JPH10313232A - Inductor circuit, resistance circuit and filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resistance circuit which can stably operate without being affected by external impedance by not connecting a 1st terminal to the current output of a voltage-current converting element. SOLUTION: In this resistance circuit, the voltage-current converting element 104 converts the voltage between terminals 1a and 1b into currents and supplies the currents to the terminals 1a and 1b. The voltage-current converting element 104 has a gain G1 . A terminal 1c is grounded temporarily to the middle-point potential between the terminals 1a and 1b; and the current flowing to the terminal 1a is i11 and the current flowing from the terminal 1b is i12 . Here, i11 =0 and i12 =G1 ×v1 /2 (v1 is the voltage between the terminals 1a and 1b) and the impedance viewed from the input is represented as Zi =v1 /i1 =2/G1 , so that the impedance at the terminal 1a can be increased. A current output terminal is only the terminal 1b, so the influence of the external impedance is hardly exerted on the terminal 1b and stable operation is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an inductor circuit, a resistance circuit, and a filter.

[0002]

2. Description of the Related Art FIG. 13 shows a principle diagram of a conventional equivalent resistance.

In FIG. 1, reference numeral 101 denotes a voltage-current conversion element which converts a voltage between 1a and 1b into a current and
Apply current to a and 1b. Here, assuming that the gain of the voltage-current conversion element is G ₁ , the voltage between the terminals 1 a and 1 b is v ₁ , and the current flowing into the terminal 1 a is i ₁ , the following relationship holds: i ₁ = G ₁ × v ₁ (1) .

Therefore, the impedance Z _i seen from the input is
Is

[0005]

[Outside 1] It can be seen that it looks like a resistor from the outside.

A gyrator is known as a technique for realizing an inductor in an IC chip. The gyrator is a circuit network having an impedance inverting action, and an LC filter can be realized in an IC chip by using the impedance inverting action.

FIG. 14 shows the principle of the gyrator.

[0008] The gyrator is a two-port network,
a and 10b are primary terminals, and 20a and 20b are secondary terminals. Reference numerals 102 and 103 denote voltage / current conversion elements, respectively. The reference numeral 102 converts a voltage on the secondary side and allows a current to flow to the primary side. Also, 103 converts the voltage on the primary side and allows a current to flow on the secondary side. Here, the voltage-to-current conversion gain of the element 102 is G ₁₀ , the voltage-to-current conversion gain of the element 102 is G ₂₀ , and the terminal 10
a, v ₁ the voltage between 10b, terminals 20a, the voltage between 20b v _2, current i ₁ flowing from the terminal 10a, the terminal 20
If the current flowing from a is i ₂ ,

[0009]

[Outside 2] Holds.

When a capacitor of size C is connected to the terminal on the secondary side, the impedance Z _i seen from the primary side becomes

[0011]

[Outside 3] From the primary side, it can be seen that it looks like an inductor.

[0012]

However, when an equivalent resistance circuit or an equivalent inductor as described above is to be realized by a transistor circuit, it is necessary to set the bias of the transistor, which complicates the entire circuit.

Further, two terminals 1a, 1b of equivalent resistance
And two terminals 10a, 10a on the primary side of the equivalent inductor.
Since b is a current output terminal, the operation of the circuit is 1
a, 1b and 10a, 10b. As a result, the operation of the circuit in a high-frequency range becomes unstable due to the pole caused by the base-collector capacitance of the voltage-current conversion transistor, and it has been difficult to use the filter for a high-frequency circuit.

Further, in order to reduce the influence of such external impedance, a buffer circuit for impedance conversion must be separately provided on the input side.

An object of the present invention is to solve the above-mentioned problems.

Another object of the present invention is to provide a resistance circuit that can operate stably without being affected by external impedance.
The point is to provide inductor circuits and filters.

[0017]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems and to achieve the object, the present invention comprises a plurality of voltage-to-current conversion means, and a primary side and a secondary side have a differential configuration with respect to an input. And a first terminal and a second terminal pair circuit.
And a third terminal and a fourth terminal constitute a secondary terminal, and the first terminal comprises the first terminal.
A voltage between the first terminal and the virtual ground on the primary side and a current output of the first voltage / current converting means connected to the third terminal; The voltage between the second terminal and the second terminal is input, and the current output is the fourth terminal.
A voltage between the third terminal and the fourth terminal; and a current output connected to the second terminal. A third voltage-current converter, wherein the first terminal is not connected to a current output of any of the voltage-current converters in the circuit.

