Voltage Management Device

Abstract

The voltage management device (100) includes a first transistor (116) coupled between a first supply voltage (112) and a second supply voltage (124). The voltage management device includes a second transistor (120) coupled between the first supply voltage (112) and the second supply voltage (124). The voltage management device (100) 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 management device (100) is also configured to provide a second current (146) proportional to a difference in the first supply voltage (112) and a difference in the gate-to-source voltages of the first transistor (116) and the second transistor (120). The voltage management device (100) is configured to compare the first current (126) with the second current (146) and determine a voltage value that will cause the first supply voltage (112) to change state in response to the first supply voltage (112) crossing a threshold value.

Description

[Technical field]

[0001] A voltage supervisor is useful in many applications to monitor a supply voltage and detect certain problems with the supply voltage. In some applications, the voltage supervisor may detect whether the power supply voltage is below or above a threshold. In response to the voltage crossing the threshold, the voltage supervisor asserts a signal. This signal is useful for taking action to ensure proper power supply operation. Summary of the Invention

[0002] In accordance with at least one example of the present description, a voltage management device includes a first transistor coupled between a first supply voltage and a second supply voltage. The voltage management device includes a second transistor coupled between the first supply voltage and the second supply voltage. The voltage management device is configured to provide a first current proportional to a difference between gate-to-source voltages of the first transistor and the second transistor. The voltage management device is also configured to provide a second current proportional to the difference between the first supply voltages and the difference between the gate-to-source voltages of the first transistor and the second transistor. The voltage management device is configured to compare the first current to the second current to determine a voltage value that causes the voltage management device to change state in response to the first supply voltage crossing a threshold.

[0003] In accordance with at least one example of the present description, a system includes a reference current generator including a current mirror, a first transistor, a second transistor, and a first resistor, where 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 the second resistor. The system includes 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. The system includes 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 the sixth transistor.

[0004] In accordance with at least one example of the present description, a voltage management device includes a reference current generator having a current mirror configured to provide a first current proportional to a difference between 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 configured to provide a second current proportional to a difference between the supply voltages and a difference between the gate-source voltages of the first transistor and the second transistor. The voltage management device includes a fourth transistor having a gate coupled to the gate of the third transistor, a source adapted to be coupled to a power supply, and a drain having a drain voltage indicative of the supply voltage being above a threshold. [Brief description of the drawings]

[0005] [Figure 1] 1 is a voltage management device according to various examples.

[0006] [Diagram 2]1 is a graph of temperature coefficient for strong inversion operation in accordance with various examples.

[0007] [Diagram 3] 1 is a series of graphs illustrating how a zero temperature coefficient is achieved in accordance with various examples.

[0008] [Figure 4] 1 is a flowchart of a method for voltage management in accordance with various examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Voltage supervisors are useful for monitoring a power supply voltage and asserting a signal if a threshold is reached. A node (called a trip node) has a voltage that flips from a high voltage to a low voltage or vice versa when the power supply voltage reaches the threshold. This voltage on the power supply that causes the trip node to flip is called the trip voltage (e.g., threshold voltage or voltage threshold). Conventional voltage supervisors have many shortcomings. For example, conventional voltage supervisors often have a quiescent current (I Q ), and have a slow response time. Also, a small threshold voltage (the threshold voltage of the monitored power supply) is often difficult to achieve in a conventional voltage management device. Furthermore, achieving a programmable threshold voltage of the monitored power supply is difficult with conventional voltage management devices. For example, if the monitored supply voltage is changed to a different voltage, the voltage management device is usually redesigned to handle the new supply voltage. Furthermore, conventional voltage management devices often occupy a large silicon area.

[0010] In the examples herein, the voltage management device is Q, 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 GS ) The first current is useful as a reference current since it does not vary with the supply voltage. The second current is directly proportional to the supply voltage, and therefore 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 the threshold, the second current exceeds the first current, so the trip node reverses from a low voltage to a high voltage. In response to the trip node reversal, the circuit is clamped to reduce I Q Reduce the increase in

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

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

[0013] In one example, the transistor 114 is a p-type FET. In one example, the transistor 114 has a threshold voltage V TH1. In other examples, different types of transistors may be useful. Transistor 114 has a source coupled to node 112 and a drain coupled to a first terminal of resistor 110. Transistor 114 also has a gate coupled to a gate of transistor 118. Transistor 116 is an n-type FET in one example. Transistor 116 has a drain coupled to a 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 connected to a first supply voltage V IN 124. The supply voltage Vref may be coupled to a voltage rail other than ground 124 that is a different voltage (second supply voltage).

