KR101190811B1 - A tunable band-pass filter for multi-biopotential signal processing system - Google Patents

Abstract

PURPOSE: A tunable band pass filter for processing a multi-bio signal is provided to reduce an occupied area using one load capacitor instead of an array of a load capacitor occupying a large area. CONSTITUTION: A tunable band pass filter for processing a multi-bio signal comprises an amplifier(100) and a variable constant-voltage rectifier(200) for controlling a bandwidth. The band pass filter comprises first and second feedback loops(300a,300b), first and second input capacitors(Cin1,Cin2), and first and second load capacitors(CL1,CL2). The amplifier controls output resistance. The amplifier comprises a differential amplification part generating an output current and a bias part generating a bias current. [Reference numerals] (200) Variable constant-voltage rectifier

Description

Band-Adjustable Bandpass Filter for Multi-Bio Signal Processing {A TUNABLE BAND-PASS FILTER FOR MULTI-BIOPOTENTIAL SIGNAL PROCESSING SYSTEM}

The present invention relates to a band-adjustable band pass filter for processing multiple bio-signals, and more particularly, to adjust the frequency characteristics of a circuit according to a frequency band of each signal when implementing multiple bio-signals in one chip. A band-adjustable band pass filter for multiple biosignal processing.

In general, the analog front-end chip circuit of a biosignal measurement system capable of measuring electroencephalogram, electrocardiogram, and electromyogram in a biosignal is capable of initial amplification and band adjustment. It can be configured as a band pass filter stage and a variable gain amplifier stage.

These biosignals differ slightly in signal size and frequency band. EEG signals exist in the frequency range of about 0.1Hz to 100Hz and have a magnitude of about 1uV to 100uV. The ECG signal is present at about 0.1Hz to 500Hz and has a size of about 100uV to 5mV. The EMG signal is present in the frequency band of about 20Hz to 1KHz, and has a slightly higher frequency characteristic, but is about 20uV to 3mV, which is lower than the ECG signal. Therefore, in order to select a gain bandwidth for each signal characteristic, a bandwidth adjustment function is required at the band pass filter stage.

1 is a circuit diagram illustrating a band-adjustable band pass filter according to a conventional embodiment, which uses a load capacitor array (C _L column) to adjust bandwidth.

Looking at the frequency characteristics of each biological signal, it can be seen that the band of the low band -3dB pass frequency (f _L ) starts from about 0.1Hz to 0.3Hz. Therefore, large resistors or large capacitors are needed to produce these characteristics in a band pass filter. To accomplish this, a pseudo resistor (R _pseudo ) using PMOS is generally used. The low band -3dB pass frequency f _L formed in FIG. 1 is determined by Equation 1 below. R _pseudo is the resistance value of the virtual resistor, and C _F is the value of the capacitor used in the feedback loop.

(Equation 1)

The high band -3 dB cutoff frequency f _H can be expressed by Equation 2 below. R _O is the output resistance of the amplifier (OTA) and C _L is the load capacitor value.

(Equation 2)

In the biosignal measurement system chip design of the present invention, the size of the capacitor occupies a large part of the chip area. Therefore, small capacitors will be the main goal of low area design. When using a capacitor column (C _L column) to implement a band pass filter as a chip, the value of the capacitor to set the high-band -3 dB cutoff frequency is assumed in the graph of Figure 2, assuming the amplifier output resistance R _O of 1.24 MΩ. This can be seen through.

On the other hand, the EEG with the lowest frequency band requires very low f _H of about 100 Hz, so a load capacitor value of approximately 1.28 nF is required when R _O is about 1.24 MΩ. In this case, the load capacitor may use a metal-insulator-metal (MIM) capacitor having an insulating layer therebetween, or may include an insulating layer between an upper poly layer and a lower poly layer. It can be implemented by using a double poly (poly 1 layer and poly 2 layers). If the capacitor is embedded in the chip and used as a capacitor array (C _L column), the capacitor occupies most of the chip used in the circuit configuration, and thus there is a problem in that the economic efficiency is lost.

In order to solve this problem, currently known methods include MOSCAP using an insulating layer formed between the gate and the channel of the MOSFET transistor.

3 is a circuit diagram illustrating a band-adjustable band pass filter designed using a MOS cap according to another exemplary embodiment.

