JPH04225609A - Mute circuit - Google Patents

Abstract

PURPOSE:To offer a means to prevent an input signal from leaking to output because of the internal resistance of a reference voltage source even if muting is given. CONSTITUTION:An input terminal 13 is connected to the reference voltage source 10 through a resistor 1, a middle point A, and the resistor 2, and the input of a voltage follower 7 is connected usually to the input terminal 13 and to the middle point A at the time of the muting by a switch 12. An operational amplifier 8 connects the output of the voltage follower circuit 7 to its forward input terminal, and the resistor R3 from an inverted input terminal to its output terminal, and the resistor R4 to the output terminal of a second operational amplifier 9 respectively, and the second operational amplifier 9 connects its output terminal to an inverted input terminal resistor R5, and this point to the reference voltage source 11 through the resistor R6 respectively, and the forward input terminal of the operational amplifier 9 is connected to the point A, and this mute circuit is constituted so that the relation of R3:R4=R5:R6 is satisfied.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mute circuit.

0002

2. Description of the Related Art The structure and operation of a conventional mute circuit will be explained below with reference to FIG. When the signal mute circuit receives a mute command from the outside, it operates the switch 29 and switches the input of the voltage follower 25, which had been connected to the signal input terminal 30, to the switch 2.
9, the reference power supply voltage is switched to 27 to prevent input signals from being output to the output terminal 31. Furthermore, since this reference voltage source 27 also serves to provide a bias voltage for the mute circuit itself, the bias voltage is applied to external signals via the resistors 21 and 22.

0003

However, in the conventional configuration described above, the resistor 22 is always present between the input bias resistor 21 and the reference voltage source 27. This resistance 22
This may be, for example, the output impedance of the reference voltage source 27 or the wiring resistance within the integrated circuit. This input bias resistor 21 and reference voltage source 27
The potential at the connection point of the resistor 22 connected to Assuming that the level of the signal coming in is VIN, and the resistance values of the resistors 21 and 22 are R21 and R22, respectively, a signal of the magnitude VIN*R22/(R21+R22) will be carried. When the mute is turned on, the signal passes through the voltage follower 25, the inverted terminal is connected to the reference voltage source 28 via the resistor 24, and the output stage operational amplifier 26 has a resistor 27 connected between it and the output terminal. It is amplified to an appropriate size and sent to output terminal 3.
It appears in 1. As described above, in the conventional configuration described above, there is a problem in that the signal leaks to the signal output terminal even though muting is applied.

An object of the present invention is to provide a mute circuit that solves the above-mentioned conventional problems.

[0005]

[Means for Solving the Problem] In order to achieve this object, the mute circuit of the present invention has one of the first resistors connected to the input terminal, and the other of the first resistors is connected to the first reference voltage source. is connected via a second resistor to the first resistor and the second resistor.
The output of the switch that selects either the connection point of the resistor or the input terminal is coupled to the non-inverting input terminal of the first operational amplifier by one or more voltage followers, and the output of the first operational amplifier is coupled to the non-inverting input terminal of the first operational amplifier. The output terminal is connected to the first operational amplifier, and there is a third resistor between the output of the first operational amplifier and the inverting input terminal, and a fourth resistor is located between the inverting input terminal and the output of the second operational amplifier. A connection point between the first resistor and the second resistor is connected to the non-inverting input terminal of the second operational amplifier, a fifth resistor is connected between the inverting input terminal and the output of the second operational amplifier, and , a second reference voltage source is connected to the inverting input terminal via a sixth resistor, and the resistance values of the third, fourth, fifth, and sixth resistors are set as R3, R4, and R4.
5 and R6, it has a configuration that satisfies the relationship R3:R4=R6:R5.

