JPH07178186A - Medical device that can be buried hypodermically - Google Patents

Abstract

PURPOSE: To provide a medical treatment device to be laid hypodermically which is sensitive to an outer magnetic field and can be used with low voltage supply and bias electric current. CONSTITUTION: A magnetic sensor 40 consists of a pair of crossing/connecting MAG-type FETs. As an outer magnetic field is applied and electric current running through half-cut drain bodies 50, 56 is increased, the electric current through half-cut drain bodies 52, 54 is reduced accordingly. Correspondingly to the reduction, the voltage of an output terminal 60 is increased, and the voltage of an output terminal 58 is reduced. A differential amplifier is installed between these two output terminals 58, 60 to detect relative changes in the voltage of the output terminals 58, 60, so that the applied outer magnetic field can be sensed.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to the field of subcutaneously implantable medical devices, and more particularly to sensors for detecting the application of magnetic fields to medical devices.

[0002]

BACKGROUND OF THE INVENTION In the field of medical devices, such as subcutaneously implantable cardiac stimulators, which are subcutaneously implanted in the patient's body, certain operating parameters of the device are non-surgical means. It is desirable to be able to change. Various methods for non-surgical communication with a device implanted under the skin have already been disclosed. Since the introduction of demand-based cardiac pacemakers, one of the most common methods of non-surgical modification of operating parameters has been to use magnetically actuated reed switches contained within a subcutaneously implanted device. The magnetic reed switch consists of a hermetically sealed cylindrical protective housing and two metal reeds. When a magnetic field is applied to a device implanted subcutaneously from outside the patient's body, the metal lead
A strong magnetic force pulls the two leads into electrical contact with each other and is arranged within the protective capsule to form an electrical circuit. When the magnetic field disappears, the leads separate and the electrical circuit disappears. For example, Terry J., who was assigned to the assignee of the present invention, Terry J.
r. ) U.S. Pat. No. 3,805,796, "Subcutaneously implantable cardiac pacemaker with adjustable parameters," issued Apr. 23, 1974, to Gombrich et al., Nov. 18, 1975. U.S. Pat. No. 3,920,005 entitled "Assessment system for heart stimulators" issued to Alferness and U.S. Pat. No. 4,066 issued Jan. 3, 1978. No. 086, "Programmable Body Stimulator", discloses such an arrangement.

The closure of reed switches is used to enable asynchronous operation for tracking and remote transmission of subcutaneously implanted pacemakers. In addition, rate and mode changes caused by the closing of reed switches are used to indicate device function and battery status. Most recently, external devices have been developed that communicate remotely with devices implanted subcutaneously by radio frequency (RF) transmission. The RF telecommunications link allows two-way communication between external devices and subcutaneously-implanted devices, and allows a wider range of operating parameters for external programs. However, the use of RF links does not eliminate the need for magnetically acting reed switches. For example,
David L. Thompson (D on February 17, 1981)
avidL. The pacemaker disclosed in U.S. Pat. No. 4,250,833 issued to Thompson entitled "Digital Cardiac Pacemaker with Immunity, Reversion and Sensitivity Reset Means" provides an external RF telemetry signal until the reed switch is closed. Will not be received and will not be processed. The configuration ensures that the subcutaneously implanted device is not unintentionally reprogrammed by an external RF signal that the patient may be exposed to.

Although magnetic reed switches are commonly used in subcutaneously implanted devices, it is known that there are still some problems. Reed switches are the only mechanical device along with the pacemaker's moving parts, and are more susceptible to damage from mechanical vibrations or mechanical shocks, or machine outages than the electronic components of the pacemaker. Although the glass encapsulation provides some protection to the leads, the capsule itself is susceptible to breakage. Moreover, advances in electronics have created smaller pacemakers, and reed switches must also be very small, thereby increasing brittleness. Also, thin pacemakers, on the order of 6 to 8 mm in thickness, prevent the reed switch from being placed at right angles to the large flat surface area of the pacemaker case. Reed switch outages are particularly undesirable in subcutaneously implantable devices because replacement involves surgery.

Reed switches must be sensitive enough to be sensitive to externally applied magnetic fields, while it is important that they are not sensitive to the magnetic fields exposed to the patient's daily activities. As a result, the manufacturing tolerance of the reed switch is reduced and the manufacturing cost is increased.

One attempt to overcome this problem with reed switches is described in US Pat. No. 3,766,928 issued to Goldberg et al. This patent discloses a potentiometer attached to a small, fully magnetized disc magnet. The second magnet is rotationally driven outside the patient to rotate the disc magnet and rotate the potentiometer. This method is mechanical in its own right and has a number of problems such as being very small and prone to breakage. In addition, manipulating the second magnet to adjust the potentiometer is more difficult and complex than manipulating the magnet required to act on the reed switch.

Another attempt to overcome the problem of reed switches was made to Thompson et al., 1981 1
It is disclosed in U.S. Pat. No. 4,301,804 entitled "Hall Effect Externally Controlled Pacemaker Switch," issued January 24 and assigned to the assignee of the present invention. This patent
Disclosed is a pacemaker that produces a strobe signal used to output current through a Hall effect element within a pacemaker pulse period each having a selected time. The presence of an external magnetic field alters the electrical properties of the Hall effect device (typically in a bipolar integrated circuit assembly process), providing a positive voltage to the pacemaker circuit when the Hall effect device is strobed. Hall effect devices are not mechanical devices and are more desirable than reed switches in that respect, but they are less sensitive than reed switches, require expensive processing and packaging, and are used preferentially in subcutaneously implantable medical devices. Has been found to be incompatible with standard linear CMOS processors.

