JPH0224259Y2 - - Google Patents

Description

[Detailed explanation of the idea] (Subject of invention) The present invention relates to an equalizer circuit.

(Purpose of the invention) An object of the invention is to provide an equalizer circuit that can improve frequency characteristics with a simple circuit configuration.

(Contents of the conventional example and its drawbacks) Fig. 1 is a circuit diagram showing an example of a conventional equalizer circuit, Fig. 2 is a circuit diagram for explaining the level adjustment section of the equalizer circuit shown in Fig. 1, Third
FIGS. 4 and 5 are circuit diagrams for explaining the conventional equalizer circuit shown in FIGS. 1 and 2.

In Figure 1, 1 is a signal input terminal, 2 is a level adjustment section, 3 is an output terminal, OP ₁ and OP ₂ are operational amplifiers, VR _A to VR _K are electronic variable resistors, and N _A to N _K are resonant circuits. , Ra, Ra′ are resistors.

Signal input terminal 1 is connected to the non-inverting input terminal of operational amplifier OP ₁ , which is a gain adjustment amplifier, and the output terminal of operational amplifier OP ₁ is connected to the non-inverting input terminal of operational amplifier OP ₂ , which is a buffer amplifier, through resistor Ra'. It is connected to the inverting input terminal and is also connected to the inverting input terminal of the operational amplifier _OP1 via a resistor Ra. The connection between the resistor Ra' and the non-inverting input terminal of the operational amplifier OP ₂ is connected to the operational amplifier OP ₁ through the level adjustment section 2 that adjusts the levels of the respective signals at frequencies _A , _B , _C , ..., _K. Connected to the inverting input terminal. The level adjustment section 2 has frequencies _A , _B , _C ,...,
Resonant circuit whose other end is grounded with _K as the resonant frequency
Electronic variable resistors VR _A , VR B _, N _A , N _B , N _C ,..., N _K for level adjustment with one end connected to a sliding terminal
The fixed terminals of VR _C ,..., VR _K are connected in parallel. The output terminal of operational amplifier OP ₂ is connected to signal output terminal 3, and the output terminal of operational amplifier OP 2 is connected to signal output terminal 3.
Connected to the inverting input terminal of OP ₂ .

Figure 2 is a circuit diagram showing the configuration of the level adjustment section described above, and shows the electronic variable resistor VR _A and the resonant circuit.
Only _NA is shown. In Figure 2,
S ₁ to S _N and S ₁ ′ to S _N ′ are analog switches (hereinafter simply referred to as switches) made of semiconductors such as transistors, and R ₁ to _{R N} and R ₁ ′ to _{R N} ′ are The resistors Ca ₁ to _{Ca N} , Ca ₁ ′ to Ca _N ′, Cb ₁ to Cb _N , and Cb ₁ ′ to Cb _N ′ are connected to the switches S ₁ to S _N and S ₁ ′ to
This is the junction capacitance (hereinafter simply referred to as capacitance) that exists equivalently between S _N ' and the ground point. The electronic variable resistor VR _A consists of a switch S ₁ , a resistor R ₁ , a resistor R ₁ ′,
A series circuit consisting of switch S ₁ ′, a series circuit consisting of switch S ₂ , resistor R ₂ , resistor R ₂ ′, switch S ₂ ′, ..., switch S _N , resistor R _N , resistor R _N ′, Series circuits consisting of switches S _N ' are connected in parallel, and the resistors of each series circuit are connected to each other and grounded via a resonant circuit N _A.

A conventional equalizer circuit will be explained below with reference to FIGS. 1 and 2. In a conventional equalizer circuit, to increase the level of the signal at frequency _A , turn on one or more of switches S ₁ to S _N , and to attenuate the level of the signal at frequency _A , turn on switch S ₁ If you want to turn on one or more of switches S 1 to S _N ′ and not change the level of the signal at frequency _A , turn off all switches S ₁ to S _N and switches S ₁ to _{S N} ′. Bye.

Here, if Ra=Ra′ Ca ₁ = Ca ₁ ′, Ca ₂ = Ca ₂ ′, ..., Ca _N = Ca _N ′, then for example, in order not to change the signal level of frequency _A , switches S ₁ to S When _N and switches S ₁ ' to S _N ' are all turned off, the equalizer circuit shown in FIGS. 1 and 2 becomes as shown in FIG. 3. In FIG. 3, Ca is the combined capacitance of the capacitances Ca ₁ to _{Ca N} , and Ca' is the combined capacitance of the capacitances Ca ₁ ' to _{Ca N} '. At this time, the composite capacitance Ca reduces the amount of negative feedback of a signal with a higher frequency than the frequency _A of operational amplifier OP ₁ (hereinafter referred to as high-frequency signal), and increases the gain of the high-frequency signal of operational amplifier OP ₁ . Therefore, the level of the high frequency signal increases.
However, since the level of the high frequency signal is attenuated by the composite capacitance Ca', the frequency characteristics of the high frequency signal eventually become flat.

