TWI682166B - Biomedical sensor and reading circuit thereof - Google Patents

Abstract

A biomedical sensor comprises a reading circuit and a computing circuit. The reading circuit inputs a buffer voltage into a tested impedance and outputs an output voltage. The computing circuit receives the output voltage from the reading circuit and calculates the impedance value and the phase value of the tested impedance, so that obtain the feature of the tested impedance rapidly and correctly.

Description

Biomedical sensor and its reading circuit

The invention relates to a biomedical sensor, in particular to a biomedical sensor with a reading circuit and a calculation circuit.

With the modernization of society, disease has become the main cause of death for humans, and malignant tumors and cardiovascular diseases have long occupied one or two of the top ten causes of death. If the disease can be detected and treated early, it can greatly improve the treatment of patients. Degree and survival rate, therefore, how to detect diseases early has become a very important part of the medical procedure. Among them, bio-electrical impedance analysis (Bio-electrical impedance analysis) by measuring the electrical characteristics (such as impedance, admittance, phase or frequency...) The qualitative or quantitative characteristics make bio-impedance detection widely used in various human health numerical detection, and how to read the electrical characteristics of the test object from the sensor correctly and quickly is the key technology of bio-impedance detection and analysis .

The main purpose of the present invention is to calculate the impedance value and phase size of the impedance to be measured by the reading circuit and the calculation circuit, so that the detection data can be accurately and quickly provided for the back-end circuit to perform characteristic analysis.

A biomedical sensor of the present invention includes a reading circuit and a calculation circuit, the reading The circuit has an impedance to be measured and a reverse amplifier, the impedance to be measured receives a buffer voltage, and the impedance to be measured outputs a sense voltage, the reverse amplifier is electrically connected to the impedance to be measured to receive the sense voltage, And the inverting amplifier outputs an output voltage, wherein the inverting amplifier has a feedback resistance. The calculation circuit has a peak detection unit, an amplitude calculation unit, an impedance calculation unit, a sampling detection unit and a phase calculation unit, the peak detection unit is coupled to the reading circuit, and the peak detection unit is used for calculation A maximum peak value and a minimum peak value of the buffer voltage and the output voltage, the amplitude calculation unit is electrically connected to the peak detection unit, the amplitude calculation unit is used to calculate the buffer voltage and the maximum peak values and the minimum peak values An amplitude of the output voltage, the impedance calculation unit is electrically connected to the amplitude calculation unit, and the impedance calculation unit is used for calculating one of the impedances to be measured according to the feedback impedance values of the amplitudes and the feedback resistance Value, the sampling detection unit is coupled to the reading circuit and the peak detection unit, the sampling detection unit is used to calculate a total sampling period based on the buffer voltage, the output voltage, the maximum peaks and the minimum peaks The phase calculation unit is electrically connected to the sampling detection unit. The phase calculation unit is used to calculate a phase value according to the total sampling number of the period and the difference between the sampling numbers of the signals.

In the present invention, the buffer voltage is input to the impedance to be measured by the reading circuit, so that the impedance to be measured outputs the sense voltage, and the sense voltage of the impedance to be measured is reversed to the output voltage. The calculation circuit calculates the impedance value and the phase value of the impedance to be measured from the buffer voltage and the output voltage, so that the back-end circuit can perform characteristic analysis on the impedance to be measured.

Please refer to FIG. 1, which is a functional block diagram of a biomedical sensor 100 according to an embodiment of the present invention. The biomedical sensor 100 includes a reading circuit 110, an analog-to-digital converter 120 and一calculation circuit 130.

Please refer to FIGS. 1 and 2. In this embodiment, the reading circuit 110 has a buffer 111, an impedance to be measured 112 and a reverse amplifier 113. The buffer 111 receives an input voltage V _in and outputs a Buffer voltage V _buf . In this embodiment, the buffer 111 is an operational amplifier. The positive input terminal receives the input voltage V _in , and the negative input terminal is electrically connected to the output terminal to form a power follower ( Voltage follower), so that the potential of the buffer voltage V _buf is the same as the input voltage V _in . Since the operational amplifier has the characteristics of high input impedance and low output impedance, it can be used to block the front-end and back-end circuits of the connection. The impedance to be measured 112 is electrically connected to the buffer 111 to receive the buffer voltage V _buf . In this embodiment, the impedance to be measured 112 is a sensing element carrying a device under test (Device under test). The impedance 112 outputs a sense voltage V _sen .

