Voltage supervisor

Abstract

To provide a voltage supervisor.SOLUTION: A voltage supervisor (100) includes a first transistor (116) coupled between a first supply voltage (112) and a second supply voltage (124), and a second transistor (120). The voltage supervisor is configured to provide a first current (126) proportional to a difference in gate-to-source voltages of the first transistor (116) and the second transistor (120). The voltage supervisor (100) is also configured to provide a second current (146) proportional to a difference in the first supply voltage (112) and the difference in gate-to-source voltages of the first transistor (116) and the second transistor (120). In addition, the voltage supervisor (100) is configured to compare the first current (126) to the second current (146) and determine a voltage value which changes a state responsive to the first supply voltage (112) crossing a threshold.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] A voltage supervisor is useful in many applications for monitoring a supply voltage and detecting certain problems related to the supply voltage. In some applications, the voltage supervisor can detect whether the power supply voltage is below or above a threshold value. In response to the voltage crossing the threshold, the voltage supervisor asserts a signal. This signal is useful for taking actions to ensure proper power supply operation.

Summary of the Invention

[0002] According to at least one example described herein, a voltage supervisor includes a first transistor coupled between a first supply voltage and a second supply voltage. The voltage supervisor includes a second transistor coupled between the first supply voltage and the second supply voltage. The voltage supervisor is configured to provide a first current proportional to a difference in gate-source voltages of the first transistor and the second transistor. The voltage supervisor is also configured to provide a second current proportional to a difference in the first supply voltage and a difference in gate-source voltages of the first transistor and the second transistor. The voltage supervisor is configured to compare the first current with the second current to determine a voltage value at which to change a state in response to the first supply voltage crossing a threshold.

[0003] According to at least one example described herein, a system includes a reference current generator including a current mirror, a first transistor, a second transistor, and a first resistor, wherein a control terminal of the first transistor is coupled to a control terminal of the second transistor, and a first current terminal of the second transistor is coupled to the first resistor. The system includes a third transistor having a control terminal coupled to the current mirror, a first current terminal adapted to be coupled to a power supply, and a second current terminal coupled to a second resistor. The system includes a fourth transistor having a control terminal coupled to a control terminal of the third transistor and a first current terminal adapted to be coupled to a power supply. The system includes a fifth transistor having a second current terminal coupled to a second current terminal of the fourth transistor, a control terminal coupled to a control terminal of the second transistor, and a first current terminal coupled to a sixth transistor.

[0004] According to at least one example described herein, a voltage management device includes a reference current generator having a current mirror configured to provide a first current proportional to a difference in gate-source voltages of a first transistor and a second transistor. The voltage management device includes a third transistor having a gate coupled to the current mirror, a source adapted to be coupled to a power supply, and a drain coupled to a resistor, the third transistor being configured to provide a second current proportional to a difference in supply voltages and a difference in gate-source voltages of the first transistor and the second transistor. The voltage management device includes a fourth transistor having a gate coupled to a gate of the third transistor, a source adapted to be coupled to a power supply, and a drain having a drain voltage indicating that the supply voltage exceeds a threshold.

Brief Description of the Drawings

[0005]

Figure 1

[0006]

Figure 2

[0007]

Figure 3

[0008]

Figure 4

DETAILED DESCRIPTION OF THE INVENTION

[0009] A voltage management device is useful for monitoring a power supply voltage and asserting a signal when a threshold value is reached. A node (referred to as a trip node) has a voltage that reverses from a high voltage to a low voltage or vice versa when the power supply voltage reaches the threshold value. This voltage of the power supply that reverses the trip node is called the trip voltage (e.g., threshold voltage or voltage threshold). Conventional voltage management devices have many drawbacks. For example, conventional voltage management devices often have a high off-stage current, also called the quiescent current (IQ), and a slow response time. Also, a small threshold voltage (the threshold voltage of the power supply being monitored) is often difficult to achieve in conventional voltage management devices. Furthermore, achieving a programmable threshold voltage for the power supply being monitored is difficult with conventional voltage management devices. For example, when the monitored supply voltage is changed to a different voltage, the voltage management device is usually redesigned to handle the new supply voltage. Additionally, conventional voltage management devices generally occupy a large silicon area.

[0010] In the examples herein, the voltage management device provides a low I Q and has a fast response time, can be scaled for a range of threshold voltages, and has a small silicon area. The voltage management device described herein uses a circuit topology with four branches through which two different currents flow. The first current is the gate-source voltage (ΔV) between two field effect transistors (FETs).GS ) is proportional to the difference. The first current is useful as a reference current because this current does not change with the supply voltage. The second current is proportional to the supply voltage, and thus, the magnitude of the second current indicates the magnitude of the supply voltage. These two currents are compared to determine the state of the trip node. In response to the supply voltage exceeding a threshold value, the second current exceeds the first current, so the trip node flips from a low voltage to a high voltage. In response to the trip node inversion, the circuit is clamped to reduce the increase in I Q of.

