Open drain output driver circuit with constant voltage slew rate

Abstract

The invention discloses an open-drain output driver circuit with a constant voltage slew rate, relates to the technical field of electronic equipment, and is used for solving the problem that in the prior art, an additional band-gap reference module is needed to provide reference current which does not change along with power supply voltage and working temperature; and the constant capability of the slew rate is completely determined by the performance of the reference current. Comprising a pull-up passage, a pull-down passage, an overflow passage and a driving pipe which act on a target node; a current detection resistor is connected in series in the pull-up path; the current detection resistor is used for detecting path current in real time and feeding back the path current as gate-source voltage of a corresponding switch tube in the overflow path in a voltage form, the shunting degree of the overflow path to the pull-up path is controlled, and the limited and constant voltage slew rate is kept. The closed-loop control provided by the invention has the advantages of accurate control and strong anti-interference capability, and the constant voltage slew rate of the open-drain output port is efficiently realized, so that the reliability and electromagnetic compatibility of the communication bus are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic equipment, and in particular to an open-drain output driver circuit with a constant voltage slew rate. Background Art

[0002] In modern electronic devices and communication systems, open-drain output is widely used in various communication buses such as 1-WIRE, I2C and I3C. Therefore, the open-drain output port driver circuit is an indispensable and important component in the entire interface circuit. If the voltage slew rate of the signal on the communication bus is higher and the signal edge is steeper, the high-frequency component will be more, which means more electromagnetic radiation (EMI) will be generated, which will affect the operation of peripheral chips. In addition, for bus systems such as 1-WIRE, which usually have long wiring lengths, overly steep signal edges may also cause overshoot and ringing on the bus. If the communication signal can obtain a limited and constant voltage slew rate, the reliability and electromagnetic compatibility of the communication bus can be effectively improved.

[0003] Therefore, there is an urgent need to provide a simpler and more efficient open-drain output driver circuit with a constant voltage slew rate. Summary of the invention

[0004] The purpose of the present invention is to provide an open-drain output driver circuit with a constant voltage slew rate, which is used to solve the problem in the prior art that an additional bandgap reference module is required to provide a reference current that does not vary with the power supply voltage and operating temperature, and the constant slew rate capability is completely determined by the performance of the reference current itself.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] In a first aspect, the present invention provides an open-drain output driver circuit with a constant voltage slew rate, comprising:

[0007] The pull-up path, pull-down path, overflow path and driving tube all act on the target node;

[0008] A second resistor is connected in series in the pull-up path; the second resistor is a current sensing resistor; the second resistor is used to detect the path current in real time, and feed back in the form of voltage as the gate-source voltage of the corresponding switch tube in the overflow path, so as to control the degree of diversion of the overflow path to the pull-up path and maintain a limited and constant voltage swing rate.

[0009] Optionally, the pull-up path includes a first switch tube, a first resistor and a second resistor; the first resistor and the second resistor are connected in series between the first switch tube and the target node;

[0010] The pull-down path includes a second switch tube; the gate of the first switch tube is connected to the gate of the second switch tube;

[0011] The overflow path includes a first switch tube, a first resistor and a fourth switch tube; one end of the first resistor is connected to the first switch tube, and the other end of the first resistor is connected to the fourth switch tube;

[0012] The driving tube includes a third switch tube and a Miller capacitor; the gate of the third switch tube is connected to the target node, one end of the Miller capacitor is connected to the gate of the third switch tube, and the other end of the Miller capacitor is connected to the drain of the third switch tube.

[0013] Optionally, the node voltage of the target node is the gate voltage of the driving tube, which is used to control the opening degree of the driving tube.

[0014] Optionally, if the data input of the open-drain output driver circuit is logic 1, the first switch tube is turned off and the second switch tube is turned on; the target node is discharged through the pull-down path until it becomes a ground voltage, and the third switch tube is turned off; at this time, the open-drain output port is in a high-impedance state, and the bus voltage will be pulled to the power supply voltage by the external pull-up resistor.