According to another aspect of the present invention, there is provided a two-terminal circuit having a first terminal and a second terminal and having a differential configuration with respect to an input. And a voltage-current conversion means having a current output connected to the second terminal, wherein the first terminal is not connected to a current output of the voltage-current conversion element. It is configured.

Further, another invention of the present application is a two-terminal circuit having a first terminal and a second terminal and having a differential configuration with respect to an input, wherein the first terminal and the second terminal are connected to each other. A first voltage-current converter having a voltage between the first terminal and the second terminal connected to the second terminal and having a current output connected to the second terminal; A two-terminal pair circuit having a resistance circuit not connected to the current output of the conversion element and a plurality of voltage-current conversion means, wherein the primary side and the secondary side are both differentially configured with respect to the input; , The third terminal and the fourth terminal
And the fifth terminal and the sixth terminal constitute a secondary terminal, and the third terminal constitutes a primary terminal.
A second voltage-current converting means having a voltage between the terminal of the first side and the virtual ground of the primary side as an input, and a current output thereof connected to the fifth terminal; The voltage between the terminal and the fourth terminal is input, and the current output is the sixth terminal.
A voltage between the fifth terminal and the sixth terminal, and a current output connected to the fourth terminal. A fourth voltage-current converter, and an inductor having the third terminal not connected to the current output of any of the voltage-current converters in the circuit.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a principle diagram of an equivalent resistance to which the present invention is applied.

The terminal 1c is virtually grounded to the midpoint potential of the terminals 1a and 1b. If the current flowing into the terminal 1a is i ₁₁ and the current flowing out of the terminal 1b is i ₁₂ , the following relationship is obtained in the circuit of FIG. Holds.

I ₁₁ = 0 (5)

[0024]

[Outside 4]

Therefore, the impedance seen from the input is

[0026]

[Outside 5] And the impedance of the terminal 1a can be increased.

In the circuit of FIG. 13, two input terminals 1
Since both a and 1b were current output terminals, the operation of the circuit was affected by the external impedance of both connected terminals.

On the other hand, in the equivalent resistance of the present embodiment shown in FIG. 1, since the current output terminal is only the terminal 1b, it is hardly affected by the external impedance of the terminal 1b, and a stable operation becomes possible.

FIG. 2 is a diagram showing a configuration when the equivalent resistance is realized by a transistor circuit.

The circuit has a differential configuration and includes 1a, 1b
Is an input terminal. Q1 and Q2 are transistors for performing voltage-current conversion, and the currents are Q5-Q6, Q7-Q8, Q
The signal is turned back by the current mirror of 9-Q10 and output only to the terminal 1b by push-pull (Q8, Q10).

Here, the gain of the voltage-current conversion is Q1,
It is determined by the gm of the differential amplifier of Q2 and the mirror ratio of the current mirror of Q5-Q6 and Q7-Q8. In this embodiment, a current source Q11 is provided, and the mirror ratio is controlled from the CONT terminal by the Q11.

FIG. 3 is a diagram showing the principle of the circuit shown in FIG.

In the circuit shown in FIG. 3, the following relationship is established.

I ₁₁ = 0 (8) i ₁₂ = G ₁ × v ₁ (9)

Therefore, the impedance seen from the input is

[0036]

[Outside 6] Becomes Thus, in the circuit of FIG. 3, the gain of the voltage-current conversion element is twice as large as that of the circuit of FIG.
The gain can be controlled from the CONT terminal.

Next, an inductor to which the present invention is applied will be described.

FIG. 4 is a principle diagram of an equivalent inductor to which the present invention is applied.

The terminal 10c is virtually grounded to the midpoint potential of the terminals 10a and 10b, and the terminal 20c is connected to the terminals 20a and 2b.
0b is virtually grounded to the midpoint potential.

The voltage on the primary side is v ₁ , the current flowing into the terminal 10a is i ₁₁ , the current flowing out from the terminal 10b is i ₁₂ ,
The voltage on the secondary side is v ₂ , the current flowing into the terminal 20a is i ₂₁ ,
When the current flowing out of terminal 20b and i _22, the following relationship is established in the circuit of FIG.

