GB2588605A

GB2588605A - An apparatus suitable for transforming an analogue temperature-dependent signal into a digital temperature-dependent signal

Info

Publication number: GB2588605A
Application number: GB1915580.3A
Authority: GB
Inventors: Matic Tomislav; Herceg Marijan
Original assignee: Nokia Technologies Oy
Current assignee: Nokia Technologies Oy
Priority date: 2019-10-28
Filing date: 2019-10-28
Publication date: 2021-05-05
Also published as: GB201915580D0

Abstract

The apparatus comprises: a first input 101 for receiving a first sensed voltage, which may be a difference ΔVbe between voltage drops across two diodes; a second input 102 for receiving a second sensed voltage, which may be a voltage drop Vbe across a single diode; and circuits 111 and 112 for providing respective first and second reference voltages VR1 and VR2, which vary at respective first and second fixed rates. Circuits 111 and 112 may each comprise a constant current source 132 and an integrating capacitor 133 (fig.3). The apparatus operates in two phases. During the first phase, a comparator 120 compares the first sensed voltage ΔVbe against the first ramp reference voltage VR1 and outputs a first logic value L1 for a period of time t1 proportional to the first sensed voltage ΔVbe. During a second phase, the comparator compares the second sensed voltage Vbe against the second ramp reference voltage VR2 and outputs a second logic value L2 for a period of time t2 proportional to the second sensed voltage (fig.7). The average value of the comparator output represents the temperature, over any number of cycles comprising the two phases. The low power circuit may operate asynchronously.

Description

TITLE

An apparatus suitable for transforming an analogue temperature-dependent signal into a digital temperature-dependent signal.

TECHNOLOGICAL FIELD

Embodiments of the present disclosure relate to transforming an analogue signal into a digital signal. Some relate to transforming an analogue temperature-dependent signal into a digital temperature-dependent signal.

BACKGROUND

Analog sensors are widely used in instrumentation, measurement and control systems. Examples of analog sensor include temperature sensors such as thermistors, negative temperature coefficient (NTC) resistors, diodes, transistors etc. It would be desirable to acquire information on a parameter sensed by an analog sensor and transform it to digital information in a simple implementation that has low power consumption.

BRIEF SUMMARY

According to various, but not necessarily all, embodiments there is provided an apparatus comprising: a first input means for receiving a sensed voltage; a voltage source means for providing a reference voltage that varies at a fixed rate; comparator means for comparing the sensed voltage against the varying reference voltage and providing an output of a defined logic value for a time period equal or substantially equal to the time required for the reference voltage to vary by an amount equal or substantially equal to the sensed voltage.

In some, but not necessarily all examples, the voltage source comprises a constant current integrator.

In some, but not necessarily all examples, the voltage source comprises a constant current source and a capacitor that is configured to be charged by the constant current source during a first phase and configured to be discharged during a second phase.

In some, but not necessarily all examples, the apparatus comprises a sensor circuit, for providing the sensed voltage, comprising: a first diode configured to be forward biased by a first constant current density to have a first voltage drop across the first diode; a second diode configured to be forward biased by a second constant current density to have a second voltage drop across the second diode; and an output for outputting a difference between the first voltage drop and the second voltage drop.

In some, but not necessarily all examples, the first diode and the second diode are diode connected bipolar junction transistors.

In some, but not necessarily all examples, the sensed voltage is proportional or substantially proportional to a temperature of a temperature sensor circuit, wherein a change in the time period is indicative of a change in temperature.

In some, but not necessarily all examples, the input means is a first input means, the sensed voltage is a first sensed voltage, the voltage source means is a first voltage source means, the reference voltage is a first reference voltage and the fixed rate is a first fixed rate; wherein the first input means is configured to receive the first sensed voltage; the first voltage source means is configured to provide the first reference voltage that varies at the first fixed rate; the apparatus further comprising: a second input means is configured to receive a second sensed voltage; a second voltage source means is configured to provide a second reference voltage that varies at a second fixed rate; and control circuitry configured to cause during a first phase comparison by the comparator means of the first sensed voltage against the varying first reference voltage and provision of an output of a defined first logic value for a time period equal or substantially equal to the time required for the first reference voltage to vary by an amount equal or substantially equal to the first sensed voltage; and during a second phase comparison by the comparator means of the second sensed voltage against the varying second reference voltage and provision of an output of a defined second logic value for a time period equal or substantially equal to the time required for the second reference voltage to vary by an amount equal or substantially equal to the second sensed voltage.

In some, but not necessarily all examples, the apparatus comprises a sensor circuit, for providing the sensed voltage, comprising: a first diode configured to be forward biased by a first constant current density to have a first voltage drop across the first diode; a second diode configured to be forward biased by a second constant current density to have a second voltage drop across the second diode; and an output for outputting a difference between the first voltage drop and the second voltage drop, wherein the first input means is configured to receive the difference between the first voltage drop across the first diode forward-biased by the first constant current density and the second voltage drop across the second diode forward biased by the second constant current density, and wherein the second input means is configured to receive the first voltage drop across the first diode forward-biased by the first constant current density In some, but not necessarily all examples, the apparatus comprises circuitry for determining a mean value of the output of the comparator means.

