JP2582257B2 - Electronic volume circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic volume circuit, and more particularly, to an electronic volume circuit that varies an attenuation rate of a signal according to an operation position of the volume.

2. Description of the Related Art FIG. 7 shows a circuit diagram of an example of a conventional electronic volume circuit. In the figure, the transistors Q _1, Q ₂ and Q _3, Q ₄ multiplier with differential circuits each are configured, the first differential circuit of transistors Q _1, Q ₂ by the output voltage Vc of the voltage source 10 and Transistor Q ₃ ,
The distribution ratio of the second differential circuit of Q4, that is, the ratio of the DC component of the current flowing through each of the resistors RL ₁ and RL ₂ is determined. For example, voltage Vc
Is 0V and the distribution rate is 0.5.

Signal from the signal source 11 is supplied to the base of the transistor Q ₅ of the operating current of the first differential circuit flows, is output from the terminal 12 is attenuated in accordance with the distribution ratio.

Problems to be Solved by the Invention Normal audio equipment is set to output a volume normally used when the volume rotation angle is set to the middle position, and when the volume circuit angle is set to the maximum position, FIG. ), The volume increases by 15 to 20 dB. In other words, the volume needs a dynamic range of 20 dB or more than the dynamic range of the power amplifier.

In the conventional circuit, a DC bias, the emitter current of the transistor Q ₅ by s signals husband from the signal source 11 I _E1 + ie
And then, the emitter current of the transistor Q ₆ due to DC bias and I _E2, the distribution ratio as d. At this time, the output voltage Vout of the terminal 12 is represented by the following equation.

Vout = RL ₁ ｛d (I _E1 + ie) + (1−d) I _E2信号 The signal component eout and the DC component V ₀₂ in the output voltage Vout are respectively eout = R _L1 · d · ie V ₀₂ = R _L1 ｛d・ I _E1 + (1−d) I _E2 ｝ Further, the DC component V ₀₁ in the collector voltage of the transistor Q ₁ is the _{V 01 = R L2 {d ·} I E2 + (1-d) I E1}. Here, the volume rotation angle is set to the maximum position and d = 0.
When it is set to 5, the following equation is obtained.

eout = 0.5R _L1 · ie V ₀₁ = R _L2 (0.5I _E1 + 0.5I _E2 ) V ₀₂ = R _L1 (0.5I _E1 + 0.5I _E2 ) where offset voltage V _0S and offset signal ratio V _0S / eou
t is given by

V _0S = (R _L1 −R _L2 ) · (I _E1 + I _E2 ) · 0.5 By the way, when the electronic regulator is connected to the next-stage power amplifier by DC coupling and used, the offset voltage _VOS is amplified by the next-stage power amplifier, and the output offset of the power amplifier increases. For this reason, it is necessary to reduce the offset signal ratio V _0S / eout of the electronic volume, and it is necessary to reduce I _E1 + I _E2 as much as possible.

By the way, as shown in FIG. 8A, the electronic volume is attenuated by 20 dB when the volume rotation angle is reduced to the middle point position with respect to the maximum volume rotation angle. When the volume rotation angle is the maximum (when the electronic volume is not attenuated), the input dynamic level of the electronic volume is the same as the input dynamic level of the next stage power amplifier, and when the volume rotation angle is set to the midpoint position (the electronic volume When the input dynamic level of the electronic volume is 20 dB lower than the input dynamic level of the next stage power amplifier.
Increase by dB. The solid line Ia in FIG. 8 (B) indicates the input level when the next stage power amplifier is saturated. That is, when the input level is above the solid line Ia, the power amplifier is saturated, and when the input level is below the solid line Ia, the power amplifier performs amplification with good linearity.

In this case, the input power level increases by 20 dB with respect to the maximum volume rotation angle (ie, ie is 10 times). It is necessary to set so that linearity can be maintained without saturation. for that purpose
I _E1 and I _E2 must be increased to some extent. As a result, I _E1 + I _E2 increases, and the offset signal ratio V _0S / eo
There was a problem that ut deteriorated.

As an example, if I _E1 / ie is 20 and the relative error between R _L1 and R _L2 is 2%, then I _E1 ≒ I _E2 , so that the offset signal ratio is V _0S /eout=40×0.02=0.8. Becomes a large value.

