FIELD

[0001] The following relates generally to the sensor arts, medical monitoring arts, core body temperature monitoring arts, and related arts.

BACKGROUND

[0002] Core body temperature is a key vital sign for assessing medical status of a patient or other medical subject. A straightforward approach for measuring a patient’s temperature is to place a patient thermometer in contact with the patient’s skin. The thermometer typically includes a thermistor (that is, a sensor whose resistance varies with temperature), thermocouple, or other temperature sensor that measures the temperature of the contacted skin. However, the measured skin temperature can differ significantly from the core body temperature. An esophageal or rectal thermometer provides a temperature measurement that is closer to the core body temperature, but at the cost of increased invasiveness and discomfort to the patient, and the esophageal or rectal temperature can still differ significantly from the core body temperature. True core body temperature measurement can be performed using more invasive probes, but this is usually not justified except in the case of critically ill patients in an intensive care ward or the like.

[0003] Some non-invasive approaches for estimating core body temperature are disclosed in Shrubsole et al., U.S. Pub. No. 2017/0100042 Al . For example, a single heat flux approach disclosed therein for performing core body temperature measurements uses two temperature sensors separated by an insulating material. Temperature measurements by the two sensors along with the thermal resistivity of the separating insulator are processed to estimate the core body temperature. Such approaches are advantageously non-invasive and estimate the core body temperature which is the temperature vital sign that is typically of greatest clinical interest in assessing patient condition.

[0004] However, a problem with such approaches is that the output of a patient thermometer which employs a heat flux approach does not comport with that of a typical analog patient thermometer. For example, existing commercial patient monitors often include one or more thermistor probe inputs to which a patient thermometer employing a single thermistor can be connected. By contrast, because the non-invasive core body temperature measurements of U.S. Pub. No. 2017/0100042 Al employ two temperature sensors and analog or digital processing (the latter requiring analog-to-digital conversion of the temperature sensor readings), the resulting temperature signal is not in the form of a standard thermistor resistance, and hence cannot be coupled with a thermistor probe input of a commercial patient monitor.

[0005] More generally, it is increasingly common for conventional analog medical sensors to be replaced by digital medical sensors. While digital medical sensors can have numerous advantages, they are not backward compatible with legacy analog medical sensors for which many patient monitors are designed to connect.

[0006] The following discloses certain improvements.

SUMMARY

[0007] In some non-limiting illustrative embodiments disclosed herein, a device is disclosed for connecting a sensor with a probe input configured to read a resistive load. The device comprises: a resistance emulation circuit configured to emulate a resistance at output terminals; a controller comprising at least one of an electronic processor and analog control circuitry, the controller configured to control the resistance emulation circuit to emulate a desired resistance at the output terminals; a buffered voltage measurement circuit having a buffered connection to the output terminals and configured to output a measurement of voltage over the output terminals; and a current measurement circuit configured to output a measurement of electrical current across the output terminals. The controller is further configured to determine a measured emulated resistance from the measurement of voltage over the output terminals and the measurement of electrical current across the output terminals and to calibrate the control of the resistance emulation circuit to match the measured emulated resistance with the desired resistance. In some embodiments, the resistance emulation circuit includes a capacitor configured to be switchable between being electrically connected across the output terminals or electrically disconnected from the output terminals. In some embodiments, the controller is further configured to determine the desired resistance by converting a temperature to the desired resistance using a temperature -to-thermistor resistance conversion operation.

[0008] In some non-limiting illustrative embodiments disclosed herein, a core body temperature (CBT) thermometer comprises a CBT sensor assembly including a first temperature sensor and a second temperature sensor separated by an insulating material or layer, and CBT processing electronics comprising a device as set forth in the immediately preceding paragraph. In the CBT thermometer, the controller is further configured to determine the temperature from a first temperature measured by first temperature sensor and a second temperature measured by the second temperature sensor and a resistance or resistivity of the insulating material or layer.

