JPS6033619Y2 - Secondary state variable circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a secondary state variable circuit suitable for use in, for example, a frequency equalizer built into an audio amplifier and capable of freely changing frequency characteristics.

First, FIG. 1 shows the basic configuration of a positive input type secondary state variable circuit.

That is, the adder/subtractor 1 arranged at the first stage of this secondary state variable circuit has positive and negative input terminals, and the input signal e1 is supplied to the positive terminal.

A first integrator 2 is connected to the next stage of the adder/subtractor 1,
A second integrator 3 is connected to the next stage of the first integrator 2.

The output of the first integrator 2 is a coefficient ω.

The output of the second integrator 3 is fed back to the positive terminal of the adder/subtractor 1 through the coefficient unit 4 with a coefficient ω It is fed back to the terminal.

Here, when a signal el is applied to the input terminal 6, an output signal e from the output terminal 7 of the adder/subtractor 1 is obtained.

h is 2 eoh”S2+VS+6).

"°ei"'■ Output terminal 8 of first integrator 2
The output signal from e.

h is 5 eob”s2+9S+ mo2°eI ””■
Also, the output signal eα from the output terminal 9 of the second integrator 3
is eα=S2+F+ (RI02°el ””■), and bypass (high-pass), band-pass (band-pass), and low-pass (low-pass) quadratic transfer functions can be realized, respectively.

However, S=jω=j・2πf ・・
・■(f: frequency, j = j-1), and in either case, the center frequency is f.

is f, =ω, /2π...
■It is given by.

Next, FIG. 2 shows an example of a circuit in which the principle circuit shown in FIG. 1 is specifically constructed using resistors, capacitors, and operational amplifiers (so-called OP amplifiers).

That is, the adder/subtractor 1 in FIG. 1 is replaced by the operational amplifier 1 in FIG.
1, and similarly below, the first integrator 2 is the operational amplifier 1.
2, a resistor 16 and a capacitor 17, and a second integrator 3 corresponds to an operational amplifier 13, a resistor 18, and a capacitor 9.

Here, when the resistance values of the resistors 10 and 10' are respectively R1, the resistor 14 is RBs, the resistor 15 is Rc1, the resistor 16 and 18 are each R1, and the capacitance value of the capacitor 7°19 is CI, then from the output terminal 8 The obtained signal e is Rc 1 -2...S.

. , R”sum°8”0”...■S・+2・
RB・±, S 1±1 R, −+f(, oR, 1C, (R, work 0 work) 2.

The central angular frequency ω in this case. , and the Q value is 1...■ ω0mi2'rrf,="G Q=44...■RB, and the output level H0 at the center frequency is Roux-feed・e!...■B It is expressed as

As is clear from these formulas (1) to (2), by changing R1 or C, f can be set independently in Q.

By changing RB or Rc, f.

Although it is possible to change Q independently, there is a drawback that when changing RB or Re, even H8 inevitably changes.

That is, Q and milk cannot be changed independently, and it is very difficult to change Q while keeping the output level constant, for example.

This invention was made in view of these circumstances,
The Q value and the output level H8 can be changed independently, for example, while keeping the output level constant.
The purpose of this invention is to provide a secondary state variable circuit whose value can be changed.

Hereinafter, a preferred embodiment of the secondary state variable circuit according to the present invention will be described with reference to FIG.

FIG. 3 shows an embodiment of the present invention, in which the first stage operational amplifier 21
operates as an adder/subtractor.

The input terminal 6 to which the input signal e1 is supplied is connected to the positive terminal of the operational amplifier 21 via a resistor 24.

The output terminal of this operational amplifier 21 is connected to a first integrating circuit 22.

This integrating circuit 22 is composed of an operational amplifier 26, a resistor 27, and a capacitor 28.

The output terminal of this first integrating circuit 22 is connected to the second integrating circuit 2.
3, and this second integrating circuit 23 is constituted by an operational amplifier 29, a resistor 30, and a capacitor 31.

Further, the output terminal of the first integrating circuit 22 is connected to a resistor 25.
It is connected to the positive terminal of the operational amplifier 21 via the above, forming a feedback circuit.

A part of this feedback circuit, for example, resistor 25 and operational amplifier 2
A connection point with the positive terminal of No. 1 is grounded via a variable resistor 32.

Here, the resistance values of the respective resistors are R^ for the resistors 20 and 20', RB for the resistor 24, R3 for the feedback resistor 25, and Rv for the variable resistor 32, and the resistance values for each of the integrating circuits 22 and 23. The output e from the first integrating circuit 22 is RI and the capacitance value is CI.

b is eob=-2* Rc/RS RB+(Ro/Rv) RIC□ S2+2・RB/Rv, 5 (RB/Rv)+RoRICI+(R, Stone) °eL [Phase] (For example, RB/RV is , resistance values RB and Rv are connected in parallel, and is generally aRbRa/Rb5Ra+Rb.

) is given by

In this case, the central angular frequency ω. , Q value, and ω.

The output level when ω〇32frfO=1 R,C.

...0 CRB/Rv)+Rc-RBRV+RcRv+RBR8
Q'' 2(R,/RV) 2RBRV...0 = -RcRB-e1...0.

Therefore, by changing only the resistance value Rv of the variable resistor 32, only the Q value can be changed independently for fo and Ho.

Of course, by changing R+ (or cr), only f can be changed independently, as in the case of FIG. 2 described above.

In this case, each resistor 27.30 is changed in conjunction with each other.

Moreover, the above is the bandpass output signal e. Although we have only considered b, the bypass output signal e.

h, low-pass output signal e.

Similarly, while keeping Ho constant, the Q value and f
.

can be changed independently.

Moreover, when changing the Q value, it is only necessary to change the resistance value RV of one variable resistor 32, and there is no need to change the resistance values of two or more resistances in conjunction, resulting in good operability. becomes.

Furthermore, since there is no need to change the resistance value RB of the input resistor 24 connected to the signal input terminal 6, it is possible to suppress the change in input impedance to an extremely small value.

As is clear from the above description, the secondary state variable circuit according to the present invention includes at least an adder/subtractor, such as an operational amplifier 21, a first integrator circuit 22, and a second integrator circuit 23.
In a secondary state variable circuit constructed by sequentially connecting
The positive terminal of the adder/subtractor is used as a signal input terminal, and the first
It is characterized in that a variable resistor 32 is inserted and connected between a part of a feedback circuit that feeds back the output of the integrating circuit 22 to the positive terminal of the adder/subtracter and the ground.

Therefore, by changing the resistance value of the variable resistor 32, only the Q value can be changed independently, regardless of the output level H8.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing the principle configuration of a positive input type secondary state variable circuit, Figure 2 is a circuit diagram showing a specific example of the configuration of Figure 1, and Figure 3 is a secondary state according to the present invention. FIG. 2 is a circuit diagram showing an example of a variable circuit. 21... Operational amplifier serving as an adder/subtractor, 22...
...First integrating circuit, 23... Second integrating circuit, 32... Variable resistor.

Claims (1)

[Scope of utility model registration request] In a secondary state variable circuit configured by sequentially connecting at least an adder/subtractor, a first integrator, and a second integrator, the positive terminal of the adder/subtractor is used as a signal input terminal, and the first integrator A secondary state variable circuit characterized in that a variable resistor is inserted and connected between a part of a feedback circuit that feeds back the output of the adder/subtracter to the positive terminal of the adder/subtracter and ground.