CN112294279B - Integrated invasive blood pressure sensor - Google Patents
Integrated invasive blood pressure sensor Download PDFInfo
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- CN112294279B CN112294279B CN202011177844.5A CN202011177844A CN112294279B CN 112294279 B CN112294279 B CN 112294279B CN 202011177844 A CN202011177844 A CN 202011177844A CN 112294279 B CN112294279 B CN 112294279B
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- 230000036772 blood pressure Effects 0.000 title claims abstract description 49
- 239000010409 thin film Substances 0.000 claims abstract description 119
- 238000004806 packaging method and process Methods 0.000 claims abstract description 37
- 229920000106 Liquid crystal polymer Polymers 0.000 claims abstract description 36
- 239000004977 Liquid-crystal polymers (LCPs) Substances 0.000 claims abstract description 35
- 238000000034 method Methods 0.000 claims abstract description 32
- 239000007788 liquid Substances 0.000 claims abstract description 28
- 230000008569 process Effects 0.000 claims abstract description 24
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims description 24
- 238000006243 chemical reaction Methods 0.000 claims description 15
- 239000004408 titanium dioxide Substances 0.000 claims description 12
- 238000004891 communication Methods 0.000 claims description 11
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 10
- 238000005538 encapsulation Methods 0.000 claims description 10
- 229910052719 titanium Inorganic materials 0.000 claims description 10
- 239000010936 titanium Substances 0.000 claims description 10
- 239000000758 substrate Substances 0.000 claims description 9
- 230000008054 signal transmission Effects 0.000 claims description 3
- 239000012528 membrane Substances 0.000 description 18
- 239000010408 film Substances 0.000 description 16
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 9
- 229910052710 silicon Inorganic materials 0.000 description 9
- 239000010703 silicon Substances 0.000 description 9
- 238000005516 engineering process Methods 0.000 description 6
- 238000010586 diagram Methods 0.000 description 3
- 238000002360 preparation method Methods 0.000 description 3
- 238000007789 sealing Methods 0.000 description 3
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 210000004369 blood Anatomy 0.000 description 2
- 239000008280 blood Substances 0.000 description 2
- 210000001124 body fluid Anatomy 0.000 description 2
- 239000010839 body fluid Substances 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 230000001105 regulatory effect Effects 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 241001465754 Metazoa Species 0.000 description 1
- 230000004075 alteration Effects 0.000 description 1
- 238000009530 blood pressure measurement Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000000750 progressive effect Effects 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 230000011664 signaling Effects 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
- A61B5/021—Measuring pressure in heart or blood vessels
- A61B5/0215—Measuring pressure in heart or blood vessels by means inserted into the body
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
- A61B5/021—Measuring pressure in heart or blood vessels
- A61B5/0215—Measuring pressure in heart or blood vessels by means inserted into the body
- A61B5/02156—Calibration means
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- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Cardiology (AREA)
- Heart & Thoracic Surgery (AREA)
- Molecular Biology (AREA)
- Physiology (AREA)
- Biophysics (AREA)
- Pathology (AREA)
- Engineering & Computer Science (AREA)
- Biomedical Technology (AREA)
- Vascular Medicine (AREA)
- Medical Informatics (AREA)
- Physics & Mathematics (AREA)
- Surgery (AREA)
- Animal Behavior & Ethology (AREA)
- General Health & Medical Sciences (AREA)
- Public Health (AREA)
- Veterinary Medicine (AREA)
- Measuring Pulse, Heart Rate, Blood Pressure Or Blood Flow (AREA)
- Measuring Fluid Pressure (AREA)
Abstract
The invention provides an integrated invasive blood pressure sensor, comprising: the thin film piezoresistive bridge is configured as a Wheatstone balance bridge and consists of two interdigital thin film piezoresistors which are not connected with each other and two single strip thin film piezoresistors which are not connected with each other, and when the resistance value of the two interdigital thin film piezoresistors is a steady state value, the two voltages output by the thin film piezoresistive bridge are equal; an integrated die configured to process a voltage output by the thin film piezoresistive bridge; the liquid crystal polymer comprises a first packaging area and a second packaging area, wherein the first packaging area bears two interdigital thin film piezoresistors, and the second packaging area bears two single strip thin film piezoresistors and the integrated chip, and the first packaging area bears two interdigital thin film piezoresistors, and the second packaging area bears two single strip thin film piezoresistors and the integrated chip, wherein: the bottom of the first packaging area is a U-shaped pressure acting cavity, the pressure acting cavity is in contact with liquid, and the pressure formed by the liquid is conducted to the interdigital thin film piezoresistor through the pressure acting cavity, so that the resistance value of the interdigital thin film piezoresistor is changed.