[0011] FIG. 1 is a voltage management device 100 according to various examples of this specification. The voltage management device 100 includes a start section 102, a reference current generator 104, and a current clamp 106. The voltage management device 100 can also be described as having four vertical branches, and its operation will be described below. The start section 102 includes a transistor 108 and a resistor 110. The transistor 108 is an n-type FET in one example. The transistor 108 is, in one example, a native transistor having a threshold voltage (V TH ) of about -100 mV. In other examples, another low or slightly negative V TH native transistors having can be used. Native transistors are various FETs that are intermediate between enhancement mode and depletion mode. In other examples, different types of transistors may be useful. By using a transistor having a relatively low threshold voltage V TH , the voltage management device 100 can monitor lower supply voltage levels. When the threshold voltage V TH of the transistor is relatively high, the transistors in the voltage management device 100 may not be able to operate at a low voltage level sufficient to adequately monitor lower supply voltages. The source of the transistor 108 is coupled to the first terminal of the resistor 110, and the drain is coupled to the node 112. In one example, the supply voltage V INIt is provided at node 112. The gate of transistor 108 is coupled to the second terminal of resistor 110. In the examples of this specification, the gate of a transistor may also be referred to as a control terminal. The source or drain of a transistor may also be referred to as a current terminal. The startup section 102 is useful in one example for starting the voltage management device 100. In response to starting the voltage management device 100, the startup section 102 becomes inactive. The operation of the startup section 102 will be described below.

[0012] The voltage management device 100 includes a reference current generator 104. The reference current generator 104 has two vertical branches in this example. In other examples, different types of reference current generators are useful for providing a reference current. The first branch of the reference current generator 104 includes transistor 114, resistor 110, and transistor 116. The second branch of the reference current generator 104 includes transistor 118, transistor 120, and resistor 122. In one example, the reference current generator operates to provide a current I1 (described below) that is used by the voltage management device 100 as a reference for determining whether the supply voltage exceeds a predetermined threshold.

[0013] Transistor 114 is a p-type FET in one example. In one example, transistor 114 is a low-threshold voltage transistor having a threshold voltage V of about 400 - 500 mV. TH In other examples, different types of transistors may be useful. Transistor 114 has a source coupled to node 112 and a drain coupled to the first terminal of resistor 110. Transistor 114 also has a gate coupled to the gate of transistor 118. Transistor 116 is an n-type FET in one example. Transistor 116 has a drain coupled to the second terminal of resistor 110. The drain of transistor 116 is also coupled to the gate of transistor 116. Transistor 116 has a source coupled to ground 124. In other examples, the rail at ground 124 is the first supply voltage V provided at node 112. INIt can be coupled to a voltage rail other than ground 124, which is a different voltage (a second supply voltage).

[0014] In the second branch of the reference current generator 104, the transistor 118 has a source coupled to node 112 and a drain coupled to the gate of the transistor 118. The drain of the transistor 118 is also coupled to the drain of the transistor 120. The transistor 118 is, in one example, a p-type FET. The transistor 120 has a gate coupled to the gate of the transistor 116. The transistor 120 also has a source coupled to the first terminal of the resistor 122. The transistor 120 is, in one example, an n-type FET. The second terminal of the resistor 122 is coupled to ground 124.

[0015] In one example, the transistor 118 is a low threshold voltage transistor with a threshold voltage V TH of about 400 - 500 mV. In other examples, different types of transistors may be useful. Transistors 114 and 118 have a "1" in the adjacent circles. This "1" indicates that transistors 114 and 118 are of the same size. Since transistors 114 and 118 are configured as a current mirror, the current flowing through transistor 114 is approximately equal to the current flowing through transistor 118. Since the gates of transistors 114 and 118 are connected and the sources are connected, the gate-source voltage V GS is the same. In one exemplary operation, the current I127 flows through the transistor 114 and the current I1126 flows through the transistor 118. The currents I1126 and I127 are approximately equal in one example. The current I1126 and its use in the voltage management device 100 will be described below.

[0016] In one example, the transistor 116 is a low threshold voltage transistor having a threshold voltage V TH of about 400 - 500 mV. In one example, the transistor 120 has a threshold V THIn other examples, different types of transistors may be useful.

[0017] The start-up section 102 operates as follows: Initially, the supply voltage V at node 112 IN When V is low (e.g., less than 2 volts) and no current is yet being generated in the voltage management device 100, the node 128 is at ground (0 V). Also, no current I 127 is flowing through the resistor 110, so the first terminal of the resistor 110 is at ground. Next, the V of the transistor 108 GS is 0V, which is enough for transistor 108 to turn on and start conducting current. The current conducted by transistor 108 acts as a starting current and charges the parasitic capacitance at node 128, thereby increasing the voltage potential at node 128 and turning on transistor 116. Turning on transistor 116 causes the other devices (transistors 114, 118, and 120) to start conducting current in their respective current mirror arrangements, and the conducted current increases until a steady state is achieved. The positive feedback in the two leftmost branches of voltage supervisor 100 helps to reach the steady state. The starting section 102, in one example, ensures that voltage supervisor 100 does not have zero current and remains inoperative.