In some, but not necessarily all examples, the mean value is determined over a period defined by a combination of the first phase and the second phase or the second phase and the first phase.

In some, but not necessarily all examples, the period has a constant frequency and a pulse width modulation that varies with changes in temperature.

In some, but not necessarily all examples, the first voltage source means and the second voltage source means operate alternately and asynchronously.

In some, but not necessarily all examples, the first voltage source means and the second voltage source means alternately share a common constant current source.

According to various, but not necessarily all, embodiments there is provided an apparatus comprising: a first input configured to receive a first sensed voltage; a second input configured to receive a second sensed voltage; a first voltage source configured to provide a first reference voltage that varies at a first fixed rate; a second voltage source configured to provide a second reference voltage that varies at a second fixed rate; a comparator; and control circuitry configured to during a first phase control comparison by the comparator of the first sensed voltage against the varying first reference voltage and provide an output of a defined first logic value for a time period equal to the time required for the first reference voltage to vary by an amount equal to the first sensed voltage; and during a second phase control comparison by the comparator of the second sensed voltage against the varying second reference voltage and provide an output of a defined second logic value for a time period equal to the time required for the second reference voltage to vary by an amount equal to the second sensed voltage.

According to various, but not necessarily all, embodiments there is provided an apparatus comprising: a first input for receiving a sensed voltage; a voltage source configured to provide a reference voltage that varies at a fixed rate; a comparator configured to compare the sensed voltage against the varying reference voltage and provide an output of a defined logic value for a time period equal or substantially equal to the time required for the reference voltage to vary by an amount equal or substantially equal to the sensed voltage.

According to various, but not necessarily all, embodiments there is provided an integrated circuit configured to provide the apparatus.

According to various, but not necessarily all, embodiments there is provided examples as claimed in the appended claims.

BRIEF DESCRIPTION

Some example embodiments will now be described with reference to the accompanying drawings in which: FIG 1 shows an example embodiment of the subject matter described herein; FIG 2A shows another example embodiment of the subject matter described herein; FIG 2B shows another example embodiment of the subject matter described herein; FIG 3 shows another example embodiment of the subject matter described herein; FIG 4 shows another example embodiment of the subject matter described herein; FIG 5 shows another example embodiment of the subject matter described herein; FIG. 6A & 6B show another example embodiment of the subject matter described herein; FIG. 7A, 7B & 7C show another example embodiment of the subject matter described herein; FIG. 8A shows another example embodiment of the subject matter described herein; FIG. 8B shows another example embodiment of the subject matter described herein; FIG. 9 shows another example embodiment of the subject matter described herein; FIG. 10A shows another example embodiment of the subject matter described herein FIG. 10B shows another example embodiment of the subject matter described herein; and FIG. 10C shows another example embodiment of the subject matter described herein;

DETAILED DESCRIPTION

FIG 1 illustrates an example of an apparatus 100. The apparatus 100 transforms a sensed parameter (a sensed voltage) that is sensed by an analog sensor to a digital signal (logic value) in a simple implementation that has low power consumption. The apparatus 100 is therefore a form of analogue-to-digital converter.

The apparatus 100 comprises: a first input means 101 for receiving a sensed voltage; a voltage source means 111 for providing a reference voltage that varies at a fixed rate; 10 and comparator means 120 for comparing the sensed voltage against the varying reference voltage and providing an output 121 of a defined logic value for a time period equal or substantially equal to the time required for the reference voltage to vary by an amount equal or substantially equal to the sensed voltage.

In the example illustrated the apparatus comprises a first input 101 for receiving a sensed voltage AVBE, a voltage source 111 for providing a reference voltage VR1 that varies at a fixed rate with time; and a comparator 120.

FIG 2A illustrates an example of how the reference voltage VR1 varies at a fixed rate by AVBE in time FIG 2B illustrates an example of how the output 121 of the comparator 120 varies between logic L1 and logic L2. The output 121 is at logic Li for time ti The output 121 is a 1-bit output digital signal.

The comparator 120 is configured to compare the sensed voltage AVBE against the time-varying reference voltage VR, and provide an output 121 of a defined logic value Li for a time period 'El equal or substantially equal to the time ti required for the reference voltage VRi to vary by an amount equal or substantially equal to the sensed voltage AVBE.

A change in the time period ti.for logic L1 in the output 121, is indicative of a change in the sensed voltage AVBE. The output 121 is therefore a pulse width modulated signal where the pulse width modulation is proportional to the sensed voltage AVBE. The pulse is initiated at the start of the time period ti when the output 121 changes from to a defined logic value L1 from a defined logic value L2. The pulse is terminated at the end of the time period ti when the output 121 changes from the defined logic value L1 to the defined logic value L2 when a change in the time-varying reference voltage VR1 from pulse initiation has reached the sensed voltage AVBE.

As will be described below, when the sensed voltage AVBE is temperature dependent, a change in temperature causes a proportional change in the time period ti. A change in the time period ti is indicative of a change in the temperature. A constant can be used to convert the time period ti to a temperature value T. In some examples the first input 101 is configured to receive a difference between a first voltage drop V1 across a first diode forward-biased by a first constant current density and a second voltage drop V2 across a second diode forward-biased by a second constant current density.

