Band-gap reference voltage starting circuit based on numerical control adjustable threshold value and high robustness

Abstract

The invention provides a band-gap reference voltage starting circuit based on a numerical control adjustable threshold and high robustness, and relates to the field of bandgap circuits, the band-gap reference voltage starting circuit comprises a threshold detection module, a latch, a PTAT current core module and a current mirror, positive temperature coefficient current and negative temperature coefficient current are mutually counteracted to obtain first-order compensated PTAT current, and the first-order compensated PTAT current is used for starting the bandgap reference voltage starting circuit. The current bias voltage is input into a current mirror module, and a plurality of currents are copied and input into other modules in the circuit so as to ensure normal work of a chip. Meanwhile, a branch in the current mirror generates reference voltage through reference current, the reference voltage is input to a threshold detection module to detect whether the PTAT current core module works at an ideal working point or not, if the PTAT current core module does not work at a target working point, copied current in the current mirror is far lower than a target value, and reference voltage output is far lower than the target value. And the threshold detection module works, and the circuit is restarted and forcibly dragged back to the target working point.

Description

Technical Field

[0001] This invention relates to the field of bandgap circuits, and more particularly to a bandgap reference voltage start-up circuit based on a numerically controlled adjustable threshold and high robustness. Background Technology

[0002] As CMOS process nodes continue to evolve, the operating voltage of integrated circuits is constantly decreasing to meet the increasingly stringent energy efficiency requirements of high-performance computing, mobile devices, and IoT applications. This trend has led to a rapid expansion of applications in low-voltage operating environments. However, the decrease in power supply voltage also presents significant challenges to analog circuit design, particularly in bandgap reference voltage source circuits.

[0003] Under low-voltage conditions, the potential difference between the static operating points in traditional bandgap reference circuits decreases, and the intervals between operating points become closer, making the circuit more susceptible to offset, noise, and process variations. This phenomenon causes many traditional analog startup circuits to fail to reliably guide the bandgap reference core to the only correct stable operating point, potentially causing it to remain at a pseudo-operating point (or degenerate point). Furthermore, non-ideal coupling between the startup circuit and the core circuit can introduce new non-ideal operating states. These unexpected operating modes not only reduce the circuit's startup reliability but also severely impact the bandgap reference's key performance indicators—especially its temperature characteristics—introducing additional nonlinear variables, leading to a deterioration in the temperature coefficient and a decrease in accuracy. This ultimately limits the stability and reliability of the entire chip system under wide temperature range and low-voltage conditions.

[0004] The startup circuit of a bandgap reference voltage source is crucial for its reliable operation. Currently, common startup circuits mainly focus on two core issues: how to detect the power-on state and effectively disturb the core circuit. However, existing solutions all have compromises in terms of power consumption, reliability, and accuracy. Summary of the Invention

[0005] This invention provides a bandgap reference voltage startup circuit based on numerically controlled adjustable threshold and complete shutdown technology. The circuit is mainly used to reliably start the core circuit of the bandgap reference voltage during chip power-up and to shut down the startup circuit after startup is complete, reducing power consumption while ensuring that complete shutdown does not affect bandgap temperature drift performance.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A start-up circuit based on a numerically controlled adjustable threshold and a highly robust bandgap reference voltage is provided, including: Threshold detection module, latch, PTAT current core module and current mirror; The threshold detection module is used to detect whether the PTAT current core module is working at the core operating point. If it is working at the core operating point, it jumps to the shutdown stage; if it is not working at the target operating point, the current replicated in the current mirror is much lower than the target value, which causes the reference voltage output to also be much lower than the target value. By restarting the circuit, it is forced to return to the target operating point. The latch is used to store the detection result of the threshold detection module. When the detection result is that it is not working at the target operating point, a high level is input to the Nmos switch Mn1 to turn on the Nmos switch Mn1. The PTAT current core module generates a large current and outputs a reference voltage greater than the threshold, which reduces the high level output of the threshold detection circuit and reduces the current of the PTAT current core module until it stabilizes at the target operating point. The PTAT current core module is used to generate PTAT current by canceling out positive temperature coefficient current and negative temperature coefficient current and inputting it into the current mirror. The current mirror is used to copy the input PTAT current into multiple currents, one of which is output to the threshold detection module to generate a reference voltage through the reference current, which is used to detect whether it is working at the core operating point.

