Current sense amplifier

Abstract

The present invention addresses the problem of easily setting an offset voltage of a post-amplifier. The present invention is provided with: a preamplifier (10) that obtains a preamplifier positive output (vc) and a preamplifier negative output (vb) corresponding to the difference between the upper voltage and the lower voltage of a current detection resistor (R0); and a post-amplifier (12) which has a positive input terminal to which the positive output of the pre-amplifier is input and a negative input terminal to which the negative output of the pre-amplifier is input, and which obtains a post-amplifier output (vout). A post-amplifier (12) includes: a positive-side input resistor (R4b) disposed on an input path leading to a positive input terminal; a negative-side input resistor (R4a) disposed on an input path leading to the negative input terminal; the feedback resistor (R5) is configured on a feedback path from the output end of the post amplifier to the negative input end; and a resistance network that connects the positive input terminal to the reference power supply and the ground, supplies an offset voltage to the positive input terminal, said offset voltage being obtained by dividing the voltage of the reference power supply by resistance, and has a combined resistance value corresponding to the resistance value of the feedback resistor.

Description

TECHNICAL FIELD

[0001] The present application relates to a current sense amplifier that detects a current flowing in a current detection resistor. BACKGROUND

[0002] In a drive circuit that drives a load such as a motor, a drive transistor that controls a drive current is used. In order to control the drive current of the motor, it is necessary to detect a current flowing in the drive transistor, and a current sense amplifier is used to detect the drive current of the motor.

[0003] Here, as the drive transistor, a power MOSFET is used in most cases, but the power MOSFET is relatively large in order to pass a large current, and is externally used from a semiconductor substrate that constitutes the drive circuit.

[0004] In this case, a current detection resistor is connected in series to the power MOSFET outside the semiconductor substrate, and a voltage drop in the current detection resistor is detected by the current sense amplifier inside the semiconductor substrate, whereby the drive current of the motor can be detected.

[0005] [BACKGROUND ART LITERATURE]

[0006] [PATENT LITERATURE]

[0007] [Patent Literature 1] Japanese Patent Laid-Open No. 7-113826 SUMMARY

[0008] [PROBLEMS TO BE SOLVED BY THE INVENTION]

[0009] In such a current sense amplifier, a single-ended output at a required offset voltage is desired, and it is also desired that noise and the like be as little as possible at this time.

[0010] [TECHNICAL MEANS FOR SOLVING THE PROBLEMS]

[0011] The current sensing amplifier of one aspect of the present invention includes: a preamplifier having a preamplifier positive input to which an upper side voltage of a current detection resistor is input, a preamplifier negative input to which a lower side voltage of the current detection resistor is input, a preamplifier positive output obtained at a positive output in correspondence with a difference between the upper side voltage and the lower side voltage, and a preamplifier negative output obtained at a negative output; and a postamplifier having a postamplifier negative input to which the preamplifier negative output is input, a postamplifier positive input to which the preamplifier positive output is input, and a postamplifier output obtained in correspondence with a difference between the preamplifier positive output and the preamplifier negative output; and the postamplifier includes: a second operational amplifier having the preamplifier negative output input to a second operational amplifier negative input, the preamplifier positive output input to a second operational amplifier positive input, and a second operational amplifier output obtained based on a difference between them; a second operational amplifier positive side input resistor disposed on an input path to the second operational amplifier positive input; a second operational amplifier negative side input resistor disposed on an input path to the second operational amplifier negative input; a second operational amplifier feedback resistor disposed on a feedback path from a second operational amplifier output to the second operational amplifier negative input; and a resistor network connecting the second operational amplifier positive input to a reference power supply and a ground, and having a combined resistance value from the second operational amplifier positive input to the reference power supply and the ground corresponding to a resistance value of the second operational amplifier feedback resistor.

[0012] The resistor network preferably includes: a setting resistor having one end connected to the second operational amplifier positive input; and a voltage dividing resistor obtaining a voltage divided at a middle point of a plurality of series-connected resistors disposed between the reference power supply and the ground; and the other end of the setting resistor is connected to the middle point.

[0013] Preferably, it includes: an insertion resistor inserted between the other end of the setting resistor and the middle point; a parallel resistor having one end connected to the ground; and a switch selectively connecting either of a connection point of the setting resistor and the insertion resistor and the other end of the parallel resistor to the middle point; and by the switch, it is possible to maintain the resistance value from the other end of the setting resistor to the reference power supply and the ground and change the voltage supplied to the other end of the setting resistor.