Please refer to FIG. 2, the inverting amplifier 113 is electrically connected to the impedance to be measured 112 to receive the sensing voltage V _sen , and the inverting amplifier 113 outputs an output voltage V _out . In this embodiment, the inverting The amplifier 113 has an operational amplifier 113a and a feedback resistor 113b. A negative input terminal of the operational amplifier 113a is electrically connected to the impedance to be measured 112. A positive input terminal of the operational amplifier 113a receives a voltage V. The feedback resistance ends 113b is electrically connected between the negative input terminal of the operational amplifier and an output terminal 113a of the operational amplifier 113a of the output terminal outputs the output voltage V _out, since the operational amplifier having a high input impedance 113a The characteristic of such that the current flowing through the impedance to be measured 112 is substantially equal to the current flowing through the feedback resistor 113b, so that the calculation circuit 130 at the back end can calculate the characteristics of the impedance to be measured 112 based on the characteristic.

其中，

為該緩衝電壓，

為該輸入電壓，

為該緩衝器111之增益，而該輸出電壓V _out與該緩衝電壓V _buf之間的轉移函數可表示為：

其中，

為該輸出電壓，

為該運算放大器113a之增益，

為該回授電阻113b的阻抗值，

為該待測阻抗112之該阻抗值，根據上述兩式，該輸出電壓V _out及該輸入電壓V _in之間的關係式可表示為：

將上式整理後，該待測阻抗112之該阻抗值可由下式求得：

而若

及

均遠大於1，則上式可簡化為：

由計算式可知，最後一項之

為計算該待測阻抗112之該阻抗值的主要誤差來源，若

遠大於

時可將主要誤差最小化，但實際上該運算放大器113a之增益會隨著操作頻率的上升而下降，使得該生醫感測器100在該待測阻抗112之操作頻率與該運算放大器113a的增益之間須取得平衡，使得該反向放大器113需要根據該待測阻抗112操作頻率進行設計，因此，較佳的，該回授電阻113b為一可變電阻，而可藉由調整該回授電阻113b之阻抗讓該讀取電路110適用於不同操作頻率之該待測阻抗112。 The transfer function between the buffer voltage V _buf and the input voltage V _in can be expressed as:

among them,

For this buffer voltage,

For this input voltage,

Is the gain of the buffer 111, and the transfer function between the output voltage V _out and the buffer voltage V _buf can be expressed as:

among them,

For this output voltage,

Is the gain of the operational amplifier 113a,

Is the impedance value of the feedback resistor 113b,

For the impedance value of the impedance 112 to be measured, according to the above two equations, the relationship between the output voltage V _out and the input voltage V _in can be expressed as:

After finishing the above formula, the impedance value of the impedance to be measured 112 can be obtained by the following formula:

And if

and

Both are much greater than 1, then the above formula can be simplified to:

From the calculation formula, we know that the last item

To calculate the main error source of the impedance value of the impedance 112 to be measured, if

Much larger than

The main error can be minimized, but in fact the gain of the operational amplifier 113a will decrease as the operating frequency increases, so that the operating frequency of the biomedical sensor 100 at the impedance 112 to be measured and the operational amplifier 113a The gain must be balanced so that the inverting amplifier 113 needs to be designed according to the operating frequency of the impedance 112 to be measured. Therefore, preferably, the feedback resistor 113b is a variable resistor, which can be adjusted by adjusting the feedback The impedance of the resistor 113b makes the reading circuit 110 suitable for the impedance 112 to be measured at different operating frequencies.

Please refer to FIG. 1, the analog-to-digital converter 120 is electrically connected to the reading circuit 110 to receive the buffer voltage V _buf and the output voltage V _out , and the analog-to-digital converter 120 is used to connect the buffer voltage V _buf and The output voltage V _out is converted from an analog signal to a digital signal. The calculation circuit 130 is electrically connected to the analog-to-digital converter 120 to receive the digital buffer voltage V _buf and the output voltage V _out .