[0007] Preferably, the PTAT current core module includes a bipolar junction transistor Q1, a bipolar junction transistor Q2, a resistor R1, a resistor R3, a resistor R3a, a field-effect transistor MP2, a field-effect transistor Mp3, and an operational amplifier.

[0008] More preferably, in the PTAT current core module, the current flowing through resistor R1 generates a voltage difference ΔVbe between the emitters of bipolar junction transistor Q1 and bipolar junction transistor Q2 that is proportional to the absolute temperature. The voltage difference ΔVbe and the base-emitter voltage Vbe of Q1 are superimposed on each other in a specific ratio through a resistor network composed of resistors R3 and R3a to finally generate the PTAT reference current.

[0009] Preferably, the current mirror replicates the reference current through the Pmos gate voltage output by the PTAT current core module, and then replicates it into multiple currents through the Nmos current mirror, which are then output to various functional modules.

[0010] Preferably, the current mirror includes a field-effect transistor MP4 and a resistor R4.

[0011] Preferably, the threshold detection module includes a startup circuit, a digitally adjustable switch, a comparator, resistors R6, R7, and R8.

[0012] More preferably, when the comparator outputs a signal whose current is much lower than the target value, the bandgap reference is forced to leave the degeneracy point, and the latch locks this start signal; in addition, when the bandgap reference enters a stable operating state, the start circuit immediately shuts down the threshold detection module, reduces its own power consumption, and the system enters steady-state operation.

[0013] Preferably, after power-on, the bistable input of the latch to the gate of the field-effect transistor Mn1 in the PTAT current core module is a low level 0, achieving complete turn-off.

[0014] Compared with existing technologies, the high-stability bandgap reference start-up circuit based on numerically controlled adjustable threshold and complete turn-off technology provided by this invention brings the following significant advantages: 1. High startup reliability, completely eliminating degenerate point locking: By introducing a comparator with state latching function, this invention can actively and forcibly pull the bandgap reference core circuit out of the degenerate operating point (non-ideal operating point) with zero current or low current. The stability of the startup circuit is improved by using the threshold detection method of the comparator, which is similar to digital control, and the operating point shift will not occur.

[0015] 2. Extremely low static power consumption, meeting green energy-saving requirements: This invention innovatively adopts a "complete shutdown upon task completion" architecture. After successfully starting the bandgap reference circuit, the power supply current path of core functional modules such as the comparator is completely cut off by controlling the switching transistor, thereby reducing their static power consumption.

[0016] 3. Lossless output accuracy, eliminating potential sources of interference: Because the startup circuit is physically isolated from the core circuit after completing its function, it completely eliminates the load effect and leakage current interference that may be caused to the sensitive nodes of the bandgap reference by voltage divider resistors or leakage paths in traditional startup circuits. This characteristic ensures the long-term stability and accuracy of the bandgap reference output voltage.

[0017] 4. High design flexibility, enhancing circuit versatility: By introducing digital control codes to programmatically adjust the startup voltage threshold, this invention enables a single circuit design to flexibly adapt to the needs of various chips with different process corners and power supply voltage specifications (such as 1.0V, 1.2V, 1.5V). Attached Figure Description

[0018] Figure 1 This is a structural diagram of the bandgap reference voltage start-up circuit based on numerically controlled adjustable threshold and high robustness of the present invention.

[0019] Figure 2This is a preferred embodiment of the bandgap circuit of the PTAT current core module of the present invention.

[0020] Figure 3 This is a circuit example diagram of a preferred embodiment of the current mirror of the present invention.

[0021] Figure 4 This is a design example diagram of a threshold detection module and a latch according to a preferred embodiment of the present invention.

