JPH06132751A - Sound quality adjustment circuit - Google Patents

Abstract

PURPOSE:To miniaturize a circuit and to reduce the number of pins by switching adjustment output from a control means to a non-inversion input terminal or an inversion input terminal in an operational amplifier means, supplying it and adjusting the emphasis or attenuation of an input signal. CONSTITUTION:When only the signal component of a frequency band to be adjusted is made to pass through a filter 12, a control circuit 11 adjusts the gain of the passed frequency component by switching an array 14. The control circuit 11 amplifies the signal component of the band, which is thus selected, by a buffer amplifier circuit 15 at a prescribed amplification factor, and supplies it to impression voltage switching circuits 16 and 17. The impression voltage switching circuits 16 and 17 add filter output S1 to the non-inversion input terminal through an input resistance RX1 when the input signal VIN is to be attenuated, and add it to the inversion input terminal through a feedback resistance RX2 when the input signal is to be emphasized.

Description

Detailed Description of the Invention

[0001]

[Table of Contents] The present invention will be described in the following order. Field of Industrial Application Conventional Technology Problems to be Solved by the Invention (FIGS. 4 and 5) Means for Solving the Problems (FIGS. 1 and 2) Action (FIG. 3) Embodiments (FIGS. 1 to 3) The invention's effect

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a volume control circuit, and is particularly suitable for application to a circuit for adjusting transfer characteristics by serial data.

[0003]

2. Description of the Related Art Conventionally, a sound quality adjusting circuit is a function circuit widely used as an essential function for audio equipment. In this circuit, an audible band is divided into two bands, a low band and a high band, There is a so-called graphic equalizer capable of subdividing an audible band into 5 bands, 7 bands or more from those of a simple circuit having a 2-band structure for adjusting the emphasis or attenuation of each band and adjusting each of them.

Various circuits such as a parametric equalizer in which the center frequency f0 and the bandwidth Q of each band of the graphic equalizer can be arbitrarily set have been considered.

[0005]

By the way, in recent years, there has been an increasing demand for a function of controlling the sound quality adjustment circuit via a microcomputer. This is to support remote control, and to meet the requirement to store the setting conditions as a plurality of types of patterns so that an optimal sound field can be obtained according to the sound source and environment.

[0006] In addition, the control by the micro computer is possible because the circuit can be separated from the operation panel and the structure is free, and the operation by the touch key can be realized from the rotary knob.

By the way, in this case, it is necessary to decode the serial data generated by the microcomputer by the sound quality adjusting circuit and set the characteristics of the circuit. Normally, when such serial data is generated, not only the control data of the sound quality adjustment circuit but also volume adjustment, balance, fader (volume balance of speakers arranged before and after), loudness on / off, input switching, etc. Often, the control data is added to form serial data. The word length of data is generally 20 to 40 bits.

The adjustment by such serial data is
Instead of the adjustment by the volume type variable resistors RB and RT of the negative feedback type sound quality adjusting circuit 1 shown in FIG. 4, the resistance value is selected by the decoding circuit 2 shown in FIG.

That is, the decoding circuit 2 sequentially takes in the serial data D, stores it, and converts it into parallel data through the shift register 3, the latch circuit 4, and the binary-parallel conversion circuit 5 to form a variable resistor. The switch row 7 is used for switching so as to select any one of the resistor rows 6.

As the decoding circuit 2, a CMOS integrated circuit is generally used because it is suitable for a large-scale digital circuit and a resistor and a switch circuit are easily realized, and other capacitors and operational amplifiers are externally attached. It is configured by the circuit element of. Therefore, in the conventional case, the digital circuit, the resistor array, and the switch array in the sound quality adjusting circuit are CMOS.
The integrated circuit and the analog circuit are configured by an external circuit.

However, recently, in order to improve the mounting rate, there is a demand for integration in one chip including an analog circuit portion. However, in the circuit as shown in FIG. 4, there is a problem that the number of pins is increased because at least four pins are required to externally connect the capacitors C1 and C2, and the number of bands to be adjusted like the graphic equalizer is increased. When it increased, there was a problem that the number of pins increased too much.

The present invention has been made in consideration of the above points, and an object thereof is to propose a sound quality adjusting circuit which is much smaller and has a smaller number of pins than the conventional one.

[0013]

In order to solve such a problem, according to the present invention, an input signal VIN is applied to a non-inverting input terminal through input resistors RO1 and RX1 and an output signal VOUT is connected to an output terminal. Feedback resistors RO2, R
Operational amplifier means OP1 which feeds back to the inverting input terminal via X2
And a control means 11 for extracting a predetermined frequency component from the input signal VIN and adjusting and outputting the gain of the extracted frequency component, and an adjusted output output from the control means 11 for the non-inverting input of the operational amplification means OP1. And switching means 10 and 17 for adjusting the emphasis or attenuation of the input signal VIN.

