KR102160673B1 - Current-reuse low power instrumentation amplifier and fully differential differential amplifiers included therein - Google Patents

Abstract

The present invention relates to a current reuse instrumentation amplifier. A low power instrumentation amplifier according to one embodiment of the present invention includes: an electrode unit including a first electrode and a second electrode for detecting an electrocardiogram signal; a fully differential difference amplifier having a non-inverting input terminal (+ terminal) connected to the first electrode and the second electrode; an AC coupling feedback circuit for receiving an output of the fully differential difference amplifier to be fed back to an inverting input terminal (- terminal) of the fully differential difference amplifier through a feedback structure, wherein the AC coupling feedback circuit includes a variable capacitor and a pseudo resistor; and a resistance regulator for adjusting the magnitude of the pseudo resistance included in the AC coupling feedback circuit. The current reuse instrumentation amplifier has a high input impedance by using a current feedback instrumentation amplifier (CFIA) structure, and can secure a high power supply rejection ratio (PSRR) and a common mode rejection ratio (CMRR) by adopting the fully differential difference amplifier (FDDA). In addition, an AC-coupled capacitive feedback structure can be used to remove unnecessary low frequency components.

Description

Current-reuse low power instrumentation amplifier and fully differential differential amplifiers included therein.

The present invention relates to a current reuse low-power instrumentation amplifier for detecting and amplifying an electrocardiogram signal, and a fully differential differential amplifier included therein.

[Explanation of nationally supported R&D]

This study was made with the support of the Ministry of Health and Welfare, a technology development project for commercialization of micro medical robots (development of a diagnostic module for micro medical robots, task identification number: 1465029326, detailed task number: HI19C0642040019).

An electrocardiogram is a record of the heart's electrical activity at a set time. The electrocardiogram is used not only to measure the rate and consistency of the heartbeat, but also to determine if there is any damage to the heart and to equipment such as an electrocardiogram. For this reason, it has been widely used and studied in the field of cardiology from the past to the present. In addition, not only in the field of cardiology, such as a cardiac pacemaker that detects ECG signals with low power and high-quality ECG signals to detect ECG signals in mobile environments such as ubiquitous healthcare, or a pacemaker for treating heart diseases such as arrhythmia by detecting ECG signals. It is also being actively researched in the field of engineering.

In order to detect an ECG signal, an instrumentation amplifier (IA) is generally used.

1 is a conventional trans-conductance amplifier (OTA, Operational Trans-conductance Amplifier) having a current reuse structure for detecting an electrocardiogram signal. In the prior art, an inverter-based differential input stage for low noise and a class AB output stage for a wide output range and high Gm/I efficiency were applied by applying a current reuse structure. The biasing of the class AB output stage is combined with the input stage to realize current reuse and further reduce power consumption. The prior art achieves low power consumption and equivalent input noise, but when a circuit is configured based on such an operational amplifier (see FIG. 2), it has a low input impedance. In addition, it is difficult to detect high-quality ECG signals because it cannot achieve a high common mode rejection ratio (CMRR). Therefore, in order to detect a high quality ECG signal, a structure of an instrumentation amplifier having a high input impedance and a high common mode rejection rate is required.

A Low-Noise, Low-Power Amplifier With Current-Reused OTA for ECG Recordings, IEEE Transactions on Biomedical Circuit and Systems, Vol. 12, No.3, June 2018

The present invention relates to a current reuse instrumentation amplifier and a fully differential differential amplifier included therein. The current reuse instrumentation amplifier has a high input impedance by using a current feedback instrumentation amplifier (CFIA) structure, and a high power rejection ratio (PSRR, Power) by adopting a Fully Differential Difference Amplifier (FDDA). Supply Rejection Ratio) and Common Mode Rejection Ratio (CMRR) can be secured.

The low-power measuring amplifier according to an embodiment of the present invention includes an electrode unit including a first electrode and a second electrode for detecting an electrocardiogram signal; A fully differential differential amplifier to which the first and second electrodes and a non-inverting input terminal (+ terminal) are connected; An AC coupling feedback circuit that receives the output of the fully differential amplifier and feeds it back to the inverting input terminal (-terminal) of the fully differential amplifier through a feedback structure, wherein the AC coupling feedback circuit includes a variable capacitor and a pseudo resistor ( An AC coupling feedback circuit, including a pseudo resistor); And a resistance regulator that adjusts the magnitude of the pseudo resistance included in the AC coupling feedback circuit.

