JPH0775298B2 - Filter circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a filter circuit, and more particularly to a filter circuit suitable for being integrated into an IC. In other words, the present invention relates to an active filter configured by using a resistor, a capacitor, and an amplification element, rather than a conventional reactance filter (passive filter) that uses an inductor.

[Conventional technology]

When a circuit including a filter is integrated into an IC, an active filter is generally used, and instead of constructing a given high-order transfer function at once as in the case of a reactance filter, a quadratic function is used. A method is used in which a function filter circuit is used as a unit circuit and these are connected in cascade to realize a required overall transfer function.

Note that, as a document describing a technique related to a filter circuit suitable for making into an IC, there are, for example, JP-A-55-45224 and JP-A-55-45266.

[Problems to be solved by the invention]

In the above-mentioned prior art, a quadratic function filter circuit can be constructed by using two integrators each composed of an amplifier and a capacitor connected as its load, and the resonance angular frequency ω ₀ of the filter circuit is the same as those of the above two. The capacitance Q of the capacitor is proportional to the product of the capacitance values thereof, and Q representing the sharpness of the resonance characteristic is proportional to the ratio of the capacitance values.

In order to obtain a filter circuit having a high Q with ω ₀ fixed, it is necessary to reduce the capacitance value of one capacitor and simultaneously increase the capacitance value of the other capacitor. However, since there is a parasitic capacitance that does not appear in the circuit diagram inside the IC, the capacitance value of the capacitor used in the filter circuit must be large enough to ignore the parasitic capacitance and cannot be made too small. Furthermore, increasing the capacitance value of the capacitor increases the IC chip area.
A problem occurs when trying to obtain a filter circuit having a high Q.

It is an object of the present invention to provide a filter circuit that can obtain a high Q without greatly changing the capacitance value of the capacitor.

[Means for solving problems]

The above object is to provide a pair of positive and negative differential input terminals and one output terminal between the input side (hereinafter referred to as the filter input side) and the output side (hereinafter referred to as the filter output side) in the filter circuit. The amplifier circuit includes first and second amplifier circuits as an amplifier circuit that converts the difference voltage applied between the differential input terminals into a current and outputs the current from the output terminal, and one end of the first and second amplifier circuits is provided at the output terminal of the first amplifier circuit. And a first capacitor that is connected to, and integrates an output current from the first capacitor to take out as a signal voltage, and is taken out by the first capacitor to one of a pair of positive and negative differential input terminals of the second amplifier circuit. A second capacitor that supplies a signal voltage and integrates an output current from the output terminal of the second amplifier circuit to take out as a signal voltage is provided, and the signal voltage taken out by the second capacitor is supplied to the first capacitor. Amplification of It is fed back to either one of a pair of positive and negative differential input terminals of the path and the other remaining input terminal of the second amplifier circuit, and this is supplied to the filter output side, and the filter input side is connected to the first amplifier circuit. In the filter circuit configured to be connected to the other remaining input terminal, the difference voltage as an input signal input to a pair of positive and negative differential input terminals of the first amplifying circuit is equal to that in the first amplifying circuit. , A third amplifying circuit that amplifies the voltage with the opposite polarity and supplies the amplified voltage to the other end of the first capacitor,
And it is achieved by using the first amplifier circuit and the third amplifier circuit in common.

[Action]

In the filter circuit described above, a difference voltage input to the first amplification circuit is added to the signal voltage extracted by the first capacitor, and the difference voltage is input to the third amplification circuit with the polarity opposite to that of the first amplification circuit.
The signals voltage-amplified by the amplifier circuit are added through the first capacitor. Accordingly, the Q of the filter circuit is Q = Q ₀ / (1-M), where M is the gain of the third amplifier circuit and Q ₀ is the case without the third amplifier circuit.
Therefore, Q of the filter circuit becomes 1 / (1-M) times due to the gain M of the third amplifier circuit. That is, since Q (= Q ₀ ) of the filter circuit without the third amplifier circuit is proportional to the capacitance ratio of the first and second capacitors as described above, the filter circuit described above changes the capacitance value of the capacitor. A high Q can be obtained without making a large change. Moreover, since the first amplifier circuit and the third amplifier circuit are combined, the number of required elements can be reduced.