Description
Technical Field
The invention relates to the technical field of blood pressure sensors, in particular to an integrated invasive blood pressure sensor.
Background
Because silicon-based piezoresistive pressure sensing technology is compatible with integrated circuit technology and is easy to achieve miniaturization, the technology is widely applied to the field of invasive blood pressure sensors. However, such a sensor has disadvantages of poor linearity, small measurement range, and additional design of an external wired circuit for an application process, so that it is limited in the application process. For example, bridge arm resistance values in different silicon processes may deviate by up to 20% from nominal values, resulting in a large zero-point imbalance of the bridge output, and thus a large linearity error. The current methods for optimizing the performance of the pressure sensor are various, including solving the linearity problem by using a zero-pressure offset compensation resistor technology, correcting a thin film resistor network by using laser, compensating an external resistor and the like; and shielding wires are adopted in signal transmission to reduce transmission interference and the like. However, by adopting any process method, the problems caused by the defects of uneven thickness of the silicon cup, chamfer of the silicon cup, larger thickness tolerance of the silicon film and the like in the process of the semiconductor silicon process are difficult to completely overcome. Meanwhile, the process compensation method and the anti-interference measure are required to relate to additional multi-process technology, and finally the product yield of the invasive blood pressure sensor is reduced.
Disclosure of Invention
The invention aims to provide an integrated invasive blood pressure sensor so as to solve the problem that the output of the traditional invasive blood pressure sensor bridge has larger zero point offset so as to cause linear error.
In order to solve the above technical problems, the present invention provides an integrated invasive blood pressure sensor, comprising:
The thin film piezoresistive bridge is configured as a Wheatstone balance bridge and consists of two interdigital thin film piezoresistors which are not connected with each other and two single strip thin film piezoresistors which are not connected with each other, and when the resistance value of the two interdigital thin film piezoresistors is a steady state value, the two voltages output by the thin film piezoresistive bridge are equal;
an integrated die configured to process a voltage output by the thin film piezoresistive bridge;
The liquid crystal polymer comprises a first packaging area and a second packaging area, wherein the first packaging area bears two interdigital thin film piezoresistors, and the second packaging area bears two single strip thin film piezoresistors and the integrated chip, and the first packaging area bears two interdigital thin film piezoresistors, and the second packaging area bears two single strip thin film piezoresistors and the integrated chip, wherein:
the bottom of the first packaging area is a U-shaped pressure acting cavity, the pressure acting cavity is in contact with liquid, and the pressure formed by the liquid is conducted to the interdigital thin film piezoresistor through the pressure acting cavity, so that the resistance value of the interdigital thin film piezoresistor is changed.
Optionally, in the integrated invasive blood pressure sensor, the interdigital thin film piezoresistor includes a first piezoresistor component and a second piezoresistor component, wherein:
the first piezoresistive component and the second piezoresistive component are comb-shaped, and the comb teeth of one of the first piezoresistive component and the second piezoresistive component are inserted between the tooth spaces of the other of the first piezoresistive component and the second piezoresistive component to form an crossed arrangement.
