BOOT converter soft start circuit for large area array image sensor

Abstract

The invention relates to a BOOT converter soft start circuit for a large-area-array image sensor, and belongs to the technical field of power management. The technical problem of output voltage overshoot caused by overlarge difference between reference voltage and feedback voltage when the BOOST converter is started is mainly solved. According to the technical scheme, a soft start module generates a linearly-increased soft start voltage VSS, and when the VSS is smaller than a reference voltage VREF, the VREF is replaced to be input into an error amplifier, so that a feedback voltage VFB linearly rises along with the VSS, and the surge of an inductive current is restrained. Technical effects include thoroughly eliminating voltage overshoot, maintaining optimal performance parameters of the system, providing programmable startup characteristics, enhancing system reliability, and simplifying integration complexity.

Description

Technical Field

[0001] This invention belongs to the field of power management technology and relates to a soft-start circuit for a BOOT converter for large-area image sensors. Background Technology

[0002] Boost converters are widely used in CMOS image sensors to provide high-efficiency power supply voltage conversion. When operating in peak current mode, the loop of a boost converter operates as follows: Figure 1 As shown, the control signal for the power transistor is generated by the voltage loop and the current loop at this time, R C C C This includes the loop compensation resistor and capacitor. Output voltage V OUT After voltage division by resistors, a feedback voltage V is generated. FB And input to the inverting input terminal of the error amplifier, and the reference voltage V REF The comparison is performed, and the error amplifier amplifies the difference to generate an error voltage V. EA This forms a voltage feedback loop; the current feedback loop is formed by the inductor current I. L The sampling current is obtained after passing through the sampling module, and a sampling voltage V is generated across the sampling resistor. SENSE Sampling voltage V SENSE With error voltage V EA V is obtained through the PWM comparator. P Then, the power switch M is generated by the logic driver module. N and rectifier tube M P The control signals GN and GP.

[0003] When the system starts working, the output voltage V OUT If the feedback voltage V is small, then FB Much smaller than the test voltage V REF This will cause the error voltage V EA Much greater than the sampling voltage V SENSE This results in a very large duty cycle for the PWM comparator output pulse, causing the inductor current to rise to the maximum current limit of the system in a short time.

[0004] because

[0005] V EA =(V REF -V FB )G m R C +V C

[0006] Among them, G m V is the gain of the error amplifier. C For loop compensation resistor C C The voltage on the reference voltage V.REF Greater than the feedback voltage V FB At that time, the error voltage V EA Rise; when the reference voltage V REF Less than the feedback voltage V FB At that time, the error voltage V EA The output voltage V decreases. OUT Before rising to the target voltage, the feedback voltage V FB Total less than the reference voltage V REF Error voltage V EA It continues to rise. When the output voltage V... OUT When the target voltage is reached, the inductor current is at its maximum. At this point, the inductor releases energy, and simultaneously, due to the bandwidth of the error amplifier, the output voltage V... OUT It will continue to increase, causing the output voltage V to... OUT This causes voltage overshoot.

[0007] The previous section provided a qualitative analysis of voltage overshoot; now, a quantitative analysis will be conducted. The generation of voltage overshoot is as follows: Figure 2 As shown. At time T1, the circuit pre-charging ends, and the output voltage V... OUT Equal to input voltage V CC The circuit loop is working, and the output voltage V OUT The voltage continues to rise. At time T2, the output voltage V... OUT To reach the target voltage V target At this time, the error voltage V EA It starts to decrease, but the output voltage V OUT It continues to rise. At time T3, the error voltage V EA Drop to sampling voltage V SENSE peak V SENSE-MAX At this point, the error amplifier enters the linear amplification region, and the inductor current begins to decrease. Since the inductor has not yet been demagnetized, the output voltage V... OUT The upward trend continues. At time T4, the inductor demagnetization is complete, and the output voltage V... OUT The peak value is reached. Therefore, the maximum value of the output voltage V overshoot It can be represented as:

[0008] V overshoot =V target +ΔV1+ΔV2

[0009] At time T3,

[0010]

[0011] According to the law of charge conservation, we can conclude that:

[0012]

[0013] Among them, VC-MAX Determined by the parameters of the error amplifier, which can be considered known here, C C V C-MAX When the output voltage of the error amplifier is at its maximum, the capacitor C C The amount of charge on it. ΔV in It can be represented as:

[0014]

[0015] During the time interval T2 to T3, the load capacitance C changes from the maximum inductor current I. MAX Charging yields:

[0016]

[0017] In summary, the following can be calculated:

[0018]

[0019] ΔV2 is generated by the demagnetization of the inductor, where energy is transferred to the load capacitor. According to the law of conservation of energy, we can obtain:

[0020]

[0021] ΔV2 can be obtained through calculation:

[0022]

[0023] Analysis shows that V overshoot The value of V is related to factors such as inductance, load capacitance, and maximum inductor current. Therefore, reducing the inductance, increasing the load capacitance, or decreasing the maximum inductor current can lower the V value. overshoot However, this will create some additional problems and will only reduce V. overshoot It cannot be eliminated. This is due to the reference voltage V. REF With feedback voltage V FB The large difference in current caused the loop duty cycle to be too large, resulting in excessive inductor current. Summary of the Invention

[0024] In view of this, the purpose of this invention is to provide a soft-start circuit for a BOOT converter for large-area image sensors, which generates a soft-start voltage V through a soft-start module. SS , replacing the reference voltage V REF Input error amplifier, so that the feedback voltage V FB With soft-start voltage V SS Slowly increase, decrease V FB The difference between the voltage and the reference voltage prevents the inductor current from increasing rapidly, thereby reducing or even eliminating voltage overshoot.

[0025] To achieve the above objectives, the present invention provides the following technical solution:

[0026] A soft-start circuit for a BOOT converter for a large-area image sensor includes a soft-start module and an error amplifier; the soft-start module is configured to generate a soft-start voltage V. SS The error amplifier includes an inverting input, a non-inverting input, and an output; wherein the inverting input is configured to receive a feedback voltage V. FB The positive input terminal is configured to switchably receive a reference voltage V. REF Or the soft-start voltage V SS During the startup phase, when the soft-start voltage V... SS Less than the reference voltage V REF At that time, the soft-start voltage V SS The feedback voltage V is input to the positive input terminal, causing the feedback voltage V to... FB Following the soft-start voltage V SS The voltage rises linearly, thus reducing the voltage overshoot of the BOOST converter output voltage; where BOOST converter represents a boost converter, BOOST; soft-start voltage V SS Indicates the soft-start voltage; reference voltage V REF Indicates the reference voltage; feedback voltage V FB This indicates the feedback voltage.

[0027] Furthermore, the soft-start module includes a capacitor C1 and a charging circuit; the charging circuit is configured to charge the capacitor C1 with a constant current to generate a linearly increasing soft-start voltage V. SS .

[0028] Furthermore, the soft-start module also includes a discharge tube M13; the discharge tube M13 is configured to discharge the charge of the capacitor C1 before startup.

[0029] Furthermore, the charging circuit includes a current mirror and an adjustment unit; the current mirror is configured to provide a charging current; the adjustment unit is configured to control the switching on and off of the current mirror to adjust the soft-start voltage V. SS The rising slope.

[0030] Furthermore, the error amplifier includes a first MOSFET M1, a second MOSFET M2, and a third MOSFET M3; the gate of the first MOSFET M1 is connected to the inverting input terminal to receive the feedback voltage VFB; the gate of the second MOSFET M2 is configured to receive the reference voltage V REF The gate of the third MOS transistor M3 is configured to receive the soft-start voltage V. SS Wherein, when the soft-start voltage V SS Less than the reference voltage V REFAt this time, the third MOSFET M3 is turned on and the second MOSFET M2 is turned off, causing the soft-start voltage V to be... SS Input is given to the positive input terminal; when the soft-start voltage V SS Greater than or equal to the reference voltage V REF At that time, the second MOSFET M2 is turned on and the third MOSFET M3 is turned off, causing the reference voltage V to... REF Input to the positive input terminal.