Further, in the present invention, the control means 11 is
A filter circuit 12 for extracting a predetermined frequency component from the input signal VIN and gain control circuits 13, 14, 15 for adjusting the gain based on serial data D given from the outside are provided.

Further, in the present invention, the filter circuit 1
2 should be either a low pass filter, a band pass filter or a high pass filter.

Further, in the present invention, a plurality of control means 11 for extracting frequency components different from each other, and the adjustment signals output from the control means 11 corresponding to the control means 11 are non-inverted by the operational amplification means OP1. A plurality of switching means 16 and 17 are provided for switching to the input terminal or the inverting input terminal, and the adjusted output of each control means is independently switched and supplied to the non-inverting input terminal or the inverting input terminal of the operational amplifier OP1. , The enhancement or attenuation of the input signal is adjusted for each frequency component.

[0017]

The predetermined frequency component of the input signal VIN can be emphasized or attenuated by switching and supplying the adjustment signal of the predetermined frequency band extracted from the input signal VIN to the non-inverting input terminal or the inverting input terminal of the operational amplifier OP1. It is possible to adjust the amount of adjustment that is emphasized or attenuated by adjusting the gain of the control means 11. Since the two sets of controls can be adjusted independently in this way, the number of switches required for the adjustment can be further reduced compared to the conventional case.

Further, by configuring the band to be adjusted as the filter 12, the capacitance may be grounded at one end, so that the number of terminals required for external connection of the capacitance can be further reduced compared to the conventional case.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, reference numeral 10 indicates a sound quality adjusting circuit as a whole, and an operational amplifier circuit OP1 constituting a differential amplifier circuit.
The signal component of a predetermined band is extracted from the input signal VIN and injected into either one of the non-inverting input terminal and the inverting input terminal of the input signal, and the input signal VIN of the corresponding band is attenuated or emphasized.

In the case of this embodiment, the control circuit 11 used for extracting the predetermined frequency component is only one system, and is used for adjusting the high tone.

The tone control circuit 10 inputs the input signal VIN to the non-inverting input terminal via the input resistors RO1 and RX1 and inputs the output signal VOUT to the inverting input terminal via the feedback resistors RO2 and RX2. The input applied to the non-inverting input is input to the control circuit 11 constituted by the filter 12, the resistor array 13, the switch array 14 and the buffer amplifier circuit 15.

Here, the control circuit 11 adjusts the gain of the passed frequency component by switching the switch train 14 when only the signal component of the frequency band to be adjusted is passed through the filter 12. . The control circuit 11 amplifies the signal component of the band thus selected by the buffer amplification circuit 15 at a constant amplification factor and supplies it to the applied voltage switching circuits 16 and 17.

The applied voltage switching circuits 16 and 17 include a filter output S1 output from the control circuit 11 and a ground potential GN.
Either one of D is input resistor RX1 or feedback resistor RX2
It is designed to be supplied to. Here, the applied voltage switching circuits 16 and 17 add the filter output S1 to the non-inverting input terminal via the input resistor RX1 when it is desired to attenuate the input signal VIN, and through the feedback resistor RX2 when it is desired to emphasize it conversely. It is designed to add to the inverting input terminal.

In the above configuration, the transfer function of the control circuit 11 is -H (S), and the resistance values of the input resistors RO1, RX1 and the feedback resistors RO2, RX2 are RO = RO1 = R.
Assuming that the relationship of O2 and RX = RX1 = RX2 holds, the operation when the input signal VIN is attenuated will be analyzed.

In this case, the filter output S1 has an input resistance R
It is added to the non-inverting input terminal via X1, and if this state is seen from the point A, it can be regarded as a two-terminal circuit in which the input resistor RX1 is connected to the input / output terminal. Therefore, the impedance Z (S) is

[Equation 1] Is expressed as

Transfer function TC (S) between input and output at this time
Is calculated as

[Equation 2] Given in. The transfer function TC of the sound quality adjustment circuit 10
(S) becomes 1 when the transfer function H (S) is 0, and as the transfer function H (S) of the control circuit 11 increases, the transfer function T
C (S) becomes smaller. It can be seen that the input signal VIN can be attenuated in this way.

On the other hand, the operation of emphasizing the input signal VIN will be analyzed. In this case, the filter output S1
Is added to the inverting input terminal via the feedback resistor RX2, and the transfer function TB (S) between the input and output in this state.
Is the expression

[Equation 3] Becomes

The transfer function TB represented by the equation (3)
(S) is an inverse function of the transfer function TC (S) expressed by the equation (2). Therefore, when the transfer function is expressed in decibel [dB], it becomes symmetrical with respect to the axis of T (S) = 1, and the characteristics at the time of attenuation and the characteristics at the time of emphasis can be made to be opposite to each other.

In this way, the applied voltage switching circuits 16 and 17 are
It is possible to switch between the attenuation and the emphasis by switching the output of, but the absolute value of the adjustment amount at that time can be adjusted by adjusting the gain of the control circuit 11. For example, the filter 12 is a high-pass filter,
When the gain of the control circuit 11 is gradually decreased from the maximum value,
As shown in, the absolute value of the adjustment amount is L (+1), L (+
2), L (+3) or L (-1), L (-2), L (-
It becomes gradually smaller with 3).

