A method for suppressing bandgap reference cold start false operating points

Abstract

The application discloses a band gap reference cold start false working point inhibition method, and relates to the technical field of analog integrated circuits. In view of the problem that, when the band gap reference is started at low temperature, the starting current of the junction leakage current sharply decreases with the decrease of temperature, and the core stops at a false working point with low output, the method injects a complementary absolute temperature starting current which increases with the decrease of temperature into the band gap reference core through a starting injection branch in the cold start stage, so that the starting current is stronger with the decrease of temperature, the gap of the junction leakage current is filled, and the core is driven from the zero current degenerate equilibrium point to the normal working point; then, a state signal representing the working state of the core is collected, and the starting injection branch is pulled off after it is determined that the core has established the normal working point. The application can eradicate the low temperature false working point by using only one starting branch which is stronger with the decrease of temperature and is turned off after being started, does not introduce reference error, and is suitable for power management, data conversion and other chips working in a wide temperature range.

Description

Technical Field

[0001] This invention relates to the field of analog integrated circuit technology, and in particular to a method for suppressing the cold-start spurious operating point of a bandgap reference. Background Technology

[0002] Bandgap voltage references are among the most fundamental modules in analog and mixed-signal integrated circuits, providing a reference that is as independent of temperature, supply voltage, and process technology as possible for analog-to-digital converters, digital-to-analog converters, low-dropout linear regulators, and oscillators. The basic principle is to proportionally add a voltage proportional to absolute temperature to a voltage complementary to absolute temperature, causing their temperature coefficients to cancel each other out, resulting in a low-temperature drift reference of approximately 1.2 volts. However, this type of self-biased structure has an inherent characteristic: the circuit equations describing its operating state have more than one solution.

[0003] Self-biased bandgap references have at least two stable equilibrium points: one is the normal operating point where all branch currents are at their design values, and the other is the zero-current degenerate equilibrium point where all branch currents are nearly zero. Upon power-up, the circuit can very well fall into the zero-current degenerate equilibrium point and remain stable, with an output almost zero. Therefore, almost all bandgap references are equipped with a startup circuit that injects a small current into the core upon power-up, kicking the circuit from zero to the normal operating point, and then exiting once normal operation is established. To save area and power consumption, many startup circuits make this kick-out current very small, commonly using the subthreshold current of the MOSFET when it is turned off, or the junction leakage current of the reverse-biased PN junction or drain-substrate junction.

[0004] The circuit works well at room temperature by utilizing the junction leakage current for startup; although the junction leakage current is small, it is sufficient to kick the circuit out of zero. However, the junction leakage current has a peculiar characteristic that is often overlooked: it decreases sharply as the temperature drops. The reverse saturation junction leakage current is approximately proportional to the cube of the absolute temperature, multiplied by an exponential factor related to the silicon bandgap. This is a well-known conclusion in semiconductor device physics. It can decrease several times for every 10 degrees Celsius drop in temperature, often dropping to around 2 nanoamps at -40 degrees Celsius, far below the room temperature value. Thus, a strange phenomenon occurs: the colder the circuit, the weaker the startup force. In certain low-temperature batches or during a particular low-temperature power-on, this junction leakage current is too small to completely kick the core to the normal operating point. The core is kicked out of zero but fails to climb to the normal operating point, stopping halfway in an intermediate state with very low current. At this time, the output voltage also appears to have a decent value, but it is lower than the design value. This intermediate state is what this invention calls the pseudo-operating point.

[0005] The most troublesome aspect of this type of fault is its insidious nature. It only occurs intermittently at low temperatures and cannot be reproduced at room temperature; once the probe is placed on the chip and it heats up slightly by a few degrees Celsius, the junction leakage current rises, the circuit returns to its normal point, and the fault disappears immediately. Everything is normal during testing, but when installed in a complete system in cold environments, it occasionally outputs incorrect values. Downstream analog-to-digital converters and voltage regulators then interpret these incorrect values ​​as true, making the fault almost impossible to trace. When troubleshooting intermittent abnormal outputs in outdoor instruments and vehicle units during cold winters, the inventors, after several attempts, finally traced the root cause to this cold-start spurious operating point of the bandgap reference. Ultimately, existing solutions entrust the starting force to a physical quantity in the exact opposite direction; they rely on the junction leakage current, which decreases with decreasing temperature, while low temperatures are precisely when starting force is most needed. Existing methods only focus on whether it can start at room temperature, without considering the direction in which the starting force changes with temperature.

[0006] Therefore, a method is needed to suppress the spurious operating point of the bandgap reference cold start, so that the startup injection current increases rather than decreases at low temperatures without significantly increasing circuit complexity and normal operating power consumption, thus making up for the gap of junction leakage current at low temperatures. This ensures that the core can be reliably driven from the zero current degenerate equilibrium point to the normal operating point at any operating temperature. At the same time, the startup branch should automatically exit after normal operation is established, so as not to continuously inject current into the core and not to introduce reference error. Summary of the Invention

[0007] In view of the problem in the above-mentioned background technology that the bandgap reference is stuck at a false operating point due to the decrease of the starting current as the temperature decreases during cold start, the present invention provides a method for suppressing the false operating point of the bandgap reference during cold start, as well as a corresponding suppression device, chip and electronic device.

