Current sense amplifier

Abstract

Easily set the input voltage of the preamplifier. [Solution] The preamplifier 10 includes a preamplifier positive output vc and a preamplifier negative output vb corresponding to the difference between the upper and lower voltages of a current sensing resistor R0. The preamplifier 10 has a first operational amplifier opa1 to which the upper voltage is input to the negative input terminal of the first operational amplifier and the lower voltage is input to the positive input terminal of the first operational amplifier, and which obtains a positive output and a negative output of the first operational amplifier based on the difference between these. The connection point between the negative input resistor of the first operational amplifier and the negative input terminal of the first operational amplifier is connected to a constant voltage source via a first input adjustment resistor, and the connection point between the positive input resistor of the first operational amplifier and the positive input terminal of the first operational amplifier is connected via a second input adjustment resistor. The aforementioned It is connected to a constant voltage source.

Description

Technical Field

[0007] ,

[0001] The present disclosure relates to a current sense amplifier that detects a current flowing through a current detection resistor.

Background Art

[0002] In a drive circuit that drives a load such as a motor, a drive transistor for controlling a drive current is used. In order to control the drive current of the motor, it is necessary to detect the current flowing through 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 often used. However, since this power MOSFET conducts a large current, it is relatively large-sized and is often used externally attached to a semiconductor substrate constituting the drive circuit.

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

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In such a current sense amplifier, it is desirable to be able to operate by accepting a negative input voltage.

Means for Solving the Problems

[0007] A current sense amplifier according to one embodiment of the present disclosure has a preamplifier having a positive input terminal to which the upper voltage of a current sensing resistor is input and a negative input terminal to which the lower voltage of the sensing resistor is input, and a preamplifier that obtains a positive output at the positive output terminal and a negative output at the negative output terminal according to the difference between the upper voltage and the lower voltage, wherein the preamplifier has a first operational amplifier that receives the upper voltage at the negative input terminal of the first operational amplifier and the lower voltage at the positive input terminal of the first operational amplifier, and obtains a positive output and a negative output of the first operational amplifier based on the difference between these, and the upper voltage is input to the negative input terminal of the first operational amplifier A first operational amplifier negative input resistor is placed in the input path; a first operational amplifier positive input resistor is placed in the path through which the lower voltage is input to the positive input terminal of the first operational amplifier; a first operational amplifier first negative feedback resistor is placed between the positive output and the negative input of the first operational amplifier; a second operational amplifier second negative feedback resistor is placed between the negative output and the positive input of the first operational amplifier; the connection point between the first operational amplifier negative input resistor and the negative input terminal of the first operational amplifier is connected to a constant voltage source via a first input adjustment resistor; and the connection point between the first operational amplifier positive input resistor and the positive input terminal of the first operational amplifier is connected to a constant voltage source via a second input adjustment resistor.

[0008] A current sense amplifier according to another embodiment of the present disclosure has a preamplifier having a preamplifier positive input terminal to which the upper voltage of a current sensing resistor is input, and a preamplifier negative input terminal to which the lower voltage of the sensing resistor is input, and the preamplifier has a preamplifier positive output at the positive output terminal and a preamplifier negative output at the negative output terminal according to the difference between the upper voltage and the lower voltage, wherein the preamplifier has an input gain stage to which the upper voltage and the lower voltage are input, and to which an input gain stage negative output and an input gain stage positive output are obtained based on the difference between the two, and the input gain stage positive output and the input gain stage negative output are two p-channel transients Each of the two p-channel transistors is connected to a positive power supply via a sta, the gates of the two p-channel transistors are connected to each other, and further connected to the negative output and positive output of the preamplifier via two pull-up resistors, respectively, the positive output and negative output of the input gain stage are connected to the gates of the n-channel transistors, respectively, and the sources of each n-channel transistor are connected to the negative output and positive output of the preamplifier, respectively, and the n-channel transistors are native-type or depletion-type transistors with a relatively small on-gate-source voltage.

