CN210036902U

CN210036902U - Digital liquid level sensor based on magnetoresistive sensor cross point array

Info

Publication number: CN210036902U
Application number: CN201920269522.XU
Authority: CN
Inventors: 詹姆斯·G·迪克; 伊拉姆帕瑞蒂·维斯瓦纳坦
Original assignee: MultiDimension Technology Co Ltd
Current assignee: MultiDimension Technology Co Ltd
Priority date: 2019-03-04
Filing date: 2019-03-04
Publication date: 2020-02-07
Anticipated expiration: 2029-03-04

Abstract

The utility model discloses a digital level sensor based on magnetoresistive sensor crosspoint array, include: a plurality of TMR magnetic sensor chips; the microcontroller is electrically connected with the row decoder and the column decoder; the TMR magnetic sensor chip comprises a plurality of MTJ elements, a diode is connected between each row of MTJ elements and a row lead or a column lead, and the TMR magnetic sensor chip is addressed through data decoded by a row decoder and a column decoder based on the formula Address ═ m + [ Mx (n-1) ], wherein the Address represents an Address value, and m represents a current row value; the microcontroller is used for scanning the address of the TMR magnetic sensor chip, finding out the address of the MTJ element in the highest activation state, converting the address value into a liquid level value in linear proportion relation with the address value, and transmitting the liquid level value to the output interface; a permanent magnet and a protective tube. The power consumption of the sensor elements is greatly minimized by powering only one sensor chip element at a time.

Description

Digital liquid level sensor based on magnetoresistive sensor cross point array

Technical Field

The utility model relates to a digital liquid level measurement system, more specifically say, especially relate to a digital liquid level sensor based on magnetoresistive sensor crosspoint array.

Background

The use of magnetic field sensors for level sensors is well known in the art. The most common sensors (e.g. reed switch) are arranged in a linear array in a tube immersed in the liquid, and a permanent magnet is attached to a float which moves along the outside of the tube as the level of the liquid surface changes and then uses electronics to determine which switches are closed by the permanent magnet to determine the level of the liquid.

In patent application publication WO2015/034656, a typical example "resistive level/temperature sensor and transmitter" is shown, in which an array of reed switches is attached to an array of series resistors, such that when the reed switches are activated by a permanent magnet, it shorts a portion of the array of resistors to ground, changing the resistance of the array in linear proportion to the level of the liquid being measured. Thus, the array resistor provides a simple way of measuring the liquid level. This classical design has low resolution due to the large size of the reed switch, is easily damaged due to the glass encapsulation of the reed switch and the mechanical properties of the switch mechanism, and is expensive to assemble. In addition, since the readout is impedance-type, it is sensitive to noise and temperature, and therefore requires calibration of the thermometer.

To overcome the drawbacks of the impedance design, other level sensors are designed to detect the digital state of the reed switch, including open or closed. The difficulty with this design is solving the problem of a large number of reed switches. One common approach is to use a cross-point array structure, with each reed switch located at the intersection of a row and column lead in an array of row and column leads. Since the reed switch has an infinite resistance value in the open state and a very small resistance value in the closed state, which switch in the array is closed can be detected by scanning all possible row and column leads. One typical example is the canadian patent publication CA2,179,457, "method and apparatus for measuring fluid level using a level indicator gauge having a reed switch that determines the position of a magnetic float," which designs the reed switch with the disadvantages that the reed switch is fragile and expensive to assemble, resolution is limited by the relatively large size of the reed switch, and due to leakage currents in the cross-point array, cannot be applied to sensors that do not have infinite resistance in the open state, which relies on the use of a two-port sensor with a change in resistance, a typical three-port magnetic switch other than a reed switch providing a voltage output rather than a change in resistance.

