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JPH0511776

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
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DESCRIPTION JPH0511776
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
electronic volume of attenuation type, which is a volume unit of audio equipment, and more
particularly to a circuit for canceling out the deviation of attenuation to improve its performance.
[0002]
2. Description of the Related Art FIG. 3 is a circuit diagram partially showing a conventional
circuit using an electronic volume in a block diagram. In FIG. 3, reference numeral 1 denotes a
semiconductor integrated circuit, for example, an electronic volume, 2 denotes a buffer amplifier
such as an operational amplifier whose output is connected to the electronic volume 1, and 3
denotes a microcomputer connected to the input side of the buffer amplifier 2.
[0003]
In the electronic volume 1, 4 is a reference voltage circuit for generating a reference voltage
Vref, 5 is a reference side circuit whose input side is connected to the reference voltage circuit 4
to be described in detail later, 6 is a base on the output side of the reference side circuit 5. Are
connected to the differential transistor 7 is a power supply voltage line of + VCC connected to the
collector of the differential transistor 6 8 is a control side circuit to be described in detail later,
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the input side is connected to the buffer amplifier 2 9 is this A differential transistor whose base
is connected to the output side of the control side circuit 8, 10 is connected between the collector
of the differential transistor 9 and the power supply voltage line 7, and has a current / voltage
signal conversion resistance of R1. Reference numeral 11 is connected to the emitters of the
differential transistors 6 and 9, and is a current source having a current value of I0. The collector
of differential transistor 9 is connected to the outside, and collector currents I1 and I2 flow
through the collectors of differential transistors 6 and 9, respectively.
[0004]
Next, the operation of the above-described conventional circuit will be described. The reference
side circuit 5 sets the base potential of the differential transistor 6 based on the reference voltage
Vref from the reference voltage circuit 4, whereby a collector current I 1 flows in the collector of
the differential transistor 6.
[0005]
On the other hand, when the PWM output is supplied from the microcomputer 3 to the control
circuit 8 as the control voltage VC through the buffer amplifier 2 by an external operation, the
control circuit 8 generates the differential transistor 9 based on the control voltage VC. The
collector current I2 flows to the collector of the differential transistor 9, and the collector voltage
of the differential transistor 9 is output to the outside as the volume. The collector voltage of the
differential transistor 9 changes in accordance with the amount of attenuation set by the balance
between the collector current I1 and the collector current I2, and the volume decreases if the
amount of attenuation is large.
[0006]
Next, the reference circuit 5 and the control circuit 8 will be described in detail with reference to
the circuit diagram of FIG. In the reference circuit 5, 51 is a transistor whose base is connected to
the reference voltage circuit 4, 52 is connected between the emitter of the transistor 51 and the
ground and has a resistance of R2 and 53 is a power supply voltage of + VCC. A current mirror
connected to the line 7 and having a collector connected to the collector of the transistor 51 and
its own base; 54 a current mirror having an emitter connected to the supply voltage line 7 and a
base connected to the base of the current mirror 53; Is a transistor whose collector is connected
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to the power supply voltage line 7 and whose base is connected to the collector of the current
mirror 54, 56 is connected between the emitter of this transistor 55 and the power supply
voltage line 12 of -VCC and has a current value of I3. , And 57 are a plurality of diodes connected
in series, and one of the diodes 57 is connected to the The cathode of the last diode is connected
to ground.
[0007]
Further, in the control circuit 8, 81 is a buffer amplifier such as an operational amplifier in which
one input terminal, for example, + is connected to the buffer amplifier 2 and the other input
terminal-and the output terminal are connected, 82 is an output terminal of this buffer amplifier
81 Connected between the ground and the ground, resistance R3 resistance, 83 is a mirror with
its emitter connected to the resistance 82 and its own base and its collector connected to the
supply voltage line 12, 84 is a supply voltage to the collector A current mirror connected to the
line 12 and whose base is connected to the base of the current mirror 83, 85 is a current mirror
whose emitter is connected to the supply voltage line 7 and whose base is connected to the
emitter of the current mirror 84 and its own base, 86 is a current mirror whose emitter is
connected to the power supply voltage line 7 and whose base is connected to the base of the
current mirror 85; A transistor connected to the collector of the mirror 86 and having a collector
connected to the power supply voltage line 7, 88 is a current source connected between the
emitter of the current mirror 87 and the power supply voltage line 12 and has a current value of
I4, and 89 is A plurality of diodes connected in series, the anode of one of the diodes 89 is
connected to the collector of the current mirror 86 and the base of the transistor 87, and the
cathode of the last diode is grounded.