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

[0015] In one example, transistor 118 has a threshold voltage V THThe transistors 114 and 118 are low threshold voltage transistors with a threshold voltage of approximately 400-500 mV. In other examples, different types of transistors may be useful. Transistors 114 and 118 have a "1" in a circle next to them. The "1" indicates that transistors 114 and 118 are similarly sized, and that transistors 114 and 118 are configured as a current mirror such that the current through transistor 114 is approximately equal to the current through transistor 118. The gates of transistors 114 and 118 are connected and the sources are connected, so that the gate-to-source V GS are the same. In one example operation, current I1127 flows through transistor 114 and current I1126 flows through transistor 118. Currents I1126 and I127 are approximately equal in one example. Current I1126 and its use in voltage management device 100 are described below.

[0016] In one example, transistor 116 has a threshold voltage V of about 400-500 mV. TH In one example, transistor 120 is a low threshold voltage transistor having a threshold V of approximately −100 mV. TH In 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 GSis 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 IN It provides a reference current I1126 that does not change with variations in V GS is represented by V1, which is the voltage between a node 128 coupled to the gate of transistor 116 and a common potential (ground in some examples) 124. GS is represented as 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. Thus, the voltage at node 130 is the gate-to-source voltage of transistors 116 and 120. VG Since it is the difference between ΔVGS It is called.

[0020] The current I1126 flows through transistor 120 and resistor 122 (R BOT ) Since the voltage across resistor 122 is known, the current I1 126 is calculated by equation (1). I1 = (ΔV GS ) / (R BOT ) (1)

[0021] As shown in equation (1), the current I1126 is proportional to the supply voltage V IN The value of the current I1126 does not change with the two gate-source voltages V GS The supply voltage V IN As changes in these two V GS The difference between the two remains the same. GS As one value increases, the other increases by the same amount. GS As the value decreases, the other decreases by a similar amount. Current I1126 is this ΔV GS This ΔV GS The value is the supply voltage V IN Therefore, the current I1126 also does not change with the supply voltage V IN Therefore, the current I1126 does not change with the supply voltage V IN has risen above a 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 has a threshold voltage V TH1. Transistor 132 is a low threshold voltage transistor with a threshold voltage of approximately 400-500 mV. In other examples, different types of transistors may be useful. Transistor 132 may be approximately identical to transistors 114 and 118 in one example. Transistor 132 has a "1" in a circle next to it, 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 (because 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. A drain of transistor 132 is coupled to node 138 and to the drain of transistor 134. Because transistor 132 forms part of a current mirror with transistors 114 and 118, the current I 129 flowing through transistor 132 is approximately equal to the current I 126 flowing through transistor 118.

[0023] Transistor 134 has a threshold V TH 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 to 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 a node 138, which is coupled to the drain of transistor 134.

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

[0026] In one example, transistor 142 has a threshold voltage V of about 400-500 mV. TH 1. In other examples, different types of transistors may be useful. Transistor 142 has a "2" in a circle next to it, indicating that transistor 142 is approximately twice the size of transistors 114, 118, and 132, and therefore can conduct approximately twice as much current as those three transistors. Transistor 142 is also configured to act as a current mirror with transistors 114, 118, and 132 when the voltage at node 112 is an appropriate amount above the trip point.

[0027] A current I2 146 flows through resistor 144. The current I2 146 is proportional to the supply voltage V at node 112 (as shown in equation (2) below): IN is the current that varies with the supply voltage V IN It is useful to determine whether V exceeds a threshold. IN rises slowly and approaches the threshold. Current I2 146 flows through transistor 142. The gate-source voltage V across transistor 134 GSis V2, which is the voltage between node 128 and node 130 as described above. In one example, transistors 120 and 134 are identical devices and their gates are connected, so that the gates of transistors 120 and 134 are at the same voltage. The current through transistor 120 is current I1126, and the current through transistor 134 is current I129, which is similar to I1126 (due to the current mirror). Because the currents through transistors 120 and 134 are the same and the gates of transistors 120 and 134 are at the same voltage, 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 It becomes.

[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 I 129 combines with current I 146 to generate current I 148 through transistor 136. The current through resistor 144 is current I 146, and the voltage at the second terminal of resistor 144 is ΔV GS Therefore, the voltage at the first terminal of resistor 144 determines the voltage drop across resistor 144 and is useful for determining the value of current I2 146.

