JPH01261907A - Rc active biquartic circuit - Google Patents

Abstract

PURPOSE:To improve design efficiency of respective characteristic filters by eliminating a part of respective circuit elements which coincide with the transmission functions of the filters when the design of the filters is requested. CONSTITUTION:An RC active biquartic circuit consists of operational amplifiers 10-40, resistances R1-R6 and RA-RD, and capacitors C1-C6, and one input terminal 50 and three output terminals 60-80 are provided. With selecting one of the output terminal 60-80 as a filter output terminal, eliminating a part of the operational amplifiers, the resistances and the capacitors so that the transmission function coincides with the transmission function of the filter to be designed and deciding the values of the remaining circuit elements, the filters of various characteristic of a low-pass characteristic, a high pass characteristic, a band-pass characteristic, an all-pass characteristic and a notch characteristic, etc., can be obtained.

Description

Detailed Description of the Invention (Objective of the Invention) (Industrial Application Field) The present invention provides low-pass characteristics, bypass characteristics, band-pass characteristics, all-pass characteristics, and notch characteristics by reducing the number of circuit elements from one basic circuit. This invention relates to an RC active biquad circuit that can obtain outputs with various filter characteristics such as.

(Prior Art) As is well known, there are several types of RC active biquad circuits, such as a low-pass type, a bypass type, a band-pass type, an all-pass type, a low-pass notch type, and a bypass notch type.

Conventionally, in order to obtain this type of RC active biquad circuit, it was necessary to design each type separately, and to perform processing such as setting the transfer function or adjusting the dynamic range of the output signal according to each application. Ta.

FIG. 2 is a circuit diagram showing a low-pass notch type of this type of conventional RC active biquad circuit, which is composed of operational amplifiers 1 to 4, resistors r1 to r1o, and capacitors C1 to C2.

This circuit has one input terminal 5 and three output terminals 6, 7.
．． 8 is provided.

First, consider the transfer function of this circuit.

Here, the voltage at the input terminal 5 is v5, and the voltage at the operational amplifier 3 is
The voltage at the output terminal 8 of C8 is C1r2r3
°1°2”', (1).

At this time, resistor r, C7, C9, capacitor C1, C
If the value of 2 is selected as the initial value, then the values of each other element will be the same.

However, this value is under the condition of r - C6.

Next, consider the dynamic range of the output signals at the output terminals 6 and 7 of the operational amplifier 1 and the operational amplifier 2.

Here, the voltage at output terminals 6 and 7 is
and C7, the dynamic range of the output horn signal is:
°1°2'2r3r5.

Substituting each element value determined earlier into this formula, we get ω0 S ■6r7Q −=−1・□ (2),
From this, the dynamic range of the output signal at the output terminal 6 is determined by the ratio of the resistors r7 and C9, and the dynamic range of the output signal at the output terminal 7 is determined by the ratio of the resistors r7 and C9.
and C9, and the product of capacitor C2 and resistor r2.

The above is an example of how to consider the transfer function and the dynamic range of the output signal when designing a low-pass notch type RC active pi-quad circuit, but these conditions can also be evaluated using the same method for other types of circuits. It will be considered.

As mentioned earlier, in this type of conventional RC active biquad circuit, each type of circuit was designed individually, so a transfer function was required for each circuit for each application, and moreover, the transfer function was They tended to become more complex.

Additionally, a lot of time is required to study the values of each element for adjusting the dynamic range of the output signal of each operational amplifier constituting the RC active biquad circuit.

(Problem to be Solved by the Invention) As described above, in the conventional RC active biquad circuit, the circuits for each application are individually designed, and a transfer function is required for each circuit. This transfer function tends to become complicated, and in addition, it takes time to consider the values of each element for adjusting the dynamic range of the output signal, resulting in a reduction in design efficiency.

The present invention has been made in view of the above-mentioned circumstances, and when obtaining a filter circuit for each purpose, its transfer function is simplified, and the study of each element value related to dynamic range adjustment of the output signal is also shortened. It is an object of the present invention to provide an RC active biquad circuit that is useful for increasing design efficiency, such as being able to be implemented in a short amount of time.

[Structure of the Invention] (Means for Solving the Problem) The RC active biquad circuit of the present invention includes a large number of circuit elements including at least an operational amplifier, a resistor, and a capacitor between one input terminal and a plurality of output terminals. It consists of one basic circuit that selects one output terminal and obtains an output from the output terminal that has filter characteristics for each application in accordance with the reduction in the number of circuit elements. It is something that

(Function) The RC active biquad circuit of the present invention is composed of one basic circuit that takes all uses into consideration. By removing some of the circuit elements such as operational amplifiers, resistors, and capacitors, and determining the values of the remaining circuit elements to match the transfer function of It is possible to obtain a filter having desired characteristics such as.

(Example) Hereinafter, an example of the present invention will be described in detail based on the accompanying drawings.

FIG. 1 is a circuit diagram showing an embodiment of the RC active biquad circuit according to the present invention, and includes operational amplifiers 10 to 4.
0, resistors R1 to R6 and RA to RD1 capacitor C1
~C6.

This circuit has one input terminal 50 and three output terminals 60.
．． 70.80 is provided.

In FIG. 1, if we consider the transfer function by assuming that the voltage at the input terminal 50 is V5 and the voltage at the output terminal 80 of the operational amplifier 30 is V8, (the following is a blank space) + 1
11I II
, III! 0 of 1
〉〉〉〉.

However, this value is under the conditions that RA=RB and Ro=Ro.

