SIGNAL GAUGE

Abstract

There is provided an analog signal gauge that monitors an analog signal at a node and a non-volatile memory element to store an event that occurs at the node when a certain criteria, such as exceeding a maximum safe threshold, is satisfied. This way, the analog signal gauge can help to provide an accurate picture of the operating characteristics in the analog circuit which it is monitoring, including indications of faults that occur in the analog system.

Claims

1. An analog signal gauge, comprising: a conditioning circuit, configured to monitor an analog signal at a node in an analog circuit; and at least one non-volatile memory (NVM) element configured to store analog information, wherein the conditioning circuit is configured to compare the analog signal with a first threshold and to record analog information about an event in the NVM element by charging or discharging the NVM, in response to the analog signal exceeding the first threshold.

2. An analog signal gauge according to claim 1, wherein the recorded analog information corresponds to an adjustable level of the first threshold.

3. An analog signal gauge according to claim 2, wherein the recorded analog information represents an extent to which the analog signal exceeds the first threshold.

4. An analog signal gauge according to claim 1, wherein the conditioning circuit is further configured to log an event each time the first threshold is exceeded.

5. An analog signal gauge according to claim 1, wherein the conditioning circuit is further configured to compare the analog signal with an n.sup.th threshold, and to log an event each time the analog signal exceeds or goes below the n.sup.th threshold, wherein n2, and wherein a larger value of n causes a greater rate of charging or discharging of the NVM element.

6. An analog signal gauge according to claim 4, wherein the conditioning circuit is further configured to cause the NVM element to be reset to its original state of charge or discharge when the analog signal drops below a reset threshold, the reset threshold being lower than the first threshold.

7. An analog signal gauge according to claim 6, wherein the conditioning circuit further comprises a breakdown-type device such as a Zener diode or a p-n junction diode for setting the reset threshold.

8. An analog signal gauge according to claim 1, wherein the conditioning circuit comprises a comparator for comparing the analog signal with a first threshold, n.sup.th threshold and/or reset threshold.

9. An analog signal gauge according to claim 1, wherein the conditioning circuit comprises a timer, and the conditioning circuit is configured to start the timer when the analog signal goes over the first threshold, and to stop the timer when the analog signal goes below the threshold, and to record in the NVM element the time spent over the threshold.

10. An analog signal gauge according to claim 9, wherein the conditioning circuit is further configured to compare the analog signal with the first threshold, and to log an event if the analog signal remains over the threshold for more than a predetermined amount of time.

11. An analog signal gauge according to claim 1, further comprising a control circuit, wherein the control circuit is configured to control a first aspect of the analog circuit if a first condition is met.

12. An analog signal gauge according to claim 1, further comprising a read circuit, configured to read the NVM element.

13. An analog signal gauge according to claim 12, wherein the read circuit includes a register, and the read circuit is only accessible if correct code is entered into the register.

14. An analog signal gauge according to claim 1,herein the analog signal gauge is for monitoring an analog signal in an internal power supply or an analog subsystem.

15. An analog signal gauge according to claim 1, included in an integrated circuit.

16. An analog signal gauge according to claim 15, in combination with the analog circuit configured to be monitored.

17. A method of monitoring an analog signal by an analog signal gauge, the analog signal gauge comprising a conditioning circuit and at least one non-volatile memory (NVM) element wherein the method comprises: monitoring, by the conditioning circuit, an analog signal at a node in an analog circuit; and comparing by the conditioning circuit. the analog signal with a first threshold: recording, by the conditioning circuit, analog information about an event in the NVM element including by charging or discharging the NVM element, in response to the analog signal exceeding the first threshold.

18. The method of claim 17, wherein the analog information corresponds to an adjustable level of the first threshold.

19. The method of claim 18, wherein the recorded analog information corresponds to an adjustable level of the first threshold.

20. The method of claim 18, wherein the method further comprises: comparing, by the conditioning circuit, the analog signal with an n.sup.th threshold; and logging an event each time the analog signal exceeds or goes below the n.sup.th threshold, the logging comprising charging or discharging the NVM element, wherein n2, and wherein a larger value of n causes a greater rate of charging or discharging of the NVM element.

21. The method of claim 18, the recorded analog information represents an extent to which the analog signal exceeds the first threshold.

22. The method of claim 21, wherein the recorded analog information includes information about a magnitude by which the analog signal exceeds the first threshold.

