JPH0712131B2 - Electronic volume circuit - Google Patents

Description

The present invention relates to an electronic volume circuit having improved temperature characteristics and the like.

[Conventional technology]

Conventionally, in an electronic volume circuit including a differential transistor pair, a volume output is obtained by controlling a current distribution ratio of the differential transistor pair based on a differential voltage applied to the differential transistor pair.

For example, as shown in FIG. 2, in the electronic volume circuit (EVR) 2, an input signal V _i is applied to an input terminal 4,
At the same time, the control voltage V _c is applied to the control input terminal 6, the volume output V _o corresponding to the control voltage V _c is taken from the output terminal 8.

In this case, the control voltage V _c is applied through the terminal 18 by setting the reference point level by the reference voltage V _ref applied to the terminal 12 from the reference voltage source 10 and the resistors 14 and 16, centering the reference point level. The upper and lower levels are arbitrarily set by adjusting the resistance 20 and the variable resistance 22 with the power supply voltage _Vcc .

Then, it is necessary to correct the temperature characteristic and the variation in the characteristic due to the forward drop voltage V _F of the diode used in such an electronic volume circuit. In order to adjust the reference point level, the semi-fixed resistor 24 And diode
26 is added.

[Problems to be Solved by the Invention]

However, such semi-fixed resistor 24 and diode 26
Is difficult to set accurately, and
There are disadvantages that the cost of parts is high, the adjustment range is narrow, the amount of attenuation of the gain control unit and the variation in each circuit when setting the gain cannot be suppressed, and the temperature characteristic is not sufficiently improved.

Therefore, the present invention has been made for the purpose of reliably suppressing temperature characteristics and variations in characteristics.

[Means for Solving the Problems]

The electronic volume circuit of the present invention, as shown in FIG. 1, is a voltage / current conversion circuit 40 for converting an input signal V _i into a current.
And a voltage source (reference voltage source 70) having a positive temperature coefficient, and a control voltage input for setting an arbitrary control voltage V _c by _dividing the reference voltage V _ref applied from this voltage source by the variable resistor 61. It has a circuit 60 and a pair of differential pairs 51 and 52, distributes the current from the voltage / current conversion circuit 40 to each differential pair 51 and 52 by the control voltage V _c , and And a differential circuit 50 whose distribution rate k is adjusted.

[Action]

With this configuration, a current corresponding to the input signal V _i is obtained by the voltage / current conversion circuit 40 and flows to the differential circuit 50.

The differential circuit 50 has a pair of differential pairs 51 and 52, and a signal current of opposite phase superimposed on the constant current I _o is input to each differential pair 51 and 52. Control voltage input circuit 60, since setting an arbitrary control voltage V _c, at each differential pair 51 and 52, current distribution is made in accordance to the control voltage V _c, it is subtracted by the current mirror circuit, a constant current component Are canceled out and only the signal component is extracted.

As a result, the passage gain (attenuation) is adjusted for the current corresponding to the input signal V _i , and the volume output is obtained.

Then, in the control voltage input circuit 60 for obtaining the control voltage V _c , a reference voltage V _ref having a positive temperature coefficient is generated by using a voltage source (reference voltage source 70) having a positive temperature characteristic, and the reference voltage V _ref is generated.
The V _ref is _divided by the variable resistor 61 and is used as the control voltage V _c for the gain control of the differential circuit 50.
50 theoretical temperature characteristics and variations in characteristics are offset.

〔Example〕

FIG. 1 shows an embodiment of the electronic volume circuit of the present invention.

The input signal V _i is applied to the input terminal 30 from the signal source 32 via the capacitor 34. This input signal V _i is converted into a voltage / current conversion circuit 40 for converting into a current according to the signal amplitude.
Added to. The voltage / current conversion circuit 40 is a transistor
The differential circuit is composed of 401, 402, resistors 403, 404, 405 and a constant current source 406, and a bias voltage V _B is applied to the bases of the transistors 401, 402 from a bias circuit (not shown). Therefore, each transistor 40
The collector of 1,402, the signal current i flows corresponding to the amplitude of the input signal V _i with respect to the shunt current I _o of the constant current 2I _o set by the constant current source 406. Set each resistance value of resistors 403 and 404.
If R _i / 2, the signal current i is Becomes

A differential circuit 50 whose gain is adjusted is provided on the collector side of each of the transistors 401 and 402 of the voltage / current conversion circuit 40. The differential circuit 50 is provided with a pair of differential pairs 51 and 52 corresponding to the respective transistors 401 and 402. The differential pair 51 has transistors 511 and 512, and the differential pair 52 has transistors 521 and 522.
A current (I _o ± i) including the signal current i corresponding to the input signal V _i flows through each differential pair 51, 52.

A control voltage V _c for gain adjustment is applied from the control voltage input circuit 60 to the bases of the transistors 511 and 522 and the bases of the transistors 512 and 521 of the differential circuit 50 through the control input terminals 53 and 54.

The control voltage input circuit 60 is a reference voltage source with a positive temperature characteristic.
The control voltage V _c is formed by dividing the reference voltage V _{ref of} 70 by the variable resistor 61 and the resistor 62 connected in series at an arbitrary voltage division ratio. Variable resistance
61 is adjusted to obtain an arbitrary control voltage V _c .

