voltage monitor

Abstract

A voltage monitor (100) includes a first transistor (116) coupled between a first supply voltage (112) and a second supply voltage (124). The voltage monitor (100) includes a second transistor (120) coupled between the first supply voltage (112) and the second supply voltage (124). The voltage monitor (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) and the first supply voltage (112). The voltage monitor (100) is also configured to provide a second current (146) proportional to a difference of the first supply voltage (112) and the difference in gate-to-source voltages of the first transistor (116) and the second transistor (120). The voltage monitor (100) is configured to compare the first current (126) and the second current (146) to determine a voltage value that changes state in response to the first supply voltage (112) exceeding a threshold.

Description

Background Technology

[0001] Voltage monitors are used in many applications to monitor power supply voltage and detect specific problems related to it. In some applications, voltage monitors can detect whether the power supply voltage has dropped below a threshold or risen above a threshold. In response to the voltage exceeding the threshold, the voltage monitor asserts a signal. This signal can be used to take action to ensure proper power supply operation. Summary of the Invention

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

[0003] According to at least one example described, a system includes a reference current generator comprising 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 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 a sixth transistor.

[0004] According to at least one example described, a voltage monitor includes a reference current generator having a current mirror configured to provide a first current proportional to the difference between the gate-to-source voltages of a first transistor and a second transistor. The voltage monitor 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 and supply a second current proportional to the difference between the gate-to-source voltages of the first transistor and the second transistor. The voltage monitor includes 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 indicating that the supply voltage is above a threshold. Attached Figure Description

[0005] Figure 1 It is a voltage monitor based on various examples.

[0006] Figure 2 It is a chart of temperature coefficients for strong reversal operations based on various examples.

[0007] Figure 3 It is a collection of charts demonstrating how to achieve a zero temperature coefficient through various examples.

[0008] Figure 4 It is a flowchart of methods for voltage monitoring based on various examples. Detailed Implementation

[0009] Voltage monitors are used to monitor power supply voltage and assert a signal when a threshold is reached. A node (called a switching node) has a voltage that flips from high to low voltage or vice versa when the power supply voltage reaches a threshold. This voltage of the power supply that causes the switching node to flip is called the switching voltage (e.g., threshold voltage or voltage threshold). Conventional voltage monitors have numerous drawbacks. For example, conventional voltage monitors typically have a high off-stage current (also known as quiescent current (Ik)). Q Furthermore, conventional voltage monitors suffer from slow response times. Moreover, achieving small threshold voltages (the monitored threshold voltage of a power supply) is typically difficult in conventional voltage monitors. Additionally, achieving programmable threshold voltages for a power supply in a conventional voltage monitor is challenging. For example, if the monitored supply voltage changes to a different voltage, the voltage monitor typically needs to be redesigned to handle the new supply voltage. Furthermore, conventional voltage monitors generally occupy a large silicon area.

[0010] In the examples presented in this article, the voltage monitor provides a low IL QIt features a fast response time, scales up to a threshold voltage range, and has a small silicon area. The voltage monitor described herein uses a circuit topology with four branches, through which two different currents flow. The first current is the difference (ΔV) between the gate-to-source voltages of the two field-effect transistors (FETs). GS The first current is proportional to the supply voltage. It can be used as a reference current because it does not change with the supply voltage. The second current is proportional to the supply voltage, and therefore its magnitude indicates the magnitude of the supply voltage. These two currents are compared to determine the state of the switching node. In response to the supply voltage exceeding a threshold, the switching node flips from low to high voltage because the second current exceeds the first current. In response to the switching node, the circuit is clamped to reduce IT. Q The increase.

[0011] Figure 1 This is a voltage monitor 100 according to various examples described herein. The voltage monitor 100 includes a startup section 102, a reference current generator 104, and a current clamp 106. The voltage monitor 100 can also be described as having four vertical branches, as described in the operation below. The startup section 102 includes a transistor 108 and a resistor 110. In one example, the transistor 108 is an n-type FET. In one example, the transistor 108 has a threshold voltage (Vt) of approximately -100mV. TH Native transistors. In other instances, transistors with different low V values ​​can be used. TH Or a smaller negative value for V TH Native transistors. Native transistors are various FETs that exist between enhancement mode and depletion mode. In other instances, different types of transistors may be available. By using a relatively low threshold voltage V... TH The transistor, voltage monitor 100 can monitor lower supply voltage levels. If the transistor's threshold voltage V... TH If the voltage is relatively high, then the transistor in voltage monitor 100 will not be able to operate at a sufficiently low voltage level to adequately monitor the lower supply voltage. The source of transistor 108 is coupled to the first terminal of resistor 110 and the drain is coupled to node 112. In one example, a supply voltage V is provided at node 112. IN The gate of transistor 108 is coupled to the second terminal of resistor 110. In the examples herein, the gate of the transistor may also be referred to as the control terminal. The source or drain of the transistor may also be referred to as the current terminal. In one example, startup section 102 can be used to start voltage monitor 100. In response to starting voltage monitor 100, startup section 102 becomes inactive. The operation of startup section 102 is described below.