The electronic volume circuit has a finite dynamic range, and this dynamic range is increased by increasing I _E1 and I _E2 (≒ I _E2 ). When the maximum output of the output dynamic range is performed with the volume rotation angle at the midpoint position, the linearity of the input signal can be maintained.
When I _E1 and I _E2 are set, the solid line Ib in FIG. 8 (B) represents the input level that can maintain the linearity, that is, the dynamic range, and the linearity can be maintained in a region below the solid line Ib. In the region above the solid line Ib, linearity cannot be maintained.

However, even in the area where the linearity can be maintained in terms of the dynamic range below the solid line Ib,
In the shaded area above the solid line Ia, the next stage power amplifier is saturated. That is, it is useless to increase I _E1 and I _E2 in order to secure a dynamic range so that the linearity can be maintained up to the input level of the solid line Ib in the above-mentioned hatched portion, and I _E1 + I _E2 is large. However, there is a problem that the offset signal ratio is deteriorated.

The present invention has been made in view of the above points, and an object of the present invention is to provide an electronic volume circuit in which an offset voltage is reduced and an offset signal ratio is improved.

Means for Solving the Problems The present invention provides a volume that generates a voltage corresponding to an operation position, and an output voltage of the volume, and the operation position of the volume passes from a minimum position to a maximum position through a midpoint position. And a differential circuit that reduces the current flowing through the first current source and increases the current flowing through the second current source as
A clamp circuit that clamps a current flowing through the second current source from an operation position of the volume to a maximum position near the midpoint position, wherein a second circuit is provided as the operation position of the volume changes from the minimum position to the maximum position. A current ratio generator for increasing the current ratio between the current source and the first current source; a compression circuit driven in accordance with the current of the first current source and differentially amplifying while logarithmically compressing the input signal; An expansion circuit driven in accordance with the current of the second current source and differentially amplifying and outputting the signal supplied from the compression circuit while exponentially expanding the signal. The dynamic lens is reduced by clamping the current flowing through the second current source over the position, and the signal attenuation rate is varied based on the current ratio according to the operation position of the volume.

In the present invention, the current value of each of the first current source for driving the compression circuit and the second current source for driving the expansion circuit is varied according to the operation position of the volume, and the attenuation rate of the signal is varied. I have. At this time, the current value of the second current source is clamped to be substantially constant from the midpoint position of the volume to the maximum position, so that the offset voltage is kept small. From the midpoint position of the volume to the maximum position, the dynamic range is reduced to reduce the current value of the first current source, but the level of the input signal is also reduced, so that the reduction of the dynamic range does not pose any problem.

Embodiment FIG. 1 is a circuit configuration diagram of an embodiment of the circuit of the present invention, and FIG. 2 is a circuit configuration diagram of an embodiment of a current ratio generator of the circuit of FIG.

In Figure 1, a constant voltage generated by the reference voltage circuit 20 is applied to both ends of the volume VR _1. A voltage corresponding to the volume rotation angle (operation position) is output from the movable contact piece of the volume VR ₁ , and this voltage is supplied to the current ratio generator 21. Current ratio generator 21 determines the first current source 22, a current value of s second current source 29 respectively corresponding to the voltage supplied from the regulator VR _1. The current sources 22 to 28 are linked, and the current sources 22
When I _A current is passed, the current sources 24 and 25 respectively is electric current I _A, a current source 23,26～28 each is set to flow a current I _A / 10 for example. The current source 29 and 30 interlocked to flow the same current I _B to each other.

PNP transistors Q ₁₁ and Q ₁₂ are NPN transistors Q
_13, Q ₁₄ respectively and are Darlington connected, the differential circuit by the transistors Q ₁₁ to Q ₁₄ is configured. The emitters of the transistors Q ₁₁ and Q ₁₂ are current sources 24 and 25, respectively.
Is connected to the collector is connected to the s current source 27, 28 respectively, between these emitter resistor RE is connected, the signal voltage Va is supplied from the base signal source 31 of the transistor Q _11. For this reason, the collector current of the transistor Q ₁₁ is Becomes Here the first term current current source 27 is passed, the second term is the base current of the transistor Q _13. That is, the operation point if the amplification degree of h _FE is sufficiently sized transistor Q ₁₃ can be regarded as constant, it is possible to obtain characteristics of a good linearity low distortion in full dynamic range.

