JPH07154202A - Multipurpose filter - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a multi-purpose filter having a simple structure and less temperature dependence of filter characteristics. [Configuration] differential amplifier Q _1A to Q an integrating circuit 21A, one end of the capacitor 36A is connected to the output side of _6A, the differential amplifier Q _1B to Q _6B integration circuit one end of the capacitor 36B is connected to the output side of the 21B is connected in tandem to form an integrating circuit 21A.
From the output side to the input side V _b2, respectively feedback is applied to the input side V _b1 of the integration circuit 21A from the output of the integrator circuit 21B. The input and output terminals when used as a filter differential amplifier Q _1A to Q _6A, the input of the Q _1B to Q _6B, outputs, thereby selecting from the both ends of the capacitor 36A, 36B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multipurpose filter capable of obtaining various filter characteristics.

[0002]

2. Description of the Related Art A multipurpose filter shown in FIG. 1 is provided. In FIG. 1, 1 indicates an input terminal and 2 indicates an output terminal. The input terminal 1 is connected to the inverting input terminal of the first stage operational amplifier 4 via the resistor 3. This operational amplifier 4 forms an integrating circuit, and the characteristic of itself is determined by a resistor 5 and a capacitor 6 which form a feedback resistance. The output terminal of the operational amplifier 4 is connected to the inverting input terminal of the operational amplifier 8 of the next stage via the resistor 7. This operational amplifier 8 also forms an integrating circuit, and the characteristic of itself is determined by the resistor 7 and the capacitor 9 which form the input resistance. The output of the operational amplifier 8 is amplified by the inverting amplifier 10 and then fed back to the inverting input terminal of the operational amplifier 4 of the first stage via the resistor 11. The inverting amplifier 10 is composed of an operational amplifier 12.

In this case, a bandpass output is obtained from the output terminal of the operational amplifier 4, and a lowpass output is obtained from the output terminal of the operational amplifier 12. The operational amplifier 13 forms an adder, and the bandpass output and the lowpass output can be supplied to the inverting input terminal (input terminal of the adder) of the operational amplifier 13. Also,
The input signal from the input terminal 1 can also be supplied to the inverting input terminal.

If only the output signal of the operational amplifier 4, that is, the bandpass output is supplied to the operational amplifier 13, the bandpass output can be obtained at the output terminal 2. If only the output signal of the operational amplifier 12, that is, the low-pass output is supplied to the operational amplifier 13, the low-pass output can be obtained at the output terminal 2.

Further, if both the input signal and the bandpass output are supplied to the operational amplifier 13, a trap output can be obtained at the output terminal 2 because the phases of both signals are opposite to each other. Operational amplifier 1 for both input signal and low-pass output
If it is supplied to 3, the high-pass output is similarly obtained at the output terminal 2.

[0006]

By the way, such a multipurpose filter requires four high gain operational amplifiers. That is, the operational amplifiers 4, 8, 12, and 13.
Then, it is necessary to discretely connect these operational amplifiers 4, 8, 12, and 13 with resistors and capacitors.
Therefore, the structure becomes complicated.

The characteristics of the multipurpose filter are determined by the characteristics of the integrating circuit formed by the operational amplifiers 4 and 8 and the value of the feedback resistor 11. Specifically, it is determined by the constants of the resistors 5, 7, 11 and the capacitors 6, 9. When the temperature coefficient of these constants is large, the filter has temperature characteristics that cannot be ignored. Therefore, resistors 5, 7, 11 and capacitors 6, 9 having a small temperature coefficient, that is, expensive ones are required.

The present invention has been made in consideration of such circumstances, and an object thereof is to provide a multipurpose filter having a simple structure and having less temperature dependency of filter characteristics.

[0009]

In order to solve the above-mentioned problems, according to the present invention, there is provided a first integrating circuit having a first capacitor having one end connected to the output side of the first differential amplifier. And a second one end of which is connected to the output side of the second differential amplifier.
And a second integration circuit having a capacitor of
A circuit element other than the first and second capacitors is provided between the output side of the first integration circuit and the output side of the second integration circuit and the input side of the first integration circuit. 1,
Second feedback circuits are connected to each other, and the gains of the first and second integrating circuits are controlled from the outside of the integrated circuit.
A bandpass to be designed by configuring the first differential amplifier, the first capacitor, the second differential amplifier, the second capacitor, and the first and second feedback circuits by an integrated circuit. According to the characteristics of the filter such as a trap, a low pass filter, or the like, either the input of the first and second differential amplifiers or both ends of the first and second capacitors are selected as an input terminal, and There is provided a multipurpose filter adapted to select either one of the inputs of the first and second differential amplifiers and both ends of the first and second capacitors as an output terminal.