A fully differential differential amplifier according to another embodiment of the present invention comprises: a first current reuse input unit receiving a differential voltage input; A second current reuse input unit receiving a feedback differential voltage input; Class AB biasing in which a voltage at both ends is changed by at least one of a differential input voltage input to the first current reuse input unit and a feedback differential input voltage input to the second current reuse input unit; A class AB output unit for outputting a differential output voltage according to the voltage across the class AB biasing; And a common mode feedback unit detecting a common mode voltage of the differential output voltage and comparing the detected common mode voltage with a reference voltage to control a magnitude of the differential output voltage, wherein the feedback differential input voltage is the class AB The differential output voltage output from the output unit is provided by being negatively fed back through a feedback circuit.

The low-power instrumentation amplifier that reuses current proposed in the present invention uses a current feedback instrumentation amplifier structure, and uses a fully differential-differential amplifier that uses a high-performance current reuse structure to provide very low current, high DC gain, and a full range of output. It has high input impedance and high CMRR and PSRR to remove offset due to heavy load driving, mismatch of electrodes, and can provide the advantage of removing unnecessary low frequencies as needed.

Particularly, the fully differential differential amplifier includes a current reuse structure, and the input stage is combined with class AB biasing based on an inverter to share the currents of the two stages in the input stage, thereby reducing the power consumption of the amplifier while simultaneously having the effect of reducing the power consumption of the amplifier. , PMOS's trans-conductance can be combined to provide high trans-conductance. In addition, high open-loop gain can be obtained by using a cascode structure at the input stage of a fully differential amplifier, and a wide output range and high Gm/I efficiency can be obtained by applying a class AB structure at the output stage. In addition, the fully differential differential amplifier detects the common mode signal of the instrumentation amplifier by applying a common mode detection circuit for high CMRR, compares it with a reference voltage through an error amplifier, and feeds the output signal back to the internal current source. , Common mode Feedback Loop).

1 is an operational trans-conductance amplifier (OTA) having a current reuse structure for detecting an electrocardiogram signal according to the prior art.
2 is an exemplary diagram illustrating a circuit based on an operational amplifier according to the prior art.
3 shows an exemplary circuit structure of a current reuse instrumentation amplifier according to an embodiment of the present invention.
4 is a graph simulating an output signal of a current reuse measuring amplifier according to an embodiment of the present invention.
5 shows an exemplary circuit structure of a fully differential differential amplifier according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION The detailed description of the present invention to be described later refers to the accompanying drawings, which illustrate specific embodiments in which the present invention may be practiced. These embodiments are described in detail enough to enable a person skilled in the art to practice the present invention. The various embodiments of the present invention are different from each other, but need not be mutually exclusive. For example, certain shapes, structures, and characteristics described herein may be implemented in other embodiments without departing from the spirit and scope of the present invention in relation to one embodiment. Further, the position or arrangement of individual components within each disclosed embodiment may be changed without departing from the spirit and scope of the present invention. Accordingly, the detailed description to be described below is not described in a limiting sense, and the scope of the present invention is limited only by the appended claims along with all scopes equivalent to those claimed by the claims. Like reference numerals in the drawings refer to the same or similar functions in various aspects.

The terms used in the present specification have selected general terms that are currently widely used as possible while considering functions, but this may vary according to the intention or custom of a technician working in the field or the emergence of new technologies. In addition, in certain cases, there are terms arbitrarily selected by the applicant, and in this case, the meaning will be described in the description of the corresponding specification. Accordingly, terms used in the present specification should be interpreted based on the actual meaning of the term and the entire contents of the present specification, not a simple name of the term.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings.

3 shows an exemplary circuit structure of a current reuse instrumentation amplifier according to an embodiment of the present invention. 4 is a graph simulating an output signal of a current reuse measuring amplifier according to an embodiment of the present invention. 5 shows an exemplary circuit structure of a fully differential differential amplifier according to an embodiment of the present invention.

3 to 5, the current reuse measuring amplifier 10 according to an embodiment of the present invention includes an electrode unit 100, a fully differential differential amplifier 110, an AC coupling feedback circuit 120, and a resistance regulator ( 130).

The current reuse measurement amplifier 10 according to the embodiments and an apparatus or unit constituting the same may have a side that is entirely hardware, or partially hardware and partially software.

The electrode unit 100 includes a first electrode 101 and a second electrode 102 for detecting an electrocardiogram signal. The first electrode 101 and the second electrode 102 are for detecting an electrocardiogram recorded in the form of a wavelength by analyzing the electrical activity of the heart, and may be attached to the outside of the body to detect a cardiac signal. However, the present invention is not limited thereto, and the first electrode 101 and the second electrode 102 are configured to be included in a cardiac operation assisting device disposed inside the body and in the heart, so that the ECG signal is transmitted to the fully differential differential amplifier 110. Can provide.