[Embodiment] The operation principle of the present invention will be described below with reference to FIG.

FIG. 1 is a block diagram showing a basic configuration of a filter circuit of the present invention. In FIG. 1, 1 is an input terminal, 2 and 3 are coefficient circuits, 4 is an amplifier circuit for amplifying and outputting a differential voltage as an input signal, 5 and 6 are amplifier circuits that convert the differential voltage as an input signal into a current and output the current, 7 is an output terminal, C ₁ and
C ₂ is a capacitor.

The signal input from the input terminal 1 is supplied to the coefficient circuits 2 and 3, and the output of the coefficient circuit 2 is supplied as one input of the amplifier circuit 4 and the amplifier circuit 5. The output of the amplifier circuit 4 is connected to the output of the amplifier circuit 5 via the capacitor C ₁ and is also connected to one input of the amplifier circuit 6. Further, the output of the coefficient circuit 3 is amplified by the amplifier circuit 6 via the capacitor C _2.
And the output terminal 7 and the other input of the amplifier circuits 4, 5 and 6.

Next, the operation of this filter circuit will be described.

As shown in FIG. 1, the input voltage input from the input terminal 1 is Vin, and the coefficient circuits 2 and 3 that determine the magnitude of the input voltage Vin.
B, a, the gain of the amplifier circuit 4 is M, the conversion gain for converting the voltage difference between the signals input in the amplifier circuits 5 and 6 into a current,
That is, the mutual conductances are g _m1 and g _m2 . The signal voltage derived from the connection point between the amplifier circuit 5 and the capacitor C ₁ and supplied as one input of the amplifier circuit 6 is V ′, and the output voltage taken out from the output terminal 7 is V _out .

The input voltage V _in input from the input terminal 1 is multiplied by the coefficient b by the coefficient circuit 2 and output as the magnitude of b · V _in . The amplifier circuit 5 converts the difference voltage between the output of the coefficient circuit 2 and the output voltage V _out into a current and outputs the current, which is output by the capacitor C ₁
Is integrated and extracted as a voltage, and at the same time, a signal obtained by amplifying the difference voltage between the output voltage V _out and the output signal of the coefficient circuit 2 from the amplifier circuit 4 is added via the capacitor C ₁ .
The signal voltage V'is obtained. When the angular frequency of the input signal is ω, the signal voltage V'is expressed by the following equation.

Here, C ₁ : capacitance value of the capacitor C ₁ S: Laplace operator Next, the output voltage V _out is similarly expressed by the following equation.

When the transfer function H ₁ (S) of the filter circuit according to the present invention is obtained from the above equations (1) and (2), it is expressed by the following equation.

Where C ₂ : capacitance value of capacitor C ₂ Then, the above equation (3) becomes Therefore, by weighting the coefficients a and b, a quadratic function filter circuit such as a high-pass filter or a phase shift circuit can be obtained.

Further, Q of the filter circuit shown in the above equation (5) is a value determined by the capacitance values of the capacitors C ₁ and C ₂ and the mutual conductances g _m1 and g _m2 of the amplifier circuits 5 and 6 with respect to the gain M of the amplifier circuit 4. Therefore, there is an advantage that the resonance angular frequency ω ₀ of the filter circuit is not affected by the gain M of the amplifier circuit 4 at this time. Therefore, when designing a filter circuit, select the values of the capacitors C ₁ and C ₂ and the mutual conductances g _m1 and g _m2 that satisfy the required resonance angular frequency ω ₀ within the range of numerical values suitable for IC conversion. The Q of the filter circuit has an advantage that it can be designed to a required value by the gain M of the amplifier circuit 4.

Further, the amplifier circuit 5 and the capacitor C ₁ and the amplifier circuit 6 and the capacitor C ₂ respectively constitute an integrating circuit, which can be realized by the circuit shown in FIG.