Using drain split field effect transistors called MAG (most useful gain) type FETs as an alternative to using mechanical reed switches or Hall effect devices for magnetic field detection and measurement. Have been proposed in the prior art. It is similar to a conventional field effect transistor (FET), but the drain of a MAG type FET is divided into two and the drain halves are insulated from each other. Application of magnetic field to MAG type FET element
Increasing the current difference in the two drain halves. This difference is directly proportional to the strength of the applied magnetic field. Similar to Hall effect devices, MAG FETs have the advantage of being semiconductor devices, but some problems associated with conventional MAG FETs are also known. One issue is the sensitivity of these devices to magnetic fields. In general, MA
The gain constant of the G-type FET is small, and the difference between the drain currents in the drain halves is rather small for a given change in magnetic field strength. It is desirable to maximize the gain of the MAG FET in order to be readily available for sensing and measuring external magnetic fields. It has been disclosed in the prior art that the gain constant of a MAG-type FET is increased by increasing the bias current of the MAG-type FET in a steady state (for example, “New High Gain MOS Magnetic Field Sensor by Misra”). "-" Sensors and Actuators "(Sensors and Actuat)
ors) pp. 213-221, 1986 edition). In addition, many prior art discuss the operation of MAG-type FETs by supplying a voltage of 5-10 volts and a bias current of 10-620 microamps (see, for example, "New High Gain" by Misra et al. MOS Magnetic Field Sensor Array "-IEEE Semiconductor Circuit Journal 2nd
Volume 5, Issue 2, Pages 623-625, 1990 1990
"Design of CMOS Oscillator with Magnetic Field Frequency Modulation" by Moon and Nathan et al.-IEEE Semiconductor Circuit Journal, Volume SC-22, No. 2, 230-
(See page 232, April 1987). However, such power supply voltages and bias currents are not available in subcutaneously implantable pacemakers. It must operate with a power supply of 1-3 volts and a bias current of 10-100 nanoamps.

Another prior art method has been to use an array of MAG-FET devices in a tree-like arrangement and to combine drain halves derived from individual MAG-FETs to achieve sensitivity to magnetic fields. I need.
The effect of the magnetic field is measured by the additive effect of the current difference in each of the pair of drain halves. ((For example, "New high gain MOS by Misra, et al.
Magnetic field sensor "-" Sensor and actuator "(S
21th edition of "Enors and Actuators"
See page 3-221, 1986 edition). However, this solution requires a higher level of supply voltage. This is because the threshold voltage of the connected MAG type FETs is an additional one. More complex MAG type F
The use of ET devices results in a corresponding increase in overall circuit area and drain current for the sensor. Therefore, the prior art for increasing the gain constant of the MAG type FET device is a subcutaneous implantable medical device that must maintain a small size, long-term stability, reliability, minimum power supply voltage level, and minimum drain current. Not suitable for application to equipment.

It is therefore an object of the present invention to provide a non-mechanical element that is sufficiently sensitive to an external magnetic field and is useful in the context of a subcutaneously implantable medical device. The present invention is also to enable the magnetic sensor to be used at low supply voltages and bias currents available in subcutaneously implanted medical devices. The present invention further provides that the magnetic acting element can be easily manufactured using conventional CMOS processing techniques. It is also an object to make the magnetic action element sufficiently sensitive to an external magnetic field even when a low supply voltage and a bias current of a medical device that can be implanted subcutaneously are supplied.

[0011]

In order to achieve the above object, a subcutaneously implantable medical device according to the present invention includes an integrated circuit formed on a silicon substrate, and is provided with an external magnetic field for changing an operating condition. A voltage-sensitive subcutaneously implantable medical device in which the integrated circuit comprises a source, a gate defining a first planar channel region, and a first drain split FET. , A source, a gate defining a second planar channel region and third and fourth
A second drain split FET having a plurality of drain halves and a plurality of FET elements having a differential amplifier for producing the output voltage, wherein the first drain half is the fourth drain element.
The second drain split FET is connected to the drain half, the second drain half is connected to the third drain half, the source of the first drain split FET is connected to a power source, and the second drain split FET is connected. The source is connected to a current source, a bias current flows through the first, second, third and fourth drain halves and a portion of the bias current is coupled to the first drain halves and the first drain halves. 4 drain half, the rest of the bias current flows through the second drain half and the third drain half, and a magnetic field perpendicular to the first and second planar channel regions is the bias current. Of the bias current is reduced and the remainder of the bias current is decreased, and the differential amplifier voltage is changed in response to the increase of the portion of the bias current to decrease the remainder of the bias current. It is obtained by the configuration.

In the medical device for subcutaneous implantation according to the present invention, the first drain split type FET is a P-channel drain split type FET, and the second drain split type FET is used.
Can be an N-channel FET.

The subcutaneously implantable medical device according to the present invention includes an integrated circuit formed on a silicon substrate and is sensitive to an external magnetic field applied to change the operating condition. A source, a gate defining first planar channel region, and first and second drain halves, connected to a bias circuit including a power supply,
The drain division type FET includes a drain division type FET in which a bias current flows through the drain division half, and a plurality of FET elements including a differential amplifier connected between the first and second drain halves to generate an output voltage. An external magnetic field applied to the type FET increases the bias current in the first drain half and decreases the bias current in the second drain half, and the output voltage of the differential amplifier is Varying in proportion to the increase in the bias current in the one-drain half and the decrease in the bias current in the second drain half, the application of the external magnetic field to the output voltage of the differential amplifier The configuration is made to be actualized by the voltage change.