[0018] After current I 127 starts to flow through transistor 114, the voltage drop across resistor 110 increases, which causes the voltage at the source of transistor 108 to be sufficiently higher than the voltage at the gate of transistor 108 so that transistor 108 turns off. This is because the voltage drop across resistor 110 becomes equal to the -V GS Resistor 110 is sized so that the voltage drop across resistor 110 is large enough to keep transistor 108 off during normal operation of voltage management device 100.

[0019] The first and second branches of the voltage management device 100 are connected to a supply voltage V INProvide a reference current I1126 that does not change with the variation of GS V of transistor 116 is represented by V1, which is the voltage between node 128 coupled to the gate of transistor 116 and common potential (ground in some examples) 124. V of transistor 120 GS is represented by V2. V2 is the voltage between node 128 and node 130. The difference between V1 and V2 is equal to the voltage across resistor 122, which is also the voltage at node 130. Therefore, the voltage at node 130 is the difference in gate-source voltages V G of transistors 116 and 120, so it is called ΔV GS .

[0020] Current I1126 flows through transistor 120 and resistor 122 (R BOT ). Since the voltage across resistor 122 is known, current I1126 is calculated by Equation (1). I1=(ΔV GS ) / (R BOT ) (1)

[0021] As shown in Equation (1), current I1126 does not change with supply voltage V IN . The value of current I1126 is determined by the difference between the two gate-source voltages V GS of transistors 116 and 120, and the value of resistor 122. As supply voltage V IN changes, the difference between these two V GS remains the same. As the value of one ΔV GS increases, the other also increases by the same amount. As the value of one ΔV GS decreases, the other also decreases by the same amount. Current I1126 is proportional to this ΔV GS value, and this ΔV GS value does not change with supply voltage V IN . Therefore, current I1126 also does not change with supply voltage V IN . For this reason, current I1126 is useful as a reference current for determining whether supply voltage V IN has risen above the threshold.

[0022] The third branch of the voltage management device 100 includes transistors 132, 134, and 136. Transistor 132 is, in one example, a p-type FET. In one example, transistor 132 is a low-threshold voltage transistor with a threshold voltage V TH of approximately 400 to 500 mV. In other examples, different types of transistors may be useful. Transistor 132 may be substantially the same as transistors 114 and 118 in one example. Transistor 132 has a "1" in the adjacent circle, indicating that transistor 132 is approximately the same size as transistors 114 and 118 and can conduct a similar amount of current as transistors 114 and 118 (since transistor 132 is also part of the current mirror formed by transistors 114 and 118). Transistor 132 has a gate coupled to the gate of transistor 118 and a source coupled to node 112. The drain of transistor 132 is coupled to node 138 and the drain of transistor 134. Since transistor 132 forms part of the current mirror having transistors 114 and 118, the current I129 flowing through transistor 132 is approximately equal to the current I1126 flowing through transistor 118.

[0023] Transistor 134 is, in one example, an n-type (FET) native transistor having a threshold V TH of approximately -100 mV. In other examples, different types of transistors may be useful. Transistor 134 has a drain coupled to the drain of transistor 132 at node 138. Transistor 134 has a gate coupled to the gate of transistor 120. Transistor 134 also has a source coupled to node 140 and the drain of transistor 136. In one example, transistor 134 is the same transistor as transistor 120.

[0024] Transistor 136 has a drain coupled to the source of transistor 134 and a source coupled to ground 124. Transistor 136 also has a gate coupled to node 138, which is coupled to the drain of transistor 134.

[0025] The third branch of voltage management device 100 includes a side branch having a current clamp 106 that includes transistor 142. The side branch also includes resistor 144. Transistor 142 has a gate coupled to the gate of transistor 132 and a source coupled to node 112. The drain of transistor 142 is coupled to the first terminal of resistor 144. The second terminal of resistor 144 is coupled to node 140.

[0026] In one example, transistor 142 is a low-threshold voltage transistor having a threshold voltage V of about 400 - 500 mV. TH In other examples, different types of transistors may be useful. Transistor 142 has a "2" in the adjacent circle, indicating that transistor 142 is about twice the size of transistors 114, 118, and 132, and thus can conduct about twice the current of those three transistors. Transistor 142 is also configured to act as a current mirror including transistors 114, 118, and 132 when the voltage at node 112 is an appropriate amount above the trip point.

[0027] Current I2146 flows through resistor 144. Current I2146 is a current that varies with the supply voltage V at node 112 (as shown in equation (2) below) and is useful for determining whether the supply voltage V has exceeded the threshold. In one example, V IN rises slowly and approaches the threshold. Current I2146 flows through transistor 142. The gate-source voltage V across transistor 134 IN is IN is GSis V2, which is the voltage between node 128 and node 130 as described above. In one example, transistors 120 and 134 are the same device, and their gates are connected, so the gates of transistors 120 and 134 are at the same voltage. The current flowing through transistor 120 is current I1126, and the current flowing through transistor 134 is current I129, which is the same as I1126 (due to the current mirror). The currents through transistors 120 and 134 are the same, and the gates of transistors 120 and 134 are at the same voltage, so the sources of transistors 120 and 134 are also at the same voltage. The voltage at the source of transistor 120 is the voltage at node 130. As described above, that voltage is ΔV GS Therefore, the voltage at node 140 is also ΔV GS as well.