[0014] It is preferable to be able to change the resistance values of the second operational amplifier feedback resistor and the setting resistor, and when the resistance value of the second operational amplifier feedback resistor has been changed, to maintain the combined resistance value of the resistor network to be the same as the resistance value of the second operational amplifier feedback resistor by changing the resistance value of the setting resistor.

[0015] In addition, the current sense amplifier of the present application is inputted with a pair of input signals corresponding to the voltage drop of the current detection resistor, and obtains an amplifier output, and includes: a positive input terminal to which a positive side signal of the pair of input signals is inputted; a negative input terminal to which a negative side signal of the pair of input signals is inputted; an output terminal to output an amplifier output corresponding to the difference between the positive side signal and the negative side signal; a positive side input resistor arranged in an input path to the positive input terminal; a negative side input resistor arranged in an input path to the negative input terminal; a feedback resistor arranged in a feedback path from the output terminal to the negative input terminal of the second operational amplifier; and a resistor network connecting the positive input terminal with a reference power supply and a ground terminal, and the combined resistance value from the positive input terminal to the reference power supply and the ground terminal corresponds to the resistance value of the feedback resistor of the second operational amplifier.

[0016] [Effects of the Invention]

[0017] According to the post-amplifier of the present application, the offset voltage of the output can be set by the resistor network without using components such as a buffer amplifier that can become a cause of noise mixing.

[0018] In addition, the resistance value of the resistor network can be changed using a switch, so that the offset voltage of the post-amplifier can be adjusted without changing the gain. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a circuit diagram showing the configuration of the current sense amplifier of the embodiment.

[0020] Figure 2 is a graph showing the common mode operation of the operational amplifier opal in the pre-amplifier 10.

[0021] Figure 3 is a graph showing the detailed configuration of the operational amplifier opal.

[0022] Figure 4 is a graph showing the configuration in the case where the p-channel transistors Mp3 and Mp4 are used instead of the n-channel transistors Mn 1 and Mn2 in the configuration of Figure 3 DETAILED DESCRIPTION

[0023] Hereinafter, the embodiment of the present application will be described with reference to the drawings. Note that the following embodiment does not limit the present application, and configurations in which a plurality of examples are selectively combined are also included in the present application.

[0024] "Overall Configuration"

[0025] Figure 1 ​is a circuit diagram showing the configuration of a current sense amplifier according to an embodiment. The current sense amplifier 100 detects a current flowing in a current detection resistor R0 connected in series to a load. Here, the load is, for example, a motor, and a drive current flowing in the load, such as a motor, is controlled by a drive transistor connected in series to the load and the current detection resistor R0. The drive current is controlled, for example, using PWM control. As the transistor, for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is used.

[0026] The current sense amplifier 100 includes two blocks of a preamplifier 10 and a postamplifier 12. In this example, the current sense amplifier 100 is formed as a semiconductor integrated circuit in a semiconductor substrate, and the current detection resistor R0 is externally provided to the semiconductor substrate and connected in series to the drive transistor and the load outside the semiconductor substrate.

[0027] To the preamplifier 10, both end voltages (an upper side voltage vip and a lower side voltage vin) of the current detection resistor R0 are input to a preamplifier positive input and a preamplifier negative input, respectively. The preamplifier 10 outputs a positive side output voltage and a negative side output voltage corresponding to a difference between the upper side voltage vip and the lower side voltage vin as a preamplifier negative output vb and a preamplifier positive output vc.

[0028] The upper side voltage vip is input to a negative input (-) of an operational amplifier opal via a negative input resistor Rla. The lower side voltage vin is input to a positive input (+) of the operational amplifier opal via a positive input resistor Rlb. The operational amplifier opal is referred to as a first operational amplifier.

[0029] A positive output and a negative input of the operational amplifier opal are connected by a negative feedback resistor R3a, and a negative output and a positive input are connected by a negative feedback resistor R3b. A pair of outputs of the operational amplifier opal directly become outputs of the preamplifier 10. A voltage of the preamplifier negative output vb is set to vb, and a voltage of the preamplifier positive output vc is set to vc. The preamplifier negative output vb is input to a postamplifier negative input of the postamplifier 12, and the preamplifier positive output vc is input to a postamplifier positive input of the postamplifier 12.

[0030] Further, in the present embodiment, the negative input of the operational amplifier opal is connected to a reference power supply vref outputting a reference voltage vref via a first input adjustment resistor R2a, and the positive input is connected to the reference power supply vref outputting the reference voltage vref via a second input adjustment resistor R2b. In addition, a power supply that supplies the reference voltage vref to the operational amplifier opal is referred to as a constant voltage source.