FIG 3 illustrates an example of a voltage source, for example the voltage source 111. In this example, but not necessarily all examples, the voltage source 111 comprises a constant current integrator 131 that produces the reference voltage VIRi.

The constant current integrator 131 comprises a constant current source 132 and a capacitor 133 that is configured to be charged by the constant current source 132 during a first phase and configured to be and remain discharged during a second phase. The voltage across the capacitor 133 provides the reference voltage VRi. The first phase corresponds to the time period ti in FIG 2A where the reference voltage VIR, rises at a constant rate. The constant rate dV/dt= I/C is defined by the constant current I provided by the constant current source 132 and the capacitance C of the capacitor 133. The first phase corresponds to a period of logic L1 in FIG 2B and the second phase corresponds to period of logic L2 in FIG 2B.

FIG 4 illustrates an example of a sensor circuit 200. In this example, but not necessarily all examples, the sensor circuit 200 is configured as a temperature sensor circuit. The temperature sensor circuit 200 provides an analogue sensed voltage AVBE that varies with temperature.

The temperature sensor circuit 200 comprises two parallel-connected, forward-biased, diodes where the sensed voltage AVBE is a voltage difference between the diodes.

The sensor circuit 200 comprises a first diode 210 configured to be forward biased by a first constant current density ji to have a first voltage drop V1 across the first diode 210; and a second diode 220 configured to be forward biased by a second constant current density j2 to have a second voltage drop V2 across the second diode 220.

When the first diode 210 and the second diode 220 have the same physical geometries, the sensor circuit 200 comprises a first diode 210 configured to be forward biased by a first constant current 11 to have a first voltage drop V1 across the first diode 210; and a second diode 220 configured to be forward biased by a second constant current 12 to have a second voltage drop V2 across the second diode 220.

The sensor circuit 200 comprises an output for outputting a difference AVBE between the first voltage drop V1 and the second voltage drop V2.

The first diode 210 is configured to be forward biased by a first constant current source 212 that provides a first electric current Ii. The second diode 220 is configured to be forward biased by a second constant current source 222 that provides a second electric current 12 In this example the first diode 210 and the second diode 220 are the same and have the same junction geometry. Therefore the ratio of Ii! 12 is the same as ji/ j2.