[0029] Supply voltage V IN In response to the trip node being tripped, the voltage at the first terminal of resistor 144 becomes approximately V IN This is because transistor 142 is turned on and has a negligible voltage drop across it. Transistor 142 is approximately twice the size of transistors 114, 118, and 132 and is part of the current mirror formed by these transistors. Thus, transistor 142 has the capacity to conduct approximately twice the current I1126. However, transistor 142 is capable of conducting approximately twice the current I1126 when compared to the supply voltage V INand ground 124 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 full amount of current it is capable of conducting. Thus, the current I2 146 through transistor 142 is less than twice the current I1 126 in this example. V IN The drain voltage of transistor 142 is close to the source voltage of transistor 142, and its source voltage is close to the supply voltage V IN Therefore, the voltage at the drain of transistor 142 is also at the supply voltage V IN Therefore, resistor 144 (R TOP ) is the supply voltage V IN Equation (2) shows the value of current I2146. I2=(V IN -ΔV GS ) / (R TOP ) (2)

[0030] V IN During the operating conditions described above where the voltage threshold at which V falls below the trip node tripping voltage threshold, the current I2146 is equal to the supply voltage V, not twice the value of I1126. IN It varies directly with the value of

[0031] The current flowing through each of the first three branches of the voltage management device 100 is described above. The fourth branch of the voltage management device 100 includes transistors 150, 152, 154, and a TRIP node 156. In one example, transistor 150 has a threshold voltage V of approximately 400-500 mV. TH1. In other examples, different types of transistors may be useful. Transistor 150 has a "k" in a circle next to it, indicating that transistor 150 is approximately "k" times the size of transistors 114, 118, and 132 and therefore can conduct approximately "k" times the current of transistors 114, 118, and 132 because 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 a TRIP node 156 and to the drain of transistor 152.

[0032] Transistor 152 has a threshold V 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, in one example, has a threshold voltage V TH 124. In one example, 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 Transistor 154 has a "1" in a circle next to it, while transistor 136 has a "2" in a circle next to it. These numbers indicate that transistor 136 is approximately twice the size of transistor 154 in this example.

[0034] As discussed above, currents I1 129 (approximately equal to I1 126) and I2 146 combine to create current I3 148, as shown in equation (3). I1+I2=I3(3)

[0035] The current flowing through transistor 136 is current I3 148, and transistor 136 is twice the size of transistor 154. The gates of transistors 136 and 154 are tied together, and the sources of transistors 136 and 154 are also tied together at ground 124. Thus, the gate-to-source V GS are the same. Because transistor 136 is approximately twice the size of transistor 154, transistor 136 conducts approximately twice the current as transistor 154. The current through transistor 136 is current I3 148, and therefore the current through transistor 154 is I3 / 2, shown in FIG. 1 as current 158. In one example, transistors 136 and 154 act as a second current mirror in voltage management device 100, with the current being 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 (e.g., kI1) the current I1126. As discussed above with respect to equation (1), the current I1126 is IN Since the current kI1 does not depend on the supply voltage V IN Therefore, it does not depend on the supply voltage V IN As V rises, current kI1 remains approximately constant over time. However, current I3 148 is a combination of currents I129 (approximately equal to I1 126) and I2 146, which is a function of V IN depends on the supply voltage V IN As the supply voltage V rises, the current 158 ​​(e.g., I3 / 2) at the bottom of the fourth branch also rises. In response to the current 158 ​​rising above the current kI1 in the fourth branch, the TRIP node 156 switches state. Specifically, IN In response to TRIP node 156 falling below a monitored voltage threshold, current kI1 pulls TRIP node 156 to a high voltage. When supply voltage VIN increases (this is because the current 158 ​​increases with the supply voltage V IN As current kI1 changes with kI2 (which may occur because current kI1 does not change), TRIP node 156 is pulled to a low voltage. The voltage at TRIP node 156 that causes the node to flip is the trip voltage (e.g., a 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). TIFF0007663291000001.tif621

[0038] Current I158 is half of current I3148 calculated by equation (5) TIFF0007663291000002.tif635

[0039] The TRIP node 156 begins to reverse as the current 158 ​​becomes equal to the current kI1. The trip voltage is shown in equation (6). TIFF0007663291000003.tif636

[0040] Equation (6) is the trip voltage V TRIP But multiplied by a constant, ΔV GS The constant is the resistor 144 (R TOP ) and resistor 122 (R BOT ) 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 vary in the same way, the process variations can be offset according to equation (6). The constant k is the relative device size, which is constant and does not change substantially with process or temperature. The trip voltage V TRIP The main variation of ΔV GS In one example, the transistors herein are subject to a process variation that affects ΔV GSThe trip voltage V TRIP does not change significantly with temperature.

