JPS6241450Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for removing residual signals in an electronic volume.

Electronic potentiometers have been widely used recently because they do not require any contacts in the signal transmission system and are suitable for remote control applications, but the maximum attenuation is around 80 dB, which is lower than the 100 dB of a general variable resistor. Therefore, it was not possible to completely narrow down the transmitted signal due to insufficient attenuation.

The present invention was developed in consideration of this point, and is designed to cancel the residual signal when the attenuation amount of the electronic volume is maximized by connecting a muting circuit to the electronic volume without causing any audible unnaturalness. In this way, the above-mentioned problems are attempted to be solved.

An embodiment of the present invention will be described below with reference to the drawings. In Fig. 1, 1, which acts as an electronic volume circuit, attenuates the input signal applied to the input terminal _1a via the capacitor C1 in inverse proportion to the control DC voltage _V1 as the first control voltage applied to the control terminal 1b. The control DC voltage V ₁ is obtained by dividing the power supply voltage V _CC by a variable resistor VR. And this electronic volume 1
The output of is connected to analog switch 2 as a muting circuit via capacitor C ₂ and input resistor R ₃ .
is being input.

This analog switch 2 is a P channel FET
It consists of an N-channel FET and an inverter, and conduction is established between the input and output by applying a high-level control voltage as a second control voltage to the control terminal 2a, and disconnected by applying a zero-level control voltage. _R5 is the output resistance.

Reference numeral 3 denotes a comparator consisting of an operational amplifier, and a reference voltage V 2 for comparison obtained by dividing the power supply voltage V _CC by resistors R ₁ and R ₂ is applied to the inverting input terminal 3 a, and a reference voltage V ₂ for comparison, which is obtained by dividing the power supply voltage V CC by resistors R 1 and R 2, is applied to the non-inverting input terminal 3 b. A control voltage V ₁ for the electronic volume 1 obtained by the variable resistor VR is applied. Therefore, this comparator outputs a low level when V ₁ ≦ V ₂ , but since a single power supply V _CC is used, a residual voltage of about 1 V is generated even in that case, so this residual voltage is connected to a Zener diode.
I try to cancel it with ZD.

In the above, the control voltage V ₁ by the variable resistor VR
If is large, the attenuation amount of electronic volume 1 is small,
The smaller the value, the larger it will be, so set the reference voltage V ₂ to a value equal to the control voltage V ₁ at the maximum attenuation (80 dB).
Set.

When V ₁ >V ₂ , the output of the comparator 3 is at a high level, so the analog switch 2 is conductive, and the signal attenuated by the electronic volume 1 is output as is as the output signal e ₀ . After that, the control voltage V ₁ is reduced by the variable resistor VR, and V ₁
When ≦V ₂ , the output of comparator 3 becomes low level and becomes lower than the Zener voltage of Zener diode ZD.
No voltage is applied to a, and therefore the analog switch 2 is cut off. Therefore,
At this time, a residual signal is output from the electronic volume 1 even though it is at maximum attenuation, but that signal is muted by the analog switch 2, so the output voltage e ₀ becomes zero. Since muting is performed at the time of maximum attenuation in this manner, there is no unnaturalness in the auditory sense when listening to audio.

From the above, according to the present invention, when the electronic volume reaches its maximum attenuation, the muting circuit works, so it is theoretically possible to reduce the attenuation to -∞, thereby completely eliminating the residual signal and noise of the electronic volume. In addition, it becomes possible to remove them without causing any unnatural sound.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of an embodiment of the present invention, Fig. 2 is a characteristic diagram of the input voltage to the comparator 3, Fig. 3 is a control signal characteristic diagram of the analog switch, and Fig. 4 is a characteristic diagram of the output signal. be. 1...Electronic volume, 2...Analog switch, 3...Comparator.

Claims (1)

[Claims for Utility Model Registration] An electronic volume circuit that is inserted into a signal transmission circuit and whose attenuation amount of an input signal is controlled by a first control voltage; a muting circuit that receives a second control voltage and cuts off the output signal; one input is the first control voltage applied to the electronic volume circuit; the other input is a reference voltage; and a comparator that generates an output when the electronic volume circuit is set to a value that controls the amount of attenuation to a maximum, and the output of the comparator is used as the second control voltage. removal circuit.