Since reed switches are fragile and result in expensive manufacturing costs, it is often desirable to use a magnetoresistive sensor or a hall sensor to detect the position of a magnetic float in a liquid level sensor. Magnetoresistive switch sensors are often used as a replacement for reed switch to perform measurements. The output of the switch sensor is typically a digital voltage, making it useful for linear resistive array level sensor complexes, but they are useful for digital architectures. In the patent application "digital level sensor" published as WO2014/114259, a digital level sensor design using magnetoresistive switches is disclosed. In this design, the digital output of the level sensor is connected to the encoder such that the digital value of the encoder represents the position of the highest activated reluctance switch. This is a simple robust design, but it suffers from high power consumption due to the need to power all digital switches simultaneously. To address this problem, level sensors can be developed with small passive two-port MTJ elements arranged in a cross-point array.

SUMMERY OF THE UTILITY MODEL

In order to overcome the above-mentioned problem among the prior art, the utility model provides a digital level sensor based on magnetoresistive sensor crosspoint array to realize reducing the average power consumption of sensor element, and still simplified the digital circuit requirement of handling every sensor output. Adding diodes in series with the MTJ elements allows multiple arrays of small passive MTJ elements to be arranged in a cross-point lattice column architecture. In addition, because passive sensor elements are used, small bare sensor slices may be used, sensors arranged in level sensors using chip-on-board (COB) technology or other small Chip Scale Packages (CSP). In addition, arranging multiple sensor chips within a single slice may increase sensor measurement resolution.

The embodiment of the utility model provides a digital level sensor based on magnetoresistive sensor crosspoint array, include: the TMR magnetic sensor comprises a PCB, a plurality of TMR magnetic sensor chips arranged on the PCB, M row lead wires and N column lead wires arranged on the PCB, wherein M and N are integers more than or equal to 1;

the PCB is provided with a microcontroller, a row decoder and a column decoder, wherein the microcontroller is electrically connected with the row decoder and the column decoder; a column decoder is connected to the TMR magnetic sensor chip by a column lead, a row decoder is connected to the TMR magnetic sensor chip by a row lead, each TMR magnetic sensor chip comprises a plurality of MTJ elements, the MTJ elements are electrically connected in an array of M rows by N columns of MTJ elements, a diode is connected between each row of MTJ elements and the row lead or the column lead, the TMR magnetic sensor chip is addressed by data decoded by the row decoder and the column decoder and based on the formula Address ═ M + [ M x (N-1) ], where Address represents an Address value, where M represents a value of a current row, ranging from: m is greater than or equal to 1 and less than or equal to M, n represents the value of the current column, and the range is: n is more than or equal to 1 and less than or equal to N;

the microcontroller is used for scanning the address of the TMR magnetic sensor chip, finding out the address of the MTJ element in the highest activation state, converting the address value into a liquid level value in linear proportion relation with the address value, and transmitting the liquid level value to the output interface;

the permanent magnet is attached to the magnetic floater, moves along the long axis direction of the PCB and changes the magnetic field state of the MTJ element near the permanent magnet, and the magnetic floater floats along with the liquid surface immersed by the liquid level sensor;

and a protection pipe surrounding the PCB.

Further, one end of each row of MTJ elements on each of the TMR magnetic sensor chips is electrically connected to one or more column lead pads, one or more column lead pads are all connected to one column lead, and the other end of each row of MTJ elements is respectively electrically connected to one row lead pad.

Further, each row of MTJ elements comprises one MTJ element or a string of MTJ elements formed of at least two MTJ elements connected in series.

Further, the PCB board is a flexible PCB board.

Further, the TMR sensor chip is connected to the PCB board by wire bonding or flip chip, and has a linear or bipolar response.

Further, the diode is integrated on the TMR magnetic sensor chip and connected in series between each row of MTJ elements and a row lead pad disposed in the row.

Further, the diode is integrated on the TMR magnetic sensor chip and connected in series between each row of MTJ elements and a column lead pad electrically connected thereto.

