JPH0738552B2 - Frequency equalization circuit - Google Patents

Description

The present invention relates to a frequency equalizer circuit, and more particularly to a frequency equalizer circuit with improved Q characteristics.

(Prior Art) A frequency equalization circuit that adjusts a frequency characteristic to a desired characteristic is widely used to compensate for a change in the frequency characteristic of a signal transmission line. Further, this frequency equalization circuit is also used as a so-called graphic equalizer for changing the output sound of the audio device to the sound quality desired by the user.

Conventionally, the frequency equalization circuit used as a graphic equalizer divides a predetermined band of the entire audible frequency band into a plurality of bands, and an LC resonance circuit is provided corresponding to each divided region, and the frequency characteristics (amplitude characteristics) of each LC resonance circuit are provided. Is controlled by changing the circuit constant to adjust the overall frequency characteristic.

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

In FIG. 4, the signal from the signal source P is supplied to the non-inverting input of the operational amplifier G ₁ through the resistor R ₄₁ . Operational amplifier
The inverting input of the G _1, the output of the amplifier G ₁ is being feedback-connected via the resistor R _42. Further, an LC resonance circuit in which a variable resistor R ₄₃ is connected in series, a capacitor C ₄₁ and a coil L ₄₁ , and one end of which is grounded is connected to one of terminals T ₁ and T ₂ via the operation of switch S ₄ . Connected to. Terminal T ₁ is resistance R
₄₁ connected to the non-inverting input of amplifier G ₁ and the terminal
T ₂ is connected to the inverting input of amplifier G ₁ . Switch S ₄
When the resonance circuit is connected to the terminal T _1, the input to the amplifier G ₁ is smaller by the partial pressure of the resistor R ₄₁ and a variable resistor R _43, amplifier G ₁ has a damping characteristic. On the other hand, when the switch S is connected to the terminal T ₂ , the amplifier G ₁ has an amplification characteristic. The attenuation amount and the amplification amount are determined by the variable amount of the variable resistor R ₄₃ connected in series with the resonance circuit.

In the conventional frequency equalization circuit, the circuit shown in FIG. 4 is provided for each divided band, and the amplification amount and the attenuation amount of the circuit are adjusted by the variable resistor R _43.
By changing the resistance value of, the entire frequency band characteristic is adjusted.

(Problems to be Solved by the Invention) FIG. 5 shows frequency characteristics of a conventional frequency equalization circuit as shown in FIG.

In FIG. 5, the resonance frequency f ₀ is 1 KHz, and the vertical axis shows the level.

As can be seen from FIG. 5, the Q characteristic of the frequency characteristic of the conventional frequency equalization circuit is lowered as the output level of the amplifier G ₁ is lowered.

Therefore, when the audio frequency band is divided into many divided band areas (usually 5 to 14 divisions) like an audio device, the difference between the characteristics of adjacent divided bands is reduced because the level change due to the frequency shift is reduced. However, there is a problem that not only the frequency division becomes less and the significance of the band division becomes weaker, but also it becomes difficult to obtain a desired frequency characteristic.

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

(Means for Solving the Problems) In order to solve the above-mentioned problems, a frequency equalization circuit according to the present invention includes a series resonance circuit connected via a resistor to an input terminal connected to a signal source, and the series resonance circuit. And a resistor, a buffer amplifier for impedance conversion of a signal from the connection point, a switch for selectively inputting the output of the buffer amplifier to an inverting or non-inverting input of an operational amplifier via a variable resistor, and a signal source from the signal source. Input means for inputting a signal via another resistor to the non-inverting input of the operational amplifier is provided, and an amplitude characteristic centered on the resonance frequency of the resonance frequency of the series resonance circuit is output.

Further, a series resonance circuit connected via a resistor to an input terminal connected to a signal source, a buffer amplifier for impedance-converting a signal from a connection point of the series resonance circuit and the resistor, and an output of the buffer amplifier Input means for inputting one to an inverting input of the operational amplifier and the other to a non-inverting input via the variable resistor, and input means for inputting a signal from the signal source via the other resistor to the non-inverting input of the operational amplifier. And
An amplitude characteristic centered on the resonance frequency of the resonance frequency of the series resonance circuit is output.

(Example) Next, this invention is demonstrated in detail, referring drawings.

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

The signal source P is connected to the non-inverting input of the amplifier G ₁ via the resistor R ₁ as in the conventional circuit of FIG. Signal source P
Is also connected to the other end of the series resonance circuit of the capacitor C ₁ and the coil L ₁ whose one end is grounded and whose resistor R ₄ is connected in series. The junction of resistor R ₄ and capacitor C ₁ is connected to the non-inverting input of amplifier G ₂ . The output of the amplifier G ₁ is connected to the inverting input of the amplifier G ₁ through the resistor R _2. The output of the high input impedance buffer amplifier G ₂ is connected to the inverting input of a high input impedance buffer amplifier G _2, is connected through a variable resistor R ₃ to the switch S _1. The variable resistor R _3, the terminal T ₁ by the operation of switches S ₁
And T ₂ are switched and connected.