Referring to FIGS. 1 and 3, the calculation circuit 130 has a peak detection unit 131, an amplitude calculation unit 132, an impedance calculation unit 133, a sample detection unit 134, and a phase calculation unit 135. The peak detection unit 131 is electrically connected to the analog-to-digital converter 120 to receive the digital buffer voltage V _buf and the output voltage V _out , and the peak detection unit 131 calculates the buffer voltage V _buf and the output voltage V, respectively M _out of a maximum peak and a minimum peak B.

其中，

為該緩衝電壓V _buf之該振幅，

及

分別為該緩衝電壓V _buf的該最大峰值及該最小峰值，

為該輸出電壓V _out之該振幅，

及

分別為該輸出電壓V _out的該最大峰值及該最小峰值，

為該類比數位轉換器120的一電源電壓，n為該類比數位轉換器120的一位元數。 Referring to FIG. 3, the amplitude calculation unit 132 is electrically connected to the peak detection unit 131 to receive the maximum peak values M and the minimum peak values B of the buffer voltage V _buf and the output voltage V _out , and the amplitude calculation The unit 132 calculates an amplitude of the buffer voltage V _buf and the output voltage V _out according to the maximum peaks M and the minimum peaks B, but since the maximum peaks M and the minimum peaks B are digital signals, it is necessary to It can be calculated only after it is converted into an analog signal. In this embodiment, the calculation formula of the amplitude calculation unit 123 for calculating the amplitude is:

among them,

Is the amplitude of the buffer voltage V _buf ,

and

Are the maximum peak value and the minimum peak value of the buffer voltage V _buf ,

Is the amplitude of the output voltage V _out ,

and

Are the maximum peak value and the minimum peak value of the output voltage V _out ,

Is a power supply voltage of the analog-to-digital converter 120, and n is a single-bit number of the analog-to-digital converter 120.

其中，

為該待測阻抗112之該待測阻抗值，

為該回授電阻113b之該回授阻抗值，該阻抗計算單元133輸出該待測阻抗值供後端電路分析。 Referring to FIG. 3, the impedance calculation unit 133 is electrically connected to the amplitude calculation unit 132 to receive the amplitudes of the buffer voltage V _buf and the output voltage V _out , and the impedance calculation unit 133 is based on the amplitudes and the feedback A feedback impedance value of the resistor 113b calculates a measured impedance value of the measured impedance 112. In this embodiment, the impedance calculation unit 133 calculates the calculated impedance value of the measured impedance 112 as:

among them,

Is the measured impedance value of the measured impedance 112,

For the feedback impedance value of the feedback resistor 113b, the impedance calculation unit 133 outputs the impedance value to be measured for back-end circuit analysis.

Please refer to FIGS. 3 and 4, the sampling detection unit 134 is coupled to the reading circuit 110 and the peak detection unit 131, the sampling detection unit 134 is based on the buffer voltage V _buf , the output voltage V _out , the The maximum peak value M and the minimum peak values B calculate the total number of samples in one cycle and the difference in number of samples between signals. In this embodiment, the sampling detection unit 134 has a judgment element 134a, an initial sampling register 134b, and a sampling number register 134c. The judgment element 134a is electrically connected to the digital-to-analog converter 120 and the peak value The detecting unit 131, the initial sampling register 134b and the sampling number register 134c are electrically connected to the determining element 134a.

Please refer to FIG. 4, in calculating the total number of samples in the period, the judging element 134a first stores an input initial value of the received buffer voltage _Vbuf into the initial sampling register 134b, and converts the analog-to-digital converter A sample number of 120 is accumulated in the sample number register 134c. Next, the judging element 134a compares whether the magnitude of the buffer voltage V _buf received subsequently is equal to the magnitude of the input initial value, and at the same time judges whether the buffer voltage V _buf has passed its maximum peak value and the minimum peak value, that is The judging element 134a judges whether the buffer voltage V _buf has completed a complete cycle, if so, stops the accumulation of the sampling number, and outputs the sampling number stored in the sampling number register 134c as the total sampling number of the period, and The number of samples of the buffer voltage V _buf in a complete cycle is obtained, otherwise, the accumulation of the number of samples is continued.