[0008] According to one aspect of the present invention, a method for suppressing the spurious operating point of a bandgap reference during cold start is provided. The bandgap reference includes a bandgap reference core and a start-up injection branch. The bandgap reference core has a normal operating point and a zero-current degenerate equilibrium point where the current is nearly zero. The method includes: during the cold start phase of powering on the bandgap reference, injecting a start-up current into the bandgap reference core through the start-up injection branch. The start-up current is a current complementary to absolute temperature, increasing with decreasing temperature and decreasing with increasing temperature. The amplitude of the start-up current at low temperature is greater than that at room temperature. Under the action of the start-up current, the bandgap reference core is... The zero-current degenerate equilibrium point transitions to the normal operating point; the voltage or current at the nodes in the bandgap reference core that monotonically change as the core branch current increases from zero to the design value is collected as a status signal characterizing the operating state of the bandgap reference core; based on the status signal, it is determined whether the bandgap reference core has established the normal operating point; after determining that the bandgap reference core has established the normal operating point, the status signal pulls a shutdown control node to control the switching device in the startup injection branch to disconnect and shut down the startup injection branch; after the bandgap reference core enters normal operation, it stops injecting the startup current through the startup injection branch.

[0009] According to another aspect of the present invention, a device for suppressing spurious operating points during cold start of a bandgap reference is provided, comprising a bandgap reference core, a start-up injection unit, an operating detection unit, and a shutdown control unit; the start-up injection unit is used to inject a start-up current that increases with decreasing temperature into the bandgap reference core during the cold start phase; the operating detection unit is used to collect a status signal characterizing the operating state of the bandgap reference core and determine whether a normal operating point has been established; the shutdown control unit is used to shut down the start-up injection unit after determining that a normal operating point has been established.

[0010] According to another aspect of the present invention, a chip is provided, including the above-described bandgap reference cold-start spurious operating point suppression device. According to yet another aspect of the present invention, an electronic device is provided, including the above-described chip.

[0011] The beneficial effects of this invention are as follows: the startup injection current is constructed as a current that increases with decreasing temperature and is complementary to the absolute temperature, so that the startup force increases with decreasing temperature, which precisely makes up for the gap of junction leakage current at low temperature. This ensures that the bandgap reference core can be reliably driven from the zero current degenerate equilibrium point to the normal operating point at any operating temperature, eliminating the occasional false operating point at low temperature in existing startup schemes that rely on junction leakage current. At the same time, after the bandgap reference core itself establishes the normal operating point, it pulls the shutdown control node to shut down the startup injection branch, so that no current is injected into the core after normal operation. This neither introduces reference error nor increases static power consumption. The entire suppression can be accomplished with only one startup branch that becomes stronger as the temperature gets colder and shuts down immediately after startup. Attached Figure Description

[0012] Figure 1 A flowchart of a method for suppressing cold-start spurious operating points of a bandgap reference according to an embodiment of the present invention;

[0013] Figure 2 This is a schematic diagram of the structure of a device for suppressing cold-start spurious operating points of a bandgap reference according to an embodiment of the present invention; Figure 3 A schematic diagram of the operating point curve, zero-current degenerate equilibrium point, pseudo-operating point, and normal operating point of the bandgap reference core; Figure 4 This is a comparison curve of the start-up current and junction leakage current as a function of temperature in one embodiment of the present invention; Figure 5 The above is a comparison waveform diagram of a cold start process at -40 degrees Celsius between an embodiment of the present invention and an existing start-up scheme relying on junction leakage current. Figure 6 This is a comparison chart of the cold start success rate of an embodiment of the present invention and an existing start-up scheme based on junction leakage current at different temperatures; Figure 7 This is a schematic diagram of the transistor-level circuit of the bandgap reference core and the CTAT start-up injection branch provided in an embodiment of the present invention; Figure 8 This is a circuit detail diagram of the CTAT start-up injection branch and automatic shutdown in one embodiment of the present invention. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. The specific process nodes, temperature values, current values, resistance values, voltage values, and threshold values ​​used in the following embodiments are illustrative examples and do not constitute a limitation on the scope of protection of this invention. Those skilled in the art can adjust the corresponding parameters according to actual application scenarios, and the adjusted implementation methods still fall within the scope of protection of this invention.

[0015] The following explains several key terms involved in this invention. The bandgap reference core refers to a self-biased circuit composed of paired bipolar transistors, resistors, and current mirrors or operational amplifiers. It generates a voltage component proportional to temperature and a voltage component complementary to absolute temperature, and adds them proportionally to obtain a reference voltage. Due to self-biasing, the currents in each branch are mutually biased, and the circuit equations describing its steady state have a zero solution in addition to the normal operating point. The normal operating point refers to the operating state where the currents in each branch of the bandgap reference core reach their design values, and the output is stable at the design reference value. The zero-current degenerate equilibrium point, i.e., the state corresponding to the aforementioned zero solution, refers to a stable equilibrium state where the currents in each branch of the bandgap reference core are nearly zero, mutually self-biased, but none of them can start. If no external starting current is applied upon power-up, the core may stop at this point, and the output will be nearly zero.