Referring to FIG. 3, a band pass filter using a MOS cap as a load capacitor (C _L ) column for an accurate comparison between a method using a MOS cap and a conventional method using a metal-insulator-metal (MIM) capacitor is used. The configured method has the characteristics as shown in FIG. In this case, it is assumed that the virtual resistance (R _pseudo ) of the amplifier is the same. Assuming the amplifier's output resistance, R _o, is about 1.24 MΩ, we need about 38 PMOS or NMOS transistors of about 100 u / 20 u to make f _H of about 100 Hz.

From these results, it can be seen that if MOS cap is used to implement the load capacitor column (C _L column), the area can be smaller than that of MIM (Metal-Insulator-Metal) capacitor. However, there is a problem that even this is still too large to be embedded in the chip.

The present invention has been made to solve the above-mentioned problems, an object of the present invention is to implement a multi-biological signal to adjust the frequency characteristics of the circuit according to the frequency band of each signal when trying to implement a plurality of bio-signals in one chip To provide a band-adjustable band pass filter for processing.

Another object of the present invention is to provide a band pass filter that adjusts the bandwidth without using a load capacitor array in which the chip area is increased, as in the conventional method, to adjust the high band -3 dB cutoff frequency of the band pass filter.

을 조절하여 회로 면적을 최소화하면서 대역폭 조절이 가능한 대역 통과 필터를 제안한다. 이러한 방법을 사용하면 칩 면적을 많이 차지하게 되는 여러 개의 커패시터 열(array)이 하나로 대치되어 칩 면적을 현저히 줄일 수 있고, 이 커패시터 열을 구동하는 증폭기 구동능력도 최소화할 수 있어 전력 소모가 적은 칩 회로 구현이 가능하다.
To do this, the -3 dB cutoff frequency is proportional to the output resistance R _O of the amplifier (OTA) (Equation 2), which adjusts the transconductance (g _m ) of the amplifier (OTA).

We propose a band pass filter with adjustable bandwidth while minimizing circuit area. This method replaces several capacitor arrays that occupy a large area of the chip with a single chip, thereby significantly reducing the chip area and minimizing the amplifier driving ability to drive the capacitor array. Circuit implementation is possible.

One aspect of the present invention to achieve the above object, an amplifier having a non-inverting and inverting input / output terminal, the transconductance value is changed according to the external bias voltage to adjust the output resistance; A variable constant voltage rectifier for selectively changing the bias voltage to supply the amplifier; A first feedback loop formed by connecting a first feedback capacitor and a first resistor in parallel between a non-inverting input terminal and an inverting output terminal of the amplifier; A second feedback loop formed by connecting a second feedback capacitor and a second resistor in parallel between an inverting input terminal and a non-inverting output terminal of the amplifier; First and second input capacitors each connected in series to non-inverting and inverting input terminals of the amplifier; And first and second load capacitors respectively connected in series between the inverting and non-inverting output terminals of the amplifier and the ground, respectively, and obtaining a gain bandwidth according to multiple bio signals inputted to the non-inverting and inverting input terminals of the amplifier. The present invention provides a band-adjustable band pass filter for multiple biosignal processing, which is controlled and output to the non-inverting and inverting output terminals of the amplifier.

Here, the first and second input capacitors preferably have the same size as the first and second feedback capacitors.

Preferably, the high band −3 dB cutoff frequency may be changed by the variable bias voltage output from the variable constant voltage rectifier.

Preferably, the high band -3 dB cutoff frequency f _H of the amplifier is calculated by Equation 6 below.

(Equation 6)

Here, gm _OTA is a transconductance value of the amplifier, and C _L is a value of the first or second load capacitor.

Preferably, the amplifier is an operational transconductance amplifier (OTA), which differentially distributes and amplifies a bias current according to a difference between two signals received through the first and second input terminals to generate an output current. Amplification unit; And a bias unit configured to generate the bias current by using the variable bias voltage output from the variable constant voltage rectifier in the differential amplifier.

Preferably, the variable constant voltage ammeter has an inverting (-) and non-inverting (+) input terminal and one output terminal, and an amplification receiving an external input voltage (V _in ) through the inverting (-) input terminal. Way; A transistor (M14) having a gate terminal connected to an output terminal of the amplifying means, a power supply voltage terminal (VDD) connected to the source terminal thereof, and a non-inverting (+) input terminal of the amplifying means connected to a drain terminal thereof; A plurality of transistors M15 to M19 having their source terminals connected in parallel to the non-inverting (+) input terminals of the amplifying means, and their gate and drain terminals being connected to each other in common; A switch unit having one end of a switch connected to each of the drain terminals of the plurality of transistors M15 to M19 and selectively switching; And an external bias and gate terminal, the source terminal of which is connected to the other end of each switch and the bias voltage (VC) terminal of the switch, and the drain terminal of which is connected to ground (M20). ) May be included.