[0012] Voltage monitor 100 includes a reference current generator 104. In this example, reference current generator 104 has two vertical branches. In other examples, different types of reference current generators may be used to provide a reference current. The first branch of reference current generator 104 includes transistor 114, resistor 110, and transistor 116. The second branch of 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 voltage monitor 100 as a reference to determine whether the supply voltage has exceeded a predetermined threshold.

[0013] In one example, transistor 114 is a p-type FET. In one example, transistor 114 has a threshold voltage V of approximately 400mV to 500mV. TH A low threshold voltage transistor. In other instances, different types of transistors may be used. 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. In one instance, transistor 116 is an n-type FET. 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 instances, the rail at ground 124 may be coupled to a voltage other than the first supply voltage V provided at node 112. IN The voltage track of the voltage (second supply voltage).

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

[0015] In one example, transistor 118 has a threshold voltage V of approximately 400mV to 500mV. THA low threshold voltage transistor. In other instances, different types of transistors may be used. Transistors 114 and 118 have a "1" immediately adjacent to them in a circle. This "1" indicates that transistors 114 and 118 are similar in size, and since transistors 114 and 118 are configured as current mirrors, the current flowing through transistor 114 will be approximately equal to the current flowing through transistor 118. Since the gates and sources of transistors 114 and 118 are connected together, the gate-to-source voltage V of transistors 114 and 118 is... GS They are the same. In one example operation, current I127 flows through transistor 114, and current I1126 flows through transistor 118. In one example, current I1126 is approximately equal to I127. Current I1126 and its use in voltage monitor 100 are described below.

[0016] In one example, transistor 116 has a threshold voltage V of approximately 400mV to 500mV. TH A low threshold voltage transistor. In one example, transistor 120 has a threshold voltage V of approximately -100mV. TH The native transistor. In other instances, different types of transistors may be available.

[0017] The startup section 102 operates as follows. Initially, when the supply voltage V at node 112... IN When the voltage is low (for example, below two volts) and no current has been formed in the voltage monitor 100, node 128 is grounded (0V). Furthermore, since no current I 127 flows through resistor 110, the first terminal of resistor 110 is grounded. Subsequently, the V of transistor 108... GS The voltage is 0V, which is sufficient to turn on transistor 108 and begin conducting current. The current conducted by transistor 108 acts as a startup 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 other devices (transistors 114, 118, and 120) to begin conducting current in their respective current mirror arrangements, and the conducted current increases until a steady state is reached. Positive feedback in the two leftmost branches of voltage monitor 100 helps to reach a steady state. In one example, startup section 102 ensures that voltage monitor 100 does not have zero current and does not remain inoperable.

[0018] After current I127 begins to flow through transistor 114, the voltage drop across resistor 110 increases, causing the voltage at the source of transistor 108 to be sufficiently higher than the voltage at the gate of transistor 108 in order to turn off transistor 108. This is because the voltage drop across resistor 110 is equal to -V of transistor 108. GSResistor 110 is sized such that the voltage drop across resistor 110 is large enough to keep transistor 108 off during normal operation of voltage monitor 100.

[0019] The first two branches in voltage monitor 100 provide voltage independent of the supply voltage V IN The reference current I1126 changes with the change in voltage. The V of transistor 116... GS V1, denoted by V1, is the voltage between node 128, coupled to the gate of transistor 116, and common potential (in some instances, ground) 124. V1 of transistor 120... GS V2 is the voltage between nodes 128 and 130. The difference between V1 and V2 is equal to the voltage across resistor 122, which is also the voltage at node 130. The voltage at node 130 is therefore called ΔV. GS Because it is the gate-to-source voltage V of transistors 116 and 120. GS difference.

[0020] Current I1 126 flows through transistor 120 and resistor 122 (R) BOT Since the voltage across resistor 122 is known, the current I1 126 is calculated in equation (1):

[0021]

[0022] As seen in Equation 1, the current I1 126 does not change with the supply voltage V. IN And it changes. The value of current I1 126 is determined by the gate-to-source voltage V of transistors 116 and 120. GS The difference between them is determined by the value of resistor 122. When the supply voltage V IN When they change, these two V's GS The difference between values ​​remains constant. When a V GS When the value increases, another V GS The value also increases by a similar amount. When a V GS When the value decreases, another V GS The value also decreases by a similar amount. Current I1 = 126 and this ΔV GS The value is proportional, and this ΔV GS The value does not change with the supply voltage V IN Therefore, the current I1 126 does not change with the supply voltage V. IN And it changes. For this reason, the current I1 126 can be used as a reference current to help determine the supply voltage V. IN Has it risen above the threshold?