Further, the device also comprises a row selection MOSFET, a column selection MOSFET and a comparison circuit; the drain of the row selection MOSFET is electrically connected to the row lead, the gate of the row selection MOSFET is connected to the output terminal of the row decoder, the source of the row selection MOSFET is connected in series to one end of a first resistor R1 and a first input terminal of the comparison circuit, and the electrical node between the row selection MOSFET and the first resistor R1 is output as an output voltage V_outThe other end of the first resistor R1 is connected to a power supply voltage VCC; the column decoder is electrically connected with the grid electrode of the column selection MOSFET; two second resistors R2 are connected in series between the power supply voltage VCC and ground, and the middle point of the two second resistors R2 outputs the reference voltage V_refAnd is connected to a second input terminal of the comparison circuit, an output terminal of the comparison circuit is electrically connected with the microcontroller, and the comparison circuit outputs a voltage V_outLess than reference voltage V_refTime-out high level signal value, at output voltage V_outGreater than or equal to reference voltage V_refA low level signal value is output, wherein the output level signal value represents an activation value of an MTJ element in the TMR sensor chip being addressed.

Further, zero level setting means are included for setting the liquid level in a zero filling level state when no MTJ element is activated and the magnetic float position is at the bottom most position past the sensor.

Further, the magnetic field generated by the permanent magnet activates the MTJ elements over a distance greater than the separation between the two MTJ elements but less than the three MTJ element separation, and the fill level value is calculated by inserting the permanent magnet between the two MTJ elements.

Further, the TMR sensor chip selects a magnetoresistive sensor chip having two ports.

Further, the TMR sensor chip is packaged by CSP.

The embodiment of the utility model provides a digital level sensor based on magnetoresistive sensor cross point array, through utilizing a small amount of parts and through only supplying power for a sensor chip component once and greatly minimize sensor element's consumption. The utility model discloses a digital level sensor accomplishes the digital measurement of liquid level through reliable, quick and low cost's mode.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

Fig. 1 is a schematic partial cross-sectional view of a digital liquid level sensor based on a cross-point array of magnetoresistive sensors according to an embodiment of the present invention;

fig. 2 is a block diagram of a digital liquid level sensor based on a cross-point array of magnetoresistive sensors according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of a chip-on-board layout of a TMR magnetic sensor chip for placing several MTJ elements;

fig. 4 is a schematic diagram of a connection structure of a TMR magnetic sensor chip and row and column pads according to an embodiment of the present invention;

fig. 5 is a schematic diagram of another connection structure of a TMR magnetic sensor chip and row and column pads according to an embodiment of the present invention;

fig. 6 is a schematic diagram of another connection structure of a TMR magnetic sensor chip and row and column pads according to an embodiment of the present invention;

fig. 7 is a schematic diagram illustrating a layout of a PCB according to an embodiment of the present invention;

fig. 8 is a schematic diagram of another PCB layout according to an embodiment of the present invention;

fig. 9 is a schematic diagram of a switching circuit of a cross-point architecture magnetoresistive sensor configuration and a row-column lead arrangement according to an embodiment of the present invention;

fig. 10 is a schematic diagram of a cross-point architecture magnetoresistive sensor according to an embodiment of the invention, linearized along a long axis of a PCB board.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.

Fig. 1 is the embodiment of the utility model provides a digital level sensor's based on magnetic resistance sensor crosspoint array local cross section schematic diagram, fig. 2 is the embodiment of the utility model provides a digital level sensor's based on magnetic resistance sensor crosspoint array structural block diagram, refer to fig. 1 and fig. 2, this digital level sensor based on magnetic resistance sensor crosspoint array includes: a PCB board 8, a plurality of TMR magnetic sensor chips 1 disposed on the PCB board 8, M row leads (not shown) and N column leads (not shown) disposed on the PCB board 8, wherein M and N are integers of 1 or more;

a microcontroller 5 is arranged on the PCB 8, and the microcontroller 5 is used for scanning the address of the TMR magnetic sensor chip 1, finding out the address of the MTJ element in the highest activation state, converting the address value into a liquid level value in a linear proportional relation with the address value, and transmitting the liquid level value to the output interface 4;

wherein the MTJ element of the highest activation state may be an MTJ element closest to a liquid level height among the MTJ elements that are activated. A row decoder 41 and a column decoder 42 may be included in the digital logic circuit 3. The output interface 4 of the digital sensor may be an I/O interface in the form of an IC chip or an interface board, etc.