The reference voltage source 70 includes transistors 701, 702, 703, 704, 70.
For the constant current circuit consisting of 5 and resistors 706, 707, 708, an output circuit consisting of a transistor 710 and resistors 711, 712 is provided to form a reference voltage V _ref , which is passed through a buffer amplifier 713 to the control input terminal 53 side. In addition to.

Therefore, when the current flowing from the differential pair 51 to the transistor 401 is I _o and the current flowing from the transistor 802 to the transistor 512 is I ₁ , the current distribution ratio k corresponds to the current input to the differential pairs 51 and 52. It is defined as the ratio of output current I ₁ / I _o , And the signal component is also divided by I ₁ / I _o . Therefore,
Differential circuit with current distribution rate k set by control voltage V _c
The current drawn from 50 becomes k (I _o ± i) and is applied to the subtraction circuit 80. The subtraction circuit 80 includes transistors 801, 802 on the collector side of the transistors 512, 521 of the differential circuit 50.
By installing a current mirror circuit composed of the resistors 803 and 804, the current is subtracted, the constant current _Io component is canceled out, and the signal current component (−2k · i) is taken out, and the current / voltage conversion circuit 90 Added to.

The current / voltage conversion circuit 90 includes an operational amplifier 901 and a resistor 902.
If the resistance value of the resistor 901 is R ₀ , the signal current component (−2k · i) and the resistance value R ₀
Convert to the voltage 2k · i · R ₀ given by the product of and. Therefore, the output signal V _o (= 2k · i · R ₀ ) as the volume output is taken out from the output terminal 100.

In such a configuration, the resistance values R _i / 2 of the resistors 403 and 404 are
(Combined resistance value of the resistor 403 and 404: R _i), the current distribution ratio k, the total gain (attenuation ratio) as an electronic volume circuit A
_v is And is proportional to the current distribution rate k of the differential circuit 50. Therefore, if the variation factor of the current distribution rate k can be suppressed, the variation of the resistance values R _o and R _i can be canceled out.
The total gain A _v becomes stable.

Here, looking at the relationship between the control current V _c and the current distribution rate k, The characteristic voltage V _T is given by V _T = K · T / q, where K is the Boltzmann constant, T is the absolute temperature, and q is the electron charge.

Further, the reference voltage V _ref set by the reference voltage source 70 is such that the emitter area ratio of the transistor 704 to the transistor 705 of the reference voltage source 70 is 1: n, and the resistance values of the resistors 708 and 712 are R _c and R _r.
Then, Becomes

When this reference voltage V _ref is divided by the resistance division ratio m: (1-m) (0 ≦ m ≦ 1) by adjusting the variable resistor 61 of the control voltage input circuit 60, the control voltage V _c becomes Then, from equations (4) and (6), And the characteristic voltage V _T related to temperature is deleted from the left side and the right side in the equation (7), the current distribution rate k
Becomes k = (1 + n ^{Rr · m / Rc} ) ^-1 (8). That is, the current distribution rate k is uniquely determined by determining the emitter area ratio n, the resistance values R _c and R _r, and the resistance voltage dividing ratio m.

Moreover, the emitter area ratio n of the transistor 704 to the transistor 705 is determined by the transistors 704 and 705, and the resistance values R _c and R _r are the same as those of the resistors 708 and 712. Resistance values
Since R _c and R _r are constants determined by the relative ratio, variations in the elements can be canceled out. Therefore, if these are fixed,
The current distribution rate k can be uniformly set for each electronic volume circuit by the resistance voltage dividing ratio m.

Therefore, by setting the reference voltage V _ref with the reference voltage source 70 having a positive temperature characteristic and dividing it by the control voltage input circuit 60 to obtain the control voltage V _c , theoretical temperature characteristics and element variations Can be compensated for and the effects can be eliminated. That is, since matching in the same chip of the IC can be realized with high accuracy, volume characteristics with extremely little variation can be obtained, and the conventional semi-fixed resistor 24 and the correction diode 26 shown in FIG. 2 are unnecessary. Becomes
In addition to simplifying the circuit configuration, it is possible to eliminate the instability of the circuit due to the external element. As long as the reference points of the resistor 712 and the resistor 62 are common, the same characteristics can be realized even if a reference potential other than GND is applied.

〔The invention's effect〕

As described above, according to the present invention, since the attenuation gain is set by the control voltage obtained by dividing the reference voltage having the positive temperature characteristic, the theoretical variation in the temperature characteristic and the element characteristic is eliminated. It is possible to reduce the conventional correction diode and resistance, simplify the circuit configuration, and realize highly reliable and highly accurate volume characteristics.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an electronic volume circuit of the present invention, and FIG. 2 is a circuit diagram showing a conventional electronic volume circuit. 40 …… Voltage / current conversion circuit 50 …… Differential circuit 51, 52 …… Differential pair 60 …… Control voltage input circuit 61 …… Variable resistance 70 …… Reference voltage source (voltage source)

Claims (1)

[Claims] 1. A voltage / current conversion circuit for converting an input signal into a current, a voltage source having a positive temperature characteristic, and a reference voltage applied from this voltage source is divided by a variable resistor to an arbitrary control voltage. And a control voltage input circuit that obtains, and has a pair of differential pairs, and distributes the current from the voltage / current conversion circuit to each differential pair by the control voltage,
An electronic volume circuit having a differential circuit in which a current distribution ratio for each differential pair is adjusted.