[0031] Furthermore, the soft-start voltage V SS The rising slope satisfies: the bandwidth f of the error amplifier EA Greater than the soft start time t ss The reciprocal of, that is Among them, f EA t represents the bandwidth of the error amplifier. ss Indicates the soft-start voltage V SS From the initial value to the reference voltage V REF The time required.

[0032] Furthermore, the soft-start voltage V SS The linear increase in voltage causes the inductor current of the BOOST converter to increase slowly, thereby eliminating output voltage overshoot; where output voltage overshoot is expressed as:

[0033] V overshoot =V target +ΔV1+ΔV2

[0034] Among them, V target ΔV1 represents the voltage increment caused by the charging of the load capacitor, and ΔV2 represents the voltage increment caused by the energy transfer of the inductor.

[0035] Furthermore, the formula for calculating ΔV1 is:

[0036]

[0037] Among them, I MAX Represents the maximum inductor current, C represents the load capacitance, and R... C C represents the loop compensation resistor. C Represents the loop compensation capacitor, R F1 and R F2 This represents the voltage divider resistor, V C-MAX The compensation capacitor C represents the maximum output voltage of the error amplifier. C The voltage on it, V sense-MAX G represents the peak value of the sampled voltage. m This indicates the transconductance of the error amplifier.

[0038] Furthermore, the formula for calculating ΔV2 is as follows:

[0039]

[0040] Where L represents the inductance value.

[0041] Furthermore, the soft-start circuit is integrated into the BOOST converter, which includes a voltage loop and a current loop; the voltage loop includes a voltage divider network and the error amplifier, used to compare the feedback voltage V. FB The current loop includes a sampling module and a pulse width modulation comparator for generating control signals for the power switching transistors, in relation to the input voltage.

[0042] The beneficial effects of this invention are as follows: This invention provides a soft-start circuit in which, when the system loop is working, the soft-start module generates a linearly increasing soft-start voltage V. SS And input to the error amplifier. When the soft-start voltage V SS Less than the reference voltage V REF When, it replaces the reference voltage V REF Input error amplifier, with feedback voltage V FB Error amplification is performed. Soft-start voltage V SS The feedback voltage V increases linearly, therefore... FB With the soft-start voltage V SS The feedback voltage V was increased slowly, thus reducing its size. FB The difference between the voltage and the reference voltage prevents the inductor current from increasing rapidly, thereby reducing or even eliminating voltage overshoot.

[0043] (1) This invention replaces the traditional fixed reference voltage with a soft-start voltage to achieve a linear rise in the feedback voltage. This mechanism allows the inductor current to grow steadily, fundamentally avoiding the surge in inductor current caused by the excessive difference between the reference voltage and the feedback voltage during the startup of a traditional BOOST converter. The ΔV1 and ΔV2 components in the voltage overshoot formula are synchronously suppressed, and the target output voltage is accurately established.

[0044] (2) Unlike traditional solutions that suppress overshoot by sacrificing inductor size or load capacitance, this invention keeps the core component parameters of the converter unchanged. The power inductor can still be designed according to the principle of optimal efficiency, and the load capacitance maintains the best transient response capability, ensuring that the large-area image sensor obtains the highest power quality during the stable operation phase.

[0045] (3) The soft-start voltage slope is dynamically adjustable via a current mirror, enabling intelligent control of the startup process. A gentler slope ensures ultra-low overshoot risk, suitable for precision scenarios such as medical imaging; a steeper slope shortens the boost time, meeting the rapid startup requirements of industrial testing. This feature allows a single-circuit solution to cover diverse application scenarios.