[0015] Optionally, if the data input is logic 0, the second switch tube is turned off and the first switch tube is turned on; the target node is charged through the pull-up path until it becomes the power supply voltage to turn on the third switch tube. At this time, the open-drain output port presents a low-resistance path to ground, and the bus voltage will be pulled down to near the ground voltage by the internal driver tube.

[0016] Optionally, when a reference current is not used to provide the path current of the pull-up path, the path current of the pull-up path varies with the power supply voltage and the operating temperature. At low temperature and high voltage, the path current of the pull-up path increases exponentially; at high temperature and low voltage, the path current of the pull-up path decreases exponentially.

[0017] Optionally, if the path current of the pull-up path is too large, the fourth switch tube is turned on and the overflow path is turned on.

[0018] Optionally, when the path current of the pull-up path increases, the gate-source voltage of the fourth switch tube also increases, the on-resistance of the fourth switch tube as a switch becomes smaller, the larger the current diverted by the overflow path, the greater the degree of slowdown in charging the target node.

[0019] Optionally, when the current diverted by the overflow path is greater than a preset current value, the path current of the pull-up path decreases, the voltage across the second resistor decreases, the gate-source voltage of the fourth switch tube decreases, the on-resistance of the fourth switch tube as a switch increases, the current diverted by the overflow path decreases, and the degree of slowing down the charging speed of the target node is weakened.

[0020] Compared with the prior art, the present invention provides an open-drain output driver circuit with a constant voltage slew rate, comprising: a pull-up path, a pull-down path, an overflow path and a driving tube, all of which act on the target node; a current-sensing resistor is connected in series in the pull-up path; the current-sensing resistor is used to detect the path current in real time, and feed back the gate-source voltage of the corresponding switch tube in the overflow path in the form of voltage, control the shunting degree of the overflow path to the pull-up path, and maintain a limited and constant voltage slew rate. The present invention detects the path current in real time by connecting the current-sensing resistor in series in the pull-up path, and feeds back the sensed result in the form of voltage as the gate-source voltage of the fourth switch tube, thereby controlling the shunting degree of the overflow path to the pull-up path, and finally achieving a limited and constant voltage slew rate; no additional bandgap reference module is required to provide a reference current, and no comparator or switch array is required, thereby effectively saving the layout area and reducing the chip cost. In addition, the closed-loop control proposed by the present invention has the advantages of precise control and strong anti-interference ability, and efficiently realizes the constant voltage slew rate of the open-drain output port, thereby improving the reliability and electromagnetic compatibility of the communication bus. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0022] Figure 1 It is a schematic diagram of a conventional open-drain output driver without slew rate limitation in the prior art;

[0023] Figure 2 It is a schematic diagram of an open-drain output driver circuit in the prior art;

[0024] Figure 3 A schematic diagram of an open-drain output driver circuit with a constant voltage slew rate provided by the present invention.

[0025] Reference numerals:

[0026] 1-pull-up path, 2-pull-down path, 3-overflow path, 4-driving tube, M1-first switch tube, M2-second switch tube, M3-third switch tube, M4-fourth switch tube, R1-first resistor, R2-second resistor, C-Miller capacitor, G-target node. DETAILED DESCRIPTION

[0027] In order to clearly describe the technical solutions of the embodiments of the present invention, in the embodiments of the present invention, words such as "first" and "second" are used to distinguish the same items or similar items with basically the same functions and effects. For example, the first threshold and the second threshold are only used to distinguish different thresholds, and their order is not limited. Those skilled in the art can understand that words such as "first" and "second" do not limit the quantity and execution order, and words such as "first" and "second" do not necessarily limit them to be different.

[0028] It should be noted that, in the present invention, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

[0029] In the present invention, "at least one" means one or more, and "plurality" means two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone, where A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, at least one of a, b or c can mean: a, b, c, the combination of a and b, the combination of a and c, the combination of b and c, or the combination of a, b and c, where a, b, c can be single or multiple.