[0016] The so-called spurious operating point refers to a state where, after power-on, the bandgap reference core neither reaches the zero-current degenerate equilibrium point nor the designed normal operating point, but rather remains in a stable or metastable state between the two, where the current in each branch is significantly lower than the design value, and the output voltage is lower than the design reference value but not zero. At the spurious operating point, the reference outputs an erroneous voltage that appears valid but is actually too low. For example, if the design reference value is 1.203 volts, the spurious operating point may only output 0.74 volts, but the downstream circuit uses this low value as the correct reference. Figure 3 As shown, the current transmission relationship of the two mutually biased branches of the bandgap reference core is plotted on the same coordinate system. The two curves generally have three intersection points. The lowest intersection point corresponds to the zero current degenerate equilibrium point, the highest intersection point corresponds to the normal operating point, and there may be an intersection point in the middle. Once the core falls near the middle intersection point, it exhibits a false operating point. The role of the starting current is to push the operating point from the lowest intersection point all the way through the middle intersection point to the highest intersection point.

[0017] The startup injection branch refers to a branch connected between the power supply and the bandgap reference core, specifically used to inject startup current into the core during the cold start phase. It contains a switching device controlled by a shutdown control node; once the core starts up, this switching device is turned off, and the startup injection branch exits. In this paper, "complementary to absolute temperature" refers to the characteristic that a physical quantity decreases as absolute temperature increases and increases as absolute temperature decreases. Correspondingly, the temperature-complementary current (CTAT current) is a current whose amplitude decreases as absolute temperature increases and increases as absolute temperature decreases. A simple and commonly used source of CTAT current is to apply the base-emitter voltage of a bipolar transistor across a resistor. The base-emitter voltage is the voltage between the base and emitter of the bipolar transistor, with a temperature coefficient of approximately -2 millivolts per degree Celsius. The lower the temperature, the larger the voltage, and the larger the current obtained across the fixed resistor, thus naturally increasing with cold temperatures. The junction leakage current refers to the tiny current flowing through structures such as reverse-biased PN junctions and drain-substrate junctions in the off state. Its main component is the reverse saturation current, which is approximately proportional to the cube of the absolute temperature multiplied by an exponential factor related to the silicon bandgap. Therefore, it decreases sharply as the temperature decreases, and can decrease by several times for every 10 degrees Celsius decrease in temperature.

[0018] The state signal refers to an electrical quantity that monotonically changes as the bandgap reference core evolves from the zero-current degenerate equilibrium point to the normal operating point. It can be the current of a mirror current branch or the voltage of a bias node. This invention uses it to determine whether the core has truly started up. The mirror current branch refers to a branch from the bandgap reference core through a current mirror that replicates a current proportional to the core branch current. The bias node refers to a node within the bandgap reference core whose potential swings from an extreme potential to a normal bias potential as the core establishes its normal operating point. The turn-off threshold is a state signal threshold used to determine whether the bandgap reference core has established its normal operating point, taken between the level corresponding to the zero-current degenerate equilibrium point and the level corresponding to the normal operating point. The turn-off control node is a node whose potential is driven by the state signal, thereby controlling the on / off state of the start-up injection branch. The switching devices in the start-up injection branch are controlled by this node; after the core starts up, this node turns off the switching devices, and the start-up injection branch exits. The operating temperature range refers to the temperature range within which the chip is designed to operate normally, such as -40 degrees Celsius to 85 degrees Celsius for industrial grade and -40 degrees Celsius to 125 degrees Celsius for automotive grade.

[0019] Figure 1 This is a flowchart illustrating a method for suppressing spurious operating points during cold start of a bandgap reference, as provided in an embodiment of the present invention. Figure 1As shown, the method can be completed by a startup injection branch, a working detection circuit, and a shutdown control circuit integrated inside the chip and located in the same power supply domain as the bandgap reference core, including steps S1 to S3.

[0020] In step S1, during the cold start phase of powering on the bandgap reference, a starting current is injected into the bandgap reference core via the starting injection branch. This starting current is configured to be a complementary current to the absolute temperature, increasing with decreasing temperature and decreasing with increasing temperature, so that its amplitude at low temperatures is greater than its amplitude at room temperature. Under the action of this starting current, the bandgap reference core transitions from the zero-current degenerate equilibrium point to the normal operating point. This step is the core of the invention. Existing starting methods relying on junction leakage current fail at low temperatures because the reverse saturated junction leakage current it depends on decreases sharply with decreasing temperature, becoming smaller as the temperature gets colder. However, cold start requires the most current, and the two directions are opposite. The invention reverses the temperature trend of the starting current, making it increase with decreasing temperature. Thus, the starting current increases instead of decreasing at low temperatures, precisely making up for the gap left by the junction leakage current at low temperatures. Figure 4 As shown, the two curves of starting current and junction leakage current as a function of temperature are plotted together. The junction leakage current is a curve that collapses rapidly as the temperature decreases, while the starting current is a curve that rises as the temperature decreases. The two curves move in opposite directions. Therefore, at the coldest end, it is the starting current that fills the gap where the junction leakage current collapses, so that the total starting drive capability is not lower than the lower limit required to kick the core out of zero in the entire temperature range.