[0046] (4) The discharge tube design ensures that the capacitor's initial state is zero, eliminating the startup voltage deviation caused by historical charge. The dual-input structure of the error amplifier enables seamless switching between the soft-start voltage and the reference voltage, avoiding voltage jitter caused by switching transients. The entire startup process conforms to the error amplifier bandwidth constraints, ensuring loop stability.

[0047] (5) The soft-start module only requires the addition of basic components such as capacitors and MOSFETs, and is compatible with standard CMOS technology. Figure 4 The circuit structure shown can be directly integrated into the BOOST control chip without the need for external discrete components. Figure 5 Simulation results show that the proposed scheme maintains the same steady-state performance as the traditional scheme under the condition of zero overshoot.

[0048] (6) To address the synchronous power supply requirements of gigabit-level pixel units in large-area image sensors, the voltage overshoot eliminated by this invention can prevent sensitive pixel units from breaking down. The smooth startup characteristics are particularly suitable for multi-stage cascaded power supply architectures, providing core power assurance for high-resolution imaging systems.

[0049] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0050] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0051] Figure 1 To generate control signals;

[0052] Figure 2 This is due to the generation of voltage overshoot;

[0053] Figure 3 It is a soft-start model;

[0054] Figure 4 It is a soft-start circuit;

[0055] Figure 5 The results are simulation results for the soft-start circuit. Detailed Implementation

[0056] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0057] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures, and should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0058] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0059] This invention provides a soft-start circuit to solve the problem of output voltage V during boosting of a BOOST converter. OUT The resulting voltage overshoot.

[0060] To suppress output voltage overshoot during BOOST converter loop operation, the BOOST converter employs a soft-start mode for voltage boosting, generating a linearly increasing soft-start voltage V through a soft-start circuit. SS Replacing V during startup REF Input error amplifier, making V FB With soft-start voltage V SS The rise is slow, thus enabling a soft start for the BOOST converter.

[0061] Soft start model such as Figure 3 As shown, the soft-start voltage V increases linearly by charging the capacitor with current. SS M4 is the discharge transistor for the capacitor. M1, M2, and M3 are the input transistors of the error amplifier, with the inverting input terminal M1 connected to the feedback voltage V.FB There are two MOSFETs at the positive input terminal, each connected to the reference voltage V. REF and soft-start voltage V SS At the start of the soft-start phase, the soft-start voltage V... SS Less than the reference voltage V REF When M2 is off and M3 is on, M1 and M3 form a differential pair. At this time, the feedback voltage V... FB With soft-start voltage V SS Rise. When the soft-start voltage V SS Increase to reference voltage V REF When M2 is turned on and M3 is turned off, M1 and M2 form a differential pair. At this time, the feedback voltage V FB With reference voltage V REF Rise. Soft-start voltage V SS The smaller the slope, the lower the output voltage V. OUT A smoother rise will result in a longer voltage boost time. However, the soft-start voltage V... SS The slope cannot be too large; it must be within the bandwidth of the error amplifier to ensure the feedback voltage V. FB Timely follow the soft start voltage V SS The voltage rises without causing voltage overshoot. Therefore, the soft-start time t SS and the bandwidth f of the error amplifier EA Need to maintain f EA >1 / t SS This is to suppress voltage overshoot.

[0062] Soft start circuit such as Figure 4 As shown, when PG changes from low to high, the BOOST converter enters the soft-start phase. At this time, M13 is briefly turned on to discharge the charge on capacitor C1. Then, M13 is turned off, and the bias current charges capacitor C1, resulting in a linearly increasing soft-start voltage V. SS K SS-Change The switching on / off state of M6 can be adjusted to control the current mirror formed by M7 and M8, thereby controlling the charging current of the capacitor and changing the soft-start voltage V. SS The charging speed.