[0028] Transistor 136 is at the bottom of the third branch of voltage management device 100. At the drain of transistor 136 (e.g., node 140), current I129 combines with current I2146 to produce current I3148 flowing through transistor 136. The current through resistor 144 is current I2146, and the voltage at the second terminal of resistor 144 is ΔV GS Therefore, the voltage at the first terminal of resistor 144 is useful for determining the voltage drop across resistor 144 and for determining the value of current I2146.

[0029] Supply voltage V IN In response to supply voltage V being lower than the threshold voltage to trip the trip node, the voltage at the first terminal of resistor 144 is approximately V IN with a small error. This is because transistor 142 is turned on and the voltage drop across it can be ignored. Transistor 142 is approximately twice the size of transistors 114, 118, and 132 and is part of the current mirror formed by these transistors. Therefore, transistor 142 has the ability to conduct approximately twice current I1126. However, transistor 142 is supplied with voltage V INThe voltage difference between it and ground 124 is sized such that it is not large enough to generate such a large amount of current to flow through transistor 142. The voltage at the drain of transistor 142 is close to the voltage at the source of transistor 142 as described above, which means that transistor 142 does not conduct the entire amount of current that it can conduct. Therefore, the current I2146 through transistor 142 is less than twice the current I1126 in this example. V IN Until the voltage V reaches the voltage threshold that trips the trip node, the drain voltage of transistor 142 is close to the source voltage of transistor 142, and its source voltage is the supply voltage V IN at. Therefore, the voltage at the drain of transistor 142 is also close to the supply voltage V IN . Therefore, the voltage at the first terminal of resistor 144 (R TOP ) is close to the supply voltage V IN . Equation (2) shows the value of current I2 146. I2=(V IN -ΔV GS ) / (R TOP ) (2)

[0030] V IN During the above-described operating state where it is below the voltage threshold that trips the trip node, the current I2146 does not double the value of I1126, but changes directly with the value of the supply voltage V IN .

[0031] The current flowing through each of the first three branches of voltage management device 100 has been described above. The fourth branch of voltage management device 100 includes transistors 150, 152, 154, and TRIP node 156. In one example, transistor 150 has a threshold voltage V of about 400 - 500 mV THis a low-threshold voltage transistor having. In other examples, different types of transistors may be useful. Transistor 150 has "k" in the adjacent circle, which indicates that transistor 150 is approximately "k" times the size of transistors 114, 118, and 132, and thus can conduct approximately "k" times the current of those transistors since it is part of the current mirror formed by those transistors. The source of transistor 150 is coupled to node 112. The gate of transistor 150 is coupled to the gate of transistor 142. The drain of transistor 150 is coupled to TRIP node 156 and to the drain of transistor 152.

[0032] Transistor 152 is, in one example, an n-type (FET) native transistor having a threshold V of about -100 mV. TH In other examples, different types of transistors may be useful. Transistor 152 has a gate coupled to the gate of transistor 134 and a source coupled to the drain of transistor 154. In one example, transistor 152 is identical to transistors 120 and 134.

[0033] Transistor 154 is, in one example, a reference threshold voltage transistor having a threshold voltage V TH of about 700 mV. In other examples, different types of transistors may be useful. Transistor 154 has a source coupled to ground 124 and a gate coupled to the gate of transistor 136. In one example, transistor 136 also has a threshold voltage V TH of about 700 mV and is a reference voltage threshold transistor. Transistor 154 has "1" in the adjacent circle, while transistor 136 has "2" in the adjacent circle. These numbers indicate that transistor 136 is approximately twice the size of transistor 154 in this example.

[0034] As described above, current 1 129 (substantially equal to I1126) and I2146 combine to create current I3148 as shown in Equation (3). I1 + I2 = I3 (3)

[0035] The current flowing through transistor 136 is current I3148, and transistor 136 is twice the size of transistor 154. The gates of transistors 136 and 154 are both coupled, and the sources of transistors 136 and 154 are also coupled together at ground 124. Therefore, the gate-source voltage V GS across transistors 136 and 154 is the same. Since transistor 136 is approximately twice the size of transistor 154, transistor 136 conducts approximately twice the current of transistor 154. The current through transistor 136 is current I3148, so the current through transistor 154 is I3 / 2 as shown in FIG. 1 as current 158. In one example, transistors 136 and 154 operate as a second current mirror within voltage management device 100, and the current is scaled in response to transistors 136 and 154 being different sizes.

