Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
  • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
  • H02H3/08—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current
  • H02H3/10—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current additionally responsive to some other abnormal electrical conditions
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C29/00—Checking stores for correct operation ; Subsequent repair; Testing stores during standby or offline operation
  • G11C29/02—Detection or location of defective auxiliary circuits, e.g. defective refresh counters
  • G11C29/028—Detection or location of defective auxiliary circuits, e.g. defective refresh counters with adaption or trimming of parameters
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C29/00—Checking stores for correct operation ; Subsequent repair; Testing stores during standby or offline operation
  • G11C29/04—Detection or location of defective memory elements, e.g. cell constructio details, timing of test signals
  • G11C29/50—Marginal testing, e.g. race, voltage or current testing
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C5/00—Details of stores covered by group G11C11/00
  • G11C5/005—Circuit means for protection against loss of information of semiconductor storage devices
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C7/00—Arrangements for writing information into, or reading information out from, a digital store
  • G11C7/04—Arrangements for writing information into, or reading information out from, a digital store with means for avoiding disturbances due to temperature effects
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
  • H02H5/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal non-electric working conditions with or without subsequent reconnection
  • H02H5/005—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal non-electric working conditions with or without subsequent reconnection responsive to ionising radiation; Nuclear-radiation circumvention circuits
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C29/00—Checking stores for correct operation ; Subsequent repair; Testing stores during standby or offline operation
  • G11C29/04—Detection or location of defective memory elements, e.g. cell constructio details, timing of test signals
  • G11C2029/0409—Online test
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C29/00—Checking stores for correct operation ; Subsequent repair; Testing stores during standby or offline operation
  • G11C29/04—Detection or location of defective memory elements, e.g. cell constructio details, timing of test signals
  • G11C29/50—Marginal testing, e.g. race, voltage or current testing
  • G11C2029/5002—Characteristic

Definitions

• the present invention for which a patent is applied, has as its main object a method for the generation of an optimal supply current threshold for the protection of integrated circuits against the effect called Single Event Latchup (SEL) and the devices and arrangement that use it.
• SEL Single Event Latchup
• the present invention refers to a method for the determination of an optimum threshold for the protected device supply current, which maximizes the probability of real SEL detection and minimizes the probability of spurious mitigations actions triggering and the devices and the arrangement which use said method to avoid destruction by overcurrent upon the occurrence of SEL in the susceptible elements of an electronic equipment.
• This method predicts the limit value of the supply current to be used for deciding to interrupt the supply of power to the protected devices, using sample values of its supply current acquired from each of them, the level of the radiation flux and the temperature of the environment.
• the present invention has practical and industrial application in electronic devices, such as integrated circuits, used in environments susceptible to suffer from ionizing radiation, such as geostationary satellites and remote sensing low orbit satellites.
• parasitic structures normally present a high impedance to the supply voltage; but when the values of the current gains (b) of the parasitic bipolar transistors that compose them are high enough, a small charge induced by a particle of radiation in the sensitive region of the transistors is enough to make them suffer a transition to a very low impedance condition short circuiting the power supply.
• a redundant system with monitoring is used. As soon as the supervisor detects that the system that is active in nominal operation stops working according to the initial specifications, it switch to the redundant module, as can be seen in US patent 10,048,997 B2 granted to Hamilton Sundstrand Corporation in 2018. This is done to protect the integrity of the higher level functional entity by disconnecting the faulted unit and replacing it with its redundancy to prevent the fault propagation to a higher level and not to prevent the destruction of the affected electronic component. It is important to remark here that a SEL event always originates at the component level and not at the system level.
• the damage produced by SEL depends on the energy delivered by the power supply circuit to the point in the integrated circuit where the effect occurs and the magnitude of that energy will depend on the amount of time during which the power supply continues delivering its power. It is estimated that if this time is less than a minimum value, the damage is negligible. This implies very fast speed of response if the damage is to be avoided by interrupting the power supply. Furthermore, once this SEL phenomenon has occurred, the only way to return to normal Operating condition is to extend the interruption for the period required to achieve the extinction of the effect.
• Limiting the power delivered during the event is a valid alternative to achieve such mitigation when the other alternatives described above cannot or should not be used.
• One way to implement the limitation is through the use of a high internal impedance of the power supply as can be seen in US patent 9,391,448 B2 granted to The Boeing Company in the year 2016.