Each of the transistors Q ₁₃ and Q ₁₄ performs a current / voltage conversion to compress the logarithm of the signal, and a diode D ₁ commonly connected to the emitter thereof is used to match the operating point with the differential circuit of the next stage. It is for shifting.

The transistors Q ₁₅ and Q ₁₆ are connected to the current mirror circuit of the transistors Q ₁₇ and Q ₁₈ and the current source 30 to form a differential circuit, and convert a voltage signal applied between these bases to voltage / current conversion. To perform exponential expansion of the signal. Current signal output from the collector of the transistor Q ₁₆ is the resistance R
It is converted to a voltage signal by _L and output from the terminal 32.

FIG. 3 shows the principle circuit of the above circuit. In FIG. 3, transistors Q ₂₁ and Q ₂₂ constituting a differential circuit and diodes Da and Db for performing logarithmic compression are transistors Q _{11 to} Q _{14 in} FIG.
It corresponds to. In FIG. 3, the output voltage Vb is expressed as _{Vb = (I 3 -I 4)} R L. On the other hand, assuming that the series resistance r _{E of} each of the transistors Q ₂₁ and Q ₂₂ is sufficiently smaller than the resistance RE, the currents I ₁ and I ₂ are represented by the following equations.

I ₁ = I _A / 2 + Va / (2 · RE) = I _A / 2 + ie (1) I ₂ = I _A / 2−ie (2) where ia = Va / (2 · RE) transistors Q _21, Q ₂₂ respectively of collector voltage V _B is a diode Da, is expressed by the following equation from the forward voltage drop V _BE1, V _BE2 of Db.

V _B = V _BE1 −V _BE2 (3) Here, transistors Q ₁₃ and Q constituting diodes Da and Db
_{When the} reverse saturation current of the ₁₄ junctions between the collector and the base is defined as I ₀ , and the Boltzmann constant k, the charge amount of electrons q, and the absolute temperature T are obtained, the following equation is obtained.

From equation (3) On the other hand, the collector currents I ₃ and I _{4 of} the transistors Q ₁₅ and Q _{16 respectively}
Is I ₃ = I ₄ when V _B = 0. Also, transistors Q ₁₇ ,
Since Q ₁₈ is a current mirror circuit, the transistors Q ₁₇ and Q ₁₈
The respective collector currents I ₃ and I ₅ are the same.

Here, when a signal arrives and V _B ≠ 0, I ₃ ≠ I ₄ . At this time, the base-emitter voltages of the transistors Q ₁₅ and Q ₁₆ are V _BE3 and V _{BE4, respectively,} and I ₃ = I _B / 2 + ib (7) I ₄ = I in the same manner as in the equations (1) and (2). _B / 2−ib (8) Vb = (I ₃ −I ₄ ) · _RL = 2 · I b · _{RL L} (9) V _B = V _BE3 −V _BE4 (10) From equations (10) and (12) Here, from equations (6) and (13), Here, if R _L / R _E −m, According to the equation (17), the current sources 22 and 2 in the circuit of FIG.
9 each of the current I _A, has been shown to be able to vary the attenuation amount by varying the ratio of I _B.

In the current ratio generating section shown in FIG.
_{31, Q 33, Q 34,} Q 35 current I _B flowing through the second current source 29 while decreasing the current I _A flowing through the first current source 22 in accordance with volume rotational angle changes in the maximum position from the minimum position The transistors Q ₃₂ , Q _{36 to} Q ₄₀ and the resistors R ₃₀ , R ₃₁ supply a current flowing through the second current source 29 from the vicinity of the midpoint position to the maximum position of the volume rotation angle. A clamping circuit for clamping is configured. Transistor Q ₃₁ is supplied to the base of the transistor Q ₃₃ to shift the reference voltage output from the reference voltage circuit 20, transistor Q ₃₅ is volume VR
Supplied to the base of the transistor Q ₃₄ shifts the voltage output from the _first movable contact piece. The emitter area of the transistor Q _33, Q ₃₄ respectively is 1:20, for example.