Referring to fig. 1, PCB board 8 can be selected to the bar, and then conveniently makes level sensor into the bar, makes things convenient for level sensor to the detection of liquid level, the experience effect when promoting the user to use.

Referring to fig. 1, the level sensor further comprises a switching circuit 7. The TMR magnetic sensor chips 1 are arranged on a strip-shaped PCB board 8, wherein the microcontroller 5 scans the addresses of the TMR magnetic sensor chips 1, in particular the addresses of the MTJ elements each TMR magnetic sensor chip 1 comprises, and finds the address of the MTJ element in the highest activation state, and records the state of each MTJ element in each TMR magnetic sensor chip simultaneously with the output interface 4 (which may be, for example, the above-mentioned I/O interface), including the activated state and the inactivated state, and as mentioned above, the MTJ element in the highest activation state may be the MTJ element closest to the liquid level height among the activated MTJ elements.

The PCB 8 is a flexible PCB. The strip-shaped PCB 8 is placed in the protective tube 31, meanwhile, the permanent magnet 10 is attached to the magnetic floater 11, and the magnetic floater 11 floats along with the liquid surface immersed by the liquid level sensor; the permanent magnet 10 and the magnetic float 11 are also placed outside the protective tube 31. The permanent magnet 10 moves along the long axis direction of the PCB board 8 and changes the magnetic field state of the TMR magnetic sensor chip in the vicinity of the permanent magnet, and the permanent magnet also floats up and down with respect to the liquid surface.

The distance of the MTJ elements in the TMR magnetoresistive sensor chip 1 along the long axis of the strip PCB, the size of the TMR magnetoresistive sensor chip 1 and the size of the floating permanent magnet 10 determine the measurement accuracy for achieving the liquid level measurement. The top end of the strip-shaped PCB board is provided with a microcontroller 5 and other digital logic circuits with I/O interfaces. These digital Logic circuits, such as row decoders and column decoders, may be programmed on a Complex Programmable Logic Device (CPLD) IC 6 shown in fig. 1 for selecting the row leads and column leads of the MTJ elements. The microcontroller 5 provides address inputs to the row and column decoder select lines, the outputs of the row decoder and the column decoder for driving a particular MTJ element to activate the particular MTJ element. The state of the TMR magnetic sensor chip excited will be recorded by the microcontroller 5 and the MTJ element activated will be recorded by the microcontroller 5.

FIG. 3 is a schematic diagram of a chip-on-board layout of a TMR magnetic sensor chip for placing several MTJ elements; as shown in fig. 3, the chip-on-board pad may accommodate 16 TMR magnetoresistive sensor chips, which may be used for the design of MTJ elements including 16 × 16. Here the package pad has one column lead pad 12 to commonly connect one end of all 16 MTJ elements and a separate row lead pad 13 to connect the other end of each 16 MTJ elements. In each row of wires, a number of bonding pads 14 may also be included, and these bonding pads 14 are used for series connection of the MTJ element strings in each row arrangement by wire bonding to form a single row of MTJ element strings.

Fig. 4 is a schematic diagram of a connection structure of a TMR magnetic sensor chip and row and column pads provided in an embodiment of the present invention, in which the structure of the corresponding diode 9 is in the form of an on-chip diode; one end of each row of MTJ elements 16 on each TMR magnetic sensor chip is electrically connected to one or more column lead pads 12, one or more column lead pads 12 are connected to one column lead, and the other end of each row of MTJ elements is electrically connected to one row lead pad 13, respectively.