• the impedance becomes high only at the time the event occurs. If this power control is performed at a very high level in a system, the current monitored for triggering the power interruption will be the sum of all the supply currents from the components. Its value will always be much higher than the peak current produced in the SEL affected component. In these circumstances the protection performance for detecting the variation in power consumption produced by the occurrence of a SEL in an integrated circuit is poor and the speed of response is slow.
• Event detection can be done in several ways.
• One possible way was presented in the patent applications: CN 103762558 A filed in the year 2014 and CN108494240A/CN208401733U filed in the year 2018.
• the characteristic parameter used to detect the presence of a SEL is the growth rate of the supply current of the device to be protected.
• the event can also be detected by measuring the sudden temperature change in the component that undergoes SEL as proposed by US patent 9,793,899 B1 granted to Xilinx in 2017.
• This strategy can only be applied if the power breaking mechanism and the temperature measurement are implemented within the same chip. This should be so because of the need to avoid the delays that would occur if the process was performed by an external element. Because of this we must discard its use for the protection of integrated circuits intended for mass market products, which are not designed to contain this type of mechanism.
• the most frequently used mechanism to detect SEL events is to monitor the magnitude of the supply current consumed by the protected device. It has been used for specific cases by the main space agencies and several integrated circuit manufacturers provide specific products for that purpose. This mechanism is present in the patent CA1,287,103C granted to Microsemi Semiconductor in 1986 where the detection is made from the peak of supply current demanded by the load during a SEL event. This particular case uses a mechanism external to the device to be protected, but is restricted to those cases where switching type regulators are used to keep the voltage level on the device.
• two different criteria can be used: a) switch off the power when the value of the supply current is exactly below the minimum current produced by SEL or b) switch off the power when the value of the supply current is exactly above the highest value acceptable as normal consumption.
• the guarantee of having cancelled the risk of destructive SEL is achieved.
• the devices of interest microcontrollers, memories, programmable logic, etc.
• the devices of interest are extremely complex and therefore a great diversity of SEL modes can be expected. It is because there can be many types of sensitive points within each device and each of them can present different sensitivities and different values of intrinsic current limitation during the SEL occurrence.
• the first is that a radiation test is required for any device of interest in order to determine the protection threshold to be applied for each case. The cost and time involved in the preparation and execution of such tests would considerably reduce the advantages of using these components.
• the second is that the accumulated damage produced by total radiation dose (TID) increases the average value of the supply current during the lifetime, causing the fixed protection threshold originally established to become less effective.
• TID total radiation dose
• diodes that most integrated circuits use internally to protect themselves from the electrostatic discharge that they frequently suffer during handling.
• these diodes act as an alternative path for the power supply. They sustain the SEL condition even when the power from the supply circuit has been completely cut off. In this case, the supply of power through the inputs is avoided by limiting the parasitic supply currents by means of series resistors.
• the normality or abnormality of the event is determined by setting a protection threshold value that separates the two conditions. All of them require the setting of a permanent protection threshold during the design stage or eventually the choosing between two fixed levels during the operation phase.
• a very original proposal has been recently made by the company HARRIS Corporation whose patent US 9,960,593 B2, granted in 2018, for a device that could solve these limitations. It includes a controller which creates a database with signature vectors components that allow the identification of normal and abnormal power consumption profiles. These vectors not only include data profiles of the supply current consumption but also its correlation with the operating states of the protected device and the equipment in which it is operating.
• One of the main drawbacks of this proposal is that the generation of such a database implies an exhaustive process of tests under nominal and anomalous conditions whose result will be specific to each particular application. Because of this its cost may be equivalent to that of testing the device to be protected to determine its tolerance to the radiation environment conditions it will have to withstand.
• the method of comparison with a supply current threshold would be superior for its simplicity and speed of action if it were possible to solve the problem of the evolution of power consumption in all circumstances of the lifetime without over-dimensioning the protection threshold at the beginning of it. This is impossible if a fixed threshold is established a priori because it must always be higher than the worst peak of supply current expected throughout the lifetime of the protected device. Therefore, in most cases it will be well above the actual power consumption of the device at the beginning of its life, increasing the risk of destruction.
• This protection threshold is taken as a reference for initiating a mitigation process. This is performed by applying a self-adjustment of the threshold along the protected device lifetime.
• a variable reference threshold it is possible to minimize the risk of spurious mitigation and maximize the level of protection of the device.