[0009] A current sense amplifier according to yet another embodiment of the present disclosure has a preamplifier having a preamplifier positive input terminal to which the upper voltage of a current sensing resistor is input, and a preamplifier negative input terminal to which the lower voltage of the sensing resistor is input, and the preamplifier has a preamplifier that provides a preamplifier positive output to the positive output terminal and a preamplifier negative output to the negative output terminal according to the difference between the upper voltage and the lower voltage, wherein the preamplifier has an input gain stage to which the upper voltage and the lower voltage are input, and which provides an input gain stage negative output and an input gain stage positive output based on the difference between them, and the input gain stage positive output and the input gain stage negative output are two p-channels Each of the p-channel transistors is connected to a positive power supply, the gates of the two p-channel transistors are connected to each other, and further connected to the negative output and positive output of the preamplifier via two pull-up resistors, respectively, the positive output and negative output of the input gain stage are connected to the gates of the p-channel source follower transistors, the source of each p-channel source follower transistor is connected to the negative output and positive output of the preamplifier, respectively, and each p-channel source follower transistor operates by receiving a constant current from a constant current source. Furthermore, it is preferable to include a post-amplifier having a post-amplifier negative input terminal to which the negative output of the preamplifier is input, and a post-amplifier positive input terminal to which the positive output of the preamplifier is input, and to obtain a post-amplifier output corresponding to the difference between the positive output of the preamplifier and the negative output of the preamplifier. [Effects of the Invention]

[0010] According to the preamplifier described herein, the input voltage can be easily adjusted. [Brief explanation of the drawing]

[0011] [Figure 1] This is a circuit diagram showing the configuration of a current sense amplifier according to an embodiment. [Figure 2] This figure shows the common-mode operation of the operational amplifier opa1 in the preamplifier 10. [Figure 3] This diagram shows the detailed configuration of the op-amp opa1. [Figure 4] This figure shows the configuration when p-channel transistors Mp3 and Mp4 are used instead of n-channel transistors Mn1 and Mn2 in the configuration of Figure 3. [Modes for carrying out the invention]

[0012] The embodiments of this disclosure will be described below with reference to the drawings. The embodiments described below are not limiting to this disclosure, and configurations formed by selectively combining multiple examples are also included in this disclosure.

[0013] "Overall structure" Figure 1 is a circuit diagram showing the configuration of a current sense amplifier according to an embodiment. The current sense amplifier 100 detects the current flowing through a current sensing resistor R0 connected in series with the load. Here, the load is, for example, a motor, and the current flowing through the load, for example, the motor's drive current, is controlled by a drive transistor connected in series with the load and the current sensing resistor R0. For this drive current control, for example, PWM control is used. As the transistor, for example, a MOSFET (metal-oxide-semiconductor field-effect transistor) is used.

[0014] The current sense amplifier 100 includes two blocks: a preamplifier 10 and a postamplifier 12. In this example, the current sense amplifier 100 is formed as a semiconductor integrated circuit within a semiconductor substrate, while the current sensing resistor R0 is externally mounted to the semiconductor substrate and connected in series with the drive transistor and load outside the semiconductor substrate.

[0015] The voltages across the current sensing resistor R0 (upper voltage vip, lower voltage vin) are input to the positive input terminal and negative input terminal of the preamplifier 10, respectively. The preamplifier 10 outputs the positive output voltage vb and the negative output voltage vc, which correspond to the difference between the upper voltage vip and the lower voltage vin, respectively.

[0016] The upper voltage vip is input to the negative input terminal (-) of the operational amplifier opa1 via the negative input resistor R1a. The lower voltage vin is input to the positive input terminal (+) of the operational amplifier opa1 via the positive input resistor R1b. The operational amplifier opa1 is referred to as the first operational amplifier.

[0017] The positive output terminal and the negative input terminal of the operational amplifier opa1 are connected by the negative feedback resistor R3a, and the negative output terminal and the positive input terminal are connected by the negative feedback resistor R3b. A pair of outputs of the operational amplifier opa1 directly serve as the outputs of the preamplifier 10. Let the voltage of the preamplifier negative output vb be vb, and the voltage of the preamplifier positive output vc be vc. The preamplifier negative output vb is input to the postamplifier negative input terminal of the postamplifier 12, and the preamplifier positive output vc is input to the postamplifier positive input terminal of the postamplifier 12, respectively.