[0041] As mentioned above, the voltage management device 100 is programmable for various voltage thresholds. The values ​​of resistors 122 and 144 are set to the trip voltage V TRIP It can also be adjusted to vary the trip voltage V TRIP The value of k (relative device size) can also be adjusted to change the trip voltage V TRIP The topology of the voltage management device 100 provides this programmability because the same circuit can be used to fine-tune different trip voltages V TRIP In some instances, the trip voltage V TRIP In another example, a variable resistor can be used to vary the trip voltage V by switching the resistor on and off. TRIP can be adjusted.

[0042] Another feature of the voltage management apparatus 100 in various examples is that the current I2 146 is limited after the trip point is reached. While the current I1 126 is independent of the supply voltage, the current I2 146 is not. The current clamp 106 is IN The current clamp 106 is useful for limiting the current I2 146 as the supply voltage V IN This prevents the current I2 146 from increasing after the supply voltage V reaches a certain value. IN At this certain value of I1126, the voltage supply V IN There is sufficient voltage margin between the supply voltage V and ground 124. When the current flowing through transistor 142 reaches twice the current I126, transistor 142 saturates. Thus, IN rises above a certain value, no additional current will flow through the branches 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, to prevent variations with temperature, transistors 116 and 120 are GS The transistors 116 and 120 should be sized such that the temperature coefficient of GS If the temperature coefficient of is near zero, then the value of current I1126 will also be more resistant to temperature changes, allowing current I1126 to be useful as a reference current.

[0044] Two methods are described herein for achieving a near-zero temperature coefficient, one involving using a transistor in strong inversion operation and another involving using a transistor in weak inversion operation. In strong inversion operation, the V GS is the threshold voltage V TH Overdrive voltage V OV is the threshold voltage V TH Gate-source voltage V exceeds GS In weak inversion operation (e.g., in the subthreshold region), the transistor is driven at a threshold voltage V TH Gate-source voltage V below GS Works with.

[0045] First, in the example of strong reversal behavior, V GS =V TH +V OV Moreover, equation (7) shows the difference between these voltages. ΔV GS = ΔV TH +ΔV OV (7)

[0046] ΔV GSis the difference in gate-to-source voltage between transistor 116 and transistor 120, as described above with respect to FIG. 1. In one example, transistor 116 is a low voltage transistor (LVT), and the variables relating to transistor 116 in the equations below are marked with the subscript LVT. In this example, transistor 120 is a native transistor (NAT), and the variables relating to transistor 120 in the equations below are marked with the subscript NAT. The variables in equation (7) can be expanded based on the operating region in which the transistors are operating. For strong inversion operation, ΔV OV is the V of transistor 116 OV to the V of transistor 120 OV It is equal to minus ΔV OV Substituting these terms into equation (8), we obtain ΔV GS = ΔV TH +[V OV(LVT) -V OV(NAT) ] (8)

[0047] The current I1126 in FIG. 1 is defined in equation (9). where k' is the process transconductance parameter, which is a constant that depends on the process technology used to fabricate the integrated circuit, and W / L is the ratio of the channel width to the channel length (for transistor 120 in this example, but equation (9) can also be used to find the current through other transistors). V OV Solving equation (9) for V OV(LVT) and V OV(NAT) For both, the solution V OV Substituting this, we obtain equation (10). TIFF0007663291000005.tif1054

[0048] ΔV TH is a positive value, and the threshold voltage V TH to the threshold voltage V of the transistor 120 TH In one example, the threshold voltage VTH is greater than zero, and the threshold voltage V 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). TIFF0007663291000006.tif742

[0050] In this example, the LVT and NAT transistors are the same size, so the W / L variable is the same for each transistor and can be moved out of the brackets as shown in equation (11). The next step is to remove ΔV TH Temperature coefficient of ΔV TH The goal is to identify the temperature coefficient of the term that adds to ΔV TH The temperature coefficient of the other terms in equation (11) (which is ΔV OV should be offset by

[0051] ΔV TH is process dependent and cannot be adjusted to achieve zero temperature coefficient. OV For the term, the size of the transistor can be modified (by modifying the W and L terms). The W and L variables are TH ΔV in the appropriate direction to cancel the temperature coefficient of OV It can be adjusted to change the temperature coefficient of the term, e.g., ΔV TH If the temperature coefficient of is θ, then the other terms should be -θ so that they cancel. Also, k' is the mobility (μ) of the device times the oxide capacitance C OX (k'=μC OX ).

