Current measurement circuit

Abstract

To provide a current measurement circuit capable of performing high-accuracy current measurement without performing fuse trimming.SOLUTION: A current measurement circuit includes a first current-voltage conversion circuit that converts a current to be measured into a first voltage, a second current-voltage conversion circuit that converts a reference current into a second voltage, and a first comparator that outputs a comparison result between the first voltage and the second voltage.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The disclosed technology relates to a current measurement circuit.

Background Art

[0002] As a technology related to an AD converter that measures current, the following technology is known. For example, in Patent Document 1, a current / voltage conversion circuit that converts the current input from a current input terminal into a voltage, a voltage / current conversion circuit that converts the voltage converted by this current / voltage conversion circuit into a current, and a current from a current source and the current converted by the voltage / current conversion circuit are compared, and an A / D converter equipped with a current comparator that outputs the current input from the current input terminal as a digital signal according to the comparison result is described.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Generally, a semiconductor integrated circuit having an NFC (Near Field Communication) function requires a mechanism for measuring the radio wave intensity and adjusting the capacitance C from the measurement result when incorporating the capacitance C of the LC antenna. In order to measure the radio wave intensity, it is necessary to measure the voltage or current. Since there is a limiter circuit for the purpose of suppressing an excessive rise in voltage, voltage measurement is difficult. Therefore, a current measurement method is generally used.

[0005] The current measurement circuit used in NFC needs to operate in a state where sufficient power is not supplied, and a low operating current is required. For this reason, a configuration simpler than that of a general AD converter is used as the current measurement circuit.

[0006] However, since a simple-configuration current measurement circuit has a large measurement error, adjustment by FUSE trimming is required. Therefore, in a semiconductor process without a FUSE, it has been difficult to form a simple-configuration current measurement circuit having appropriate current measurement accuracy.

[0007] The disclosed technology has been made in view of the above points, and an object thereof is to provide a current measurement circuit capable of performing high-precision current measurement without performing FUSE trimming.

Means for Solving the Problems

[0008] The current measurement circuit according to the disclosed technology includes a first current-voltage conversion circuit that converts a measurement target current into a first voltage, a second current-voltage conversion circuit that converts a reference current into a second voltage, and a first comparator that outputs a comparison result between the first voltage and the second voltage.

Effects of the Invention

[0009] According to the current measurement circuit according to the disclosed technology, it is possible to perform high-precision current measurement without performing FUSE trimming.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2A

Figure 2B

Figure 3

Figure 4

Figure 5A

Figure 5B

Figure 6

Figure 7

Figure 8A

Figure 8B

Figure 9

Figure 10

Figure 11A

Figure 11B

Embodiments for Carrying Out the Invention

[0011] First, the current measurement circuit according to the comparative example will be described. FIG. 1 is a circuit diagram showing an example of the configuration of a current measurement circuit 10X according to the comparative example. The current measurement circuit 10X according to the comparative example includes a current mirror circuit D x , a resistance element R a and a comparator C X .

[0012] The current mirror circuit D Xhas transistors M0 and M1 which are P-channel MOSFETs (metal-oxide-semiconductor field-effect transistors). For transistor M0, the source is connected to the power supply line VDD, and the gate is connected to its own source and the gate of transistor M1. To the drain of transistor M0, the current to be measured (hereinafter referred to as the measured current I m is input in the form of a sink current. For transistor M1, the source is connected to the power supply line VDD, the gate is connected to the gate of transistor M0, and the drain is connected to one end of the resistor element R a . The other end of the resistor element R a is connected to the ground line. The connection point between the drain of transistor M1 and the resistor element R a is connected to the non-inverting input terminal of the comparator C X .

[0013] The measured current I m flows through transistor M0, and the mirror current I a flows through transistor M1 and the resistor element R mm . The mirror ratio of the current mirror circuit D X is 1:1, so I m =I mm . The voltage V a generated by the flow of the mirror current I mm (=I m ) through the resistor element R a is input to the non-inverting input terminal of the comparator C X . The reference voltage V X is input to the inverting input terminal of the comparator C ref . The comparator C X compares the voltage V a with the reference voltage V ref and outputs the comparison result.