[0018] In this embodiment, the negative input terminal of the operational amplifier opa1 is connected to the reference power supply vref that outputs the reference voltage vref via the first input adjustment resistor R2a, and the positive input terminal is connected to the reference power supply vref via the second input adjustment resistor R2b. Note that the power supply that supplies the reference voltage vref to the operational amplifier opa1 is called a constant voltage source.

[0019] In this way, the preamplifier 10 is a fully differential amplifier, and the gain is determined by the resistance values of the resistors R1a, R1b, R3a, and R3b described above. Also, the DC voltages of the negative input terminal and the positive input terminal of the operational amplifier opa1 are set by the resistance values of the input adjustment resistors R2a and R2b.

[0020] The postamplifier 12 has an operational amplifier opa2 inside. A pair of outputs of the preamplifier 10, namely the preamplifier negative output vb and the preamplifier positive output vc, are respectively input to a pair of inputs of the operational amplifier opa2. 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 the second operational amplifier.

[0021] The operational amplifier opa2 is a single-ended operational amplifier with one output, and a post-amplifier output vout that is a single voltage output can be obtained. Then, the post-amplifier output vout becomes the output signal of the current sense amplifier 100. The operational amplifier opa2 can obtain a single post-amplifier output vout suitable for input to an ADC (analog-to-digital converter).

[0022] A feedback resistor R5 is arranged in the feedback path from the output terminal to the negative input terminal of the operational amplifier opa2. In this example, the feedback resistor R5 has a variable resistance value. Depending on the circuit specifications, feedback resistors R5 with different resistance values can be adopted.

[0023] The positive input terminal of the operational amplifier opa2 is connected to the reference power supply vref of the reference voltage vref and the ground gnd via a resistor network 14. One end of a setting resistor R6 in the resistor network 14 is connected to the positive input terminal of the operational amplifier opa2. In this example, the setting resistor R6 has a variable resistance value. Depending on the circuit specifications, a setting resistor R6 with a resistance value corresponding to the resistance value of the feedback resistor R5 can be adopted.

[0024] A plurality of voltages obtained by dividing the reference voltage vref are switchably supplied to the other end of the setting resistor R6 via a switchable resistor group.

[0025] That is, the other end of the setting resistor R6 is connected to the midpoint between two divided resistors R8a and R8b connected in series between the reference voltage vref and the ground gnd via an insertion resistor R7. Also, the other end of a parallel resistor R9 whose one end is connected to the ground gnd is connected to the contact s1 of the switch SW, and the connection point of the setting resistor R6 and the insertion resistor R7 is connected to the contact s0 of the switch SW. The switch SW can switch and connect the connection point of the divided resistors R8a and R8b to the contact s1 or the contact s0.

[0026] When the switch SW selects contact s0, the other end of setting resistor R6 is directly connected to the connection point of divider resistors R8a and R8b, and the voltage obtained by dividing the reference voltage vref by divider resistors R8a and R8b is supplied to the other end of setting resistor R6.

[0027] When contact s1 is selected by switch SW, the other end of setting resistor R6 is connected to the connection point of divider resistors R8a and R8b via insertion resistor R7, and a parallel resistor R9 is connected in parallel to divider resistor R8b. That is, the other end of setting resistor R6 is connected to the reference power supply vref via insertion resistor R7 and divider resistor R8a, and is also connected to ground GND by the parallel connection of insertion resistor R7, divider resistor R8b and parallel resistor R9.

[0028] "Preamplifier Operation" <Adjusting the input voltage va> Figure 2 shows the common-mode operation of the operational amplifier opa1 in the preamplifier 10.

[0029] In this example, the input vicm (vicm=(vip+vin) / 2) is input to the negative input terminal of opa1, and a single output vocm (vocm=(vb+vc) / 2) is obtained. The resistances of each path are assumed to be R1=R1a=R1b, ​​R2=R2a=R2b, and R3=R3a=R3b. This allows us to simulate the operation of opa1 when there is no voltage between the positive and negative input terminals.

[0030] Without the input adjustment resistor R2, the input voltage va of the op-amp opa1 should be the voltage between vicm and vocm. If we set the resistor R3 = 2 * R1 and the voltages vicm = -2V and vocm = 2V, then the input voltage va = -0.67V < 0V, as shown below.