Optionally, in the integrated invasive blood pressure sensor, the interdigital thin film piezoresistor and the single strip thin film piezoresistor both comprise a titanium thin film layer and a titanium dioxide thin film which are overlapped,
The titanium thin film layer is arranged between the substrate of the liquid crystal polymer and the titanium dioxide thin film;
the resistance values of the two interdigital thin film piezoresistors and the two single strip thin film piezoresistors are consistent.
Optionally, in the integrated invasive blood pressure sensor, the method further includes:
A first encapsulation layer configured to seal the first encapsulation region to form a first cavity, the two interdigital thin film piezoresistors being contained within the first cavity;
And the second packaging layer is configured to seal the second packaging region to form a second cavity, and two single strip thin film piezoresistors and integrated chips are accommodated in the second cavity.
Optionally, in the integrated invasive blood pressure sensor, the first cavity is filled with an insulating liquid, and the insulating liquid conducts the pressure on the surface of the first cavity to the two interdigital thin film piezoresistors.
Optionally, in the integrated invasive blood pressure sensor, the integrated chip is integrated on the substrate of the liquid crystal polymer through a CMOS process, including:
the differential operational amplifier circuit is configured to amplify the voltage generated by the thin film piezoresistive bridge to form an analog amplified signal;
the analog-to-digital conversion circuit is configured to filter, sample, hold and encode the analog amplified signal and then convert the analog amplified signal into a digital signal;
a communication circuit configured to transmit the digital signal to a receiving device;
a calibration digital-to-analog conversion circuit configured to adjust the voltage output by the differential operational amplifier circuit to zero when the pressure of the liquid is not received by the pressure acting cavity;
and the state machine is configured to process the digital signal, judge whether the calibration digital-to-analog conversion circuit is calibrated in place according to the digital signal, and control the signal transmission of the communication circuit.
Optionally, in the integrated invasive blood pressure sensor, the communication circuit includes an SPI interface, an I2C interface, a USB interface, a UART interface, an RS-485 interface, a CAN-bus interface, and/or a radio frequency chip.
Optionally, in the integrated invasive blood pressure sensor, the differential operational amplifier circuit is a chopper-stabilized operational amplifier.
Optionally, in the integrated invasive blood pressure sensor, the thin film piezoresistive bridge further includes a constant current source formed by an MOS tube.
Optionally, in the integrated invasive blood pressure sensor, during the calibration process, the calibration digital-to-analog conversion circuit outputs an analog voltage, and the analog voltage is applied to any one of the connection parts of the two interdigital thin film piezoresistors and the single strip thin film piezoresistor, so that the two voltages output by the thin film piezoresistor bridge are equal.
In the integrated invasive blood pressure sensor provided by the invention, the membrane piezoresistive bridge is formed by two mutually unconnected interdigital membrane piezoresistors and two mutually unconnected single-strip membrane piezoresistors, the first packaging area bears the two interdigital membrane piezoresistors, the second packaging area bears the two single-strip membrane piezoresistors and the integrated chip, the bottom of the first packaging area is in contact with liquid through the U-shaped pressure acting cavity, and the pressure formed by the liquid is conducted to the interdigital membrane piezoresistors through the pressure acting cavity, so that the resistance value of the interdigital membrane piezoresistors is changed, the purpose of designing the pressure sensitive resistor by adopting an interdigital structure to form a Wheatstone bridge is realized, the matching of the pressure sensitive resistor in the process preparation process is more facilitated, and the zero point balance of the membrane piezoresistors without external force is ensured to the greatest extent.
Specifically, the titanium film layer is directly plated on the liquid crystal polymer, so that the stress between the titanium dioxide film and the liquid crystal polymer can be effectively buffered, and the adhesiveness between the titanium dioxide film and the liquid crystal polymer is increased, so that the whole piezoresistive structure is more reliable.
The first cavity is filled with an insulating liquid (such as pure water) which conducts the pressure on the surface of the first cavity to the two interdigital thin film piezoresistors. The insulating liquid can more sensitively measure the difference between the internal and external pressure of the first cavity than air. The first cavity can receive external force in 360 degrees in all directions and conduct the external force to the two interdigital thin film piezoresistors through insulating liquid, so that detection is more sensitive.