[0010]

According to the above configuration of the present invention, various filter characteristics can be obtained by selecting the input terminal and the output terminal.

Thus, the transfer function in each filter characteristic depends on the characteristics (s ₁ , s ₂ and r _a , r _a ′, r _b , r _b ′, r _c , r _c ′) of the integrating circuits 21A and 21B. This is because the temperature characteristics of these transfer functions are IC
It means that it will be extremely improved by conversion.

Further, it is not necessary to discretely connect the operational amplifier and various CR circuit networks, and the circuit configuration can be extremely simplified.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing an embodiment of the multipurpose filter of the present invention, the structure of the present invention will be briefly described. The present invention multi-purpose filter, for example, as shown in FIG. 3, the integration circuit 21A is connected at least 2 Dantate genus having a differential amplifier Q _1A to Q capacitor 36A to one end on the output side connected in _7A, subsequent integration The circuit has a circuit in which a signal is fed back from the output side of the circuit 21B to the input side of the preceding integrating circuit 21A, and the differential connection is made in cascade connection according to the filter characteristics such as bandpass, trap and lowpass to be designed. Two inputs of the amplifier and one of both ends of the capacitors 36A and 36B in the preceding and following stages are selected as an input terminal, and two inputs of the differential amplifier connected in cascade and the capacitors 36 in the preceding and following stages are connected.
Either of the two ends of A and 36B is selected as the input terminal.

According to this structure, the two inputs of the differential amplifier and both ends of the capacitor are appropriately used as input terminals, so that various types of filters can be formed without changing the structure of the integrating circuit. Since the temperature dependence of the transfer functions of the two integrating circuits is small, various filter characteristics having excellent temperature characteristics can be realized with a simple circuit configuration of two integrating circuits.

An embodiment of the multipurpose filter of the present invention will be described below with reference to FIGS. FIG. 2 shows an integrating circuit 21 used in this embodiment. In this figure, an input terminal 22 is connected to the base of an npn type transistor Q ₁ . Then, this transistor Q ₁ is differentially connected to another npn-type transistor Q ₂ . That is, the emitters of the transistors Q ₁ and Q ₂ are commonly connected via equivalent resistors 23 and 24, and this connection point is connected to the collector of the npn-type transistor Q ₈ . The base of the transistor Q ₂ has a reference voltage source 2
Connect 5.

The transistor Q ₈ is a constant current circuit (4 in FIG. 3).
1A and 41B). That is, the power supply terminal 26 is connected to the anode of the diode 28 via the resistor 27, and the cathode thereof is grounded via the resistor 29. Then, the anode of the diode 28 is connected to the base of the transistor Q ₈ , and the emitter thereof is grounded via the resistor 30. Let the constant current of this constant current circuit be I ₁ .

The collectors of the differentially connected transistors Q ₁ and Q ₂ are npn-type transistors Q ₃ and Q _{4, respectively.}
Connect the emitter of. These transistors Q ₃ , Q ₄
Each collector of is connected to the power supply terminal 26, and each emitter of is connected to the voltage source 31. These transistors Q ₃ and Q ₄ convert current into voltage by utilizing the forward characteristic of the pn junction. Then, a voltage corresponding to the collector current of the transistors Q ₁ and Q ₂ is obtained at each emitter.

The emitters of the transistors Q ₃ and Q ₄ are connected to the bases of the npn type transistors Q ₅ and Q ₆ , respectively. Transistors Q ₅ and Q ₆ are also differentially connected. That is, the emitters of the transistors Q ₅ and Q ₆ are commonly connected, and this connection point is grounded via the collector-emitter bus of the npn-type transistor Q ₉ and the series circuit of the resistor 32.

This transistor Q ₉ is also a constant current circuit (see FIG. 3).
42A and 42B). That is, the power supply terminal 26 is connected to the anode of the diode 34 via the variable resistor 33, and the cathode of the diode 34 is connected to the resistor 3
Ground via 5. Then, the anode of the diode 34 is connected to the base of the transistor Q ₉ . The constant current of this constant current circuit is I ₂ . The above circuit is described in US Pat. No. 3,676,789.

As will be described later, the gain of the integrating circuit is controlled by the ratio of the constant current I ₂ and the constant current I ₁ described above. Although this integrating circuit is composed of an IC (integrated circuit), the variable resistor 33 is externally attached and adjusted, and thereby the constant current I _{2, in} other words, the gain of the integrating circuit can be controlled.