The utility model discloses the PCB Board adopts chip-on-Board Package (Chips on Board, COB) or chip level Package (Chips Package, CSP) technique, the utility model discloses use COB packaging technology as an example, COB packaging pad that wherein the TMR sensor chip used has a row lead wire pad and is connected to a plurality of lines lead wire pads of row lead wire pad. Wherein the number of COB package pads corresponds to the number of column elements. The MTJ element is provided on the TMR magnetic sensor chip 1, and pads are provided to accommodate a plurality of MTJ elements. A pad used in a TMR magnetic sensor chip has a column lead pad and M row lead pads for designing M x N array type MTJ elements. The plurality of TMR magnetic sensor chips are arranged linearly in the long axis direction of the PCB board, and a plurality of MTJ elements included therein are connected in a cross point structure. The number of TMR magnetic sensor chips corresponds to the number of columns of MTJ elements.

Referring to fig. 4, fig. 4 is schematically illustrated with each row of MTJ elements including one MTJ element. A diode 9 is integrated on the TMR magnetic sensor chip and connected in series between each row of MTJ elements and a row lead pad 13 provided in the row. The row lead pad 13 is connected to the diode 9, wherein the diode 9 acts as a barrier to prevent current flow into the unselected MTJ elements.

Fig. 5 is a schematic diagram of another connection structure of a TMR magnetic sensor chip and row and column pads according to an embodiment of the present invention; the structure of its corresponding diode 9 is in the form of an off-chip diode.

Fig. 6 is a schematic diagram of another connection structure of the TMR magnetic sensor chip and the row pad and the column pad according to an embodiment of the present invention, referring to fig. 6, optionally, a diode 9 is integrated on the TMR magnetic sensor chip and connected in series between each row of MTJ elements and the column lead pad 12 electrically connected thereto.

Optionally, each row of MTJ elements comprises one MTJ element or a string of MTJ elements formed by at least two MTJ elements connected in series.

Optionally, the TMR sensor chip is connected to the PCB board by wire bonding or flip chip and has a linear or bipolar response.

Fig. 7 is a schematic diagram of a layout of a PCB according to an embodiment of the present invention; fig. 8 is a schematic diagram of another PCB layout according to an embodiment of the present invention; as shown in fig. 7 and 8, fig. 7 and 8 show a complete schematic of the strip PCB board and the microcontroller unit and other digital logic circuits 3. The MTJ elements of the TMR sensor chips are addressed from the bottom-most MTJ element up to the top-most MTJ element of the TMR sensor chip. In other words, the starting address of the bottom-most sensor is zero, and the top-most sensor has the highest address bits. The strip-shaped PCB may also use TMR switch-type sensor elements other than linear sensor elements. The magnetic orientation of the floating permanent magnet 10 determines the switching properties of the MTJ element in the TMR sensor used on a PCB board. As shown in fig. 7, if the moving direction of the permanent magnet 10 is parallel to the detection axis of the digital sensor (for example, the moving direction of the permanent magnet 10 in fig. 7 is the Y-axis direction and the detection axis of the digital sensor is also the Y-axis, and both are parallel), a single-pole type switching sensor may be used. If the magnetization axis of the permanent magnet 10 is different from the digital sensor detection axis (corresponding to the case shown in fig. 8, the magnetization axis of the permanent magnet 10 is the X axis, and the detection axis of the digital sensor is the Y axis, which are different), a bipolar switching sensor may be used. The location of the MTJ element in the preferred TMR sensor chip is the middle location of the PCB along the X-axis, while wire bonds for the row wire pads, column wire pads, and diodes occupy both side locations of the PCB along the X-axis.