Next, in order to increase the level of the signal of frequency _A , for example, when only switch S ₁ is turned on,
The equalizer circuit shown in Figures 1 and 2 is
It will look like the figure. In Figure 4, the composite capacitance Ca
Since the capacitor Cb ₁ is inserted in parallel with the operational amplifier
The amount of negative feedback of the high frequency signal of OP ₁ is reduced, and the operational amplifier
Since the gain of the high frequency signal of OP ₁ increases, the level of the high frequency signal increases. As a result, the frequency characteristic of the high frequency signal becomes such that the level of the high frequency signal increases.

Next, when only switch S ₁ ' is turned on to attenuate the level of the signal of frequency _A , the equalizer circuit shown in FIGS. 1 and 2 becomes as shown in FIG. 5. In FIG. 5, since the capacitor Cb ₁ ' is inserted in parallel with the composite capacitor Ca', the level of the high frequency signal is attenuated. As a result, the frequency characteristic of the high frequency signal becomes such that the level of the high frequency signal is attenuated.

As mentioned above, conventional equalizer circuits cannot obtain ideal frequency characteristics as an equalizer circuit when increasing or decreasing the level of a signal at a certain frequency, and the stability of the equalizer circuit decreases, resulting in has the disadvantage that it may oscillate.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides an input signal terminal, a gain adjustment amplifier whose non-inverting input terminal is connected to the input terminal, and the amplifier. a first resistor interposed between the output terminal and the inverting input terminal to form a feedback circuit; a second resistor having one end connected to the output terminal;
is inserted between the other end of the resistor and the inverting input terminal, and is connected to a variable resistance element that changes the impedance on the inverting input terminal side and the second resistor side, and the variable resistance element. an equalizer circuit comprising a level adjustment circuit consisting of a resonant circuit, wherein the output terminal of the amplifier is connected to a connection between the variable resistance element and the resonant circuit through at least a capacitive element for correcting frequency characteristics; This is what I did.

(Embodiment of the invention) Figure 6 shows the first equalizer circuit according to the invention.
7 is a circuit diagram illustrating a level adjustment section of the equalizer circuit shown in FIG. 6, and FIG. 8, FIG. 9, and FIG.
FIG. 11 is a circuit diagram for explaining the equalizer circuit shown in FIG. 7 and FIG. 7, and FIG. 11 is a diagram showing the frequency characteristics of the equalizer circuit.

In FIGS. 6 and 7, the same components as in FIGS. 1 and 2 are given the same reference numerals, and their explanations will be omitted. C _A to _{C K} are capacitors for correcting frequency characteristics, and R _A to R _K are resistors for correcting frequency characteristics.
The signal input terminal 1 is connected to the non-inverting input terminal of an operational amplifier OP ₁ which is a gain adjustment amplifier, and the output terminal of the operational amplifier OP ₁ is connected to a resistor which is a second resistor.
Operational amplifier which is a buffer amplifier through Ra′
It is connected to the non-inverting input terminal of OP ₂ and also connected to the operational amplifier OP ₁ through the first resistor, the resistor Ra.
is connected to the inverting input terminal of The connection between the resistor Ra' and the non-inverting input terminal of the operational amplifier OP ₂ is connected to the operational amplifier OP ₁ through the level adjustment section 2 that adjusts the levels of the respective signals at frequencies _A , _B , _C , ..., _K. Connected to the inverting input terminal. The level adjustment unit 2 includes a resonant circuit _N A , whose other end is grounded and whose resonant frequencies are _A , _B , _C , ..., _K.
Electronic variable resistors for level adjustment connected to sliding terminals at one end of N _B , N _C , ..., N _K VR _A , VR _B , VR _C ,
..., the fixed terminals of VR _K are connected in parallel. The connection between the output terminal of operational amplifier OP ₁ and resistor Ra is connected to the connection between electronic variable resistor VR _A and resonant circuit N _A through a series circuit consisting of resistor R _A and capacitor C _A. , electronic variable resistor through a series circuit consisting of resistor R _B and capacitor C _B
It is connected to the connection between VR _B and the resonant circuit N _B , and is connected to the connection between the electronic variable resistor VR _C and the resonant circuit N _C via a series circuit consisting of a resistor R _C and a capacitor C _C , and... , is connected to the connection between the electronic variable resistor VR _K and the resonant circuit N _K via a series circuit consisting of a resistor R K _and a capacitor C _K. The output terminal of the operational amplifier OP ₂ is connected to the signal output terminal 3 and also to the inverting input terminal of the operational amplifier OP ₂ .