[0031] va=vicm*R3 / (R1+R3)+vocm*R1 / (R1+R3) =(-2V)*2 / 3+2*1 / 3=-0.67V<0V

[0032] Furthermore, if we set the input adjustment resistor R2 to R2 = 2 * R1 and the reference voltage to vref = 3V, then the input voltage va = 0.25V > 0V, as shown below. va=(-2 / 3)V*2 / (2 / 3+2)+3V*2 / 3 / (2 / 3+2) =0.25V>0V

[0033] In this way, by adjusting the resistance value of the input adjustment resistor R2, the input voltage va of the operational amplifier opa1 can be adjusted to the desired range.

[0034] Therefore, in the configuration shown in Figure 1, even if the lower voltage vin of the current sensing resistor R0 is a negative voltage, the input voltage va of the operational amplifier opa1 can be made positive by adjusting the resistance values ​​of the input adjustment resistors R2a and R2b.

[0035] Common-mode feedback Figure 3 shows the detailed configuration of the operational amplifier opa1. As shown, the upper voltage vip and the lower voltage vin are input to the positive and negative input terminals of the input gain stage gm, respectively. The input gain stage gm outputs a positive current output iop and a negative current output ion to the two inputs according to the difference.

[0036] The positive current output iop is connected to the drain of p-channel transistor Mp1. The source of p-channel transistor Mp1 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 p-channel transistor Mp2. The source of p-channel transistor Mp2 is connected to the positive power supply VDD.

[0037] The drain of the p-channel transistor Mp1 is connected to the gate of the n-channel transistor Mn1. The drain of the n-channel transistor Mn1 is connected to the power supply vdd, and its source is connected to a current source ib1 that carries current ib1, as well as to the positive output vop that outputs the preamplifier negative output vb.

[0038] The drain of the p-channel transistor Mp2 is connected to the gate of the n-channel transistor Mn2. The drain of the n-channel transistor Mn2 is connected to the power supply vdd, and its source is connected to the current source ib2, which carries current ib2, and also to the negative output von, which outputs the preamplifier positive output vc.

[0039] The gates of the p-channel transistors Mp1 and Mp2 are connected in common, to which the positive output vop is connected via pull-up resistor Rb1, and the negative output von is connected via pull-up resistor Rb2.

[0040] Therefore, a 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. Also, a 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.

[0041] Here, the gate voltage of p-channel transistors Mp1 and Mp2 when they are ON is the source voltage minus the gate-source voltage vgson of p-channel transistors Mp1 and Mp2 when they are ON, i.e., vdd-vgson. Since the gates of p-channel transistors Mp1 and Mp2 are connected to the positive output vop and the negative output von by pull-up resistors Rb1 and Rb2, the output common voltage is (vop+von) / 2 = vdd-vgson.

[0042] Thus, the output common voltage is close to the power supply voltage vdd and is determined in accordance with the power supply voltage vdd. Therefore, the adjustment range can be made relatively large, making it easy to correct the input common voltage to the op-amp opa1 using input adjustment resistors R2a and R2b, and allowing the input common voltage of the op-amp opa1 to be set relatively high.

[0043] In particular, this example employs native-type or depletion-type transistors for the n-channel transistors Mn1 and Mn2. Because native-type or depletion-type transistors have a small on-time gate-source voltage vgson, the drain-source voltages of the p-channel transistors Mp1 and Mp2 can be set to values ​​necessary and sufficient for operation.

[0044] Figure 4 shows the configuration when p-channel transistors Mp3 and Mp4 are used instead of n-channel transistors Mn1 and Mn2 in the configuration of Figure 3.

[0045] In this configuration, a current source ib1 is placed between the source of p-channel transistor Mp3 and the power supply vdd, and the drain of p-channel transistor Mp3 is connected to ground GND. A current source ib2 is also placed between the source of p-channel transistor Mp4 and the power supply vdd, and the drain of p-channel transistor Mp4 is connected to ground GND. The source of p-channel transistor Mp3 is connected to the positive output vop, and the source of p-channel transistor Mp4 is connected to the negative output von. In this case, p-channel transistors Mp3 and Mp4 operate according to the output of the input gain stage gm, producing the positive output vop and the negative output von. The common voltage between the positive output vop and the negative output von is (vop + von) / 2 = vdd - vgson. Therefore, a relatively high input common voltage can be set in the operational amplifier opa1. The potential of the output of the input gain stage gm is the power supply voltage vdd - 2vgson, allowing the drain-source voltages of p-channel transistors Mp1 and Mp2 to be set to the necessary and sufficient values ​​for operation.