[0023] The third branch of the voltage monitor 100 includes transistors 132, 134, and 136. In one example, transistor 132 is a p-type FET. In one example, transistor 132 has a threshold voltage V of approximately 400mV to 500mV. TH A low threshold voltage transistor. In other instances, different types of transistors may be used. In one instance, transistor 132 may be approximately equivalent to transistors 114 and 118. Transistor 132 has a "1" in a circle immediately adjacent to it, indicating that transistor 132 is approximately the same size as transistors 114 and 118 and is capable of conducting a similar amount of current as transistors 114 and 118 (due to the fact that 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, together with transistors 114 and 118, forms part of the current mirror, the current I129 flowing through transistor 132 is approximately equal to the current I1126 flowing through transistor 118.

[0024] In one example, transistor 134 has a threshold voltage V of approximately -100mV. TH An n-type (FET) native transistor. In other instances, different types of transistors may be used. 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 the drain of transistor 136 and to node 140. In one instance, transistor 134 is an equivalent transistor to transistor 120.

[0025] 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.

[0026] The third branch of the voltage monitor 100 includes a side branch having a current clamp 106 containing a transistor 142. The side branch also includes a resistor 144. The transistor 142 has a gate coupled to the gate of a transistor 132 and a source coupled to node 112. The drain of the transistor 142 is coupled to a first terminal of the resistor 144. A second terminal of the resistor 144 is coupled to node 140.

[0027] In one example, transistor 142 has a threshold voltage V of approximately 400mV to 500mV. THA low threshold voltage transistor. In other instances, different types of transistors may be used. Transistor 142 has a "2" immediately adjacent to it in the circle, indicating that transistor 142 is approximately twice the size of transistors 114, 118, and 132, and is therefore capable of conducting approximately more than twice the current of those three transistors. Transistor 142 is also configured, along with transistors 114, 118, and 132, to act as a current mirror when the voltage at node 112 is sufficiently above the switching point.

[0028] Current I2 146 flows through resistor 144. Current I2 146 varies with the supply voltage V at node 112. IN The changing current (as shown in Equation 2 below) can be used to determine the supply voltage V. IN Has the threshold been exceeded? In one instance, V IN The voltage rises slowly and approaches the threshold voltage. Current I2 146 flows through transistor 142. The gate-to-source voltage V across transistor 134... GS V2 is the voltage between nodes 128 and 130, as described above. In one example, transistors 120 and 134 are equivalent devices with their gates connected, therefore the gates of transistors 120 and 134 are at the same voltage. The current flowing through transistor 120 is current I1 126, and the current flowing through transistor 134 is a current I 129 similar to I1 126 (due to a 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 will also be at the same voltage. The voltage at the source of transistor 120 is the voltage at node 130. As described above, this voltage is ΔV. GS Therefore, the voltage at node 140 is also ΔV. GS .

[0029] Transistor 136 is located at the bottom of the third branch of voltage monitor 100. At the drain of transistor 136 (e.g., node 140), current I 129 combines with current I2 146 to form current I3 148 flowing through transistor 136. The current through resistor 144 is current I2 146, and the voltage at the second terminal of resistor 144 is ΔV. GS Therefore, the voltage at the first terminal of resistor 144 can be used to determine the voltage drop across resistor 144 and the value of current I2 146.

[0030] In response to the supply voltage V IN Below the threshold voltage that causes the switching node to switch, the voltage at the first terminal of resistor 144 is approximately V. INThis results in a slight error. This is because the voltage drop across transistor 142 is negligible when it is turned on. 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 the current I1 126. However, transistor 142 is sized such that the supply voltage V IN The voltage difference between transistor 142 and ground 124 is not large enough to generate enough current to flow through transistor 142. The voltage at the drain of transistor 142 is close to the voltage at its source, as described above, meaning that transistor 142 is not conducting enough current to its capacity. Therefore, in this example, the current I2 146 flowing through transistor 142 is less than twice the current I1 126. Until V IN Only when the voltage threshold required to cause the switching node to switch is reached does the drain voltage of transistor 142 approach the source voltage of transistor 142, and the source voltage is at the supply voltage V. IN Therefore, the voltage at the drain of transistor 142 is also close to the supply voltage V. IN Therefore, resistor 144 (R TOP The voltage at the first terminal is close to the supply voltage V. IN Equation (2) indicates the value of current I2 146:

[0031]

[0032] In the above description of V IN During operating conditions below the voltage threshold that causes the switching node to switch, the current I2146 varies with the supply voltage V. IN The value changes directly, rather than being twice the value of I1 126.