Because the first cavity is filled with liquid, the 360-degree range around the first cavity can conduct pressure, the pressure can be stressed, conducted and detected in all directions, the pressure measurement is free of dead angles, and the device is suitable for measuring blood pressure in a human body.
Drawings
FIG. 1 is a schematic diagram of an integrated invasive blood pressure sensor circuit in accordance with an embodiment of the present invention;
FIG. 2 is a schematic diagram of the structure of an integrated invasive blood pressure sensor in accordance with an embodiment of the present invention;
FIG. 3 is a schematic top view of an integrated invasive blood pressure sensor structure in accordance with an embodiment of the present invention;
FIG. 4 is a schematic diagram of a thin film piezoresistive bridge circuit integrated with an invasive blood pressure sensor according to an embodiment of the present invention;
The figure shows: 10-thin film piezoresistive bridge; 11-interdigital thin film piezoresistance; 12-single strip thin film piezoresistance; a 20-differential operational amplifier circuit; 30-an analog-to-digital conversion circuit; 40-a communication circuit; 50-state machine; 60-calibrating the digital-to-analog conversion circuit; 71-a substrate of liquid crystalline polymer; 72-a pressure application chamber; 73-a first encapsulation layer; 74-a first cavity; 75-a second encapsulation layer; 76-a second cavity; 100-integrated chip.
Detailed Description
The integrated invasive blood pressure sensor according to the present invention will be described in further detail with reference to the accompanying drawings and specific embodiments. Advantages and features of the invention will become more apparent from the following description and from the claims. It should be noted that the drawings are in a very simplified form and are all to a non-precise scale, merely for convenience and clarity in aiding in the description of embodiments of the invention.
In addition, features of different embodiments of the application may be combined with each other, unless otherwise specified. For example, a feature of the second embodiment may be substituted for a corresponding feature of the first embodiment, or may have the same or similar function, and the resulting embodiment may fall within the scope of disclosure or description of the application.
The invention provides an integrated invasive blood pressure sensor, which aims to solve the problem that the output of the traditional invasive blood pressure sensor bridge has larger zero point offset so as to cause linear error.
To achieve the above idea, the present invention provides an integrated invasive blood pressure sensor, as shown in fig. 2, comprising: the thin film piezoresistive bridge 10 is configured as a Wheatstone balance bridge, and consists of two interdigital thin film piezoresistors 11 which are not connected with each other and two single strip thin film piezoresistors 12 which are not connected with each other, and when the resistance value of the two interdigital thin film piezoresistors 11 is a steady state value, the two voltages output by the thin film piezoresistive bridge 10 are equal; an integrated die 100 configured to process the voltage output by the thin film piezoresistive bridge 10; the liquid crystal polymer comprises a first packaging region and a second packaging region, wherein the first packaging region bears two interdigital thin film piezoresistors 11, and the second packaging region bears two single strip thin film piezoresistors 12 and the integrated chip 100, and the first packaging region bears two interdigital thin film piezoresistors 11, the second packaging region bears two single strip thin film piezoresistors 12 and the integrated chip 100, and the first packaging region comprises: the bottom of the first packaging region is a "U" -shaped pressure acting cavity 72, the pressure acting cavity 72 is in contact with the liquid, and the pressure formed by the liquid is conducted to the interdigital thin film piezoresistor 11 through the pressure acting cavity 72, so that the resistance value of the interdigital thin film piezoresistor 11 is changed.