[0006]

[Operation] With this configuration, when mute is turned on, even if the signal resistance-divided by the first resistor and the second resistor is transmitted to the first operational amplifier through the voltage follower, the first operational amplifier and the second operational amplifier The operational amplifier can cancel the transmitted signal and set it so that it does not appear at the output terminal.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure and operation of a mute circuit according to an embodiment of the present invention will be explained below with reference to the drawings. As shown in FIG. 1, the switch is connected to a connection point B, and a signal input from an input terminal 13 is applied with a bias voltage from a reference voltage source 10 through a resistor 2 and a resistor 1, and is applied to a voltage follower 7. is input to the normal rotation terminal of When a mute signal is applied from the outside, the switch 12 conducts the connection point A and the input of the voltage follower 7, and transmits the potential of the connection point A to the next stage operational amplifier 8. However, this problem is solved by the invention. As described in the above section, a signal is input to the connection point A from the input terminal 13 and is resistance-divided by the resistors 1 and 2. The potential of this connection point A is V
Let it be A. The operational amplifier 8 is a non-inverting amplifier whose gain is determined by the resistors 3 and 4. If the output of the operational amplifier 8 is V0, the resistance values of the resistors 3 and 4 are R3 and R4, and the output of the operational amplifier 9 is VC, then The formula holds true.

V0=(1+R3/R4) [VA-VC×R3/(
R4+R3)] (1) However, the gain of the operational amplifier is assumed to be infinite. As can be seen from equation (1), VA=VC×
In the case of R3/(R4+R3), the output has a signal component of 0. Transforming this equation, VC=VA(1+R4/R3)(2) On the other hand, the input of the operational amplifier 9 is connected to the connection point A, the gain is determined by the resistors 5 and 6, and the reference voltage source 11
is a DC biased non-inverting amplifier. Therefore, the resistance values of resistor 5 and resistor 6 are R5 and R6, respectively.
Then, VC=VA(1+R5/R6)(3), and since R3:R4=R6:R5, (
Equation 2) and Equation (3) are equivalent. This means that even though muting is applied, the signal leaking from the input stage can be canceled by the output stage amplifier, making it completely silent.

Next, when muting off, switch 1 is pressed.
2, the input terminal and the voltage follower are electrically connected and the input signal to which a bias voltage is applied by the reference voltage source 10, the resistor 2, and the resistor 1 is transmitted to the operational amplifier 8 via the voltage follower, and The signal is amplified and output from the output terminal. In this case, the output voltage V0 is VIN, where the input signal voltage is VIN.
0=(1+R3/R4) [VIN-VC×R3/(R4
+R3)] (4). Substituting equation (3) into equation (4), V0=(1+R3/R4)(VIN-VA)(
5), and the signal level is smaller than the conventional example by multiplying the voltage at connection point A by the gain of operational amplifier 8, but normally the resistance value of resistor 1 is much smaller than the resistance value of resistor 2. Since it is large, VIN>VA, and the output voltage decreases only slightly when mute is turned off.

Although one voltage follower 7 is used in the example, a plurality of voltage followers 7 may be used as necessary.

[0011]

Effects of the Invention: By using an operational amplifier that amplifies the signal added at the input stage as a bias circuit for the output stage operational amplifier, the signal leaked at the input stage even when muted is removed from the output stage. This makes it possible to realize an excellent mute circuit that provides the effect of canceling the signal.

[Brief explanation of the drawing]

[Fig. 1] Circuit diagram of a mute circuit according to an embodiment of the present invention.

[Figure 2] Circuit diagram of conventional mute circuit

[Explanation of symbols]

1,6 Resistance 7 Voltage follower 8,9 Operational amplifier 10, 11 Reference voltage source 12 Switch 13 Input terminal 14 Output terminal

Claims (1)

[Claims] Claim 1: One of the first resistors is connected to the input terminal,
The other of the first resistors is connected to a first reference voltage source via a second resistor, and a switch selects either the connection point between the first resistor and the second resistor or the input terminal. The output of is controlled by one or more voltage followers,
The output terminal is connected to the non-inverting input terminal of the first operational amplifier, and the output terminal is connected to the output of the first operational amplifier. a fourth resistor is provided between the input terminal and the output of the second operational amplifier, and a connection point between the first resistor and the second resistor is connected to the normal input terminal of the second operational amplifier;
A fifth resistor is connected between the inverting input terminal and the output of the second operational amplifier, and a second reference voltage source is connected to the inverting input terminal via a sixth resistor. A mute circuit configured to satisfy the relationship R3:R4=R6:R5, where the resistance values of the fourth, fifth, and sixth resistors are R3, R4, R5, and R6.