According to the band-adjustable band pass filter for multi-body signal processing according to the present invention as described above, it is possible to use a single load capacitor instead of implementing a capacitor that occupies a large area by arranging dozens of load capacitor arrays. There is an advantage that can be realized in area.

을 변경함으로써 대역폭을 조절하게 되어 회로의 면적을 최소화할 수 있으며, 실제 스위치가 내장된 정전압 정류기가 추가되지만 부하 커패시터에 비하면 현저하게 작은 면적을 차지하므로 전체적인 면적을 크게 줄일 수 있는 이점이 있다.Further, according to the present invention, the amplifier output resistance by adjusting the transconductance of the amplifier through the change of the bias voltage (VC) due to the switch operation in the variable constant voltage rectifier

By changing the bandwidth, the circuit area can be adjusted to minimize the area of the circuit. In addition, the constant voltage rectifier with the built-in switch is added, but since it occupies a significantly smaller area than the load capacitor, the overall area can be greatly reduced.

In addition, according to the present invention, since it is not necessary to drive the capacitor array (array), it is possible to design a small drive current of the amplifier, there is an advantage that can be implemented a low-power consumption band pass filter.

1 is a circuit diagram illustrating a band-adjustable band pass filter according to a conventional embodiment.
FIG. 2 is a graph showing an example of an AC test result for the circuit diagram of FIG. 1.
3 is a circuit diagram illustrating a band-adjustable band pass filter designed using a MOS cap according to another exemplary embodiment.
4 is a graph showing an example of an AC test result for the circuit diagram of FIG. 3.
5 is a circuit diagram illustrating a band-adjustable band pass filter for processing multiple biosignals according to an embodiment of the present invention.
FIG. 6 is a circuit diagram for describing in detail the amplifier of FIG. 5.
FIG. 7 is a circuit diagram for describing in detail the variable constant voltage rectifier of FIG. 5.
FIG. 8 is a graph illustrating an output bias voltage VC according to a switching operation of the circuit diagram of FIG. 7.
FIG. 9 is a graph illustrating a change in the high band −3 dB cutoff frequency of the band pass filter according to the output bias voltage VC of the variable constant voltage rectifier of FIG. 7.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the following embodiments of the present invention may be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

)와 관계 있음을 응용하여 이득 대역폭을 조절하는 것을 특징으로 한다.
First, a band-adjustable band pass filter for processing multiple bio signals according to an embodiment of the present invention includes a band pass filter circuit and a bias voltage VC having only one load capacitor without a conventional load capacitor array. It consists of an amplifier that can change the value of the transconductance (g _m ), and a constant voltage regulator that can change the bias voltage (VC). This architecture eliminates the need for additional load capacitors and the high-band -3dB cutoff frequency of the amplifier.

) To adjust the gain bandwidth.

FIG. 5 is a circuit diagram illustrating a band-adjustable band pass filter for processing multiple biosignals according to an embodiment of the present invention. FIG. 6 is a circuit diagram for explaining the amplifier of FIG. 5 in detail. It is a circuit diagram for demonstrating concretely a constant voltage rectifier.

5 to 7, a band-adjustable band pass filter for processing multiple biosignals according to an embodiment of the present invention includes an amplifier 100, a variable constant voltage rectifier 200 for bandwidth adjustment, And first and second feedback loops 300a and 300b, first and second input capacitors C _in1 and C _in2 , first and second load capacitors C _L1 and C _L2 , and the like.

Here, the amplifier 100 has non-inverting (+) and inverting (-) input / output terminals, and the value of the transconductance (g _m ) is changed according to the external bias voltage (VC) so that the output resistance R _O ) To adjust the function.

As shown in FIG. 6, the amplifier 100 is referred to as a folded cascade amplifier and generally has an operational transconductance amplifier (OTA) having a large gain and a large output resistance value. When the bias voltage VC changes, the current I _D flowing in the drain of the transistor M1 is changed by Equation 3 above, and the current total transconductance (g _m ) of the amplifier, that is, the output resistance R _O. ) Value changes.

That is, the amplifier 100 divides and amplifies a bias current according to a difference between two signals received through the first and second input terminals V _{in +} and V _in− , and generates a differential current 110. And a bias unit 120 generating the bias current using the variable bias voltage VC output from the variable constant voltage rectifier 200 to the differential amplifier 110.