[0036] At the top of the fourth branch, the current flowing through transistor 150 is k times current I1126 (e.g., kI1). As described above with respect to equation (1), since current I1126 does not depend on supply voltage V IN neither does current kI1 depend on supply voltage V IN . Therefore, as supply voltage V IN rises, current kI1 remains approximately constant over time. However, current I3148 is a combination of current I129 (approximately equal to I1126) and I2146, and since current I2146 depends on V IN , as supply voltage V IN rises, the current 158 (e.g., I3 / 2) at the bottom of the fourth branch also rises. In response to current 158 rising above current kI1 in the fourth branch, TRIP node 156 switches state. Specifically, in response to supply voltage V IN falling below the monitored voltage threshold, current kI1 pulls TRIP node 156 to a high voltage. The more supply voltage VIN increases (which can occur because current 158 changes with supply voltage V IN and current kI1 does not change), the TRIP node 156 is pulled to a low voltage. The voltage at the TRIP node 156 that inverts the node is the trip voltage (e.g., threshold voltage or voltage threshold).

[0037] The currents kI1 and 158 can be calculated, and the trip voltage can also be calculated. The current kI1 through transistor 150 is shown in Equation (4). kI1 = k(ΔV GS / R BOT ) (4)

[0038] The current 158 is half of the current I3148 calculated by Equation (5) I 158 =[[(V IN -ΔV GS ) / R TOP +(ΔV GS / R BOT )] / 2 (5)

[0039] The TRIP node 156 begins to invert as current 158 becomes equal to current kI1. The trip voltage is shown in Equation (6). V TRIP =[1+(2k - 1)·(R TOP / R BOT )]ΔV GS (6)

[0040] Equation (6) shows that the trip voltage V TRIP is directly proportional to ΔV GS multiplied by a constant. The constant is the ratio of resistor 144 (R TOP ) to resistor 122 (R BOTis a function of these two resistors 122 and 144. The values of these two resistors 122 and 144 may deviate from their design values based on process variations when the voltage management device 100 is manufactured. However, if they change in the same way, the process variations can be canceled out according to Equation (6). The constant k is the relative device size, which is constant and does not substantially change with the process or temperature. The trip voltage V TRIP The main variation of is the process variation that affects ΔV GS In one example, the transistors herein can be sized such that the temperature coefficient of ΔV GS is approximately zero. In that case, the trip voltage V TRIP also does not change significantly with temperature.

[0041] As described above, the voltage management device 100 is programmable for various voltage thresholds. The values of the resistors 122 and 144 can be adjusted to change the trip voltage V TRIP Also, in order to change the trip voltage V TRIP the value of k (relative device size) can also be adjusted. Therefore, in the examples herein, the trip voltage V TRIP can be finely adjusted. The topology of the voltage management device 100 provides this programmability, which means that the same circuit is useful for providing another trip voltage V TRIP In some examples, a variable resistor can be used to change the trip voltage V TRIP In other examples, the resistance can be changed by switching resistors on or off, and the trip voltage V TRIP can be adjusted.

[0042] Another feature of the voltage management device 100 in various examples is that after reaching the trip point, the current I2146 is limited. The current I1126 is independent of the supply voltage, but the current I2146 is not. The current clamp 106 is useful for limiting the current I2146 as the supply voltage V IN rises. The current clamp 106 is for the supply voltage VIN prevents the current I2146 from increasing after reaching a certain value. The supply voltage V IN at this certain value allows the transistor 142 to provide a current approximately twice that of the current I1126, so there is sufficient voltage margin between the voltage supply V IN and the ground 124. When the current flowing through the transistor 142 reaches twice the current I1126, the transistor 142 saturates. Therefore, when the supply voltage V IN rises above a certain value, no additional current flows into the branch of the voltage management device 100.

[0043] After the voltage management device 100 is manufactured, the trip voltage V TRIP cannot be changed unless a variable resistor is used. Therefore, in order to prevent changes due to temperature, the transistors 116 and 120 should be sized such that the temperature coefficient of ΔV GS is approximately zero. When the temperature coefficient of ΔV GS between the transistor 116 and the transistor 120 is approximately zero, the value of the current I1126 also exhibits increased resistance to temperature changes, thereby enabling the current I1126 to be useful as a reference current.

[0044] Two methods for achieving a temperature coefficient close to zero are described herein. One method involves using a transistor in strong inversion operation, and the other method involves using a transistor in weak inversion operation. In strong inversion operation, the V GS of the transistor is much greater than the threshold voltage V TH . The overdrive voltage V OV is the gate-source voltage V TH that exceeds the threshold voltage V GS . In weak inversion operation (e.g., the region below the threshold), the transistor operates at a gate-source voltage V TH that is below the threshold voltage V GS .