[0033] The above describes the current flowing through each of the first three branches of voltage monitor 100. The fourth branch of voltage monitor 100 includes transistors 150, 152, 154, and a switching node 156. In one example, transistor 150 has a threshold voltage V of approximately 400mV to 500mV. TH A low threshold voltage transistor. In other instances, different types of transistors may be used. Transistor 150 has a "k" immediately adjacent to it in a circle, indicating that transistor 150 is approximately "k" times the size of transistors 114, 118, and 132, and is therefore capable of conducting approximately "k" times more current than those transistors, as 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 switching node 156 and to the drain of transistor 152.

[0034] In one example, transistor 152 has a threshold voltage V of approximately -100mV. TH An n-type (FET) native transistor. In other instances, different types of transistors may be used. Transistor 152 has a gate coupled to the gate of transistor 134 and a source coupled to the drain of transistor 154. In one instance, transistor 152 is equivalent to transistors 120 and 134.

[0035] In one example, transistor 154 has a threshold voltage V of approximately 700mV. TH A standard threshold voltage transistor is used. In other instances, different types of transistors may be available. Transistor 154 has a source coupled to ground 124 and a gate coupled to the gate of transistor 136. In one instance, transistor 136 also has a threshold voltage V of approximately 700mV. TH The standard voltage threshold transistors. Transistor 154 has a "1" immediately adjacent to it in a circle, while transistor 136 has a "2" immediately adjacent to it in a circle. In this example, these numbers indicate that transistor 136 is approximately twice the size of transistor 154.

[0036] As described above, current I 129 (approximately equal to I1 126) combines with I2 146 to form current I3 148, as shown in equation (3):

[0037] I1 + I2 = I3 (3)

[0038] The current flowing through transistor 136 is I3 148, and transistor 136 is twice the size of transistor 154. The gates of transistors 136 and 154 are coupled together, and the sources of transistors 136 and 154 are also coupled together at ground 124. Therefore, the gate-to-source voltage V of transistors 136 and 154 is... GS They are the same. Since transistor 136 is approximately twice the size of transistor 154, transistor 136 conducts approximately more than twice the current of transistor 154. The current through transistor 136 is I3 / 148, therefore the current through transistor 154 is I3 / 2. Figure 1 The current is shown as 158. In one example, transistors 136 and 154 operate as a second current mirror in voltage monitor 100, wherein the current is scaled proportionally in response to the different sizes of transistors 136 and 154.

[0039] At the top of the fourth branch, the current flowing through transistor 150 is k times the current I1 126 (e.g., kI1). The current kI1 is independent of the supply voltage V. IN This is because the current I1126 is independent of the supply voltage V.IN As described above regarding Equation 1. Therefore, when the supply voltage V IN As the voltage increases, the current kI1 remains approximately constant with time. However, when the supply voltage V... IN As the voltage increases, the current I3 148 at the bottom of the fourth branch (e.g., I3 / 2) will also increase. This is because the current I3 148 is a combination of the currents I129 (approximately equal to I1 126) and I2 146, and the current I2 146 is dependent on V. IN In response to the current 158 ​​rising above the current kI1 in the fourth branch, the switching node 156 switches states. Specifically, in response to the supply voltage V... IN If the voltage is below the monitored threshold, the current kI1 will pull the switching node 156 to a high voltage. When the supply voltage V... IN The increase is sufficient to raise the current 158 ​​above the current kI1 (this is possible because the current 158 ​​increases with the supply voltage V). IN When the current kI1 changes (but not when the current kI1 changes), the switching node 156 is pulled to a low voltage. The voltage at the switching node 156 that causes the node to flip is the switching voltage (e.g., the threshold voltage or voltage threshold).

[0040] The currents kI1 and 158 can be calculated, as well as the switching voltage. The current kI1 passing through transistor 150 is shown in equation (4):

[0041]

[0042] The current 158 ​​is half of the current I3 148, and its calculation is given in equation (5).

[0043]

[0044] When current 158 ​​equals current kI1, the switching node 156 begins to flip. The switching voltage is shown in equation (6):

[0045]

[0046] Equation (6) shows the switching voltage V TRIP With ΔV GS Multiplying by a constant results in a direct proportion. This constant is the resistor 144 (R). TOP ) and resistor 122 (R BOT The values ​​of the two resistors 122 and 144 are derived from their design values ​​based on process variations during the manufacture of the voltage monitor 100. However, if they vary in the same way, then the process variations can be canceled out according to equation (6). The constant k is relative to the device size and is constant and will remain substantially unchanged with process or temperature. Jumping voltage V TRIPThe main change is the effect on ΔV GS The process changes. In one example, the transistor in this paper can be made to a certain size such that ΔV GS The temperature coefficient is approximately zero. In this case, the switching voltage V TRIP It will also not change significantly with temperature.