When switch S ₁ is connected to terminal T ₁ , the amplifier
Attenuation output of attenuation _{R 3 / (R 1 + R} 3) from the G ₁ is obtained, when the switch S is connected to the terminal T ₂ are amplification degree from the amplifier G ₁ of _{(R 2 + R 3) /} R 3 An amplified output is obtained. This attenuation and amplification degree are determined by the resistance value of the variable resistor R ₃ .

The signal from the signal source P is always resistor R ₄ , capacitor C ₁ ,
It is applied to the series circuit of coil L ₁ , and it is a high input impedance buffer amplifier from the connection point of resistor R ₄ and capacitor C _1.
It is output with low impedance at G ₂ .

Resonant frequency of series resonant circuit , The impedance of L ₁ and C ₁ to the non-inverting input of the amplifier G ₂ becomes substantially zero, so that the signal level becomes substantially zero and the output becomes substantially zero, and at a frequency greatly separated from the resonance frequency f ₀ , L _{Since the} impedance composed of ₁ and C ₁ approaches infinity, the signal from the signal source P is input to the non-inverting input of the amplifier G ₂ as it is, and the output becomes substantially equal to the signal source output.

Therefore, this circuit has an inverse resonance characteristic, and its Q is
It is expressed by Q = 2IIf ₀ L ₁ / R ₄ , and Q is constant regardless of the input level.

As described above, in the present invention, the signal is always applied as an independent resonance circuit instead of connecting the series resonance circuit directly to the signal path to increase or decrease the level as in the conventional frequency equalization circuit. Since the voltage is added to or subtracted from the original signal (signal from the signal source) while using the voltage as a voltage source via a buffer amplifier, the Q of the resonance circuit does not change even if the level of addition or subtraction is changed.

The frequency characteristic of the frequency equalization circuit shown in FIG. 1 is shown in FIG.

As is clear from FIG. 2, Q does not depend on the level and always takes a constant value. Therefore, fine level adjustment is possible.

Another embodiment of the frequency equalizing 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 ₁ of the embodiment of FIG.

In FIG. 3, the semiconductor inductor consisting of resistors R ₃₅ , R ₃₆ , capacitor C ₃₂ and amplifier G ₃ is the coil of FIG.
It is provided instead of L ₁ . In the figure, resistors R ₃₁ and R ₃₂ correspond to resistors R ₁ and R ₂ , respectively. The variable resistor R ₃₃ corresponds to the resistor R ₃ in FIG. 1, but is not switched by the switch S.

As described above, according to the present invention, the resonance circuit is directly connected to the signal source, and the signal to the series resonance circuit is impedance-converted through the buffer amplifier to obtain the signal based on the original signal. Since the amplitude characteristic around the resonance frequency of the series resonance circuit is adjusted, the Q of the resonance circuit can be maintained constant, and Q does not change even with a minute level change, and more precise frequency equalization is possible. .

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a frequency equalizing circuit according to the present invention, FIG. 2 is a diagram showing a resonance characteristic of the circuit shown in FIG. 1, and FIG. 3 is a diagram showing a frequency equalizing circuit according to the present invention. FIG. 4 is a circuit diagram showing another embodiment, FIG. 4 is a conventional frequency equalization circuit diagram,
FIG. 5 is a diagram showing the resonance characteristic of the conventional circuit shown in FIG. R _{1 to} R ₄ …… Resistor, C ₁ …… Capacitor, L ₁ …… Coil,
G ₁ , G ₂ …… Amplifier T ₃ …… Input, T ₄ …… Output

Claims (2)

[Claims] 1. A series resonance circuit connected to an input terminal connected to a signal source via a resistor, a buffer amplifier for impedance-converting a signal from a connection point of the series resonance circuit and the resistor, and the buffer amplifier. A switch for selectively inputting the output of the above-mentioned to the inverting or non-inverting input of the operational amplifier via a variable resistor, and an input means for inputting a signal from the signal source via another resistor to the non-inverting input of the operational amplifier. And
A frequency equalization circuit, which outputs an amplitude characteristic centered on a resonance frequency of a resonance frequency of the series resonance circuit. 2. A series resonance circuit connected to an input terminal connected to a signal source via a resistor, a buffer amplifier for impedance-converting a signal from a connection point of the series resonance circuit and the resistor, and the buffer amplifier. Input means for inputting the output of the above through a variable resistor, one to the inverting input of the operational amplifier and the other to the non-inverting input, and a signal from the signal source via another resistor to the non-inverting input of the operational amplifier. And a frequency equalizer circuit for outputting an amplitude characteristic centered on the resonance frequency of the series resonance circuit resonance frequency.