FIG. 2 is a circuit diagram showing a specific example of an integrating circuit including a capacitor and an amplifying circuit.

In FIG. 2, the resistor R _{1 is connected to} the emitter of the transistor Q ₁ .
The resistor R ₂ is connected to the emitter of the transistor Q _{2, and the} other ends of the resistors R ₁ and R ₂ are connected to the constant current source A ₁ , respectively, and the transistors Q ₁ and Q _{2 form} a differential pair. . The base of the transistor Q ₁ is connected to the input terminal T ₁ and the input signal voltage
V _in is applied and the base of transistor Q ₂ is applied with bias voltage V _B1 .

Furthermore, the collector current of the transistor Q ₂ is a differential pair transistor with an emitter connected to the collector of Q ₂ .
Shunted by Q _3, Q _4. The base of the transistor Q ₃ are applied with a bias voltage V _B2, the base of the transistor Q ₄ is connected to the control terminal T _2, the control voltage V _C to moderate the extent of the shunt is applied to the terminal T _2.

The collector of the transistor Q ₄ is connected to the collector of the transistor Q ₅ and also connected to the load capacitor C whose other end is grounded. Furthermore, the collector is also connected to the output terminal T ₃ and produces an output voltage V _out . The base of transistor Q ₅ is the base of the transistor Q _6, is connected to the collector, and a current mirror operation, current approximately equal to the collector current of the transistor Q ₆ flows as substantially constant current to the collector of the transistor Q _5.

On the other hand, the respective emitters of the transistors Q ₇ and Q ₈ are connected and also connected to the constant current source A ₂ . Constant current source
The current value of A ₂ is a value of I _0/2 1/2 of the current I ₀ of the constant current source A _1. The bases of the transistors Q ₇ and Q ₈ are connected to the bases of the transistors Q ₃ and Q ₄ , respectively, and have a similar current shunting function. Therefore transistor Q ₄
The collector current of the collector current and Q _3, the collector current of Q _6, the collector current of Q ₅ is are substantially equal to each other.

In such a configuration, the input voltage at the terminal T ₁ is V _in , the output voltage at the terminal T ₃ is V _out , and
AC current flowing in the collector of Q ₂ is i _s , transistor Q ₃ ,
Dividing ratio of current i _s due to Q ₄ (ratio of flowing into collector of Q ₄ )
Is K, and the emitter resistances of transistors Q ₁ and Q ₂ are r _e. Is established and i _s flows into the capacitor C, so that the output voltage V _out is obtained. If the angular frequency of the signal is ω, S: It becomes Laplace operator, and if we obtain the transfer function H ₂ (S) of this circuit from the equations (7) and (8), Therefore, it is shown that the gain is an integrating circuit represented by K / C · (R ₁ + R ₂ + 2r _e ). The emitter resistance r _e is determined by the emitter current I _E. k: Boltzmann's constant T: Absolute temperature q: Represented by electron charge, r _e = 2 at room temperature with an emitter current of 100 μA
It is 60Ω. Further, if the resistors R ₁ and R ₂ are made equal to each other and R _E is made sufficiently larger than the emitter resistance r _e , the equation (9) becomes almost It is represented by.

Further, when the integrated capacitor changes in the values of the capacitor capacitance C and the resistance R _E and the integral gain changes, the shunt ratio of the signal current flowing through the collector of the transistor Q ₄ is controlled by controlling the control voltage V _C of the control terminal T _2. It is possible to control K to obtain a desired integral gain.

Here, K / 2R _E shown in the equation (11) is the mutual conductance g _m1 and g of the amplifier circuits 5 and 6 described in FIG.
It corresponds to _m2 .

Next, an example in which various filter circuits according to the present invention are configured by using the integrating circuit shown in FIG. 2 in the filter circuit shown in FIG. 1 will be described below as an embodiment of the present invention.

FIG. 3 shows the coefficients a and b in FIG. 1 as a = 1 and b = 0, respectively.
A high-pass filter constructed by the above is shown as an embodiment of the present invention.

