WO2019097870A1 - Instrumentation amplifier - Google Patents

Abstract

The present invention is provided with: a differential amplifier (11) for amplifying an inputted differential signal; a bias voltage generating circuit (14) which uses, as a bias voltage, the voltage of a common mode component included in the differential signal inputted into the differential amplifier (11), and applies a bias to an inputted offset adjustment signal; and an offset adjustment circuit (13) which is connected to the differential amplifier (11), and uses the offset adjustment signal to which the bias has been applied by the bias voltage generating circuit (14), to adjust an offset component included in the differential signal inputted into the differential amplifier (11). The offset adjustment signal inputted into the bias voltage generating circuit (14) is formed from two signals which have different polarities, but the same absolute value.

Description

Instrumentation amplifier

The present invention relates to an in-amp for adjusting an offset component included in an input differential signal.

As shown in FIG. 8, the in-amp is an amplifier connected to a Wheatstone bridge circuit or the like that is a sensor (a torque sensor or a pressure sensor or the like) to amplify a differential signal input from the Wheatstone bridge circuit or the like. The instrumentation amplifier is suitable for connection to a Wheatstone bridge circuit in which the common mode is generated in principle, since the common mode component is removed and only the signal component is amplified. This instrumentation amplifier comprises a differential amplifier and a single-ended amplifier.

JP 2017-130743 A

On the other hand, the torque sensor is used for force control of the smart robot, but is affected by the stress generated during the assembly of the torque sensor or the smart robot. As a result, the torque detected by the torque sensor becomes larger than the actual torque, that is, the offset becomes larger.
On the other hand, when the offset component included in the differential signal input from the Wheatstone bridge circuit or the like is adjusted by the in-amp, generally, as shown in FIG. The way is taken. In this case, since the offset component is also amplified together with the signal component by the differential amplifier, there is a problem that the gain of the instrumentation amplifier can not be made very large.

The present invention has been made to solve the problems as described above, and it is an object of the present invention to provide an instrumentation amplifier having an offset adjustment function and capable of taking a large gain.

An instrumentation amplifier according to the present invention includes a differential amplifier for amplifying an input differential signal, and a voltage of a common mode component included in the differential signal input to the differential amplifier as a bias voltage, and an input offset The offset component included in the differential signal input to the differential amplifier is connected to the bias voltage generation circuit that biases the adjustment signal and the offset adjustment signal connected to the differential amplifier and biased by the bias voltage generation circuit. The offset adjustment signal input to the bias voltage generation circuit is characterized by comprising two signals having different polarities and the same absolute value.

According to the present invention, as configured as described above, it is possible to have an offset adjustment function and to take a large gain.

It is a figure which shows the structural example of the instrumentation amplifier concerning Embodiment 1 of this invention. It is a circuit diagram for demonstrating the principle of offset adjustment by the instrumentation amplifier which concerns on Embodiment 1 of this invention. It is a figure which shows the equivalent circuit of the Wheatstone bridged circuit to which the instrumentation amplifier which concerns on Embodiment 1 of this invention is connected. It is a figure which shows the simulation result example of the offset adjustment by the instrumentation amplifier concerning Embodiment 1 of this invention (when not dividing an offset adjustment signal equally). It is a figure which shows the simulation result example of the offset adjustment by the instrumentation amplifier which concerns on Embodiment 1 of this invention (when an offset adjustment signal is divided equally). It is a figure which shows the other structural example of the instrumentation amplifier which concerns on Embodiment 1 of this invention. It is a figure which shows the other structural example of the instrumentation amplifier which concerns on Embodiment 1 of this invention. It is a figure which shows the structure of the conventional instrumentation amplifier. It is a figure which shows the structure at the time of adding an offset adjustment function to the conventional instrumentation amplifier.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Embodiment 1
FIG. 1 is a view showing a configuration example of an in-amp (amplifier) 1 according to Embodiment 1 of the present invention. FIG. 1 also shows a Wheatstone bridge circuit 2 to which the instrumentation amplifier 1 is connected.
The instrumentation amplifier 1 is connected to a Wheatstone bridge circuit 2 or the like which is a sensor (torque sensor or pressure sensor etc.) and removes common mode components from differential signals input from the Wheatstone bridge circuit 2 etc. Perform amplification. The instrumentation amplifier 1 also has a function of adjusting the offset component included in the differential signal. Below, the case where the instrumentation amplifier 1 is connected to the Wheatstone bridge circuit 2 is shown. The instrumentation amplifier 1 includes a differential amplifier 11, a differential ADC 12, an offset adjustment circuit 13, and a bias voltage generation circuit 14, as shown in FIG.