[0021] One way to construct such a strong starting current as the temperature decreases is to incorporate a bipolar transistor in the starting injection branch. Its base-emitter voltage is applied across a starting resistor, and the starting current is obtained by dividing this voltage by the resistance. The temperature coefficient of the base-emitter voltage is approximately -2 millivolts per degree Celsius; the lower the temperature, the higher the voltage and the larger the starting current. For example, with a starting resistor of 1.5 megohms, at 27 degrees Celsius, the base-emitter voltage is approximately 0.62 volts, and the starting current is approximately 0.41 microamps. When the temperature drops to -40 degrees Celsius, the base-emitter voltage rises to approximately 0.75 volts, and the starting current rises to approximately 0.50 microamps. However, at 125 degrees Celsius, the base-emitter voltage drops to approximately 0.42 volts, and the starting current decreases to approximately 0.28 microamps. It is evident that the startup current monotonically increases with decreasing temperature throughout the entire operating temperature range, reaching approximately 1.8 times that at the low-temperature end. Simultaneously, at the same -40°C, the junction leakage current used for startup drops from approximately 60 nanoamps at room temperature to less than 2 nanoamps. This demonstrates that by implementing a CTAT startup current, the lower the temperature, the stronger the startup drive provided by this branch. The circuit details of the startup injection branch generating this CTAT startup current and automatically shutting it off after core establishment are as follows... Figure 8As shown in the figure, the starting resistor Rst and the bipolar transistor Q3, which is connected as a diode, together generate a starting current with a value equal to the base-emitter voltage divided by Rst. This current is then mirrored and injected into the bandgap reference core by the switching device Msw. The switching on and off of Msw is controlled by the turn-off control node.

[0022] In another implementation, a field-effect transistor operating in the subthreshold region with a bias point designed to increase its drain current as temperature decreases can be used to generate the startup current. In yet another implementation, a current from the base-emitter voltage branch that increases with decreasing temperature can be subtracted from a smaller temperature-proportional current to obtain a composite startup current with a negative net temperature coefficient that increases with decreasing temperature. This also allows the startup current to decrease more rapidly with rising temperature, reaching a very small value earlier at high temperatures. All the above implementations that satisfy the condition that the startup current increases with decreasing temperature and that the low-temperature amplitude is greater than the room-temperature amplitude fall within the scope of this invention, and this invention is not limited thereto.

[0023] The amplitude of the startup current is set according to the minimum drive current required for the bandgap reference core to move away from the zero-current degenerate equilibrium point, with a margin at the lower limit of the operating temperature range. Optionally, the amplitude of the startup current at the lower limit of the operating temperature range is greater than 1.5 times its amplitude at the upper limit, to ensure sufficient overdrive even at the lowest operating temperature, allowing the core to pass the intermediate intersection point in one go and reach the normal operating point without stopping at the dummy operating point. It should be noted that the startup current should not be too large. An excessively large startup current at room temperature and high temperature will overdrive the core and prolong the settling time. Therefore, it is made into a CTAT (Current Cross-Actuation Current) that only increases significantly at low temperatures, which precisely balances the seemingly contradictory requirements of being large enough at low temperatures and not being too large at room temperature and high temperatures.

[0024] In step S2, the voltage or current at the nodes in the bandgap reference core that monotonically changes as the core branch current increases from zero to the design value is acquired. This acquired voltage or current serves as a status signal characterizing the operating state of the bandgap reference core. Based on this status signal, it is determined whether the bandgap reference core has established a normal operating point. When the bandgap reference core is at the zero-current degenerate equilibrium point, the current in each branch is nearly zero; when it is at the normal operating point, the current in each branch is at the design value. The core branch current monotonically changes between these two points. Therefore, only one electrical quantity reflecting the magnitude of this current is needed to determine whether the core has established a normal operating point. In one implementation, a mirror current branch is copied from the current mirror of the bandgap reference core, and the mirror current is sent to a sampling resistor and converted into a voltage as a status signal. In another implementation, the voltage of a bias node in the bandgap reference core is directly acquired as the status signal.

[0025] The judgment is made by comparing the status signal with the turn-off threshold. When the core establishes its normal operating point, the status signal exceeds the turn-off threshold; when the core is at the zero-current degenerate equilibrium point, the status signal falls below the turn-off threshold. This turn-off threshold is typically taken near the midpoint between the level corresponding to the zero-current degenerate equilibrium point and the level corresponding to the normal operating point, for example, about half the level corresponding to the normal operating point. Its specific value can be determined by design simulation scanning the level distribution of the status signal before and after the core starts up under all temperature and process angles. In cases where the core starts up slowly, such as at low temperatures or slow process angles, the value can be appropriately lowered to avoid misjudging the core as established before it is fully established. Since replicating a branch of the current mirror and converting the current to voltage for comparison are mature technologies in analog circuits, their specific connections will not be elaborated here.