[0009] In some non-limiting illustrative embodiments disclosed herein, a resistance emulation method is disclosed. A resistance emulation circuit comprising a switched charge storage circuit is switched at a switching frequency to present an emulated resistance at output terminals. During the switching, the emulated resistance is measured using a buffered voltage measurement circuit to measure voltage over the output terminals and a current measurement circuit to measure electrical current across the output terminals. Furthermore during the switching, the switching frequency is dynamically calibrated to match the measured emulated resistance with a desired resistance. In some embodiments, the current measurement circuit measures electrical current in a discharge sub-circuit of the switched charge storage circuit. In some embodiments, the measuring of the emulated resistance includes buffering the connection of the buffered voltage measurement circuit to the output terminals using at least one operational amplifier, and the current measurement circuit includes at least one operational amplifier. In some embodiments, the current measurement circuit comprises a transimpedance amplifier. In some embodiments, the resistance emulation method further includes determining the desired resistance by converting a temperature to the desired resistance using a temperature -to-thermistor resistance conversion operation.

[0010] In some non-limiting illustrative embodiments disclosed herein, a CBT thermometer comprises: a CBT sensor assembly including a first temperature sensor and a second temperature sensor separated by an insulating material or layer; a resistance emulation circuit; and an electronic processor. The electronic processor is programmed to: (i) compute a core body temperature from a first temperature measured by first temperature sensor and a second temperature measured by the second temperature sensor and a resistance or resistivity of the insulating material or layer; (ii) convert the computed core body temperature to a desired resistance using a temperature -to-thermistor resistance conversion operation; and (iii) control the resistance emulation circuit to emulate the desired resistance at output terminals.

[0011] In some non-limiting illustrative embodiments disclosed herein, a CBT thermometer as set forth in the immediately preceding paragraph further includes a measurement circuit connected with the resistance emulation circuit to dynamically measure emulated resistance at the output terminals. The measurement circuit includes a buffered voltage measurement circuit and a current measurement circuit. The electronic processor is further programmed to calibrate the control of the resistance emulation circuit to match the dynamically measured emulated resistance with the desired resistance.

[0012] One advantage resides in providing a medical sensor employing advanced technology such as digital processing, and that is compatible with a patient monitor probe input designed for standard analog medical sensor.

[0013] Another advantage resides in more particularly providing a patient thermometer employing advanced technology such as multiple temperature sensors and analog or digital processing, and which is also compatible with a standard thermistor probe input of a patient monitor or other standard temperature readout device.

[0014] Another advantage resides in more particularly providing a patient thermometer that non-invasively estimates core body temperature and is also compatible with a standard thermistor probe input of a patient monitor or other standard temperature readout device.

[0015] Another advantage resides in providing a medical sensor or patient thermometer with one or more of the foregoing advantages and that meets stringent medical measurement accuracy requirements, but with reduced manufacturing cost through the use of less costly electronic components that do not have tight tolerance specifications.

[0016] Another advantage resides in providing a medical sensor or patient thermometer with one or more of the foregoing advantages and that meets stringent medical measurement accuracy requirements including insensitivity to operating temperature of the medical sensor or patient thermometer.

[0017] A given embodiment may provide none, one, two, more, or all of the foregoing advantages, and/or may provide other advantages as will become apparent to one of ordinary skill in the art upon reading and understanding the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention.

[0019] FIGURE 1 diagrammatically illustrates a patient thermometer designed to estimate core body temperature according to a first embodiment.

[0020] FIGURE 2 diagrammatically illustrates a patient thermometer designed to estimate core body temperature according to a second embodiment. [0021] FIGURE 3 diagrammatically illustrates a more detailed implementation of the calibration circuitry of the patient thermometers of FIGURES 1 and 2.