[0045] First, in an example of strong inversion operation, V GS =V TH +VOV It is. Also, Equation (7) shows the difference between these voltages. ΔV GS = ΔV TH + ΔV OV (7)

[0046] ΔV GS is, as described above with respect to FIG. 1, the difference in the gate-source voltage between transistor 116 and transistor 120. In one example, transistor 116 is a low-voltage transistor (LVT), and the variables related to transistor 116 in the following equation are suffixed with the subscript LVT. In this example, transistor 120 is a native transistor (NAT), and the variables related to transistor 120 in the following equation are suffixed with NAT. The variables in Equation (7) can be extended based on the operating region in which the transistor is operating. In the case of strong inversion operation, ΔV OV is equal to the difference between V OV of transistor 116 and V OV of transistor 120. Substituting these terms into ΔV OV results in Equation (8). ΔV GS = ΔV TH + [V OV(LVT) - V OV(NAT) (8)

[0047] The current I1126 in FIG. 1 is defined in Equation (9). TIFF2025094279000002.tif619 Here, k' is the process transconductance parameter, which is a constant depending on the process technology used to manufacture the integrated circuit, and W / L is the ratio of the channel width to the channel length (in this example for transistor 120, but Equation (9) is also used to find the current through other transistors). Solving Equation (9) for V OV and substituting its solution V OV(LVT) and V OV(NAT) for both V OV results in Equation (10). TIFF2025094279000003.tif1054

[0048] ΔV TH is a positive value and is equal to the threshold voltage V of transistor 116 TH minus the threshold voltage V of transistor 120 TH In one example, the threshold voltage V of transistor 116 TH is greater than zero, and the threshold voltage V of transistor 120 TH is approximately zero or slightly less than zero. Therefore, ΔV TH is greater than zero.

[0049] Equation (11) is a rearrangement of Equation (10). TIFF2025094279000004.tif742

[0050] In this example, since the LVT transistor and the NAT transistor are the same size, the W / L variables are the same for each transistor and can be moved outside the parentheses as shown in Equation (11). The next step is to identify the temperature coefficient of ΔV TH in Equation (11) and the temperature coefficient of the term added to ΔV TH To achieve a zero temperature coefficient, the temperature coefficient of ΔV TH should be canceled out by the temperature coefficient of the other terms in Equation (11) (which is equal to ΔV as shown in Equation (7)). OV

[0051] ΔV TH is process-dependent and thus cannot be adjusted to achieve a zero temperature coefficient. For the ΔV OV term, the size of the transistor can be modified (by modifying the W and L terms). The W and L variables can be adjusted to change the temperature coefficient of the ΔV TH term in the appropriate direction to cancel out the temperature coefficient of the ΔV OV term. For example, if the temperature coefficient of ΔV TH is θ, the other terms should be -θ so that they cancel each other out. Also, k' is the mobility (μ) of the device × oxide capacitance C OX ​(k’ = μC OX ) is equal to.

[0052] Figure 2 is a graph 200 of the temperature coefficient for strong inversion operation according to an example. Graph 200 graphs the reciprocal of (k’ / 2)(W / L) versus the reciprocal of temperature. The reciprocal of (k’ / 2)(W / L) is graphed on the y-axis. The x-axis is the temperature in degrees Celsius. Curve 202 is the reciprocal of (k’ / 2)(W / L) for an LVT device such as transistor 116. Curve 204 is the reciprocal of the term (k’ / 2)(W / L) for a NAT device such as transistor 120. As seen in graph 200, the reciprocal of this term for LVT (curve 202) has a lower slope than the reciprocal of this term for NAT (curve 204). When these two terms are subtracted (which is done in the last part of equation (11)), the result is a negative temperature coefficient. Thus, ΔV TH added to equation (11) The second term (the radical multiplied by the term in parentheses) on the right side of TIFF2025094279000005.tif724 decreases with an increase in temperature. This means that the second term as described above has a negative temperature coefficient. The second term can be adjusted by changing the W and L values (of the LVT and NAT transistors of the same size) until its absolute value becomes equal to the absolute value of ΔV TH . When their absolute values are equal, the second term cancels out ΔV TH , and the resulting temperature coefficient is approximately zero.

[0053] In the second case of subthreshold or weak inversion operation, ΔV GS = ΔV TH + ΔV OV . Similar mathematical substitutions as described above are made for this type of operation. However, in the case of subthreshold operation, the ΔV OV term is different from that in the case of strong inversion operation. In one example, subthreshold operation is characterized by equation (12). TIFF2025094279000006.tif843

[0054] The logarithmic term in Equation (12) (which corresponds to ΔV OV ) is adjusted in the same way as the above-described strong inversion operation in order to cancel the temperature coefficient term of ΔV TH . The logarithmic term can be adjusted by adjusting the W and L variables for one or both of the LVT and NAT transistors.

[0055] Figure 3 is a set of graphs showing the cancellation of the temperature coefficient in the operation below the threshold. Graph 300 is a graph of ΔV TH (volts) versus temperature (degrees Celsius). The temperature coefficient is shown as curve 302. Curve 302 has a positive slope of about 0.13 as shown in Graph 300.

[0056] Graph 304 is a graph of ΔV OV versus temperature. The temperature coefficient is shown as curve 306. Curve 306 has a negative slope, has a slope of about 0 at the left end of curve 306, has a slope of about -0.2 at the center of curve 306, and has a slope of about -0.3 at the right end of curve 306.

[0057] In one example, when the slope of ΔV OV is made equally negative when the slope of ΔV TH is positive, it becomes an umbrella-shaped curve like curve 310 shown in Graph 308. Graph 308 is a graph of ΔV GS versus temperature and is the result of combining curves 302 and 306. In curve 310, the first point (left end) and the last point (right end) have the same V GS . Therefore, as the temperature rises, curve 310 does not show an increase or decrease in slope. Instead, it becomes an umbrella-shaped curve. Curve 310 is not completely horizontal, so there is some effect caused by the change in temperature, but it is close to horizontal, so the effect is small in some examples.