In FIG. 3, the circuit components corresponding to the amplifier circuit 4 in FIG. 1 are designated by the reference numerals in the 400s, and the circuit components corresponding to the amplifier circuit 5 are designated by the reference numerals in the 500s. The circuit components corresponding to the amplifier circuit 6 are designated with the reference numerals in the 600s.

In addition, circuit components corresponding to the amplifier circuits 5 and 6 in FIG. 1 that are the same as those in the circuit shown in FIG. 2 have the same reference numerals up to the second digit, and will be described with reference to FIGS. 1 and 2. Those having the same or the same functions as those described above are denoted by the same reference numerals, and detailed description thereof will be omitted.

Further, the control voltage V _C and the bias voltage V _B1 for controlling the diversion ratio explained in FIG. 2 are also common to the circuits corresponding to the amplifier circuits 5 and 6 shown in FIG.

In FIG. 3, the coefficient b of the coefficient circuit 2 in FIG.
Since it is 0, the base of the transistor Q ₅₀₁ is the input signal V _in
Bias power supply, which is separated from the
Since V _B3 is connected and the coefficient a of the coefficient circuit 3 is 1, the input voltage V _in input from the input terminal 1 is directly supplied to the capacitor C ₂ .

The amplifier circuit 4 in FIG. 1 shares a part of the circuit with the amplifier circuit 5 for the convenience of the circuit configuration. The collector of the transistor Q ₅₀₁ is AC-grounded through a resistor R ₄₀₁ , and the transistor Q ₅₀₁ is grounded. _The signal derived from the connection point between the collector of ₅₀₁ and the resistor R ₄₀₁ is supplied to the capacitor C ₁ via an emitter follower composed of a transistor Q ₄₀₁ and a constant current source A ₄₀₁ .

Transistors Q _{510 to} Q ₅₁₃ , constant current source A _503, and transistors Q _{610 to} Q ₆₁₃ and constant current source A ₆₀₃ constitute a DC level shift type EMIFTA follower, and transistor Q ₉ makes current mirror operation more accurate. It is a base current compensation transistor for.

The transfer function H ₃ (S) of the circuit shown in FIG. 3 is expressed by the following equation when obtained in the same manner as described with reference to FIGS. 1 and 2.

Here, R ₅₀₁ = R ₅₀₂ = R _E1 and R ₆₀₁ = R ₆₀₂ = R _E2 .

Also M = R ₄₀₁ / 2R _E1 (13) Then, the above equation (12) is the same as the transfer function when a = 1 and b = 0 in the equation (6) shown in FIG.
It is the high-pass filter of the next function.

It is obvious that the effects of the present invention are the same as those of the embodiments shown in FIGS. 1 and 2 in the embodiment of FIG. Further, in the embodiment shown in FIG. 3, the circuit corresponding to the amplifier circuit 4 in FIG. 1 is partially shared with the circuit corresponding to the amplifier circuit 5, so that the effect of reducing the number of circuit constituent elements can be achieved. is there.

By the way, looking at the above equations (13), (14), and (15), M
Is a function of the resistance R _E1 , and ω ₀ and Q are also resistance R
It is recognized that neither Q nor ω ₀ with respect to M, which is a function of _E1 , is completely independent. Then, in the description of the embodiment shown in FIG. 1, the resonance angular frequency ω ₀ is not affected by the gain M from the equation (4), and Q is the value of ω ₀ from the equation (5). After that, there is a contradiction with what has already been stated that the gain M can be designed to a required value independently of this, but this is a circuit corresponding to the amplifier circuit 4, as already described. This is because the number of circuit constituent elements has been reduced by partially sharing a circuit corresponding to the amplifier circuit 5 with the circuit corresponding to the amplifier circuit 5.
The above-mentioned matters described in relation to the figure are valid.

In the embodiment shown in FIG. 3, (13), (14), (1
As is clear from the equation (5), the resistances R _E1 , R _E2 and the capacitance value C
After setting ω ₀ by ₁ and C ₂ , ω is set by the resistor R _401.
Q can be freely set independently of ₀ .