[0031] As such, the preamplifier 10 is a full differential amplifier, and the gain thereof is determined by the resistance values of the resistors Rla, Rlb, R3a, and R3b described above. In addition, the DC voltages of the negative input terminal and the positive input terminal of the operational amplifier opal are set in accordance with the resistance values of the input adjustment resistors R2a and R2b.

[0032] The postamplifier 12 has an operational amplifier opa2 inside. The pair of preamplifier negative output vb and preamplifier positive output vc of the preamplifier 10 are input to a pair of inputs of the operational amplifier opa2, respectively. That is, the preamplifier outputs vb and vc are input to the negative input terminal (-) and the positive input terminal (+) of the operational amplifier opa2 through the negative-side input resistor R4a and the positive-side input resistor R4b, respectively. The operational amplifier opa2 is referred to as a second operational amplifier.

[0033] The operational amplifier opa2 is a single-ended operational amplifier having one output, and obtains a postamplifier output vout as a single voltage output. Furthermore, the postamplifier output vout becomes an output signal of the current sense amplifier 100. Through the operational amplifier opa2, a single postamplifier output vout suitable for input to an ADC (analog-digital converter) can be obtained.

[0034] A feedback resistor R5 is disposed on a feedback path from the output terminal of the operational amplifier opa2 to the negative input terminal. In this example, the resistance value of the feedback resistor R5 is variable. Depending on the specifications of the circuit, a feedback resistor R5 having a different resistance value can be employed.

[0035] The positive input terminal of the operational amplifier opa2 is connected to a reference power source vref of a reference voltage vref and a ground terminal gnd via a resistor network 14. One end of a setting resistor R6 among the resistor network 14 is connected to the positive input terminal of the operational amplifier opa2. In this example, the resistance value of the setting resistor R6 is variable. Depending on the specifications of the circuit, a setting resistor R6 having a resistance value corresponding to the resistance value of the feedback resistor R5 can be employed.

[0036] To the other end of the setting resistor R6, a plurality of voltages obtained by dividing the reference voltage vref are supplied in a switchable manner via a group of resistors capable of switchable connection.

[0037] That is, the other end of the setting resistor R6 is connected to the connection point of the two voltage dividing resistors R8a, R8b via the insertion resistor R7, and the two voltage dividing resistors R8a, R8b are connected in series between the reference voltage vref and the ground gnd. In addition, the other end of the parallel resistor R9 connected to the ground gnd at one end is connected to the contact sl of the switch SW, and the connection point of the setting resistor R6 and the insertion resistor R7 is connected to the contact sO of the switch SW. The switch SW can switch the connection point of the voltage dividing resistors R8a and R8b to be connected to the contact sl or the contact sO.

[0038] In the case where the contact sO is selected by the switch SW, the other end of the setting resistor R6 is directly connected to the connection point of the voltage dividing resistors R8a and R8b, and a voltage obtained by dividing the reference voltage vref by the voltage dividing resistors R8a, R8b is supplied to the other end of the setting resistor R6.

[0039] In the case where the contact sl is selected by the switch SW, the other end of the setting resistor R6 is connected to the connection point of the voltage dividing resistors R8a and R8b via the insertion resistor R7, and the parallel resistor R9 is connected in parallel to the voltage dividing resistor R8b. That is, the other end of the setting resistor R6 is connected to the reference voltage vref via the insertion resistor R7 and the voltage dividing resistor R8a, and is connected to the ground gnd by being connected in parallel to the insertion resistor R7 and the voltage dividing resistor R8b and the parallel resistor R9.

[0040] "Operation of the preamplifier"

[0041] <Adjustment of the input voltage va>

[0042] Figure 2 is a graph showing the common mode operation of the operational amplifier opal in the preamplifier 10.

[0043] In this example, the input vicm (vicm = (vip + vin) / 2) is input to the negative input of the operational amplifier opal, and the output vocm (vocm = (vb + vc) / 2) is obtained as a single output. The resistances of the respective paths are assumed to be Rl = Rla = Rlb, R2 = R2a = R2b, and R3 = R3a = R3b. Thus, the operation of the operational amplifier opal at the time of no voltage between the positive and negative inputs can be simulated.