PET A TUFT) DESCRIPTION

[0022] With reference to FIGURE 1, a non- invasive core body temperature (CBT) thermometer includes a non-invasive CBT sensor assembly 10 and CBT processing electronics 12. The illustrative non-invasive CBT sensor assembly 10 includes two temperature sensors TS1, TS2 separated by an insulating material or layer Ins. The two temperature sensors TS1, TS2 may, by way of non-limiting illustration, comprise thermistors, thermocouples, or so forth. When used for measuring patient temperature, one of the two temperature sensors (namely sensor TS1 in the illustrative example) is placed in thermal contact with skin 14 of the patient. The other temperature sensor (namely sensor T2 in the illustrative example) is spaced apart from the first temperature sensor TS1 by a distance d _sep by the insulator Ins. The non-invasive CBT sensor assembly 10 produces two analog signals: one output by the temperature sensor TS1, and the other output by the temperature sensor TS2. Denoting the temperature measured by the temperature sensor TS1 contacting the skin 14 as T 1 and the temperature measured by the temperature sensor TS2 as T 2, and further denoting the estimate of the core body temperature as TO, the temperatures TO, Tl, and T2 are related as follows (see Shrubsole et al., U.S. Pub. No. 2017/0100042 Al): where R is the thermal resistance of the insulator Ins and R ₀ is the thermal resistance of the body. (Since the ratio R ₀ /R ₁ appears in Equation (1) and the areas of the effective resistors are about the same, resistivity values can be equivalently used). Various approaches such as those described in Shrubsole et al., can be used to estimate R ₀ and thereby obtain an estimate TO of the core body temperature using Equation (1). It is also to be appreciated that the non-invasive CBT sensor assembly 10 and described single heat flux approach for processing measurements TO and Tl is an illustrative example, and that other types of non-invasive CBT sensor assemblies may be employed, such as one with actuators for adjusting the separation d _sep to provide additional data for estimating R ₀ , or use of the dual heat flux approach, various combinations thereof, or so forth. In each such design, the CBT sensor assembly outputs two (or more) sensor readings and CBT processing electronics 12 perform signal and/or data processing in the analog and/or digital domain in order to generate the CBT temperature estimate TO which is a digital value (in the illustrative examples) or an analog value that is not embodied as a thermistor resistance.

[0023] The CBT thermometer 10, 12 further has output terminals 16 which are connectable with a standard thermistor probe input 18 of a patient monitor 20 or other standard temperature readout device (e.g. dedicated handheld thermometer readout device). By“connectable” it is understood that the output terminals 16 comprise an output connector physically shaped and sized to mate with the standard thermistor probe input 18 of the temperature readout device 20. For example, the output terminals 16 may comprise a standard M12 connector, a standard RTD connector, or any other standardized thermistor connector that is designed to mate with the standard thermistor probe input 18 of the temperature readout device 20.

[0024] With continuing reference to FIGURE 1 and with further reference to FIGURE 2, turning now to the patient monitor or other standard temperature readout device 20, this device includes the standard thermistor probe input 18 which is designed to read a standard thermistor. Such a standard thermistor presents a resistance whose value depends on the temperature of the thermistor. Thus, the readout device 20 is designed to read the resistance (denoted R here) of the thermistor connected to the thermistor probe input 18 and to convert that resistance to a temperature reading. To read the resistance R of the thermistor, as shown in FIGURE 1 the readout device 20 can include voltage excitation circuit 22 which applies an excitation voltage (U _m ) to the thermistor and measures the resulting electrical current. The resistance is then applied voltage U _m divided by the measured electrical current. Alternatively, as shown in FIGURE 2 the readout device 20 can employ a current excitation circuit 24 which applies an excitation electrical current (Im) to the thermistor and measures the resulting electrical voltage. The resistance is then the measured voltage divided by the applied current I _m . Whichever excitation circuit 22, 24 is used, the result is the thermistor resistance R, and the temperature readout device 20 further includes analog control circuitry and/or a digital microprocessor or microcontroller (not shown) which converts the thermistor resistance R to a temperature reading using a look-up table or empirical mathematical function T(R) for the particular type of thermistor being read. The look-up table or mathematical function T(R) is known for the particular type of thermistor being used and the microprocessor or microcontroller is programmed to apply it, or alternatively an op-amp circuit or the like performs analog control signal processing to convert thermistor resistance R to an electrical signal that is proportional to the temperature reading. Typically, the patient monitor or other readout device 20 includes other components such as a display 26 for displaying the temperature reading (and other acquired patient data in the case of a multi-function patient monitor and a keyboard, soft keys, buttons, switches, and/or other user input device(s) 28 by which the user can configure and/or control the readout device 20 (e.g., in some readout devices the user may be able to select the thermistor type and the microprocessor or microcontroller then applies the look-up table or mathematical function T(R) that is appropriate for that thermistor type.