The differential amplifier 11 amplifies the differential signal input from the Wheatstone bridge circuit 2. The differential amplifier 11 includes operational amplifiers 1101 and 1102, feedback resistors 1103 and 1104, and a gain setting resistor 1105.

The non-inverting input terminal of the operational amplifier 1101 is connected to one of the pair of output terminals of the Wheatstone bridge circuit 2. The voltage of the signal input to the non-inverting input terminal of the operational amplifier 1101 is Vi1, and the voltage of the signal output from the output terminal of the operational amplifier 1101 is Vo1.

The non-inverting input terminal of the operational amplifier 1102 is connected to the other of the pair of output terminals of the Wheatstone bridge circuit 2. The voltage of the signal input to the non-inverting input terminal of the operational amplifier 1102 is Vi2, and the voltage of the signal output from the output terminal of the operational amplifier 1102 is Vo2.

One end of the feedback resistor 1103 is connected to the inverting input terminal of the operational amplifier 1101, and the other end is connected to the output terminal of the operational amplifier 1101. Note that the resistance value of the feedback resistor 1103 is Rf.

One end of the feedback resistor 1104 is connected to the inverting input terminal of the operational amplifier 1102, and the other end is connected to the output terminal of the operational amplifier 1102. The resistance value of the feedback resistor 1104 is taken as Rf.

One end of the gain setting resistor 1105 is connected to the inverting input terminal of the operational amplifier 1101 and one end of the feedback resistor 1103, and the other end is connected to the inverting input terminal of the operational amplifier 1102 and one end of the feedback resistor 1104. The resistance value of the gain setting resistor 1105 is Rg.

The differential ADC (analog-digital converter) 12 converts the differential signal input from the differential amplifier 11 into a differential signal. The differential ADC 12 has a noninverting input terminal connected to the output terminal of the operational amplifier 1101 and the other end of the feedback resistor 1103, and an inverting input terminal connected to the output terminal of the operational amplifier 1102 and the other end of the feedback resistor 1104.

The offset adjustment circuit 13 is connected to the differential amplifier 11 and adjusts an offset component included in the differential signal input from the Wheatstone bridge circuit 2 to the differential amplifier 11 by the input offset adjustment signal. The offset adjustment circuit 13 includes adjustment resistors 1301 and 1302.

One end of the adjustment resistor 1301 is connected to the inverting input terminal of the operational amplifier 1101, one end of the feedback resistor 1103, and one end of the gain setting resistor 1105. The voltage of the signal input to the other end of the adjustment resistor 1301 is Vt1, and the resistance value of the adjustment resistor 1301 is Rt.

One end of the adjustment resistor 1302 is connected to the inverting input terminal of the operational amplifier 1102, one end of the feedback resistor 1104, and the other end of the gain setting resistor 1105. The voltage of the signal input to the other end of the adjustment resistor 1302 is Vt2, and the resistance value of the adjustment resistor 1302 is Rt.

The signal input to the adjustment resistor 1301 and the signal input to the adjustment resistor 1302 constitute an offset adjustment signal which is a differential signal. The voltage of the offset adjustment signal is three times the voltage of the offset component included in the differential signal input from the Wheatstone bridge circuit 2.

The bias voltage generation circuit 14 sets the voltage of the common mode component included in the differential signal input from the Wheatstone bridge circuit 2 to the differential amplifier 11 as a bias voltage, and biases the offset adjustment signal input to the offset adjustment circuit 13. Call. The bias voltage generation circuit 14 includes operational amplifiers 1401-1404 and resistors 1405-1411.

The non-inverting input terminal of the operational amplifier 1401 is connected to one of the pair of output terminals of the Wheatstone bridge circuit 2, and the inverting input terminal is connected to the output terminal.
The non-inverting input terminal of the operational amplifier 1402 is connected to the other of the pair of output terminals of the Wheatstone bridge circuit 2, and the inverting input terminal is connected to the output terminal.