FIG. 7 is a circuit diagram showing the configuration of the level adjustment section 2 described above, showing only the electronic variable resistor VR _A and the resonant circuit _NA . The electronic variable resistor VR _A consists of a switch S ₁ , a resistor R ₁ , a resistor R ₁ ′,
A series circuit consisting of switch S ₁ ′, a series circuit consisting of switch S ₂ , resistor R ₂ , resistor R ₂ ′, switch S ₂ ′, ..., switch S _N , resistor R _N , resistor R _N ′, Series circuits consisting of switches S _N ' are connected in parallel, and the resistors of each of the series circuits are connected to each other and grounded via a resonant circuit N _A.

The equalizer circuit will be explained below with reference to FIGS. 6 and 7. To increase the level of the signal at frequency _A , turn one of the switches S ₁ to S _N
If you want to attenuate the level of the signal of frequency _A by turning on one or more switches, turn one or more of the switches S ₁ ′ to S _N ′ ON, and if you want to leave the level of the signal of frequency _A unchanged, Switch S ₁ ~
It is sufficient to turn off S _N and all switches S ₁ ′ to S _N ′.

Here, if Ra=Ra′ Ca ₁ = Ca ₁ ′, Ca ₂ = Ca ₂ ′, ..., Ca _N = Ca _N ′, first, in order not to change the signal level of frequency _A , for example, switch S ₁ ~ _SN and switch
When S ₁ ′ to S _N ′ are all turned off, the series circuit consisting of capacitor C _A and resistor R _A becomes disconnected from the connection between operational amplifier OP ₁ and resistor R _A , so
The equalizer circuit shown in FIG. 6 and FIG.
It will look like the figure. In Figure 8, Ca is the capacity Ca ₁
The combined capacity of ~ _CaN , Ca' is the combined capacity of _Ca1 '~ _CaN '. At this time, the amount of negative feedback of the high-frequency signal of the operational amplifier _OP1 is reduced by the composite capacitor Ca, and the gain of the high-frequency signal of the operational amplifier _OP1 is increased, so that the level of the high-frequency signal increases. However, since the level of the high frequency signal is attenuated by the composite capacitance Ca', the frequency characteristics of the high frequency signal eventually become flat.

Next, in order to increase the level of the signal of frequency _A , for example, when only switch S ₁ is turned on,
The impedance of the resonant circuit N _A for high-frequency signals becomes very large, and since R ₁ < Ra,
The equalizer circuit shown in FIG. 6 and FIG.
It will look like the figure. At this time, the capacitance Cb ₁ becomes the composite capacitance Ca
Since the negative feedback amount of the high-frequency signal of operational amplifier OP ₁ decreases and the gain of the high-frequency signal of operational amplifier OP ₁ increases, the level of the high-frequency signal becomes as shown in Fig. 11. increases like A. but,
A series circuit consisting of capacitor C _A and resistor R _A is a resistor.
Since it is inserted in parallel with Ra, the amount of negative feedback of the high-frequency signal of operational amplifier OP ₁ increases, the level of the high-frequency signal decreases, and the frequency characteristic of the high-frequency signal changes to B shown in Figure 11. It will be improved as follows.

Next, in order to attenuate the level of the signal at frequency _A , for example, when only switch S ₁ ' is turned on,
The impedance of the resonant circuit N _A for high-frequency signals becomes very large, and the equalizer circuit shown in FIGS. 6 and 7 becomes as shown in FIG. 10. At this time, since the capacitor Cb ₁ ' is inserted in parallel with the composite capacitor Ca', the level of the high-frequency signal becomes D as shown in Fig. 11.
Decrease as follows. However, the capacitance C _A and the resistor R _A
Since a series circuit consisting of is inserted in parallel with the resistor Ra', the level of the high frequency signal increases and the frequency characteristics of the high frequency signal are improved as shown in C shown in FIG.