[0025] As previously discussed, however, the CBT thermometer 10, 12 does not employ a single thermistor whose resistance can be directly read and converted to a patient temperature reading. Instead, the CBT 10, 12 includes (at least) two temperature sensors TS1, TS2 (which may or may not be thermistors) and analog and/or digital processing performed by the CBT processing electronics 12 in order to generate the CBT reading 70 which is not embodied as a thermistor resistance. In the illustrative example, the CBT processing electronics 12 include analog-to-digital converters A/D that digitize the thermistor readings 71, 72 of respective temperature sensors TS1, TS2 and these digitized thermistor readings 71, 72 are processed by a controller comprising an electronic processor 30 (for example, a microprocessor or microcontroller operatively connected with a memory device such as a ROM, PROM, EPROM, flash memory or so forth storing suitable processor-executable software or firmware to perform the disclosed processing) which performs a core body temperature estimation process to output the CBT estimate 70, for example by way of Equation (1). It will be appreciated that the controller may additionally or alternatively comprise analog control circuitry, for example embodied as one or more operational amplifier (op amp) circuits implementing the mathematical operations of Equation (1). However, the CBT estimate 70 is a digital value stored in the electronic processor 30; whereas, the temperature readout device 20 has a standard thermistor probe input 18 which cannot read this digital CBT value 70.

[0026] To provide backward compatibility with the standard thermistor probe input 18 of the temperature readout device 20, the CBT processing electronics 12 further include a resistance emulation circuit that emulates the thermistor resistance (for a chosen thermistor type) corresponding to the CBT estimate 70 at the output terminals 16 of the CBT thermometer 10, 12. To this end, a controller comprising the electronic processor 30 (or in alternative embodiments, a controller implemented as analog control circuitry, or again alternatively a controller implemented as a combination of electronic circuitry and an electronic processor) is further programmed to convert the CBT estimate TO to the corresponding thermistor resistance RCBT using a suitable look-up table or function denoted as TO > RCBT in FIGURES 1 and 2, and then to convert the thermistor resistance R _CBT 1° ^a suitable control signal for controlling the resistance emulation circuit to emulate the resistance R _CBT using a suitable look-up table or function denoted as RCBT > f in FIGURES 1 and 2 (where / denotes the control signal which is, or corresponds to, a frequency in the illustrative embodiment). The look-up table or function denoted as TO > RCBT is simply the inverse of the look-up table or empirical mathematical function T(R) for the particular type of thermistor that the temperature readout device 20 expects to have connected at the standard thermistor probe input 18. The look-up table or function RCBT > f is the appropriate mapping for the particular type of resistance emulation circuit that is implemented by the CBT processing electronics 12; that is, the output / of this look-up table or function should be appropriate to cause the resistance emulation circuit to emulate the particular resistance RCBT ^a t the output terminals 16 of the CBT thermometer 10, 12. The output / may not actually be equal to the desired frequency, but rather may for example be a voltage appropriate for application to a voltage- controlled oscillator (VCO) or other electronic component for setting the operating frequency of the resistor emulation circuit. Furthermore, the controller comprising the electronic processor 30 computes the control signal / as a digital value that is converted to an analog control signal by a digital-to-analog converter denoted as D/A in FIGURES 1 and 2. In general, the resistance emulation circuit 40, 42 comprises a switched charge storage circuit (storing charge in the capacitor C in the illustrative examples), and the controller 30 is configured to control the resistance emulation circuit 40, 42 to emulate the desired resistance RCBT ^a t the output terminals 16 by controlling the switching frequency / of the resistance emulation circuit.

[0027] The processing to generate the control signal / from the CBT estimate TO is implemented in FIGURES 1 and 2 by way of first conversion operation TO > RCBT followed by second conversion operation RCBT > f. Alternatively, the electronic processor 30 could be programmed to apply a single conversion operation TO > f that directly converts the CBT estimate TO to the control signal / for controlling the resistor emulation circuit. The approach of FIGURES 1 and 2 in which two serial conversion operations are performed has an advantage, however, in that it allows for the CBT thermometer 10, 12 to be easily configured to provide output at the terminals 16 for a variety of different thermistor types, simply by having different look-up tables or functions TO > RCBT for the different thermistor types and choosing the appropriate one using a user control such as a physical switch for setting the thermistor type at the CBT thermometer 10, 12 or an equivalent software configuration setting. In general, the first conversion operation TO > RCBT is a temperature -to-thermistor resistance conversion, that is, the first conversion operation TO > RCBT outputs the resistance R _CBT that a thermistor (of the particular type being emulated) would output when the thermistor is at the temperature TO.