That is, the differential amplifier 110 _applies the bias current supplied through the bias unit 120 according to the difference between the two signals input through the first and second input terminals V _{in +} and V _in− , respectively, to the transistor M2. Amplify by dividing by the drain current of the transistor and the drain current of the transistor M3.

The differential amplifier 110 may include transistors M2 and M3 that receive differential voltages of the first and second input terminals V _{in +} and V _in− , and a plurality of transistors M4 to M13 for amplifying the output current. Include.

The bias unit 120 includes a transistor M1 serving as a current source by the DC bias voltage VC, supplies a predetermined current to the differential amplifier 110 using the bias voltage VC, and M1) plays this role.

Meanwhile, reference numeral VDD denotes a power supply voltage terminal, VSS denotes a ground terminal, and V _{out +} and V _out− denote first and second output voltage terminals, respectively.

In addition, the variable constant voltage rectifier 200 selectively changes the bias voltage VC to supply the amplifier 100.

As shown in FIG. 7, the variable constant voltage rectifier 200 has an inverting (-) and non-inverting (+) input terminal and one output terminal, and an external input voltage ( V _in ) and the gate terminal is connected to the output terminal of the amplifier 210, the power supply voltage terminal (VDD) is connected to its source terminal and the ratio of the amplifier 210 to the drain terminal thereof. A plurality of source terminals are connected in parallel to a transistor M14 to which an inverting (+) input terminal is connected, and a non-inverting (+) input terminal of an amplifier 210, respectively, and the gate and drain terminals thereof are commonly connected to each other. One end of the switch is connected to each of the transistors M15 to M19 and the drain terminals of the plurality of transistors M15 to M19, and a switch unit 220 for selectively switching and an external bias and gate The terminal is connected and the source terminal It is connected to the other end of each switch and the bias voltage (VC) terminal provided in the switch unit 220, the drain terminal is configured to include a transistor (M20) and the like connected to the ground.

The first feedback loop 300a includes a first feedback capacitor C _F1 and the first feedback between the non-inverting (+) input terminal (V _in ) and the inverting (-) output terminal (V _out ) of the amplifier 100. The first resistor R ₁ is formed as a virtual resistor R _pseudo connected in parallel with the capacitor C _F1 .

The second feedback loop 300b includes the second feedback capacitor C _F2 and the second feedback between the inverting (-) input terminal (V _in ) and the non-inverting (+) output terminal (V _out ) of the amplifier 100. The second resistor R ₂ is formed as a virtual resistor R _pseudo connected in parallel with the capacitor C _F2 .

The first and second input capacitors C _in1 and C _in2 are connected in series to the non-inverting (+) and inverting (−) input terminals V _in of the amplifier 100, respectively.

The first and second load capacitors C _L1 and C _L2 are connected in series between the inverting (-) and non-inverting (+) output terminals V _out and the ground (GND) of the amplifier 100, respectively. .

Meanwhile, the first and second input capacitors C _in1 and C _in2 may have the same size as the first and second feedback capacitors C _F1 and C _F2 .

In the present invention configured as described above, in order to design a band pass filter capable of adjusting bandwidth with low area and low power, a method of adjusting the bandwidth by adjusting the output resistance (R _O ) of the amplifier without using a capacitor column unlike the conventional method. Suggested.

First, in the present invention, all circuits are designed to operate in a subthreshold region for a low power design, and the bias current in the subthreshold region has a very small value to reduce the current consumption of the circuit. Can be. At this time, the transconductance (gm) value of the amplifier circuit is designed to have a value proportional to the current value.

Equations 3 and 4 below are MOSFET current and transconductance (gm) formulas in the subthreshold region.

(Equation 3)

(Equation 4)

Meanwhile, the band pass filter circuit used in the present invention uses a first and second input capacitors C _in1 and C _in2 and the first and second feedback capacitors C _F1 and C _F2 of the same size to obtain a gain of 0 dB. You can, but you can change it as needed. The high band -3 dB cutoff frequency is shown in Equation 5 below. Equation 5 is equivalent to the high-band -3dB cutoff frequency of the resistor capacitor filter (Gm-C) structure.