[0030] Conventional open-drain output drivers without slew rate limitation are Figure 1 As shown, the input signal directly controls the gate voltage of the driver tube 4 after passing through the inverter. Figure 2 As shown, the reference current is used as the pull-up path 1 of the inverter, and the gate voltage of the driver tube 4 is controlled to increase by charging the capacitor with a constant current, thereby limiting the voltage slew rate of the open-drain output signal to be constant. The advantage of this solution is that the slew rate is limited and constant, and the disadvantage is that an additional bandgap reference module is required to provide a reference current that does not change with the power supply voltage and operating temperature, and the constant slew rate capability is completely determined by the performance of the reference current itself.

[0031] In order to solve the problems in the prior art, the present invention provides an open-drain output driver circuit with a constant voltage slew rate. Next, the solution provided by the embodiment of this specification is described in conjunction with the accompanying drawings:

[0032] The present invention provides an open-drain output driver circuit with a constant voltage slew rate. Figure 3 As shown, it may include:

[0033] All act on the pull-up path 1, the pull-down path 2, the overflow path 3 and the driving tube 4 of the target node G;

[0034] A second resistor R2 is connected in series in the pull-up path 1; the second resistor R2 is a current sensing resistor; the second resistor R2 is used to detect the path current in real time, and feed back in the form of voltage as the gate-source voltage of the corresponding switch tube in the overflow path 3, to control the degree of diversion of the pull-up path 1 by the overflow path 3, and maintain a limited and constant voltage swing rate.

[0035] based on Figure 3 The structural diagram of the present specification can further refine the open-drain output driver circuit with a constant voltage slew rate provided by the present invention, which is described below.

[0036] The pull-up path 1 includes a first switch tube M1, a first resistor R1 and a second resistor R2; the first resistor R1 and the second resistor R2 are connected in series between the first switch tube M1 and the target node G.

[0037] The first switch tube M1 may be a PMOS switch tube, the first resistor R1 may be a current limiting resistor, and the second resistor R2 may be a current sensing resistor.

[0038] The pull-down path 2 includes a second switch tube M2 ; a gate of the first switch tube M1 is connected to a gate of the second switch tube M2 .

[0039] The second switch tube M2 may be an NMOS switch tube.

[0040] The overflow path 3 includes a first switch tube M1 , a first resistor R1 and a fourth switch tube M4 ; one end of the first resistor R1 is connected to the first switch tube M1 , and the other end of the first resistor R1 is connected to the fourth switch tube M4 .

[0041] The fourth switch tube M4 may be a PMOS switch tube.

[0042] The driving tube 4 includes a third switch tube M3 and a Miller capacitor C; the gate of the third switch tube M3 is connected to the target node G, one end of the Miller capacitor C is connected to the gate of the third switch tube M3, and the other end of the Miller capacitor C is connected to the drain of the third switch tube M3.

[0043] The number of switches and resistors in the above structure can be increased or decreased according to actual needs. The fourth switch M4 can be a PMOS switch, a triode, a switch, a voltage-controlled switch, a voltage-controlled resistor, etc.

[0044] Therefore, if Figure 3 As shown, the simple and efficient closed-loop control circuit provided by the present invention includes: a pull-up path 1, a pull-down path 2, an overflow path 3 and a driving tube 4. Among them, the pull-up path 1 is composed of a PMOS switch tube (first switch tube M1), a current limiting resistor (first resistor R1) and a current detection resistor (second resistor R2). The pull-down path 2 is composed of an NMOS switch tube (second switch tube M2). The overflow path 3 is composed of a PMOS switch tube (first switch tube M1), a current limiting resistor (first resistor R1) and a PMOS switch tube (fourth switch tube M4). The driving tube 4 is composed of a PMOS switch tube (third switch tube M3) and a Miller capacitor C. The pull-up path 1, the pull-down path 2 and the overflow path 3 all act on the target node G, and the node voltage is the gate voltage of the driving tube 4, which is responsible for controlling the degree of opening of the driving tube 4.

[0045] Figure 3 In the structure, a current sensing resistor (second resistor R2) is added to the pull-up path 1 to detect the path current in real time, and the sensed result is fed back in the form of voltage as the gate-source voltage of the fourth switch tube M4, thereby controlling the degree of diversion of the overflow path 3 to the pull-up path 1, and finally achieving a limited and constant voltage slew rate.