One end of the resistor 1405 is connected to the output terminal of the operational amplifier 1401.
One end of the resistor 1406 is connected to the output terminal of the operational amplifier 1402.
One end of the resistor 1407 is connected to the other end of the resistor 1405 and the other end of the resistor 1406, and the other end is connected to the ground.

The non-inverting input terminal of the operational amplifier 1403 is connected to the other end of the resistor 1405, the other end of the resistor 1406, and one end of the resistor 1407, and the output terminal is connected to the other end of the adjustment resistor 1301.
The non-inverting input terminal of the operational amplifier 1404 is connected to the other end of the resistor 1405, the other end of the resistor 1406, and one end of the resistor 1407, and the output terminal is connected to the other end of the adjustment resistor 1302.

One end of the resistor 1408 is connected to the inverting input terminal of the operational amplifier 1403, and the other end is connected to the other end of the adjustment resistor 1301 and the output terminal of the operational amplifier 1403.
One end of the resistor 1409 is connected to the inverting input terminal of the operational amplifier 1404, and the other end is connected to the other end of the adjustment resistor 1302 and the output terminal of the operational amplifier 1404.

One end of the resistor 1410 is connected to the inverting input terminal of the operational amplifier 1403 and one end of the resistor 1408. Note that the voltage of the signal input to the other end of the resistor 1410 is Vt1 ′.
One end of the resistor 1411 is connected to the inverting input terminal of the operational amplifier 1404 and one end of the resistor 1409. Note that the voltage of the signal input to the other end of the resistor 1411 is Vt2 ′.

The signal input to the resistor 1410 and the signal input to the resistor 1411 constitute an offset adjustment signal which is a differential signal. Further, the signal input to the resistor 1410 and the signal input to the resistor 1411 have different polarities and the same absolute value (includes substantially the same meaning). The voltage of the offset adjustment signal is three times the voltage of the offset component included in the differential signal input from the Wheatstone bridge circuit 2.
Note that the signal input to the resistor 1410 and the signal input to the resistor 1411 may be generated using, for example, a trimmer resistor as shown in FIG. 9 or generated using a DAC (digital analog converter) You may

Next, the principle of the offset adjustment by the instrumentation amplifier 1 configured as described above will be described with reference to FIG. In the instrumentation amplifier 1 shown in FIG. 2, the differential ADC 12 and the bias voltage generation circuit 14 are not shown.
As shown in FIG. 2, the current flowing through the feedback resistor 1103 is set to If1, the current flowing through the gain setting resistor 1105 is set to Ig1, and the current flowing through the adjustment resistor 1301 is set to It1. Further, the current flowing through the feedback resistor 1104 is set to If2, and the current flowing through the adjustment resistor 1302 is set to It2.

First, solving the circuit equation for the point a shown in FIG. 2 gives the following equations (1) to (4).
If1 =-(It1 + Ig1) (1)
If1 = (Vo1-Vi1) / Rf (2)
It1 = (Vt1-Vi1) / Rt (3)
Ig1 = (Vi2-Vi1) / Rg (4)

Substituting the equations (2) to (4) into the equation (1), the following equation (7) is obtained through the following equations (5) and (6).
(Vo1-Vi1) / Rf =-{(Vt1-Vi1) / Rt + (Vi2-Vi1) / Rg} (5)
(Vo1-Vi1) =-Rf * {(Vt1-Vi1) / Rt + (Vi2-Vi1) / Rg}
=-{(Rf / Rt) x (Vt1-Vi1) + (Rf / Rg) x (Vi2-Vi1)} (6)
Vo1 = Vi1- (Rf / Rt) * Vt1 + (Rf / Rt) * Vi1- (Rf / Rg) * Vi2 + (Rf / Rg) * Vi1 (7)

If the equation (7) is further organized, the following equation (8) is obtained.
Vo1 = {1+ (Rf / Rt) + (Rf / Rg)} * Vi1- (Rf / Rg) * Vi2- (Rf / Rt) * Vt1 (8)