[0047] As described above, the voltage monitor 100 can be programmed for various voltage thresholds. The values ​​of resistors 122 and 144 can be adjusted to switch the voltage V. TRIP The value of k (relative to device size) can also be adjusted to change the switching voltage V. TRIP Changes. Therefore, in the examples in this paper, the switching voltage V... TRIP It can be finely tuned. The topology of the voltage monitor 100 provides this programmability, meaning the same circuit can be used to provide different switching voltages V. TRIP In some instances, a variable resistor can be used to make the switching voltage V... TRIP Changes. In other instances, a resistor can be connected or disconnected to change the resistance and adjust the switching voltage V. TRIP .

[0048] Another feature of the voltage monitor 100 in the example is that it limits the current I2 146 after reaching the switching point. The current I1 126 is independent of the supply voltage, but the current I2 146 is not. The current clamp 106 can be used to adjust the supply voltage V according to the voltage change. IN The current I2 146 is increased and limited. Current clamp 106 prevents the current I2 146 from exceeding the supply voltage V. IN Increase after reaching a specific value. (Based on the supply voltage V) IN At the specified value, the voltage supply V IN There is sufficient voltage margin between transistor 142 and ground 124 to allow transistor 142 to supply a current approximately twice that of current I1126. If the current flowing through transistor 142 reaches twice the current I1126, then the transistor saturates. Therefore, if the supply voltage V IN If the voltage is increased beyond the specified value, then no additional current will flow through the branch of the voltage monitor 100.

[0049] After creating voltage monitor 100, the switching voltage V... TRIP It cannot be changed unless a variable resistor is used. Therefore, to prevent changes with temperature, transistors 116 and 120 should be sized such that ΔV GS The temperature coefficient is approximately zero. If the ΔV between transistors 116 and 120... GS Since the temperature coefficient is approximately zero, the value of current I1 126 will also be more resistant to temperature changes, which allows current I1 126 to be used as a reference current.

[0050] This paper describes two methods to achieve a near-zero temperature coefficient: one method involves using a transistor in strong inversion operation, and the other involves using a transistor in weak inversion operation. In strong inversion operation, the transistor's Vt GS Significantly higher than the threshold voltage V TH Overdrive voltage V OV It is the gate-to-source voltage V GS Exceeding the threshold voltage V TH In weak inversion operation (e.g., subthreshold region), the transistor operates below the threshold voltage V. TH Gate-to-source voltage V GS operate.

[0051] First, in an example of a strong reversal operation, V GS =V TH +V OV Furthermore, equation (7) shows the differences in these voltages:

[0052] ΔV GS =ΔV TH +ΔV OV (7)

[0053] ΔV GS It is the difference between the gate-source voltages of transistors 116 and 120, as mentioned above. Figure 1 As described. In one example, transistor 116 is a low-voltage transistor (LVT) and the variables related to transistor 116 in the following equations will have the subscript LVT. In this example, transistor 120 is a native transistor (NAT) and the variables related to transistor 120 in the following equations will have the subscript NAT. The variables in equation (7) may be extended based on the operating region in which the transistor operates. For strong inversion operation, ΔV OV Equal to the V of transistor 116 OV Subtract the V of transistor 120 OV Substitute ΔV OV These terms yield equation (8):

[0054] ΔV GS =ΔV TH +[V OV(LVT) –V OV(NAT) (8)

[0055] The definition in equation (9) Figure 1 The current I1 in the middle is 126:

[0056]

[0057] Where k′ is the process transconductance parameter, a constant dependent on the process technology used to fabricate the integrated circuit; and W / L is the ratio of channel width to channel length (in this example for transistor 120, although Equation 9 is also used to find the current through other transistors). Solving Equation (9) yields V OV And the solution V OV Substitute V OV(LVT) and V OV(NAT) The two yielded equation (10):

[0058]

[0059] ΔV TH It is a positive value and equal to the threshold voltage V of transistor 116. TH Subtract the threshold voltage V of transistor 120 TH In one example, the threshold voltage V of transistor 116 TH The threshold voltage V of transistor 120 is greater than zero. TH It is approximately zero or slightly less than zero. Therefore, ΔV TH Greater than zero.