[0008]
Next, the operation of the reference circuit 5 and the control circuit 8 will be described.
In the reference circuit 5, when the reference voltage Vref is applied to the base of the transistor
51 from the reference voltage circuit 4, the current I3 is set based on the reference voltage Vref
and the resistance value R2 of the resistor 52. When the current I3 is set, a current flows
through the current mirrors 53 and 54 and the diode 57, the diode 57 operates, and the base
potential VF of the transistor 55 is set. As a result, the emitter potential VCA of the transistor 55
is set, which becomes the base potential of the differential transistor 6.
[0009]
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On the other hand, in the control side circuit 8, the control voltage VC is applied from the buffer
amplifier 2 to the input terminal + of the buffer amplifier 81, and the current I4 is set based on
the control voltage VC and the resistance value R3 of the resistor 82. When the current I4 is set,
current flows through the current mirrors 83, 84, 85 and 86 and the diode 89, the diode 89
operates, and the base potential VG of the transistor 87 is set. As a result, the emitter potential
VCB of the transistor 87 is set, which becomes the base potential of the differential transistor 9.
[0010]
In the conventional circuit as described above, since the emitter potentials of the differential
transistors 6 and 9 are the same, the collector current I2 is changed by changing the base
potential of the differential transistor 9. Thus, the balance between the collector current I1 and
the collector current I2 is changed to change the attenuation amount. Therefore, when a
deviation occurs in the reference voltage Vref from the reference voltage circuit 4, the reference
side circuit 5 is affected to cause a deviation in the base potential of the differential transistor 6,
so that the collector current I1 and the collector current I2 There is a problem that the balance is
broken and a deviation occurs between the actual attenuation amount and the set attenuation
amount, and the electronic volume 1 becomes unstable.
[0011]
The present invention has been made to solve such problems, and it is possible to eliminate the
influence on the attenuation amount due to the deviation of the reference voltage and to increase
the accuracy of the electronic volume, thereby eliminating the deviation of the attenuation
amount of the electronic volume. The purpose is to obtain a circuit.
[0012]
The offset cancellation circuit of the attenuation amount of an electronic volume according to the
present invention comprises a reference side transistor to which a reference voltage is applied,
and an attenuation type electronic volume by varying the balance of the collector current of the
control side transistor. A first means for inverting the polarity of the reference voltage to output
an amplified voltage, and dividing the output voltage of the first means into a large number, and
selecting one of them according to an external command as a control voltage And a second
means for applying the control voltage to the control side transistor.
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[0013]
In the present invention, the reference voltage is inverted in polarity by the first means and
amplified voltage is outputted, and the output voltage of the first means is divided into multiple
by the second means, one of which is an external A command is selected to be a control voltage,
and this control voltage is applied to the control side transistor in the electronic volume.
[0014]
An embodiment of the present invention will be described hereinbelow with reference to the
drawings.
In FIG. 1, reference numeral 1 denotes an electronic volume similar to that shown in FIG. 3, and
reference numeral 20 denotes a circuit connected to the electronic volume 1 to cancel the
deviation of the attenuation amount.
[0015]
The shift cancellation circuit 20 is connected to an inverting amplifier as a first means, such as
an operational amplifier 21, and to an output terminal of the inverting amplifier 21, and is
connected between the microcomputer 3 and the control circuit 8 in the electronic volume 1. A D
/ A converter 22 is provided as a second means.
Furthermore, the inverting amplifier 21 is connected to the reference voltage circuit 4 in the
electronic volume 1 via the gain setting resistor 23 of one of the input terminals, for example, of
the resistance value R4, and via the gain setting resistor 24 of the resistance value R5. And the
other input terminal + is grounded.