Since the gain of the amplifier 100 is a single gain, the current flowing to the output by the input signal can be represented by a transconductance (gm _OTA ) value, which means that the inverse of the transconductance (gm _OTA ) means a resistance value. . That is, as shown in Equation 2 and Equation 5 it can be seen that the transconductance (gm _OTA ) of the amplifier 100 acts as the inverse of the resistance in the resistor-capacitor filter. Therefore, the conventional band pass filter maintains the transconductance (gm _OTA ) of the amplifier 100 at a fixed value and adjusts the bandwidth of the load capacitor array based on Equation 2 above.

In the present invention, the bandwidth is adjusted by changing the transconductance (gm _OTA ) of the amplifier 100 without using a load capacitor array for low area design. The transconductance (gm _OTA ) is adjusted by adjusting the constant current value based on Equation 4 above. The constant current value of the amplifier 100 shown in FIG. 6 is determined by the bias voltage VC output from the rectifier shown in FIG.

(Eq. 5)

FIG. 6 is a circuit diagram illustrating an amplifier 100 used in a bandwidth-adjustable band pass filter circuit proposed in the present invention, and a common mode voltage feedback circuit (CMFB) necessary for a differential output is omitted, and a constant current value of an input terminal is determined. The gate voltage of the PMOS transistor M1 is connected to an external bias voltage VC terminal.

In addition, the bias voltage VC output from the variable constant voltage rectifier 200 is connected to an external terminal, and the change of the voltage changes the current of the transistor M1 of the amplifier 100, thereby causing a transconductance ( gm _OTA ) to adjust the high pass -3dB cutoff frequency of the bandpass filter.

The variable constant voltage rectifier 200 used in this application is designed to adjust the output voltage through the switching operation in the circuit, as shown in FIG. The basic structure takes the form of a constant voltage rectifier using a conventional amplifier. However, by adjusting the number of PMOS transistors participating in the intermediate current flow through the switching operation, the resistance value is adjusted to adjust the output bias voltage VC.

8 illustrates an example of a measurement result of the output bias voltage VC according to the switching operation of the variable constant voltage rectifier. FIG. 9 is an example of a measurement result of a high band -3 dB cutoff frequency of a band pass filter examined according to a change in the output bias voltage VC of the variable constant voltage rectifier shown in FIG. 8. As we have seen so far, the band pass filter in the present invention adjusts the transconductance (gm _OTA ) of the circuit through the conversion of the bias voltage (VC) without the use of capacitor strings, thereby allowing the high band -3 dB cutoff frequency of the band pass filter. You can see that it adjusts.

The correct operation of the band pass filter circuit that can adjust the bandwidth according to the present invention has been described above. As such, the circuit proposed in the present invention can be said to be used for low-area design not only in the field of multiple bio-signal measurement but also in analog circuits.

On the other hand, only the signal components between the band-pass filter of the invention is to remove signal components with frequency f _H or more signal components of the frequency f _L or less as shown in a graph of FIG 2, frequency f _L and the frequency f _H selectively passing Filter. Here, the frequency f _L and the frequency f _H are typically defined by Equations 1 and 2 above.

At this time, the frequency f _L used for the biosignal processing must be very low, and the resistance to implement this becomes very large. To implement a typical very large resistance in a semiconductor chip is very expensive because it takes up a lot of chip area. Therefore, when the OFF state leakage current of the MOS transistor is used, a very large resistance is obtained. This is called a virtual resistor (R _pseudo ) and can be realized at an economical price by implementing tens of Gohm resistors with a small chip area.

In addition, the capacitor used in the feedback loop, with a very large resistance, is also used to determine the frequency f _L (see equation 1). On the other hand, the total amplifier gain C _in / C _{F in a} desired frequency band is determined by C _F. Input capacitors C _in1 and C _in2 also determine the overall amplifier gain within the frequency band.

In the case of a general biosignal, the DC value needs to be removed, so the frequency f _L is about 0.3 Hz to 0.8 Hz low, which is the same for almost all applications. However, the frequency f _H must vary depending on the application.

That is, the frequency f _H is determined by Equation 2 above, and in the prior art, the amplifier (OTA) output resistance is fixed, and the load capacitor column (C _L column) is arranged and selectively taken and implemented. Capacitor rows (C _L columns) are also expensive because they make the semiconductor chip area very large. Fixing the load capacitors and selectively changing the amplifier (OTA) output resistance allows for a small chip area.