[0044] In the case where the input adjustment resistor R2 is not present, the input voltage va of the operational amplifier opal should be the voltage between vicm and vocm. In the case where the resistances are set to R3 = 2 * Rl and the voltages are set to vicm = -2 V and vocm = 2 V, the input voltage va = -0.67 V < 0 V as shown below.

[0045] va = vicm * R3 / (Rl + R3) + vocm * Rl / (Rl + R3)

[0046] = (-2V) * 2 / 3 + 2 * 1 / 3 = -0.67V < 0V

[0047] In addition, in a case where the input adjustment resistance R2 is set to R2 = 2 * Rl and the reference voltage is set to vref = 3V, the input voltage va = 0.25V > 0V as shown below.

[0048] va = (-2 / 3)V * 2 / (2 / 3 + 2) + 3V * 2 / 3 / (2 / 3 + 2)

[0049] = 0.25V > 0V

[0050] In this way, by adjusting the resistance value of the input adjustment resistance R2, the input voltage va of the operational amplifier opal can be adjusted to a desired range.

[0051] Therefore, in the configuration of Figure 1 Even if the lower side voltage vin of the current detection resistance R0 is a negative voltage, the input voltage va of the operational amplifier opal can be made a positive voltage by adjusting the resistance value of the input adjustment resistance R2a, R2b.

[0052] <Common Mode, Feedback>

[0053] Figure 3 is a diagram showing a detailed configuration of the operational amplifier opal. In this way, the upper side voltage vip and the lower side voltage vin are input to the positive input terminal and the negative input terminal of the input gain stage gm, respectively. The input gain stage gm outputs a positive current output iop and a negative current output ion in correspondence with the difference between the two input terminals.

[0054] The positive current output iop is connected to the drain of the p-channel transistor Mpl. The source of the p-channel transistor Mpl is connected to the positive power supply vdd of the power supply voltage vdd. The negative current output ion is connected to the drain of the p-channel transistor Mp2. The source of the p-channel transistor Mp2 is connected to the positive power supply vdd.

[0055] The gate of the n-channel transistor Mn1 is connected to the drain of the p-channel transistor Mpl. The drain of the n-channel transistor Mn1 is connected to the power supply vdd, the source is connected to the current source ibl which flows the current ibl, and is connected to the positive output vop of the output preamplifier negative output vb.

[0056] The gate of the n-channel transistor Mn2 is connected to the drain of the p-channel transistor Mp2. The drain of the n-channel transistor Mn2 is connected to the power supply vdd, the source is connected to the current source ib2 which flows the current ib2, and is connected to the negative output von of the output preamplifier positive output vc.

[0057] The gates of p-channel transistors Mp1 and Mp2 are connected in a common manner. The positive output vop is connected to the gate via pull-up resistor Rb1, and the negative output von is connected to the gate via pull-up resistor Rb2.

[0058] Therefore, the voltage corresponding to the positive current output iop of the input gain stage gm is output from the source of the n-channel transistor Mn1 to the positive output vop. Conversely, the voltage corresponding to the negative current output ion of the input gain stage gm is output from the source of the n-channel transistor Mn2 to the negative output von.

[0059] Here, the gate voltage when p-channel transistors Mp1 and Mp2 are turned on is the value obtained by subtracting the gate-source voltage vgson when p-channel transistors Mp1 and Mp2 are turned on from the source voltage, i.e., vdd - vgson. The gates of p-channel transistors Mp1 and Mp2 are connected to the positive output vop and the negative output von through pull-up resistors Rb1 and Rb2, so the common output voltage is (vop + von) / 2 = vdd - vgson.

[0060] In this way, the output common voltage is close to and determined by the power supply voltage Vdd. Therefore, the adjustment range can be relatively large, making it easy to use the input adjustment resistors R2a and R2b to correct the input common voltage of operational amplifier OPA1 and set the input common voltage of operational amplifier OPA1 to a relatively high value.

[0061] In this particular example, the n-channel transistors Mn1 and Mn2 are either native type or depletion type transistors. Native type or depletion type transistors have a smaller gate-source voltage vgson when turned on, thus enabling the drain-source voltage of the p-channel transistors Mp1 and Mp2 to reach the required and sufficient value for operation.

[0062] Figure 4 This indicates that p-channel transistors Mp3 and Mp4 are used instead. Figure 3 The diagram shows the configuration of the n-channel transistors Mn1 and Mn2 in the structure.