With continued reference to fig. 2, the proposed solution includes different component blocks, such as pads for row and column decoders of the TMR magnetic sensor chip and a microcontroller unit for scanning and reading the state of the TMR magnetic sensor chip. FIG. 2 is schematically illustrated with a digital sensor comprising 1024 MTJ elements, which can be expressed as 2 of 10 bytes in length¹⁰. The row and column leads being separated and sharing the same number of 2⁵A bit line. Thus, in this case, the row and column leads are 32 x 32, which can produce 1024 possible combinations. Each MTJ element is addressed using row and column decoders. Changes in the state or value of the TMR magnetic sensor chip may be read on the row leads, and the comparator further compares the value with its reference value and provides a digital output that is read by the microcontroller at a later time.

Fig. 9 is a schematic diagram of a switch circuit of a cross-point architecture magnetoresistive sensor configuration and a row-column lead arrangement according to an embodiment of the present invention, where the switch circuit is a part of a digital liquid level sensor based on a cross-point array of magnetoresistive sensors, and fig. 9 is a schematic diagram of a PCB layout taking a 3 × 3MTJ element 16 configured in a cross-point architecture as a digital liquid level sensor as an example, referring to fig. 9, optionally, the digital liquid level sensor based on a cross-point array of magnetoresistive sensors further includes a row selection MOSFET44, a column selection MOSFET7, and a comparison circuit 24; the drain of the row select MOSFET44 is electrically connected to the row lead, the gate of the row select MOSFET7 is connected to the output terminal of the row decoder (not shown in the figure), the source of the row select MOSFET44 is connected in series to one end of a first resistor R1 and a first input terminal of the comparison circuit 24, the electrical node between the row select MOSFET44 and a first resistor R1 outputs the output voltage Vout, and the other end of the first resistor R1 is connected to the power supply voltage VCC; a column decoder (not shown) is electrically connected to the gate of column select MOSFET 7; two second resistors R2 are connected in series between the power supply voltage VCC and the ground, the middle point of the two second resistors R2 outputs the reference voltage Vref and is connected to the second input terminal of the comparison circuit 24, the output terminal Gout of the comparison circuit is electrically connected to a microcontroller (not shown in the figure), the comparison circuit 24 outputs a high level signal value when the output voltage Vout is less than the reference voltage Vref and outputs a low level signal value when the output voltage Vout is equal to or greater than the reference voltage Vref, wherein the output level signal value represents the activation value of the MTJ element in the addressed TMR sensor chip.

Fig. 10 is a schematic diagram of a cross-point architecture magnetoresistive sensor according to an embodiment of the invention, linearized along a long axis of a PCB board. As shown in fig. 10, fig. 10 depicts how a cross-point architecture magnetoresistive sensor is linearized along the long axis of a strip PCB board and shows the sensor wiring arrangement and its respective switching circuitry. For example, fig. 10 shows 3 × 3MTJ elements, wherein each 3 columns of MTJs belong to one element block, and fig. 10 is schematically illustrated by including three

element blocks

451, 452, 453, each corresponding to one column lead, and the corresponding rows of each element block are connected to the same row lead. One end of each MTJ element 16 of the column leads in each element block is connected together, and the other end of each MTJ element 16 is connected to the corresponding row lead, as illustrated by the row leads being m, (m +1) and (m +2), and the column leads being n, (n +1) and (n +2), where m is greater than or equal to 1 and n is greater than or equal to 1. The column leads are ultimately connected to ground and the row leads are connected to VCC. Where the row lead is connected to a power supply VCC through a reference resistor R1, the change in sensor resistance caused by an external magnetic field is detected by the row lead. Another combination is possible by connecting VCC to the column lead and the row lead to ground, and detecting a change in sensor resistance on the column lead that is connected to VCC through a reference resistance R1. The calculation order address values for the 3 × 3 case are shown in table 1 below:

TABLE 1

The sequential address values in Table 1 are calculated using the sum of the current row number and the sum of the products of the total number of rows and the previous column number, expressed as:

addressing the TMR magnetic sensor chip by the data decoded by the row decoder and the column decoder and based on the formula Address ═ m + [ M x (n-1) ], where Address represents the Address value, where m represents the value of the current row, in the range: m is greater than or equal to 1 and less than or equal to M, n represents the value of the current column, and the range is: n is more than or equal to 1 and less than or equal to N. The microcontroller scans the address of the TMR magnetic sensor chip 1 and finds the address of the highest active TMR magnetic sensor chip 1 and converts this address into a level value, which is then passed to the output interface.