[0041]

[Outside 7]

[0042]

[Outside 8]

Therefore, when a capacitor is connected to the secondary side, the impedance seen from the primary side is:

[0044]

[Outside 9] And the input impedance of the terminal 1a can be increased.

In the inductor using the gyrator shown in FIG. 14, since the two terminals 10a and 10b on the primary side are both current output terminals, the operation of the circuit is affected by both connected external impedances. .

On the other hand, in the circuit shown in FIG. 4, since the current output terminal is only 10b, it is hardly affected by the external impedance of the terminal 10a, and stable operation is possible. Further, there is no need to provide a buffer for impedance conversion on the input side, and the circuit scale can be reduced.

Next, a case where the equivalent inductor is realized by a transistor circuit will be described.

FIG. 5 is a diagram showing a circuit configuration when the equivalent inductor is realized by a transistor circuit.

The circuit has a differential configuration, and 10a, 1
0b is an input terminal on the primary side, and 20a and 20b are input terminals on the secondary side. A capacitor is connected to the input terminal on the secondary side. Q101 and Q102 are transistors for converting the voltage on the primary side into a voltage-current, and the voltage-current conversion gain is set by the resistor R1.

Q103 and Q104 are transistors for converting the voltage on the secondary side into a voltage-current converter.
Q105-Q106, Q107-Q108, Q109-
The signal is turned back by the current mirror of Q110, and is output only to the primary terminal 10b by push-pull (Q108, Q110).

Here, the gain of the voltage-current conversion on the secondary side is gm of the differential amplifier of Q103 and Q104 and Q105.
-Q106, Q107-Q108 are determined by the mirror ratio of the current mirror.

In the circuit of FIG. 2, the mirror ratio can be controlled from the terminal CONT by using the current source of Q111.

FIG. 6 is a diagram showing the principle of the circuit shown in FIG. 5. In FIG. 6, the following equation is established.

[0054]

[Outside 10]

[0055]

[Outside 11]

Therefore, when a capacitor is connected to the secondary side, the impedance seen from the primary side is

[0057]

[Outside 12] Becomes As described above, in the circuit of FIG. 6, the gain of the voltage-current conversion circuit that receives the secondary-side voltage as input is doubled as compared with the circuit of FIG. 4, and the gain is controlled from the CONT terminal. Can be.

As described above, also in the circuits of FIGS. 5 and 6, only the current output terminal 1b is provided, so that it is hardly affected by the external impedance of the terminal 1a, and a stable operation is possible. Therefore, by using the inductor of this embodiment, it becomes possible to integrate a filter having stable characteristics up to a high frequency range in an IC chip.

FIG. 7 is a diagram showing a configuration of a filter using the equivalent resistance shown in FIGS. 2 and 3 and the equivalent inductor shown in FIGS.

In the figure, 201 is the equivalent inductor shown in FIGS. 5 and 6, C 202 is a capacitor, 203 is FIG.
3 is the equivalent resistance. This circuit is a low-pass filter with a slightly high-frequency boost, and by using the equivalent resistors of FIGS. 2 and 3 and the equivalent inductors of FIGS.
Good characteristics are obtained up to the high frequency range.

Next, an embodiment in which the equivalent resistance of FIGS. 2 and 3 and the equivalent inductor of FIGS. 5 and 6 are used for a filter in a digital VTR will be described.

FIG. 8 is a diagram showing a configuration of a digital VTR to which the present invention is applied.

In FIG. 8, a magnetic head 3 for tracing a magnetic tape 301 on which data such as images and sounds is recorded.
02 from the head amplifier 30
3. The signal is amplified by 50 to 60 dB.

The reproduction signal from the head amplifier 303 has its frequency / amplitude characteristics controlled by a reproduction equalizer 304 having a configuration described later, and is output to a data detection circuit 305.

The data detection circuit 305 has the reproduction equalizer 3
The digital data is detected by comparing the level of the data equalized by 04 with a predetermined threshold value, and is output to the D-flip-flop 310 and the phase detection circuit 306.

The phase detection circuit 306 is connected to the data detection circuit 30
The phase difference between the output data from S.5 and the clock from the multiplication circuit 309 is detected and output to the loop filter 307 as a phase error signal.