[0063] In this configuration, a current source ib 1 is arranged between the source of the p-channel transistor Mp3 and the power supply vdd, and the drain of the p-channel transistor Mp3 is connected to the ground gnd. Also, a current source ib 2 is arranged between the source of the p-channel transistor Mp4 and the power supply vdd, and the drain of the p-channel transistor Mp4 is connected to the ground gnd. Further, the source of the p-channel transistor Mp3 is connected to the positive output vop, and the source of the p-channel transistor Mp4 is connected to the negative output von. In this case, the p-channel transistors Mp3, Mp4 operate in accordance with the output of the input gain stage gm, and the positive output vop and the negative output von are obtained. Further, the common output voltage of the positive output vop and the negative output von becomes (vop+von) / 2=vdd-vgson. Therefore, a relatively high input common voltage can be set in the operational amplifier opal. The output potential of the input gain stage gm becomes the power supply voltage vdd-2vgson, and the voltage between the drain and the source of the p-channel transistors Mpl and Mp2 can be made to be a value sufficient for operation.

[0064] "Operation of the post-amplifier"

[0065] Returning to Figure 1 The operation of the post-amplifier 12 will be described. The post-amplifier 12 is a single-ended amplifier that obtains a single output voltage vout in correspondence with the difference of the input voltages vb, vc. Further, the amplification and the offset voltage are set in accordance with the resistance values of the plurality of resistors around the operational amplifier opa2.

[0066] First, the resistances are assumed to be R8=R8a=R8b, R4=R4a=R4b as in the setting made when obtaining the normal operation.

[0067] The gain of the post-amplifier 12 is R5 / R4, and in this case, the resultant resistance value between the positive input terminal of the operational amplifier opa2 and the power supply and the ground of the other end of the resistance network should be equal to R5. Further, the resultant resistance value at this time is calculated assuming that the reference power supply vref and the ground gnd are short-circuited. This is because the reference power supply vref is assumed to be connected to the ideal power supply with a resistance of 0 ohm, and the ideal power supply is set to 0 V for calculation when considering the resistance value.

[0068] Therefore, when sO is selected in the switch SW,

[0069] R5=R6+R8 / 2.

[0070] In this case, the offset voltage vd of the output of the operational amplifier opa2 with respect to the ground gnd is:

[0071] vd=vref*R8 / (R8+R8)=vref / 2.

[0072] On the other hand, when s1 is selected in the switch SW,

[0073] R5 = R6 + R7 + (R8 / 2) / / R9. Further, the mark " / / " indicates a parallel connection.

[0074] Here, the condition when s0 is selected in the switch SW must be maintained,

[0075] R8 / 2 = R7 + (R8 / 2) / / R9.

[0076] The resistance value of the parallel connection ( / / ) of R8 / 2 and R9 is:

[0077] (R8 / 2) / / R9 = (R8 / 2 * R9) / [(R8 / 2) + R9] ; therefore,

[0078] R7 = R8 * R8 / [2 * (R8 + 2 * R9)].

[0079] When s1 is selected in the switch SW, in the case where it is desired to set the offset voltage vd = vref / 8,

[0080] (R9 / / R8) / (R9 / / R8 + R8) = 1 / 8,

[0081] As long as, for example, R9 = R8 / 6,

[0082] R7 = R8 * R8 / [2 * (R8 + 2 * R9)] = (3 / 8) * R8, and thus the resistance values of the resistors R9, R7 are set.

[0083] As such, according to the present embodiment, by switching of the switch SW, it is possible to set the offset voltage of the post-amplifier 12 to the appropriate two values (vref / 2, vref / 8).

[0084] In particular, the setting of the offset voltage can be performed by setting the resistance values of the resistors R7, R8a, R8b, R9, and can be performed independently of the resistors R5, R6, that is, independently of the gain setting. Further, by changing the resistance values of the resistors R5, R6, it is possible to set the gain of the operational amplifier op2. In Figure 1 In the above, the resistors R5, R6 are expressed as variable resistors, indicating that the gain can be changed.

[0085] In the case where the gain of the post-amplifier 12 is changed to 5 times to 40 times, R5 = 5 * R4 to 40 * R4, and R6 + R8 / 2 = 5 * R4 to 40 * R4. In the case where R6 = 0, R8 / 2 = 5 * R4, and R8 = 10 * R4. That is, it is possible to make the resistance value of the resistor R8 as large as 10 * R4, and the range of selection at the time of setting the offset voltage is large.

[0086] "Effects of Embodiments"

[0087] The resistance network with the voltage setting switch of the post-amplifier can remove the buffer amplifier that can generate offset or noise.