In this example, the current I = p*12 The voltage difference AVBE = V2-V1 = riV-r loge (12/11) = qV-r loge (1/p) Where VT is the thermal voltage kT/q and n is a constant ideality factor. ;Therefore dAVBE/ dT = constant It is therefore possible to detect and measure changes in temperature T by detecting or measuring changes in the sensed voltage AVBE. ;The sensor circuit 200 is therefore configured to sense temperature. The sensed voltage is analogue and is proportional to temperature of the diodes 210, 220 of the sensor circuit 200. ;Referring back to FIG 1 and 2B, a change in the time period t is indicative of a change in the sensed voltage AVBE. which is indicative of a change in temperature T. A change in the time period ti is proportional to a change in the sensed voltage AVBE. which is proportional to a change in temperature T at the sensor circuit 200. ;The first diode 210 and the second diode 220 are, in some examples, silicon junction diodes. ;In the example illustrated the first diode 210 and the second diode 220 are diode-connected bipolar junction transistors 230. ;In this particular example, the bipolar transistors 230 are PNP bipolar junction transistors. ;The PNP bipolar junction transistors 230 may be formed in a common silicon substrate, for example, using CMOS processes. ;FIG 5 illustrates an example of an apparatus 100 as illustrated in FIG 1. The apparatus 100 transforms a sensed parameter (a sensed voltage) that is sensed by an analog sensor to a digital signal (logic value) in a simple implementation that has low power consumption. The apparatus 100 is therefore a form of analogue-to-digital converter. ;The apparatus 100 is similar to that described with reference to FIG 1 and comprises: a first input 101 configured to receive a sensed voltage AVBE; a first voltage source means 111 configured to provide a first reference voltage VR, that varies at a first fixed rate; comparator means 120 for, during a first phase, comparing the first sensed voltage AVBE against the varying first reference voltage VRiand providing an output 121 of a defined first logic value L1 for a time period ti equal (or substantially equal) to the time required for the first reference voltage VR1 to vary by an amount equal (or substantially equal) to the first sensed voltage AVBE The apparatus 100 illustrated in FIG 5 additionally comprises: a second input 102 configured to receive a second sensed voltage VBE; and a second voltage source means 112 configured to provide a second reference voltage VR2 that varies at a second fixed rate; and comparator means 120 for, during a second phase, comparing the second sensed voltage VBE against the varying second reference voltage VR2 and providing an output 122 of a defined second logic value L2 for a time period t2 equal (or substantially equal) to the time t2 required for the second reference voltage VR2 to vary by an amount equal (or substantially equal) to the second sensed voltage VBE. ;Referring back to FIG 4, the first input 101 is configured to receive the difference AVBE between the first voltage drop V1 across the first diode 210 forward-biased by the first constant current density and the second voltage drop V2 across the second diode 220 forward biased by the second constant current density; and the second input 102 is configured to receive the first voltage drop V1 (VBE) across the first diode 210 forward-biased by the first constant current density. ;During the first phase, a trigger threshold of the comparator means 120 is set to the first sensed voltage AVBE. During the first phase, the first input 101 receives the first sensed voltage AVBE. As illustrated in FIG 7A, the first voltage source 111 provides a first reference voltage VR1 that varies at the first fixed rate. The reference voltage VR1 varies at a first fixed rate by AVBE in time ti. The comparator means 120 compares the first sensed voltage AVBE against the varying first reference voltage VR1 and, as illustrated in FIG 7C, provides an output 121 of a defined first logic value L1 for a time period t1 equal (or substantially equal) to the time required for the first reference voltage VR1 to vary by an amount equal (or substantially equal) to the first sensed voltage AVBE. The output of the comparator means 120 is logic value L1 while the first sensed voltage AVBE is greater than the time-varying first reference voltage VR1. The output of the comparator changes from logic L1 to logic L2 when the time-varying first reference voltage VIR, equals the first sensed voltage AVBE. ;During the second phase, the second input 102 receives the second sensed voltage VBE. As illustrated in FIG 7B, the second voltage source 112 provides a second reference voltage VR2 that varies at the second fixed rate. The reference voltage VR2 varies at a second fixed rate by VBE in time t2. The comparator means 120 compares the second sensed voltage VBE against the time-varying second reference voltage VR2 and, as illustrated in FIG 7C, provides an output 122 of a defined second logic value L2 for a time period t2 equal (or substantially equal) to the time required for the second reference voltage VR2 to vary by an amount equal (or substantially equal) to the second sensed voltage VBE The output of the comparator means 120 is logic value L2 while the second sensed voltage VBE is greater than the time-varying second reference voltage VR2. The output of the comparator means 120 changes from logic L2 to logic L1 when the time-varying second reference voltage VR2 equals the first sensed voltage AVBE The first phase can immediately precede and/or immediately follow the second phase. ;The second phase can immediately precede and/or immediately follow the first phase. ;The apparatus 100 is configured for asynchronous operation in this example. The The output of the comparator means 120 changing from logic Li to logic L2 triggers an end of the first phase and can trigger a beginning of a second phase. The output of the comparator means 120 changing from logic L2 to logic L1 triggers an end of the second phase and can trigger a beginning of a first phase. ;In some but not necessarily all examples, the comparator means 120 is provided by a single comparator 120 as illustrated in FIG 6. FIGS illustrates operation of the apparatus 100 during the first phase when the switches of the switching means 140 are down. FIG 6 illustrates operation of the apparatus 100 during the second phase when the switches of the switching means 140 are up. ;The apparatus 100 uses switch means 140 to switch between using first voltage source 111 in the first phase and a second voltage source 112 in the second phase and to switch the order of applying the voltage source reference voltage and the sensed voltage to the inverting (-) and non-inverting (+) inputs of the comparator 120. ;For example, in the first phase as illustrated in FIG 6 when the switches are down, the first sensed voltage AVBE is applied to the non-inverting (+) input of the comparator 120 and the time-varying first reference voltage VR1 is applied to the inverting (-) input of the comparator 120. The output of the comparator 120 is logic HIGH while the first sensed voltage AVBE is greater than the time-varying first reference voltage VRi. The output of the comparator changes for logic HIGH to logic LOW when the time-varying first reference voltage VRI equals the first sensed voltage AVBE. The change in output of the comparator terminates the first phase and starts the second phase by changing the switches from down to up. ;In the second phase as illustrated in FIG 6 when the switches are up, the second sensed voltage VIBE is applied to the inverting (-) input of the comparator 120 and the time-varying first reference voltage VR2 is applied to the non-inverting (+) input of the comparator 120. The output of the comparator 120 is logic LOW while the first sensed voltage VBE is greater than the time-varying first reference voltage VR1. The output of the comparator 120 changes for logic LOW to logic HIGH when the time-varying second reference voltage VR2 equals the second sensed voltage VBE The change in output of the comparator 120 terminates the second phase and starts the first phase by changing the switches from up to down. ;In this example, the first and second phases repeat. Each combination of first and second phase forming a period. The period repeats with a constant frequency. The width of the logic HIGH pulse is indicative of temperature at the sensor circuit 200 providing the first and second sensed voltages. The width of the logic HIGH pulse can be averaged across multiple periods. The mean value, over the period, of the output pulse train is proportional to the measured temperature. This enables use of the single period as the measurement cycle. ;In other examples, the first and second phases occur once as a single period. The width of the logic HIGH pulse is indicative of temperature and can be measured in a single period. ;For example, the first phase can start by applying the first sensed voltage AVBE to the non-inverting (+) input of the comparator 120 and an initially zero-valued time-varying first reference voltage VR1 to the inverting (-) input. The termination of the first phase starts the second phase. The termination of the second phase ends the measurement period or cycle. ;For example, the second phase can start by applying the second sensed voltage AVBE to the inverting (-) input of the comparator 120 and an initially zero-valued time-varying second reference voltage VR2 to the non-inverting (+) input. The termination of the second phase starts the first phase. The termination of the first phase ends the measurement period or cycle. ;In the example of the apparatus 100 illustrated in 6, the first voltage source means 111 and the second voltage source means 112 alternately share a common constant current source 150. This alternation can be controlled by switch means 140 (not illustrated). The first voltage source means 111 uses the common constant current source 150 during the first phase. The second voltage source means 112 uses the common constant current source 150 during the second phase. The first voltage source 111 and the second voltage source 112 operate alternately and asynchronously. ;It will be appreciated that the asynchronous operation of the apparatus 100 allows it to operate without a clock and reduces power consumption and circuit complexity The sensed voltages (AVBE and VBE), define the threshold of the shared comparator 120, while the voltage sources 111, 112 have constant, possibly different, slopes. ;Let a represent a ratio of the second rate of change (of the second reference voltage VR2) to the first rate of change (of the first reference voltage VR1). ;For a fixed value of a, VBE aAVBE is a constant that is independent of temperature. The time ti is proportional to aAVBE and the time t2 is equally proportional to VBE. The sum of ti and t2 (the period) is a constant independent of temperature. ;The first sensed voltage AVBE is proportional to absolute temperature (PTAT) and the other second sensed voltage (VBE) is used to establish reference voltage VBE + aAVBE. ;The value aAVBE / (VBE + aAVBE) provides the temperature sensed. ;This is the mean value of the 1-bit output 121, 122 over the period. ;Voltage VBE for T = 0 K is equal to 1.2 V (the semiconductor bandgap energy for silicon) and aAVBE for T = 0 K is equal to OV. The value a is preferably controlled so that the reference voltage (VBE + aAVBE) is equal to 1.2 V (the semiconductor bandgap energy for silicon). Voltage VBE for T = X K is equal to 0 V and aAVBE for T = X K is equal to 1.2V (the semiconductor bandgap energy for silicon). The voltage VBE decreases linearly at a rate 1.21X between OK and X K. The voltage aAVBE increases linearly at a rate 1.21X between OK and X K. The temperature T between 0 and X K can be determined as: X* aAVBE/(VBE + aAVBE). The reference voltage can be any constant voltage, but if the reference voltage is equal to (VBE + aAVBE) = the semiconductor bandgap energy (1.2 V for silicon), the highest resolution for the maximal dynamic range of the analog sensing circuit is obtained. For silicon, X can be approximately 600 K. FIG 8A illustrates an example of an apparatus 100 similar to that illustrated in FIG 6. However, in this example the details of the first voltage source 111 and the second voltage source 112 are illustrated as are the switches of the switch means 140 used to switch between first and second phases.