The subcutaneously implantable medical device according to the present invention includes an integrated circuit formed on a silicon substrate, and is sensitive to the application of an external magnetic field for changing the operating condition. , A source, a gate defining the first planar channel region, and a first, a second, and a third triple drain divider having a drain split, which are connected to a bias circuit including a power supply to provide a bias current. Established,
A part of the bias current flows through each of the first, second and third triple drain division bodies, and the triple drain FE.
A plurality of FETs including a differential amplifier connected between T and the first and third drain division bodies to generate the output voltage.
An external magnetic field applied to the drain split FET to increase the bias current in the first triple drain split and a bias current in the third triple drain split. And the output voltage of the differential amplifier varies proportionally to the increase of the bias current in the first triple drain divider and the decrease of the bias current in the third triple drain divider. The application of the external magnetic field is made apparent by the voltage change in the output voltage of the differential amplifier.

The subcutaneously implantable medical device according to the present invention has fourth, fifth and sixth triple drain split bodies, and the fourth triple drain split body is the first triple stack. Connecting to a drain split, the fifth triple drain split connecting to the second triple drain split, and the sixth triple drain split to the third triple drain split. Connected to the bias circuit and having an active load including a second triple drain FET, the portion of the bias current flowing through the first triple drain divider being the fourth portion. Also flows through the triple drain split of
The portion of the bias current flowing through the second triple drain split also flows through the fifth triple drain split and the bias current flows through the third triple drain split. And the external magnetic field increases the bias current that has flowed through the first and fourth triple drain splits, and the third and third drain splits. The bias current flowing through the triple drain divider of No. 6 is reduced, and the output voltage of the differential amplifier is reduced to the first and the fourth.
Can be varied in proportion to the increase in the bias current in the triple drain splitting element and the decrease in the bias currents in the third and sixth triple drain splitting elements.

The subcutaneously implantable medical device according to the present invention includes an integrated circuit formed on a silicon substrate, and is sensitive to the application of an external magnetic field for changing the operating condition. A plurality of cascaded first and second drain split FETs, the first drain split FET being connected to a regulated current drain, and the second drain split FET being the plurality of first drain split FETs. A first drain split FET connected to the adjusted current drain, the first drain split FET producing a first output current, the second drain split FET producing a second output current, and 1, a positive feedback oscillator that produces an oscillating output having a duty cycle that varies in proportion to the second output current, wherein the external magnetic field applied to the integrated circuit is the first output. Flow increases, and decreases the second output current, the application of the external magnetic field can be configured to vary the aforementioned duty cycle of the oscillation signal.

The subcutaneously implantable medical device according to the present invention has a low-pass filter for receiving the oscillation signal and generating an output voltage proportional to the average voltage of the oscillation signal,
The change in the duty cycle may cause the change in the output voltage.

The subcutaneously implantable medical device according to the present invention includes an integrated circuit formed on a silicon substrate and is sensitive to the application of an external magnetic field for changing the operating condition. , A plurality of drain split type FEs that receive a plurality of digital input signals and have a plurality of output lines
T including the plurality of digital input signals to select the plurality of drain split type FETs to connect to the plurality of output lines, each of the plurality of drain split type FETs defining a source and a planar channel region. Gates, and first and second drain halves, wherein the planar channel region of each of the plurality of drain split FETs has a different dimension than the other plurality of drain split FETs. A circuit, a source, a gate defining a planar channel region, and another pair of drain split FETs including third and fourth drain halves, and a differential amplifier producing an output voltage. Multiple FEs including
The drain split type FE selected by the above
The first drain half of T is connected to the fourth drain half and the second drain half of the selected drain split FET is connected to the third drain half. , The drain-splitting FEs, wherein the plurality of sources of the drain-split FET including the multiplexed active load are connected to a power supply and form the other pair.
The source of T is connected to a current source, and a bias current flows through the first and second drain halves and the third and fourth drain halves of the selected drain split FET, the bias current Flow through the first drain half and the fourth drain half of the selected drain split FET, and the balance of the bias current is the drain split FFT of the selected drain split FET. A magnetic field flowing through the second drain half and the third drain half and perpendicular to the first planar channel region and the second planar channel region of the selected drain split FET is the bias current. Of the bias current and the remaining portion of the bias current are reduced, and the differential amplifier output voltage is increased by the increase of the bias current by the portion of Changes according to the reduction of the remainder of the bias current, the extent of said alteration can also be configured to variably depending on which of the plurality of drain split type FET is selected.

The subcutaneously implantable medical device according to the present invention may be arranged such that the bias current is in the range of 10 to 100 microamperes.

The subcutaneously implantable medical device according to the present invention may be configured such that the first and second planar channel regions have a width / height ratio of 1: 1.