[0014] The operation of the current measurement circuit 10X according to the comparative example will be described below. In the current measurement circuit 10X, the voltage V a is represented by the following formula (1), respectively. Va =R a ×I mm =R a ×I m ···(1)

[0015] V a =V ref The measured current I at which this occurs m is defined as the current threshold I th . The comparator C X determines whether the measured current I m is greater than or less than the current threshold I th . In the current measurement circuit 10X, suppressing the variation of the current threshold I th is important for improving the current measurement accuracy. I m =I th When this is the case, the following equations (2) and (3) hold. R a ×I m =V ref ···(2) I m =V ref / R a =I th ···(3)

[0016] Here, assume that the current threshold I th varies due to manufacturing variations. The current threshold I th can be said to vary due to the variation of the resistance element R a from equation (3). Therefore, the varied current threshold I th ´ is represented by the following equation (4). In equation (4), R a ´ is the resistance element R a whose resistance value has varied. I th ´=V ref / R a ´×I ref ···(4)

[0017] Generally, resistance elements formed in a semiconductor process are formed with an error of ±20% with respect to the design value. Therefore, the current threshold I thIt also varies by ±20% with respect to the design value. That is, according to the current measurement circuit 10X according to the comparative example, the measurement error of the current becomes ±20%.

[0018] FIG. 2A is a graph showing an example of the relationship between the current I to be measured m and the voltage V a and the reference voltage V ref . The intersection of the straight line indicating the voltage V m proportional to the current I to be measured a and the straight line indicating the reference voltage V ref maintained at a constant level becomes the current threshold I th .

[0019] FIG. 2B shows a case where the resistance value of the resistance element R a varies from the case shown in FIG. 2A. The intersection of the straight line indicating the fluctuated voltage V a ' and the straight line indicating the reference voltage V ref becomes the fluctuated current threshold I th '. When the resistance element R a varies to R a ', the slope of the straight line indicating the voltage V a ' becomes larger than the slope of the straight line indicating the voltage V a . As a result, the intersection position with the straight line indicating the reference voltage V ref shifts to the left. This means that as the resistance element R a varies in the increasing direction, the current threshold I th varies in the decreasing direction. Thus, according to the current measurement circuit 10X according to the comparative example, since the variation of the resistance element R a is directly reflected in the variation of the current threshold I th , the measurement error becomes large. In order to reduce the measurement error, it is conceivable to adjust the resistance value of the resistance element R a by FUSE trimming, but it is difficult to cope in a semiconductor process without a FUSE being provided.

[0020] Hereinafter, embodiments of the disclosed technology will be described with reference to the drawings. In each drawing, substantially the same or equivalent components or parts are given the same reference numerals.

[0021] [First Embodiment] FIG. 3 is a circuit block diagram showing an example of the configuration of a current measurement circuit 10 according to the first embodiment of the disclosed technology. The current measurement circuit 10 measures the magnitude of a measurement target current I m by determining it using a current threshold value. The current measurement circuit 10 has a function of measuring the magnitude of the measurement target current I m . The current measurement circuit 10 can be used as a simple AD converter. The current measurement circuit 10 may constitute a part of a semiconductor integrated circuit having, for example, an NFC function. The current measurement circuit 10 includes current-voltage conversion circuits A1, B1, and a comparator C1. The determination unit U1 is constituted by the current-voltage conversion circuits A1, B1, and the comparator C1.

[0022] The current-voltage conversion circuit A1 receives the measurement target current I m . The current-voltage conversion circuit A1 converts the measurement target current I m into a voltage V a1 . That is, the magnitude of the voltage V a1 is proportional to the magnitude of the measurement target current I m .

[0023] The current-voltage conversion circuit B1 receives a reference current I ref . The current-voltage conversion circuit B1 converts the reference current I ref into a voltage V b1 . That is, the magnitude of the voltage V b1 is proportional to the magnitude of the reference current I ref .

[0024] The comparator C1 compares the voltage V a1 with the voltage V b1 and outputs a comparison result. Specifically, when the voltage V a1 is greater than the voltage V b1 , the comparator C1 outputs a high-level output signal S out1 , and when the voltage V a1 is less than the voltage V b1 , the comparator C1 outputs a low-level output signal S out1 .

[0025] FIG. 4 is a circuit diagram showing an example of a detailed configuration of the current measurement circuit 10. The current-voltage conversion circuit A1 is a measurement target current I m generates a mirror current I mm1 which is proportional to the magnitude of the current mirror circuit D a1 and the mirror current I mm1 flows through the resistor element R a1 . The current mirror circuit D a1 is a P-channel MOSFET (metal-oxide-semiconductor field-effect transistor) transistor M a0 and M a1 . The transistor M a0 has its source connected to the power supply line VDD and its gate connected to its own source and the gate of the transistor M a1 . The drain of the transistor M a0 is input with the measurement target current I m in a sink current manner. The transistor M a1 has its source connected to the power supply line VDD, its gate connected to the gate of the transistor M a0 , and its drain connected to one end of the resistor element R a1 . The other end of the resistor element R a1 is connected to the ground line. The connection point between the drain of the transistor M a1 and the resistor element R a1 is connected to the non-inverting input terminal of the comparator C1.