The collector of the transistor Q ₃₃ is connected to a current source 22, it is connected to the collector of the emitter and the transistor Q ₃₉ of the collector Q ₃₈ of the transistor Q _34. With Torajisuta Q ₃₉ collector of the transistor Q ₄₀ constituting the current mirror circuit is connected to the collector of the current source 29 and transistor Q _36. The emitter area of each of the transistors Q ₃₉ and Q ₄₀ is 2: 1 and the emitter area of each of the transistors Q ₃₄ and Q ₃₆ is 20: 1.

Now volume VR ₁ the rotation angle is rotated from the midpoint position in the smaller direction to lower the output voltage of the movable contact piece, the collector current transistor of the transistor Q ₃₃ Q ₃₄
Next than the collector current large, thereby increasing as the current I _A flowing through the current source 22 shown in solid line II a of FIG. 4,
Current I _B flowing through the current source 29 decreases as shown by the solid line II b of FIG. 4, the current ratio I _B / I _A is changed as a broken line III.

Meanwhile the volume VR ₁ to increase the output voltage of the movable contact piece is rotated in the direction in which the rotation angle is increased, increasing the collector current of the transistor Q ₃₄ while decreasing the current I _A of the current source 22, the resistor R the collector potential of Tonranjisuta Q ₃₄ is reduced by ₃₁ voltage drop. This resistor R ₃₁
Voltage drop of the transistor Q ₃₈ conducts at the time when a voltage drop substantially identical resistors R ₃₀ being supplied with current (volume rotation angle is substantially midpoint) by the transistor Q _32, the collector of the transistor Q ₃₄ The current is transistor Q ₃₉
It is also supplied from the transistor Q ₃₈ as well. At this time, the emitter of the transistor Q ₃₉ is the resistance R ₃₁ is connected, the impedance during conduction of the transistor Q ₃₈ is smaller than the impedance during conduction of the transistor Q _39, transistor after conduction of the transistor Q ₃₈ Q increase of ₃₄ of the collector current of transistor Q ₃₈ supplies the majority. This current I _B of the current source 29 is clamped.

The output of the movable contact piece the rotation angle of the volume VR ₁ as a small collector current of the transistor Q ₄₀ when the voltage -V _E is absorbed by the transistor Q _36. Therefore, when the rotation angle of the volume is minimum position, all the collector current of the transistor Q ₄₀ flows through the transistor Q _36, current source 29 is a current I _B
Is cut off to zero.

Current ratio I _B / I _A in the equation (19) is varied corresponding to the rotational angle of the volume VR ₁ in the above current ratio generation unit.
Since the signal from the signal source 31 is not used at all in the current ratio generating section, there is no adverse effect on the distortion factor or the like.

Here, when the volume rotation angle is the maximum (when there is no attenuation by the electronic volume), the input dynamic level of the electronic volume is the same as the input dynamic level of the power amplifier of the next stage, and the volume rotation angle is set to the midpoint position. At this time (when the electronic volume is attenuated by 20 dB), the input dynamic level of the electronic volume increases by 20 dB with respect to the input dynamic level of the power amplifier in the next stage. The solid line V in FIG. 5 shows the input level when the next stage power amplifier is saturated. That is, when the input level is above the solid line V, the power amplifier is saturated, and when the input level is below the solid line V, the power amplifier performs amplification with good linearity.

The input dynamic range of the electronic volume circuit is a differential circuit (transistor Q ₂₁ ,
Q ₂₂₎ depending on the current I _A flowing through the current source, the current I _A fourth
Because of the characteristic shown by the solid line IIa in the figure, the dynamic range becomes the characteristic shown by the solid line IV in FIG. 5, and the dynamic range decreases in a region where the volume rotation angle is larger than the middle point position. However, when the input level is higher than the solid line V in FIG. 5, the power amplifier connected to the next stage of the electronic regulator circuit is saturated, so that the reduction of the dynamic range shown by the solid line IV does not cause any problem.