The first voltage source 111 is, as illustrated in FIG 3 formed from a constant current source 132 and a capacitor 133 of value Cl. The second voltage source 112 is, as illustrated in FIG 3 formed from a constant current source 132 and a capacitor 133 of value 02.

As illustrated in FIG 6 the first voltage source 111 and the second voltage source 112 use a common constant current source 150 that is switched alternately between charging capacitor Cl (first phase) and charging capacitor C2 (second phase) with a current I. The first rate (of increase of the first reference voltage VR1) is dV/dt=1/C1. The second rate (of increase of the second reference voltage VR2) is dV/dt=1/C2. Therefore a, the ratio of the second rate of change (of the second reference voltage VR2) to the first rate of change (of the first reference voltage VR1) is C1/C2.

The capacitor Cl is discharged during the second phase. The capacitor 02 is discharged during the first phase.

The ratio of the two capacitances a = C1/02 can be chosen to ensure a particular constant value of the reference voltage (VBE + aAVBE) for different temperatures.

The circuit is asynchronous and the output of the comparator 120 controls the switches SC2, SD2, SC1, SDi, SRI, SR2, SAv, Sv.

With reference to the switches, the term 'open' or 'not conducting' will refer to the switch being open circuit (not conducting between its poles) and the term 'closed' or 'conducting' will refer to the switch being closed-circuit (conducting between its poles).

During the first phase, the output of the comparator is HIGH. This closes switch SR, and switch SAv. The first reference voltage VR1 is applied by capacitor Cl (through closed (conducting) switch SRI) to the inverting input of the comparator 120 and the first sensing voltage AVBE is applied from the first input 101 (through closed (conducting) switch SAv) to the non-inverting input of the comparator 120.

At the start of the first phase, the output of the comparator goes from LOW to HIGH.

Switch SCi from the constant current source 150 to capacitor Cl is closed (conducting) , the switch SRI from the capacitor Cl to the inverting input of the comparator 120 is closed (conducting) and the switch SDI from capacitor Cl to ground is opened (non-conducting). The capacitor Ci is charged by the constant current source 150 via closed (conducting) switch SCland its voltage is applied via the closed (conducting) switch SRI to the inverting input of the comparator 120.

The switch SC2from the constant current source 150 to capacitor C2 is opened (nonconducting), the switch SR2 from the capacitor C2 to the non-inverting input of the comparator 120 is opened (non-conducting) and the switch SD2 from capacitor 02 to ground is closed (conducting). The capacitor C2 is discharged to ground via closed (conducting) switch SD2.