[0063] The soft-start circuit was simulated, and the results are as follows: Figure 5 As shown. When the converter is operating normally, the soft-start circuit generates a linearly increasing soft-start voltage V. SS By adjusting K SS-Change V can be changed SS The rising slope of V. Calculations show that V... SS The two slopes are 6.9V / ms and 1.39V / ms, respectively, and the time required to boost to 0.5V is 72.5μs and 360μs, respectively.

[0064] Example 1: Basic Working Process of Soft Start Circuit

[0065] 1.1 Startup Initialization: When the system enable signal PG changes from low level to high level, the discharge tube M13 briefly conducts, completely discharging the charge of capacitor C1 to ground.

[0066] 1.2 Soft-start voltage generation: After M13 is turned off, the bias current source charges capacitor C1 at a constant current through the current mirror structure, generating a linearly rising soft-start voltage VSS.

[0067] 1.3 Error Amplifier Switching:

[0068] When V SS <V REF At that time, M3 is turned on and M2 is turned off in the error amplifier, V SS Input to the positive terminal;

[0069] Feedback voltage V FB Follow V SS The inductor current increases linearly at a controlled rate.

[0070] 1.4 Mode Switching: When V SS ≥V REF When M2 is on and M3 is off, the reference voltage V... REF Upon connection to the positive terminal, the system enters a steady-state operating mode.

[0071] Example 2: Programmable soft-start slope control

[0072] 2.1 Slope Adjustment Mechanism: External Input Signal K SS-Change By controlling the on / off state of MOSFET M6, the mirror ratio of the current mirrors M7-M8 is changed, thereby adjusting the charging current of capacitor C1.

[0073] 2.2 Bandwidth Matching Design:

[0074] When a steep slope is set (e.g., 6.9V / ms), the soft-start time t is automatically shortened. ss ;

[0075] When setting a gentle slope (e.g., 1.39V / ms), extend t... ss ;

[0076] Always satisfy f EA >1 / tSS, ensuring the error amplifier bandwidth covers voltage tracking requirements.

[0077] 2.3 Dynamic Response Verification: Under load change scenarios, the soft-start module automatically reconstructs V based on a preset slope. SS To maintain the output voltage without overshoot.

[0078] Example 3: The physical process of overshoot suppression

[0079] 3.1 ΔV1 elimination stage:

[0080] Soft start enables maximum inductor current I MAX Reduced to less than 30% of the traditional model;

[0081] From the formula ΔV1∝I MAX It can be seen that the voltage increment ΔV1 decreases significantly;

[0082] 3.2 ΔV2 elimination stage:

[0083] Inductor energy storage formula 1 / 2·L·I MAX 2 Middle I MAX Controlled decline;

[0084] The voltage increment ΔV2 during energy conservation conversion decreases synchronously;

[0085] 3.3 Overshoot to Zero Verification:

[0086] V overshoot =V target +ΔV1+ΔV2→ΔV1≈0,ΔV2≈0

[0087] The output voltage is directly stabilized at V target Statistical value.

[0088] Finally, it should be noted that 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 preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A soft-start circuit for a BOOT converter for a large-area image sensor, characterized in that: It includes a soft-start module and an error amplifier; the soft-start module is configured to generate a soft-start voltage V. SS The error amplifier includes an inverting input, a non-inverting input, and an output; wherein the inverting input is configured to receive a feedback voltage V. FB The positive input terminal is configured to switchably receive a reference voltage V. REF Or the soft-start voltage V SS During the startup phase, when the soft-start voltage V... SS Less than the reference voltage V REF At that time, the soft-start voltage V SS The feedback voltage V is input to the positive input terminal, causing the feedback voltage V to... FB Following the soft-start voltage V SS The voltage rises linearly, thus reducing the voltage overshoot of the BOOST converter output voltage; where BOOST converter represents a boost converter, BOOST; soft-start voltage V SS Indicates the soft-start voltage; reference voltage V REF Indicates the reference voltage; feedback voltage V FB This indicates the feedback voltage.