[0021]

The present invention is implemented in a CMOS device including a cross-connect arrangement of two drain split field effect transistors (MAG type FETs). Each MAG when there is no external magnetic field
The total drain current in a FET is equal to that of the MAG F
Divide into each drain half of ET. Each MAG type FE
An external magnetic field directed perpendicular to the channel plane in T
It causes a deviation in the drain current in each drain half, increasing the Lorentz force exerted on the carriers injected into the MAG FET. Since the total amount of drain current in each MAG-type FET does not change,
Of drain current in one of the drain halves is accompanied by a corresponding decrease in drain current in the other half of the drain. Thus, the presence and strength of the external magnetic field manifests itself as a difference in voltage or current in each MAG FET between the two drain halves. Therefore, the high gain difference between the cross-connected MAG FETS produces an output indicative of the application of an external magnetic field. In accordance with one aspect of the invention, the novel drain split cross-connect doubles the voltage difference resulting from the application of a given magnetic field. The increased voltage differential and low drain current of the device make the device particularly suitable for use in subcutaneously implanted pacemakers and the like.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A shows an N channel drain split MAG type F.
It is a perspective view of ET10. Like the conventional N-channel FET, the drain split MAG type FET 10 has a P
It includes an N-type substrate 12 having a well 32. In the P well 32, N-type source 14 and drain region 16 are alternately formed. There is also a metal source 18 and a gate 20 as in the conventional FET structure. The gate 20 covers a channel region 22 arranged between the source region 14 and the drain region 16. However, unlike conventional FETs, the metal drain of the MAG FET 10 is split into two separate halves 24, 26 that are electrically isolated from each other. FIG. 1B is a perspective view of a P-channel drain split MAG type FET 10 having the same configuration as that of FIG. M
The AG type FET 10 'is given the same reference numeral as that in FIG. The MAG-type FET 10 'differs from the MAG-type FET 10 only in the wafer processing steps and the absence of P-wells.

Those skilled in the semiconductor arts will find that Lorentz forces are exerted on the injected carriers if a magnetic field is applied to the MAG FET 10 in the direction indicated by arrow 28 perpendicular to the plane of the channel region 22. Then you will understand correctly. So-called "right hand rule"
You can use to determine the direction of the Lorentz force. If the thumb of a person's right hand is directed in the direction of the magnetic field, the Lorentz force resulting from that field is exerted in the direction of the bent finger of that person's right hand. Therefore Figure 1
In the FET 10 of (A), the magnetic field in the direction of the arrow 28 is perpendicular to the arrow 28 and is directed in the direction indicated by the arrow 30 (the vertical direction between the drain half body 24 and the drain half body 26). Gives Lorentz power. F in FIG. 1 (B)
In ET10, the magnetic field in the direction of arrow 28, the magnetic field in the direction of arrow 28 is perpendicular to arrow 28 and is in the direction indicated by arrow 30 '(perpendicular between drain half 24 and drain half 26). Is applied (the direction opposite to that of FIG. 1A)). The directions of the arrows 30 and 30 'facing each other in FIGS. 1A and 1B are due to electrons and holes which are the main carriers of the FETs 10 and 10'.

As a result of this Lorentz force, as described above, a large amount of the drain current of the MAG type FET 10 that flows through the drain halves 24 and 26 normally equally flows to the drain half halves 26 side, and the drain half halves 24 side. Will be less. In particular,
When the MAG-type FET 10 is biased, the total IT ampere current flowing through the drain halves 24, 26 is 0.5 IT amperes in the drain halves 26 in the absence of an external magnetic field. Flows through the drain half 24. When an external magnetic field is applied, the total drain current is the same at IT amps, but (0.5IT + i) amps flows in the drain half 26,
The (0.5 IT-i) ampere flows into the drain half 24. That is, a difference of 2i amps occurs between the currents flowing through the drain halves 24, 26. Each drain half 2
The measurement of the difference of 2i ampere of the current flowing in 4, 26 is
It can be used to determine the presence and strength of external magnetic fields.

FIG. 2A is an equivalent circuit diagram of the MAG type FET 10. FIG. 2B is another equivalent circuit diagram of the MAG type FET 10. In FIGS. 2A and 2B, as in FIG. 1, reference numeral 18 is a source terminal of the MAG type FET 10, reference numeral 20 is a gate terminal, and reference numerals 24 and 26 are two drain halves. Show.

In FIG. 3, a magnetic sensor 40 according to one embodiment of the present invention is shown in an equivalent circuit, and FIG.
Two MAG type FETS 42 and 44 are shown as in (B). A sensor 40 including a P-channel MAG type FET is shown by a broken line 42, and an N-channel MAG type F
ET showed 44 by the broken line. For example, the power supply voltage VDD from the battery is applied to the power supply terminal 4 of the MAG type FET 42.
6 will receive. The power terminal 48 of the MAG FET 44 is connected to a regulated current source 49. A negative supply voltage NVDD is applied to the silicon substrate on which the sensor 40 is formed.
(Hereinafter, also referred to as VSS) is supplied. The drain half 54 of the MAG type FET 42 is the MAG type FET 44.
And the drain half 50 of the MAG FET 42 is connected to the drain half 52 of the MAG FET 44. The first output terminal 58 connects to the drain halves 54 and 56, and the second output terminal 60 connects to the drain halves 50 and 52. In the figure, the voltage VDD
The terminal for receiving the voltage is indicated by ◯, and the terminal for receiving the voltage NVDD or VSS is indicated by −.

The MAG FET 42 operates within the sensor 40 as an active load. When there is no external magnetic field, the current in each drain half 50 and the MAG type FET 4
The two currents 54 are equal and the respective output terminals 58, 60
Are equal at voltage levels near the center point between VDD and VSS, as before. MAG type FET 42, 4
4 are physically aligned with each other on the substrate, and the sensor 40
The external magnetic field applied to the drain halves 50, 56 or drain halves 52 and 54 depends on the polarity of the magnetic field.
Each MAG type FET 42, due to the Lorentz force applied to
The drain current in 44 becomes "integrated".