[0058] 4 is a flow chart of a method 400 for voltage monitoring, in accordance with various examples herein. Although method 400 is described with reference to FIGS. 1-3, any system configured to perform the method in any suitable order is within the scope of this description. In one example, the components in FIG. 1 perform method 400.

[0059] The method 400 begins at step 410 where the voltage management device 100 provides a first current, the first current being a gate-to-source voltage V GS In one example, the current mirror of transistors 114 and 118 provides a first current I1126. The first current I1126 is proportional to the difference between the V GS In one example, transistor 116 is a first transistor and transistor 120 is a second transistor.

[0060] The method 400 continues at step 420 where the voltage management device 100 provides a second current, the second current being a function of the difference between the supply voltages and the gate-to-source voltages V of the first and second transistors. GS In one example, the second current is current I2 146 as described above in equation (2). Equation (2) shows that current I2 146 is proportional to the difference between V IN -ΔV GS In one example, transistors 116 and 120 are first and second transistors, respectively, while transistor 142 is a third transistor providing a second current.

[0061] The method 400 continues at step 430 where the voltage management device 100 compares the first current to the second current to determine the state of the voltage node, which changes state if the supply voltage exceeds a threshold. As discussed above with respect to FIG. INWhen the current 158 rises beyond the current kI1 due to the rise of , the TRIP node 156 changes its state. In one example, the transistor 150 is the fourth transistor, and the transistor 152 is the fifth transistor that conducts the current kI1. The transistor 154 is the sixth transistor that conducts the current 158 as part of the second current mirror including the transistor 136. In other examples, any suitable method is useful for comparing the first current with the second current.

[0062] The examples described herein can be used in a vast number of applications. Any end - device system that benefits from accurate voltage monitoring circuit elements can benefit from the examples herein due to the scalable and compact design of the voltage management device 100. The voltage management device 100 functions independently of the operating region of the transistors. That is, in one example, the voltage management device 100 can reduce the area used by using transistors in strong inversion. In another example, the transistor is useful in operations below the threshold for low - IQ operation.

[0063] In the voltage management device 100, the constant that determines the direct proportional relationship between the trip point and ΔV GS is scalable and not process - dependent. The constant can be scaled in two ways (current mirror ratio and resistance ratio). By scaling in two ways, the trip point can be finely programmed without significantly increasing the silicon area.

[0064] In the voltage management device 100, the IQ of the described topology is independent of the increase in V IN after reaching the trip point. This independence is achieved by using the current clamp 106 in the branch of the voltage management device 100 that carries the current I2146 dependent on V IN .

[0065] In some examples, the voltage management device 100 operates in the range of about 1.0 volt to about 5.0 volts. Also, the voltage monitoring device 100 self-starts by the startup section 102. The response time for the voltage management device 100 is fast compared to conventional systems.

[0066] The term "coupled" is used throughout this specification. This term can encompass connections, communications, or signal paths that enable a functional relationship consistent with the description in the specification. For example, when device A provides a signal to control device B to perform a certain operation, in a first example, device A is coupled to device B, or in a second example, when an intervening component C does not substantially change the functional relationship between device A and device B and device B is controlled by device A via the control signal provided by device A, device A is coupled to device B via the intervening component C.

[0067] A device "configured" to perform a certain task or function can be configured by the manufacturer at the time of manufacture to perform that task or function (e.g., programmed and / or hardwired), or can be configured (or reconfigured) by the user after manufacture to perform those functions and / or other additional or alternative functions. Such configurations can be via the device's firmware and / or software programming, via the configuration and / or layout of hardware components, via the interconnection of the device, or via a combination thereof.

[0068] Circuits or devices described herein as including specific components may instead include components coupled to those components and adapted to form the described circuits or devices. For example, a structure described as including one or more semiconductor elements (such as transistors), one or more passive elements (such as resistors, capacitors, and / or inductors), and / or one or more sources (such as voltage sources and / or current sources) may instead include only semiconductor elements within a single physical device (such as a semiconductor die and / or an integrated circuit (IC) package), and may be adapted, for example, by an end user and / or a third party, during or after manufacture, to be coupled to at least some of the passive elements and / or sources as described above to form the described structure.

[0069] Although the use of specific transistors is described herein, other transistors (or equivalent devices) may be used instead. For example, a p-type metal oxide silicon FET (“MOSFET”) may be used instead of an n-type MOSFET with little or no change to the circuit. Further, other types of transistors (such as bipolar junction transistors (BJTs)) may be used.

[0070] The circuits described herein are reconfigurable to include replaced components in order to provide at least partially similar functionality to that available prior to component replacement. A component shown as a resistor generally represents any one or more elements coupled in series and / or parallel to provide the amount of impedance represented by the shown resistor, unless otherwise specified. For example, a resistor or capacitor shown and described herein as a single component may instead be multiple resistors or capacitors coupled in parallel between the same nodes, respectively. For example, a resistor or capacitor shown and described herein as a single component may instead be multiple resistors or capacitors coupled in series between the same two nodes as a single resistor or capacitor, respectively.