• the determination of this reference threshold was made under conditions of high uncertainty since there is no certainty that, among the data used to calculate it, there is any erroneous data produced by having been acquired during a SEL.
• the strategy proposed here is based on the fact that, throughout the lifetime of the protected device, the ambient radiation conditions fluctuate through high and low levels and, therefore, the levels of risk of using a SEL current peak as an input for the calculation of the threshold also fluctuate.
• the method consists of determining in real time the protection threshold from the instantaneous values of the supply current of the protected device (or other equally relevant parameter for the purpose), when the measurement conditions are safe, i.e. when the probability of a SEL event is negligible because the radiation level to which it is exposed is very low. In addition, it suspends such determination when the radiation levels are so high that the probability of SEL occurrence exceeds a certain risk level.
• FIG. 1 The figure shows a typical CMOS integrated circuit supply current profile during normal operation and its evolution due to environmental radiation damage along its lifetime. It includes a fixed reference threshold for detection of possible SEL events.
• FIG. 2 The figure shows an idealization of the statistical distributions of supply current consumption as a percentage of the total operating time.
• the supply currents considered here are the current consumption of the individual integrated circuit, the current consumption of the electronic printed circuit board or equipment on which the individual integrated circuit operates and the different currents demanded by the integrated circuit in different SEL events in the same device.
• FIG. 3a Flow chart of the operating mode determination process.
• FIG. 3b Flow chart of the processes executed by the Protection Unit according to the determined operating mode.
• FIG. 4 Block diagram of a possible implementation of the Protection Arrangement against a SEL event using the proposed method.
• FIG. 5 Block diagram of a possible implementation of the Protection Unit against a SEL event using the proposed method.
• FIG 6 The figure shows a typical supply current consumption profile of a CMOS integrated circuit in normal operation and its evolution due to radiation damage during its lifetime, together with an optimal reference threshold estimated by the proposed device for protection against the occurrence of a SEL event.
• FIG 1 shows the effect of the aging produced by the radiation through the representation of the evolution of the supply current consumption of the protected device.
• the threshold imposed (100) to protect the device against a SEL until the end of its lifetime.
• the need to achieve this objective forces the over-dimension (102) of the protection threshold during most of its lifetime. This is due to the fact that to avoid spurious mitigations, the supply current threshold (100) must be set very far (102) from the normal consumption values (101) which causes a certain number of possible destructive SEL current peaks to be undetected because they are below the threshold.
• the statistical distributions of the values of: (a) the supply current consumed by the protected device (200), (b) the supply current consumed by the electronic board or equipment in which it is used (202) and (c) the different possible currents that can be produced by a SEL (204) are ideally represented; assuming that they follow a normal distribution.
• the purpose of this diagram is to show more clearly the different effectiveness that results from applying the method of interrupting the supply current of a whole piece of equipment or electronics board and of an individual integrated circuit that undergoes the SEL. Note that the mean (208) and standard deviation (210) of the supply current distribution of the equipment containing it (202) is much higher than the mean (207) and standard deviation (209) of the protected integrated circuit (200).
• this average (208) is composed by the sum of the averages of all the currents of all the components operating on the board or equipment and its standard deviation (210) is a function that depends on the accumulation of all the standard deviations of all those devices. Therefore, to avoid spurious actions, the protection thresholds (201 and 203) must be located to the right of the average current of the protected element (207 and 208) whatever it is, at certain distance of it. The more these thresholds are shifted to the right, the more the probability of false negatives (205) increases, i.e. destructive conditions that will not be detected. Note how it is much more likely that the supply currents of the equipment or board will overlap with the values of the SEL currents (205 and 206) than the latter will overlap with the supply currents consumed by the integrated circuit to be protected.
• This strategy relies on defining as the optimal threshold that which is as low as the value of the maximum peak of supply current consumed by the protected device without producing any spurious mitigation action.
• the method presented here calculates a real-time estimate of the protection threshold to be used in the following instant. It is based on the measurement of the value of the supply current of the protected device during its normal operation. It is processed by means of an estimation algorithm such as a function of the maximum value of the type:
• I(t) is the instantaneous value of the supply current in time t.
• / is the average value of the supply current consumed by the device of interest.
• s is the standard deviation of the supply current consumed by the device of interest.
• n is an experimentally determined factor that in some implementations can be a function of temperature.
• the radiation flux to which they are exposed is highly variable.