In this circuit, one of the output terminals 60, 70, and 80 is selected as the filter output terminal, and some operational amplifiers are connected so that the aforementioned transfer function matches the transfer function of the filter to be designed. By removing the resistor or capacitor and determining the values of the remaining circuit elements, filters with various characteristics such as low-pass characteristics, bypass characteristics, band-pass characteristics, all-pass characteristics, and notch characteristics can be obtained.

As an example, in comparison with the 1ζ conventional circuit shown in FIG. 2, a method of designing a notch filter will be described when the output terminal 80 is selected as the filter output terminal.

The -film shape of the transfer function T(S) of this notch filter is It can be expressed as

Now, in order to obtain a transfer function matching the above transfer function T(S) in the circuit of FIG.
6. Ro1R9 and capacitors c3 and C4 can be deleted.

As a result, the transfer function of the circuit in Fig. 1 is C2R3°1
62R2R5 can be obtained.

Comparing the transfer function of the circuit of this embodiment and the transfer function of the conventional circuit [expressed by equation (1)], we find that the transfer function of the circuit of this embodiment is a polynomial with respect to S in the denominator and numerator. It can be seen that each coefficient is expressed only in the form of the product of the resistance value and the capacitance value of the capacitor, achieving simplification.

This cutting resistor R1, capacitor c1. If the value of c2 is selected as the initial value, the values of the other elements are determined individually.

Next, the dynamic range of the output signals at the output terminals 60 and 70 of the operational amplifier 10 and the operational amplifier 20 will be considered.

Here, if the voltages at the output terminals 60 and 70 are V6 and 7, respectively, there is a relationship of 7V6 V2V5 [see equation (4)].

By substituting each element value determined earlier into this formula, output terminal 6
The dynamic range of the output signal at 0 and 70 is as follows.

This indicates that the dynamic range of the output signal at the output terminal 60 and the output terminal 70 is both determined by the product of the capacitor C and the resistor R1.

Regarding this point, in the conventional circuit, the dynamic range of the output signal at the output terminal 6 is determined by the ratio of the resistors r7 and C9 [see equation (2)], and the dynamic range of the output signal at the output terminal 7 is determined by the ratio of the resistors r7 and C9. Because it is determined by the product of capacitor c2 and resistor r2 [(3)
[see formula], separate adjustments are required at each relevant location, and the constraints on each element value also increase.

On the other hand, in the circuit shown in Figure 1, the dynamic range can be adjusted simultaneously by the product of the capacitor C1 and the resistor R1, and the adjustment work is much easier than in the conventional circuit. The conditions are also extremely small and I start to resist it.

In addition, in the circuit of FIG. 1, by selecting the output terminal 80 of the operational amplifier 30 as the filter output terminal and changing the circuit elements to be deleted as appropriate, it is possible to obtain filter outputs with low-pass characteristics, bypass characteristics, and all-pass characteristics. can.

For example, in order to obtain an output with low-pass characteristics from the output terminal 80 in the circuit shown in FIG. Resistance R
, Ro, R9, and the capacitors C3, C4, and C6, and there is a method that deletes the operational amplifier 40, the resistors R, R, R, R, and the capacitors C4, 6CD, and C6.

Here, if RA=R8, the former transfer function T(S) is as follows, and the latter transfer function T(S) is C1C2R5C1C2R2R5.

Similarly, in order to obtain an output with bypass characteristics from the output terminal 80 in the circuit of FIG.
, a method of removing resistors R1, R6, Ro1Ro1 capacitors C, C4, and an operational amplifier 40. Resistance R1, R3, R
6. There is a method of removing Ro, R8, and capacitor C4.

Here, if RA=RB, then the former V5C
2s2+-8+ C2R3C1C2R2R5, and the latter transfer function T(S) becomes C1C2R5C1C2R2R5.

Furthermore, in order to obtain an output with all-pass characteristics from the output terminal 80 in the circuit shown in FIG. 1, there are two methods: omitting the capacitor CSC and omitting the resistors R3 and R4.

Here, assume that RA-RBlRo-R9 is C2R3
C1C2R2R5, and the latter transfer function T(S) is: In addition to this, in the circuit of FIG. Alternatively, from 70, filter outputs with notch characteristics, low-pass characteristics, bypass characteristics, and all-pass characteristics can be obtained separately through deletion processing of appropriate circuit elements as described above.

(Effects of the Invention) As explained above, according to the RC active biquad circuit of the present invention, one basic circuit takes into consideration all characteristics such as low-pass characteristics, bypass characteristics, band-pass characteristics, all-pass characteristics, and notch characteristics. Since the configuration consists of circuits,
When a request to design a filter for a certain application arises, a filter with the desired characteristics can be obtained by removing some of the circuit elements so as to match the transfer function of the filter. This has the excellent advantage that the design efficiency of filters having the above-mentioned characteristics can be dramatically increased by simplifying the transfer function and making it easier to adjust the dynamic range of the output signal.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of an RC active bi-hrad circuit according to the present invention, and FIG. 2 is a circuit diagram showing an example of a conventional RC active bi-quad circuit of this type. 1.2, 3.4.10.20, 30.40... operational amplifier, 5, 50... input terminal, 6.7, 8°60.7
0.80...Output terminal, r1-r1o, R1-R6,
RA-Ro...Resistance, C1-C2, C1-C6...
Capacitor, V5. V5...Input terminal ffff. V ~ V, V ~ V8... Output terminal voltage.

Claims (1)

[Claims] A large number of circuit elements including at least an operational amplifier, a resistor, and a capacitor are connected between one input terminal and a plurality of output terminals, and after selecting one output terminal, each of the circuit elements is connected from the output terminal to the output terminal. An RC active biquad circuit comprising one basic circuit capable of obtaining an output having filter characteristics for each application according to the reduction of the RC active biquad circuit.