Similarly, for the point b shown in FIG. 2, the following equation (9) can be obtained by solving and arranging the circuit equation.
Vo2 = {1+ (Rf / Rt) + (Rf / Rg)} * Vi2- (Rf / Rg) * Vi1- (Rf / Rt) * Vt2 (9)

Here, since the finally required output signal is the difference between the voltage Vo1 and the voltage Vo2, taking the difference between the equations (8) and (9) gives the following equation (10).
Vo1-Vo2 = {{1+ (Rf / Rt) + (Rf / Rg)} * Vi1- (Rf / Rg) * Vi2- (Rf / Rt) * Vt1}-{{1+ (Rf / Rt) + (Rf) / Rg)} * Vi2- (Rf / Rg) * Vi1- (Rf / Rt) * Vt2} (10)

The following equation (11) is obtained by arranging the equation (10).
Vo1-Vo2 = {1 + 2 * (Rf / Rg) + (Rf / Rt)} * Vi1- {1 + 2 * (Rf / Rg) + (Rf / Rt)} * Vi2- (Rf / Rt) * (Vt1-Vt2) )
= {1 + 2 x (Rf / Rg) + (Rf / Rt)} x (Vi1-Vi2)-(Rf / Rt) x (Vt1-Vt2) (11)

Here, when Rt = Rg, equation (11) becomes the following equation (12).
Vo1-Vo2 = {1 + 3 * (Rf / Rg)} * (Vi1-Vi2)-(Rf / Rg) * (Vt1-Vt2) (12)

Next, the differential signal input from the Wheatstone bridge circuit 2 to the differential amplifier 11 will be considered with reference to the equivalent circuit of the Wheatstone bridge circuit 2 shown in FIG.
In FIG. 3, Vs1 and Vs2 represent voltages of signal components included in the differential signal input to the differential amplifier 11, Voff represents voltages of offset components included in the differential signal, and Vcom represents the differential Represents the voltage of the common mode component contained in the signal.
Here, voltages Vi1 and Vi2 of differential signals input to the differential amplifier 11 are expressed by the following equations (13) and (14), respectively.
Vi1 = Vs1 + Voff + Vcom (13)
Vi2 = Vs2 + Vcom (14)

Substituting the equations (13) and (14) into the equation (12) gives the following equation (15).
Vo1-Vo2 = {1 + 3 * (Rf / Rg)} * {(Vs1 + Voff + Vcom)-(Vs2 + Vcom)}-(Rf / Rg) * (Vt1-Vt2)
= {1 + 3 x (Rf / Rg)} x {(Vs 1-Vs 2) + Voff}-(Rf / Rg) x (Vt 1-Vt 2)
= {1 + 3 x (Rf / Rg)} x (Vs 1-Vs 2) + {1 + 3 x (Rf / Rg)} x Voff-(Rf / Rg) x (Vt 1-Vt 2) (15)

Expression (15) shows the differential signal output from the differential amplifier 11 before offset adjustment. Then, in the equation (15), the offset component is amplified as {1 + 3 × (Rf / Rg)} × Voff. Therefore, the offset adjustment signal of the voltage (Vt1-Vt2) represented by the following equation (16) is injected into the differential amplifier 11 using the offset adjustment circuit 13.
(Vt1-Vt2) = 3 × Voff (16)

That is, the following equation (17) is obtained by substituting the equation (16) into the equation (15). Thus, the instrumentation amplifier 1 can amplify only the signal component of the differential signal input to the differential amplifier 11 without amplifying the offset component.
Vo1-Vo2 = {1 + 3 * (Rf / Rg)} * (Vs1-Vs2) + {1 + 3 * (Rf / Rg)} * Voff-3 * (Rf / Rg) * Voff
= {1 + 3 x (Rf / Rg)} x (Vs1-Vs2) + Voff (17)

Further, by using the offset adjustment circuit 13, as shown in the following equations (18) and (19), the gain can be made larger than that of the conventional instrumentation amplifier. In equations (18) and (19), G1 represents the gain in the instrumentation amplifier 1 according to the first embodiment, and G2 represents the gain in the conventional instrumentation amplifier.
G1 = 1 + 3 × (Rf / Rg) (18)
G2 = 1 + 2 × (Rf / Rg) (19)

On the other hand, the offset adjustment signal input to the offset adjustment circuit 13 may not be any value as long as equation (16) is satisfied.