The loop filter 307 performs a filtering process on the phase error signal, and returns a negative feedback to the oscillator 308 and the reproduction equalizer 304. The signal output from the oscillator 308 is multiplied to a double frequency by the multiplication circuit 309, and the D-flip-flop 310 and the demodulator 31
It is output as one operation clock.

With this configuration, a clock phase-synchronized with the reproduced data can be stably obtained.

The D-flip-flop 310 latches the output data of the data detection circuit 305 in accordance with the above-mentioned clock, and outputs it to the demodulator 311. The demodulator 311 performs digital demodulation processing on the latched data and outputs the data to the error correction decoding circuit 312.

The error correction decoding circuit 312 corrects an error in the reproduction data using the parity data added at the time of recording, and the signal processing circuit 313 performs inverse quantization opposite to that at the time of recording.
The reproduction data is restored by performing processing such as inverse DCT.

Next, the equalizer 304 in FIG. 8 will be described.

FIG. 9 is a diagram showing the configuration of the reproduction equalizer 304. In a digital VTR, a wide band pulse waveform is transmitted, so that a group delay characteristic in a pass band in an equalizer needs to be as flat as possible. If the group delay characteristic is not flat, distortion on the screen such as ringing and smear is conspicuous, and a satisfactory filter circuit is not obtained simply by satisfying the specification of the amplitude characteristic.

Therefore, in the present embodiment, as shown in FIG. 9, a group delay filter is provided after the one-stage LC network to correct the group delay characteristic of the amplitude filter. It is assumed that the amplitude and group delay characteristics of the amplitude filter in FIG. 9 are shown in FIGS. 10 (a) and 10 (b). In order to correct the group delay characteristic of this amplitude filter, a parallel LC network and two
Using the group delay filters of the stages, the group delay characteristics shown in FIG. 10C are respectively applied to share the low-frequency group delay, and ripples remain in the band as shown in FIG. However, a substantially flat group delay characteristic can be obtained.

In the equalizer shown in FIG. 9, a resistor network 1 in which an equivalent resistor ER ₁ 417 is connected in series with a resistor R ₁ 401 of an amplitude filter, and a resistor R ₄ 407 of a group delay filter 1
Figure a resistor network 2 connects the equivalent resistance ER ₂ 418 in series, the provided resistor network 3 that connects the equivalent resistor ER ₃ 419 to the resistor R ₇ 413 series of the group delay filter 2, these equivalent resistance of each resistor network The resistance value can be controlled by using the equivalent resistance shown in FIG.

[0075] In addition, the amplitude filter inductor L ₁ 40
2. The inductor L ₂ 408 of the group delay filter 1 and the inductor L ₃ 414 of the group delay filter 2 are constituted by the equivalent inductors shown in FIG. 6 so that the inductance can be controlled.

Next, the cutoff frequency f0 and Q (Quality Factor) of the amplitude filter shown in FIG.

[0077]

[Outside 13] By controlling the equivalent resistance ER1 and the equivalent inductor L1, the cutoff frequency and Q value of the amplitude filter can be controlled.

That is, for example, when the cutoff frequency of the amplitude filter is changed by controlling the inductance to achieve the target frequency characteristic, the value of Q greatly changes depending on the inductance. As a result, will produce a peak in gain at the cutoff frequency, in this embodiment, since the control equivalent resistance ER ₁ using the same control signal as the control signal of the equivalent inductor, with the change of the cutoff frequency It is possible to prevent the value of Q from greatly changing.

Further, the cutoff frequency f _{0 of the} group delay filter 1
And Q are

[0080]

[Outside 14] By controlling the equivalent resistance ER ₂ and the equivalent inductor L ₂ , the cutoff frequency and Q of the group delay filter can be controlled.

As described above, since the equivalent resistance ER ₂ is also controlled for the group delay filter using the same control signal as the control signal for the equivalent inductor, the value of Q greatly fluctuates as the cutoff frequency changes. Can be prevented.

Therefore, the cutoff frequency can be adjusted to the target frequency by the feedback loop, and the variation of Q can be suppressed to a small value. Thus, a filter circuit having excellent amplitude characteristics and group delay characteristics can be realized on an integrated circuit. Can be.

Since the circuits shown in FIGS. 2 and 5 are used as the equivalent resistance and the equivalent inductor, the influence of external impedance can be reduced, and an equalizer with stable characteristics up to a high frequency range can be realized.