The applied magnetic field causes the drain halves 50, 5
Increasing the current through 6 causes a corresponding decrease in the current in drain halves 52 and 54. Drain half body 5
The current in 2 is reduced, while the current in drain half 50 is increased, tending to increase the voltage at output terminal 60. Conversely, while the current in drain half 56 is increased, drain half 54 is
The voltage at output terminal 58 tends to decrease because the current in In the case where the applied magnetic field increases the current in the drain halves 52, 54, there is a corresponding decrease in the current in the drain halves 50, 56. In this case, the voltage at output terminal 58 increases and the voltage at output terminal 60 decreases. As will be appreciated by those skilled in the design of electronic circuits, two output terminals 5
The differential amplifier located between 8 and 60 is connected to the output terminal 5
Can be used to sense relative voltage changes of 8 and 60,
This provides an indication of the externally applied magnetic field.

FIG. 4 shows a schematic diagram of a subcutaneously implantable pacemaker utilizing the magnetic sensor of the present invention.
The circuit of FIG. 4 includes a very high gain differential amplifier coupled between the cross-connected drains of two drain split MAG FETs, shown as blocks 70 and 72. Element 7
4, 76, 78, 80, 82, 84, 86, 88, 9
0, 92, 94, 96, 98, 100 and 102 constitute a conventional differential amplifier and produce an output voltage at terminal MF. The current source connects to the circuit of FIG. 4 at terminal 110. The current source is applied to a current galvanometer including the elements 104, 106 and the regulated output current from the current galvanometer is provided to the power terminal of the MAG FET 72. Trimming of the wafer working deviation is accomplished via a resistor (not shown) between the NVDD power supply and terminal 112. The resistor is tuned even when the device of FIG. 4 is in a zero strength magnetic field.

In FIG. 5, the representation of the drain split transistor of FIG.
Is represented diagrammatically. In FIG. 5, the MAG type F
One drain half of ET 70 is shown at 70a and a second drain half at 70b. Similar to the MAG type FET 42 in the circuit of FIG.
The ET 70 is a P-channel device that acts as an active load. The MAG type FET 70 is connected to the circuit of FIG. 4 via terminals LD1 and LD2. A MAG-type FET 72 is shown schematically in FIG. 6 using the representation of the drain split transistor of FIG. 2B. In FIG. 6, one drain half of the MAG FET 72 is shown at 72a, and M
The second drain half of the AG FET 72 is shown at 72b. The MAG type FET 72 has terminals DIF0 and DIF0.
It is an N-channel device connected to the circuit of FIG. 4 via IF1 and DIF2.

As shown in FIGS. 4 to 6, the FET 8
Drain half body 7 of MAG type FET 72 through 4 and 90
The drain half 70a of the MAG type FET 70 is connected to 2b. Similarly, through the FETs 86 and 92, the MAG type FE
The drain half body 70b of the MAG type FET 70 is connected to the drain half body 72b of T72. Of course inevitable C
Due to the MOS action deviation, the drain halves 70a, 72
The bias current through a is the drain halves 70b, 72.
equal to the bias current through b. The FETs 74-102 forming the differential amplifier are biased, so that when there is no external magnetic field, the voltage at the output terminal MF is VDD.
(Or NVDD). Since the FETs 74-102 forming the differential amplifier have a very high gain,
A slight change in the current through the drain half that results from the application of an external magnetic field causes a voltage change at the output terminal MF to NVDD (or VDD).

Since the circuit of FIG. 4 forms part of the circuit in a subcutaneously implantable pacemaker, the sensor 40 has a low drain current and a minimum positive and negative voltage supply level VD.
It is essential to work with D, NVDD. At the same time, it is desirable to ensure that the circuit of FIG. 4 remains very sensitive to external magnetic fields. As mentioned earlier, numerous prior art references disclose that the sensitivity of a MAG-FET device to magnetic fields may be enhanced by increasing the power supply level and bias current of the device. However, the present inventors have found that +1.8 to +
A 1200 V / Tesla sensitivity was achieved by operating the circuit of FIG. 4 with a supply voltage of 3.0 V and a bias current of 10 to 100 nanoamps. This sensitivity is approximately 1,000 of the previously published values (see, for example, Misra's paper already mentioned).
Double.

The circuit sensitivity of the circuit of FIG. 4 to the external magnetic field, the gain constant of the differential amplifier circuit, and the current drain characteristic are
Affected by various element sizes. The inventors consider many different combinations of device sizes. As will be appreciated by those skilled in the design of electronic circuits, a critical parameter of FFT devices is the channel size, referred to as the ratio of channel length to channel width (W / L). Table 1 shows a list of element sizes used in the circuit of FIG.

[Table 1]

The circuit of FIG. 4, which uses the channel sizes of Table 1, is presently preferred by the inventor, but plans two additional implementations. The first alternative embodiment is MAG
The elements shown in Table 1 are adopted except the type FET elements 70a and 70b, and the ratio of the length to the width (w / l) is 158 μ / 316.
158 μ / 5 μ is used instead of μ. In the second alternative embodiment, the MAG type FET devices 70a and 70b are 3 μ / 31.
It has a w / l ratio of 6μ.