The above-mentioned transistors Q ₅ and Q ₆ amplify the differential output obtained at the emitters of the transistors Q ₃ and Q _{4 in} the preceding stage, and the amplified output is supplied to the capacitor 36 by the current mirror circuit. ing. That is, the collector of the transistor Q ₅ is connected to the power supply terminal 26 via the diode 37 connected in the forward direction, and the cathode of the diode 37 is connected to the base of the npn-type transistor Q ₇ . The emitter of the transistor Q ₇ is connected to the power supply terminal 26, the collector is connected to one end of the capacitor 36, and the output terminal 38 is led out from this connection point. Then, the other end of the capacitor 36 is grounded.

[0022]

In such an integrating circuit, in short, a current corresponding to the input signal Vin is supplied to the capacitor 36, and the integrating circuit of the input signal Vin is obtained as the voltage across the capacitor 36. This will be described below. The current values and voltage values used in the following description are as shown in FIG.

That is, the collector currents I _c1 and I _c2 of the transistors Q ₁ and Q ₂ are And the base-emitter voltages V _{be3 and} V _be4 of the transistors Q ₃ and Q ₄ are Is. Here, I ₀ is the reverse saturation current, k is the Boltzmann constant, T is the absolute temperature, and q is the electron charge.

The base potentials V _b5 and V _b6 of the transistors Q ₅ and Q ₆ are As a result, the base-to-base voltage V _bb of the transistors Q ₅ and Q ₆ is Is.

On the other hand, when the signal components of the collector currents of the transistors Q ₅ and Q ₆ are + i _out and -i _out , the base-emitter voltage of the transistors Q ₅ and Q ₆ is From this point, when the base-to-base voltage V _bb of the transistors Q ₅ and Q ₆ is _calculated , Becomes

From the above equations (1) and (2) From this, it can be seen that an integrated output is obtained from the output terminal 38.

[0028]

Next, an embodiment of the multipurpose filter of the present invention using the integrating circuit 21 will be described with reference to FIG. In this example, the integrating circuit 21 of FIG. 2 is cascade-connected in two stages. In FIG. 3, the portions corresponding to those of FIG. 2 are designated by the corresponding reference numerals and detailed description thereof is omitted. Specifically, the suffix A is associated with the integrating circuit 21A in the first stage, and the suffix B is associated with the integrating circuit 21B in the subsequent stage. In FIG. 3, the constant current circuit formed by the transistor Q _{8 of} FIG.
The constant current circuit composed of the transistor Q ₉ is
Represented by 2A and 42B.

In FIG. 3, reference numerals 43 to 50 denote terminals,
A desired filter characteristic is obtained by selecting an input terminal and an output terminal from these terminals 43 to 50. The filter characteristics are low-pass filter, high-pass filter, band-pass filter, and trap characteristics.

In this example, the terminals 43 and 44 are connected to the resistor 51,
Via 52, they are respectively connected to the bases of the transistors Q _1A and Q _2A of the first-stage integrating circuit 21A. Terminals 45 and 46 are respectively connected to both ends of the capacitor 36A of the integrating circuit 21A of the first stage. And this capacitor 36
The base of the npn-type transistor 53 is connected to one end of the hot wire of A, the collector of the transistor 53 is connected to the power supply terminal 26, and the emitter thereof is grounded via the constant current circuit 54. This transistor 53 constitutes an emitter follower circuit, and its emitter is fed back to the base of the transistor Q _2A through the resistor 60 and the resistor 5
It is connected via 5 to the base of the transistor Q _1B of the integrating circuit 21B at the next stage.

Transistor Q _1B of the integrating circuit 21B at the next stage
A terminal 47 is also connected to the terminal via a resistor 56. The other terminal 48 is connected to the transistor Q _2B . In addition, from the both ends of the capacitor 36B of the integrating circuit 21B at the next stage to the terminal 4
9 and 50 are respectively derived, and the base of a transistor 57 forming an emitter follower circuit is connected to one end of the hot wire. The collector of this transistor 57 is connected to the power supply terminal 2
Connect to 6. Then, the emitter is connected to the constant current circuit 58.
Is connected to the base of the transistor Q _1A of the first-stage integration circuit 21A via a resistor 59.

Next, the operation of this embodiment will be described. First, the equation (3) obtained for the integrating circuit 21 of FIG. 2 is applied to this FIG. The signal voltage V ₁ ~V ₈ and the resistance value _{r a, r 'a, r} b,
r ′ _b , r _c , and r ′ _c are as illustrated.

In the first-stage integrating circuit 21A, the base input voltage V _b1 of the transistor Q _1A is And the base of the transistor Q _2A is the input voltage V _b2
But Is. These are obtained from the theory of superposition. The input signal Vin is Vin = _Vb1 − _Vb2 . Therefore, the output voltage of the integrating circuit 21A, that is, the voltage V ₀₁ across the capacitor 36A is Is.