FIG. 11 is a diagram showing the configuration of the oscillator 308 in the present embodiment.

In FIG. 11, a voltage-controlled current source 420 drives a secondary filter (resonant circuit) using L ₄ and C ₄ .
The resonance frequency of the secondary filter

[0086]

[Outside 15] To oscillate.

The frequency characteristic of the filter 4 that determines the oscillation frequency of the oscillator 308, when the reference current of the gyrator is a center value, is 1/1 / f of the reproduction data transmission speed (reproduction clock frequency) fb as shown in FIG. Fb / 2 which is 2
Therefore, oscillation occurs with fb / 2 as the center frequency. The frequency of the output of the oscillator 308 is doubled by the frequency multiplier 309 and supplied to the digital circuit for reproduction as the clock of the frequency fb.

In this embodiment, the inductor L4 in FIG. 11 is constituted by the equivalent inductor shown in FIG.
As in 04, the oscillation frequency can be controlled by controlling the current source Q111 of the gyrator by the output of the loop filter 307, and a clock synchronized with the reproduced data can be obtained.

If the values C ₃ and C ₄ of the capacitors used in the group delay filter 2 and the filter 4 are the same,
The cutoff frequency of the group delay filter 2 including the stray capacitance of the gyrator can always be fb / 2, and the value C ₂ of the capacitor used in the group delay filter 1 can be easily obtained based on the group delay filter 2. it can.

As described above, the equivalent resistance and the equivalent inductor of each filter are the equivalent resistance and the equivalent inductor shown in FIGS. 2 and 5, and the variation of the absolute value of the R value and the C value of each filter is used for data detection. Oscillator 30 obtained from the PLL circuit of FIG.
8 by controlling the gyrator and the equivalent resistance in each filter of the reproduction equalizer by using the same control signal as the control current of the gyrator (inductor), which is the control signal of No. 8, and adjusting the cutoff frequency to a regular frequency. A change in characteristics can be reduced, and stable characteristics up to a high frequency range can be realized.

[0091]

As described above, according to the resistor circuit of the present invention, a current is output from only one terminal,
The influence of the external impedance of the other terminal can be reduced, and stable operation can be achieved.

Further, according to the inductor of the present invention, since current is output from only one terminal on the primary side, the influence of the external impedance of the other terminal can be reduced, and stable operation can be achieved. Become.

Further, according to the filter of the present invention, a filter whose characteristics are stable up to a high frequency range can be formed in an IC chip.

[Brief description of the drawings]

FIG. 1 is a principle diagram of an equivalent resistance according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of an equivalent resistance according to an embodiment of the present invention.

FIG. 3 is a principle diagram of the circuit of FIG. 2;

FIG. 4 is a principle diagram of an equivalent inductor as an embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of an equivalent inductor as an embodiment of the present invention.

FIG. 6 is a principle diagram of the circuit of FIG. 5;

FIG. 7 is a diagram showing a configuration of a filter using the circuits of FIGS. 2 and 5;

FIG. 8 is a diagram showing a configuration of a digital VTR as an embodiment of the present invention.

FIG. 9 is a diagram showing a configuration of a reproduction equalizer in FIG. 8;

FIG. 10 is a diagram for explaining characteristics of the equalizer of FIG. 10;

FIG. 11 is a diagram showing a configuration of an oscillator in FIG. 8;

FIG. 12 is a diagram for explaining the operation of the circuit of FIG. 11;

FIG. 13 is a diagram showing a configuration of a conventional equivalent resistance.

FIG. 14 is a diagram showing a configuration of a conventional gyrator.