[0060] Equation (11) is a rearrangement of equation (10):

[0061]

[0062] In this example, the LVT transistor is the same size as the NAT transistor, so the W / L variable is the same for each transistor and can be moved outside the parentheses, as shown in equation (11). The next step is to confirm ΔV TH The temperature coefficient and its relationship with ΔV in equation (11) TH The temperature coefficient of the summation terms. To achieve a zero temperature coefficient, ΔV TH The temperature coefficient should be determined by another term in equation (11) (equal to ΔV). OV The temperature coefficients, as shown in equation (7), are offset.

[0063] ΔV TH It is process-dependent, therefore it cannot be adjusted to achieve a zero temperature coefficient. Regarding ΔV OV The size of the transistor can be modified (by modifying the W and L terms). The W and L variables can be adjusted to adjust ΔV. OV The temperature coefficient of the term changes in the appropriate direction to offset ΔV. TH The temperature coefficient. For example, if ΔV TH If the temperature coefficient is Θ, then the other term should be -Θ, causing the terms to cancel each other out. Furthermore, k′ equals the device mobility (μ) multiplied by the oxide capacitance C. OX (k′=μC OX).

[0064] Figure 2 This is a graph 200 showing the temperature coefficient of a strong reversal operation based on an example. Graph 200 depicts the relationship between the reciprocal of (k′ / 2)(W / L) and temperature. The reciprocal of (k′ / 2)(W / L) is plotted on the y-axis. The x-axis is temperature in degrees Celsius. Curve 202 is the reciprocal of (k′ / 2)(W / L) for an LVT device (e.g., transistor 116). Curve 204 is the reciprocal of (k′ / 2)(W / L) for a NAT device (e.g., transistor 120). As seen in graph 200, the reciprocal of this term for the LVT (curve 202) has a lower slope than the reciprocal of this term for the NAT (curve 204). If these two terms are subtracted (in the last part of equation (11)), the result is a negative temperature coefficient. Therefore, with ΔV TH The second term added on the right side of equation (11)

[0065]

[0066] The radical multiplied by the term in parentheses decreases as temperature increases. This means that the second term shown above has a negative temperature coefficient. The second term can be adjusted by changing the W and L values ​​(for LVT and NAT transistors of the same size) until its absolute value equals ΔV. TH The absolute value of ΔV. If those absolute values ​​are equal, then the second term cancels out ΔV. TH And the resulting temperature coefficient is approximately zero.

[0067] For the second case of subthreshold operation or weak inversion operation, ΔV GS =ΔV TH +ΔV OV For this type of operation, a similar mathematical substitution as described above is applied. However, for subthreshold operations, ΔV OV This differs from the case of a strong inversion operation. In one instance, the subthreshold operation is characterized by equation (12):

[0068]

[0069] To offset ΔV TH The temperature coefficient term is adjusted by changing the logarithmic term in equation (12) to equal ΔV. OV This is similar to the strong inversion operation described above. The logarithmic term can be adjusted by adjusting the W and L variables for either or both of the LVT and NAT transistors.

[0070] Figure 3 This is a collection of graphs showing the offset of the temperature coefficient during subthreshold operation. Graph 300 is ΔV THA graph showing the relationship between (in volts) and temperature (in degrees Celsius). The temperature coefficient is shown as curve 302. Curve 302 has a positive slope of approximately 0.13, as indicated in graph 300.

[0071] Chart 304 shows ΔV OV A graph relative to temperature. The temperature coefficient is shown as curve 306. Curve 306 has a negative slope, with the slope at the left edge of curve 306 being approximately zero, the slope in the middle of curve 306 being approximately -0.2, and the slope at the right edge of curve 306 being approximately -0.3.

[0072] In one instance, if ΔV OV The negative value of the slope and ΔV TH If the positive values ​​of the slopes are equal, the result is an umbrella-shaped curve, as shown in curve 310 in Figure 308. Figure 308 shows ΔV GS The graph is relative to temperature, and is a result of combining curves 302 and 306. On curve 310, the initial point (leftmost) and the endpoint (rightmost) are in a V-shape. GS Therefore, as temperature increases, curve 310 does not show an increasing or decreasing gradient; instead, the result is an umbrella-shaped curve. In some instances, curve 310 is not perfectly horizontal, thus indicating an effect due to temperature change, but since the curve is nearly horizontal, this effect is small.

[0073] Figure 4 This is a flowchart of method 400 for voltage monitoring based on various examples in this paper. Although method 400 is combined Figures 1 to 3 This description is not intended to describe anything, but any system configured to execute the methods in any suitable order falls within the scope of this description. In one example, Figure 1 The component executes method 400.