FIG. 12 is a circuit diagram showing a second embodiment of the equalizer circuit according to the present invention, and FIGS. 13 and 14 are circuit diagrams for explaining the equalizer circuit shown in FIG. 12.

In Fig. 12, Fig. 1, Fig. 2, and Fig. 6
Components that are the same as those of the equalizer circuit shown in FIG. 7 and FIG. 2' is a level adjustment section, VR _A ' to VR _K ' are variable resistors, and N _A ' to N _K ' are resonance circuits. The signal input terminal 1 is connected to a non-inverting input terminal of an operational amplifier OP ₁ , and the output terminal of the operational amplifier OP ₁ is connected to a non-inverting input terminal of an operational amplifier OP ₂ via a resistor Ra′. It is connected to the inverting input terminal of operational amplifier OP ₁ via resistor Ra. The connection between the resistor Ra' and the non-inverting input terminal of the operational amplifier OP ₂ is a level adjustment section 2' that adjusts the level of each signal at frequencies _A , _B , _C ,..., _K.
is connected to the inverting input terminal of operation OP ₁ through. The level adjustment section 2' has frequencies _A , _B , _C ,...,
Resonant circuit whose other end is grounded with _K as the resonant frequency
Variable resistors VR _A ′, VR _B ′, VR _C ′,…, with one end of N _A ′, N B ′, N _C ′,…, N _{K ′ connected} to the sliding terminal
The fixed terminals of VR _K ′ are connected in parallel. In addition, variable resistors VR _A ′, VR _B ′,
VR _{C ′} , . The connection between the output terminal of operational amplifier OP ₁ and resistor Ra is connected to the connection between variable resistor VR _A ′ and resonant circuit N _A ′ through a series circuit consisting of resistor R _A and capacitor C _A. connected to the connection between the variable resistor VR _B ′ and the resonant circuit N _B ′ through a series circuit consisting of a resistor R _B and a capacitor C _B , and a resistor (not shown below)
connected to the connection between the variable resistor VR _C ′ and the resonant circuit N _C ′ through a series circuit consisting of R _C and capacitance _{C C} ;
..., are connected to the connection between the variable resistor VR _K ′ and the resonant circuit N _K ′ via a series circuit consisting of a resistor R _K and a capacitor C _K . The output terminal of the operational amplifier OP ₂ is connected to the signal output terminal 3 and also to the inverting input terminal of the operational amplifier OP ₂ . The resonant circuits N _A ′ to N _K ′ are, for example, equivalent LC series resonant circuits using an operational amplifier OP ₃ .
The resonant circuit N _A ' will be explained with reference to the drawings and FIG. 14.

In FIGS. 13 and 14, the same components as those of the equalizer circuits shown in FIGS. 1 and 2, FIGS. 6 and 7, and FIG. Omitted. In Figures 13 and 14, C ₁ to C ₃ are capacitors, RC ₁ to _{RC 2} are resistors,
OP ₃ is an operational amplifier.

One end of the capacitor C ₁ is connected to the sliding terminal of the variable resistor VR _A ′, and the other end of the capacitor C ₁ is connected to the non-inverting input terminal of the operational amplifier OP ₃ through the capacitor C 2 , and the other end is connected to the non-inverting input terminal of the operational amplifier OP 3 . ₁ is grounded through. The output terminal of the operational amplifier OP ₃ is connected to the capacitor via the resistor RC ₂ .
It is connected to the connection between C ₁ and capacitor C ₂ and also to the inverting input terminal of operational amplifier OP ₃ . Further, the capacitance C ₃ indicated by a broken line is an equivalent input capacitance existing between the non-inverting input terminal of the operational amplifier OP ₃ and the ground point.

In Figure 12, when increasing the level of the signal at frequency _A , the sliding terminal of variable resistor VR _A ' is placed on the left; when attenuating the level of the signal at frequency _A , the sliding terminal of variable resistor VR _{A '} is placed on the left side. If the level of the signal of frequency _A is not to be changed, the sliding terminal of variable resistor VR _A ' may be placed in the center position.

First, in Fig. 12, for example, in order not to change the level of the signal of frequency _A , a variable resistor is
When the sliding terminal of VR _A ' is placed in the center position, the sliding terminal is grounded as described above. Therefore, the input side (capacitance C _A side) of the resonant circuit N _A ' is grounded, and the frequency characteristics of the high frequency signal become flat.

