JPH05110359A - Volume control circuit - Google Patents

Abstract

PURPOSE:To obtain a volume characteristic in matching with the audible sense of human being and independently of temperature. CONSTITUTION:A current (i) expressed in expression is generated by applying feedback to an input side of n-stages of transistor (TR) group 1 from an amplifier M so as to set a voltage at the input side to zero, where vT is kT/q, k is the Boltzmann's constant, T is an absolute temperature, q is a charge and Kr is an emitter resistance. Then the current (i) expressed in the equation I is multiplied with (a) to generate a current iX expressed in equation II, where iO is a constant and r' is a base resistance. The attenuation is controlled by changing the constant (a).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a volume control circuit having good control characteristics.

[0002]

2. Description of the Related Art A conventional volume control circuit is
For example, a volume R having the configuration shown in FIG. 6 is used. Such a volume control circuit has the characteristics shown in FIG. This characteristic is
It is non-linear as shown in FIG. That is, in this characteristic, when the input signal level is high, the change amount of the output is small with respect to the change of the control amount of the volume.
On the contrary, when the input signal level is low, the change amount of the output is large with respect to the change of the control amount of the volume.

[0003]

The characteristic of the conventional volume control circuit is that it is not suitable for human hearing because the relationship between the volume control amount and the output is non-linear.

The present invention has been made in order to solve the above problems, and an object thereof is to obtain a volume characteristic suitable for human hearing because the relationship between the volume control amount and the output is linear. To do.

[0005]

A volume control circuit of the present invention comprises a first circuit (circuit of FIG. 1) including n stages of transistors (transistor group 1) for generating a current i represented by the following equation: = (V _T / K _r ) log _e n (where V _T = kT / q, k is the Boltzmann constant,
T is the absolute temperature, q is the charge amount, and K _r is the emitter resistance of the transistor. ) The current i indicated by the above formula include a constant current source 10 multiplied a (current amplification factor), and a second circuit for generating a current i _x which is represented by the following formula (circuit of FIG. 2), i _x = i _o × e ^{− (ar ′ / Kr) logen} (where i _o is a constant and r ′ is a base resistance). The first current source 20 has a constant current source 20 whose constant current is the current i _x shown in the above equation. 3 circuit (circuit of FIG. 3).

[0006]

In the volume control circuit having the above structure, the first circuit (circuit of FIG. 1) including the n-stage transistors (transistor group 1) generates the current i represented by the following equation, i = (V _T / K _r ) log _e n The second circuit (the circuit of FIG. 2) including the constant current source 10 obtained by multiplying the current i shown by the above equation by a (current amplification factor) causes the current i shown by the following equation. _x is generated and i _x = i _o × e ^{− (ar ′ / Kr) logen} The third circuit (the circuit of FIG. 3) having the constant current source 20 whose constant current is the current i _x shown in the above equation is The attenuation amount is changed by changing the a (current amplification factor).

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram showing an input side potential difference of 0 in an embodiment of a volume control circuit of the present invention. In FIG. 1, the voltage V is applied across the series circuit of the resistor r _P and the diode d. The base of the n-stage NPN transistor group 1 is connected to the connection point p between the resistor r _P and the diode d. The collector of the transistor group 1 is connected to the voltage V via the resistor r _q , and the emitter thereof is grounded via the resistor k _r .
The connection point q between the resistor r _q and the collector of the transistor group 1 is the non-inverting input terminal of the amplifier M, and the connection point p is the amplifier M.
It is connected to the inverting input terminal of. The output of the amplifier M is fed back to the voltage V. The resistors r _p and r _q are set to have the same resistance value.

As shown in FIG. 1, this circuit feeds feedback from the amplifier M to the input side of the transistor group 1 to change the voltage V, and two input points p and q of the amplifier M.
It operates so as to make the potential difference of 0. If the potentials at the points p and q are equal, the resistance values of the resistors r _p and r _q are equal, so that an equal current i flows through the resistor k _r and the diode d as shown in FIG. Since the potential at the point p is the forward voltage of the diode d, which is equal to the sum of the base-emitter voltage of the n-stage transistor group 1 and the voltage drop of the resistor K _r , the formula (1) is established. V _T log _e (i / i _s ) = V _T log _e (i / _{n s} ) + K _r i (1) Further, by solving equation (1), equation (2) is obtained. i = (V _T / K _r ) log _e n (2) where V _T = kT / q, where k is the Boltzmann constant and T
Is the absolute temperature and q is the amount of charge. Further, i _s is a reverse current.

FIG. 2 shows the configuration of a circuit including the circuit of FIG. 1 as a constant current source. In FIG. 2, the constant current source 10
Is a portion corresponding to the circuit of FIG. The voltage V _CC is applied to the series circuit of the resistor r _o and the diode d _o , and the input of the amplifier M ₁ is connected to the connection point s. The output of the buffer amplifier M ₁ (gain is 1) is N through the resistor r ′.
It is connected to the base of the PN transistor t. Also,
A constant current source 10 is connected to the base of the NPN transistor t.