[0026] The measurement target current I a0 flows through the transistor M m , and the mirror current I a1 and the resistor element R a1 flows through the mirror current I mm1 . In the present embodiment, the mirror ratio of the current mirror circuit D a1 is 1:1, and therefore I m = I mm1 . The mirror current I a1 flows through the resistor element R mm1 (= I mThe voltage V generated by the flow of a1 is input to the non-inverting input terminal of the comparator C1.

[0027] The current-voltage conversion circuit B1 is a current mirror circuit D that generates a mirror current I ref proportional to the magnitude of the reference current I refm1 and a resistor element R b1 through which the mirror current I refm1 flows. The current mirror circuit D b1 includes transistors M b1 and M b0 which are P-channel MOSFETs. The source of the transistor M b1 is connected to the power supply line VDD, and the gate is connected to its own source and the gate of the transistor M b0 . The reference current I b1 is input to the drain of the transistor M b0 in a sink current manner. The source of the transistor M ref is connected to the power supply line VDD, the gate is connected to the gate of the transistor M b1 , and the drain is connected to one end of the resistor element R b0 . The other end of the resistor element R b1 is connected to the ground line. The connection point between the drain of the transistor M b1 and the resistor element R b1 is connected to the inverting input terminal of the comparator C1. b1

[0028] The reference current I b0 flows through the transistor M ref , and the mirror current I b1 flows through the transistor M b1 and the resistor element R refm1 . In this embodiment, the mirror ratio of the current mirror circuit D b1 is 1:1, and thus I ref = I refm1 . The voltage V b1 generated by the flow of the mirror current I refm1 (= I ref ) through the resistor element R b1is input to the inverting input terminal of the comparator C1.

[0029] The operation of the current measurement circuit 10 according to this embodiment will be described below. In the current measurement circuit 10, the voltages V a1 and V b1 are represented by the following equations (5) and (6), respectively. V a1 = R a1 × I mm1 = R a1 × I m ···(5) V b1 = R b1 × I refm = R b1 × I ref ···(6)

[0030] V a1 = V b1 When the value of the measurement target current I m is defined as the current threshold I th1 The comparator C1 determines whether the measurement target current I m is greater than or less than the current threshold I th1 In the current measurement circuit 10, suppressing the variation of the current threshold I th1 is important for improving the current measurement accuracy. When I m = I th1 the following equations (7) and (8) hold. R a1 × I m = R b1 × I ref ···(7) I m = R b1 / R a1 × I ref = I th1 ···(8)

[0031] Here, it is assumed that the current threshold I th1 varies due to manufacturing variations. The current threshold I th1 is obtained from equation (8) for the resistance elements R a1 and R b1It can be said that it varies due to the variation. Therefore, the fluctuated current threshold I th1 ´ is represented by the following formula (9). In formula (9), R a1 ´ and R b1 ´ are the resistance elements R with their resistance values fluctuated a1 and R b1 respectively. I th1 ´ = R b1 ´ / R a1 ´ × I ref ···(9)

[0032] When the resistance elements R a1 and R b1 formed by the semiconductor process are of the same type, the tendency of the variation of their resistance values is the same. For example, when the resistance element R a1 is formed with a +10% error with respect to the design value, the resistance element R b1 is also formed with a +10% error with respect to the design value. Therefore, the following formula (10) holds, and formula (11) below is derived from formulas (8) to (10). Formula (11) indicates that even if the respective resistance values of the resistance elements R a1 and R b1 vary, the current threshold I th1 does not vary. R b1 ´ / R a1 ´ = R b1 / R a1 ···(10) I th1 ´ = I th1 ···(11)

[0033] Figure 5A is a graph showing an example of the relationship between the current I m to be measured and the voltages V a1 , V b1 . The intersection of the straight line indicating the voltage V m proportional to the current I a1 to be measured and the straight line indicating the voltage V b1 maintaining a constant level is the current threshold I th1 .

[0034] Figure 5B shows the resistance elements R a1 and Rb1 Shows the case where each resistance value has changed from the case shown in FIG. 5A. The resistance element R a1 The voltage V that changes with the change of a1 The straight line indicating V′ and the resistance element R b1 The voltage V that changes with the change of b1 The intersection of the straight line indicating V′ is the changed current threshold I th1 ′.