By transforming equation (7), the following equation (20) is obtained.
Vo1 = Vi1- (Rf / Rg) * (Vi2-Vi1)-(Rf / Rt) * (Vt1-Vi1) (20)
From this equation (20), it can be understood that when the value of (Vt1-Vi1) is large, the voltage Vo1 of the signal output from the operational amplifier 1101 may be saturated. The same applies to the voltage Vo2 of the signal output from the operational amplifier 1102.

Therefore, using the bias voltage generation circuit 14, the voltage of the common mode component included in the differential signal input from the Wheatstone bridge circuit 2 to the differential amplifier 11 is used as a bias voltage, and the offset adjustment signal is input to the offset adjustment circuit 13. Bias the At this time, by optimizing the resistance values of the resistors 1405 to 1411 in the bias voltage generation circuit 14, voltages Vt1 and Vt2 represented by the following equations (21) and (22) are obtained. As a result, (Vt1-Vi1) and (Vt2-Vi2) can be reduced, and saturation of the voltages Vo1 and Vo2 of the signal output from the differential amplifier 11 can be avoided. In equations (21) and (22), VB is a bias voltage, which is expressed by the following equation (23).
Vt1 = VB−Vt1 ′ (21)
Vt2 = VB−Vt2 ′ (22)
VB = (Vi1 + Vi2) / 2 (23)

As described above, by using the offset adjustment circuit 13 and the bias voltage generation circuit 14 to input an offset adjustment signal of a voltage satisfying the equations (16), (21) and (22) to the differential amplifier 11, a differential The offset component contained in the differential signal input to the amplifier 11 can amplify only the signal component without amplification. On the other hand, by devising the method of inputting the offset adjustment signal, the gain can be further increased.

Hereinafter, in order to simplify the description, signal components included in the differential signal input to the differential amplifier 11 will be omitted. That is, the equations (13) and (14) become as the following equations (24) and (25).
Vi1 = Voff + Vcom (24)
Vi2 = Vcom (25)

Further, substituting Formulas (24) and (25) into Formula (23), the following Formula (26) is obtained.
VB = (Vi1 + Vi2) / 2 = Vcom + (Voff / 2) (26)

Further, when equation (26) is substituted into equations (21) and (22), the following equations (27) and (28) are obtained.
Vt1 = {Vcom + (Voff / 2)}-Vt1 '(27)
Vt2 = {Vcom + (Voff / 2)}-Vt2 '(28)

And if Formula (24), (25), (27) is substituted in Formula (8), the following Formula (29) will be obtained.
Vo1 = {1+ (Rf / Rt) + (Rf / Rg)} * (Voff + Vcom)-(Rf / Rg) * Vcom- (Rf / Rt) * {{Vcom + (Voff / 2)}-Vt1 '}
= {1 + (Rf / Rt) + (Rf / Rg)} x Voff + {1 + (Rf / Rt)} x Vcom-(Rf / Rt) x Vcom-(Rf / Rt) x (Voff / 2) + (Rf) / Rt) × Vt1 ′
= {1 + (1/2) x (Rf / Rt) + (Rf / Rg)} x Voff + Vcom + (Rf / Rt) x Vt 1 '(29)

Here, when Rg = Rt = R, the equation (29) becomes the following equation (30).
Vo1 = {1+ (1/2) * (Rf / R) + (Rf / R)} * Voff + Vcom + (Rf / R) * Vt1 '
= {1 + (3/2) x (Rf / R)} x Voff + Vcom + (Rf / R) x Vt1 '(30)

Similarly, substituting Formulas (24), (25), and (28) into Formula (9), the following Formula (31) is obtained.
Vo2 = {1+ (Rf / Rt) + (Rf / Rg)} * Vcom- (Rf / Rg) * (Voff + Vcom)-(Rf / Rt) * {{Vcom + (Voff / 2)}-Vt2 '}
= {1 + (Rf / Rt)} x Vcom-(Rf / Rg) x Voff-(Rf / Rt) x Vcom-(Rf / Rt) x (Voff / 2) + (Rf / Rt) x Vt 2 '
= Vcom-{(Rf / Rg) + (1/2) x (Rf / Rt)} x Voff + (Rf / Rt) x Vt 2 '(31)