Next, in FIG. 4, the coefficients a and b in FIG.
A phase shift circuit configured by setting = 1 will be shown as another embodiment of the present invention. Also, in FIG. 4, the same components as those described in FIG. 3 are designated by the same reference numerals, and detailed description thereof will be omitted.

The transfer function H ₄ (S) of the circuit shown in FIG. 4 is expressed by the following equation when calculated in the same manner as described in the above embodiments.

Here, as in FIG. 3, R ₅₀₁ = R ₅₀₂ = R _E1 R ₆₀₁ = R ₆₀₂ = R _E1 . Further, M, ω ₀ , and Q are (13) (1
4) Assuming the same as Eq. (15), Eq. (16) is the same as the transfer function when a = 1 and b = 1 in Eq. (6) shown in FIG. It is a phase shift circuit. Further, it is apparent that the effects of the present invention are the same as those of the above-described embodiments in the embodiment of FIG.

Next, in FIG. 5, the coefficients a and b in FIG.
Yet another embodiment of the present invention in which = 1 is shown. In FIG. 5, the same components as those described in FIG. 3 are designated by the same reference numerals, and detailed description thereof will be omitted.

The transfer function H ₅ (S) of the circuit shown in FIG. 5 is expressed by the following equation when calculated in the same manner as described in the above embodiments.

Here, R ₅₀₁ = R ₅₀₂ = R _E1 R ₆₀₁ = R ₆₀₂ = R _E2 as in the case shown in FIG. Further, M, ω ₀ , and Q are (13) (1
4) If it is the same as the equation (15), the equation (16) is the same as the transfer function when a = 0 and b = 1 in the equation (6) shown in FIG. It is a combined filter circuit of low pass filter and band pass filter. Further, it is apparent that the effects of the present invention are the same as those of the above-described embodiments also in the embodiment of FIG.

Further, in each of the embodiments shown in FIGS. 3, 4, and 5, the second
The integrating circuit shown in the figure is used.
It is apparent that the effects of the present invention can be obtained in the same manner by using the circuits disclosed in Japanese Patent Laid-Open No. 224 and Japanese Patent Laid-Open No. 55-45266.

[Effect of the Invention] According to the present invention, the Q of the filter circuit can be increased by the gain of the added amplifier circuit. Therefore, it is possible to obtain a high Q without significantly changing the value of the capacitor or the like. is there. Moreover, of the required three amplifier circuits, one amplifier circuit also serves as two amplifier circuits, which is advantageous in that it can be integrated into an IC and can help reduce costs.

[Brief description of drawings]

FIG. 1 is a block diagram showing the basic circuit configuration of the present invention, and FIG.
FIG. 3 is a circuit diagram showing a concrete circuit of the integrating circuit, and FIGS. 3 to 5 are circuit diagrams showing an embodiment of the present invention. Explanation of symbols 1 …… Input terminal, 2,3 …… Coefficient circuit, 4,5,6 …… Amplifier circuit, C ₁ , C ₂ …… Capacitor, 7 …… Output terminal.

Claims (6)