[0028] The resistance emulation circuit suitably depends on the type of excitation mode to be used in reading the thermistor.

[0029] In the example of FIGURE 1, the readout device 20 uses the voltage excitation circuit 22 which applies excitation voltage (U _m ) to the standard thermistor probe input 18 and measures the resulting electrical current, and the resistance is then applied voltage U _m divided by the measured electrical current. To emulate the resistance in this case an illustrative resistance emulation circuit 40 is employed, which includes a capacitor C and two single pole double throw (SPDT) switches SW1 , SW2 which are operated at the frequency /. In the resistance emulation circuit 40, the amount of charge Q for each cycle is Q = C U _meas where Q may be expressed in units of Coulombs or A-s, for example. When the switches SW1, SW2 are switched at the frequency /, this results in an electric current of I = f C U _meas where / may be suitably expressed in units of Coulomb/s or amperes [A], for example. The emulated resistance (R _emu ) is: which may be suitably expressed in units of V/A or ohms [W] It is assumed in this evaluation that the capacitor C becomes fully charged to the applied voltage U _meas during the charging period and becomes fully discharged during the discharging phase.

[0030] In the example of FIGURE 2, the readout device 20 uses the current excitation circuit 24 which applies excitation electrical current (I _m ) to the standard thermistor probe input 18 and measures the resulting electrical voltage, and the resistance is then the measured voltage divided by the applied current I _m . To emulate the resistance in this case an illustrative resistance emulation circuit 42 is employed, which includes the capacitor C and the two single pole double throw (SPDT) switches SW1, SW2 which are operated at the frequency /, and further includes a capacitor C _b placed in parallel across the terminals 16. This allows the measuring current to continue through the capacitor C _b while the switches SW1, SW2 are in the discharging position. The load current due to the charging and discharging cycle of the capacitor C is Q = C U _meas , just as in the voltage driven case of FIGURE 1. When the switches are in the discharging position, the generated measuring current from the current excitation circuit 24 flows into the capacitor C _b . When the excitation current I _m and the current I _j flowing in the resistance emulation circuit 42 are different, then the capacitor C _b will be charged or discharged until an equilibrium is obtained at a certain voltage level U _m . In that condition, l _m = / _/ = / C U _m . From this it follows that the emulated impedance R _emu is: which is the same as for the voltage driven case of FIGURE 1.

[0031] Although not illustrated, for the voltage driven case of FIGURE 1 it is contemplated to have an input capacitor at the thermistor emulation input, which will decouple the impedance measuring system in the instrument from the switching behavior of the switched capacitor circuit.

[0032] Comparing FIGURES 1 and 2, it is seen that the illustrative resistance emulation circuit 40 and the illustrative resistance emulation circuit 42 differ by the addition of the capacitor C _b placed in parallel across the output terminals 16 in the circuit 42, which is not present in the circuit 40. The capacitor C _b in the circuit of FIGURE 2 allows the measuring current to continue through the capacitor C _b while the switches SW1 , SW2 are in the discharging position, so that the emulated resistance can be measured using the current excitation circuit 24 which applies excitation electrical current (I _m ) and measures the resulting electrical voltage. Although not shown in FIGURE 1, the capacitor C _b is also optionally present in some variant embodiments of the voltage driven situation of FIGURE 1. For example, in some cases, the circuitry of the resistance measuring equipment 24 is not able to follow the fast transients of the switches SW1 and SW2, leading to measurement errors. Having the capacitor C _b in the circuit of FIGURE 1 in such cases advantageously smooths these transients (bandwidth limitation), making the dynamic behavior of the variant resistance emulation circuit 40 modified by further including capacitor C _b compatible with the dynamic range of the resistance measuring equipment. [0033] A difficulty with both the resistance emulation circuit 40 of FIGURE 1 and the resistance emulation circuit 40 of FIGURE 2 is that the emulated resistance R _emu is very sensitive to the precise capacitance value of the capacitor C. This might be addressed by manufacturing the resistance emulation circuit with the capacitor C being a component manufactured to tight tolerance specifications. However, such a capacitor is typically substantially more expensive than an otherwise equivalent capacitor that is manufactured to looser tolerance specifications. Furthermore, even if the capacitor C is manufactured to tight tolerance specifications, the actual capacitance can vary significantly as a function of temperature of the capacitor C (which in turn typically depends on the operating temperature of the CBT processing electronics 12). Since a CBT thermometer is commonly used in clinical situations for which an oral or rectal thermometer is deemed to be insufficiently accurate, it is undesirable for the non-invasive CBT thermometer 10, 12 to exhibit inaccuracies due to loose manufacturing tolerances and/or temperature variations in the capacitor C of the resistance emulation circuit 40, 42.