[0035] The resistance element R a1 Changes to R a1 ′, so that the slope of the straight line indicating the voltage V a1 ′ is greater than the slope of the straight line indicating the voltage V a1 . The resistance element R b1 Changes to R b1 ′, so that the level of the voltage V b1 ′ is higher than the level of the voltage V b1 . As a result, the position in the horizontal axis direction of the intersection of the straight line indicating the voltage V a1 ′ and the straight line indicating the voltage V b1 ′ is the same as before the change. This means that the current threshold I a1 and R b1 does not change due to the change in each resistance value (I th1 ′ = I th1 ). th1 ) is shown.

[0036] As described above, according to the current measurement circuit 10 according to the embodiment of the disclosed technology, the variation of the current threshold I th1 due to manufacturing variations can be suppressed, so that high-precision current measurement can be performed without performing FUSE trimming.

[0037] [Second Embodiment] FIG. 6 is a circuit block diagram showing an example of the configuration of a current measurement circuit 10A according to a second embodiment of the disclosed technology. The current measurement circuit 10A determines the measurement target current I m by using two current thresholds, so as to measure the measurement target current I mIt has a function of measuring the magnitude. The current measurement circuit 10A has current-voltage conversion circuits A2 and B2 and a comparator C2 in addition to the current-voltage conversion circuits A1, B1 and the comparator C1. The current-voltage conversion circuits A1, B1 and the comparator C1 constitute a determination unit U1, and the current-voltage conversion circuits A2, B2 and the comparator C2 constitute a determination unit U2. Since the configuration of the determination unit U1 is the same as that of the current measurement circuit 10 according to the above-described first embodiment, the description thereof is omitted.

[0038] The current-voltage conversion circuit A2 receives the current I to be measured m as an input. The current-voltage conversion circuit A2 converts the current I to be measured m into a voltage V a2 . That is, the magnitude of the voltage V a2 is proportional to the magnitude of the current I to be measured m .

[0039] The current-voltage conversion circuit B2 receives the reference current I ref as an input. The current-voltage conversion circuit B2 converts the reference current I ref into a voltage V b2 . That is, the magnitude of the voltage V b2 is proportional to the magnitude of the reference current I ref .

[0040] The comparator C2 compares the voltage V a2 with the voltage V b2 and outputs a comparison result. Specifically, when the voltage V a2 is greater than the voltage V b2 , the comparator C2 outputs a high-level output signal S out2 , and when the voltage V a1 is less than the voltage V b1 , the comparator C2 outputs a low-level output signal S out2 .

[0041] FIG. 7 is a circuit diagram showing an example of the detailed configuration of the current measurement circuit 10A. The current-voltage conversion circuit A2 has a mirror current I m proportional to the magnitude of the current I to be measured mm2Current mirror circuit D that generates a2 and mirror current I mm2 flows through resistor element R a2 and has. Current mirror circuit D a2 is transistor M which is a P-channel MOSFET a0 and M a2 has. Transistor M a0 has its source connected to the power supply line VDD and its gate connected to its own source and the gate of transistor M a2 . The drain of transistor M a0 is input with the current I to be measured m in a sink current manner. Transistor M a2 has its source connected to the power supply line VDD, its gate connected to the gate of transistor M a0 , and its drain connected to one end of resistor element R a2 . The other end of resistor element R a2 is connected to the ground line. The connection point between the drain of transistor M a2 and resistor element R a2 is connected to the non-inverting input terminal of comparator C2.

[0042] The measured current I a0 flows through transistor M m , and the mirror current I a2 flows through transistor M a2 and resistor element R mm2 . In this embodiment, the mirror ratio of current mirror circuit D a2 is 1:1, and therefore I m = I mm2 . The voltage V a2 generated by the mirror current I mm2 (= I m ) flowing through resistor element R a2 is input to the non-inverting input terminal of comparator C2.

[0043] The current-voltage conversion circuit B2 is a current mirror circuit D that generates a mirror current I ref proportional to the magnitude of the reference current I refm2 b2 ​and a resistor element R through which a mirror current I refm2 flows. The current mirror circuit D b2 includes a transistor M b2 which is a P-channel MOSFET b0 and M b2 . The transistor M b0 has its source connected to the power supply line VDD and its gate connected to its own source and the gates of each of the transistors M b2 . The drain of the transistor M b0 receives a reference current I ref in a sink current manner. The transistor M b2 has its source connected to the power supply line VDD, its gate connected to the gate of the transistor M b0 , and its drain connected to one end of the resistor element R b2 . The other end of the resistor element R b2 is connected to the ground line. The connection point between the drain of the transistor M b2 and the resistor element R b2 is connected to the inverting input terminal of the comparator C2.