As shown in fig. 3, in the integrated invasive blood pressure sensor, the interdigital thin film piezoresistor 11 includes a first piezoresistor component and a second piezoresistor component, where: the first piezoresistive component and the second piezoresistive component are comb-shaped, and the comb teeth of one of the first piezoresistive component and the second piezoresistive component are inserted between the tooth spaces of the other of the first piezoresistive component and the second piezoresistive component to form an crossed arrangement. The interdigital thin film piezoresistor 11 and the single strip thin film piezoresistor 12 comprise a titanium thin film layer and a titanium dioxide thin film which are overlapped, wherein the titanium thin film layer is arranged between the substrate 71 of the liquid crystal polymer and the titanium dioxide thin film; the resistance values of the two interdigital thin film piezoresistors 11 and the two single strip thin film piezoresistors 12 are consistent. Specifically, the titanium film layer is directly plated on the liquid crystal polymer, so that the stress between the titanium dioxide film and the liquid crystal polymer can be effectively buffered, and the adhesiveness between the titanium dioxide film and the liquid crystal polymer is increased, so that the whole piezoresistive structure is more reliable.
As shown in fig. 2, in the integrated invasive blood pressure sensor, further includes: a first encapsulation layer 73 configured to seal the first encapsulation region to form a first cavity 74, the two interdigital thin film piezoresistors 11 being housed within the first cavity 74; a second encapsulation layer 75 configured to seal the second encapsulation region to form a second cavity 76, the two monolithic thin film piezoresistors 12 and the integrated die 100 being housed within the second cavity 76. The first cavity is filled with insulating liquid, and the insulating liquid conducts the pressure on the surface of the first cavity to the two interdigital thin film piezoresistors. The first cavity is filled with an insulating liquid (such as pure water) which conducts the pressure on the surface of the first cavity to the two interdigital thin film piezoresistors. The insulating liquid can more sensitively measure the difference between the internal and external pressure of the first cavity than air. The first cavity can receive external force in 360 degrees in all directions and conduct the external force to the two interdigital thin film piezoresistors through insulating liquid, so that detection is more sensitive.
The integrated chip 100 is integrated on the substrate 71 of the liquid crystal polymer through a CMOS process, as shown in fig. 1, and includes: a differential operational amplifier circuit 20 configured to amplify the voltage generated by the thin film piezoresistive bridge 10 to form an analog amplified signal; an analog-to-digital conversion circuit 30 configured to filter, sample hold, and encode the analog amplified signal, and then convert the analog amplified signal into a digital signal; a communication circuit 40 configured to transmit the digital signal to a receiving device; a calibration digital-to-analog conversion circuit 60 configured to adjust the voltage output by the differential operational amplifier circuit 20 to zero when the pressure of the liquid is not received by the pressure application chamber 72; a state machine 50 configured to process the digital signal and determine from the digital signal whether the calibration digital to analog conversion circuit 60 is calibrated in place and to control signaling by the communication circuit 40.
Wherein, in the integrated invasive blood pressure sensor, the communication circuit 40 includes an SPI interface, an I2C interface, a USB interface, a UART interface, an RS-485 interface, a CAN-bus interface and/or a radio frequency chip. In the integrated invasive blood pressure sensor, the differential operational amplifier circuit 20 is a chopper-stabilized operational amplifier, and can amplify weak signals, and has high gain, low temperature drift, high common mode input range and high voltage rejection ratio. As shown in fig. 4, in the integrated invasive blood pressure sensor, the thin film piezoresistive bridge 10 further includes a constant current source formed by MOS transistors, and the current remains stable in a wide power supply voltage range (3 v to 12 v).
In the integrated invasive blood pressure sensor provided by the invention, the membrane piezoresistive bridge 10 is formed by two mutually unconnected interdigital membrane piezoresistors 11 and two mutually unconnected single-strip membrane piezoresistors 12, the first packaging area carries the two interdigital membrane piezoresistors 11, the second packaging area carries the two single-strip membrane piezoresistors 12 and the integrated chip 100, the bottom of the first packaging area is in contact with liquid through the U-shaped pressure acting cavity 72, and the pressure formed by the liquid is conducted to the interdigital membrane piezoresistors 11 through the pressure acting cavity 72, so that the resistance value of the interdigital membrane piezoresistors 11 is changed, the pressure sensitive resistors are designed to form a wheatstone bridge shown in fig. 4 by adopting an interdigital structure, the matching of the pressure sensitive resistors is more facilitated in the process preparation process, and the zero point balance of the membrane piezoresistive bridge 10 without external force is ensured to the maximum extent.