In FIG. 2, the potential of the input point s of the amplifier M ₁ is equal to the forward voltage of the diode d _o , which is equal to the sum of the voltage drop of the resistor r ′ and the base-emitter voltage of the transistor t. Therefore, it is expressed by the equation (3). V _T log _e (i _o / i _s ) = r′i ′ + V _T log _e (i _x / i _s ) ... (3) where i _o is the current flowing through the diode d _o and i ′
Is a constant current flowing through the constant current source 10. Since the base current of the NPN transistor t is small, the current i ′ is the resistance r ′.
Is almost equal to the current flowing through. Also, this current i'is as shown in FIG.
Has a value a times the current i (shown by the equation (2)) at. i _x is a current flowing through the NPN transistor t.

From the equation (3), the current i _x can be expressed by the equation (4). i _x = i _o × e ^{− (ar ′ / kr) logen} (4) However, the current i _o is expressed by the following equation. i _o = (V _CC −V _BE ) / r _o (5) where V _BE is the forward voltage of the diode d _o .

FIG. 3 shows the configuration of a circuit using the current i _x obtained in the circuit shown in FIG. 2 as a constant current. Input e _s are input to the amplifier M _2, N from the amplifier M ₂
It is supplied to the base of the PN transistor t ₁ . The NPN transistor t ₁ has its collector connected to the voltage source V _CC via the diode d ₁ and its emitter grounded via the NPN transistor t ₂ and the resistor r ₂₂ . NPN
The base of the transistor t ₂ has a resistor r ₁ and a diode d.
_The voltage divided by ₃ and the resistor r ₂₁ is supplied. Further, the base of the NPN transistor t ₃ is connected to the base of the NPN transistor t ₂ . The emitter of the NPN transistor t ₃ has a resistor r _23.
Grounded through. Also, its collector is NPN
It is connected to the voltage source V _CC through the transistor t ₄ and the diode d ₂ . The collector of the NPN transistor t ₃ is connected via a resistor r ₃ to the collector of the NPN transistor t _2. That is, the diode d ₃ and the resistor r ₂₁ ,
Transistor t ₂ , resistor r ₂₂ , and transistor t ₃
And the resistor r ₂₃ form a constant current circuit, and the same current I ₀ flows.

One end of the constant current source 20 constituted by the circuit shown in FIG. 2 is grounded, and the other end is connected to the voltage source V _CC through the NPN transistor t ₅ and the diode-connected PNP transistor t _6. There is. In addition, the constant current source 2
One end of 0 is connected to the voltage source V _CC through the NPN transistor t ₈ and the diode-connected PNP transistor t ₇ . The base of the transistor t ₅ is connected to the anode of the diode d ₁ and its collector is PN.
It is connected to the base of the P-transistor t ₉ . Also,
The base of the transistor t ₈ is connected to the collector of the transistor t _{4, and} the collector of the transistor t ₈ is connected to the base of the PNP transistor t ₁₀ .

The collector of the transistor t ₉ is grounded via a diode-connected NPN transistor t _{1 1} . The collector of the transistor t ₁₀ is grounded via the NPN transistor t ₁₂ . The bases of the transistors t ₁₁ and t ₁₂ are connected to each other. The transistors t ₅ and t ₆ and the transistor t _{9 form} a current mirror circuit, and similarly, the transistors t ₇ and t ₈ and the transistor t _{10 form} a current mirror circuit. Therefore, the same current that flows in the collector of the transistor t ₅ flows in the collector of the transistor t ₉ . Similarly, the same current that flows in the collector of the transistor t ₈ flows in the collector of the transistor t ₁₀ . The transistors t ₁₁ and t ₁₂ also form a current mirror circuit, and the same current flows between the collector and emitter of each.

The collector of the transistor t ₁₀ is connected to the output terminal and is also grounded via the resistor r _L and the constant voltage source E. The constant voltage source E is connected to the base of the transistor t ₄ .

Next, the operation will be described. Now
Assuming that the current flowing through the system of the diode d ₁ , the transistor t ₁ , the resistor r ₃ , the transistor t ₄ , and the diode d ₂ is i ₁ , the constant current I ₀ flows through the transistors t ₂ and t ₃ , respectively. _A current I ₀ + i ₁ flows through ₁ ,
A current I ₀ −i ₁ flows through the diode d ₂ .

If the current flowing through the paths of the transistors t ₇ , t ₈ , t ₅ and t ₆ is i ₂ , then the transistors t ₅ and t
₈ are connected to the constant current source 20, respectively, so that the collectors of the transistors t ₅ and t ₈ receive the current i _x /
2-i ₂ or i _x / 2 + i ₂ flows. These currents are transferred by the current mirror circuit and are transferred to the transistor t ₉
Of the current i _x / _2-i 2 flow in the collector, the transistor t
_A current i _x / 2 + i ₂ flows through 10. As a result, current flows i _x / _2-i 2 to the transistors t _11, which is connected to the transistor t ₉ series. Since the same current as the transistor t ₁₁ flows through the transistor t ₁₂ , the current i _x flows there.
/ 2-i ₂ flows. The current i _x / 2 + is applied to the transistor t _10.
i ₂ flows, because the current flows i _x / 2i ₂ transistors t _12, the resistance r is in _L current _{2i 2 (= i x / 2} + i 2 -i
_x / 2 + i ₂ ) flows.