The switch SAv that provides the first sensing voltage AVBE from the first input 101 to the non-inverting input of the comparator 120 is closed (conducting).

The switch Sythat provides the second sensing voltage VBE from the second input 102 to the inverting input of the comparator 120 is opened (non-conducting).

When the time-varying first reference voltage VR1 provided by the capacitor Cl equals the first sensing voltage AVBE, the output of the comparator 120 switches from HIGH to LOW. This ends the first phase and starts the second phase.

During the second phase, the output of the comparator 120 is LOW. This closes switch SR2and switch Sv. The second reference voltage VR2 is applied by capacitor C2 (through closed (conducting) switch 5R2) to the non-inverting input of the comparator 120 and the second sensing voltage VBE is applied from the second input 102 (through closed (conducting) switch Sv) to the inverting input of the comparator 120.

At the start of the second phase, the output of the comparator goes from HIGH to LOW.

Switch SC2from the constant current source 150 to capacitor C2 is closed (conducting), the switch SR2 from the capacitor C2 to the non-inverting input of the comparator 120 is closed (conducting) and the switch SD2 from capacitor C2 to ground is opened (nonconducting). The capacitor C2 is charged by the constant current source 150 via closed (conducting) switch SC2and its voltage is applied via the closed (conducting) switch SR2 to the non-inverting input of the comparator 120.

The switch SCifrom the constant current source 150 to capacitor Cl is opened (nonconducting), the switch SRI from the capacitor Cl to the inverting input of the comparator 120 is opened (non-conducting) and the switch SDi from capacitor Cl to ground is closed (conducting). The capacitor Cl is discharged to ground via closed (conducting) switch SDi.

The switch SAv that provides the first sensing voltage AVBE from the first input 101 to the non-inverting input of the comparator 120 is opened (non-conducting).

The switch Sythat provides the second sensing voltage VBE from the second input 102 to the inverting input of the comparator 120 is closed (conducting).

When the time-varying second reference voltage VR2 provided by the capacitor C2 equals the second sensing voltage VBE, the output of the comparator 120 switches from LOW to HIGH. This ends the second phase and starts the first phase.

The resulting pulse train at the output of the comparator 120 will have a mean value equal to aAVBE/(aAVBE + VBE), which is proportional to the measured absolute temperature. The obtained mean value can be used to obtain the temperature value in degrees Celsius.

The single-bit output digital signal of the comparator 120 can be transmitted, for example wirelessly or by electrical connection, to a remote apparatus for processing. Alternatively, the processing can occur at the apparatus 100.

FIG 8A illustrates an example of an apparatus 100 similar to that illustrated in FIG 8A. In FIG 8A switches SID1,5D2 are represented as ideal switches and the switches SC2, SC1, SRi, SR2, SAN, Sv are represented as field effect transistor switches. In FIG 8B, all the switches SC2, SD2, SC1, SDI, 5R1, 5R2, SAv, Sv are represented as ideal switches. It should be appreciated that any suitable switch can be used for switches SC2, SD2, SC1, SRi, SR2, Say, Sv and different types of switch can be used for different one of the switches SC2, SD2, SC1, SDI, SRI, SR2, SAW, Sv.

FIG 9 illustrates an example of circuitry 300 for determining a mean value of the output 121, 122 of the comparator 120. The circuitry 300 can be part of the apparatus 100 or can be remote from the apparatus 100. The output of the comparator 120 is communicated to the circuity 300, for example wirelessly using a radio transmitter.

The circuitry 300 determines a mean value of the output of the comparator across any number of periods. The mean value can then be used to provide an indication of the absolute temperature of the sensor circuit 200.

In some examples, the apparatus 400 can be configured to enable compensation arising from differences between the operation of the diodes 210 220 that does not arise from different current densities. The apparatus 400 can be configured to detect variations in the reference voltage VBE aAVBE i.e. changes in the length of the period. Measurement of the length of the period in digital domain enables temperature compensation by the apparatus 400 or circuitry 300.

The error to be compensated is a combination of a systematic error due to non-linearity of VBE(T) and a random error due to the spread on bandgap voltage. Random error due to the spread can be corrected using averaging techniques in digital domain at the receiver side. Systematic error caused by non-linearity of VBE(T) can be more significant for very low and very high temperatures compared to the mid-temperatures around X/2. The systematic error between 0 and 100 °C (273 to 373 K) may be approximately 1 mV, and may increase outside this range.

When a period change is detected, the non-linearity compensation can be performed by using a bias current or non-linear correction term to the bandgap voltage.

In some circumstances, compensation can be achieved using a feedback circuit to adjust the forward-bias of the diode-connected bipolar junction transistors 210, 220.

FIGs 10 A and 10B illustrate examples of a system 500 comprising sensor circuit 200 and the apparatus 100. The sensor circuit 200 provides the first sensing voltage AVBE, and in this example but not necessarily all examples, the second sensing voltage VBE to the apparatus 100. In this example but not necessarily all examples the sensor circuit 200 is a temperature sensor circuit that detects a temperature change or measures a temperature.