[0046] A closed-loop control effect can be achieved by adding a fourth switch tube M4 in the overflow path 3. No additional bandgap reference module is required to provide a reference current, and no comparator or switch array is required, thereby effectively saving layout area and reducing chip cost.

[0047] Furthermore, for the above Figure 3 The circuit structure in the figure has the following working principle:

[0048] If the data input is logic 1, the first switch tube M1 is turned off and the second switch tube M2 is turned on. The target node G will discharge through the pull-down path 2 until it becomes the ground voltage gnd, thereby turning off the third switch tube M3. At this time, the open-drain output port is in a high-impedance state, and the bus voltage will be pulled to the power supply voltage vdd by the external pull-up resistor. The rise time of the bus voltage in this process is completely determined by the external pull-up resistor and the load capacitor, and the present invention does not impose any restrictions on this process.

[0049] If the data input is logic 0, the second switch tube M2 is turned off and the first switch tube M1 is turned on. The target node G will be charged through the pull-up path 1 until it becomes the power supply voltage vdd, thereby turning on the third switch tube M3. At this time, the open-drain output port presents a low-resistance path to the ground, and the bus voltage will be pulled down to near the ground voltage gnd by the internal driver tube 4 (the fourth switch tube M4). The falling time of the bus voltage in this process is mainly determined by the charging speed of the target node G. It is the voltage slew rate of this process that is limited by the present invention.

[0050] In the case where a reference current is not used to provide the path current of the pull-up path 1, the path current will change significantly with the power supply voltage and the operating temperature: at low temperature and high voltage, the current increases exponentially; and at high temperature and low voltage, the current decreases exponentially. The present invention detects the path current in real time by connecting a current-sensing resistor in series in the pull-up path 1, and feeds back the sensed result in the form of voltage as the gate-source voltage of the fourth switch tube M4, thereby controlling the degree of shunting of the overflow path 3 to the pull-up path 1, and finally achieving a limited and constant voltage slew rate.

[0051] If the path current of the pull-up path 1 is too large, the fourth switch tube M4 will be turned on. At this time, the overflow path 3 is turned on, creating a direct current path from vdd to gnd, and dividing a part of the current of the pull-up path 1, thereby slowing down the charging speed of the target node G. And when the path current of the pull-up path 1 is larger, the gate-source voltage of the fourth switch tube M4 will also be larger, the on-resistance of the fourth switch tube M4 as a switch will be smaller, the current divided by the overflow path 3 will also be larger, and the degree of slowing down the charging speed of the target node G will also increase accordingly. When the overflow path 3 divides too much current, the path current of the pull-up path 1 decreases, and the voltage across the current detection resistor (the second resistor R2) decreases, that is, the gate-source voltage of the fourth switch tube M4 decreases, the on-resistance of the fourth switch tube M4 as a switch increases, and the current divided by the overflow path 3 will also decrease, and the degree of slowing down the charging speed of the target node G will be weakened accordingly. This negative feedback process realizes closed-loop control of the voltage slew rate, thereby maintaining the voltage slew rate constant.

[0052] Therefore, the open-drain output driver circuit with a constant voltage slew rate provided by the present invention can achieve at least the following technical effects:

[0053] 1) The present invention provides a simple and efficient circuit structure. By adding a fourth switch tube M4 to the circuit, a closed-loop control effect can be achieved. No additional bandgap reference module is required to provide a reference current, and no comparator or switch array is required, thereby effectively saving layout area and reducing chip cost.

[0054] 2) The closed-loop control of the present invention is based on negative feedback. Compared with the open-loop control of the traditional technical solution, the closed-loop control proposed by the present invention has the advantages of precise control and strong anti-interference ability.

[0055] 3) The present invention can simply and efficiently achieve a constant voltage slew rate of an open-drain output port, thereby improving the reliability and electromagnetic compatibility of a communication bus.

[0056] Although the present invention is described herein in conjunction with various embodiments, in the process of implementing the claimed invention, those skilled in the art may understand and implement other variations of the disclosed embodiments by viewing the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other components or steps, and "one" or "an" does not exclude multiple situations. A single processor or other unit may implement several functions listed in the claims. Certain measures are recorded in different dependent claims, but this does not mean that these measures cannot be combined to produce good results.