[0052] FIG. 2 is a graph 200 of temperature coefficient for strong inversion operation according to an example. Graph 200 graphs the inverse of (k' / 2)(W / L) versus temperature. The inverse of (k' / 2)(W / L) is graphed on the y-axis. The x-axis is temperature in degrees Celsius. Curve 202 is the inverse of (k' / 2)(W / L) for an LVT device, such as transistor 116. Curve 204 is the inverse of the term (k' / 2)(W / L) for a NAT device, such as transistor 120. As can be seen in graph 200, the inverse of this term for the LVT (curve 202) has a lower slope than the inverse of this term for the 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 is added to equation (11). The second term on the right hand side of TIFF0007663291000007.tif724 (the radical multiplied by the term in brackets) decreases with increasing temperature. This means that the second term as above has a negative temperature coefficient. The second term has a magnitude equal to ΔV TH This can be adjusted by varying the W and L values ​​(for LVT and NAT transistors of the same size) until the absolute value of ΔV is equal to that of ΔV. TH cancel each other out, resulting in a temperature coefficient that is nearly zero.

[0053] In the second case of subthreshold or weak reversal motion, ΔV GS = ΔV TH +ΔV OV Similar mathematical substitutions as above can be made for this type of operation. However, for sub-threshold operation, ΔV OV The terms are different from the case of strong inversion operation. In one example, the subthreshold operation is characterized by equation (12). TIFF0007663291000008.tif843

[0054] The logarithmic term in equation (12) (which is ΔV OV (corresponding to ΔV THThe temperature coefficient terms are adjusted in the same manner as for the strong inversion action described above to offset the temperature coefficient terms of the LVT and NAT transistors. The logarithmic terms can be adjusted by adjusting the W and L variables for either or both of the LVT and NAT transistors.

[0055] FIG. 3 is a set of graphs illustrating temperature coefficient cancellation in subthreshold operation. Graph 300 shows ΔV vs. temperature (in degrees Celsius). TH 3 is a graph of current (Volts) with the temperature coefficient shown as curve 302. Curve 302, as shown in graph 300, has a positive slope of approximately 0.13.

[0056] Graph 304 shows ΔV with respect to temperature. OV 3 is a graph of a temperature coefficient shown as curve 306. Curve 306 has a negative slope, with a slope of approximately 0 at the left end of curve 306, a slope of approximately -0.2 at the middle of curve 306, and a slope of approximately -0.3 at the right end of curve 306.

[0057] In one example, ΔV OV The gradient of is ΔV TH If the slope of ΔV is made equally negative when it is positive, it will result in an umbrella shaped curve such as curve 310 shown in graph 308. Graph 308 shows the relationship between ΔV and temperature. GS 3 is a graph of the result of combining curves 302 and 306. Curve 310 has a similar V GS Thus, as temperature increases, curve 310 does not exhibit an increasing or decreasing slope, but instead becomes an umbrella-shaped curve. Because curve 310 is not completely horizontal, there is some effect caused by changes in temperature, but because it is close to horizontal, the effect is small in some instances.

[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. IN When current 158 ​​rises above current kI1 due to a rise in current kI1, TRIP node 156 changes state. In one example, transistor 150 is a fourth transistor and transistor 152 is a fifth transistor that conducts current kI1. Transistor 154 is a sixth transistor that conducts current 158 ​​as part of a second current mirror with transistor 136. In other examples, any suitable method is useful for comparing the first current to the second current.

[0062] The examples described herein can be used in a vast number of applications. Any end equipment system that benefits from accurate voltage supervision circuitry can benefit from the examples herein due to the scalable and compact design of the voltage supervision device 100. The voltage supervision device 100 functions independent of the operating area of ​​the transistors. That is, in one example, the voltage supervision device 100 can reduce area usage by using transistors in strong inversion. In another example, the voltage supervision device 100 can reduce area usage by using transistors in low I Q Useful for operation below threshold for operation.