[0074] Method 400 begins at step 410, wherein voltage monitor 100 provides a first current, wherein the first current and the gate-to-source voltage V of the first transistor and the second transistor are... GS The difference is proportional. In one example, the current mirrors of transistors 114 and 118 provide a first current I1 126. The first current I1 126 and the V of transistors 116 and 120 are proportional. GS The difference is proportional. In one example, transistor 116 is the first transistor and transistor 120 is the second transistor.

[0075] Method 400 continues at step 420, wherein voltage monitor 100 provides a second current, wherein the second current and the supply voltage are the same as the gate-to-source voltage V of the first transistor and the second transistor. GSThe difference is proportional to the difference. In one example, the second current is current I2 146, as described in equation (2) above. Equation (2) shows the relationship between current I2 146 and V. IN –ΔV GS Proportional. In one example, transistors 116 and 120 are the first and second transistors, respectively, while transistor 142 is the third transistor that provides the second current.

[0076] Method 400 continues at step 430, wherein voltage monitor 100 compares a first current with a second current to determine the state of a voltage node, wherein if the supply voltage exceeds a threshold, then the voltage node changes state. (See above regarding...) Figure 1 As described, if the current is 158 due to the supply voltage V IN If the current increases and rises above the current kI1, then the switching node 156 changes state. In one example, transistor 150 is the fourth transistor and transistor 152 is the fifth transistor, which conducts current kI1. As part of the second current mirror with transistor 136, transistor 154 is the sixth transistor, which conducts current 158. In other examples, any suitable method can be used to compare the first current with the second current.

[0077] The examples described herein can be used in a wide range of applications. Any end-device system that benefits from an accurate voltage monitoring circuit system can benefit from the examples described herein, thanks to the scalable and compact design of the voltage monitor 100. The voltage monitor 100 operates independently of the operating region of the transistor. That is, in one example, the voltage monitor 100 can utilize a reduced area by using a transistor in strong inversion. In another example, the transistor can be used in low I... Q Subthreshold operations.

[0078] In voltage monitor 100, determine the jump point and ΔV. GS The constant representing the direct proportional relationship between them is scalable and process-independent. This constant can be scaled in two ways (current mirror ratio and resistor ratio). Scaling in both ways allows for fine-tuning of the transition points without significantly increasing the silicon area.

[0079] In the voltage monitor 100, after the transition point has been reached, the described topology I... Q Independent of the increase in V IN This independence is achieved through the load dependence of voltage monitor 100 on V. IN The current I2 146 is achieved by using a current clamp 106 in the branch.

[0080] In some instances, voltage monitor 100 operates in the range of approximately 1.0 volt to approximately 5.0 volt. Furthermore, due to the startup section 102, voltage monitor 100 is self-starting. Compared to conventional systems, voltage monitor 100 has a fast response time.

[0081] The term "coupled" is used throughout this specification. This term may encompass a connection, communication, or signaling path that achieves a functional relationship consistent with this specification. For example, if device A provides a signal to control device B to perform an action, then in a first instance, device A is coupled to device B; or in a second instance, if intervening component C substantially does not alter the functional relationship between device A and device B such that device B is controlled by device A via a control signal provided by device A, then device A is coupled to device B through intervening component C.

[0082] A device “configured to” perform a task or function may be configured by the manufacturer at manufacturing time (e.g., programmed and / or hardwired) to perform the function and / or may be configured by the user after manufacturing (or reconfigurable) to perform the function and / or other additional or alternative functions. The configuration may be achieved through firmware and / or software programming of the device, through the construction and / or layout of hardware components, and the interconnection of the device, or a combination thereof.

[0083] The circuits or devices described herein as containing specific components may alternatively be adapted to be coupled to those components to form the described circuit system or device. For example, a structure described as containing one or more semiconductor elements (e.g., transistors), one or more passive elements (e.g., resistors, capacitors, and / or inductors), and / or one or more sources (e.g., voltage and / or current sources) may alternatively contain only semiconductor elements within a single physical device (e.g., a semiconductor die and / or integrated circuit (IC) package) and may be adapted to be coupled to at least some of the passive elements and / or sources during or after manufacturing, for example by an end user and / or a third party, to form the described structure.

[0084] While the use of specific transistors is described herein, other transistors (or equivalent devices) may be used alternatively. For example, a p-type MOSFET may be used instead of an n-type silicon metal-oxide-semiconductor FET (“MOSFET”) with little or no change to the circuitry. Furthermore, other types of transistors (such as bipolar junction transistors (BJTs)) may be used.

[0085] The circuits described herein can be reconfigured to include replacement components to provide functionality at least partially similar to that available prior to the component replacement. Unless otherwise stated, components shown as resistors generally represent one or more elements coupled in series and / or parallel to provide the impedance represented by the illustrated resistor. For example, a resistor or capacitor shown and described herein as a single component can instead be multiple resistors or capacitors coupled in parallel between the same nodes. For example, a resistor or capacitor shown and described herein as a single component can instead be multiple resistors or capacitors coupled in series between the same two nodes as the single resistor or capacitor.