[0016]
Next, the operation of the above-described embodiment will be described.
The reference side circuit 5 sets the base potential of the differential transistor 6 based on the
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reference voltage Vref (usually 1.2 V) from the reference voltage circuit 4 in the same manner as
the conventional circuit. A collector current I1 flows.
[0017]
The reference voltage Vref from the reference voltage circuit 4 is also input to the displacement
cancellation circuit 20, and more specifically, to the input terminal-of the inverting amplifier 21
through the gain setting resistor 23. The inverting amplifier 21 generates an output voltage V0
(usually -5 V) based on the reference voltage Vref, the resistance value R4 of the gain setting
resistor 23, and the resistance value R5 of the gain setting resistor 24. The output voltage V0 is
divided into a large number, for example 256, by the D / A converter 22. When the PWM output
of the microcomputer 3 is supplied to the D / A converter 22 by an external operation, one of the
256 divided ones is selected Then, the control voltage VC is output from the D / A converter 22
to the control side circuit 8 in the electronic volume 1. The control voltage VC is expressed by
the following equation (1).
[0019]
In the equation (1), (R5 / R4) · Vref is the output voltage V0 of the inverting amplifier 21, and n
is set based on the PWM output from the microcomputer 3. For example, when the control
voltage VC of -5 V is output to the electronic volume 1, the output voltage V0 of the inverting
amplifier 21 = (R4 / R3) · Vref is usually -5 V, so n is set to 256.
[0020]
In the electronic volume 1, the control side circuit 8 sets the base potential of the differential
transistor 9 based on the control voltage VC, whereby the collector current I2 flows through the
differential transistor 9, and the collector current I1 and the collector current I2 The amount of
attenuation is set by the balance, and the collector voltage of the differential transistor 9 is
output to the outside.
[0021]
Here, the attenuation amount of the electronic volume 1 will be described.
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The attenuation amount ATT is the emitter potential VCA of the transistor 55 in the reference
circuit 5 and the resistance R2 of the resistor 52, the emitter potential VCB of the transistor 87 in
the control circuit 8 and the resistance R3 of the resistor 82, the reference voltage Vref and the
control From the voltage VC, it is expressed by equation (2). VT is a constant, K is a Boltzmann
constant, q is a charge amount, and T is an absolute temperature.
[0023]
The reference voltage Vref can be eliminated from the equations (1) and (2), and the attenuation
ATT can be expressed by the equation (3).
[0025]
From the equation (3), it can be seen that the attenuation ATT is not affected by the reference
voltage Vref.
This will be described based on the drawings.
[0026]
FIG. 2 is a view showing the relationship between the control voltage VC and the attenuation
amount ATT. The vertical axis is the attenuation amount ATT (dB), and the horizontal axis is the
control voltage VC (V). When the reference voltage Vref fluctuates, the direction of the deviation
ΔVS of the attenuation on the reference side (composed of the reference voltage circuit 4, the
reference side circuit 5, and the differential transistor 6) with respect to the set value of the
attenuation ATT The directions of the deviations ΔVC of the attenuation amounts of the side
circuit 8, the differential transistor 9, and the current / voltage signal conversion resistor 10
contradict each other, and they cancel each other.
[0027]
As described above, in one embodiment of the present invention, the base potential of the
differential transistor 6 and the base potential of the differential transistor 9 are both set based
on the reference voltage Vref, thereby causing the deviation of the attenuation amount on the
reference side The attenuation of the electronic volume 1 is not affected by the fluctuation of the
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reference voltage Vref because the deviations of the attenuations on the control side cancel each
other.
[0028]
As described above, the present invention reverses the polarity of the reference voltage in the
reference side transistor to which the reference voltage is applied and the electronic volume of
the attenuation type by varying the balance of the collector current of the control side transistor.
A first means for outputting an amplified voltage, and an output voltage of the first means are
divided into a large number, one of which is selected by an external command to be a control
voltage, and the control voltage is used as the control side transistor. By providing the second
means for applying, it is possible to eliminate the deviation of the attenuation amount caused by
the deviation of the reference voltage in the electronic volume, and to improve the accuracy of
the electronic volume.
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