JPS61131207A - Alternating current bias circuit for sound recording - Google Patents

Abstract

PURPOSE:To obtain a circuit which generates no click sound with an AC bias signal during reproducing operation by providing a time constant circuit which slows down the rising and falling of the DC operation voltage of a constant current circuit. CONSTITUTION:A transistor (TR) 2 for control is impressed with a control signal A at its base at time t1 to turn on, and a DC operating voltage B impressed to the constant current circuit 5 rises slowly with the time constant determined by the internal resistance of the TR 2 and a capacitor 17. A current mirror circuit 10 outputs an intermittent current which is intermitted at the same period with an AC bias frequency signal C and increases slowly as the collector current of a TR 9, thereby obtaining an AC bias signal D. When the control signal A is ceased at time t2 and the base of the TR 2 goes up to H, this TR 2 turns off, but as the capacitor 17 of the time constant circuit 16 is discharged to a resistance 18, the operating voltage B drops and the constant circuit 5 loses current constancy and its output current decreases, so that the AC bias signal falls to zero at time t3 eventually. Therefore, no click tone is generated during reproducing operation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an AC bias circuit for recording in a magnetic tape recorder.

[Prior Art] A conventional circuit of this type is shown in FIG. Third
The figure is a circuit diagram showing a conventional recording bias circuit. In the figure, (1) is a DC power supply, (2) is a control transistor that is turned on and off by applying a control signal to the base, (
3) (4) is a transistor that constitutes the constant current circuit (5), (6) is a resistor that sets the current value of the constant current circuit (5), and (7) is an intermittent switching transistor that turns on and off at the AC bias frequency. , (8) (9) is a transistor constituting the current mirror circuit (10), (11) is a transformer for appropriate amplitude of the AC bias signal,
(12) is a capacitor for making the AC bias signal waveform into a sine wave voltage by resonating with the transformer (11), and these transformer (11) and capacitor (12) constitute an AC bias application circuit (13). ing. (1
4) is a recording signal source, and (15) is a recording head.

Next, the operation will be explained with reference to FIG. Figure 4 is a signal waveform diagram. Figure 4A is the control signal applied to the base of the transistor (2), Figure B is the DC operating voltage applied to the constant current circuit (5), and Figure C is the control signal applied to the base of the transistor (2). The AC bias frequency signal applied to the base of the transistor (7) shows the AC bias signal applied from the AC bias application circuit (13) to the recording head (15).

When the L-level control signal A is applied to the base of the control transistor (2) at time t1 in Figure 4, the transistor (2) is turned on, and the transistors (3) and (4) and the resistor (6) are turned on. ) is applied to the constant current circuit (5) to start operation, and the transistor (4) connects the base-emitter voltage (approximately 0.7 V in the case of a silicon transistor) of the transistor (3) to the resistor ( 6) A collector current with a current value approximately equal to the value divided by the resistance value is caused to flow. This constant collector current is alternately switched between the transistor (7) and one transistor (8) of the current mirror circuit (10). That is, the intermittent switching transistor (7
) is turned on and off by the signal shown in Figure 4C,
When that transistor is on, no current flows through the transistor (8) and the current mirror circuit (10) does not operate.
When transistor (7) is off, transistor (8)
is turned on, and the current of the constant current circuit (5) flows through the transistor (8).
The collector current flows through transistor (9) as well as transistor (8). The intermittent current generated by the on/off of the transistor (7) output from the current mirror circuit (10) is generated by the AC bias application circuit (10).
3), the signal is converted into a sine wave with an appropriate amplitude as shown in the fourth diagram, and is applied to the recording head (15) while being superimposed on the signal from the recording signal source (14) to be recorded. 1
Next, at time t2, the control signal A disappears and the transistor (2
) becomes H level, this transistor (2
) is turned off and its collector current does not flow, and the operating voltage B to the constant current circuit (5) becomes L and its operation stops. Therefore, the collector current of the transistor (4) becomes zero, the output current of the current mirror circuit (10) also becomes zero, and the generation of the AC bias signal stops. That is, the AC bias signal is output to the recording head (15) only when the control signal A is applied to the base of the transistor (2).

[Problems to be Solved by the Invention] Since the conventional recording AC bias circuit is configured as described above, an AC bias signal of a predetermined amplitude is suddenly generated by applying the control signal A (time tl). The AC bias signal suddenly disappears when the control signal A disappears (time t2). That is, the sharp signal changes at the beginning and end of the AC bias signal are recorded. Therefore, when this is played back, there is a problem in that a click sound can be heard at the beginning and end of the AC bias signal.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide an AC bias circuit for recording that does not produce click sounds during playback.

[Means for Solving the Problems] The recording AC bias circuit according to the present invention changes the rise and fall of the DC operating voltage B of the constant current circuit by turning on and off the control transistor in the conventional circuit described above. It is equipped with a time constant circuit to make it more gradual.