Please refer to FIG. 4 again, in calculating the difference in the number of samples between the signals, the judging element 134a first judges whether the buffer voltage V _buf is at the maximum peak value, and if so, accumulates the number of samples of the analog-to-digital converter 120 to The sampling number register 134c, then, the determining element 134a determines whether the output voltage V _out is at the maximum peak value, if so, stops the accumulation of the sampling number, and outputs the sampling number stored in the sampling number register 134c as The difference in the number of samples between the signals, and the number of samples between the maximum peak value of the buffer voltage V _buf and the maximum peak value of the output voltage V _out can be obtained, otherwise, the accumulation of the sample number is continued.

其中，

為該相位值，

為該訊號間取樣數差值，

為該週期總取樣數，該相位計算單元135計算該訊號間取樣數差值與該週期總取樣數之間的比例後乘上一個週期的相位角360度而得到該相位值，最後，該相位計算單元135輸出該相位值供後端電路進行分析。 Please refer to FIG. 3, the phase calculation unit 135 is electrically connected to the sampling detection unit 134, the phase calculation unit 135 calculates a phase value according to the total number of samples in the period and the difference in the number of samples between the signals, the phase calculation unit 135 The calculation formula for calculating this phase value is:

among them,

For this phase value,

Is the difference in the number of samples between the signals,

For the total number of samples in the period, the phase calculation unit 135 calculates the ratio between the difference between the number of samples in the signal and the total number of samples in the period, and multiplies the phase angle of one cycle by 360 degrees to obtain the phase value. Finally, the phase The calculation unit 135 outputs the phase value for analysis by the back-end circuit.

By the present invention, the input buffer circuit 110 reads the voltage V _buf to the DUT 112 impedance so that the impedance test 112 outputs the sense voltage V _sen, and the measured impedance of the sense voltage 112 V _sen The reverse is the output voltage V _out , and the calculation circuit 130 can calculate the impedance value and the phase value of the impedance 112 to be measured from the buffer voltage V _buf and the output voltage V _out , so that the back-end circuit can Value and the phase value for characteristic analysis.

The scope of protection of the present invention shall be subject to the scope defined in the attached patent application. Any changes and modifications made by those who are familiar with this skill without departing from the spirit and scope of the present invention shall fall within the scope of protection of the present invention. .

100‧‧‧biomedical sensor

110‧‧‧Reading circuit

111‧‧‧Buffer

112‧‧‧ impedance to be measured

113‧‧‧Inverting amplifier

113a‧‧‧Operational amplifier

113b‧‧‧Feedback resistance

120‧‧‧Analog to Digital Converter

130‧‧‧Calculation circuit

131‧‧‧Peak detection unit

132‧‧‧ Amplitude calculation unit

133‧‧‧impedance calculation unit

134‧‧‧Sampling detection unit

134a‧‧‧judgment component

134b‧‧‧ Initial sampling register

134c‧‧‧Sampling register

135‧‧‧phase calculation unit

V _in ‧‧‧ input voltage

V _buf ‧‧‧ buffer voltage

V _sen ‧‧‧sensing voltage

V‧‧‧Voltage

V _out ‧‧‧ output voltage

M‧‧‧Maximum peak

B‧‧‧Min peak

A _vout ‧‧‧ Amplitude of buffer voltage

M _vbuf ‧‧‧Maximum peak value of buffer voltage

B _vbuf ‧‧‧Minimum peak value of buffer voltage

A _vout ‧‧‧ amplitude of output voltage

M _vout ‧‧‧Maximum peak of output voltage

B _vout ‧‧‧Minimum peak value of output voltage

Imp _z ‧‧‧The impedance value of the impedance to be measured

R _f ‧‧‧ Feedback resistance value of feedback resistance

Figure 1: A functional block diagram of a biomedical sensor according to an embodiment of the invention.

Figure 2: A circuit diagram of a reading circuit according to an embodiment of the invention.

Figure 3: A functional block diagram of a computing circuit according to an embodiment of the invention.

Fig. 4: According to an embodiment of the invention, a functional block diagram of a sampling detection unit of the calculation circuit.