[0026] In step S3, after determining that the bandgap reference core has established a normal operating point, a status signal triggers a shutdown control node to disconnect the switching device in the startup injection branch, thus shutting off the startup injection branch. After the bandgap reference core enters normal operation, the injection of startup current through the startup injection branch ceases. This step, in conjunction with step S1, ensures that the startup branch only operates when needed, and is another key technical means of this invention.

[0027] Specifically, the status signal is amplified and inverted through one or more stages before being connected to the shutdown control node. This node is connected to the control terminal of the switching device in the startup injection branch. When the core is not established, the status signal is below the shutdown threshold. The shutdown control node keeps the switching device on, and the startup injection branch injects a stronger startup current into the core as it cools. Once the core is established, the status signal exceeds the shutdown threshold. The shutdown control node flips, turns off the switching device, and the startup injection branch is cut off, reducing the startup current to zero. In this way, during normal operation, the startup injection branch no longer injects any current into the core, thus avoiding introducing its own temperature characteristics into the reference and introducing errors, and also preventing an increase in static power consumption.

[0028] This is particularly important for this invention because the startup current, CTAT, although small at room temperature and high temperature, still exists. If it is not turned off, it will continue to inject into the core during normal operation, disturbing the carefully balanced temperature curve and negatively impacting the low-temperature drift index of the reference. Optionally, after the startup injection branch is turned off, the current injected into the bandgap reference core is zero, or less than 1% of the single-branch current of the bandgap reference core during normal operation, so that its influence on the reference can be ignored.

[0029] Considering the possibility of a slow power rise at power-on or a brief pullback caused by strong interference, a hysteresis can be introduced when determining whether the core has established a normal operating point. This involves setting the threshold of the state signal corresponding to the shutdown control node's shutdown of the startup injection branch to be higher than the threshold of the state signal corresponding to the shutdown control node's reopening of the startup injection branch, thus creating a hysteresis between shutdown and reopening. This prevents the startup injection branch from repeatedly switching on and off and causing oscillations when the core fluctuates slightly near the critical point. If the core does fall back to near zero due to strong interference, the low threshold below the hysteresis will reopen the startup injection branch and rebuild the core.

[0030] Figure 2 This is a schematic diagram of a device for suppressing cold-start spurious operating points of a bandgap reference according to an embodiment of the present invention. Figure 2 As shown, to implement the above method, this embodiment provides a device for suppressing the cold-start spurious operating point of a bandgap reference, including a bandgap reference core, a startup injection unit, an operating detection unit, and a shutdown control unit. The unit division here is a schematic logical division for achieving the above functions; in actual implementation, the units can be combined or separated. The startup injection unit, connected between the power supply and the bandgap reference core, is configured to inject a startup current into the bandgap reference core during the cold-start phase that increases with decreasing temperature and decreases with increasing temperature, complementary to the absolute temperature. The operating detection unit, connected to the bandgap reference core, is configured to collect the voltage or current at nodes in the bandgap reference core that monotonically change with increasing core branch current as a status signal, and determine whether the bandgap reference core has established a normal operating point based on this signal. The shutdown control unit, connected to the operating detection unit, the startup injection unit, and a shutdown control node, is configured to shut down the startup injection unit via the shutdown control node after determining that the bandgap reference core has established a normal operating point.

[0031] In one possible implementation, the startup injection unit includes a bipolar transistor, a startup resistor, and a field-effect transistor as a switching device; the operation detection unit includes a current mirror branch and a comparator; and the shutdown control unit includes a level-flipping circuit connected between the comparator output and the control terminal of the switching device. One transistor-level circuit connection of this suppression device is as follows: Figure 7 As shown in the figure, the bandgap reference core consists of paired bipolar transistors Q1 and Q2, resistors R1 and R2, PMOS current mirrors MP1 to MP3, and operational amplifier A1. The startup injection branch consists of startup resistor Rst, bipolar transistor Q3, and field-effect transistor Msw as a switching device. The switching on and off of Msw is controlled by an inverter pulling the turn-off control node.

[0032] The suppression device provided in this embodiment is used to perform the aforementioned method. The specific working process of each unit corresponds one-to-one with each step of the aforementioned method, and can achieve the same effect as the aforementioned method. Repeated parts will not be described again.

[0033] Figure 2 The suppression device shown can be integrated into a single chip. Accordingly, this embodiment also provides a chip including the aforementioned bandgap reference cold-start spurious operating point suppression device, which can be a power management chip, analog-to-digital converter chip, microcontroller, or system-on-a-chip (SoC) or other integrated circuit requiring an on-chip reference. This embodiment also provides an electronic device including the aforementioned chip, which can be an industrial controller, automotive electronic unit, outdoor instrument, or other device requiring reliable power-on operation over a wide temperature range. Because the bandgap reference inside the chip can reliably cold-start at any operating temperature and will not stop at a spurious operating point, the electronic device will not output incorrect results due to a low reference when powered on in a cold environment.

[0034] The following is an end-to-end embodiment illustrating the method flow of the present invention, such as... Figure 1 .

