JPS6241449Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a signal attenuation circuit using an electronic volume.

Electronic volume circuits generally consist of 99 stages of differential circuits, and the amount of attenuation is adjusted depending on the level of the applied DC voltage, and the maximum amount of attenuation is approximately -
80dβ to −90dβ (0dβ=0.775V). However, this electronic volume circuit requires a large amount of current, and therefore generates a lot of noise from the transistor. Therefore, when an amplifier is connected to the next stage, that noise is greatly amplified, and even the maximum attenuation is about the same as above. Therefore, input signal leakage occurs and is amplified.

The present invention has been developed in view of this point, in which a muting element is connected to the electronic volume, and when the attenuation increases, the muting is gradually applied by the element near the maximum attenuation point of the electronic volume circuit, and the opposite is performed when the attenuation decreases. This is intended to prevent the above-mentioned noise and leaked signals from reaching the next stage amplifier, etc.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. In FIG. 1, the electronic volume circuit 1 applies to the control terminal 1a an adjusted voltage as a first control voltage obtained by dividing a constant DC voltage by a variable resistor VR, as shown in FIG. It has the attenuation characteristics shown in . In FIG. 2, the horizontal axis shows the DC voltage applied to the control terminal 1a, and the vertical axis shows the level appearing at the output terminal 1c when the input terminal 1b is set to 0dβ (=0.775V). In this case, the adjustment voltage is 2V and the attenuation amount is -90dβ, which is the maximum.

P channel FETQ ₁ constitutes a muting circuit whose drain and source are connected to electronic volume circuit 1 and amplifier 2, and voltage +B is applied to the gate as a second control voltage via resistors R ₁ and R ₂ . This minimizes the resistance value between the drain and source, but the voltage applied to the gate decreases in proportion to the degree of conduction of transistor _Q2 , increasing the resistance value between the drain and source and causing a muting effect. Let's do it. And this transistor Q ₂
is the common connection point A between resistors R ₄ and R ₅ and capacitor C
controlled by the potential of

Transistors Q ₃ and Q ₄ connected in parallel form a current switch circuit, and one transistor
A voltage V _B1 obtained by dividing voltage +B by resistors R ₆ and R ₇ is applied to the base of Q ₃ as a switch operation reference voltage. This voltage V _B1 is set at a voltage point P corresponding to the regulated voltage (2.5 V) at the control terminal 1a immediately before the attenuation of the electronic volume circuit 1 reaches its maximum (-90dβ). Resistor R ₈ is a common emitter resistance, and resistors R ₉ and R ₁₀ are collector resistances of the same value.
Therefore, in this current switch circuit, when the base voltage V _B2 of the other transistor Q ₄ connected to the control terminal 1a of the electronic volume circuit 1 via the resistor R ₁₁ is V _B2 <V _B1 , the transistor Q ₄ becomes conductive. , Q ₃ is cut off, and when V _B2 > V _B1 , the second state is the opposite.

Resistor _R4 and capacitor C constitute an integrating circuit,
The voltage across resistor _R10 generated by conduction of transistor _Q4 is applied to point A with a time constant of C· _R4 . Transistor Q ₅ becomes conductive due to the conduction of transistor Q ₃ and discharges the charge on capacitor C through resistor R ₅ .

In the above, by adjusting the variable resistor VR, the _attenuation characteristic _of the electronic volume circuit 1 becomes as shown in _{FIG .} is blocking, so transistor Q ₅ is also conducting, so transistor Q ₂ is blocking,
FETQ ₁ has the highest degree of conductivity and is connected to amplifier 2.
The signal from the electronic volume circuit 1 is input as is.

Then, the voltage applied to the control terminal 1a is gradually lowered by the variable resistor VR, and when V _B2 < V _B1 ,
Transistor Q ₃ is cut off and Q ₄ becomes conductive, the potential at point A gradually increases, which gradually improves the conductivity of transistor Q ₂ , and therefore
The resistance between the drain and source of FETQ ₁ will gradually increase. In this case, the attenuation characteristics of FETQ ₁ are as shown in Figure 3, and the electronic volume circuit 1
Attenuation, that is, mutating, starts from time t ₀ when the attenuation at point P reaches point P. Therefore amplifier 2
Attenuation level S at which noise and leakage signals are not transmitted to
Determine the time t ₁ until it becomes C・R ₄ .

Next, from the above state, when the variable resistor VR is adjusted so that V _B2 >V _B1 , the transistor Q ₄ is cut off and Q ₃ becomes conductive, which causes the transistor Q ₅ to become conductive. Therefore, the charge in capacitor C is discharged not only through the route between resistors _R4 and _R10 , resistor _R3 and transistor _Q2 , but also through the route between resistor _R5 and transistor _Q5 . The conductivity of FETQ ₂ gradually decreases, and the low resistance between the drain and source of FETQ ₁ gradually decreases, releasing the muting.

Therefore, from the above, the voltage applied to the control terminal 1a is gradually decreased by adjusting the variable resistor VR, and when the attenuation amount of the electronic volume circuit 1 reaches point P, FETQ ₁
Muting is gradually applied, and amplifier 2
noise and leakage signals are effectively attenuated. Then, if the voltage to the control terminal 1a is gradually increased, the muting by FETQ ₁ will be gradually canceled after the attenuation amount reaches point P. In this case, the overall damping characteristic is the fourth
It will look like the figure. The range above point P is the attenuation characteristic due to the DC voltage applied to the control terminal 1a of the electronic volume circuit 1, and the range below is the attenuation characteristic due to the temporal change of _FETQ1 .

From the above, according to the present invention, when the electronic volume exceeds a certain attenuation amount, the muting circuit works, so it is theoretically possible to reduce the attenuation amount to -∞, and noise and signal leakage can be completely eliminated. At the same time, the mutating circuit reduces its transmission amount approximately in proportion to the passage of time, so when used in an audio signal transmission circuit, residual noise components from a volume or electronic volume circuit, etc. are gradually reduced. This makes it more pleasing to the auditory sense. Furthermore, if the electronic volume circuit is controlled to increase the volume from this point on, the amount of attenuation will gradually decrease from the -∞ state and the volume will gradually increase, making it possible to obtain a natural auditory sensation.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of an embodiment of the present invention, Figure 2 is an electronic volume attenuation characteristic diagram, and Figure 3 is a diagram of FETQ _1.
FIG. 4 is a comprehensive attenuation characteristic diagram according to this embodiment.

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 controls the transmission amount of an output signal according to a second control voltage; and a muting circuit that controls the first control using the first control voltage applied to the electronic volume circuit as one input and a reference voltage as the other input. Switching from the first state to the second state when the voltage is set to a second value that controls the attenuation of the electronic volume circuit from the first value near the maximum attenuation to an attenuation above the maximum attenuation. a switching circuit that switches from the second state to the first state when the second value is set to the first value; and a switching circuit that switches the switching circuit from the first state to the second state. an integrating circuit that starts charging when switching from the second state to the first state, and starts discharging when switching from the second state to the first state, and the charging voltage of the integrating circuit is set to the second control voltage. A signal attenuation circuit characterized in that it is used as a signal attenuation circuit.