By the way, the offset voltage of the electronic volume circuit is a differential circuit (transistor Q ₁₅ ,
It is proportional to the current I _B that flows through the current source Q _16). Because the present invention as shown in the solid line II b in FIG. 4, volume rotation angle is clamped current I _B at a larger midpoint region,
The offset voltage is suppressed from increasing in a region where the volume rotation angle is larger than the midpoint position as shown by a broken line VII in FIG. The solid line VI in FIG. 6 shows the offset voltage of the conventional circuit shown in FIG. 7. In the conventional circuit, the offset voltage increases as the volume rotation angle increases in a region where the volume rotation angle is larger than the midpoint position. doing.

Incidentally, FIG. 4 the current I _A according to clamp the current I _B (solid line II b of FIG. 4) in order to volume rotational angle is suppressed offset voltage is greater than the midpoint location area in the present invention circuit By increasing the current ratio I _B / I _{A as shown} by the broken line III by increasing the volume rotation angle, the input / output voltage ratio Vb according to the volume rotation angle is reduced as shown by the solid line IIa.
/ Va, that is, the amount of attenuation is obtained. This is a circuit for performing logarithmic compression of an input unit divides the circuit each current source performing exponential expansion of the output unit, the current I _A, becomes possible by varying depending on the volume rotational angle s I _B respectively I have.

As described above, the offset voltage can be suppressed to a small value, so that the offset signal ratio can be significantly improved, and the DC coupling between the electronic volume circuit and the previous stage (preamplifier) and the subsequent stage (power amplifier) can be performed. And a large-capacity coupling capacitor for offset removal provided between them can be removed, and a large-capacity coupling capacitor that is difficult to integrate with a semiconductor is eliminated. The whole power amplifier can be constituted by a single semiconductor integrated circuit.

Effects of the Invention As described above, according to the electronic volume circuit of the present invention, the offset voltage can be suppressed and the offset signal ratio can be improved from the midpoint position to the maximum position of the volume operation position, thereby improving the electronic volume circuit. It is possible to remove the coupling capacitor by connecting the former stage and the latter stage by DC coupling, and it becomes possible to integrate the entire circuit into a semiconductor, which is extremely useful in practical use.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of the circuit of the present invention, FIG. 2 is a circuit diagram of an embodiment of a current ratio generator, FIG. 3 is a circuit diagram of the principle of the circuit of FIG. 1, and FIG. 5 is a diagram for explaining the operation of the circuit of FIG. 3, FIGS. 5 and 6 are diagrams for explaining the characteristics of the dynamic range and the offset voltage of the circuit of FIG. 1, and FIG. Circuit diagram of an example of a circuit, FIG.
The figure is a diagram for explaining the characteristics of the attenuation amount and the dynamic range of the circuit of FIG. 20: Reference voltage circuit, 21: Current ratio generator, 22 to 30:
Current source, 31 ...... signal source, Q ₁₁ to Q ₄₀ ...... transistor, R
₃₀ , R ₃₁ , RE, RL ...... Resistance, VR ₁ ...... Volume.

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-66509 (JP, A) JP-A-59-47821 (JP, A)

Claims (1)

(57) [Claims] 1. A volume for generating a voltage corresponding to an operation position, an output voltage of the volume being supplied, and a first position as the operation position of the volume changes from a minimum position to a maximum position through a midpoint position. While reducing the current flowing to the current source,
A differential circuit configured to increase a current flowing through the second current source; and a clamp circuit configured to clamp a current flowing through the second current source from an operation position of the volume from near the midpoint position to a maximum position. A current ratio generating unit that increases the current ratio between the second current source and the first current source as the operation position of the volume changes from the minimum position to the maximum position, and driven in accordance with the current of the first current source A compression circuit for differentially amplifying the input signal while logarithmically compressing the input signal; and an expansion circuit for differentially amplifying and outputting the signal supplied from the compression circuit driven according to the current of the second current source while exponentially expanding the signal. A dynamic range is reduced by clamping a current flowing through the second current source from the vicinity of the midpoint position of the volume to the maximum position to reduce the dynamic range, and to the current ratio corresponding to the operation position of the volume. On the basis of Electronic volume circuit, characterized by varying the attenuation factor of No..