[0044] A reference current I b0 flows through the transistor M ref , and a mirror current I b2 flows through the transistor M b2 and the resistor element R refm2 . In this embodiment, the mirror ratio of the current mirror circuit D b2 is 1:2, and thus 2I ref =I refm2 . A voltage V b2 generated by the flow of the mirror current I refm2 (=2I ref ) through the resistor element R b2 is input to the inverting input terminal of the comparator C2.

[0045] The operation of the current measurement circuit 10A according to this embodiment will be described below. Note that, regarding the determination unit U1, the fact that the above-described equations (5) to (11) hold is the same as that of the current measurement circuit 10 according to the first embodiment. In the current measurement circuit 10A, the voltage Va2 and V b2 are represented by the following formulas (12) and (13), respectively. V a2 = R a2 × I mm2 = R a2 × I m ···(12) V b2 = R b2 × I refm2 = R b2 × 2I ref ···(13)

[0046] In this embodiment, R a2 = 1 / 2R a1 and R b2 = 1 / 2R b1 are assumed. Therefore, the following formulas (14) and (15) hold for the voltages V a2 and V b2 . V a2 = R a1 / 2 × I m ···(14) V b2 = R b1 × I ref ···(15)

[0047] V a2 = V b2 The value of the measured current I m at this time is defined as the current threshold I th2 . The comparator C2 determines whether the measured current I m is greater than or less than the current threshold I th2 . In the current measurement circuit 10A, suppressing the variation of the current threshold I th2 is important for improving the current measurement accuracy. When I m = I th2 , the following formulas (16) and (17) hold. R a1 / 2 × I m = R b1 × I ref ···(16) I m = R b1 / Ra1 ×2I ref =I th2 ···(17)

[0048] As is clear from comparing Equation (8) and Equation (17), the current threshold I th2 is twice the current threshold I th1 . Thus, by using two different current thresholds I th1 and I th2 to determine the current I m to be measured, it becomes possible to improve the resolution of current measurement.

[0049] Here, it is assumed that the current threshold I th2 varies due to manufacturing variations. The current threshold I th2 can be said to vary due to the variations in the resistance elements R a1 and R b1 (R a2 and R b2 ). Therefore, the varied current threshold I th2 ' is represented by the following Equation (18). In Equation (18), R a1 ' and R b1 ' are the resistance elements R a1 and R b1 whose resistance values have varied, respectively. I th2 ' = R b1 ' / R a1 ' × 2I ref ···(18)

[0050] When the resistance elements R a1 and R b1 (R a2 and R b2 ) formed in the semiconductor process are of the same type, the tendency of the variations in their resistance values is the same. For example, when the resistance element R a1 (R a2 ) is formed with a +10% error with respect to the design value, the resistance element R b1 (R b2) is formed with an error of +10% with respect to the design value. Therefore, the above equation (10) holds, and the following equation (19) is derived from equations (10), (17), and (18). Equation (19) is for the resistance element R a1 and R b1 (R a2 and R b2 ), indicating that even if the resistance values of each vary, the current threshold I th2 does not vary. I th2 ´≒I th2 ···(19)

[0051] Figure 8A is a graph showing an example of the relationship between the current I m to be measured and the voltages V a1 , V a2 , V b1 , V b2 . The intersection of the straight line indicating the voltage V m proportional to the current I a1 to be measured and the straight line indicating the voltage V b1 maintaining a constant level is the current threshold I th1 . Similarly, the intersection of the straight line indicating the voltage V m proportional to the current I a2 to be measured and the straight line indicating the voltage V b2 maintaining a constant level is the current threshold I th2 . In this embodiment, the levels of the voltages V b1 and V b2 are the same (V b1 =V b2 ).

[0052] Figure 8B shows the case where the resistance values of the resistance elements R a1 , R b1 , R a2 and R b2 have changed from the case shown in Figure 8A. The intersection of the straight line indicating the voltage V a1 ´ that varies with the variation of the resistance element R a1 and the straight line indicating the voltage V b1 ´ that varies with the variation of the resistance element R b1 is the changed current threshold I th1 ´. Similarly, for the resistance element R a2The voltage V that varies with the variation of a2 The straight line indicating ´ and the resistance element R b2 The voltage V that varies with the variation of b2 The intersection point of the straight line indicating ´ is the variable current threshold I th2 ´.