Next, for example, in order to increase the level of the signal of frequency _A , if the sliding terminal of the variable resistor VR _A ' is placed in the left position, the equalizer circuit of FIG. 12 becomes as shown in FIG. 13. In Figure 13, the capacity
Since the amount of negative feedback of the high frequency signal of the operational amplifier _OP1 is reduced by _C3 , the level of the high frequency signal increases as shown at A in FIG. However, the series circuit consisting of capacitor C _A and resistor R _A is operational amplifier OP ₁
By inserting it between the output terminal of and the connection between the capacitor C ₁ and the sliding terminal of the variable resistor VR _A ′,
The amount of negative feedback of the high frequency signal of operational amplifier OP ₁ increases,
The frequency characteristics of the high frequency signal can be improved as shown in B shown in FIG.

Next, for example, in order to attenuate the level of the signal of frequency _A , if the sliding terminal of the variable resistor VR _A ' is placed in the right position, the equalizer circuit of FIG. 12 becomes as shown in FIG. 14. In Figure 14, the capacity
Due to _C3 , the level of the high frequency signal is attenuated as indicated by D in FIG. However, by inserting a series circuit consisting of a capacitor C _A and a resistor R _A between the sliding terminal of the variable resistor VR _A ′ and the output terminal of the operational amplifier OP ₁ , _the The amount of attenuation of high-frequency signals decreases, and the frequency characteristics of high-frequency signals become first.
Improvements can be made as shown in C shown in Figure 1.

In addition, in the above-mentioned explanation of the first and second embodiments of the equalizer circuit according to the present invention, in order to improve the frequency characteristics, the output terminal of the operational amplifier is connected to a capacitor for frequency characteristic correction and a capacitor for frequency characteristic correction. Although we have explained an example in which the variable resistor is connected to the connecting part of the resonant circuit through a series circuit consisting of a resistor, the frequency characteristics of the equalizer circuit can also be improved even if only a capacitor for frequency characteristics is inserted. Can be done.

(Effects of the Invention) Since the present invention has the above-described configuration, it has the advantage that the frequency characteristics of the equalizer can be improved with a simple circuit configuration.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a conventional equalizer circuit, FIG. 2 is a circuit diagram for explaining the level adjustment section of the equalizer circuit shown in FIG. 1, and FIG.
4 and 5 are circuit diagrams for explaining the conventional equalizer circuit shown in FIGS. 1 and 2, and FIG. 6 is a first embodiment of the equalizer circuit according to the present invention. FIG. 7 is a circuit diagram for explaining the level adjustment section of the equalizer circuit shown in FIG. 6, and FIGS. 11 is a diagram showing the frequency characteristics of the equalizer circuit, FIG. 12 is a circuit diagram showing a second embodiment of the equalizer circuit according to the present invention,
13 and 14 are circuit diagrams for explaining the equalizer circuit shown in FIG. 12. 1...Signal input terminal, 2...Level adjustment section, 3
...Output terminal, OP ₁ , OP ₂ , OP ₃ ...Operation amplifier,
S ₁ ~ _{S N} , S ₁ ′ ~ S _N ′ ... switch, VR _A ~ VR _K ......
Electronic variable resistor, VR _A ′ ~ VR _K ′……variable resistor,
N _A ~ N _K , N _A ′ ~ N _K ′……Resonant circuit, Ra, Ra′,
R ₁ ~ _{R N} , R ₁ ′ ~ R _N ′, RC ₁ ~ _{RC 3} ...Resistor, R _A
~R _K Resistor for frequency characteristic correction, Ca ₁ ~ Ca _N ,
Ca ₁ ′ ~ Ca _N ′, Cb ₁ ~ Cb _N , Cb ₁ ′ ~ Cb _N ′, C ₁ ~ C ₃ …
...Capacitance, C _A to C _K ...Capacitance for frequency characteristic correction.

Claims (1)

[Scope of utility model registration request] an input signal terminal, and a gain adjustment amplifier whose non-inverting input terminal is connected to the input signal terminal;
a first resistor interposed between the output terminal and the inverting input terminal of the amplifier and forming a feedback circuit; a second resistor having one end connected to the output terminal; and the second resistor. is inserted between the other end of the resistor and the inverting input terminal, and is connected to a variable resistance element that changes impedance on the inverting input terminal side and the second resistor side, and the variable resistance element. An equalizer circuit comprising a level adjustment circuit consisting of a resonant circuit, wherein the output terminal of the amplifier is connected to a connection portion between the variable resistance element and the resonant circuit through at least a capacitive element for correcting frequency characteristics.