23. The method of claim 21, wherein the recorded analog information includes information about a duration for which the analog signal exceeds the first threshold.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Examples of the present disclosure will now be described, by non-limiting example only, with reference to the accompanying drawings, in which:

[0037] FIG. 1 is a diagram that illustrates an analog signal gauge in accordance with a first example of the present disclosure;

[0038] FIG. 2 is a diagram that illustrates an analog signal gauge in accordance with a second example of the present disclosure;

[0039] FIG. 3 is a diagram that illustrates an analog signal gauge in accordance with a third example of the present disclosure;

[0040] FIG. 4 is a graph showing recordal of an event in accordance with a fourth example of the present disclosure;

[0041] FIG. 5 is a graph showing recordal of an event in accordance with a fifth example of the present disclosure

[0042] FIGS. 6(a) and 6(b) show aspects of the recordal of the event in accordance with the fifth example of the present disclosure;

[0043] FIG. 7 is a graph showing recordal of an event in accordance with a sixth example of the present disclosure;

[0044] FIG. 8 is a graph showing recordal of an event in accordance with a seventh example of the present disclosure;

[0045] FIG. 9 is a graph showing recordal of an event in accordance with an eighth example of the present disclosure;

[0046] FIGS. 10(a), 10(b) and 10(c) show various components of a conditioning circuit in accordance with examples of the present disclosure;

[0047] FIG. 11 shows another component of a conditioning circuit in accordance with examples of the present disclosure;

[0048] FIG. 12(a) shows yet another component of a conditioning circuit in accordance with examples of the present disclosure and FIG. 12(b) is a graph showing a measurement technique for the component of FIG. 12(a);

[0049] FIG. 13 is a flow chart that illustrates a method in accordance with a ninth example of the present disclosure;

[0050] FIGS. 14 is a flow chart that illustrates a method in accordance with a tenth example of the present disclosure; and

[0051] FIG. 15 is a flow chart that illustrates a method in accordance with an eleventh example of the present disclosure.

DETAILED DESCRIPTION

[0052] It has been recognised by the present inventors that there is a need for a way to improve detection of faults in analog devices.

[0053] Analog circuits include components which produce analog signals that vary continuously over time. These analog signals have qualities such as voltage or current that must stay within certain operating parameters, otherwise there is a risk that the analog circuit could be damaged.

[0054] When an analog circuit is damaged by an analog signal that has exceeded its operating parameters, it is often difficult to look at the damaged circuit and determine how or why the fault occurred. Especially in integrated circuits, it can also be difficult to determine the exact point, or node, within the analog circuit at which the fault occurred.

[0055] In the present disclosure, an analog signal gauge is used for monitoring a node of an analog system so that information about whether an analog signal of an analog circuit in the analog system has satisfied a first criteria.

[0056] A conditioning circuit in the analog signal gauge is configured to monitor the analog signal at a node in the analog circuit and it is also configured to record an event in at least one NVM element in response to the analog signal satisfying the first criteria.

[0057] Importantly, using the above technique of the present disclosure, the conditioning circuit writes to the NVM element but it does not read data off the NVM. When data is required to be read off the NVM, a separate read circuit may be employed. As such, the analog signal gauge is a simple device that records information about the way in which the analog system is performing without taking up much storage space. It is also possible for the analog signal gauge to be incorporated into the integrated circuit of the analog circuit which is being monitored.

[0058] FIG. 1 shows an analog signal gauge 1 that has a conditioning circuit 11 between a power rail 14 and a ground rail 15, and a NVM element 12 in accordance with a first example of the present disclosure. The conditioning circuit 11 is configured to monitor an analog signal at a node of an analog circuit. It records an event in the NVM element 12 when the analog signal satisfies a first criteria. The first criteria could be a first threshold to which the analog signal is compared. The conditioning circuit 11 is configured to log an event in the NVM element 12 when the first threshold is exceeded. The first threshold could be a voltage that is measured directly, or voltage that is determined from a direct temperature measurement, for example. The logging could be charging or discharging the NVM element, which is described in more detail below with reference to FIGS. 12(a) and 12(b).

[0059] A read circuit 13 is also shown in FIG. 1 and it is configured to read the NVM element 12, which has information stored in either analog or digital format. The digital formal will be described in greater detail below with reference to FIG. 11. Once the data is read out, it can be used to determine whether a fault has occurred in the analog system.