[0053] The resistance element R a1 Changes to R a1 ´, and as a result, the slope of the straight line indicating the voltage V a1 ´ becomes larger than the slope of the straight line indicating the voltage V a1 . The resistance element R b1 Changes to R b1 ´, and as a result, the level of the voltage V b1 ´ becomes higher than the level of the voltage V b1 . As a result, the position in the horizontal axis direction of the intersection point of the straight line indicating the voltage V a1 ´ and the straight line indicating the voltage V b1 ´ is the same as before the variation. This indicates that the current threshold I a1 and R b1 does not vary due to the variation of (I th1 ´ = I th1 th1 th1 ).

[0054] Similarly, when the resistance element R a2 changes to R a2 ´, the slope of the straight line indicating the voltage V a2 ´ becomes larger than the slope of the straight line indicating the voltage V a2 . The resistance element R b2 changes to R b2 ´, and as a result, the level of the voltage V b2 ´ becomes higher than the level of the voltage V b1 . As a result, the position in the horizontal axis direction of the intersection point of the straight line indicating the voltage V a2 ´ and the straight line indicating the voltage V b2 ´ is the same as before the variation. This indicates that the current threshold I a2 and R b2 does not vary due to the variation of (I th2 ´ = I th2 th2 th2 ).

[0055] As described above, according to the current measurement circuit 10A according to the second embodiment of the disclosed technology, the current threshold I due to manufacturing variations th1 and I th2 variations can be suppressed, so that high-precision current measurement can be performed without performing FUSE trimming.

[0056] Also, according to the current measurement circuit 10A, two different current thresholds I th1 and I th2 are used to measure the current to be measured I m is determined, so that the resolution of the current measurement can be increased as compared with the case where the current measurement is performed using one current threshold.

[0057] Also, according to the current measurement circuit 10A, V b2 =V b1 is satisfied, and the input voltages of the comparators C1 and C2 are made constant. As a result, the input voltages of the comparators C1 and C2 are kept within the allowable range and low-voltage operation becomes possible. When the input voltages and operating voltages of the comparators C1 and C2 do not pose a problem, the resistance values of all the resistance elements may be the same, and the input voltages of the respective comparators may be made different from each other.

[0058] [Third Embodiment] FIG. 9 is a circuit block diagram showing an example of the configuration of a current measurement circuit 10B according to the third embodiment of the disclosed technology. The current measurement circuit 10B determines the current to be measured I m using three or more plural current thresholds, thereby having a function of measuring the magnitude of the current to be measured I m .

[0059] The current measurement circuit 10B includes n (n≧3) determination units U1, U2, ··· U n . Each of the determination units U1, U2, ··· U n includes a current-voltage conversion circuit A m that converts the current to be measured I ak into a voltage V k , and a reference current I ref into a voltage Vbk Current-voltage conversion circuit B for conversion k and voltage V ak and voltage V bk Comparator C that outputs the comparison result with k and includes. The current measurement circuit 10B is V ak =V bk Measurement target current I at which m The current threshold I which is the value of thk Is configured to be different for each determination unit U k For each. Note that k is a code corresponding to any one of n determination units U1, U2, ··· U n And 1 ≤ k ≤ n.

[0060] Current-voltage conversion circuit A k Receives the measurement target current I m The current-voltage conversion circuit A k Converts the measurement target current I m Into voltage V ak That is, the magnitude of voltage V ak Is proportional to the magnitude of the measurement target current I m

[0061] Current-voltage conversion circuit B k Receives the reference current I ref The current-voltage conversion circuit B k Converts the reference current I ref Into voltage V bk That is, the magnitude of voltage V bk Is proportional to the magnitude of the reference current I ref

[0062] Comparator C k Compares voltage V ak And voltage V bk And outputs the comparison result. Specifically, comparator C k When voltage V ak Is greater than voltage V bk Outputs a high-level output signal S outk And when voltage V ak Is less than voltage V bk Outputs a low-level output signal S​​outk Output.

[0063] 10 is a circuit diagram showing an example of a detailed configuration of the current measuring circuit 10B. k is the current to be measured, I m The mirror current I is proportional to the magnitude of mmk A current mirror circuit D ak and the mirror current I mmk Current flows through the resistive element R ak Current mirror circuit D ak is a P-channel MOSFET transistor M a0 and M ak The transistor M a0 The source is connected to the power supply line VDD, and the gate is connected to its own source and the transistor M ak The gate of the transistor M a0 The drain of the m is input in the form of a sink current. Transistor M ak The source is connected to the power supply line VDD and the gate is connected to the transistor M a0 The drain is connected to the gate of the resistor element R ak is connected to one end of the resistor element R ak The other end of the transistor M is connected to the ground line. ak The drain and resistor R ak The connection point with comparator C k This is connected to the non-inverting input terminal of the GND terminal.