100‧‧‧biomedical sensor

110‧‧‧Reading circuit

120‧‧‧Analog to Digital Converter

130‧‧‧Calculation circuit

Claims (10)

A biomedical sensor includes: a reading circuit having an impedance to be measured and an inverting amplifier, the impedance to be measured receives a buffer voltage, and the impedance to be measured outputs a sensing voltage, the inverting amplifier electrically The impedance to be measured is connected to receive the sense voltage, and the inverting amplifier outputs an output voltage, wherein the inverting amplifier has a feedback resistance; and a calculation circuit has: a peak detection unit, coupled to the reading Take the circuit, the peak detection unit is used to calculate a maximum peak value and a minimum peak value of the buffer voltage and the output voltage; an amplitude calculation unit is electrically connected to the peak detection unit, the amplitude calculation unit is used according to the The maximum peak value and the minimum peak values to calculate an amplitude of the buffer voltage and the output voltage; an impedance calculation unit electrically connected to the amplitude calculation unit, the impedance calculation unit is used for one of the loops according to the amplitudes and the feedback resistance The impedance value is calculated as one of the impedance values to be measured; a sampling detection unit, coupled to the reading circuit and the peak detection unit, the sampling detection unit is used to determine the buffer voltage, the output voltage, The maximum peaks and the minimum peaks calculate the total sampling number of a period and the difference between the sampling numbers of a signal; and a phase calculation unit, which is electrically connected to the sampling detection unit, and the phase calculation unit is used for total sampling according to the period A phase value is calculated from the difference between the number and the number of samples between the signals. The biomedical sensor as described in item 1 of the patent application range, wherein the reading circuit has a buffer, the buffer receives an input voltage and outputs the buffer voltage, and the impedance to be measured is electrically connected to the buffer. The biomedical sensor as described in item 1 of the patent application scope, wherein the feedback resistance is a variable resistance. The biomedical sensor as described in item 1 of the patent application scope includes an analog-to-digital converter that is electrically connected to the reading circuit to convert the buffer voltage and the output voltage into digital signals The calculation circuit is electrically connected to the analog-to-digital converter to receive the buffer voltage and the output voltage of the digit. The biomedical sensor as described in item 4 of the patent application scope, wherein the calculation formula of the amplitude calculation unit for calculating the amplitude is:

among them,

Is the amplitude of the buffer voltage,

and

Are the maximum peak value and the minimum peak value of the buffer voltage,

Is the amplitude of the output voltage,

and

Are the maximum peak value and the minimum peak value of the output voltage,

Is a power supply voltage of the analog-to-digital converter, and n is a single-bit number of the analog-to-digital converter. The biomedical sensor as described in item 5 of the patent application scope, wherein the calculation formula of the impedance calculation unit to calculate the impedance value of the impedance to be measured is:

among them,

Is the impedance value of the impedance to be measured,

Is the feedback impedance value of the feedback resistance. The biomedical sensor as described in item 4 of the patent application scope, wherein the sampling detection unit has a judgment element, an initial sampling register and a sampling number register, wherein the judgment element is electrically connected to the digital The analog converter and the peak detection unit, the judging element is used to store an initial value of the buffer voltage in the initial sampling register, and accumulate a sample number of the analog digital converter to the sample number temporary Memory, wherein the judging element is used to judge whether the size of the buffer voltage is equal to the initial value of the input, and at the same time determine whether the buffer voltage has passed the maximum peak value and the minimum peak value, if so, stop the accumulation of the sampling number, and The sample number stored in the sample number register is output as the total sample number of the period. The biomedical sensor as described in item 7 of the patent application range, wherein the judging element is used to accumulate a sample number of the analog-to-digital converter to the sample number register when the buffer voltage is at the maximum peak, The sample number stored in the sample number register between the highest peak value and the input voltage and the highest peak value of the buffer voltage is output as the sample number difference between the signals. The biomedical sensor as described in item 8 of the patent application scope, wherein the calculation formula of the phase calculation unit for calculating the phase value is:

among them,

For this phase value,

Is the difference in the number of samples between the signals,

It is the total number of samples in this period. A reading circuit of a biomedical sensor includes: a buffer that receives an input voltage and outputs a buffer voltage; an impedance to be measured, electrically connected to the buffer to receive the buffer voltage, and the impedance to be measured Output a sense voltage; and a reverse amplifier electrically connected to the impedance to be measured to receive the sense voltage, and the reverse amplifier outputs an output voltage, the reverse amplifier has a feedback resistance, wherein the feedback The resistance is a variable resistance.

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