[0086] In the foregoing description, the phrase “grounding” includes chassis grounding, ground grounding, floating grounding, virtual grounding, digital grounding, common grounding, and / or any other form of grounding connection applicable to or suited to the teachings of this description. Unless otherwise stated, “about,” “approximately,” or “substantially” preceding a value means + / - 10% of that value. Modifications are possible in the described examples, and other examples are possible within the scope of the claims.

Claims

1. A voltage monitor, comprising: A first transistor is coupled between a first supply voltage and a second supply voltage; A second transistor is coupled between the first supply voltage and the second supply voltage; The voltage monitor is configured to: Provide a first current that is proportional to the difference between the gate-to-source voltages of the first transistor and the second transistor; In response to the first supply voltage being lower than a threshold, a second current is provided that is proportional to the difference between the first supply voltage and the gate-to-source voltage of the first transistor and the second transistor. The first current is compared with the second current to determine the voltage value at which the state changes in response to the first supply voltage exceeding the threshold. and The second current is clamped in response to the first supply voltage exceeding the threshold.

2. The voltage monitor of claim 1, wherein in response to the first supply voltage exceeding the threshold, the second current is greater than the first current.

3. The voltage monitor of claim 1, wherein the first transistor and the second transistor are sized to reduce the temperature coefficient of the difference between the gate-to-source voltages of the first transistor and the second transistor.

4. The voltage monitor of claim 1, wherein the gate of the first transistor is coupled to the gate of the second transistor.

5. The voltage monitor of claim 1, 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 monitor of claim 1, wherein the voltage monitor includes a third transistor coupled to the first supply voltage and coupled to a resistor, the third transistor being configured to provide the second current.

7. The voltage monitor of claim 6, wherein the third transistor is configured to clamp the second current in response to the first supply voltage exceeding the threshold.

8. The voltage monitor of claim 1, wherein the voltage monitor is configured to provide the first current using a current mirror.

9. The voltage monitor of claim 1, wherein the voltage monitor includes a first and a second resistor, the first resistor being coupled to the second transistor, the first and second resistors being sized to determine the threshold.

10. The voltage monitor of claim 1, wherein the first transistor and the second transistor are configured to bring the temperature coefficient of the difference to near zero.

11. A voltage monitoring system, comprising: A reference current generator includes 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, and the current mirror is configured to provide a first current proportional to the difference between the gate-to-source voltages of the first transistor and the second transistor. 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, wherein in response to a supply voltage below a threshold, the third transistor is configured to provide a second current proportional to the difference between the supply voltage and the gate-to-source voltages of the first and second transistors. 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; as well as The fifth transistor has 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; The voltage monitoring system is configured to: The first current is compared with the second current to determine the voltage value at which the state changes in response to the supply voltage exceeding the threshold; and The second current is clamped in response to the supply voltage exceeding the threshold.

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

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

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

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

16. The voltage monitoring system of claim 11, wherein the second current terminal of the first transistor is coupled to the current mirror, and the second current terminal of the second transistor is coupled to the current mirror.

17. The voltage monitoring system of claim 11, wherein the first transistor and the second transistor are configured such that the temperature coefficient of the difference between the gate-to-source voltages of the first transistor and the second transistor is brought to near zero.

18. A voltage monitor, comprising: A reference current generator having a current mirror configured to provide a first current proportional to the difference between the gate-to-source voltages of a first transistor and a second transistor. 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 first terminal of a resistor, wherein in response to a supply voltage below a threshold, the third transistor is configured to provide a second current proportional to the difference between the supply voltage and the gate-to-source voltages of the first and second transistors. as well as A fourth transistor has 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 indicating that the supply voltage is higher than the threshold. in: The resistor includes a second terminal coupled to the source of a fifth transistor, wherein the gate of the fifth transistor is coupled to the gate of the first transistor and the gate of the second transistor.

19. The voltage monitor of claim 18, wherein the third transistor is configured to clamp the second current in response to the supply voltage exceeding the threshold.

20. The voltage monitor of claim 18, wherein the resistor is a first resistor, and wherein the threshold is based at least in part on the value of the first resistor and the value of a second resistor coupled to the source of the second transistor.

21. The voltage monitor of claim 18, wherein the first transistor and the second transistor are sized to reduce the temperature coefficient of the difference between the gate-to-source voltages of the first transistor and the second transistor.

22. The voltage monitor of claim 18, wherein the first transistor and the second transistor are configured such that the temperature coefficient of the difference is close to zero.

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