Another configuration of the current reuse instrumentation amplifier 10, a fully differential differential amplifier 110, an AC coupling feedback circuit 120 and a resistance regulator 130 are provided through the first electrode 101 and the second electrode 102 It may be a configuration for improving and improving the quality of the ECG signal.

The fully differential differential amplifier 110 has a first electrode 101 and a second electrode 102 and a non-inverting input terminal (+ terminal) connected to each other, and differentially from the first electrode 101 and the second electrode 102 It is provided with a voltage input. In addition, the output output from the fully differential differential amplifier 110 is fed back to the inverting input terminal (-terminal) of the fully differential differential amplifier 110 through the AC coupling feedback circuit 120. The AC coupling feedback circuit 120 provides an AC-coupled capacitive feedback structure, and receives the output of the fully differential amplifier 110 as an input and passes through the feedback structure to the inverting input terminal (-terminal) of the fully differential amplifier 110. ). Since the input and output of the fully differential differential amplifier 110 includes a fully differential-differential configuration, unnecessary common mode components can be removed, and thus a high power supply rejection ratio (PSRR) and a high common mode It is possible to provide a CMRR (Common Mode Rejection Ratio).

The AC coupling feedback circuit 120 may include a variable capacitor 121 and a similar resistor 122. The input of the ECG signal provided through the first electrode 101 and the second electrode 102 is amplified by the variable capacitor 121 included in the AC coupling feedback circuit 120 to be finally output. I can. The variable capacitor 121 may include a first capacitor (C- ₁ ) and a second capacitor (C ₂ ) configured to be adjustable to 5 bits, and the input of the ECG signal (V _in ) is to the variable capacitor 121 It is amplified according to the closed-loop gain by and the output (V _out ) can be determined by the following equation. The equation according to Equation 1 below is an equation considering only the differential component.

[Equation 1]

In addition, a high frequency range of a certain range is cut off through the pseudo resistance 122 of the AC coupling feedback circuit 120. The magnitude of the resistance of the pseudo-resistance 122 is adjusted by the output (V _cont ) of the resistance regulator 130. According to the size adjustment of the similar resistor 122, the high frequency cutoff frequency of the AC coupling feedback circuit 120 may be adjusted. The ECG signal is usually known to be between 0.5 Hz and 100 Hz. The current reuse measurement amplifier 10 according to the embodiment of the present invention can be adjusted to a very low high-frequency cutoff frequency of 0.5 Hz through the pseudo resistance 122 and the resistance regulator 130 of the AC coupling feedback circuit 120. Low-frequency offset signals that do not exist can be removed. As described above, the current reuse measuring amplifier 10 according to an embodiment of the present invention can provide a function of easily adjusting the gain adjustment and the high-frequency cut-off frequency of the AC coupling capacitance feedback from the outside according to the situation. 4 is a graph simulating a result of a change in a gain of an output signal and a frequency of a specific band being cut off according to a capacitor adjustment. Referring to FIG. 4, it can be seen that the gain adjusted by the 5-bit capacitor is changed and the low frequency offset signals are removed due to the low frequency limit.

In particular, the fully differential differential amplifier 110 includes a current reuse structure, and the input terminal is combined with class AB biasing based on an inverter to share the currents of the two stages in the input terminal, thereby reducing the power consumption of the amplifier. The trans-conductance of the two input NMOS and PMOS can be combined to provide high trans-conductance. In addition, a high open loop gain can be obtained using a cascode structure at the input end of the fully differential amplifier 110, and a class AB structure is applied to the output end to have a wide output range and high Gm/I efficiency. In addition, the fully differential differential amplifier 110 detects the common mode signal of the instrumentation amplifier by applying a common mode detection circuit for high CMRR, compares it with a reference voltage through an error amplifier, and feeds back the output signal to the internal current source. It may include a loop (CMFB, Common Mode Feedback Loop).

Hereinafter, a detailed structure of the fully differential differential amplifier 110 will be described in more detail.

5 shows an exemplary structure of a fully differential differential amplifier according to an embodiment of the present invention. The fully differential differential amplifier 110 includes a first current reuse input unit 111, a second current reuse input unit 112, a class AB biasing 113, a class AB output unit 114, and a common mode feedback circuit unit 115. Include.