[0022] Figure 5 This is a flowchart illustrating the overall circuit operation of the present invention. Detailed Implementation

[0023] Please see Figure 1 As shown, Figure 1 The diagram shows the overall block diagram of the bandgap circuit. The PTAT current generation core is the core part of the bandgap. It uses the mutual cancellation of positive temperature coefficient current and negative temperature coefficient current to obtain a first-order compensated PTAT current. This current is biased and input to the current mirror module to replicate multiple currents and input them to other modules in the circuit to ensure the chip works normally. At the same time, there is a branch in the current mirror that generates a reference voltage through a reference current. This reference voltage is input to the threshold detection module to detect whether the PTAT current core module is operating at the core operating point. If it is not operating at the target operating point, the current replicated in the current mirror is much lower than the target value, causing the reference voltage output to also be much lower than the target value. The threshold detection module then activates, the circuit restarts, and it is forced back to the target operating point.

[0024] The present invention relates to a bandgap reference voltage start-up circuit based on a numerically controlled adjustable threshold and high robustness, comprising: a threshold detection module, a latch, a PTAT current core module, and a current mirror; The threshold detection module is used to detect whether the PTAT current core module is working at the core operating point. If it is working at the core operating point, it jumps to the shutdown stage; if it is not working at the target operating point, the current replicated in the current mirror is much lower than the target value, which causes the reference voltage output to also be much lower than the target value. By restarting the circuit, it is forced to return to the target operating point. The latch is used to store the detection result of the threshold detection module. When the detection result is that it is not working at the target operating point, a high level is input to the Nmos switch Mn1 to turn on the Nmos switch Mn1. The PTAT current core module generates a large current and outputs a reference voltage greater than the threshold, which reduces the high level output of the threshold detection circuit and reduces the current of the PTAT current core module until it stabilizes at the target operating point. The PTAT current core module is used to generate PTAT current by canceling out positive temperature coefficient current and negative temperature coefficient current and inputting it into the current mirror. The current mirror is used to copy the input PTAT current into multiple currents, one of which is output to the threshold detection module to generate a reference voltage through the reference current, which is used to detect whether it is working at the core operating point.

[0025] like Figure 2 As shown, Figure 2 This example demonstrates a bandgap circuit application, specifically the core of the PTAT current generation circuit. The core circuit consists of bipolar junction transistors Q1 and Q2, resistors R1, R3, R3a, MP2, Mp3, and an operational amplifier. The current flowing through resistor R1 generates a voltage difference ΔVbe between the emitters of Q1 and Q2, proportional to their absolute temperature. This ΔVbe voltage is superimposed on the base-emitter voltage Vbe of Q1 through a resistor network composed of R3 and R3a in a specific ratio, ultimately generating a PTAT reference current. During the design process, the input pair of the operational amplifier can be designed with a sufficiently large aspect ratio to allow it to operate in the subthreshold region with a large transconductance. This allows for more precise clamping of the two branch voltages, achieving higher accuracy—comparing area for improved precision.

[0026] like Figure 3 As shown, Figure 3 This is an example of a current mirror circuit. The PMOS gate voltage generated by the PTAT current is used to replicate the reference current, which is then replicated using an NMOS current mirror. The results are output to various functional modules. The branch containing Mp4 provides a bias voltage through this replicated current and resistor R4 to detect whether the circuit is starting normally. When the circuit is in a non-ideal operating point, the replicated circuit value in the Mp4 branch is much lower than the target value, so the Vbg voltage is also very small, typically less than 5mV. This Vbg is input to the threshold detection module to complete the circuit startup. In this module design, the PMOS size can be designed by using multiple PMOS units in series to improve replication accuracy, or a cascode current mirror can be used to increase the resistance to improve replication accuracy. However, cascode current mirrors consume some voltage margin. The reference voltage Vbg is generated by the replicated current from the PMOS current mirror Mp4 flowing through resistor R4.

[0027] like Figure 4 As shown, Figure 4 This paper presents a design example of a threshold detection module and a latch. The threshold detection circuit and the latch are the focus of this design. In a resistor-divider startup circuit, due to the gradual decrease in the voltage domain under deep submicron technology, the degenerate operating point is closer to that of other processes. Therefore, the resistor-divider startup circuit may cause a shift in the operating point. Furthermore, the large resistors used in the design also increase the power consumption of one branch. Therefore, this invention designs a mechanism that uses a comparator to detect the threshold, converting it into a more digital startup to maintain high reliability and complete shutdown of the startup circuit.