In FIG. 3, the potential difference ΔV _fg between the point f (point on the power supply voltage line) and the point g (connection point of the emitters of the transistors t ₅ and t ₈ ) is the voltage drop of the diode d ₁ and the base of the transistor t ₅ . Since it is the voltage obtained by adding the forward voltage between the emitters, it can be expressed by the following equation (6). ΔV _fg = V _T log _e ((I ₀ + i ₁ ) / i _s ) + V _T log _e ((i _x / 2-i ₂ ) / i _s ) (6)

Similarly, since the potential difference between the points f and g is equal to the sum of the forward voltage of the diode d ₂ and the base-emitter voltage of the transistor t ₈ , it can be expressed by the following equation (7). .. ΔV _fg = V _T log _e ((I ₀ −i ₁ ) / i _s )) + V _T log _e ((i _x / 2 + i ₂ ) / i _s ) (7)

If equation (6) is equal to equation (7), the following equation (8) is obtained. _{(I 0 + i 1) (} i x / 2-i 2) = (I 0 -i 1) (i x / 2 + i 2) ··· (8)

By solving the equation (8), the following equation (9) is obtained. _{i 2 = (1/2) × (} i x / I 0) × i 1 ··· (9)

As described above, since the current 2i ₂ flows through the resistor r _L , if the change amount of the output with respect to the constant voltage E is V _OUT , V _OUT can be obtained from the following equation. V _OUT = 2i ₂ × r _L = (i _x / I ₀ ) × i ₁ × r _L (10)

When the input variation with respect to the constant voltage E is V _IN , the following equation (11) is established. i ₁ = V _IN / r ₃ (11)

By substituting the equation (11) into the equation (10), the following equation (12) is obtained. V _OUT = (r _L / r ₃ ) × (i _x / I ₀ ) × V _IN (12)

The current I ₀ can be uniquely obtained from the following equation (13), which is established from the relationship of the voltage drop in the path of the resistor r ₁ , the diode d ₃ , and the resistor r ₂₁ . I ₀ = (V _CC −V _T log _e (I ₀ / i _s )) / (r ₁ + r ₂₁ ) ... (13)

As can be seen from the equation (12), the change amount V _OUT of the output voltage is proportional to the constant current i _x . Then, this constant current i _x is expressed by the equation (4). Therefore, the following equation is obtained. _{V OUT / V IN = (r} L / r 3) (1 / I 0) i o × e - (ar '/ kr) logen ··· (14)

As can be seen from the equation (14), this (14)
If the input / output characteristic obtained by the formula is displayed in decibels, the characteristic becomes linear. That is, the attenuation amount can be linearly controlled by appropriately adjusting the value of a (current amplification factor). Therefore, a volume characteristic ideal for human hearing can be obtained. Further, since V _T is canceled out, stable characteristics independent of temperature can be obtained.

[0028]

As described above, according to the present invention, since the volume control circuit having the exponential function characteristic is constructed, the relationship between the volume control amount and the output becomes linear when the decibel display is performed. It is possible to obtain a volume characteristic suitable for human hearing. Also,
There is an effect that a characteristic that does not depend on temperature can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a circuit for setting a potential difference on an input side to 0 in an embodiment of a volume control circuit of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a circuit using a constant current source whose constant current is the current obtained in the embodiment of FIG.

FIG. 3 is a circuit diagram showing a configuration of a circuit using a constant current source whose constant current is the current obtained in the embodiment of FIG.

FIG. 4 is a diagram showing volume characteristics in one embodiment of the volume control circuit of the present invention.

FIG. 5 is a diagram showing a volume characteristic in a conventional volume control circuit.

FIG. 6 is a diagram showing a configuration example of a volume in a conventional volume control circuit.

[Explanation of symbols]

 1 Transistor group 10, 20 Constant current source

Claims (1)

[Claims] 1. A first circuit including an n-stage transistor for generating a current i represented by the following equation: i = (V _T / K _r ) log _e n (where V _T = kT / q, k is the Boltzmann constant,
T is the absolute temperature, q is the charge amount, and K _r is the emitter resistance of the transistor. ) The current i indicated by the above formula include a constant current source that is a times, a second circuit for generating a current i _x which is represented by the following _{formula, i x = i o × e} - (ar '/ Kr) logen (Here, i _o is a constant and r'is a base resistance.) A volume control comprising a third circuit having a constant current source whose constant current is the current i _x shown in the above formula. circuit.