2. The soft-start circuit for a BOOT converter for a large-area image sensor according to claim 1, characterized in that: The soft-start module includes a capacitor C1 and a charging circuit; the charging circuit is configured to charge the capacitor C1 with a constant current to generate a linearly increasing soft-start voltage V. SS .

3. The soft-start circuit for a BOOT converter for a large-area image sensor according to claim 2, characterized in that: The soft-start module also includes a discharge tube M13; the discharge tube M13 is configured to discharge the charge of the capacitor C1 before startup.

4. The soft-start circuit for a BOOT converter for a large-area image sensor according to claim 2, characterized in that: The charging circuit includes a current mirror and an adjustment unit; the current mirror is configured to provide a charging current; the adjustment unit is configured to control the switching on and off of the current mirror to adjust the soft-start voltage V. SS The rising slope.

5. The soft-start circuit for a BOOT converter for a large-area image sensor according to claim 1, characterized in that: The error amplifier includes a first MOSFET M1, a second MOSFET M2, and a third MOSFET M3; the gate of the first MOSFET M1 is connected to the inverting input terminal to receive the feedback voltage VFB; the gate of the second MOSFET M2 is configured to receive the reference voltage V. REF The gate of the third MOS transistor M3 is configured to receive the soft-start voltage V. SS Wherein, when the soft-start voltage V SS Less than the reference voltage V REF At this time, the third MOSFET M3 is turned on and the second MOSFET M2 is turned off, causing the soft-start voltage V to be... SS Input is given to the positive input terminal; when the soft-start voltage V SS Greater than or equal to the reference voltage V REF At that time, the second MOSFET M2 is turned on and the third MOSFET M3 is turned off, causing the reference voltage V to... REF Input to the positive input terminal.

6. The soft-start circuit for a BOOT converter for a large-area image sensor according to claim 1, characterized in that: The soft-start voltage V SS The rising slope satisfies: the bandwidth f of the error amplifier EA Greater than the soft start time t ss The reciprocal of, that is Among them, f EA t represents the bandwidth of the error amplifier. ss Indicates the soft-start voltage V SS From the initial value to the reference voltage V REF The time required.

7. The soft-start circuit for a BOOT converter for a large-area image sensor according to claim 1, characterized in that: The soft-start voltage V SS The linear increase in voltage causes the inductor current of the BOOST converter to increase slowly, thereby eliminating output voltage overshoot; where output voltage overshoot is expressed as: V overshoot =V target +ΔV1+ΔV2 Among them, V target ΔV1 represents the voltage increment caused by the charging of the load capacitor, and ΔV2 represents the voltage increment caused by the energy transfer of the inductor.

8. The soft-start circuit for a BOOT converter for a large-area image sensor according to claim 7, characterized in that: The formula for calculating ΔV1 is: Among them, I MAX Represents the maximum inductor current, C represents the load capacitance, and R... C C represents the loop compensation resistor. C Represents the loop compensation capacitor, R F1 and R F2 This represents the voltage divider resistor, V C-MAX The compensation capacitor C represents the maximum output voltage of the error amplifier. C The voltage on it, V sense-MAX G represents the peak value of the sampled voltage. m This indicates the transconductance of the error amplifier.

9. The soft-start circuit for a BOOT converter for a large-area image sensor according to claim 7, characterized in that: The formula for calculating ΔV2 is: Where L represents the inductance value.

10. The soft-start circuit for a BOOT converter for a large-area image sensor according to claim 1, characterized in that: The soft-start circuit is integrated into the BOOST converter, which includes a voltage loop and a current loop. The voltage loop includes a voltage divider network and the error amplifier, used to compare the feedback voltage V. FB The current loop includes a sampling module and a pulse width modulation comparator for generating control signals for the power switching transistors, in relation to the input voltage.

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