According to the above configuration, the filter output S1 which is the frequency component of the input given to the non-inverting input terminal that has passed the predetermined band is switched to the non-inverting input terminal or the inverting input terminal and added to add the input. It is possible to switch between emphasis and attenuation of the signal VIN.

The absolute value of the adjustment amount at this time can be adjusted by adjusting the gain of the control circuit 11,
In this way, the absolute value of the adjustment amount and the switching of emphasis or attenuation can be separated, so that the switches can be reduced. For example, in increments of 2 [dB] ± 14 [d
When it is desired to realize the adjustment range of B], 15 switches are required in the prior art, but the amount of adjustment and emphasis or suppression can be switched in the present invention. Therefore, a total of 10 switches of 8 + 2 can be configured. .

Further, at this time, the transfer characteristics including the absolute value of the adjustment amount are symmetrical between the emphasis and the attenuation, and the desired characteristics can be easily obtained for the sound quality adjustment.

Further, since the adjustment band can be set by the filter circuit 12, the number of pins can be further reduced as compared with the conventional case, and thereby the shape of the IC can be further reduced. For example, in the case of a two-band sound quality adjusting circuit, two capacitors can be configured by grounding at one end, so that it is possible to configure a terminal with two pins, which was required in the prior art with four pins.

In the above-described embodiment, the case where only one treble adjustment is realized by providing one control circuit 11 used in the sound quality adjusting circuit 10 and using the filter circuit 12 as a high pass filter has been described. The invention is not limited to this, and only the bass may be adjusted.

When it is desired to adjust the emphasis or attenuation for two bands of treble and bass, two control circuits are connected in parallel, and when it is desired to adjust the emphasis or attenuation for a plurality of bands like a graphic equalizer. It suffices to connect the control circuits in parallel by the number of bands and switch the output to the non-inverting input terminal or the inverting input terminal to supply.

In the above embodiment, the case where the capacitor used in the filter circuit 12 is externally described has been described, but the present invention is not limited to this, and since the adjustment band is set by the filter, this filter is used. If the circuit 12 is constructed by a combination of the monolithic filter technology and the SCF (switched capacitor filter) technology, all the elements can be completely built in the IC.

[0038]

As described above, according to the present invention, the adjustment signal of the predetermined frequency band extracted from the input signal is switched to the non-inverting input terminal or the inverting input terminal of the operational amplifying means and supplied, and the gain of the control means is increased. By adjusting and outputting the adjustment signal, the predetermined frequency component of the input signal can be emphasized or attenuated, and the absolute value of the adjustment amount at that time can also be adjusted. As described above, since the control of the enhancement or attenuation of the signal and the control of the adjustment amount thereof can be independently adjusted, the number of switches required for the adjustment can be further reduced as compared with the conventional one.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a sound quality adjustment circuit according to the present invention.

FIG. 2 is a connection diagram showing the configuration of the control circuit.

FIG. 3 is a characteristic curve diagram for explaining the transfer characteristic.

FIG. 4 is a connection diagram showing a conventional sound quality adjustment circuit.

FIG. 5 is a block diagram for explaining the decoding circuit.

[Explanation of symbols]

1, 10 ... Sound quality adjustment circuit, 11 ... Control circuit, 12 ...
... filter, 13 ... resistor train, 14 ... switch train, 1
5 ... Buffer amplification circuit, 16, 17 ... Applied voltage switching circuit.

Claims (4)

[Claims] 1. An operational amplifier means for applying an input signal to a non-inverting input terminal via an input resistor and for feeding back an output signal to an inverting input terminal via a feedback resistor connected to an output terminal; Control means for extracting a predetermined frequency component from the signal and adjusting and outputting the gain of the extracted frequency component; and a non-inverting input terminal or inverting input terminal of the operational amplifying means for adjusting output output from the controlling means. Switch to supply
A sound quality adjusting circuit, comprising: switching means for adjusting emphasis or attenuation of the input signal. 2. The control means comprises a filter circuit for extracting a predetermined frequency component from the input signal, and a gain control circuit for adjusting the gain based on serial data given from the outside. The sound quality adjustment circuit according to item 1. 3. The filter circuit comprises a low pass filter,
The sound quality adjusting circuit according to claim 2, wherein the sound quality adjusting circuit is made of either a band pass filter or a high pass filter. 4. A plurality of control means for extracting frequency components different from each other, and a non-inverting input terminal or an inverting input terminal of the operational amplifier means for adjusting signals output from the control means corresponding to the control means. And a plurality of switching means for switching and supplying the control output to the non-inverting input terminal or the inverting input terminal of the operational amplifying means.
The sound quality adjustment circuit according to claim 1, wherein the enhancement or attenuation of the input signal is adjusted for each frequency component.