JPS602664Y2 - Low-frequency cutoff active filter - Google Patents

Description

[Detailed description of the invention] This invention is a 12db
The present invention relates to a low-cut active filter having an attenuation characteristic of /octave.

Conventionally, low-frequency cutoff active filters use non-inverting amplifiers.

As shown in FIG. 1, the router has a first bypass filter consisting of a capacitor 1 and a resistor 2 connected to an input terminal IN, and a second bypass filter consisting of a capacitor 3 and a resistor 4 connected to the first bypass filter. are cascade-connected, the output of the second bypass filter is connected to be input to the non-inverting input terminal of the non-inverting amplifier 5, and the output of the non-inverting amplifier 5 is fed back to the inverting input terminal of the non-inverting amplifier 5, The resistor 4 is connected so as to be fed back through the resistor 2, and one end of the resistor 4 is grounded to form a low-frequency cutoff active filter.

The above low-cut active filter has a 3 db attenuation at the cut-off frequency determined by resistor 2 and 4 capacitors 1 and 3, and 12 db at the input frequency below the cut-off frequency.
It operates as a low-cut active filter that produces an attenuated output with an attenuation factor of b/octave.

However, in the conventional circuit as described above, the cutoff frequency is constant and the filtering effect cannot be completely eliminated.

The present invention has been conceived in view of the above, and an object of the present invention is to provide a low-pass cutoff active filter whose cutoff frequency can be made continuously variable and whose filtering action can be completely eliminated.

Hereinafter, embodiments of the present invention will be described based on the drawings.

FIG. 2 shows a circuit diagram of one embodiment of the low-pass cutoff active filter of the present invention, and FIG. 3 shows a fourth explanation of the configuration of a variable resistor used in the low-pass cutoff active filter of the present invention.

The variable resistors 6 and 6' used in the low-pass cutoff active filter shown in FIG. 2 are variable resistors as shown in FIG. 3, and the variable resistors 6 and 6' will be explained first.

The variable resistors 6 and 6' are 7.14 as shown in FIG.
is a resistor, and 8 and 15 are conductors.

The resistors 7, 14 and the conductors 8, 15 are insulated from each other, and the resistors 7, 14 are connected to lead terminals 10, 17 and 11, 18.
The conductors 8 and 15 are configured to be drawn out to the outside by means of lead terminals 12 and 19, and a contactor 9 and 16 that slides on the resistor and the conductors 8 and 15 is provided. , the contacts 9 and 16 are configured to be drawn out to the outside via lead terminals 13 and 20.

When the contacts 9, 16 are in contact with the resistors 7, 14, the variable resistors 6, 6' perform the same function as a normal variable resistor, and the contacts 9, 16 are in contact with the conductors 8, 15. When in contact with the circuit connected to the resistor 7, 14 and the conductor 8, 15
Completely disconnect the circuit connected to the

Next, the low-pass active filter of this embodiment is constructed as shown in FIG.

That is, the capacitor 1 connected to the input terminal surface and the output terminal of the capacitor 1 are connected to the contact 9 of the variable resistor 6, and connected in series with the resistor 7 of the variable resistor 6 through the lead terminal 10 of the resistor 7. A first resistor circuit including the connected resistor 21 constitutes a first bypass filter.

Further, a capacitor 3 receiving the output of the first bypass filter and an output terminal of the capacitor 3 are connected to a contact 16 of a variable resistor 6' which is interlocked with a variable resistor 6, and are connected through a lead terminal 17 of a resistor 14. A second resistor circuit including the resistor 22 connected in series constitutes a second bypass filter, and is cascade-connected to the first bypass filter.

Ru.

The output of the second bypass filter is input to the non-inverting input terminal of the non-inverting amplifier 5, and the output of the non-inverting amplifier 5 is fed back to the inverting input terminal of the non-inverting amplifier 5.
1, the non-inverting amplifier 5 constitutes a voltage converter.