[Explanation of symbols]

 104 Voltage-current converter 201 Equivalent inductor 202 Equivalent resistance

Claims (16)

[Claims] A plurality of voltage-current converters, wherein both the primary side and the secondary side have a differential configuration with respect to an input.
A terminal pair circuit, wherein a first terminal and a second terminal constitute a primary terminal, and a third terminal and a fourth terminal constitute a secondary terminal; A first voltage-current converting means having a voltage between the first terminal and the virtual ground on the primary side, and a current output connected to the third terminal; A voltage between the third terminal and the fourth terminal, wherein a voltage between the third terminal and the fourth terminal is a voltage between the third terminal and the fourth terminal. And a third voltage-current converter having a current output connected to the second terminal, wherein the first terminal is connected to the current output of any voltage-current converter in the circuit. An inductor circuit, which is not connected. 2. The inductor circuit according to claim 1, further comprising control means for controlling a conversion gain of said third voltage-current conversion means. 3. The inductor circuit according to claim 2, wherein said control means includes a current source constituted by a transistor. 4. The inductor circuit according to claim 1, wherein each of said first, second and third voltage-current converters is constituted by a transistor. 5. A plurality of voltage-current converters, each of which has a differential configuration with respect to an input on both a primary side and a secondary side.
A terminal pair circuit, wherein a first terminal and a second terminal constitute a primary terminal, and a third terminal and a fourth terminal constitute a secondary terminal; A first voltage-current conversion means having a voltage between the first terminal and the virtual ground on the primary side, and a current output connected to the third terminal; A voltage between the third terminal and the fourth terminal, and a voltage between the third terminal and the fourth terminal. And a third voltage-current converter having a current output connected to the second terminal. The first terminal is connected to the current output of any voltage-current converter in the circuit. A filter with a disconnected inductor and a capacitor. 6. The filter according to claim 5, further comprising a resistance circuit. 7. A plurality of voltage-current converters, each of which has a differential configuration with respect to an input on both a primary side and a secondary side.
A terminal pair circuit, wherein a first terminal and a second terminal constitute a primary terminal, and a third terminal and a fourth terminal constitute a secondary terminal; A first voltage-current converting means having a voltage between the first terminal and the virtual ground on the primary side, and a current output connected to the third terminal; And a second voltage-current conversion unit having a current output connected to the fourth terminal, and a second voltage-current conversion unit connected between a virtual ground on the secondary side and the fourth terminal. A third voltage-current converting means having a voltage as an input and a current output connected to the second terminal, wherein the first terminal is connected to a current output of any voltage-current converting means in the circuit. An inductor circuit characterized in that the circuit is also disconnected. 8. A two-terminal circuit having a first terminal and a second terminal and having a differential configuration with respect to an input, wherein a voltage between a virtual ground and the second terminal is provided. And a voltage-current conversion means having a current output connected to the second terminal, wherein the first terminal is not connected to a current output of the voltage-current conversion element. circuit. 9. A two-terminal circuit having a first terminal and a second terminal and having a differential configuration with respect to an input, wherein the first terminal and the second terminal are connected to each other. Voltage-current conversion means having a voltage between the input and a current output connected to the second terminal, wherein the first terminal is not connected to a current output of the voltage-current conversion element. And the resistor circuit. 10. The resistance circuit according to claim 9, further comprising control means for controlling a conversion gain of said voltage-current conversion means. 11. The inductor according to claim 9, wherein said control means includes a current source constituted by a transistor. 12. A two-terminal circuit having a first terminal and a second terminal and having a differential configuration with respect to an input,
A voltage-current converter having a voltage between the first terminal and the second terminal as an input, and a current output connected to the second terminal; A filter comprising a resistor circuit that is not connected to the current output of the conversion element, and a capacitor. 13. The filter according to claim 12, further comprising an inductor. 14. A two-terminal circuit having a first terminal and a second terminal and having a differential configuration with respect to an input,
A first voltage-current converter having a voltage between the first terminal and the second terminal as an input, and a current output connected to the second terminal; A resistor circuit that is not connected to the current output of the first voltage-to-current conversion element; A terminal pair circuit, wherein a third terminal and a fourth terminal constitute a primary terminal, and a fifth terminal and a sixth terminal constitute a secondary terminal; A second voltage / current converting means having a voltage between the first virtual ground and the primary virtual ground, and a current output connected to the fifth terminal; And a current between the third terminal and the third terminal connected to the sixth terminal. A converter, and a voltage between the fifth terminal and the sixth terminal as an input;
A fourth voltage-current converter connected to a terminal of the circuit, and an inductor in which the third terminal is not connected to a current output of any voltage-current converter in the circuit. 15. The filter according to claim 14, further comprising a capacitor. 16. The apparatus according to claim 14, further comprising control means for controlling a conversion gain of said first voltage-current conversion means and a conversion gain of said fourth voltage-current conversion means.
The filter according to.