In the example illustrated the apparatus 100 produces an output 121, 122 that is a pulse width modulated 1-bit digital signal as previously described. The duration of the pulse changes with changes in temperature. The duration of the pulse relative to the duration of the period is indicative of temperature.

In the example illustrated in FIG 10A, the sensor circuit 200 and the apparatus 100 are formed within a single integrated circuit 400. The integrated circuit 400 can, for example, comprise a single semiconductor substrate. The components of the sensor circuit 200 and the apparatus 100 can be integrated components of the substrate, for example, formed by CMOS processes.

In the example illustrated in FIG 10B, the sensor circuit 200 and the apparatus 100 are formed within separate integrated circuits 402, 404. Each integrated circuit 402, 404 can, for example, comprise a single semiconductor substrate. The components of the sensor circuit 200 can be integrated components of the substrate of the integrated circuit 402, for example, formed by CMOS processes. The components of the apparatus 100 can be integrated components of the substrate of the integrated circuit 404, for example, formed by CMOS processes.

FIG 10 C illustrates an example of a system 500 comprising multiple sensor circuits 200 and the apparatus 100. A selected sensor circuit 200 provides the first sensing voltage AVBE, and in some examples but not necessarily all examples, the second sensing voltage VBE to the apparatus 100. In this example but not necessarily all examples the apparatus 100 detects a temperature change or measures a temperature sensed by the selected one of the sensor circuits 200. In the example illustrated the apparatus 100 produces an output 121, 122 that is a pulse width modulated 1-bit digital signal as previously described. The duration of the pulse changes with changes in temperature at the selected sensor circuit 200. The duration of the pulse relative to the duration of the period is indicative of temperature at the selected sensor circuit 200.

The system 500 comprises a selector 502 for selecting one of the sensor circuits 200. The selected sensor circuit 200 can be varied by the selector 502. In this example, the selector is a Johnson counter.

As described with reference to FIGs 10A, one, some or all sensor circuits 200 and the apparatus 100 can be formed within a single integrated circuit with the selector 502. As described with reference to FIG 10B the other sensor circuits 200 (if any) can be formed in separate integrated circuits.

Alternatively, as described with reference to FIGs 108 the apparatus 100 can be formed within a single integrated circuit with the selector 502 and the sensor circuits 200 can be formed in separate integrated circuits.

In some examples, the processing of the output 121, 122 of the apparatus 100, for example in FIGs 10A, 10B, 10C, is processed on the same substrate as the apparatus 100 using a system on chip (SoC).

The sensor circuit or sensor circuits 200 can be used for sensing temperature in different applications.

For example, a sensor circuit 200 can be used to detect overheating of an electronic component. For example it can be integrated within an integrated circuit to detect an internal temperature or internal temperature change of the integrated circuit.

For example, a sensor circuit 200 can be used to detect body temperature. It can for example be used to detect a change in body temperature and/or to measure body temperature. The sensor circuit 200 can, for example, be part of a wearable systems. The wearable system can, for example, be designed for infants, children, adults, animals. The sensor circuit 200 can, for example, be part of an implanted system that is implanted within a human or animal.

For example, a sensor circuit 200 can be used to detect environment temperature outside the sensor circuit 200. It can for example be used to detect a change in ambient external temperature and/or to measure ambient external temperature. The sensor circuit 200 can, for example, be worn by a person or animal, be placed at a particular location or component such as, for example, a battery.

As used in this application, the term 'circuit' or 'circuitry' may refer to one or more or all of the following: (a) hardware-only circuitry implementations (such as implementations in only analog and/or digital circuitry) and (b) combinations of hardware circuits and software, such as (as applicable): (i) a combination of analog and/or digital hardware circuit(s) with software/firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions and (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g. firmware) for operation, but the software may not be present when it is not needed for operation.

This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit for a mobile device or a similar integrated circuit in a server, a cellular network device, or other computing or network device.

Where a structural feature has been described, it may be replaced by means for performing one or more of the functions of the structural feature whether that function or those functions are explicitly or implicitly described.

The above described examples find application as enabling components of: automotive systems; telecommunication systems; electronic systems including consumer electronic products; distributed computing systems; media systems for generating or rendering media content including audio, visual and audio visual content and mixed, mediated, virtual and/or augmented reality; personal systems including personal health systems or personal fitness systems; navigation systems; user interfaces also known as human machine interfaces; networks including cellular, non-cellular, and optical networks; ad-hoc networks; the internet; the internet of things; virtualized networks; and related software and services.

The term 'comprise' is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use 'comprise' with an exclusive meaning then it will be made clear in the context by referring to "comprising only one.." or by using "consisting".

In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term 'example' or 'for example' or 'can' or 'may' in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus 'example', 'for example', 'can' or 'may' refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all of the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example as part of a working combination but does not necessarily have to be used in that other example.

Although embodiments have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the claims.

Features described in the preceding description may be used in combinations other than the combinations explicitly described above.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

The term 'a' or 'the' is used in this document with an inclusive not an exclusive meaning.