[0046] "Post-amp operation" Returning to Figure 1, let's explain the operation of the post-amplifier 12. The post-amplifier 12 is a single-ended amplifier that obtains a single output voltage vout depending on the difference between the input voltages vb and vc. The amplification factor and offset voltage are set by the resistance values ​​of several resistors surrounding the operational amplifier opa2.

[0047] First, to achieve typical operation, we assume that the resistors are R8=R8a=R8b and R4=R4a=R4b.

[0048] The gain of post-amplifier 12 is R5 / R4, and in this case, the combined resistance between the positive input terminal of op-amp opa2 and the power supply and ground at the other end of the resistor network should be equal to R5. Note that this combined resistance is calculated assuming that the reference power supply vref and ground GND are shorted. The reason is that the reference power supply vref is assumed to be connected to an ideal power supply with a 0-ohm resistor, and when considering resistance values, the ideal power supply is calculated as 0V.

[0049] Therefore, if s0 is selected in switch SW, R5 = R6 + R8 / 2 This is the result.

[0050] In this case, the offset voltage vd of the output of op-amp opa2 relative to ground GND is: vd = vref * R8 / (R8 + R8) = vref / 2 This is the result.

[0051] On the other hand, if s1 is selected in switch SW, R5 = R6 + R7 + (R8 / 2) / / R9 That is the case. The mark " / / " indicates a parallel connection.

[0052] Here, the conditions under which s0 is selected in switch SW must be maintained. R8 / 2 = R7 + (R8 / 2) / / R9 That is the case. The resistance values ​​of the parallel connection ( / / ) of R8 / 2 and R9 are: (R8 / 2) / / R9=(R8 / 2*R9) / [(R8 / 2)+R9)] Therefore, R7 = R8 * R8 / [2 * (R8 + 2 * R9)] This is the result.

[0053] If you want to set the offset voltage vd = vref / 8 when s1 is selected in switch SW, (R9 / / R8) / (R9 / / R8+R8)=1 / 8 And, R9 = R8 / 6, R7=R8*R8 / [2*(R8+2*R9)]=(3 / 8)*R8 You can set the resistance values ​​of resistors R9 and R7 as shown above.

[0054] Thus, according to this embodiment, the offset voltage of the post-amplifier 12 can be set to two appropriate values ​​(vref / 2, vref / 8) by switching the switch SW.

[0055] In particular, the offset voltage can be set by adjusting the resistance values ​​of resistors R7, R8a, R8b, and R9, independently of resistors R5 and R6, i.e., separate from the gain setting. Furthermore, the gain of op-amp op2 can be set by changing the resistance values ​​of resistors R5 and R6. In Figure 1, resistors R5 and R6 are represented as variable resistors, illustrating that the gain can be changed.

[0056] When the gain of post-amplifier 12 varies from 5 to 40 times, R5 = 5*R4 to 40*R4, and R6 + R8 / 2 = 5*R4 to 40*R4. When R6 = 0, R8 / 2 = 5*R4, and R8 = 10*R4. In other words, the resistance value of resistor R8 can be increased up to 10*R4, providing a wide range of choices for setting the offset voltage.

[0057] "Effects of the Embodiment" A post-amp resistor network with a voltage setting switch can eliminate buffer amplifiers that may introduce offset or noise.

[0058] In the preamplifier 10, the input voltage of the operational amplifier opa1 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, the operational amplifier opa1 can raise its input voltage above ground GND by setting the input adjustment resistor R2.

[0059] By connecting the output stage of the preamplifier 10 to the gate of a p-channel transistor whose source is connected to the power supply, the output voltage can be made close to that of the power supply, making it easier to set the common-mode input voltage of the preamplifier 10.