[0035] Example This embodiment describes the bandgap reference in a power management chip using a 0.18-micron BCD process and operating at a temperature range of -40°C to 125°C. The designed reference value is 1.203 volts. During normal operation, the current in each branch of the core is approximately 5 microamps, and the minimum drive current required for the core to move away from the zero-current degenerate equilibrium point is approximately 0.18 microamps. A parasitic vertical PNP transistor and a 1.5 megohm startup resistor are incorporated into the startup injection branch. The base-emitter voltage of the PNP transistor is applied to the startup resistor to obtain the startup current, and a P-type field-effect transistor is used as the switching device for this branch. A mirror current branch is replicated from the core current mirror, and the mirror current is converted into a status signal voltage across a 200 kΩ sampling resistor. The turn-off threshold is set to 0.5 times the level corresponding to the normal operating point.

[0036] The device was powered on in a cold storage room at -40 degrees Celsius. At the moment of power-on, the bandgap reference core fell to the zero-current degenerate equilibrium point, with the current in each branch almost zero, and the output was about 0.02 volts. At this time, the base-emitter voltage of the PNP transistor was about 0.75 volts, and the starting current obtained across the starting resistor was about 0.50 microamps. However, the junction drain current that could have been used at the same temperature was less than 2 nanoamps. It can be seen that if only the junction drain current is used, 0.002 microamps is far less than the 0.18 microamps required to break free from the zero point, and the core will either not be able to move or will only be partially moved. The 0.50 microamp starting current in this embodiment is about 2.8 times the minimum required drive current, which is sufficient to push the core past the intermediate intersection point and directly to the normal operating point. During the process of the core branch current rising from near zero to 5 microamps, the current in the mirror current branch is sent to the sampling resistor and converted into a status signal voltage, which monotonically increases from low to high. When the status signal exceeds the turn-off threshold, it is determined that the core has established a normal operating point. The status signal, through the level-flipping circuit, pulls the turn-off control node, turning off the P-type MOSFET acting as a switching device. The startup injection branch is cut off, and the startup current drops from 0.50 microamps to zero. Afterward, the measured current injected into the core by the startup injection branch is approximately 9 nanoamps, less than 1% of the single-branch current of 5 microamps, and has almost no impact on the reference. The entire cold start is completed in approximately 18 microseconds, and the output stabilizes at 1.203 volts, without any instances of stopping at a false operating point near 0.74 volts. Figure 5 The following diagram shows a comparison of waveforms between this embodiment and existing start-up schemes relying on junction leakage current during cold start-up at -40 degrees Celsius. Figure 5 As shown, the output of this embodiment climbs to 1.203 volts and stabilizes within about 18 microseconds, while the output of the existing junction leakage current start-up scheme climbs to about 0.74 volts and then stops rising, remaining at the dummy operating point for a long time.

[0037] When the same chip is powered on at a high temperature of 125 degrees Celsius, the base-emitter voltage of the PNP transistor drops to about 0.42 volts, and the startup current drops to about 0.28 microamps, which is still greater than the 0.18 microamps required to break free from zero, so the core can still start up. At the same time, the junction leakage current is relatively large at this temperature, and the combination of the two will ensure that startup is not interrupted. After the core starts up, the startup injection branch is also turned off. Since the startup current is CTAT, which is already small at high temperatures, the residual current injected into the core after shutdown is even lower and negligible. Therefore, the temperature drift curve of the reference at high temperatures is not affected by the startup branch.

[0038] As a control, under the same -40°C conditions, the startup branch was replaced with the existing startup scheme that utilizes junction leakage current, and the circuit was powered on again. The existing startup circuit, which uses junction leakage current to provide the kick-out current, draws its kick-out current from the junction leakage current of a reverse-biased junction. Since the reverse saturated junction leakage current decreases exponentially with decreasing temperature, this current is only about 1.8 nanoamps at -40°C, far less than the 0.18 microamps required for the core to escape the zero-current degenerate equilibrium point. Therefore, after being pushed away from zero by this weak junction leakage current, the core is unable to continue climbing and eventually stops at a false operating point with a core branch current of about 0.35 microamps and an output of about 0.74 volts. Because the output is not zero and appears to be operating, the downstream analog-to-digital converter uses 0.74 volts as a reference of 1.203 volts, which is equivalent to a reference value that is about 38% lower. All its conversion results exhibit a systematic deviation. This fault disappears during room temperature retesting due to leakage current recovery and the core automatically climbing back to the normal point, making it difficult to pinpoint the problem. The only difference between the two power-ups was the temperature trend of the starting current, which shows that making the starting current stronger as it gets colder is the key to eliminating the false operating point at low temperatures.