[0064] Transistor M a0 is the current to be measured, I m flows, and transistor M ak and resistive element R ak is the mirror current I mmk flows through the resistor element R ak Mirror current I mmk The voltage V generated by the flow of ak is comparator C k This is input to the non-inverting input terminal.

[0065] Current-Voltage Conversion Circuit B k generates a mirror current I ref proportional to the magnitude of the reference current I refmk using a current mirror circuit D bk and has a resistor element R refmk through which the mirror current I bk flows. The current mirror circuit D bk includes transistors M b0 and M bk which are P-channel MOSFETs. Transistor M b0 has its source connected to the power supply line VDD and its gate connected to its own source and the gate of transistor M bk . The reference current I b0 is input to the drain of transistor M ref in a sink current manner. Transistor M bk has its source connected to the power supply line VDD, its gate connected to the gate of transistor M b0 , and its drain connected to one end of the resistor element R bk . The other end of the resistor element R bk is connected to the ground line. The connection point between the drain of transistor M bk and the resistor element R bk is connected to the inverting input terminal of a comparator C k .

[0066] The reference current I b0 flows through transistor M ref , and the mirror current I bk flows through transistor M bk and the resistor element R refmk . The voltage V bk generated by the flow of the mirror current I refm2 through the resistor element R bk is input to the inverting input terminal of the comparator C k .

[0067] As described above, the current measurement circuit 10B has a current threshold I ak =V bk which is the value of the measurement target current I m . thkis configured to be different for each determination unit U k For example, the determination unit U k The current threshold value I in thk May be set to k times the current threshold value I in the determination unit U1 th1 To achieve this, for example, the current-voltage conversion circuit A k The current mirror circuit D that constitutes ak The mirror ratio of and the resistance element R ak At least one of the resistance values of may be configured to be different for each determination unit U k

[0068] The operation of the current measurement circuit 10B according to this embodiment will be described below. In the current measurement circuit 10B, the voltages V ak And V bk Are respectively represented by the following equations (20) and (21). Here, I mmk = I m I refmk = I ref Is assumed to be V ak = R ak × I mmk = R ak × I m ···(20) V bk = R bk × I refmk = R bk × I ref ···(21)

[0069] V ak = V bk The value of the measurement target current I at which m Is defined as the current threshold value I thk The comparator C k Determines whether the measurement target current I m Is greater than or less than the current threshold value I thk In the current measurement circuit 10B, suppressing the variation of the current threshold value I thk Is important for improving the current measurement accuracy. When I m = I thk The following equations (22) and (23) hold.​ R ak ×I m =R bk ×I ref ···(22) I m =R bk / R ak ×I ref =I thk ···(23)

[0070] Here, it is assumed that the current threshold I thk varies due to manufacturing variations. The current threshold I thk can be said to vary due to the variations in the resistance elements R ak and R bk . Therefore, the varied current threshold I thk ´ is represented by the following equation (24). In equation (24), R ak ´ and R bk ´ are the resistance elements R ak and R bk with their resistance values varied, respectively. I thk ´=R bk ´ / R ak ´×I ref ···(24)

[0071] When the resistance elements R ak and R bk formed in the semiconductor process are of the same type, the tendency of the variations in their resistance values is the same. For example, when the resistance element R ak is formed with a +10% error from the design value, the resistance element R bk is also formed with a +10% error from the design value. Therefore, the following equation (25) holds, and equation (26) is derived from equations (23) to (25). Equation (26) shows that even when the resistance values of the resistance elements R ak and R bk vary, the current threshold I thk does not vary.