[0057] Although the present invention has been described in conjunction with specific features and embodiments thereof, it is apparent that various modifications and combinations may be made thereto without departing from the spirit and scope of the present invention. Accordingly, this specification and the accompanying drawings are merely exemplary illustrations of the present invention as defined by the appended claims and are deemed to cover any and all modifications, variations, combinations or equivalents within the scope of the present invention. Obviously, those skilled in the art may make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, the present invention is intended to include such modifications and variations if they fall within the scope of the claims of the present invention and their equivalents.

Claims

1. A constant voltage slew rate open-drain output driver circuit, characterized in that: include: The pull-up path, pull-down path, overflow path and driving tube all act on the target node; A second resistor is connected in series in the pull-up path; the second resistor is a current sensing resistor; the second resistor is used to detect the path current in real time, and feed back in the form of voltage as the gate-source voltage of the corresponding switch tube in the overflow path, so as to control the degree of diversion of the overflow path to the pull-up path and maintain a limited and constant voltage swing rate.

2. The open-drain output driver circuit with a constant voltage slew rate according to claim 1, characterized in that: The pull-up path includes a first switch tube, a first resistor and a second resistor; the first resistor and the second resistor are connected in series between the first switch tube and the target node; The pull-down path includes a second switch tube; the gate of the first switch tube is connected to the gate of the second switch tube; The overflow path includes a first switch tube, a first resistor and a fourth switch tube; one end of the first resistor is connected to the first switch tube, and the other end of the first resistor is connected to the fourth switch tube; The driving tube includes a third switch tube and a Miller capacitor; the gate of the third switch tube is connected to the target node, one end of the Miller capacitor is connected to the gate of the third switch tube, and the other end of the Miller capacitor is connected to the drain of the third switch tube.

3. The open-drain output driver circuit with a constant voltage slew rate according to claim 1, characterized in that: The node voltage of the target node is the gate voltage of the driving tube, which is used to control the opening degree of the driving tube.

4. The open-drain output driver circuit with a constant voltage slew rate according to claim 2, characterized in that: If the data input of the open-drain output driver circuit is logic 1, the first switch tube is turned off and the second switch tube is turned on; the target node is discharged through the pull-down path until it becomes a ground voltage, and the third switch tube is turned off; At this time, the open-drain output port is in a high-impedance state, and the bus voltage will be pulled to the power supply voltage by the external pull-up resistor.

5. The open-drain output driver circuit with constant voltage slew rate according to claim 2, characterized in that: If the data input is logic 0, the second switch tube is turned off and the first switch tube is turned on; the target node is charged through the pull-up path until it becomes the power supply voltage to turn on the third switch tube. At this time, the open-drain output port presents a low-resistance path to the ground, and the bus voltage will be pulled down to near the ground voltage by the internal driver tube.

6. The open-drain output driver circuit with a constant voltage slew rate according to claim 1, characterized in that: When the reference current is not used to provide the path current of the pull-up path, the path current of the pull-up path varies with the power supply voltage and the operating temperature. At low temperature and high voltage, the path current of the pull-up path increases exponentially; at high temperature and low voltage, the path current of the pull-up path decreases exponentially.

7. The open-drain output driver circuit with a constant voltage slew rate according to claim 2, characterized in that: If the path current of the pull-up path is too large, the fourth switch tube is turned on and the overflow path is turned on.

8. The open-drain output driver circuit with a constant voltage slew rate according to claim 2, characterized in that: When the path current of the pull-up path increases, the gate-source voltage of the fourth switch tube also increases, and the on-resistance of the fourth switch tube as a switch becomes smaller. The larger the current diverted by the overflow path, the slower the charging speed of the target node.

9. The open-drain output driver circuit with a constant voltage slew rate according to claim 2, characterized in that: When the current divided by the overflow path is greater than the preset current value, the path current of the pull-up path decreases, the voltage across the second resistor decreases, the gate-source voltage of the fourth switch tube decreases, the on-resistance of the fourth switch tube as a switch increases, the current divided by the overflow path decreases, and the degree of slowing down the charging speed of the target node is weakened.

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