The present invention overcomes the above-described deficiencies of the prior art and provides a miniature, biocompatible, and highly reliable method of designing a wireless, invasive blood pressure sensor comprising three parts, namely a cup-shaped liquid crystal polymer (Liquid Crystal Polymer, LCP) or a cup-shaped LCP, a thin film piezoresistive, and an integrated chip 100. The cup-shaped LCP is a miniature, cup-shaped structure constructed using liquid crystal polymers. For convenience of description, the hollow portion of the lower portion of the cup-shaped LCP is referred to as the pressure-acting chamber 72. The membrane piezoresistor comprises four parts: two identical interdigital thin film piezoresistors R1 and R2, and two identical elongated thin film piezoresistors R3 and R4. The resistance values of the four film piezoresistors are the same; the two interdigital film piezoresistors R1 and R2 are symmetrically prepared on the upper surface of the cup-shaped LCP pressure cavity; two elongated thin film piezoresistors R3 and R4 are prepared on the upper surface of the cup-shaped LCP; the four thin film piezoresistors form a Wheatstone balance bridge 10 as shown in FIG. 4, hereinafter referred to as bridge 10. The interdigital film piezoresistor 11 and the strip film piezoresistor 12 both adopt titanium film/titanium dioxide film laminated structures with good biocompatibility, wherein a titanium film layer is arranged between an LCP substrate and a titanium dioxide film. The cup-shaped LCP upper interdigital thin film resistor is encapsulated by LCP and forms a sealed cavity inside; the upper, elongated thin film piezoresistors 12 and integrated die 100 of the cup-shaped LCP are encapsulated with LCP.
In one embodiment of the present invention, the pressure application chamber 72 is in contact with a subject such as blood or body fluid. The pressure caused by the blood or body fluid is conducted through the LCP pressure apply chamber 72 to the interdigital membrane piezoresistor 11 in the upper sealed cavity, the resistance of which changes with pressure. When no external pressure exists, in theory, no pressure difference exists between the pressure acting cavity 72 and the sealing cavity, the interdigital thin film piezoresistor 11 cannot deform, the bridge 10 balances, and the output voltage of the differential operational amplifier circuit is zero; when external pressure exists, a pressure difference exists between the pressure acting cavity 72 and the sealing cavity, the interdigital thin film piezoresistor 11 deforms, the resistance value of the interdigital thin film piezoresistor 11 positioned in the sealing cavity changes, the bridge 10 loses balance, and an output voltage proportional to the measured pressure is output.
In one embodiment of the present invention, the integrated chip 100 includes five partial circuits, i.e., differential operational amplifier, ADC (Analog-to-Digital Converter), state machine, calibration DAC (Digital-to-Analog Converter), and radio frequency circuit, which are integrated on the same silicon chip using CMOS technology. The differential operational amplifier is a fully differential, high gain operational amplifier circuit that functions to amplify weak signals generated by the bridge 10. The ADC is an analog-to-digital conversion circuit with 8-bit or above precision and low power consumption, and is used for converting an analog signal amplified by the differential operational amplifier into a digital signal. The state machine controls the radio frequency circuit to wirelessly transmit the output of the ADC and to control the calibration DAC output voltage to calibrate the voltage on the output node of the bridge 10 to ensure that the output of the sensor device is zero when no external pressure is present. The state machine is connected to the analog to digital converter output and to the bridge 10. The bridge 10 is calibrated by the output value of the analog-to-digital converter.