[Function] In this invention, the DC operating voltage of the constant current circuit changes gradually without rising and falling sharply, and the amplitude of the AC bias signal applied to the recording head also increases smoothly at the beginning. The value gradually increases and decreases smoothly at the end, so no click sound is generated during playback.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention. In the figure, (1) to (15) indicate the same parts with the same symbols as in FIG. 18).

Next, the operation will be explained with reference to the signal waveform diagram in FIG. Second
A to D in the figure are signals corresponding to A to D in FIG. 4, and indicate a control signal A, a DC operating voltage B, an AC bias frequency signal C, and an AC bias signal, respectively. First, at time t1, the control signal A is applied to the base of the control transistor (2) and the transistor (2) is turned on, but the collector current initially flows to the time constant circuit (16) and the capacitor (17).
As shown in Figure 2B, the operating voltage applied to the constant current circuit (5) rises gradually with a time constant determined by the internal resistance of the transistor (2) and the capacitor (17). I'm going down. Correspondingly, the current of the constant current circuit (5), that is, the collector current of the transistor (4), gradually increases, and finally the base-emitter voltage of the 1-herlange transistor (3) (approximately 0.0. 7V) divided by the resistance value of the resistor (6). Transistor (7) receives AC bias frequency signal C
Since the transistor (7) is turned on and off, the output current of the constant current circuit (5) changes depending on whether it is turned on or off.
The current mirror circuit (10) sends a slowly increasing intermittent current that is intermittent at the same period as the signal C to the transistor (10).
9) is output as the collector current. This intermittent output current is converted into a sine wave by the AC bias application circuit (13) as shown in the second diagram, and is applied to the recording head (15) to be recorded while being superimposed on the signal from the recording signal source (14).

Next, at time t2, the control signal A disappears and the transistor (2
) becomes ■], this transistor (2) turns off, but the capacitor (17) of the time constant circuit (16)
) is charged and the operating voltage B remains, so the constant current circuit (5) continues to operate, and the transistor (4)
The collector current flows and the AC bias signal is output. As the charging voltage of the capacitor (17) discharges into the resistor (18), the operating voltage B decreases and the constant current circuit (5
) loses its constant current property, the output current decreases, and finally reaches zero at time t3.

Correspondingly, the amplitude of the AC bias signal from the AC bias application circuit (13) gradually decreases until time t.
3, no AC bias signal is generated. Even if control signal A that rises sharply is applied in this way, operating voltage B
rises slowly, and the amplitude of the AC bias signal increases smoothly.Even if the control signal A suddenly falls, the fall of the operating voltage is gradual, and the amplitude of the AC bias signal smoothly decreases to zero. becomes. Therefore, even if such an AC bias signal is stored on the magnetic tape by the recording head (15), no click sound will be generated during reproduction.

The above two circuits may be constructed by wiring individual circuit components such as transistors and resistors, but of course they may also be constructed using semiconductor integrated circuits.

[Effects of the Invention] As described above, the present invention is provided with a time-limiting circuit that slows down the rise and fall of the DC operating voltage of the constant current circuit, so that the AC bias for recording does not generate click sounds due to the AC bias signal during playback. The circuit is i! There is an effect obtained by adding a special circuit.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a signal waveform diagram of each part thereof, Fig. 3 is a circuit diagram showing a conventional recording AC bias circuit, and Fig. 4 is a signal diagram of each part thereof. FIG. In the figure, (1) is a DC power supply, (2) is a control transistor, (5) is a constant current circuit, (7) is an intermittent switching transistor, (10) is a current mirror circuit, and (13) is a constant current circuit.
) is an AC bias signal application circuit, (14) is a recording signal source, (15) is a recording head, and (16) is a time constant circuit. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (2)

[Claims] (1) A control transistor that turns on and off according to a control signal, a constant current circuit that applies or cuts off a DC operating voltage depending on whether this transistor is turned on or off, an intermittent switching transistor that turns on or off at an AC bias frequency, and this transistor that turns on or off. , the output current of the constant current circuit is switched by turning off, and a current mirror circuit outputs an intermittent current according to this switching, and the intermittent output current of this current mirror circuit is converted into a sine wave voltage and superimposed on the recording signal. In a recording AC bias circuit equipped with an AC bias signal application circuit that applies an AC bias signal to a recording head, a time constant is provided to slow the rise and fall of the DC operating voltage of the constant current circuit due to turning on and off of the control transistor. An alternating current bias circuit for recording characterized by providing a circuit. (2) The time constant circuit includes a capacitor that is charged when the control transistor is turned on, and a resistor that discharges the charging voltage of the capacitor when the transistor is turned off, and the charging voltage of the capacitor is transferred to the constant current circuit. 2. The recording AC bias circuit according to claim 1, wherein the recording AC bias circuit is adapted to be applied as a DC operating voltage.