While implementation of the circuit of FIG. 4 using the element sizes in Table 1 is considered a preferred method of implementing the present invention, alternative embodiments may nevertheless be desirable for certain applications. For this purpose, for example, the multiplex arrangement shown in FIG. 7 was used. This circuit allows some alternative coupling of the active load provided to the magnetic sensor circuit according to the present invention. In FIG. 7, the same elements as the corresponding elements in the implementation of FIG. 4 have the same reference numerals. However, FIG. 7 further includes the multiplexer 120 shown in more detail in FIG. The multiplexer 120 receives the input signals Ll, L2 and L3 used to select one of several active loads for introduction into the magnetic sensor circuit.

Referring to FIG. 8, the multiplexer 120
Each of the elements in has a w / l ratio of 38μ / 4μ.
The multiplexer circuit 120 has the dashed lines 122 and 12 in FIG.
Includes three separate active load portions, designated 4,126. The active load portion 122 is a MAG type FET element 128.
including. The active load portion 124 is the MAG type FET device 1
Including 30. The active load portion 126 is a MAG type FET.
The element 132 is included. As will be appreciated by those skilled in the art of semiconductor circuit design, applying a positive voltage on lines Ll, L2, L3 causes active load portions 122, 124,
126 is terminals DP1, DP2, DP3, DP4, DP5
And is connected to the circuit of FIG. Therefore, the lines Ll, L
MAG type F by selecting either 2 or L3
ETs 128, 130, 132 are introduced for the magnetic sensor circuit of FIG. In this way different active load elements can be compared and tested for suitability for a particular application of the invention, and programmable sensitivity can be employed to allow varying levels of electromagnetic field strength control.

The ability to program and diagnose the MAG-type FET sensitivity allows the use of variable access levels, and the magnetic switch acts as a link to initiate programming and telecommunications. For example, to enable subcutaneous implant problem solvers to gain access to additional programmable parameters or elements with routines or features that try to prevent the diagnostician from accessing them with high magnetic thresholds. To do. Also, patients with subcutaneously implanted neural stimulators are attributed to the home with self-programming tools that allow standard programming links with limited software. Undesirable programming can occur with standard links. Higher programmable magnetic thresholds can be used to allow very limited access by the patient to programmable parameters.

Another embodiment of the present invention is shown in FIGS. Elements that are the same as the corresponding elements in the implementation of FIG. 4 are labeled with the same reference numbers. The embodiment of FIG. 9 is similar to that of FIG.
The G type FET element 142 is adopted. Active load element 140
The triple drain MAG type FET 142 is shown in FIG.
It is shown in more detail in 0,11. Active load element 140
Is a 316μ / 316μ triple drain P-channel MAG
The type FET 150. The MAG type FET 142 has 31
6μ / 316μ triple drain N channel MAG type FET
Is. The differential amplifier circuit in the embodiment of FIG.
Has a channel size of / 4μ and 15μ / 4μ, and has a terminal LD3 of the active load 140 and a triple drain MAG type FET1.
Additional FET element 1 located between terminal DIF3 of 42
44 and 146 are included.

A final embodiment of the invention is shown in FIG. In the embodiment of FIG. 12, a plurality of drain division MAG type FETs are cascade-connected to enhance the current integration effect of the external magnetic field. P channel MAG type FET 16 of FIG.
In 0, one drain half is an N-channel MAG type FE
Connect to the drain half of T162. A 10 nanoamp current source connects to the circuit at terminal 164. This current source is regulated by conventional FET devices 166, 168, 170. The current passing through the MAG-type FET 160 is connected so as to continuously pass through the "upper" MAG-type FETs collectively shown within the range of the broken line 172 in FIG.
In addition, the current passing through the MAG type FET 162 is collectively shown in FIG.
“Lower” MAG type F shown within the range of dashed line 174 of FIG.
Connect so as to pass through ET continuously. As shown in FIG. 12, the drain half 176 of the MAG type FET 160 is
The first gate 17 of the "upper" MAG FET 172, as well as the other drain halves 180 of the MAG FET.
Connect to 8. The second drain half 182 of the MAG type FET 160 is connected to the drain half 184 of the MAG type FET 162. The second drain half 186 of the MAG type FET 162 is the “lower” MAG type FET.
174 first gate 188 and other drain halves 19
Connect to 0.

As will be apparent to those skilled in the art of semiconductor design, when an external magnetic field is applied to the circuit of FIG. 12, the current integration effect described above in connection with FIG.
The current through the drain half 176 of the AG FET 160 increases and the current through the drain half 186 of the MAG FET 162 decreases correspondingly. MAG type FE
Since each T172 has the same current integration effect as that of the MAG type FET 160, the “upper” MAG type FET 172 is
Coupling increases the current through the drain half 176 and is further amplified each time through the “upper” MAG FET 172. To put it the other way around, since the current integration effect is generated by the external magnetic field, the "lower" MAG type FE
Every time it passes through each of T174, MAG type FET1
The reduced current in the drain split 186 of 62 is further reduced. Therefore, "upper" MAG type FET17
The current at the terminal IH in FIG. 12 increases in proportion to the increase in current through the drain halves. Terminal I in FIG.
The current in L decreases in proportion to the decrease in current through each drain half of the "lower" MAG FET 174. The resulting difference between the currents at terminals IH and IL is the difference between the "upper" MAG FET 172 and the "lower" M.
It reflects the additional effect of current integration through each of the AG FETs 174.