Further, the conductor 15 is connected to the input terminal IN.

In the low-pass active filter configured as described above, if the values of each resistor and capacitor are selected so as to exhibit Butterworth characteristics, when the contacts 9 and 16 are in contact with the resistors 7 and 14, respectively, The cutoff frequency f is determined by the resistance value R1 of the first resistance circuit, the resistance value R2 of the second resistance circuit, and the values of the capacitances C1 and C2 of the capacitors 1 and 3.

and the input frequency is the cutoff frequency f. 12 for input frequencies below the cutoff frequency f0.
The contacts 9 and 16 slide on the resistors 7 and 14 to connect the first resistor circuit and the second resistor circuit. As the resistance values R□ and R2 of the resistance circuit are changed, the cutoff frequency fo of this low-pass cutoff active filter changes continuously.

For example, resistance value 2Rt = R2, capacitance C1 = 0
When 2=C, the cutoff frequency f is known.

= 1/17πR2C, and the cutoff frequency f is determined by the resistance values R1 and R2.

changes continuously. Also, when selecting resistance value water□≠R2, resistors 7 and 1 of variable resistors 6 and 6'
The resistance values UR□ and UR2 of resistors 21 and 22 may be selected to be proportional to the resistance values of resistors 21 and 22, respectively, and the resistance values UR□ and UR2 may be changed in conjunction with each other.

Note that the resistors 21 and 22 are connected in series to the resistors 7 and 14 because the contacts 9 and 16 are in contact with the lead terminals 10 and 17, respectively, and the resistance values of the resistors 7 and 14 are substantially zero. This is to specify the cutoff frequency when the

Further, the minimum resistance value of the variable resistors 6 and 6' is configured such that, for example, the sliding range of the contacts 9 and 16 on the resistors 7 and 14 is limited, and the minimum resistance value is left on the extraction terminals 10 and 17 side. Then, the resistors 21 and 22 are housed within the variable resistors 6 and 6'.

Next, when the contacts 9 and 16 are moved and the contacts 9 and 16 come into contact with the conductors 8 and 15, the first capacitor 1 and the second capacitor 1 are connected because the conductor 15 is connected to the input terminal IN. The capacitor 3 is shorted and the input signal is directly input to the non-inverting amplifier 5 to completely eliminate the filtering effect.

As explained above, according to the present invention, the cutoff frequency can be continuously varied by moving the contact of the variable resistor, and the filtering effect can be completely removed by bringing the contact into contact with the conductor. can.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional low-cut active filter. FIG. 2 is a circuit diagram of a low-pass active filter according to an embodiment of the present invention. FIG. 3 is an explanatory diagram of the configuration of a variable resistor used in the low-cut active filter of the present invention. 1 and 3; capacitors, 2, 4, 21 and 22; resistors, 5; non-inverting amplifiers, 6 and 6'; variable resistors, 7
and 14; resistor, 8 and 15; conductor, 9 and 1
6; Contact.

Claims (1)

[Claims for Utility Model Registration] A first variable resistor comprising a first resistor and a first slider that slides over the first resistor and over one end of the first resistor. a first capacitor having one terminal connected to the input terminal and the other terminal connected to the first slider; and a first resistor having one end connected to the other end of the first resistor. a first bypass filter consisting of a second resistor and a conductor that are insulated from each other; and a first slider that slides over the first resistor in conjunction with the first slider. When the slider slides over the second resistor, and when the first slider slides over the first resistor, the second slider slides over the conductor.
a second variable resistor comprising a slider; and a second capacitor having one terminal connected to the other terminal of the first capacitor and the other terminal connected to the second slider; , a second resistor having one end connected to the end opposite to the conductor side of the second resistor and the other end grounded; and a second resistor connected to the non-inverting input terminal. Porchi with a moving child attached
1. A low-frequency cutoff active filter, comprising: a di-follower; a conductor is connected to the input terminal; and the output of the voltage follower is fed back to the other end of the first resistor.