[0072] R b1 ´ / R a1 ´=R b1 / R a1···(25) I thk ´ = I thk ···(26)

[0073] Figure 11A is a graph showing an example of the relationship between the current I to be measured m and the voltage V ak , V bk . The intersection of the straight line indicating the voltage V m proportional to the current I to be measured and the straight line indicating the voltage V ak maintaining a constant level is the current threshold I bk . thk

[0074] Figure 11B shows the case where the resistance values of the resistance elements R ak and R bk vary from the case shown in Figure 11A. The intersection of the straight line indicating the voltage V ak varying with the variation of the resistance element R and the straight line indicating the voltage V ak varying with the variation of the resistance element R is the fluctuating current threshold I bk . bk ´ thk

[0075] When the resistance element R ak varies to R ak ´, the slope of the straight line indicating the voltage V ak ´ becomes larger than the slope of the straight line indicating the voltage V ak . When the resistance element R bk varies to R bk ´, the level of the voltage V bk ´ becomes higher than the level of the voltage V bk . As a result, the position in the horizontal axis direction of the intersection of the straight line indicating the voltage V ak ´ and the straight line indicating the voltage V bk ´ is the same as before the variation. This indicates that the current threshold I ak does not vary due to the variation of the resistance values of the resistance elements R bk and R thk (I thk ´ = I thk ).

[0076] ​​As described above, according to the current measurement circuit 10B according to the third embodiment of the disclosed technology, the variation in the current threshold I due to manufacturing variations thk can be suppressed, so that high-precision current measurement can be performed without performing FUSE trimming.

[0077] Further, according to the current measurement circuit 10B, three or more different current thresholds I thk are used to measure the current to be measured I m is determined, so that the resolution of the current measurement can be increased as compared with the case where the current measurement is performed using one or two current thresholds.

[0078] In the first to third embodiments, each of the current mirror circuits D a1 、D a2 、D ak 、D b1 、D b2 、D bk is exemplified as being composed of a P-channel type MOSFET, but the disclosed technology is not limited to this aspect. By inputting the current to be measured I m and the reference current I ref into the current-voltage conversion circuit in the source current method, each of the current mirror circuits D a1 、D a2 、D ak 、D b1 、D b2 、D bk can also be composed of an N-channel type MOSFET.

Explanation of Signs

[0079] 10, 10A, 10B Current measurement circuit A1, A2, A n 、B1、B2、B n Current-voltage conversion circuit C1、C2、C n Comparator D a1 、D a2 、D an 、D b1 、D b2 、D bn Current mirror circuit R a1 and R a2 and R an and R b1 and R b2 and R bn resistor element U1, U2, U n judgment unit

Claims

1. A first current-voltage conversion circuit that converts a current to be measured into a first voltage; A second current-voltage conversion circuit that converts a reference current into a second voltage; A first comparator that outputs a comparison result between the first voltage and the second voltage; A current measurement circuit having the above components.

2. The first current-voltage conversion circuit includes: A first current mirror circuit that generates a first mirror current proportional to the magnitude of the current to be measured; A first resistor element through which the first mirror current flows; And has: The second current-voltage conversion circuit includes: A second current mirror circuit that generates a second mirror current proportional to the magnitude of the reference current; A second resistor element through which the second mirror current flows; And has: The current measurement circuit according to Claim 1.

3. A third current-voltage conversion circuit that converts the current to be measured into a third voltage; A fourth current-voltage conversion circuit that converts the reference current into a fourth voltage; A second comparator that outputs a comparison result between the third voltage and the fourth voltage; And further has: A first current threshold value that is the value of the current to be measured when the first voltage becomes equal to the second voltage, and a second current threshold value that is the value of the current to be measured when the third voltage becomes equal to the fourth voltage, and the two are different from each other The current measurement circuit according to Claim 1.

4. The first current-voltage conversion circuit includes: A first current mirror circuit that generates a first mirror current proportional to the magnitude of the current to be measured; A first resistor element through which the first mirror current flows; And has: The second current-voltage conversion circuit includes: A second current mirror circuit that generates a second mirror current proportional to the magnitude of the reference current; A second resistor element through which the second mirror current flows; And has: The third current-voltage conversion circuit includes: A third current mirror circuit that generates a third mirror current proportional to the magnitude of the current to be measured; A third resistor element through which the third mirror current flows; And has: The fourth current-voltage conversion circuit includes: A fourth current mirror circuit that generates a fourth mirror current proportional to the magnitude of the reference current; A fourth resistor element through which the fourth mirror current flows; And has: The current measurement circuit according to Claim 3.

5. The levels of the second voltage and the fourth voltage are the same as each other The current measurement circuit according to Claim 3 or Claim 4.

6. Each includes: A current-voltage conversion circuit that converts a current to be measured into a first voltage; A current-voltage conversion circuit that converts a reference current into a second voltage, a comparator that outputs a comparison result between the first voltage and the second voltage, having a plurality of determination units including, a current threshold value, which is a value of the current to be measured at which the first voltage becomes equal to the second voltage, being different for each of the determination units a current measurement circuit.

Images