The first current reuse input unit 111 receives differential voltage inputs V _{INP and} V _INN . Differential voltage inputs (V _INP, V _INN ) may be provided in a configuration for measuring an electrocardiogram, for example, from the first electrode 101 and the second electrode 102 of the electrode unit 100 of FIG. 3. Each can be entered. The second current reuse input unit 111 receives feedback differential voltage inputs V _{INFP and} V _INFN . The feedback differential voltage inputs (V _INFP, V _INFN ) are input by negative feedback of the differential output voltage of the fully differential differential amplifier 110 through a feedback circuit, and the feedback circuit amplifies the differential voltage input and limits unnecessary frequencies. It may be a circuit for For example, it may be an AC coupling feedback circuit 120. The first current reuse input unit 111 corresponds to the non-inverting input terminal (+ terminal) of the fully differential differential amplifier 110, and the second current reuse input unit 112 is an inverting input terminal of the fully differential differential amplifier 110 May correspond to (-terminal).

The first current reuse input unit 111 and the second current reuse input unit 112 have a cascode structure applied to the input terminal, and use the trans-conductance of NMOS and PMOS at the same time, thereby providing a high DC gain. In addition, since the feedback differential voltage inputs V _{INFP and} V _INFN and the feedback differential voltage inputs V _{INFP and} V _INFN are directly input to the gate, high input impedance can be provided. Due to the high impedance, an offset caused by mismatch of an electrode may be eliminated when measuring an electrocardiogram.

Current supply sources of the first current reuse input unit 111 and the second current reuse input unit 112 are MOSFETs biased by VCMFB and BIAS_N, respectively, and the first current reuse input unit 111 and the second current reuse input unit 112 are It may be configured to share and reuse a direct current (DC) current output from the current source. Specifically, the differential voltage inputs V _{INP and} V _INN input to the first current reuse input unit 111 are converted to current due to trans-conductance, and class AB biasing 113 by the current passing through the cascode structure. The voltage at both ends of) changes.

The voltage across the class AB biasing 113 is provided as an input to the class AB output 114, and the class AB output 114 is a differential output voltage (V) according to the voltage across the class AB biasing 113. _OUTP , V _OUTN ) are output. The class AB output unit 114 may include a class AB + output terminal 114A outputting V _OUTP and a class AB-output terminal 114B outputting V _OUTN . Through the use of the class AB structure including the class AB biasing 113 and the class AB output unit 114, crossover distortion can be removed from the output by having a constant biasing voltage, and power It has excellent efficiency and can drive heavy loads at the output stage.

The differential output voltage (V _OUTP , V _OUTN ) output from the class AB output unit 114 is negative feedback through the feedback circuit, for example, the AC coupling feedback circuit 120 as described above, and the second current reuse input unit It is provided as a feedback differential input voltage (V _INFP, V _INFN ) of (112). The feedback differential input voltages (V _INFP, V _INFN ) are converted into current due to the trans-conductance of the MOSFET of the second current reuse input unit 112, and the current passing through the cascode structure is converted into a current of the first current reuse input unit 111. The currents generated by the inputs V _{INFP and} V _INFN are combined and shared to change the voltage across the class AB biasing 113. The voltage across the changed class AB biasing 113 is input to the class AB output unit 114, so that the class AB output unit 114 has a differential output voltage corresponding to the voltage across the changed class AB biasing 113 ( V _OUTP , V _OUTN ) are output. This feedback operation is repeatedly performed as long as the fully differential differential amplifier 110 operates.

In order to improve the CMRR while the fully differential differential amplifier 110 has a wide output range, the output voltage (V _OUTP , V _OUTN ) is a value corresponding to half of the voltage drain drain (VDD) and the reference voltage (V _REF ). It must be set (e.g. V _DD = 1.8 V, V _REF = 0.9 V). The common mode feedback circuit unit 115 includes a common-mode feedback (CMFB) circuit to detect a common mode voltage of the differential output voltage, and compare the detected common mode voltage with a reference voltage to output the differential output. The voltage level can be controlled.

Specifically, the common mode feedback circuit unit 115 includes a common mode voltage signal detection unit 115A and an error amplifier 115B. The common mode voltage signal detection unit 115A receives differential output voltages V _OUTP and V _OUTN from the class AB output unit 114 and detects the common mode voltage of the differential output voltages V _OUTP and V _OUTN . . The common mode voltage detected by the common mode voltage signal detection unit 115A is provided as an input of the error amplifier 115B. The error amplifier 115B compares the detected common mode voltage with the reference voltage V _REF and feeds back the generated output voltage to the bias of the current supply source V _CMFB of the first and second current reuse input units 111 and 112. . According to the operation of the common mode feedback circuit unit 115, the common mode voltage of the differential output voltages V _OUTP and V _OUTN is adjusted to the reference voltage V _REF . For example, reducing the common-mode voltage of the differential output voltage when the common-mode voltage (V _{OUTP, OUTN} V), increase the common mode feedback differential output voltage (V _{OUTP, OUTN} V) to the circuit 115. The When the common mode voltage of the differential output voltages V _OUTP and V _OUTN decreases, the common mode voltage of the differential output voltages V _OUTP and V _OUTN increases by the common mode feedback circuit unit 115. Accordingly, CMRR can be further improved.