Here, if it is set as Rg = Rt = R, a formula (31) will become the following formula (32).
Vo2 = Vcom-{(Rf / R) + (1/2) * (Rf / R)} * Voff + (Rf / R) * Vt2 '
= Vcom-(3/2) x (Rf / R) x Voff + (Rf / R) x Vt 2 '(32)

Here, for example, it is assumed that the voltage Vt1 ′ = 0 and the voltage Vt2 ′ = 3 × Voff so as to satisfy the equation (16). In this case, the equations (30) and (32) become the following equations (33) and (34), and the voltage obtained by amplifying the offset component is superimposed on the voltages Vo1 and Vo2 of the signals output from the differential amplifier 11 .
Vo1 = (1+ (3/2) × (Rf / R)) × Voff + Vcom (33)
Vo2 = Vcom- (3/2) × (Rf / R) × Voff + 3 × (Rf / R) × Voff
= (3/2) x (Rf / R) x Voff + Vcom (34)

If the difference (Vo1-Vo2) between the equations (33) and (34) is taken, the offset component will be adjusted. However, the output range of the voltages Vo1 and Vo2 becomes narrow in the first place. I can not

Therefore, the offset adjustment signal is divided equally (including substantially equal meaning), and voltages Vt1 ′ and Vt2 ′ are set to values having different polarities and the same absolute value. That is, the voltages Vt1 ′ and Vt2 ′ are set to values satisfying the following equations (35) and (36).
Vt1 ′ = − (3/2) × Voff (35)
Vt2 '= (3/2) x Voff (36)

Accordingly, the equations (30) and (32) become the following equations (37) and (38), and the voltage obtained by amplifying the offset component can be adjusted from the voltages Vo1 and Vo2 of the signals output from the differential amplifier 11. Thus, the gain can be made large as compared with the case where the offset adjustment signal is not divided evenly.
Vo1 = {1+ (3/2) × (Rf / R)} × Voff + Vcom− (3/2) × (Rf / R) × Voff
= Voff + Vcom (37)
Vo2 = Vcom- (3/2) * (Rf / R) * Voff + (3/2) * (Rf / R) * Voff
= Vcom (38)

Examples of simulation results of offset adjustment by the instrumentation amplifier 1 according to the first embodiment of the present invention are shown in FIGS. FIG. 4 shows the case where the offset adjustment signal is not divided equally, and FIG. 5 shows the case where the offset adjustment signal is divided equally. Here, the differential signal input to the differential amplifier 11 is 30 mVpp of 1 KHz sine wave, the voltage of the offset component included in the differential signal is 100 mV, and the voltage of the common mode component included in the differential signal is The gain of the instrumentation amplifier 1 is 46 times that of 2.5 V. Since the voltage of the offset component is 100 mV, an offset adjustment signal of 300 mV is injected from equation (16). 4 and 5, reference numerals 401 and 501 indicate differential signals input to the differential amplifier 11, reference numerals 402 and 502 indicate voltages of offset components, reference numerals 403 and 503 indicate voltage Vo1, and reference numeral 404. , 504 indicate voltage Vo2, and reference numerals 405, 505 indicate differential signals output from the differential amplifier 11.

As shown in FIG. 4, when the offset adjustment signal is not divided evenly, the voltage obtained by amplifying the offset component is superimposed on the voltages Vo1 and Vo2, and it saturates near the power supply voltage (+5 V) and functions as an amplifier I understand that I did not.
On the other hand, as shown in FIG. 5, when the offset adjustment signal is divided equally, there is no voltage obtained by amplifying the offset component in the voltages Vo1 and Vo2, and the voltage changes near the common mode (+2.5 V). It functions normally as an amplifier. Further, since there is still a margin to the saturation voltage, the gain can be further increased.

The method of using the voltage of the common mode component contained in the differential signal as the bias voltage is not limited to the circuit shown in FIG. 1, and for example, the circuit shown in FIG. 6 may be used. In FIG. 6, the differential ADC 12 is not shown.
In FIG. 6, the operational amplifier 1401 and the resistor 1405 are removed from the instrumentation amplifier 1 shown in FIG.