[0039] To further verify the effectiveness of the present invention, within a temperature range of -40 degrees Celsius to 125 degrees Celsius, the bandgap reference using the present invention and the existing bandgap reference using a junction leakage current start-up scheme were each powered on 1,000 times. The cold start success rate was statistically analyzed, that is, the proportion of the output after power-on falling within ±1% of the design reference value. Figure 6 As shown, when using existing start-up schemes relying on junction leakage current, the success rate is 100% at 125°C, 100% at 27°C, drops to approximately 96.7% at -20°C, and plummets to approximately 78.4% at -40°C, meaning that more than one out of every five power-ups fails at the false operating point. With this invention, the cold start success rate at all the above temperature points is 100%, and there were no instances of failure at the false operating point in one thousand power-ups at -40°C. It is evident that the failure of existing schemes is concentrated at low temperatures, and the lower the temperature, the more severe the failure. This invention, however, because the starting current becomes stronger at colder temperatures, increases the success rate in the low-temperature region from approximately 78.4% to 100%. It should be noted that the above values ​​are simulation statistics under a given process angle and a given leakage current model. These values ​​may fluctuate depending on the process angle, leakage current parameters, and power supply slope. However, the trend that the success rate of existing schemes in the low-temperature region is significantly lower than at room temperature, while this invention achieves near-perfect scores across the entire temperature range, remains stable. This invention adds almost no extra area or power consumption. The startup injection branch uses only one more bipolar transistor and one more resistor than the conventional startup branch to shape the temperature profile, and is completely turned off during normal operation. Therefore, it does not sacrifice other benchmark performance.

[0040] The method and apparatus described in this invention are not limited to the specific topology of the bandgap reference core mentioned above. For current-mode bandgap references, voltage-mode bandgap references, bandgap references clamped by operational amplifiers, and bandgap references that are self-biased only by a current mirror without operational amplifiers, as long as there is a zero-current degenerate equilibrium point and a startup circuit is needed to kick the core out from that point, this invention can be used to make the startup current increase with decreasing temperature and automatically turn off after the core is established. The same approach applies to other self-biased current sources or reference sources that have multiple equilibrium points and require external startup. The acquisition of status signals is not limited to mirror current or bias node voltage; any electrical quantity that can monotonically change with the core from zero to normal operating point can be used as a criterion. The shutdown control can be implemented using a comparator and a level-flipping circuit, or it can be implemented directly using a threshold device; this invention is not limited to these methods.

[0041] From an overhead perspective, this invention adds almost no cost compared to conventional startup circuits. The startup injection branch only uses one more bipolar transistor and one more startup resistor to shape the current temperature profile compared to conventional startup branches that rely on junction leakage current or subthreshold current. The area increase is negligible compared to the overall bandgap reference module. Furthermore, since the startup branch is completely turned off after the core establishes its normal operating point, its quiescent current is zero or negligible during normal operation, thus not increasing the static power consumption of the bandgap reference. In other words, this invention achieves reliable cold start across the entire temperature range with minimal area overhead and completely eliminates low-temperature spurious operating points without sacrificing the reference's accuracy, temperature drift, power supply rejection ratio, or other performance indicators. This is particularly important in applications such as industrial control, automotive electronics, outdoor instruments, and aerospace, where reliable power-on in cold environments is crucial, as these applications are particularly intolerant of the reference occasionally outputting a seemingly normal but actually low value at low temperatures.

[0042] When implementing the CTAT current, the value of the startup resistor, the emitter area of ​​the bipolar transistor, and the number of stages in the startup branch can all be selected according to the magnitude of the target startup current and the temperature slope. The smaller the value of the startup resistor, the larger the startup current obtained for the same base-emitter voltage, and the stronger the low-temperature overdrive. However, the current at room temperature and high temperature also increases accordingly, requiring a trade-off between low-temperature reliability and room-temperature power consumption. For bandgap reference cores with branch currents in the microampere range, the startup resistor is typically taken as 200 kilohms to 5 megohms. Through repeated testing and simulation comparisons by the inventors, when the startup current is taken as about three times the minimum required drive current at the lower limit of the operating temperature range, sufficient overdrive margin can be maintained in the coldest low-temperature slow process corners without over-driving the core at room temperature and high temperature, thus prolonging the settling time. To make the slope of the startup current as a function of temperature steeper, the base-emitter voltages of two or more bipolar transistors can be cascaded and then applied to the startup resistor, which multiplies the equivalent temperature coefficient, thus allowing the startup current to rise higher at low temperatures and fall lower at high temperatures. The shutdown threshold can be calibrated during the design phase by performing a full-temperature, full-process-angle scan of the state signal levels before and after the core starts up. A fraction of the state signal level reached when the core just crosses the intermediate intersection point is taken as the shutdown threshold, with a downward shift margin allowed for low-temperature and slow-process corners. Once these parameters are determined during the design phase, they are fixed in the layout and require no adjustment during operation, thus not increasing operational overhead.

[0043] As a more severe scenario, consider a process angle where the same chip is subjected to a combination of low temperature and slow process angle, i.e., a temperature of -40 degrees Celsius, and both the current gain and resistance value of the bipolar transistors are biased towards the end that makes it more difficult for the core to start. In this case, the minimum drive current required for the core to escape the zero-current degenerate equilibrium point increases from approximately 0.18 μA at room temperature to approximately 0.27 μA. However, the CTAT startup current in this embodiment is still approximately 0.48 μA in this angle, with a margin of approximately 1.8 times, allowing the core to still be established on the first attempt. If the existing method of starting using junction drain current is used, the junction drain current in this angle is only about 1.5 nanoamps, less than 1% of the required 0.27 μA, and the core will almost certainly stop at the false operating point. It is evident that because the startup current increases with decreasing temperature, this invention can maintain sufficient overdrive margin even in the most unfavorable low-temperature slow angle.