[0034] To address this problem, in illustrative embodiments the resistance emulation circuit further includes (or, viewed differently, is augmented by) a calibration circuit that measures both the actual voltage and the actual current so as to directly measure the emulated resistance R _emu These measurements are fed back to the electronic processor 30 and compared with the CBT resistance R _CBT which is intended to be emulated, in order to dynamically generate a correction factor in a calibration operation denoted as Cal in FIGURES 1 and 2.

[0035] The illustrative calibration circuit of FIGURES 1 and 2 includes: (i) a buffered voltage measuring circuit 50 comprising an operational amplifier integrated circuit (op amp) OAi and four impedances Zi, Z ₂ , Z ₃ , Z ₄ collectively forming an instrumentation amplifier; and (ii) and a current measuring circuit 52 comprising an op amp OA2 and an impedance Z ₅ collectively forming a transimpedance amplifier (TIA). The current measuring circuit 52 is implemented as a virtual short circuit to the connected capacitor when the SPDT switches SW1 and SW2 are switched to the TIA input. Said another way, the current measuring circuit 52 comprises a TIA connected as a virtual short circuit in a charge storage discharge sub-circuit of the switched resistance emulation circuit 40, 42. The buffered voltage measuring circuit 50 has a buffered connection to the output terminals 16, for example buffered by the op amp OAi or, in another embodiment (see FIGURE 3), buffered by unity gain buffer amplifiers. The buffered connection ensures that the buffered voltage measuring circuit 50 does not significantly impact the emulated resistance presented at the output terminals 16. The output of the buffered voltage measuring circuit 50 is a measurement of the voltage U _meas and is digitized by an A/D converter and input to the electronic processor 30 in order to perform the calibration operation Cal; and analogously the output of the current measuring circuit 52 is a measurement of the current I _m = f and is digitized by another A/D converter and also input to the electronic processor 30 in order to perform the calibration operation Cal. In a suitable implementation of the calibration operation Cal, the actual measured resistance Rff = is computed, and a calibration factor d is determined

for use in the conversion operation RCBT > f based on comparison of the actual measured resistance R^jf _u ^{S an} d the intended resistance R _CBT that is output by the conversion operation TO > RCBT. This can be done using Equation (3) as follows. The actual measured situation is: nmeas 1

nemu (4)

factual ^' C

Whereas, the desired situation is:

In Equations (4) and (5), the unknowns are the actual frequency ( factual ) ^an d the exact capacitance C (which may differ from nominal due to finite component tolerance and/or temperature drift). The desired calibration factor is such that fdesired = factual ^{so :}

Thus, the calibration factor d is suitably computed by the calibration operation Cal as the ratio of the measured resistance Rfl% _u ^S divided by R _CBT (output by the conversion operation TO > RCBT). It will be understood that the appropriate calibration factor may be different in alternative embodiments which employ a different switched resistance emulation circuit topology. Moreover, it will be appreciated that the calibration factor d may be alternatively generated by an analog control circuit, such as an op amp circuit implementing the resistance ratio of Equation (6).

[0036] With reference to FIGURE 3, a more detailed illustrative embodiment is shown, including the illustrative resistance emulation circuit 40 with SPDT switches SW1, SW2 similar to that of FIGURE 1. In this embodiment, the buffered voltage measuring circuit 50 is implemented using op amps OAi and OA3 along with two additional op amps OAo,i and OAo,2 forming unity gain buffer amplifiers. Opamp OA3 is used to generate a DC reference level halfway between ground and supply voltage, which keeps the operating point of the op amps in the middle of the supply voltage. The unity gain buffer amplifiers OAo,i and OAo,2 serve to provide a buffered connection to the output terminals 16 and thereby ensure that the buffered voltage measuring circuit 50 does not significantly impact the emulated resistance presented at the output terminals 16. The current measuring circuit 52 is implemented in the capacitor discharge path, as a TIA stage which introduces a virtual short circuit to the connected capacitor when switched to the TIA input.