[0060] In the first example of the present disclosure, the analog signal gauge is not implemented on the same integrated circuit as the analog circuit having the node which is being monitored. In this example, the read circuit is also implemented separately. However, in other examples, the analog signal gauge and/or the read circuit may be implemented on-chip.

[0061] FIG. 2 shows an analog signal gauge 2 that has more than one conditioning circuit between a power rail 24 and a ground rail 25, and more than one NVM element. Namely, it has conditioning circuits 21a, 21b, 21c, 21d and NVM elements 22a, 22b, 22c, 22d in accordance with a second example of the present disclosure. The conditioning circuit 21a monitors an analog signal at a node in analog circuit 20a, the conditioning circuit 21b monitors an analog signal at a node in analog circuit 20b, the conditioning circuit 21c monitors an analog signal at a node in analog circuit 20c and the conditioning circuit 21d monitors an analog signal at a node in analog circuit 20d. Then, a read circuit 23, configured to read the NVM elements 22a, 22b, 22c, 22d, can be used to determine whether a first criteria has been satisfied by an analog signal at a node of one or more of the analog circuits 20a, 20b, 20c, 20d, which has been recorded by the conditioning circuits 21a, 21b, 21c, 21d in the NVM elements 22a, 22b, 22c, 22d, respectively.

[0062] Rather than each analog circuit/conditioning circuit/NVM element being implemented separately, in the second example of the present disclosure, each analog circuit 20a, 20b, 20c, 20d, each conditioning circuit 21a, 21b, 21c, 21d, each NVM element 22a, 22b, 22c, 22d and the read circuit 23 are implemented on the same integrated circuit. This provides the benefits of smaller circuit sizes and lower power consumption. Other benefits include faster response time and lower cost.

[0063] FIG. 3 shows an analog signal gauge 3 that has a plurality of NVM elements 31a . . . n to which a conditioning circuit 31 that is connected between a power rail 34 and a ground rail 35 may record data. The conditioning circuit could be for monitoring an always ON power supply or a gated power supply, for example. As data is recorded to the NVM elements and one NVM element 31a passes a final threshold, the next NVM element 32b is used, as directed by the control and read circuit 33 via a control element 36. Then, the control and read circuit 33 reads out from the plurality of NVM elements 31a . . . n. If a first condition is met in the analog circuit, the control and read circuit 33 controls a first aspect of the analog circuit. The first condition could be if the voltage at a node in the analog circuit exceeds a reset threshold voltage, then the control and read circuit 33 resets the analog circuit.

[0064] The circuits of FIGS. 1, 2 and 3 may be operated in various ways, some of which are described below with reference to FIGS. 4-9.

[0065] In the fourth example of the present disclosure as shown in FIG. 4, charge is stored in a NVM element until a voltage level at a first threshold is exceeded by an analog signal at a node of an analog circuits, at which point the conditioning circuit causes the NVM element to fully discharge. An advantage of this approach is that it is relatively simple and therefore can be relatively straightforward and inexpensive to implement in an integrated circuit with the analog system. However, in this approach, the next time the voltage level is exceeded, the next event is missed by the conditioning circuit.

[0066] In the fifth example of the present disclosure as shown in FIG. 5, charge is also stored in a NVM element until a voltage level at a first threshold is exceeded by an analog signal at a node of an analog circuits (as with the fourth example of FIG. 4), after which the NVM element fully discharges. However, when the analog signal drops below a reset threshold, the reset threshold being lower than the first threshold, the conditioning circuit is configured to cause the NVM element to be reset to its original state of charge. Therefore, when the first threshold voltage level is exceeded again, the conditioning circuit can record this event in the NVM element once again by discharging the charge that was restored.

[0067] FIGS. 6(a) and 6(b) show aspects of the recordal of the event in accordance with the fifth example described above. In FIG. 6(a), each time a voltage level at a first threshold is exceeded, the event is recorded by the conditioning circuit in at least one NVM element. In FIG. 6(b), each time each time a voltage level at a first threshold is exceeded, not only is the event is recorded by the conditioning circuit in at least one NVM element, but an indication of change in charge stored in the NVM element is also recorded by the conditioning circuit.

[0068] In the sixth example of the present disclosure shown in FIG. 7, the same reset principles as the fifth example applies. However, the first event that triggers discharge of the NVM element does not completely deplete the charge in the NVM element. Charge in the NVM element stops depleting once the voltage of the analog signal drops below the first threshold. Then, the second event triggers further depletion of the NVM element until the analog signal drops below the first threshold again. The first and second triggers may cause depletion of the NVM element at the same rate. In other examples, more than two triggers may be provided and the NVM may be discharged in response to each trigger at the same rate.