[0044] This method is also applicable in certain boundary situations. First, during power-up, the power supply voltage rises slowly. The startup injection branch begins injecting a temperature-dependent startup current into the core while the power supply is still low. As the power supply rises, the core gradually builds up. Once the status signal exceeds the shutdown threshold, the startup branch shuts off. The entire process is independent of the specific power supply ramp-up rate. Second, if the chip is subjected to strong interference during normal operation, and the power supply momentarily drops and then recovers, the core may be briefly pulled back to near zero. At this time, the status signal falls back below the hysteresis threshold, and the shutdown control node reopens the startup injection branch, injecting the increasingly strong startup current as the temperature decreases. The core is then brought back to the normal operating point. After the interference subsides, the startup branch automatically shuts off again. Third, because the startup force is deliberately strengthened at low temperatures rather than relying on accidental junction leakage current, the consistency between multiple power-ups is significantly improved. The random phenomenon of the same chip powering up normally one time but stopping at a false operating point the next time is no longer observed.

[0045] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for suppressing spurious operating points during cold start of a bandgap reference, wherein the bandgap reference comprises a bandgap reference core and a start-up injection branch, the bandgap reference core having a normal operating point and a near-zero current degenerate equilibrium point, characterized in that, The method includes: S1, During the cold start phase of powering on the bandgap reference, a starting current is injected into the core of the bandgap reference through the starting injection branch. The starting current is a CTAT current that is complementary to the absolute temperature, which increases as the temperature decreases and decreases as the temperature increases. The amplitude of the starting current at low temperature is greater than that at room temperature. Under the action of the starting current, the core of the bandgap reference transitions from the zero current degenerate equilibrium point to the normal operating point. S2, collect the voltage or current at the nodes in the bandgap reference core that monotonically change as the core branch current increases from zero to the design value, as a status signal characterizing the working state of the bandgap reference core, and determine whether the bandgap reference core has established the normal working point based on the status signal. S3, after determining that the bandgap reference core has established the normal working point, the status signal pulls a shutdown control node to control the switching device in the startup injection branch to disconnect and shut down the startup injection branch. After the bandgap reference core enters normal working, it stops injecting the startup current through the startup injection branch.

2. The method according to claim 1, characterized in that, The startup current is obtained by converting the base-emitter voltage of a bipolar transistor in the startup injection branch across a startup resistor. The base-emitter voltage increases as the temperature decreases, and the startup current increases as the base-emitter voltage decreases with temperature.

3. The method according to claim 1, characterized in that, The amplitude of the starting current at the lower limit temperature of the bandgap reference operating temperature range is greater than 1.5 times the amplitude of the starting current at the upper limit temperature of the operating temperature range.

4. The method according to claim 1, characterized in that, The status signal is taken from the mirror current branch of the bandgap reference core or the bias node corresponding to the normal operating point. The status signal exceeds a turn-off threshold after the bandgap reference core establishes the normal operating point, and is lower than the turn-off threshold when the bandgap reference core is at the zero current degenerate equilibrium point.

5. The method according to claim 1, characterized in that, After the start-up injection branch is turned off, the current injected into the bandgap reference core by the start-up injection branch is zero, or less than 1% of the single-branch current when the bandgap reference core is operating normally.

6. The method according to claim 4, characterized in that, The threshold value of the state signal corresponding to the shutdown control node shutting down the startup injection branch is higher than the threshold value of the state signal corresponding to the shutdown control node re-enabling the startup injection branch, thus creating a hysteresis between the shutdown and activation of the startup injection branch.

7. A device for suppressing spurious operating points during cold start of a bandgap reference, characterized in that, It includes a bandgap reference core, a startup injection unit, a working detection unit, and a shutdown control unit; The bandgap reference core has a normal operating point and a zero-current degenerate equilibrium point where the current is almost zero. The startup injection unit is connected between the power supply and the bandgap reference core and is used to inject startup current into the bandgap reference core during the cold start phase. The startup current is a CTAT current that is complementary to the absolute temperature, which increases as the temperature decreases and decreases as the temperature increases. The working detection unit is connected to the bandgap reference core and is used to collect the voltage or current at the nodes in the bandgap reference core that change monotonically with the increase of the core branch current, as a status signal characterizing the working state of the bandgap reference core, and to determine whether the bandgap reference core has established the normal working point based on the status signal. The shutdown control unit is connected to the working detection unit, the startup injection unit and a shutdown control node, and is used to shut down the startup injection unit via the shutdown control node after determining that the bandgap reference core has established the normal working point.

8. A chip, characterized in that, Includes the device for suppressing the bandgap reference cold start spurious operating point as described in claim 7.

9. An electronic device, characterized in that, Includes the chip described in claim 8.

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