The low-power instrumentation amplifier 10 that reuses current proposed in the present invention uses a current feedback instrumentation amplifier structure, and uses a fully differential-differential amplifier that uses a high-performance current reuse structure, so that very low current and high DC gain, full range It has high input impedance and high CMRR and PSRR to remove offset due to output range of, heavy load driving, mismatch of electrode, and can provide the advantage of removing unnecessary low frequencies as needed.

The present invention described above has been described with reference to the embodiments shown in the drawings, but these are only exemplary and those of ordinary skill in the art will appreciate that various modifications and variations of the embodiments are possible therefrom. . However, such modifications should be considered to be within the technical protection scope of the present invention. Therefore, the true technical protection scope of the present invention should be determined by the technical spirit of the appended claims.

10: current reuse instrumentation amplifier
100: electrode part
110: fully differential differential amplifier
120: AC coupling feedback circuit
130: resistance regulator

Claims (6)

An electrode unit including a first electrode and a second electrode for detecting an electrocardiogram signal;
A fully differential differential amplifier to which the first and second electrodes and a non-inverting input terminal (+ terminal) are connected;
An AC coupling feedback circuit that receives the output of the fully differential amplifier and feeds it back to the inverting input terminal (-terminal) of the fully differential amplifier through a feedback structure, wherein the AC coupling feedback circuit includes a variable capacitor and a pseudo resistor ( An AC coupling feedback circuit, including a pseudo resistor); And
Including a resistance regulator for adjusting the size of the similar resistance included in the AC coupling feedback circuit,
The fully differential differential amplifier,
A first current reuse input unit receiving a differential voltage input from the electrode unit;
A second current reuse input unit receiving a feedback differential voltage input;
Class AB biasing in which a voltage at both ends is changed by at least one of a differential input voltage input to the first current reuse input unit and a feedback differential input voltage input to the second current reuse input unit;
A class AB output unit for outputting a differential output voltage according to the voltage across the class AB biasing; And
A common mode feedback unit configured to detect a common mode voltage of the differential output voltage, and to compare the detected common mode voltage with a reference voltage to control a magnitude of the differential output voltage,
The feedback differential input voltage is provided by negative feedback of the differential output voltage output from the class AB output unit through the AC coupling feedback circuit,
The common mode feedback circuit unit,
A common mode voltage signal detection unit receiving the differential output voltage from the class AB output unit and detecting a common mode voltage of the differential output voltage; And
And an error amplifier for feeding back an output voltage generated by comparing the detected common mode voltage and a reference voltage to a bias of a current supply source of the first current reuse input unit and the second current reuse input unit. The method of claim 1,
The input of the ECG signal is amplified according to the closed loop gain of the variable capacitor. The method of claim 1,
The magnitude of the resistance is controlled by the output (V _cont ) of the resistance regulator,
A low-power measuring amplifier, characterized in that the high-frequency cut-off frequency of the AC coupling feedback circuit is adjusted according to the size adjustment of the pseudo resistance. delete A first current reuse input unit receiving a differential voltage input;
A second current reuse input unit receiving a feedback differential voltage input;
Class AB biasing in which a voltage at both ends is changed by at least one of a differential input voltage input to the first current reuse input unit and a feedback differential input voltage input to the second current reuse input unit;
A class AB output unit for outputting a differential output voltage according to the voltage across the class AB biasing; And
A common mode feedback unit configured to detect a common mode voltage of the differential output voltage, and to compare the detected common mode voltage with a reference voltage to control a magnitude of the differential output voltage,
The feedback differential input voltage is provided by negative feedback of the differential output voltage output from the class AB output unit through a feedback circuit,
The common mode feedback circuit unit,
A common mode voltage signal detection unit receiving the differential output voltage from the class AB output unit and detecting a common mode voltage of the differential output voltage; And
And an error amplifier for feeding back an output voltage generated by comparing the detected common mode voltage with a reference voltage to a bias of a current supply source of the first current reuse input unit and the second current reuse input unit. delete

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