In this case, in order to convert the output resistance of the amplifier 100 of FIG. 6, a variable constant voltage rectifier for converting the output constant voltage of the variable constant voltage rectifier 200 is designed. The variable constant voltage rectifier 200 of FIG. 7 may be implemented by selectively converting transistor resistance values by a switch to obtain an adjustable constant voltage bias voltage VC. This adjustable constant voltage bias voltage VC converts the bias supply current of the amplifier 100 of FIG. 6, thereby converting the total transconductance gm value of the amplifier 100 by Equations 3 and 4 above. In this case, the converted transconductance (gm) value changes the output resistance value of the amplifier 100 by the relationship of R ₀ = 1 / gm. This allows the frequency f _H to be selectively changed.

On the other hand, the variable constant voltage rectifier 200 of FIG. 7 is connected to a general constant voltage rectifier with a switch by connecting transistors having different resistance values (M = 1, M = 2, M = 4, M = 8, M16) to bias voltage. (VC) can be changed.

That is, in FIG. 7, the non-inverting (+) input of the amplifier 210 is equal to the inverting (−) input (V _in ), and the bias voltage VC is equal to the output resistance of the MOS transistor M20 to which the bias is connected. The output resistance of the transistors M15 to M19 selectively connected to the switch unit 220 is determined. The output resistance of the transistors M15 to M19 selected and connected to the switch unit 220 is selectively changed. You can adjust the value.

Although a preferred embodiment of a band-adjustable band pass filter for processing multiple biosignals according to the present invention has been described above, the present invention is not limited thereto, but is within the scope of the claims and the detailed description of the invention and the accompanying drawings. It is possible to carry out various modifications and this also belongs to this invention.

100: amplifier,
200: variable constant voltage rectifier,
300a and 300b: first and second feedback loops

Claims (6)

An amplifier having non-inverting and inverting input / output terminals, the transconductance value being changed according to an external bias voltage to adjust an output resistance;
A variable constant voltage rectifier for selectively changing the bias voltage to supply the amplifier;
A first feedback loop formed by connecting a first feedback capacitor and a first resistor in parallel between a non-inverting input terminal and an inverting output terminal of the amplifier;
A second feedback loop formed by connecting a second feedback capacitor and a second resistor in parallel between an inverting input terminal and a non-inverting output terminal of the amplifier;
First and second input capacitors each connected in series to non-inverting and inverting input terminals of the amplifier; And
First and second load capacitors connected in series between the inverting and non-inverting output terminals of the amplifier and ground, respectively,
Band-adjustable band pass filter for processing multiple bio-signals, characterized in that the gain bandwidth is adjusted according to the multiple bio-signals input to the non-inverting and inverting input terminals of the amplifier and output to the non-inverting and inverting output terminals of the amplifier.
The method according to claim 1,
And the first and second input capacitors have the same size as the first and second feedback capacitors.
The method according to claim 1,
Band-adjustable band pass filter for processing multiple bio-signals, characterized in that the high-band -3dB cutoff frequency is changed by the variable bias voltage output from the variable constant voltage rectifier.
The method according to claim 1,
And a high band -3 dB cutoff frequency (f _H ) of the amplifier is calculated by Equation 6 below.
(Equation 6)

Here, gm _OTA is a transconductance value of the amplifier, and C _L is a value of the first or second load capacitor.
The method according to claim 1,
The amplifier is an operational transconductance amplifier (OTA),
A differential amplifier for distributing and amplifying a bias current according to a difference between two signals received through the first and second input terminals to generate an output current; And
And a bias unit configured to generate the bias current by using the variable bias voltage output from the variable constant voltage rectifier in the differential amplifier.
The method according to claim 1,
The variable constant voltage current device,
Amplifying means having an inverting (-) and non-inverting (+) input terminal and one output terminal and receiving an external input voltage V _in through the inverting (-) input terminal;
A transistor (M14) having a gate terminal connected to an output terminal of the amplifying means, a power supply voltage terminal (VDD) connected to the source terminal thereof, and a non-inverting (+) input terminal of the amplifying means connected to a drain terminal thereof;
A plurality of transistors M15 to M19 having their source terminals connected in parallel to the non-inverting (+) input terminals of the amplifying means, and their gate and drain terminals being connected to each other in common;
A switch unit having one end of a switch connected to each of the drain terminals of the plurality of transistors M15 to M19 and selectively switching; And
An external bias and gate terminal are connected, and a source terminal thereof is connected to the other end of each switch and the bias voltage VC terminal of the switch unit, and the drain terminal thereof is connected to ground. Band-adjustable band pass filter for multiple bio-signal processing, characterized in that it comprises.

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