[0069] In the seventh example of the present disclosure as shown in FIG. 8, two different threshold levels exist and the second threshold causes discharge of the NVM element causes discharge to occur at a faster rate than the first threshold. The first time that the NVM element discharges, only a first threshold is exceeded by the voltage of the analog signal. However, the second time that the NVM element discharges, the first threshold is exceeded and then a second threshold is exceeded by the voltage of the analog signal, and exceeding the second threshold causes discharge of the NVM element causes discharge to occur at a faster rate than when the first threshold is exceeded.

[0070] In the eighth example of the present disclosure as shown in FIG. 9, n different threshold levels exist and the higher the level of the threshold that is exceeded, the faster the rate of discharge of the NVM element that occurs. As the voltage of the analog signal peaks and decreases again, dropping below the various thresholds, the rate of discharge of the NVM element reverts back to the rate of discharge when the n.sup.th threshold is exceeded. This way, the rate of discharge of the NVM element is proportional to the voltage level of monitored signal once the first threshold has been exceeded.

[0071] A flag can be set to indicate that change in charge stored in the NVM element has exceeded a predetermined amount. This flag can be set off-chip through a network connection. As shown in the example of FIG. 9 (although this flag concept may apply to any of the previous examples too), the flag is set for when the accumulated change in charge in the NVM element exceeds a predetermined amount that indicates that the analog circuit could be damaged if the over-voltage event were allowed to continue for a further period of time. Graphically, this is represented in FIG. 9 by the combined overvoltage A+B indicates that the change in charged stored in the NVM element has caused discharge of the NVM element to amount C.

[0072] When the conditioning circuit is configured to compare the analog signal with a first threshold, and to log an event in the NVM element when the first threshold is exceeded, the way in which this comparison takes place could be using a comparator 40, as shown in FIG. 10(a). When the voltage of the analog signal being monitored, or the input signal 41, exceeds the reference voltage 42, then the comparator triggers a signal 43 for the NVM element to charge or discharge.

[0073] Alternatively to the comparator, a Zener diode 50, tied between the input signal 51 and ground 52 via a first resistor 53, may be used to set the trigger voltage, as shown in FIG. 10(b). However, in other examples, any breakdown-type device may be used. In the circuit of FIG. 10(b), once the input signal 51 goes above the voltage set by the breakdown of the Zener diode 50, the gate voltage of the transistor 56, tied between the trigger voltage set by the Zener diode 50 and ground 52 via a second resistor 54, will be clamped. As the input signal rises further, a voltage will be dropped across resistor r1. Once the threshold voltage of the transistor is exceeded, it will turn on and this will trigger a signal 56 for the NVM element to charge or discharge.

[0074] A one-shot pulse generator 67 could be added to the circuit at the output of the transistor, as shown in FIG. 10(c).

[0075] In FIG. 10(c), a Zener diode 60 is tied between the input signal 61 and ground 62 via a first resistor 63, and the Zener diode 60 sets the trigger voltage. Once the input signal 61 goes above the voltage set by the breakdown of the Zener diode 60, the gate voltage of the transistor 65, tied between the trigger voltage set by the Zener diode 60 and ground 62 via a second resistor 64, will be clamped. As the input signal rises further, a voltage will be dropped across resistor r1.

[0076] Once the threshold voltage of the transistor is exceeded, it will turn on and this will trigger a signal 66 for the NVM element to charge or discharge.

[0077] The signal 66 causes the one-shot pulse generator 67 to produce pulses of fixed time periods for the NVM element to charge or discharge in response to the trigger signal 66. Each event that triggers a signal 66 causes charging or discharging of the NVM element by a certain known amount and the number of events is recorded but not the level of the event. In one example, the fixed time period could be 10 s for a first threshold. In another example with n thresholds, the fixed time period could increase as the level of n increases so as to create a dynamic charge or discharge of the NVM element. This could result in operation of the analog signal gauge as shown in FIG. 8 or 9.