[0060] According to the post-amplifier described herein, the output offset voltage can be set by a resistor network, eliminating the need to use components that cause noise interference, such as buffer amplifiers.

[0061] By making the resistance value of the resistor network connected to the positive input terminal of the post-amplifier changeable via a switch, the offset voltage of the post-amplifier can be adjusted without changing the gain. [Explanation of Symbols]

[0062] 10 preamplifiers, 12 post-amplifiers, 14 resistor networks, 100 current sense amplifiers.

Claims

1. A current sense amplifier having a preamplifier with a positive input terminal to which the upper voltage of a current sensing resistor is input, and a negative input terminal to which the lower voltage of the sensing resistor is input, wherein a positive output is obtained at the positive output terminal and a negative output is obtained at the negative output terminal according to the difference between the upper voltage and the lower voltage, The upper voltage is input to the negative input terminal of the first operational amplifier and the lower voltage is input to the positive input terminal of the first operational amplifier, and the first operational amplifier has a first operational amplifier that obtains a positive output and a negative output based on the difference between these two voltages. A first operational amplifier negative input resistor is arranged in the path through which the upper voltage is input to the negative input terminal of the first operational amplifier, A first operational amplifier positive input resistor is arranged in the path through which the lower voltage is input to the positive input terminal of the first operational amplifier, A first negative feedback resistor for the first operational amplifier is placed between the positive output and the negative input of the first operational amplifier, A second negative feedback resistor for the first operational amplifier is placed between the negative output and the positive input of the first operational amplifier, The connection point between the negative input resistor of the first operational amplifier and the negative input terminal of the first operational amplifier is connected to a constant voltage source via a first input adjustment resistor. The connection point between the positive input resistor of the first operational amplifier and the positive input terminal of the first operational amplifier is connected to a constant voltage source via a second input adjustment resistor. Current sense amplifier.

2. A current sense amplifier having a preamplifier with a positive input terminal to which the upper voltage of a current sensing resistor is input, and a negative input terminal to which the lower voltage of the sensing resistor is input, wherein a positive output is obtained at the positive output terminal and a negative output is obtained at the negative output terminal according to the difference between the upper voltage and the lower voltage, The input gain stage receives the upper voltage and the lower voltage, and obtains an input gain stage negative output and an input gain stage positive output based on the difference between them. The positive output and negative output of the input gain stage are connected to a positive power supply via two p-channel transistors, respectively. The gates of the two p-channel transistors are connected to each other and further connected to the negative output and positive output of the preamplifier via two pull-up resistors, respectively. The positive output and negative output of the input gain stage are each connected to the gate of an n-channel transistor. Each n-channel transistor has its source connected to the negative output and positive output of the preamplifier, respectively. The n-channel transistor is a native-type or depletion-type transistor with a relatively small on-time gate-source voltage. Current sense amplifier.

3. A current sense amplifier having a preamplifier with a positive input terminal to which the upper voltage of a current sensing resistor is input, and a negative input terminal to which the lower voltage of the sensing resistor is input, wherein a positive output is obtained at the positive output terminal and a negative output is obtained at the negative output terminal according to the difference between the upper voltage and the lower voltage, The aforementioned preamplifier, The input gain stage receives the upper voltage and the lower voltage, and obtains an input gain stage negative output and an input gain stage positive output based on the difference between them. The positive output and negative output of the input gain stage are connected to a positive power supply via two p-channel transistors, respectively. The gates of the two p-channel transistors are connected to each other and further connected to the negative and positive outputs of the preamplifier via two pull-up resistors, respectively. The positive output and negative output of the input gain stage are each connected to the gate of a p-channel source follower transistor. Each p-channel source follower transistor has its source connected to the negative output and positive output of the preamplifier, respectively. Each p-channel source follower transistor operates by receiving a constant current from a constant current source. Current sense amplifier.

4. A current sense amplifier according to any one of claims 1 to 3, moreover, The post-amplifier includes a post-amplifier negative input terminal to which the negative output of the preamplifier is input, and a post-amplifier positive input terminal to which the positive output of the preamplifier is input, and obtains a post-amplifier output corresponding to the difference between the positive output of the preamplifier and the negative output of the preamplifier. Current sense amplifier.

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