[0028] The threshold detection Vref is achieved through voltage division. However, to accommodate different process corners, a digitally adjustable switch is added to select different Vref values. Since the voltage difference of Vbg at different operating points is significant (approximately 700mV to 5mV), the adjustment of Vref has a wide range. Simultaneously, to avoid excessive power consumption, considering that the startup circuit only needs to complete threshold detection and corresponding circuit startup functions during power-on, the bandgap can autonomously maintain its operating state after normal startup. As long as the gain and phase margin of the positive and negative feedback loops are properly controlled during the bandgap design, the bandgap can remain stable. Therefore, after power-on and normal circuit startup, the comparator power supply can be turned off for a period of time, and the detection result can be saved using a latch to maintain the control of Mn1.

[0029] The comparator design does not require a complex structure because the voltage difference Vbg between the two operating points is too large. If Vref is chosen appropriately, the voltage difference across the comparator input transistors will differ significantly in both detection methods. Even considering device mismatch and input transistor offset, it is still relatively easy to detect the correct result. Figure 4 A five-transistor operational amplifier is used directly as a comparator. Alternatively, an additional stage of circuitry can be added to improve the drive or increase the voltage output range, enabling the latch to output a faster and more accurate start signal to the bandgap core circuit for startup. After power-on, the latch's bistable state immediately inputs a low level (0) to the gate of Mn1, achieving complete shutdown. Therefore, this is similar to using a digital method to start the bandgap circuit, improving its reliability and ensuring complete shutdown.

[0030] like Figure 5 As shown, the workflow of this patent is a state detection and control sequence, specifically including: Status monitoring phase: After the system is powered on, the startup circuit first monitors the output voltage Vbg of the bandgap reference core circuit.

[0031] Decision and branching phase: Path selection based on Vbg values: Path 1 (already started normally): If Vbg has reached the ideal operating point voltage, the process will jump directly to the shutdown stage.

[0032] Path 2 (at the degeneracy point): If Vbg exhibits degeneracy point characteristics (extremely low voltage), the startup circuit is triggered.

[0033] Forced Start and Status Latching Stage: In path two, the comparator outputs a signal to force the bandgap reference to leave the degeneracy point, while the latch locks this start signal to ensure the reliability of the operation.

[0034] Shutdown and steady-state phase: Regardless of the path taken, as long as the bandgap reference enters a stable operating state, the startup circuit immediately and completely shuts down its comparator module, reducing its own power consumption to almost zero, and the system enters steady-state operation.

[0035] The key point of this invention lies in its systematic solution to the inherent problems of traditional startup circuits through three interconnected technical features, ultimately achieving the overall goal of high performance: Adjustable threshold: The start-up voltage threshold is set by programming with digital control codes, replacing the traditional fixed threshold detection. This allows the circuit to flexibly adapt to different chip power specifications and process corners, solving the problems of rigid design and poor adaptability of traditional solutions, which is the core of flexibility.

[0036] Latch Locking and High Stability: A latch is introduced after the comparator to convert the instantaneous signal of successful startup into a stable and persistent locked state. This design ensures the irreversibility of the startup command, effectively immunizes against power supply noise and interference, and completely eliminates false triggering and oscillation, which is the fundamental guarantee for achieving high stability.

[0037] Low power consumption: By utilizing the stable signal output by the latch, the power supply to the comparator module is completely shut off immediately after startup. This physically eliminates the static current path of the startup circuit itself, achieving near-zero static power consumption.