[0071] The use of the phrase "ground" in the foregoing description includes chassis ground, earth ground, floating ground, virtual ground, digital ground, common ground, and / or any other form of ground connection applicable to or suitable for the teachings of this description. Unless otherwise specified, "about," "approximately," or "substantially" preceding a value means ±10% of that value. Modifications may be made to the exemplary examples described within the scope of the claims of the present invention, and other examples are possible.

Claims

1. 1. A voltage supervisor comprising: a first transistor coupled between a first supply voltage and a second supply voltage; a second transistor coupled between the first supply voltage and the second supply voltage; The voltage management device includes: providing a first current proportional to a difference between the gate-to-source voltages of the first transistor and the second transistor; providing a second current proportional to a difference between the first supply voltages and the difference between the gate-to-source voltages of the first transistor and the second transistor; comparing the first current to the second current to determine a voltage value that changes state in response to the first supply voltage crossing a threshold; A voltage management device configured as follows.

2. The voltage management device according to claim 1 , The second current is greater than the first current responsive to the first supply voltage crossing the threshold.

3. The voltage management device according to claim 1 , The voltage management unit, wherein the voltage management unit is configured to clamp the second current in response to the first supply voltage crossing the threshold.

4. The voltage management device according to claim 1 , A voltage management device, wherein the first transistor and the second transistor are sized to reduce a temperature coefficient of the difference between gate-to-source voltages of the first transistor and the second transistor.

5. The voltage management device according to claim 1 , A voltage management device, wherein a gate of the first transistor is coupled to a gate of the second transistor.

6. The voltage management device according to claim 1 , A voltage management device, wherein the drain of the second transistor is coupled to a current mirror and the source of the second transistor is coupled to a resistor.

7. The voltage management device according to claim 1 , The voltage management device includes a third transistor coupled to the first supply voltage and a resistor, the third transistor configured to provide the second current.

8. The voltage management device according to claim 7, The third transistor is configured to clamp the second current in response to the first supply voltage crossing the threshold.

9. The voltage management device according to claim 1 , The voltage management unit, wherein the voltage management unit is configured to provide the first current using a current mirror.

10. The voltage management device according to claim 1 , The voltage management device includes first and second resistors, the first resistor coupled to the second transistor, the first and second resistors sized to determine the threshold.

11. 1. A system comprising: a reference current generator including a current mirror, a first transistor, a second transistor, and a first resistor, the control terminal of the first transistor being coupled to the control terminal of the second transistor, and the first current terminal of the second transistor being coupled to the first resistor; a third transistor having a control terminal coupled to the current mirror, a first current terminal adapted to be coupled to a power supply, and a second current terminal coupled to a second resistor; a fourth transistor having a control terminal coupled to the control terminal of the third transistor and a first current terminal adapted to be coupled to the power supply; a fifth transistor having a second current terminal coupled to the second current terminal of the fourth transistor, a control terminal coupled to the control terminal of the second transistor, and a first current terminal coupled to a sixth transistor; Including, the system.

12. 12. The system of claim 11, The system, wherein the current mirror is a first current mirror, the system further including a second current mirror coupled to the first current terminal of the fifth transistor.

13. 12. The system of claim 11, A system, wherein a threshold voltage of the first transistor is greater than a threshold voltage of the second transistor.

14. 12. The system of claim 11, The system, wherein the first transistor is an n-channel transistor having a threshold voltage of less than about 500 millivolts.

15. 12. The system of claim 11, The system, wherein the second transistor is an n-channel native transistor.

16. 12. The system of claim 11, a second current terminal of the first transistor coupled to the current mirror and a second current terminal of the second transistor coupled to the current mirror.

17. A voltage management device, comprising: a reference current generator having a current mirror configured to provide a first current proportional to a difference between a gate-to-source voltage of a first transistor and a second transistor; a third transistor having a gate connected to the current mirror, a source adapted to be coupled to a power supply, and a drain coupled to a resistor, the third transistor configured to provide a second current proportional to a difference between supply voltages and the difference between gate-source voltages of the first transistor and the second transistor; a fourth transistor having a gate coupled to the gate of the third transistor, a source adapted to be coupled to the power supply, and a drain having a drain voltage indicative of the supply voltage being above a threshold; A voltage management device comprising:

18. 18. A voltage management device according to claim 17, The third transistor is configured to clamp the second current in response to the supply voltage crossing the threshold.

19. 18. A voltage management device according to claim 17, The voltage management apparatus, wherein the resistor is a first resistor, and the threshold value is based at least in part on a value of the first resistor and a value of a second resistor coupled to a source of the second transistor.

20. 18. A voltage management device according to claim 17, A voltage management device, wherein the first transistor and the second transistor are sized to reduce a temperature coefficient of the difference between gate-to-source voltages of the first transistor and the second transistor.

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