The percentage of liquid fill level corresponding to the address value can then be calculated using the product of the address value divided by the product of the total number of row and column elements, the relationship for calculating the fill level being expressed as:

where Fill Level represents Fill Level, Adress value represents address value, Total Columns represents Total Rows, Total Rows represents Total Columns.

The level fill value is linearly proportional to the sequential address values. When no sensor element is in the active state and the magnetic float passes the magnetic sensor, the liquid level sensor enters a default state of zero fill level.

In a practical design, the sensor elements activated by selecting the N column leads and the M row leads should occupy the bottom most position of the PCB board, and the sensor elements activated by selecting (N +2) and (M +2) should be located at the top most position of the PCB board. The above is the setting situation of the MTJ elements for the 3 × 3 array, and the present invention can also set different array forms as needed.

The embodiment of the utility model provides a digital level sensor based on magnetoresistive sensor cross point array still includes zero liquid level setting device, is activated and when the magnetism float position was located bottommost position through the sensor when not having the MTJ element, and zero liquid level setting device sets for the liquid level and is in zero filling liquid level state.

Optionally, the TMR sensor chip selects a magnetoresistive sensor chip having two ports.

Optionally, the magnetic field generated by the permanent magnet activates the MTJ elements over a distance greater than the separation between the two MTJ elements but less than the separation between the three MTJ elements, and the fill level value is calculated by inserting the permanent magnet between the two MTJ elements, and the specific activation sensor versus fill level can be seen in table 2. In this case, when two adjacent MTJ elements are activated, the microcontroller may insert a magnet having a height equal to the height of the equidistant point between the two MTJ elements. When only one MTJ element is activated, then the liquid level is presumed to be at the location of the single activated MTJ element. Table 2 below shows the relationship of the address value and the fill percentage value conversion for the computational interpolation method based on the number of activated row and column sensor elements of the 3 x 3MTJ element.

TABLE 2

For the above case shown in table 2, the fill value starts from zero when the first element is activated by the floating magnet, which is just adjacent to the first sensor, and vice versa, reaching 100% liquid fill in the case of the highest MTJ element. For the case where the float magnet is below the bottom-most sensor element or the top-most sensor element, the address value is considered to be invalid.

The address values of table 2 may be expressed as:

Adress value＝2*[RSA+(Total Rows)*(CSA-1)],

wherein RSA can be calculated according to the following formula:

and CSA can be calculated according to the following formula:

where the terms sum (m) are defined as the sum of the row sensors that are operational, sum (n) are defined as the sum of the column sensors that are operational, ACTCols are defined as the number of active column sensors, ACTRows are defined as the number of active row sensors, and Ceil [ ] represents a round-robin.

To convert the above address values into percentage filling levels, the following formula is used:

Optionally, the TMR sensor chip is packaged by CSP.

Based on the embodiments of the present invention, all other embodiments obtained by a person of ordinary skill in the art without creative efforts belong to the protection scope of the present invention. Although the invention has been shown and described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.

