JPS59172813A - Circuit for generating muting control signal - Google Patents

Abstract

PURPOSE:To generate a muting control signal for preventing an unpleasant shock sound at switch changeover by providing an exclusive logical circuit at the input stage, a charge pump circuit and an exclusive logical circuit at an output stage. CONSTITUTION:An input circuit E1 using the exclusive logical circuit so as to detect the change in plural switch inputs, the charge pump circuit CP whose charge/discharge is controlled by the output of the input circuit E1, and the exclusive logical circuit E2 of the output stage taking an output of the input circuit E1 and an output of the charge pump circuit CP as two inputs and generating a muting control signal for a prescribed time only when one of the inputs to the input circuit E1 is changed, are provided. Thus, the muting control signal to prevent the unpleasant shock sound generated at the changeover of switches SW1, SW2 is generated in this way.

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a control signal generation circuit for a mute circuit that eliminates noise (bopping noise) accompanying the switching operation of a switching circuit of an amplifier to which the switching circuit is added.

Prior Art and Problems ゛ Figure 1 shows an example of an amplifier circuit built into an auto-reverse type tape deck, where 1 is an amplifier that amplifies the input A detected from the A side of the magnetic tape, and 2 is the amplifier that amplifies the input A detected from the B side of the magnetic tape. This is an amplifier that amplifies input B. This type of tape deck has four heads, which are in contact with the magnetic tape in the playing state, two of the four heads produce stereo playback output when in forward mode, and the remaining two heads produce stereo playback output when in reverse mode. occurs. Input A indicates one of the playback stereo outputs in forward mode (the other is not shown), input B indicates that in reverse mode, and side A and side B refer to the tape surface with which each of the above two heads comes into contact. say. amplifier 1
．． The output of 2 is input to the output stage amplifier 3 through the F/R changeover switch SWb, which is switched according to the tape running direction F/R (F is forward, R is reverse), and F/R selection is thereby made. . S W a is amplifier 1 to 3
This is a changeover switch that changes the characteristics of the amplifier circuit including the magnetic tape, and is switched to the M side or the N side depending on whether the magnetic tape used is metal (M) or normal (N).

In an auto-reverse type tape deck, the running direction during playback is changed by a switch (not shown), and this switch and F
'/R changeover switch SWb is interlocked. When these switches are switched, a shock sound is generated from the speaker, but to avoid this, a mute circuit is usually used. The mute circuit is a circuit that has the function of preventing audio output from being sent to the speaker by connecting the amplifier's signal line to the ground, etc., but this circuit is activated temporarily only when switching causes a popping sound. This requires an appropriate muting control signal generation circuit. Since the popping sound also occurs when the M/N changeover switch SWa is operated, a muting control signal generation circuit is also required for this switch SWa.

FIG. 2 fal (b) shows a conventional example. In the same figure (a), when the switch SW is turned on, the muting control signal OU
However, since the circuit system is such that the signal OUT always occurs while the switch SW is on, simply
cannot be used in conjunction with the selector switch SWa or SWb shown in FIG. That is, in one state, mu1 is always
- is applied. In order to use this circuit, switch SWa etc. is used only while changeover switch SWa etc. is performing switching operation.
It is necessary to take measures such as closing the door, but it is insufficient.
It is inevitable that imperfections will remain. On the other hand, Fig. 2 fbl
differentiates the switch signal using capacitors 4 and 5,
The muting control signal is generated only temporarily during on/off, but it is difficult to create capacitors 4 and 5 with large capacitance on an integrated circuit, and this has the disadvantage of increasing the number of external components. . Also, when adding input, use a comparator of 6, 7 or 8.9 times per person.
etc., making the circuit complicated.

OBJECTS OF THE INVENTION The present invention provides an effective and easy-to-integrate mute control signal generation method for controlling a mute circuit in an amplifier equipped with a plurality of changeover switches in order to prevent the harsh shock sound generated when switching the switches. It is intended to provide a circuit.

Structure of the Invention The present invention provides an input circuit that uses one or more exclusive OR circuits to detect changes in a plurality of switch inputs, a charge pump circuit whose charging and discharging is controlled by the output of the circuit, and an input circuit that detects changes in a plurality of switch inputs using one or more exclusive OR circuits; and an exclusive OR circuit at an output stage that uses the output of the circuit and the output of the charge pump circuit as two inputs and generates a muting control signal for a certain period of time when a change occurs in one of the inputs of the input circuit. This will be described in detail below with reference to the illustrated embodiment.

Embodiment of the Invention FIG. 3 is a schematic diagram showing an embodiment of the present invention.
E2 is an exclusive OR (hereinafter abbreviated as EOR) circuit, N1~
N3 is inverter, SW+, SW2 is switch, C3
a and C3b are constant current sources, and Ca is a capacitor. In this circuit configuration, when both switches 1 and 2 are logic H (high), EOR circuit E+El power a is logic L (low), so the output of inverter N2 is H. Therefore, since switch SW+ is on (switch SW2 is off), capacitor Ca is charged. In this state, if one input 1 is set to L (timing chart ■ in Fig. 5),
By EOR circuit E1, point a becomes L-+H and switch S
(W2 is on and S-W+ is off), and at the same time, point b becomes H-L due to inverter NI.