As shown in fig. 2, the pressure-acting chamber 72 transmits a pressure change signal to the interdigital thin film piezoresistor 11 in the sealed cavity through the LCP, and the wheatstone bridge 10 composed of the interdigital thin film piezoresistor 11 and the elongated thin film piezoresistor 12 converts the pressure change into a voltage signal output. The resistance values of the 4 film piezoresistors should be the same. As shown in fig. 3 and 4, the two voltage signals out1 and out2 output by the wheatstone bridge 10 are connected to the differential operational amplifier input terminal, and the amplified signals are converted into digital signals by the ADC and finally transmitted to other receiving devices wirelessly through the radio frequency circuit. Theoretically, under no load pressure, the bridge 10 is in equilibrium, with no output voltage. In fact, however, the bridge 10 cannot reach equilibrium under no pressure due to factors such as process, and always outputs a voltage signal. In the invention, under the condition of no pressure, the bridge 10 is regulated by the DAC, so that the output voltage of the differential operational amplifier circuit is zero, and the automatic calibration function is achieved.
In the calibration process, the calibration digital-to-analog conversion circuit outputs analog voltage, and the analog voltage is applied to any one of the connection parts of the two interdigital thin film piezoresistors and the single strip thin film piezoresistor and is regulated so as to equalize the two voltages output by the thin film piezoresistor bridge.
Compared with the prior art, the invention has the beneficial effects that: the flexible LCP substrate-based invasive blood pressure sensor device is designed, has a miniature volume and can be placed into a tested object. Meanwhile, a radio frequency circuit is used, so that data wireless transmission can be realized. The LCP material adopted by the sensor has good biocompatibility, can penetrate microwaves, and has the characteristics of excellent strength, heat resistance, electric insulation, chemical corrosion resistance and the like. The pressure sensitive resistor is designed by adopting the interdigital structure, which is more beneficial to realizing resistance matching in the process preparation process, and ensures the balance of the bridge 10 without external force to the greatest extent. The present invention uses a calibration DAC and state machine for automatic calibration, and can automatically adjust the voltage to balance the bridge 10 in the absence of external forces, thereby increasing the accuracy and linearity between sensor 'pressure input-signal output'. The differential operational amplifier is used for amplifying the signals, so that the pressure signal measuring range is enlarged. Meanwhile, all devices related in the invention are integrated on one silicon wafer, so that the working reliability, signal-to-noise ratio and anti-interference performance of the invasive blood pressure sensor device are improved. The high-voltage signal and the low-voltage signal can be acquired, the measuring range is large, the application is wide, and the device can be extended to various pressure measuring occasions in cavities in the human and animal operation process. The integrated invasive blood pressure sensor provided by the invention has the advantages of high linearity, larger test range and high reliability.
The invention uses a state machine to automatically calibrate, and can automatically adjust the voltage to balance the bridge 10 when no load is applied, thereby increasing the linearity between the pressure input and the signal output of the sensor, without using a zero-pressure offset compensation resistor; the sensor is integrated with the differential signal amplifier, so that the pressure signal measurement range is enlarged, and meanwhile, the signal gain and the signal-to-noise ratio are improved; the invention integrates the digital communication interface, can directly output digital signals and improves the anti-interference performance; all devices related in the invention are integrated on one silicon chip, so that the working reliability of the invasive blood pressure sensor is improved.
In summary, the above embodiments describe in detail different configurations of the integrated invasive blood pressure sensor, and of course, the present invention includes, but is not limited to, the configurations listed in the above embodiments, and any configuration that is changed based on the configurations provided in the above embodiments falls within the scope of protection of the present invention. One skilled in the art can recognize that the above embodiments are illustrative.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other. For the system disclosed in the embodiment, the description is relatively simple because of corresponding to the method disclosed in the embodiment, and the relevant points refer to the description of the method section.
The above description is only illustrative of the preferred embodiments of the present invention and is not intended to limit the scope of the present invention, and any alterations and modifications made by those skilled in the art based on the above disclosure shall fall within the scope of the appended claims.