Similarly, regarding the integrating circuit 21B at the next stage,

Next, what kind of filter characteristics can be obtained by selecting the terminals 43 to 50 will be described. (1) When the terminal 50 is an input terminal and the terminal 45 is an output terminal. That is, this is the case where V ₇ = V _out and V ₆ = Vin. Note that V ₁ , V ₂ , V ₃ , V ₄ , and V ₅ = 0. Substituting these V _{1 to} V ₇ into equations (4) and (5), To get Similarly, by substituting V _{1 to} V ₇ into equations (6) and (7), To get Then, substituting this equation (9) into the previous equation (8) and rearranging To get From this, it can be seen that a bandpass output is obtained from the terminal 45 as an output terminal.

(2) Terminals 46 and 48 are input terminals, terminal 4
When 5 is used as the output terminal. That is, V ₇ = V _out , V
_This is the case where ₃ = V ₅ = Vin. In addition, V ₁ , V ₂ , V
₄ , V ₆ = 0. These V _{1 to} V ₇ are given by equation (4),
Substituting in (5) To get

Similarly, by substituting V _{1 to} V ₇ into equations (6) and (7), Substituting this equation (11) into equation (10) To get From this, it can be seen that in this case, the trap output is obtained from the terminal 45 as the output terminal.

(3) When the terminal 48 is the input terminal and the terminal 45 is the output terminal. That is, V ₇ = V _out , V ₅ = V
The case is in. In addition, V ₁ , V ₂ , V ₃ ,
It is assumed that V ₄ and V ₆ = 0. These V _{1 to} V ₇ are given by the formula (4)
, (5) Got from these To get

Similarly, by substituting V _{1 to} V ₇ into equations (6) and (7), Substituting this equation (13) into equation (12) To get From this, it can be seen that in this case, the low-pass output is obtained from the terminal 45 as the output terminal.

(4) When the terminal 44 is the input terminal and the terminal 45 is the output terminal. That is, V ₇ = V _out , V ₂ = V
The case is in. In addition, V ₁ , V ₂ , V ₃ ,
It is assumed that V ₄ , V ₅ , and V ₆ = 0. Substituting these V _{1 to} V ₇ into equations (4) and (5), Got from these To get

Similarly, by substituting V _{1 to} V ₇ into the equations (6) and (7), Substituting this equation (15) into equation (14) To get From this, it can be seen that in this case, a bandpass output is obtained from the terminal 45 as an output terminal.

In this case, if the base of the transistor Q _2A of the integrating circuit 21A of the first stage is selected as the output terminal, a trap output is obtained. That is, in this case, V _out =
b′V ₇ + bV ₂ , and substituting this equation for each of the above equations instead of V _out = V ₇ To get From this, it can be seen that the trap output is also obtained in this case.

[0044]

As described above, according to this embodiment, various filter characteristics can be obtained by selecting the input terminal and the output terminal. In this case, it is not necessary to connect the operational amplifier and various CR circuit networks discretely as described above, and the configuration can be extremely simplified. Further, the transfer function in each filter characteristic is the characteristic (s of the integration circuits 21A and 21B
₁ , s ₂ ) or r _a , r _a ′, r _b , r _b ′, r _c ,
It is determined by r _c ′, which means that the temperature characteristics of these transfer functions are significantly improved by making them IC. Only the variable resistor 33 needs to be taken into consideration when selecting components. It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an example of a conventional filter circuit.

FIG. 2 is a circuit diagram of an integrating circuit used in an embodiment of the present invention.

FIG. 3 is a circuit diagram of an embodiment of the multipurpose filter of the present invention.

[Explanation of symbols]

_{Q 1, Q 2 (Q 1A} , Q 1B, Q 2A, Q 2B) transistor 21 (21A, 21B) constituting a differential amplifier integrator circuit 36 (36A, 36B) capacitors 43-50 pin

Claims (1)

[Claims] 1. A first integrating circuit having a first capacitor whose one end is connected to the output side of the first differential amplifier, and a second integrating circuit.
And a second integrator circuit having a second capacitor whose one end is connected to the output side of the differential amplifier in cascade connection with the output side of the first integrator circuit and the output side of the second integrator circuit. First and second circuit elements other than the first and second capacitors are provided between the input side of the first integration circuit and the first and second capacitors.
Second feedback circuits are connected to each other, and the gains of the first and second integrating circuits are controlled from outside the integrated circuit. The first differential amplifier, the first capacitor, the second The differential amplifier, the second capacitor, and the first and second feedback circuits are formed by an integrated circuit, and the first amplifier is used in accordance with the characteristics of the filter such as bandpass, trap, and lowpass to be designed. , Selecting either the input of the second differential amplifier or both ends of the first and second capacitors as an input terminal, and inputting the first and second differential amplifiers and the first and second A multi-purpose filter that selects either of the two ends of the capacitor 2 as the output terminal.