As described above, according to the first embodiment, the differential amplifier 11 for amplifying the input differential signal and the voltage of the common mode component included in the differential signal input to the differential amplifier 11 are biased. A bias voltage generation circuit 14 for applying a voltage to the input offset adjustment signal and a bias voltage generation circuit 14 connected to the differential amplifier 11 and biased by the bias voltage generation circuit 14 are input to the differential amplifier 11 by the offset adjustment signal. And an offset adjustment circuit 13 for adjusting an offset component included in the differential signal, and the offset adjustment signal input to the bias voltage generation circuit 14 is formed of two signals having different polarities and the same absolute value. Therefore, it is possible to amplify only the signal component of the differential signal input to the differential amplifier 11 without amplifying the offset component. That. Further, in the instrumentation amplifier 1 according to the first embodiment, by connecting the offset adjustment circuit 13 to the differential amplifier 11, the gain is large compared to the case where the offset adjustment circuit is connected to the single end amplifier as in the prior art. It is possible to take. Furthermore, by dividing the offset adjustment signal evenly, it is possible to further increase the gain.

Further, by connecting the differential ADC 12 to the subsequent stage of the differential amplifier 11, a single-ended amplifier as in the prior art can be omitted. As a result, the differential signal can be processed as it is, and the noise resistance performance is improved.

Although FIG. 1 shows the case where the differential ADC 12 is used, the present invention is not limited to this, and as shown in FIG. 7, a single end amplifier 15 may be used instead of the differential ADC 12.
The single end amplifier 15 converts the differential signal input from the differential amplifier 11 into a single end signal. The single end amplifier 15 includes an operational amplifier 1501, input resistors 1502 to 1504, and a feedback resistor 1505.

One end of the input resistor 1502 is connected to the output terminal of the operational amplifier 1101 and the other end of the feedback resistor 1103, and the other end is connected to the non-inverting input terminal of the operational amplifier 1501.
One end of the input resistor 1503 is connected to the output terminal of the operational amplifier 1102 and the other end of the feedback resistor 1104, and the other end is connected to the inverting input terminal of the operational amplifier 1501.

One end of the input resistor 1504 is connected to the non-inverting input terminal of the operational amplifier 1501 and the other end of the input resistor 1502, and the other end is connected to the ground.
One end of the feedback resistor 1505 is connected to the inverting input terminal of the operational amplifier 1501 and the other end of the input resistor 1503, and the other end is connected to the output terminal of the operational amplifier 1501.

The bias voltage generation circuit 14 shown in FIG. 7 may be changed to the bias voltage generation circuit 14 shown in FIG.

In the present invention, within the scope of the invention, modifications of optional components of the embodiment or omission of optional components of the embodiment is possible.

Since the instrumentation amplifier according to the present invention has an offset adjustment function and can take a large gain, it is used in the instrumentation amplifier for adjusting the offset component included in the input differential signal. Is suitable.

1 instrumentation amplifier 2 Wheatstone bridge circuit 11 differential amplifier 12 differential ADC
13 Offset Adjustment Circuit 14 Bias Voltage Generation Circuit 15 Single-Ended Amplifier 1101, 1102 Op Amp 1103, 1104 Feedback Resistor 1105 Gain Setting Resistor 1301, 1302 Adjustment Resistor 1401 ̃ 1404 Op Amp 1405 ̃ 1411 Resistor 1501 Op Amp 1502 ̃ 1504 Input Resistor 1505 Feedback Resistor

Claims (3)

A differential amplifier that amplifies the input differential signal,
A bias voltage generation circuit that sets a voltage of a common mode component included in a differential signal input to the differential amplifier as a bias voltage and biases the input offset adjustment signal;
An offset adjustment circuit connected to the differential amplifier and configured to adjust an offset component included in the differential signal input to the differential amplifier by the offset adjustment signal biased by the bias voltage generation circuit;
The offset adjustment signal input to the bias voltage generation circuit is composed of two signals having different polarities and the same absolute value. The amplifier according to claim 1, wherein the voltage of the offset adjustment signal input to the bias voltage generation circuit is three times the voltage of the offset component included in the differential signal input to the differential amplifier. . The amplifier according to claim 1, further comprising: a differential analog-to-digital converter that converts a differential signal amplified by the differential amplifier into a differential signal.

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