When the switch SW2 is turned on, the charge in the capacitor Ca is discharged through the constant current circuit csb, so the potential Ec at point C decreases linearly, but the threshold voltage ■T of the inverter N3
Point d does not become L-H until it becomes less than h. Therefore, from the point (2) when the input 1 is set to L until Ec≦vTh, the two inputs of the FOR circuit E2, i, d, are both L, and the output δ remains L. It is this output level of 100 that has meaning as a muting control signal,
The duration is Ec≦VTh after a change occurs in input 1.
When EC≦vth, the output O becomes H.
Flip to to unmute.

After this, when input 1 remains L and the other input 2 is set to L (Fig. 5 ■), switch S W + is turned on again and capacitor Ca is charged and energized by constant current source C3a. For this reason, point d does not become HL until Ec≧VTh. During this time, that is, after input 2 is set to L, Ec≧■T
Since the output O becomes T in a pulsed manner until it reaches h, this becomes the muting control signal. At the trailing edge of this signal, point b immediately becomes L-H, so Ec≧”
This is the point when point d becomes L-H at Th. In this way, the muting control signal is generated for a certain period of time from the fall of inputs 1 and 2, but based on the same operating principle, the muting control signal is also generated for a certain period of time from the rise of inputs 1 and 2 (■■ in Figure 5). A muting control signal is generated.

Figure 4 shows input 1 of changeover switches SWa and SWb in Figure 1.
, 2 is a specific example of a circuit that generates the above-mentioned muting control signal d. This circuit includes a selector switch SWa,
Electronic transfer switch SWb controlled by SWb
a', S W b' are built in, and this is the first
It is used to switch the amplifier shown in the figure.

Transistor Q? , QB constitute an EOR circuit EI, and transistors Q, . . . Q2o constitute an EOR circuit E2. The transistor Q2□ corresponds to the inverter N1, and the area inside the dashed-dotted line frame C is a charge pump circuit extending from the inverter N2 to the impark N3.

Of these, transistors QI3 to Q15 are switches SW
＋.

SW2, corresponds to constant current source Csb, transistor Q16
are for voltage detection of capacitor Ca, diodes D3 to D4
is for level shifting. In this case, VTh in FIG. 5 is 3 stages above VBE including transistors Q and 7 and below VBEI stage of transistor Q16, so VB
It is 1.4V for 2 stages of E. I will omit the detailed explanation, but Q
1 to Q23 are transistors, ZDI to ZD3 are Zener diodes, D1 to D5 are diodes, C3+ to C3l
o is a constant current source, and Q is a muting transistor, which receives the inverted signal O' from the output and drops the signal flowing through the signal line to the ground. In this circuit, when the voltage of the power supply Vcc decreases, the constant current source C3+o is turned off, so the output d is always at L level and the inverted signal d' is always at H level. Therefore, there is an advantage that muting is automatically applied when the output of the amplifier becomes abnormal due to a power drop. For the same reason, muting is also applied when the power is turned on and off.

In the above embodiment, the case of two-man power operation (two changeover switches) was used as an example, but if the input stage FOR circuit E1 is configured as shown in Fig. 6, a common circuit can be used for even more switch inputs. Can generate muting control signals.

Effects of the Invention As described above, according to the present invention, a muting control signal can be generated for a certain period of time from a change point using a common circuit for a plurality of switch inputs.

Furthermore, since only one capacitor is used, there are advantages in that there are fewer external components and fewer terminals.

[Brief explanation of drawings]

Figure 1 is a configuration diagram showing an example of an amplifier circuit with a changeover switch.
Fig. 2 is a block diagram of a conventional muting control signal generation circuit, Fig. 3 is a block diagram showing an embodiment of the present invention, Fig. 4 is a circuit diagram showing a specific example thereof, and Fig. 5 is a block diagram of a conventional muting control signal generation circuit. FIG. 6 is a diagram showing the configuration of the input stage applied to a large amount of power. In the figure, El is an exclusive logic circuit (input circuit) at the input stage, and c
p is a charge pump circuit, and E2 is an exclusive OR circuit at the output stage. Applicant Fujitsu Co., Ltd.

Claims (1)

[Claims] An input circuit that uses one or more exclusive OR circuits to detect changes in a plurality of switch inputs, a charge pump circuit whose charging and discharging is controlled by the output of the circuit, and an output of the input circuit and the charge pump. and an exclusive OR circuit at an output stage that generates a muting control signal for a certain period of time when one of the inputs of the input circuit generates the output of the circuit by two people. control signal generation circuit.