the configuration of an appearance signal type determination circuit according to an embodiment of the present invention.

In the figure, 1 is a signal reproduced from a magneto-optical disk (hereinafter referred to as "
An input terminal 2 receives a signal reproduced from a compact disc (hereinafter referred to as an "rCD signal"). Reference numeral 3 designates an integrating circuit that integrates the CD signal supplied to the input terminal 2 to extract its DC component, and 4 represents an inverter that inverts the polarity of the output of the integrating circuit 3. Further, 5.6 is a comparison circuit, 7 is a NOR gate, 8 is a diode, 9 is a capacitor, 10 is a resistor, and 12 is an output terminal for a type determination signal.

First, it is assumed that a magneto-optical signal as exemplified by waveform a in FIG. 2 is supplied to the input terminal 1. At this time,
No CD signal is supplied to the input terminal 2, and the integrating circuit 3 outputs a voltage waveform of negative polarity and low frequency components caused by weak noise input, offset, and the like. The inverter 4 outputs a voltage waveform C having a positive polarity and a low frequency component by inverting the polarity of this waveform C.

The comparison circuit 5 compares the voltage value of the voltage waveform a and the voltage value of the voltage waveform C of the magneto-optical signal, and as illustrated in the waveform d of FIG. Output voltage. On the other hand, the comparator circuit 6 compares the voltage value of the voltage waveform a and the voltage value of the voltage waveform s of the magneto-optical signal, and as illustrated in the waveform e of FIG. Outputs a certain voltage.

As a result, the output terminal of the NOR gate 7 has the waveform f in FIG.
As illustrated in FIG. 2, the outputs of comparison circuits 5 and 6 rise to high only during a period when both outputs are low. Therefore, the holding voltage of the capacitor 9 charged from the positive power source through the resistor 10 is charged only during the period when the output of the NOR gate 8 rises to high level, as illustrated in the voltage waveform g in FIG. In other periods, it decreases as the discharge progresses.

In this way, during the period when the magneto-optical signal is being supplied to the input terminal 1, the holding voltage of the capacitor 9 is maintained at approximately 0 volts, and a high signal indicating that the magneto-optical signal is appearing is output from the inverter 11 to the output terminal. 12 and is supplied to an automatic switching circuit for supplying a magneto-optical signal to a demodulation circuit.

On the other hand, no magneto-optical signal is supplied to input terminal 1,
When the CD signal is supplied to input terminal 2, the voltage waveform of the amplitude of the signal supplied from input terminal 1 will not exceed the voltage value range of C, and the outputs of comparator circuits 5 and 6 will be low. maintain the condition. As a result, the output of the NOR gate 7 remains high, and no discharge path is formed for the capacitor 9. Therefore, from the inverter 11, C
A low signal indicating that the D signal appears is output terminal 1.
2 is output.

Although the configuration of the window comparator that compares the absolute value of amplitude on both the positive and negative polarity sides has been illustrated above, it is also possible to adopt a configuration that compares the amplitudes on one of the positive and negative polarity sides.

Furthermore, although a configuration has been exemplified in which a discharge path is formed in the capacitor only during the period when the amplitude of the magneto-optical signal exceeds the DC component of the CD signal, a configuration may be adopted in which this amplitude relationship is reversed and the opposite determination result is output.

Furthermore, although a configuration has been exemplified in which the amplitude of the AC component of the magneto-optical signal and the DC component of the CD signal are compared, a configuration may also be adopted in which the DC component of the magneto-optical signal and the amplitude of the AC component of the CD signal are compared.

Effects of the Invention As explained in detail above, the circuit for determining the type of appearing signal of the present invention compares a capacitor charged from a power source via a resistor with the DC component of one AC signal and the DC component of the other AC signal. A comparison circuit forms a discharge path in the capacitor when the former is large or small, and detects the appearance of one of the above AC signals when the voltage of the capacitor becomes above or below a predetermined value. Since the configuration includes a voltage detection circuit that performs a voltage detection circuit, the type of the appearing signal can be automatically determined without irregular jumps in the determination result.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of a determination circuit according to an embodiment of the present invention, and FIG. 2 is a waveform diagram for explaining the operation of the determination circuit of FIG. 1. 1. Input terminal for magneto-optical signal, 2. Input terminal for CD signal, 3. Integrating circuit, 4. Inverter, 5.6. Comparison circuit, 7. NOR gate, 8. Diode, 9.・
Capacitor, 10...Resistor, 11...Inverter, 1
2... Judgment signal output terminal. Patent applicant: NEC Home Electronics Co., Ltd.

Claims (1)

[Claims] A circuit that determines which of two types of alternating current signals that never appear at the same time is present, which includes a capacitor that is charged from a power source via a resistor, and one of the alternating current signals. , a comparison circuit that compares the DC component of the other AC signal and forms a discharge path to the capacitor when the former is large or small; A circuit for determining the type of appearing signal, comprising: a voltage detection circuit for detecting that one of the alternating current signals appears.