The inventor has made available the current difference between the terminals IH, IL resulting from the application of an external magnetic field to the circuit of FIG. 12 to control the duty cycle of a known positive feedback oscillator. thinking. The application of the magnetic field in this way can be indicated by a change in the duty cycle of the oscillator. It is expected that changes in the average voltage of the duty cycle modulated signal will be obtained by low pass filtering of the signal. No adjustment is needed in this example.

In each of the embodiments of the present invention described above, a MAG type FET element is used instead of the currently used reed switch, for example, a subcutaneously implantable pacemaker, electric defibrillator, defibrillator. Alternatively, it can be used separately from a subcutaneously implantable medical device such as a nerve stimulator. Further, the MAG type FET element can be formed as a part of the CMOS integrated circuit. In both cases, there are restrictions regarding the packaging of the MAG-type FET circuit and the placement of the MAG-type FET circuit within the encapsulation body of the subcutaneously implantable device.

The CMOS integrated circuit is generally packaged in a Kovar covered ceramic leadless chip carrier, such a construction being a MAG type F according to the invention.
Not suitable for ET circuits. It may tend to interfere with or divert external magnetic fields. In addition, the circuit including the MAG-type FET device according to the present invention is placed in a device implanted subcutaneously, away from other ferromagnetic materials that may be contained in the device. Although the embodiments of the present invention described above demonstrate a semiconductor magnetic sensor that can operate with low bias currents and supply voltages, this magnetic sensor is particularly suitable for use in subcutaneously implantable medical devices. .

Although various embodiments of the present invention have been disclosed,
The present invention is capable of various other changes and modifications,
It is not limited to those described above.

[0045]

Since the subcutaneously implantable medical device according to the present invention is as described above, a non-mechanical magnetic sensor sensitive to an external magnetic field can be used with a low supply voltage and bias current. Magnetic sensor is a conventional CMO
There is an effect that it can be easily manufactured by using S processing technology.

[Brief description of drawings]

FIG. 1 is a perspective view of a drain split type FET used in a magnetic sensor according to an embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of the drain split type FET of FIG.

FIG. 3 is a circuit diagram showing a cross connection of drain split type FETs according to the present invention.

FIG. 4 is a circuit diagram of a magnetic sensor circuit according to an embodiment of the present invention.

5 is a schematic diagram of a P-channel MAG type FET in the circuit of FIG.

6 is a schematic diagram of an N-channel MAG type FET of the circuit of FIG.

FIG. 7 is a schematic view of another embodiment of the magnetic sensor circuit according to the present invention.

FIG. 8 is a schematic diagram of a multiplexer of the circuit of FIG.

FIG. 9 is a schematic view of another embodiment of the magnetic sensor according to the present invention.

10 is a schematic diagram of a P-channel MAG type FET of the circuit of FIG.

11 is a schematic diagram of an N-channel MAG type FET of the circuit of FIG.

FIG. 12 is a schematic view of another embodiment of the magnetic sensor according to the present invention.

[Explanation of symbols]

10, 10 ', 42, 44, 70, 72 N channel drain split MAG type FET 12 N type substrate 14 source region 16 drain region 18 metal source 20 gate 22 channel region 24, 26, 50, 52, 54, 56, 70a , 70
b, 176, 180, 182, 184, 186, drain half halves 40 magnetic sensor 84, 86, 90, 92 FET 120 multiplexer 122, 124, 126 active load portion 128, 130, 132 MAG type FET device 140 active load device 142 triple drain MAG type FET element 150 triple drain P channel MAG type FET 144, 146, 166, 168, 170 FET element 160 P channel MAG type FET 162 N channel MAG type FET

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor David Thompson 55432 Fried Ray North East Onon Daga Street, Minnesota, United States 1660 (72) Inventor Gary Nelson, Illinois, United States 60194 Schaumburg Colwyn Drive 1322

Claims (12)