[Claims] 1. A pair of positive and negative first and second input terminals (Q50
1, Q502 base), a first output terminal (Q502 collector) that converts a voltage difference between the input terminals into a current and outputs the current, and a signal current output from the first output terminal (Q502 collector) and a phase A first amplifier circuit (Q501, Q502, R501, R502, A501) having a second output terminal (Q501 collector) that outputs a signal current inverted by 180 degrees, and the second output terminal (Q501 One end is connected to the collector, and the first and second input terminals (Q501, Q) of the first amplifier circuit are connected.
A first resistor (R401) useful for extracting a signal voltage corresponding to the differential voltage of the 502 base), and a first shunt for shunting and outputting the signal current output from the first output terminal (Q502 collector). Means (Q503, Q504)
And a first capacitor (C1), one end of which is connected to the output terminal (Q504 collector) of the first shunting means and which outputs an integrated voltage by integrating the output current of the shunting means, forming a positive / negative pair A second amplifier circuit including third and fourth input terminals (Q601, Q602 base) and a third output terminal (Q602 collector) for converting the voltage difference between the input terminals into a current and outputting the current ( Q601, Q602, R601, R602, A601) and second shunting means (Q603, Q604) for shunting and outputting the signal current output from the third output terminal (Q602 collector).
And a second capacitor (C2), one end of which is connected to the output terminal (Q604 collector) of the second shunting means and which outputs an integrated voltage by integrating the output current of the shunting means. The integrated voltage extracted from the first capacitor (C1) is supplied to the third input terminal (Q601 base) of the second amplifier circuit via the impedance conversion circuit (Q510) and the level shift circuit (Q511 to Q513). The integrated voltage extracted from the second capacitor (C2) is output as a filter output (V _out ) via an impedance conversion circuit (Q610), and the output voltage is supplied to a level shift circuit (Q611 to Q613). The signal voltage supplied to the second and fourth input terminals (Q502, Q602 base) of the first and second amplifier circuits, respectively, via the first resistor (R401), and the impedance conversion circuit ( Q401) Is supplied to the other end of said first capacitor (C1) via, connecting the first input terminal of said first amplifier (Q 501 base) to AC ground potential, and said second capacitor (C
A filter circuit characterized in that an input signal is supplied from the other end of 2). 2. The filter circuit according to claim 1, wherein the integrated voltage extracted from the first capacitor (C1) is passed through an impedance conversion circuit (Q510) and a level shift circuit (Q511 to Q513). First, the third amplifier of the second amplifier circuit
Is supplied to the input terminal (Q601 base) of the second capacitor (C2), and the integrated voltage extracted from the second capacitor (C2) is output as a filter output (V _out ) without passing through the impedance conversion circuit (Q610). The voltage is supplied to the second and fourth input terminals (Q502, Q602 base) of the first and second amplification circuits without passing through the level shift circuits (Q611 to Q613), respectively, and the first resistance ( A filter circuit characterized in that the signal voltage extracted from R401) is supplied to the other end of the first capacitor (C1) without passing through an impedance conversion circuit (Q401). 3. A pair of positive and negative first and second input terminals (Q50
1, Q502 base), a first output terminal (Q502 collector) that converts a voltage difference between the input terminals into a current and outputs the current, and a signal current output from the first output terminal (Q502 collector) and a phase A first amplifier circuit (Q501, Q502, R501, R502, A501) having a second output terminal (Q501 collector) that outputs a signal current inverted by 180 degrees, and the second output terminal (Q501 One end is connected to the collector, and the first and second input terminals (Q501, Q) of the first amplifier circuit are connected.
502 base) a first resistor (R401) useful for extracting a signal voltage corresponding to the differential voltage, and a first shunt for shunting and outputting the signal current output from the first output terminal (Q502 collector). Means (Q503, Q504)
And a first capacitor (C1), one end of which is connected to the output terminal (Q504 collector) of the first shunting means and which outputs an integrated voltage by integrating the output current of the shunting means, forming a positive / negative pair A second amplifier circuit including third and fourth input terminals (Q601, Q602 base) and a third output terminal (Q602 collector) for converting the voltage difference between the input terminals into a current and outputting the current ( Q601, Q602, R601, R602, A601) and second shunting means (Q603, Q604) for shunting and outputting the signal current output from the third output terminal (Q602 collector).