Claims (8)
1. An integrated invasive blood pressure sensor, comprising:
The thin film piezoresistive bridge is configured as a Wheatstone balance bridge and consists of two interdigital thin film piezoresistors which are not connected with each other and two single strip thin film piezoresistors which are not connected with each other, and when the resistance value of the two interdigital thin film piezoresistors is a steady state value, the two voltages output by the thin film piezoresistive bridge are equal;
an integrated die configured to process a voltage output by the thin film piezoresistive bridge;
the liquid crystal polymer comprises a first packaging area and a second packaging area, wherein the first packaging area bears two interdigital thin film piezoresistors, the second packaging area bears two single strip thin film piezoresistors and the integrated chip, and the liquid crystal polymer is flexible;
A first encapsulation layer configured to seal the first encapsulation region to form a first cavity, the two interdigital thin film piezoresistors being contained within the first cavity;
and a second packaging layer configured to seal the second packaging region to form a second cavity, wherein the two single-strip thin film piezoresistors and the integrated chip are accommodated in the second cavity, and wherein:
The bottom of the first packaging area is a U-shaped pressure acting cavity, the pressure acting cavity is contacted with liquid, the pressure formed by the liquid is conducted to the interdigital thin film piezoresistor through the pressure acting cavity, so that the resistance value of the interdigital thin film piezoresistor is changed,
The first cavity is filled with insulating liquid, receives external force in 360 degrees in all directions and is conducted to the two interdigital thin film piezoresistors through the insulating liquid.
2. The integrated invasive blood pressure sensor according to claim 1, wherein the interdigital thin film piezoresistor comprises a first piezoresistor component and a second piezoresistor component, wherein:
the first piezoresistive component and the second piezoresistive component are comb-shaped, and the comb teeth of one of the first piezoresistive component and the second piezoresistive component are inserted between the tooth spaces of the other of the first piezoresistive component and the second piezoresistive component to form an crossed arrangement.
3. The integrated invasive blood pressure sensor according to claim 1, wherein the interdigital thin film piezoresistor and the single strip thin film piezoresistor each comprise a titanium thin film layer and a titanium dioxide thin film which are stacked,
The titanium thin film layer is arranged between the substrate of the liquid crystal polymer and the titanium dioxide thin film;
the resistance values of the two interdigital thin film piezoresistors and the two single strip thin film piezoresistors are consistent.
4. The integrated invasive blood pressure sensor according to claim 1, wherein the integrated chip is integrated on the substrate of the liquid crystal polymer by CMOS process, comprising:
the differential operational amplifier circuit is configured to amplify the voltage generated by the thin film piezoresistive bridge to form an analog amplified signal;
the analog-to-digital conversion circuit is configured to filter, sample, hold and encode the analog amplified signal and then convert the analog amplified signal into a digital signal;
a communication circuit configured to transmit the digital signal to a receiving device;
a calibration digital-to-analog conversion circuit configured to adjust the voltage output by the differential operational amplifier circuit to zero when the pressure of the liquid is not received by the pressure acting cavity;
and the state machine is configured to process the digital signal, judge whether the calibration digital-to-analog conversion circuit is calibrated in place according to the digital signal, and control the signal transmission of the communication circuit.
5. The integrated invasive blood pressure sensor according to claim 4, wherein the communication circuit comprises an SPI interface, an I2C interface, a USB interface, a UART interface, an RS-485 interface, a CAN-bus interface, and/or a radio frequency chip.
6. The integrated invasive blood pressure sensor of claim 4 in which the differential operational amplifier circuit is a chopper-stabilized operational amplifier.
7. The integrated invasive blood pressure sensor of claim 4 in which the thin film piezoresistive bridge further comprises a constant current source of MOS transistors.
8. The integrated invasive blood pressure sensor according to claim 4, wherein during calibration, the calibration digital-to-analog conversion circuit outputs an analog voltage that is applied to either of the two inter-digital thin film piezoresistive and single strip thin film piezoresistive connections, the analog voltage being adjusted to equalize the two voltages output by the thin film piezoresistive bridge.
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