JPH0641388Y2 - Active filter circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an active filter circuit capable of obtaining a combined characteristic of a secondary low-pass filter characteristic and a secondary notch filter characteristic.

[Conventional technology]

Conventionally, this type of active filter circuit has been constructed by connecting a secondary low-pass filter using an operational amplifier 20 and a secondary notch filter 3 using an operational amplifier 30 in series, as shown in FIG. 2, for example. .

[Problems to be solved by the device]

However, the above-mentioned active filter circuit requires the two operational amplifiers 20 and 30, and accordingly, miniaturization, cost reduction, and power reduction of the circuit are hindered.

Therefore, an object of the present invention is to provide an active filter circuit which uses one operational amplifier and can realize the above-described combined characteristic of the secondary low-pass filter characteristic and the secondary notch filter characteristic.

〔Example〕

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

This active filter circuit 4 uses an operational amplifier 50 having a first input section (that is, a positive side input section) 51, a second input section (that is, a negative side input section) 52, and an output section 53. A first resistor 71, a second resistor 72, a third capacitor 63 and a fourth capacitor are provided between the first input sections 51 of the 50.
Connect in series with 64 in this order to connect the first resistor
Connection between 71 and second resistor 72 and output of operational amplifier 50
The first capacitor 61 is connected between 53, the connection between the second resistor 72 and the third capacitor 63 and the ground, and the operational amplifier.
A second capacitor 62, a fifth resistor 75, and a seventh resistor 77 are connected between the first input unit 51 and the second input unit 52 of the 50, respectively, and the third capacitor 63 and the fourth capacitor 64
The fourth resistor 74 and the third resistor 73 are respectively connected between the connection part of the operational amplifier 50 and the ground and between the output part 53 of the operational amplifier 50, and between the second input part 52 and the output part 53 of the operational amplifier 50. A sixth resistor 76 is connected and the output 53 of the operational amplifier 50 is connected to the output 42.

The input voltage is V _i , the output voltage is V _o , the capacities of the _first to _fourth capacitors 61 to 64 are C _{1 to} C ₄ , respectively, and the conductances of the first to seventh resistors 71 to 77 ( When the reciprocal of resistance is g ₁ to g ₇ , respectively, the transfer function V _o / V _i of the active filter circuit 4 is expressed by the following equation. Here, S is the angular frequency represented by jω.

However, On the other hand, the composite characteristic of the secondary low-pass filter characteristic and the secondary notch filter characteristic as described above is expressed by the following equation (∫∫
Indicates that the fractions are connected).

Where ω ₁ is the cutoff angular frequency of the secondary lowpass filter, Q ₁ is the sharpness of the secondary lowpass filter, ω ₂ is the resonance point of the secondary notch filter, Q ₂ is the sharpness of the secondary notch filter, and S is Angular frequency represented by jω.

Therefore, the coefficient and the constant of the frequency S in the denominator numerator of the above equations (1) and (2) are equal to each other,
That is, A = ω ₁ ² , B = O, C = ω ₁ ² ω ₂ ² , D = (ω ₁ /
Q ₁ ) + (ω ₂ / Q ₂ ), E = ω ₁ ² + ω ₂ ² + (ω ₁ ω ₂ / Q ₁ Q ₂ ), and F = (ω ₁ ω ₂ ² / Q ₁ ) + (ω ₁ ² By selecting the capacitances C _{1 to} C ₄ and the conductances g _{1 to} g ₇ so as to satisfy ω ₂ / Q ₂ ), it is possible to obtain the desired combined characteristic as described above in the active filter circuit 4. , The active filter circuit 4 is so selected.

The calculation of the coefficient equivalence value can be performed by a well-known numerical calculation method.

[Effect of device]

As described above, according to the present invention, the combined characteristic of the secondary low-pass filter characteristic and the secondary notch filter characteristic can be realized by using one operational amplifier, and as a result, the circuit can be downsized and the cost can be reduced. And power saving can be achieved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an active filter circuit according to an embodiment of the present invention. FIG. 2 is a circuit diagram showing a conventional active filter circuit having a composite characteristic of a secondary low-pass filter characteristic and a secondary notch filter characteristic. 4 ... Active filter circuit according to the embodiment, 41 ... Input end, 42 ... Output end, 50 ... Operational amplifier, 51 ... First input section, 52
... Second input section, 53 ... Output section, 61-64 ... Capacitor, 71-
77 ... Resistor.

Claims (1)

[Scope of utility model registration request] 1. When the input voltage is V _i and the output voltage is V _o ,
The transfer function V _o / V _i is Where ω ₁ is the cutoff angular frequency of the secondary lowpass filter, Q ₁ is the sharpness of the secondary lowpass filter, ω ₂ is the resonance point of the secondary notch filter, Q ₂ is the sharpness of the secondary notch filter, and S is An active filter circuit that realizes a characteristic represented by the angular frequency represented by jω, comprising: a first input section (51), a second input section (52), and an output section (5
The operational amplifier (50) having 3) is used, and the first resistor (71) and the second resistor (72) are provided between the input end (41) and the first input section (51) of the operational amplifier (50). ), The third capacitor (6
3) and the fourth capacitor (64) connected in series in this order are connected, and the connection between the first resistor (71) and the second resistor (72) and the operational amplifier (50) are connected. The first capacitor (61) is connected between the output section (53) and the second resistor (7
Between the connection between 2) and the third capacitor (63) and ground,
A second capacitor (62), a fifth resistor (75) and a seventh resistor (77) are provided between the first input section (51) and the second input section (52) of the operational amplifier (50). Connected to each other, between the connection between the third capacitor (63) and the fourth capacitor (64) and ground, and the output part (53) of the operational amplifier (50).
A fourth resistor (74) and a third resistor (73) are connected in between respectively, and a sixth resistor is provided between the second input section (52) and the output section (53) of the operational amplifier (50). (76) is connected, and the output part (53) of the operational amplifier (50) is connected to the output end (42). The capacitances of the first to fourth capacitors (61 to 64) are respectively C ₁ ~ C ₄ and the 1st to 7th resistors (71 to 77)
Where the conductances of g ₁ to g ₇ are respectively, the transfer function V _o / V _i of the active filter circuit is expressed by the following equation, However, Then, A = ω ₁ ² , B = O, C = ω ₁ ² ω ₂ ² , D = (ω ₁
/ Q ₁ ) + (ω ₂ / Q ₂ ), E = ω ₁ ² + ω ₂ ² + (ω ₁ ω ₂ / Q ₁ Q ₂ ), and F = (ω ₁ ω ₂ ² / Q ₁ ) + (ω ₁ An active filter circuit characterized in that the capacitances C _{1 to} C ₄ and the conductances g _{1 to} g ₇ are selected so as to satisfy ² ω ₂ / Q ₂ ).