JPH03143007A - Frequency equalization circuit - Google Patents

Abstract

PURPOSE:To attain more accurate frequency equalization by connecting a resonance circuit directly to a signal source and adjusting the frequency characteristic of a series resonance circuit near the resonance frequency based on an original signal and a signal resulting from the signal given to the said series resonance circuit After impedance conversion through a buffer amplifier. CONSTITUTION:A signal source P connects to a noninverting input of an amplifier G1 via a resistor R1 and also connects to other terminal of a series resonance circuit comprising a capacitor C1 connecting to ground through a coil L1 and connecting to a resistor R4 in series./A connecting point between the resistor R4 and the capacitor C1 connects to a buffer amplifier G2 applying impedance conversion to a signal coming from the connecting point, and the frequency characteristic of the series resonance circuit around its resonance frequency is adjusted based on an output of the buffer amplifier G2 and a signal from the signal source. Thus, the frequency equalizing circuit whose Q characteristic is constant is realized and accurate frequency equalization is implemented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a frequency equalization circuit, and particularly to a frequency equalization circuit with improved Q characteristics.

(Prior Art) Frequency equalization circuits that adjust frequency characteristics to desired characteristics are widely used to compensate for changes in frequency characteristics of signal transmission paths. Further, this frequency equalization circuit is also used as a so-called graphic equalizer for changing the sound quality output from an audio device to the sound quality desired by the user.

Conventionally, a frequency equalization circuit used as a graphic equalizer divides a predetermined band of the entire audible frequency band into a plurality of regions, provides an LC resonant circuit corresponding to each divided region, and calculates the frequency characteristics and amplitude characteristics of each LC resonant circuit. is controlled by changing circuit constants to adjust the overall frequency characteristics.

FIG. 4 shows an example of a frequency equalization circuit that changes the frequency characteristics of a specific band (the above-mentioned divided area).

In FIG. 4, the signal from signal source P is applied to the non-inverting input of operational amplifier G through resistor R41. The output of the amplifier G is connected to the inverting input of the operational amplifier G, through the resistor R4.
A return connection is made via 2. In addition, variable resistor R43
are connected in series, capacitor C41 and coil L4
1, one end of which is grounded, is connected to either terminal T or T2 through the operation of switch S4. Terminal T is connected to the connection point between resistor R4 and the non-inverting input of amplifier G1;

connected to the inverting input of When the resonant circuit is connected to the terminal T1 by the switch S4, the input to the amplifier G1 is reduced by the voltage division between the resistor R6 and the variable resistor Ro, and the amplifier G1 has an attenuation characteristic, while the switch S is connected to the terminal T1. , the amplifier G has amplification characteristics.The amount of attenuation and the amount of amplification are determined by the variable amount of the variable resistor R4 connected in series with the resonant circuit.

In the conventional frequency equalization circuit, the circuit shown in FIG.
, to adjust the overall frequency band characteristics.

(Problems to be Solved by the Invention) The frequency characteristics of the conventional frequency equalization circuit as shown in FIG. 4 are shown in FIG.

In FIG. 5, the resonant frequency f0 is IKHz, and the vertical axis indicates the level.

As understood from FIG. 5, the Q characteristic of the frequency characteristic of the conventional frequency equalization circuit decreases as the output level of the amplifier G decreases.

Therefore, level changes due to frequency deviations are reduced, so the audible frequency band can be divided into many subband areas like an audio device! ! I! (usually 5 to 14), the difference between the characteristics of adjacent divided bands decreases, which not only reduces the significance of band division, but also makes it difficult to obtain the desired frequency characteristics. there were.

Therefore, an object of the present invention is to provide a frequency equalization circuit with a constant Q characteristic.

(Means for Solving the Problems) In order to solve the above problems, a frequency equalization circuit according to the present invention includes a series resonant circuit connected to a signal source via a resistor, and a connection between the series resonant circuit and the resistor. and an MWI amplifier that impedance converts a signal from a point, and adjusts a frequency characteristic centering on the resonant frequency of the series resonant circuit based on the output of the M-town amplifier and the signal from the signal source. .

(Example) Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a frequency equalization circuit according to the present invention.