That is any reference to X comprising a/the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use 'a' or 'the' with an exclusive meaning then it will be made clear in the context. In some circumstances the use of 'at least one' or 'one or more' may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer and exclusive meaning.

The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and also to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result.

In this description, reference has been made to various examples using adjectives or adjectival phrases to describe characteristics of the examples. Such a description of a characteristic in relation to an example indicates that the characteristic is present in some examples exactly as described and is present in other examples substantially as described.

Whilst endeavoring in the foregoing specification to draw attention to those features believed to be of importance it should be understood that the Applicant may seek protection via the claims in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not emphasis has been placed thereon.

I/we claim:

Claims

CLAIMS1. An apparatus comprising: a first input means for receiving a sensed voltage; a voltage source means, for providing a reference voltage that varies at a fixed rate; comparator means for comparing the sensed voltage against the varying reference voltage and providing an output of a defined logic value for a time period equal or substantially equal to the time required for the reference voltage to vary by an amount equal or substantially equal to the sensed voltage.
2. An apparatus as claimed in any preceding claim, wherein the voltage source comprises a constant current integrator.
3. An apparatus as claimed in any preceding claim, wherein the voltage source comprises a constant current source and a capacitor configured to be charged by the constant current source during a first phase and configured to be discharged during a second phase.
4. An apparatus as claimed in any preceding claim, comprising a sensor circuit, for providing the sensed voltage, comprising: a first diode configured to be forward biased by a first constant current density to have a first voltage drop across the first diode; a second diode configured to be forward biased by a second constant current density to have a second voltage drop across the second diode; and an output for outputting a difference between the first voltage drop and the second voltage drop
5. An apparatus as claimed in claim 4, wherein the first diode and the second diode are diode connected bipolar junction transistors.
6. An apparatus as claimed in claim 5, wherein the sensed voltage is proportional or substantially proportional to a temperature of the sensor circuit, wherein a change in the time period is indicative of a change in temperature.
7. An apparatus as claimed in any preceding claim, wherein the input means is a first input means, the sensed voltage is a first sensed voltage, the voltage source means is a first voltage source means, the reference voltage is a first reference voltage and the fixed rate is a first fixed rate; wherein the first input means is configured to receive the first sensed voltage; the first voltage source means is configured to provide the first reference voltage that varies at the first fixed rate; the apparatus further comprising: a second input means configured to receive a second sensed voltage; a second voltage source means configured to provide a second reference voltage that varies at a second fixed rate; and control circuitry configured to cause during a first phase comparison by the comparator means of the first sensed voltage against the varying first reference voltage and provision of an output of a defined first logic value for a time period equal or substantially equal to the time required for the first reference voltage to vary by an amount equal or substantially equal to the first sensed voltage; and during a second phase, comparison by the comparator means of the second sensed voltage against the varying second reference voltage and provision of an output of a defined second logic value for a time period equal or substantially equal to the time required for the second reference voltage to vary by an amount equal or substantially equal to the second sensed voltage.
8. An apparatus as claimed in claim 7 when dependent upon claim 4, comprising a sensor circuit, for providing the sensed voltage, comprising: a first diode configured to be forward biased by a first constant current density to have a first voltage drop across the first diode; a second diode configured to be forward biased by a second constant current density to have a second voltage drop across the second diode; and an output for outputting a difference between the first voltage drop and the second voltage drop, wherein the first input means is configured to receive the difference between the first voltage drop across the first diode forward biased by the first constant current density and the second voltage drop across the second diode forward biased by the second constant current density, and wherein the second input means is configured to receive the first voltage drop across the first diode forward-biased by the first constant current density.
9. An apparatus as claimed in claim 7 or 8, comprising circuitry for determining a mean value of the output of the comparator means.
10. An apparatus as claimed in claim 9, wherein the mean value is determined over a measurement period defined by a combination of the first phase and the second phase or the second phase and the first phase.
11. An apparatus as claimed in claim 10, wherein the measurement period defined by a combination of the first phase and the second phase or the second phase and the first phase has a constant frequency and a pulse width modulation that varies with changes in temperature.
12. An apparatus as claimed in any of claims 7 to 11, wherein the first voltage source means and the second voltage source means operate alternately and asynchronously.
13. An apparatus as claimed in any of claims 7 to 12, wherein the first voltage source means and the second voltage source means alternately share a common constant current source.
14. An apparatus comprising a first input configured to receive a first sensed voltage; a second input configured to receive a second sensed voltage; a first voltage source configured to provide a first reference voltage that varies at a first fixed rate; a second voltage source configured to provide a second reference voltage that varies at a second fixed rate; a comparator; and control circuitry configured to during a first phase control comparison by the comparator of the first sensed voltage against the varying first reference voltage and provide an output of a defined first logic value for a time period equal to the time required for the first reference voltage to vary by an amount equal to the first sensed voltage; and during a second phase control comparison by the comparator of the second sensed voltage against the varying second reference voltage and provide an output of a defined second logic value for a time period equal to the time required for the second reference voltage to vary by an amount equal to the second sensed voltage.
15. An integrated circuit configured to provide the apparatus as claimed in any preceding claim.