[Claims] 1. A subcutaneously implantable medical device including an integrated circuit formed on a silicon substrate and sensitive to application of an external magnetic field for changing a working condition, wherein the integrated circuit is a source, a first plane. A first drain-split FET having a gate defining a channel region and first and second drain halves, a source, a gate defining a second planar channel region, and a second having third and fourth drain halves A plurality of FET elements having a drain split FET and a differential amplifier for generating the output voltage, wherein the first drain half is connected to the fourth drain half and the second drain half is Connected to the third drain half, the source of the first drain split FET connected to a power supply, the source of the second drain split FET connected to a current source, Ias current is the first,
Flowing through the second, third and fourth drain halves, a portion of the bias current flowing through the first drain half and the fourth drain half, and the rest of the bias current being the second. Flowing through the drain halves and the third drain halves, the magnetic field perpendicular to the first and second planar channel regions increasing the portion of the bias current and decreasing the remainder of the bias current; A subcutaneously implantable medical device characterized in that the differential amplifier voltage changes in response to the increase in the portion of the bias current to reduce the remainder of the bias current. 2. The subcutaneously implantable medical device according to claim 1, wherein the first drain split type FET is a P channel drain split type FET, and the second drain split type FET is an N channel FET. 3. The bias current is 10 to 100.
The subcutaneously implantable medical device of claim 1 in the microampere range. 4. The channel regions of the first and first planes are 1:
The subcutaneously implantable medical device of claim 1 having a width / height ratio of 1. 5. A subcutaneously implantable medical device comprising an integrated circuit formed on a silicon substrate and sensitive to the application of an external magnetic field to alter the operating conditions, wherein the integrated circuit comprises a source, a first planar channel. A drain split FET having a gate defining a region and first and second drain halves, connected to a bias circuit including a power supply, and flowing a bias current through the first and second drain split halves; And a plurality of FET elements including a differential amplifier connected between the first and second drain halves to generate an output voltage, and the external magnetic field applied to the drain split type FET is the first drain halves. While increasing the bias current in the second drain split half and decreasing the bias current in the second drain split half, the output voltage of the differential amplifier in the first drain half Varying in proportion to an increase in bias current and a decrease in bias current in the second drain half, the application of the external magnetic field is manifested by the voltage change in the output voltage of the differential amplifier. A medical device that can be implanted subcutaneously, characterized in that 6. The bias current is 10 to 100.
The subcutaneously implantable medical device according to claim 5, which is in a microampere range. 7. The first and second planar channel regions are 1:
The subcutaneously implantable medical device of claim 5 having a width / height ratio of 1. 8. A subcutaneously implantable medical device comprising an integrated circuit formed on a silicon substrate and sensitive to the application of an external magnetic field to alter the operating conditions, wherein the integrated circuit comprises a source, a first planar channel. It comprises first, second, and third triple drain splits having a region-defining gate and drain split, connected to a bias circuit including a power supply to establish a bias current, A part is connected between the triple drain FET that flows through each of the first, second, and third triple drain split bodies and the first and third drain split bodies to generate the output voltage. A plurality of FET elements including a dynamic amplifier, the external magnetic field applied to the drain split type FET increases the bias current in the first triple drain split body, and Reducing the bias current in the heavy drain divider such that the output voltage of the differential amplifier increases the bias current in the first triple drain divider and the bias current in the third triple drain divider. Implantable medical device characterized in that the application of the external magnetic field is manifested by the voltage change in the output voltage of the differential amplifier. 9. A fourth, fifth, and sixth triple drain split body, wherein the fourth triple drain split body is the first triple drain split body.
A third drain split, the fifth triple drain split connects to the second triple drain split, and the sixth triple drain split connects to the third triple drain split. An active load including a second triple drain FET connected to the body and connected to the bias circuit, wherein a portion of the bias current flowing through the first triple drain divider is the fourth. Flow through the third triple drain split, and the balance of the bias current that flows through the second triple drain split also flows through the fifth triple drain split, and the third triple drain split. The bias current flowing through the split body also flows through the sixth triple drain split body, and the external magnetic field increases the bias current flowing through the first and fourth triple drain split bodies. And reducing the bias current flowing through the third and sixth triple drain dividers such that the output voltage of the differential amplifier is the bias current in the first and fourth triple drain dividers. 9. The implantable medical device according to claim 8, wherein the implantable medical device is variable in proportion to the increase and the decrease of the bias current in the third and sixth triple drain partitions. 10. A subcutaneously implantable medical device comprising an integrated circuit formed on a silicon substrate and sensitive to the application of an external magnetic field to alter the operating conditions, wherein the integrated circuit comprises a plurality of cascaded cascaded devices. A first drain split FET, the first drain split FET is connected to a regulated current drain, and the second drain split FET is coupled to the plurality of first drain split FETs; Connected to a regulated current drain, the first drain split FET producing a first output current, the second drain split FET producing a second output current, and the first and second output currents A positive feedback oscillator is also provided that produces an oscillating output having a duty cycle that varies proportionally, and an external magnetic field applied to the integrated circuit increases the first output current. And said reducing the second output current, the external magnetic field applied implantable medical devices, characterized by varying the duty cycle of the oscillation signal. 11. The method of claim 10, further comprising a low pass filter that receives the oscillating signal and produces an output voltage proportional to an average voltage of the oscillating signal, the duty cycle change causing the output voltage change. Medical device that can be implanted subcutaneously. 12. A subcutaneously implantable medical device comprising an integrated circuit formed on a silicon substrate and sensitive to the application of an external magnetic field to alter the operating conditions, wherein the integrated circuit receives a plurality of digital input signals. Receiving a plurality of output lines, including a plurality of drain split type FETs, wherein the plurality of digital input signals select the plurality of drain split type FETs to connect to the plurality of output lines, and the plurality of drains Each of the split FETs includes a source, a gate defining a planar channel region, and first and second drain halves, the planar channel region of each of the plurality of drain split FETs being the other of the plurality of other split FETs. Split drain type FE
A multiplexed active load circuit having a different dimension than T, a source, a gate defining a planar channel region, and a drain split type F including third and fourth drain halves.
Another pair of ETs and a plurality of FET elements including a differential amplifier that produces an output voltage, wherein the first drain half of the selected drain split type FET is the fourth drain element. A drain split FET connected to the drain half and the second drain half of the selected drain split FET connected to the third drain half and including the multiplexed active load.
The sources of the plurality of drains are connected to a power source, and the sources of the drain-split FETs forming the other pair are connected to a current source, and a bias current of the drain-split FETs is selected. A part of the bias current flows through the first and second drain halves and the third and fourth drain halves, and the first drain half and the fourth drain halves of the selected drain split FET. Flowing through the drain halves and the remainder of the bias current through the second drain halves and the third drain halves of the selected drain split FFT, the selected drain split FETs A magnetic field perpendicular to the first planar channel region and the second planar channel region of the bias current increases the portion of the bias current and increases the bias current. And the differential amplifier output voltage changes in response to the increase in the portion of the bias current and the decrease in the remainder of the bias current, the extent of the change varying between the plurality of drains. A subcutaneously implantable medical device characterized by being variable depending on which of the split type FETs is selected.