And a second capacitor (C2), one end of which is connected to the output terminal (Q604 collector) of the second shunting means and which outputs an integrated voltage by integrating the output current of the shunting means. The integrated voltage extracted from the first capacitor (C1) is supplied to the third input terminal (Q601 base) of the second amplifier circuit via the impedance conversion circuit (Q510) and the level shift circuit (Q511 to Q513). , The integrated voltage extracted from the second capacitor (C2) is output as a filter output (V _out ) through an impedance conversion circuit (Q610), and the output voltage is output through a level shift circuit (Q611 to Q613). Are supplied to the second and fourth input terminals (Q502, Q602 base) of the first and second amplifier circuits, respectively, and the signal voltage extracted from the first resistor (R401) is supplied to the impedance conversion circuit (Q401). ) Through Supply to the other end of the first capacitor (C1), and an input signal is supplied from both the first input terminal (Q501 base) of the first amplifier and the other end of the second capacitor (C2). A filter circuit comprising: 4. The filter circuit according to claim 3, wherein the integrated voltage extracted from the first capacitor (C1) is passed through an impedance conversion circuit (Q510) and a level shift circuit (Q511 to Q513). First, the third amplifier of the second amplifier circuit
Is supplied to the input terminal (Q601 base) of the second capacitor (C2), and the integrated voltage extracted from the second capacitor (C2) is output as a filter output (V _out ) without passing through the impedance conversion circuit (Q610). The voltage is supplied to the second and fourth input terminals (Q502, Q602 base) of the first and second amplification circuits without passing through the level shift circuits (Q611 to Q613), respectively, and the first resistance ( A filter circuit characterized in that the signal voltage extracted from R401) is supplied to the other end of the first capacitor (C1) without passing through an impedance conversion circuit (Q401). 5. A pair of positive and negative first and second input terminals (Q50
1, Q502 base), a first output terminal (Q502 collector) that converts a voltage difference between the input terminals into a current and outputs the current, and a signal current output from the first output terminal (Q502 collector) and a phase A first amplifier circuit (Q501, Q502, R501, R502, A501) having a second output terminal (Q501 collector) that outputs a signal current inverted by 180 degrees, and the second output terminal (Q501 One end is connected to the collector, and the first and second input terminals (Q501, Q) of the first amplifier circuit are connected.
A first resistor (R401) useful for extracting a signal voltage corresponding to the differential voltage of the 502 base), and a first shunt for shunting and outputting the signal current output from the first output terminal (Q502 collector). Means (Q503, Q504)
And a first capacitor (C1), one end of which is connected to the output terminal (Q504 collector) of the first shunting means and which outputs an integrated voltage by integrating the output current of the shunting means, forming a positive / negative pair A second amplifier circuit including third and fourth input terminals (Q601, Q602 base) and a third output terminal (Q602 collector) for converting the voltage difference between the input terminals into a current and outputting the current ( Q601, Q602, R601, R602, A601) and second shunting means (Q603, Q604) for shunting and outputting the signal current output from the third output terminal (Q602 collector).
And a second capacitor (C2), one end of which is connected to the output terminal (Q604 collector) of the second shunting means and which outputs an integrated voltage by integrating the output current of the shunting means. The integrated voltage extracted from the first capacitor (C1) is supplied to the third input terminal (Q601 base) of the second amplifier circuit via the impedance conversion circuit (Q510) and the level shift circuit (Q511 to Q513). , The integrated voltage extracted from the second capacitor (C2) is output as a filter output (V _out ) through an impedance conversion circuit (Q610), and the output voltage is output through a level shift circuit (Q611 to Q613). Are supplied to the second and fourth input terminals (Q502, Q602 base) of the first and second amplifier circuits, respectively, and the signal voltage extracted from the first resistor (R401) is supplied to the impedance conversion circuit (Q401). ) Through Is supplied to the other end of the first capacitor (C1), the other end of the second capacitor (C2) is connected to an AC ground potential, and the first input terminal (Q501 base) of the first amplifier is connected. The filter circuit is characterized in that the input signal is supplied from the filter circuit. 6. The filter circuit according to claim 5, wherein the integrated voltage extracted from the first capacitor (C1) is passed through an impedance conversion circuit (Q510) and a level shift circuit (Q511 to Q513). First, the third amplifier of the second amplifier circuit
Is supplied to the input terminal (Q601 base) of the second capacitor (C2), and the integrated voltage extracted from the second capacitor (C2) is output as a filter output (V _out ) without passing through the impedance conversion circuit (Q610). The voltage is supplied to the second and fourth input terminals (Q502, Q602 base) of the first and second amplification circuits without passing through the level shift circuits (Q611 to Q613), respectively, and the first resistance ( A filter circuit characterized in that the signal voltage extracted from R401) is supplied to the other end of the first capacitor (C1) without passing through an impedance conversion circuit (Q401).