[0038] The technical solution of this invention is not limited to the specific implementation methods described above. Regarding the detection mechanism, in addition to a programmable threshold comparator, a low-power comparator or other equivalent circuit can be used to detect the power supply voltage to meet the power consumption and accuracy requirements under different process conditions. Similarly, the state locking mechanism is not limited to a latch implementation. In practical applications, a monostable circuit, a flip-flop, or other logic structures with holding functions can be used to lock the signal, thereby ensuring the uniqueness and reliability of the startup process. As for the energy-saving isolation mechanism, in addition to using a power switch, it can also be implemented through a power gating unit, switched capacitor isolation, or a dynamic power management circuit. These alternative methods can also cut off the power path of the detection module after startup, achieving the purpose of reducing power consumption and avoiding interference.

[0039] The above embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A start-up circuit based on a numerically controlled adjustable threshold and a highly robust bandgap reference voltage, characterized in that, include: Threshold detection module, latch, PTAT current core module and current mirror; The threshold detection module is used to detect whether the PTAT current core module is working at the target operating point. If it is working at the core operating point, it jumps to the shutdown stage; if it is not working at the target operating point, the current replicated in the current mirror is much lower than the target value, which causes the reference voltage output to also be much lower than the target value. By restarting the circuit, it is forced to return to the target operating point. The latch is used to store the detection result of the threshold detection module. When the detection result is that it is not working at the target operating point, a high level is input to the Nmos switch Mn1 to turn on the Nmos switch Mn1. The PTAT current core module generates a large current and outputs a reference voltage greater than the threshold, which reduces the high level output of the threshold detection circuit and reduces the current of the PTAT current core module until it stabilizes at the target operating point. The PTAT current core module is used to generate PTAT current by canceling out positive temperature coefficient current and negative temperature coefficient current and inputting it into the current mirror. The current mirror is used to copy the input PTAT current into multiple currents, one of which is output to the threshold detection module to generate a reference voltage through the reference current, which is used to detect whether it is working at the core operating point.

2. The bandgap reference voltage start-up circuit based on numerically controlled adjustable threshold and high robustness according to claim 1, characterized in that, The PTAT current core module includes a bipolar junction transistor Q1, a bipolar junction transistor Q2, a resistor R1, a resistor R3, a resistor R3a, a field-effect transistor MP2, a field-effect transistor Mp3, and an operational amplifier.

3. The bandgap reference voltage start-up circuit based on numerically controlled adjustable threshold and high robustness according to claim 2, characterized in that, In the PTAT current core module, the current flowing through resistor R1 generates a voltage difference ΔVbe between the emitters of bipolar junction transistors Q1 and Q2 that is proportional to the absolute temperature. The voltage difference ΔVbe and the base-emitter voltage Vbe of Q1 are superimposed on each other in a specific ratio through a resistor network composed of resistors R3 and R3a to finally generate the PTAT reference current.

4. The bandgap reference voltage start-up circuit based on numerically controlled adjustable threshold and high robustness according to claim 1, characterized in that, The current mirror replicates the reference current through the Pmos gate voltage output by the PTAT current core module, and then replicates it into multiple currents through the Nmos current mirror, which are then output to various functional modules.

5. The bandgap reference voltage start-up circuit based on numerically controlled adjustable threshold and high robustness according to claim 1, characterized in that, The current mirror includes a field-effect transistor MP4 and a resistor R4.

6. The bandgap reference voltage start-up circuit based on numerically controlled adjustable threshold and high robustness according to claim 1, characterized in that, The threshold detection module includes a startup circuit, a digitally adjustable switch, a comparator, resistors R6, R7, and R8.

7. The bandgap reference voltage start-up circuit based on numerically controlled adjustable threshold and high robustness according to claim 6, characterized in that, When the current replicated by the comparator output is much lower than the target value, the bandgap reference is forced to leave the degeneracy point. The latch stores the comparison result of the threshold detection and inputs a low level to the Nmos switch Mn1 to turn it off. In addition, when the bandgap reference enters a stable working state, the startup circuit immediately shuts down the threshold detection module, reduces its own power consumption, and the system enters steady-state operation.

8. The bandgap reference voltage start-up circuit based on numerically controlled adjustable threshold and high robustness according to claim 1, characterized in that, After power-on, the bistable input of the latch to the gate of the field-effect transistor Mn1 in the PTAT current core module is low level 0, achieving complete turn-off.

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