Signal source P is connected to the non-inverting input of amplifier G1 via resistor R1, similar to the conventional circuit of FIG. The signal source P is also connected to the other end of a series resonant circuit consisting of a capacitor C port and a coil L, in which a resistor R4 is connected in series and one end is grounded. The connection point between resistor R4 and capacitor C2 is connected to the non-inverting input of amplifier G. The output of amplifier G is connected via a resistor R2 to the inverting input of amplifier Gl. The output of the high input impedance buffer amplifier G2 is connected to the inverting input of the high input impedance buffer amplifier G2, and is also connected to the switch S through a variable resistor R1. This variable resistance R3 is
The terminals T1 and T are switched and connected by the operation of the switch S.

When switch S is connected to terminal T, an attenuated output with attenuation R1/(R1+R4) is obtained from amplifier G, and when switch S is connected to terminal T, an attenuated output is obtained from amplifier G1. An amplified output of (R2+R,)/Rs is obtained. This attenuation and amplification degree are determined by the resistance value of the variable resistor R3.

The signal from signal source P is always connected to resistor R4 and capacitor C.
2, is applied to the series circuit of coil L, and resistor R4
The high input impedance buffer amplifier G2 lowers the impedance of the signal from the connection point between the signal and the capacitor CI, and outputs the signal.

At the resonant frequency of the series resonant circuit, the impedance of Ll and CI to the non-inverting input of amplifier G2 is approximately zero, so the signal level is approximately zero,
The output also becomes approximately zero, and at a frequency far away from the resonant frequency f0, the impedance consisting of L and C1 approaches infinity, so the signal from the signal source P is input almost as is to the non-inverting input of the amplifier G2, and the output is is approximately equal to the signal source output.

Therefore, this circuit has anti-resonant characteristics, and its Q is:
It is expressed as Q=2πfoL+/R1, and Q is constant regardless of the input level.

As described above, in this invention, unlike conventional frequency equalization circuits, the series resonant circuit is not directly connected to the signal path to increase or decrease the level, but instead is used as an independent resonant circuit to constantly apply the signal. Since the voltage is added to or subtracted from the original signal (signal from the signal source) using a buffer amplifier as a voltage source, the Q of the resonant circuit does not change even if the level of addition and subtraction is changed.

The frequency characteristics of the frequency equalization circuit shown in FIG. 1 are shown in FIG.

As is clear from FIG. 2, Q always takes a constant value regardless of the level. Therefore, minute level adjustment becomes possible.

Another embodiment of the frequency equalization circuit according to the present invention is shown in FIG.

The embodiment of FIG. 3 is characterized in that a semiconductor inductor, which is advantageous for integration, is used instead of the coil L of the embodiment of FIG. 1.

In Fig. 3, resistor R12, Ri6, capacitor C1
2 and amplifier G, a semiconductor inductor is connected to the first
It is provided in place of the coil L shown in the figure. In the figure, resistors R3 and R,2 correspond to resistors R and R2, respectively.

Variable resistor R1 corresponds to resistor R1 in FIG. 1, but is not switched by switch S.

(Effects of the Invention) As explained above, in the present invention, a resonant circuit is directly connected to a signal source, and a signal obtained by impedance conversion of the signal to this series jl: resonant circuit through a buffer amplifier and an original signal. Since the frequency characteristics near the resonant frequency of the series resonant circuit are adjusted based on this, the Q of the resonant circuit can be maintained constant, and the Q does not change even with minute level changes, allowing more precise frequency equalization. becomes.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the frequency equalization circuit according to the present invention, FIG. 2 is a diagram showing the resonance characteristics of the circuit shown in FIG. 1, and FIG. 3 is a circuit diagram showing an embodiment of the frequency equalization circuit according to the invention. A circuit diagram showing another embodiment, FIG. 4 is a conventional frequency equalization circuit diagram,
FIG. 5 is a diagram showing the resonance characteristics of the conventional circuit shown in FIG. 4.

Claims (1)

[Claims] It includes a series resonant circuit connected to a signal source via a resistor, and a buffer amplifier that converts the impedance of a signal from a connection point between the series resonant circuit and the resistor, and the output of the buffer amplifier and the signal from the signal source. A frequency equalization circuit that adjusts a frequency characteristic centering on the resonance frequency of the series resonant circuit based on.