[0037] Advantageously, the voltage and current measurement circuits 50, 52 and associated control provide dynamic calibration of the emulated resistance at the output terminals 16. By“dynamic calibration” it is meant that the emulated resistance is adjusted in real time based on the voltage over the output terminals 16 measured using the buffered voltage measurement circuit 50 and the electric current across the output terminals 16 measured using the current measurement circuit 52. The dynamic calibration automatically corrects for any difference between the actual capacitance of the capacitor C and its design-basis capacitance and thereby may allow for use of a capacitor of lower tolerance than would otherwise be required in order to meet a given temperature accuracy specification. Furthermore, the dynamic calibration automatically adjusts for any change in the capacitance of the capacitor C due to a change in temperature of the capacitor C, or more generally, automatically adjusts for any change in the resonance properties of the switched charge storage circuit. This adjustment for temperature variation occurs in real time due to the dynamic calibration, which means that temperature effects are automatically compensated, thereby improving accuracy of the resistance emulation circuit.

[0038] The illustrative embodiments are merely examples, and a wide range of variants are contemplated. For example, if the capacitor C has sufficiently tight tolerance and low temperature dependence, then it is contemplated to implement a CBT thermometer such as that of FIGURE 1 or of FIGURE 2 with the voltage and current measurement circuits 50, 52 and the calibration operation Cal omitted. In other variants, the illustrative resistance emulation circuit 40 or illustrative resistance emulation circuit 42 may be implemented as another type of switched resistance emulation circuit, for example replacing the SPDT switches SW1 , SW2 with another type of switching element, and/or employing a different switched charge storage circuit topology such as employing a different charge storage element in place of the illustrative capacitor C, such as an inductance or an reactance; and/or adding additional trim resistance(s); and/or so forth. While in the illustrative embodiment the input to the illustrative resistance emulation circuit 40 or illustrative resistance emulation circuit 42 is an a.c. signal of frequency /, other types of inputs may be supplied depending upon the resistance emulation circuit topology and ancillary circuitry. For example, if the switched resistance emulation circuit includes a voltage controlled oscillator (VCO) that controls the switching frequency, then the control signal may be a d.c. voltage that serves as the input to the VCO.

[0039] Still further, it will be appreciated that the illustrative resistance emulation circuit

40 or illustrative resistance emulation circuit 42 or other switched charge storage circuit (with or without the voltage and current measurement circuits 50, 52 and associated control providing dynamic calibration of the emulated resistance, depending upon a specific implementation) may be employed to facilitate connection of substantially any type of medical sensor with a standard thermistor probe input 18 of a patient monitor or other standard temperature readout device 20. By way of some further examples, the temperature -based medical sensor that is coupled with the standard thermistor probe input 18 via the electrical circuitry 40, 42, 50, 52 with suitable programming of the electronic processor 30 may include (but is not limited to): a digital oral thermometer that outputs a digital oral temperature value that is converted using the T0>R _CBT and Rc _BT >f conversions (where TO in such an oral thermometer embodiment represents the digital oral thermometer reading); a digital rectal thermometer that outputs a digital rectal temperature value that is converted using the T0>RCBT and RcBT>f conversions (where TO in such a rectal thermometer embodiment represents the digital rectal thermometer reading); a thermocouple- based medical thermometer of any type that outputs a thermocouple voltage that is converted to a temperature TO and then further converted using the T0>RCBT and RcBT>f conversions (where TO in such a thermocouple -based thermometer embodiment represents the thermometer reading corresponding to the measured thermocouple voltage); and so forth. Still further, the approach is contemplated for use in non-medical settings, e.g. to convert a temperature measured by an automotive sensor to an equivalent thermistor resistance value.

[0040] As still yet further contemplated variant embodiments, the disclosed approaches may be employed to couple substantially any type of digital or analog sensor reading to a probe input designed to measure a resistance using either the voltage excitation circuit 22 or an equivalent, or using the current excitation circuit 24 or an equivalent.

[0041] The invention has been described with reference to the preferred embodiments.

Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.