[0078] Alternatively to FIG. 10(c), using the circuit of FIG. 11, the input signal 71 may be digitalised, encoded in the digital domain and then converted back to an analog signal before a trigger signal 76 is sent to the NVM element. The circuit of FIG. 11 includes an analog-to-digital converter (ADC) 72, and encoder 73 and a digital-to-analog converter (DAC) 74. A reference voltage 75 is provided to the DAC 74 for stable and accurate conversion. The trigger signal 76 may modulate the pulse width and the amount change in charge stored in the NVM element so as to create a dynamic charge or discharge of the NVM element.

[0079] Floating gate technology may be used to hold electrical charge in a NVM element in order to store data, as shown in FIG. 12(a).

[0080] In the floating gate transistor 80, which acts as a non-volatile memory element, there is a floating gate 81 and a control gate 82. The two gates 81, 82 are separated from one another by a thin dielectric material, for example, an oxide layer 83. The floating gate 81 is isolated from the oxide layer and so any electrons placed on the floating gate are trapped. As a result, the memory element is non-volatile.

[0081] The floating gate transistor 80 works by adding (charging) or removing (discharging) electrons to and from the floating gate 81. The state of a bit, 0 or 1, depends on whether the floating gate 81 is charged or uncharged. When electrons are present on the floating gate 81, current cannot flow through the transistor and the bit state is 0. When electrons are removed from the floating gate 81, current is allowed to flow and the bit state is 1.

[0082] A tunnelling layer 84 lies between the floating gate 81 and a substrate 85 of the floating gate transistor 80. When a strong electric field is applied between a negatively charged source 86 and the positively charged control gate 82, electrons drawn into the floating gate 81 via a channel between the 87 that lies between the source 86 and the drain 88. The electrons move from the source 86 through the thin oxide layer 83 to the floating gate 81, where they are trapped. In an alternative method, a high current could be applied through the channel 87 to give electrons sufficient energy to break through the oxide layer 83. A positive charge can also be applied to the control gate 82, which attracts the electrons from the channel 87 into the floating gate 81, where they are trapped. In both methods, the amount of trapped charge changes the threshold voltage of the floating gate 81 that can be used as the first threshold to which the analog signal voltage is compared.

[0083] FIG. 12(b) shows how the threshold voltage of the floating gate 81 can be measured. A sense resistor can be connected at the drain 88 of the floating gate transistor 80. With a known value of the sense resistance, the voltage drop across sense resistor can be converted to a current I.sub.ds, which is plotted against the control gate voltage V.sub.G to create a V.sub.G vs. I.sub.ds graph. A tangent can be plotted at the linear portion of the curve to find an intercept point in order to find the threshold voltage of the floating gate 81.

[0084] To remove trapped charge from the floating gate 81, the NVM element can be exposed to ultraviolet light, which causes electrons to leak away from the floating gate 81. Alternatively, a negative charge can be applied to the control gate 82, and a positive charge can be applied to the source 86 and the drain 88, which causes electrons to flow from the floating gate 81 to the channel 87.

[0085] FIG. 13 is a flow chart that illustrates a method in accordance with a ninth example of the present disclosure. At step S101, the conditioning circuit monitors an analog signal at a node in an analog circuit. Then, at step S102, the conditioning circuit records an event in the NVM element in response to the analog signal satisfying a first criteria.

[0086] FIG. 14 is a flow chart that illustrates a method in accordance with a tenth example of the present disclosure. At step 201, the conditioning circuit monitors an analog signal at a node in an analog circuit. Then, at step S202, the conditioning circuit compares the analog signal with a first threshold, and at step S203, the conditioning circuit logs an event in the NVM element when the first threshold is exceeded, wherein the logging comprises charging or discharging the NVM element.

[0087] FIG. 15 is a flow chart that illustrates a method in accordance with an eleventh example of the present disclosure. At step 301, the conditioning circuit monitors an analog signal at a node in an analog circuit. Then, at step S302, the conditioning circuit compares the analog signal with an n.sup.th threshold, wherein n2, and logs an event each time the analog signal exceeds or goes below the n.sup.th threshold, the logging comprising charging or discharging the NVM element, wherein a larger value of n causes a greater rate of charging or discharging of the NVM element.

[0088] The above description relates to particularly preferred aspects of the disclosure, but it will be appreciated that other implementations are possible. Variations and modifications will be apparent to the skilled person, such as equivalent and other features which are already known and which may be used instead of, or in addition to, features described herein. Features that are described in the context of separate aspects or examples may be provided in combination in a single aspect or example. Conversely, features which are described in the context of a single aspect or example may also be provided separately or in any suitable sub-combination.