• the amplitude of this fluctuation can be as much as five or six orders of magnitude and its fluctuation period of an hour, aproximately.
• a preferred implementation of the proposed method is based on the execution of three processes: a) the mode determination process, b) the protection threshold calculation and refreshing process, and c) the power interruption process.
• a Flow chart showing the Mode Determination Process is shown in FIG 3a.
• the Radiation Flux Meter measures periodically (it could be between every two seconds or every two minutes) the flux of ionizing radiation from the environment in which it is operating (302).
• the Radiation Flux Comparator compares the level of ionizing radiation flux measured (304) with the threshold set in the Radiation Flux Reference level. If the level guarantee that the probability of a SEL is low enough, the Radiation Flux Measurement Unit will determine that the mode will be Learning (303). Otherwise, it will be Protection (301).
• the magnitude of the Reference Threshold for the Radiation Flux could be recorded permanently at the factory in a ROM memory or could be changed by commands from the ground station; using a rewritable, non-volatile and radiation-tolerant memory.
• the process shown in Fig. 3a is carried out using a radiation detector and its associated circuitry exposed to ionizing radiation, to produce a status signal defining the Operation Mode shared by all the protected devices on the satellite electronics.
• FIG 3b shows a flowchart for the processes associated to each protected electronic device carried out in each Protection Unit(s) as a function of the Operation Mode and the measured parameter on the electronic device.
• the initial conditions are set up (305) and a delay occurs (306) to avoid acquiring the transient values of the in-rush current from the protected device and its power filter.
• the Current Sensor measures (308) the value of the supply current consumed by the device of interest and check (307) the status of the mode signal.
• the protection unit starts the process of calculating and refreshing the protection threshold.
• the Optimum Threshold Calculation unit (513 - shown in Fig. 5 below) acquires the supply current values and, from them, calculates the new threshold (310) and stores it (311) in the Reference Register.
• the mode indicated by the external signal switches to the Protection mode (307).
• the calculation/updating operations of the supply current values used to calculate the protection threshold are suspended, and the device goes on to permanently check whether a SEL has been produced.
• the mode of operation is Protection
• the Protection Unit goes on to execute the interruption mitigation process upon the occurrence of a SEL.
• the acquired value is compared (316) with that of the protection threshold. If the measured supply current value is lower than the value of the reference threshold, the measurement (308) and comparison (316) process is repeated indefinitely. If, on the other hand, the supply current consumed is above this threshold, the protection device turns the power supply off immediately (317).
• the power supply is kept off (318) for the minimum time necessary to ensure the total extinction of the SEL.
• the device automatically reconnects the power (319) repeating the whole process from the beginning (300).
• FIG. 4 a block diagram can be seen representing a preferred realization of the layout using the method by a series of Protection Units (405) for the different protected devices.
• These Protection Units (405) are very small integrated circuits located externally very close to the corresponding protected electronic device (407). They all share the same information on the state of the ambient ionizing radiation flux but calculate different optimal protective current thresholds for each case.
• the Radiation Flux Meter (402) periodically measures the ambient radiation flux within which the arrangement operates.
• the Radiation Flux Comparator module (403) compares radiation flux level measured periodically by the Radiation Flux Meter
• FIG 5 shows a block diagram of the Protection Unit (405), which allows to execute a SEL mitigation process using the optimal current reference value for each case.
• This unit is composed of two modules: the Optimal Current Threshold Calculation Unit (513) and the Power Supply Control Unit (514). The operation of both is conditioned by the radiation flux level indicated by the mode signal status (503).
• the Reference Calculator (501) receives periodically samples of the supply current that also feeds the Supply Current Comparator (506). While in this mode the module calculates the optimal current threshold and updates it on the Reference Register (502) according to the evolution of the supply current. For the calculation, you can use one of the algorithms mentioned above, such as the maximum value function or the statistical function based on the calculation of the average and standard deviation of the current samples, to estimate the value of the protection threshold with which you update the corresponding register in real time.
• the Reference Calculator block (501) stops calculating and refreshing the optimal current threshold in the Reference Register
• Each Protection Unit (405) is connected in series between the VDC power supply (504) and the protected device (407) so that the supply current can be quickly interrupted by an electronic switch (508) in case a SEL is detected. This detection is achieved by continuously comparing the instantaneous value of the supply current of the protected device (407) with the value of the current Reference Register (502), using the Supply Current Comparator (506).