Claims

1. A digital liquid level sensor based on a cross-point array of magnetoresistive sensors, comprising: the TMR magnetic sensor comprises a PCB, a plurality of TMR magnetic sensor chips arranged on the PCB, and M row lead wires and N column lead wires arranged on the PCB, wherein M and N are integers more than or equal to 1;

the microcontroller, the row decoder and the column decoder are arranged on the PCB and electrically connected with the row decoder and the column decoder; the column decoder is connected with the TMR magnetic sensor chip through the column lead wire, the row decoder is connected with the TMR magnetic sensor chip through the row lead wire, each TMR magnetic sensor chip comprises a plurality of MTJ elements, the MTJ elements are electrically connected into an array of MTJ elements of M rows and N columns, and a diode is connected between each row of MTJ elements and the row lead wire or the column lead wire; the permanent magnet is attached to the magnetic floater, moves along the long axis direction of the PCB and changes the magnetic field state of the MTJ element near the permanent magnet, and the magnetic floater floats along the liquid surface immersed by the liquid level sensor;

a protection tube surrounding the PCB.

2. The digital level sensor based on a magnetoresistive sensor cross-point array of claim 1, wherein one end of each row of MTJ elements on each TMR magnetic sensor chip is electrically connected to one or more column lead pads, one or more column lead pads are connected to one column lead, and the other end of each row of MTJ elements is electrically connected to one row lead pad, respectively.

3. Digital liquid level sensor based on a magnetoresistive sensor cross-point array according to claim 2, characterized in that each row of MTJ elements comprises one MTJ element or a string of MTJ elements formed by at least two MTJ elements connected in series.

4. A magnetoresistive sensor cross-point array-based digital liquid level sensor as claimed in claim 1, wherein the PCB is a flexible PCB.

5. A magnetoresistive sensor cross-point array based digital liquid level sensor according to claim 1, where the TMR magnetic sensor chip is connected to the PCB board by wire bonding or flip chip and has a linear or bipolar response.

6. A magnetoresistive sensor cross-point array based digital liquid level sensor according to claim 3, characterized in that the diode is integrated on the TMR magnetic sensor chip and connected in series between each row of MTJ elements and the row lead pads arranged in that row.

7. A magnetoresistive sensor cross-point array based digital liquid level sensor according to claim 3, characterized in that the diode is integrated on the TMR magnetic sensor chip and connected in series between each row of MTJ elements and the column lead pad electrically connected thereto.

8. The magnetoresistive sensor cross-point array-based digital liquid level sensor of claim 2, further comprising a row select MOSFET, a column select MOSFET, and a comparison circuit; the drain of the row selection MOSFET is electrically connected to the row lead, the gate of the row selection MOSFET is connected to the output terminal of the row decoder, the source of the row selection MOSFET is connected in series to one end of a first resistor R1 and a first input terminal of the comparison circuit, and the electrical node between the row selection MOSFET and the first resistor R1 is output as an output voltage V_outThe other end of the first resistor R1 is connected to a power supply voltage VCC; the column decoder is electrically connected with the grid electrode of the column selection MOSFET; two second resistors R2 are connected in series between the power supply voltage VCC and ground, and the middle point of the two second resistors R2 outputs the reference voltage V_refAnd is connected to a second input terminal of the comparison circuit, an output terminal of the comparison circuit is electrically connected with the microcontroller, and the comparison circuit outputs a voltage V_outLess than reference voltage V_refTime-out high level signal value, at output voltage V_outGreater than or equal to reference voltage V_refA time-out low level signal value, wherein the output level signal value indicates that the signal is being outputThe activation value of the MTJ element in an addressed TMR magnetic sensor chip.

9. The magnetoresistive sensor cross-point array-based digital liquid level sensor of claim 1, further comprising a zero level setting device that sets the liquid level in a zero fill level state when no MTJ element is activated and the magnetic float position is at a bottom-most position past the sensor.

10. The digital level sensor based on a cross-point array of magnetoresistive sensors as claimed in claim 1 wherein the TMR magnetic sensor chip selects a two-port magnetoresistive sensor chip.

11. A magnetoresistive sensor cross-point array based digital liquid level sensor according to claim 1, characterized in that the TMR magnetic sensor chip is packaged by CSP.