[0063] In the voltage management device 100, the trip point and ΔV GS The constants that determine the direct proportionality between are scalable and process independent. The constants can be scaled in two ways: current mirror ratios and resistor ratios. Scaling in two ways allows finely programming the trip points without a significant increase in silicon area.

[0064] In the voltage management device 100, the I Q is the V after the trip point is reached IN This independence is independent of the increase in V IN This is accomplished by using a current clamp 106 in a branch of the voltage management device 100 that carries a current I2 146 that depends on

[0065] In some examples, the voltage management apparatus 100 operates in a range of about 1.0 volts to about 5.0 volts, and is self-starting via the starting section 102. The response time for the voltage management apparatus 100 is fast as compared to conventional systems.

[0066] The term "couple" is used throughout this specification. This term may encompass any connection, communication, or signal path that enables a functional relationship consistent with the description of the specification. For example, in a first example, device A is coupled to device B if device A provides signals to control device B to perform certain operations, or in a second example, device A is coupled to device B via an intervening component C if the intervening component C does not substantially change the functional relationship between devices A and B and device B is controlled by device A via control signals provided by device A.

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

[0068] A circuit or device described herein as including certain components may instead be adapted to be coupled to those components to form the described circuit or device. 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 and / or current sources) may instead include only semiconductor elements within a single physical device (e.g., a semiconductor die and / or integrated circuit (IC) package) and may be adapted, for example, by an end user and / or a third party, at or after manufacture, to be coupled to the passive elements and / or at least some of the aforementioned sources to form the described structure.

[0069] Although the use of particular transistors is described herein, other transistors (or equivalent devices) may be substituted. For example, a p-type metal oxide silicon FET ("MOSFET") may be substituted for an n-type MOSFET with little or no modification to the circuit. Additionally, other types of transistors (such as bipolar junction transistors (BJTs)) may be used.

[0070] The circuits described herein are reconfigurable to include replaced components to provide functionality at least partially similar to that available prior to the 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 resistor shown, unless otherwise indicated. For example, a resistor or capacitor shown and described herein as a single component may instead be multiple resistors or capacitors, respectively, coupled in parallel between the same nodes. For example, a resistor or capacitor shown and described herein as a single component may instead be multiple resistors or capacitors, respectively, coupled in series between the same two nodes as a single resistor or capacitor.

[0071] Use of the term "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 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 illustrative examples described and other examples are possible within the scope of the present claims.

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; Including, providing a first current proportional to a difference between a gate-to-source voltage of the first transistor and a gate-to-source voltage of the second transistor; providing a second current proportional to a difference in the first supply voltages and a difference in gate-to-source voltages between 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; clamping the second current in response to the first supply voltage crossing the threshold. A voltage management device configured as follows.

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

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

4. 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.

5. 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.

6. The voltage management device according to claim 1 , The voltage management apparatus further comprising a third transistor coupled to the first supply voltage and to a resistor, the third transistor configured to provide the second current.

7. The voltage management device according to claim 6, The voltage management apparatus, wherein the third transistor is further configured to clamp the second current in response to the first supply voltage crossing the threshold.

8. The voltage management device according to claim 1 , The voltage management unit further configured to provide the first current using a current mirror.

9. The voltage management device according to claim 1 , a first resistor coupled to the second transistor, the first resistor being sized to determine the threshold; and a second resistor coupled to the second transistor, the first resistor being sized to determine the threshold.

10. 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 first resistor, the third transistor 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; 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 fifth transistor having a source coupled to the second terminal of the first resistor and a gate coupled to the gate of the first transistor and to the gate of the second transistor; A voltage management device comprising:

11. The voltage management device according to claim 10, The third transistor is configured to clamp the second current in response to the supply voltage crossing the threshold.

12. The voltage management device according to claim 10, The voltage management apparatus, wherein the threshold 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.

13. The voltage management device according to claim 10, A voltage management apparatus, wherein the first transistor and the second transistor are sized to reduce a temperature coefficient of a gate-to-source voltage difference between the first transistor and the second transistor.

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

15. 15. The system of claim 14, The system further includes a second current mirror coupled to the first current terminal of the fifth transistor.

16. 15. The system of claim 14, A system, wherein a threshold voltage of the first transistor is greater than a threshold voltage of the second transistor.

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

18. 15. The system of claim 14, The system, wherein the second transistor is an n-channel native transistor.

19. 15. The system of claim 14, a second current terminal of the first transistor coupled to the first current mirror and a second current terminal of the second transistor coupled to the first current mirror.

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