• a parallel switch (508) is also included with the protected circuit in order to provide a low impedance path for the parasitic currents entering through the inputs so that they are not able to sustain the SEL.
• a Timer (507) extends the power interruption long enough (e.g. 50-100 microseconds) to ensure that the SEL effect is extinguished and switch the power supply back on once this process has been completed.
• a summary of the operations performed in the different modes can be seen in TABLE 1.
• this table shows the operations performed by the Protection Unit (405).
• this unit dedicates all its time to estimate the optimum threshold and refresh the reference (502). If the measured supply current exceeds the value of the protection threshold, this value is adjusted without interrupting the power supply of the protected device. If the radiation level is high (Protection mode) then the Reference Calculator module (501) stops estimating the new threshold and stops refreshing the Reference Register (502). At the same time, the Supply Current Comparator (506) verifies that the supply current consumed by the protected device (407) does not exceed the previously established threshold value. If this happens, i.e. if a SEL occurs in these conditions, the Protection Unit (405) switchs off the protected device power supply until the undesirable condition becomes extinguished.
• Learning mode this unit dedicates all its time to estimate the optimum threshold and refresh the reference (502). If the measured supply current exceeds the value of the protection threshold, this value is adjusted without interrupting the power supply of the protected device. If the radiation level is high (Protection mode) then the Reference Calculator module (
• An example of the many possible preferred implementations of the Protection Unit (405) consists of an integrated circuit that requires no more than a few pins (let's say six, approximately) to perform its function. Two are connected in series between the power supply (504) and the protected device (510), one reads the operating mode signal (503), one inform the rest of the equipment if a mitigation is taking place (512) and the fifth connects to ground (509).
• This integrated circuit uses analog and digital technologies. The analog one performs the measurements (505), the comparison with the reference threshold (506) and the power interruption (508) for a limited period of time (507). It also uses digital technology including the Reference Calculator (501) and the Reference Register
• CMOS image sensor as a radiation detector (402) with associated logic for operation.
• This implementation is extremely useful because in addition to its low cost it has the ability to detect protons and heavy ions that are the main type of particles that can produce SEL in these applications.
• the protection arrangement (406) in Fig. 4 includes one or more Ambient Temperature Measurement Units (not illustrated) connected to one or more of the SEL Protection Units (405) in Fig. 5.
• the Temperature Measurement Unit consists of a temperature sensor configured to operate within the range of ambient temperatures in which the protected devices (407) have to operate. It provides them with a signal that is representative of the ambient temperature that the Protection Unit (405) uses to estimate the protection threshold for the next instant. For example, it can be used as an extra factor in any of the proposed algorithms whose value will be modulated by thermal cycles that occur inside the satellite when switching from the full sun exposition to the eclipse condition.
• FIG 6 shows the effect of aging by radiation through the representation of the evolution of the supply current consumption of the protected device. It can be seen here how none of the supply current peaks in normal operation (601) reaches the threshold imposed (800) to protect the device against a SEL occurrence.
• the threshold is permanently adjusted avoiding spurious mitigations, independently of the consumption fluctuations derived from the thermal cycles of the environment and independently of the total ionizing radiation aging of the protected device.
• SEL Single Event Latchup, is an undesirable effect that can occur in CMOS technology devices by which a low internal impedance between the power terminals causes the device destruction.
• SEL Mitigation is the process by which the destructive consequences of SEL are avoided.
• Spurious Mitigation Rate is the percentage of mitigation processes that are executed without a SEL having occurred.
• Protected Device is the SEL-susceptible CMOS technology device whose possible destruction is to be avoided through the mitigation process.
• Destruction Risk Level is the probability that there is a destructive SEL current value that is not detected because it is below the protection current threshold used to initiate a SEL mitigation process.
• Protection Current Threshold is the value of the supply current consumed by the protected device taken as a reference to identify a SEL and initiate a mitigation process. The definition of the value of this threshold determines the rate of spurious mitigations and the level of risk of destruction. It is not always possible to zero both figures simultaneously and the relationship between them is inverse, i.e. the higher the spurious mitigation rate, the lower the risk of destruction.
• Optimum Protection Current Threshold is the value of the Protection Current Threshold that simultaneously minimizes the Spurious Mitigation Rate and the Risk of Destruction. This value is immediately above the maximum value of the supply current consumed by the protected device and evolves as it ages due to the effect of accumulated damage from the radiation received.

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• 2019
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