[0088] In the pre-amplifier 10, the input voltage of the operational amplifier opal can be adjusted by setting the resistance value of the input adjustment resistor R2 (R2a, R2b). Even if the input to the current sense amplifier 100 is a negative voltage, by setting the input adjustment resistor R2, the operational amplifier opal can make the input voltage higher than the ground gnd.

[0089] By connecting the output stage of the pre-amplifier 10 to the gate of the p-channel transistor connected to the source and the power supply, the output voltage close to the power supply can be obtained, so that the common mode input voltage of the pre-amplifier 10 can be more easily set.

[0090] According to the post-amplifier of the present application, the offset voltage of the output can be set by the resistance network without using components such as buffer amplifiers that can become a cause of noise mixing.

[0091] The resistance value of the resistance network connected to the positive input terminal of the post-amplifier can be changed using a switch, so that the offset voltage of the post-amplifier can be adjusted without changing the gain.

[0092] [Explanation of symbols]

[0093] 10: pre-amplifier

[0094] 12: post-amplifier

[0095] 14: resistance network

[0096] 100: current sense amplifier

Claims

1. A current sensing amplifier, comprising: A preamplifier having a positive input terminal receiving an upper voltage from an input current sensing resistor and a negative input terminal receiving a lower voltage from the input current sensing resistor; corresponding to the difference between the upper and lower voltages, a positive output is obtained at the positive output terminal, and a negative output is obtained at the negative output terminal; and A post-amplifier has a negative input terminal that is input to the negative output of the pre-amplifier and a positive input terminal that is input to the positive output of the pre-amplifier, and obtains a post-amplifier output corresponding to the difference between the positive output and the negative output of the pre-amplifier; and The post-amplifier includes: The second operational amplifier inputs the negative output of the preamplifier to the negative input terminal of the second operational amplifier and inputs the positive output of the preamplifier to the positive input terminal of the second operational amplifier, and obtains the output of the second operational amplifier based on their difference; The positive input resistor of the second operational amplifier is configured on the input path leading to the positive input terminal of the second operational amplifier; The negative input resistor of the second operational amplifier is configured on the input path leading to the negative input terminal of the second operational amplifier; The feedback resistor of the second operational amplifier is configured on the feedback path from the output of the second operational amplifier to the negative input of the second operational amplifier; and A resistor network connects the positive input terminal of the second operational amplifier to a reference power supply and ground, and the combined resistance value from the positive input terminal of the second operational amplifier to the reference power supply and ground corresponds to the resistance value of the feedback resistor of the second operational amplifier.

2. The current sensing amplifier according to claim 1, wherein The resistor network includes: a set resistor, one end of which is connected to the positive input terminal of the second operational amplifier; and a voltage divider resistor to obtain a voltage divided at the midpoint of a plurality of series-connected resistors configured between a reference power supply and ground; and the other end of the set resistor is connected to the midpoint.

3. The current sensing amplifier according to claim 2, comprising: Insert a resistor between the other end of the set resistor and the midpoint; A parallel resistor, one end of which is connected to the ground electrode; as well as A switch that selectively connects either the connection point of the set resistor and the insertion resistor, or the other end of the parallel resistor, to the intermediate point; and The switch can maintain the resistance value from the other end of the set resistor to the reference power supply and ground, and change the voltage supplied to the other end of the set resistor.

4. The current sensing amplifier according to claim 3, wherein The resistance values ​​of the feedback resistor of the second operational amplifier and the set resistor can be changed. When the resistance value of the feedback resistor of the second operational amplifier has been changed, the combined resistance value of the resistor network is maintained to be the same as the resistance value of the feedback resistor of the second operational amplifier by changing the resistance value of the set resistor.

5. A current sensing amplifier, wherein a pair of input signals corresponding to the voltage drop across a current sensing resistor are input to obtain an amplifier output; and comprising: The positive input terminal receives the positive signal of the pair of input signals. The negative input terminal receives the negative side signal of the pair of input signals. The output terminal outputs the amplifier output corresponding to the difference between the positive signal and the negative signal; A positive input resistor is configured on the input path leading to the positive input terminal; The negative input resistor is configured on the input path leading to the negative input terminal; A feedback resistor is configured on the feedback path from the output terminal to the negative input terminal of the second operational amplifier; as well as A resistor network connects the positive input terminal to a reference power supply and ground, and the combined resistance value from the positive input terminal to the reference power supply and ground corresponds to the resistance value of the feedback resistor of the second operational amplifier.

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