Programmable gain operational amplifier PGA, self-correction system and self-correction method thereof

Abstract

A programmable gain operational amplifier PGA comprises an integrated operational amplifier A21, a driver A22, a programmable resistor R21, a resistor R22, a resistor R23, a programmable resistor R24, a resistor R25, a switch S1, a switch S2, a switch S3 and a switch S4. A switch S1 is connected between the in-phase input end of the integrated operational amplifier A21 and the input port VIP2 of the programmable gain operational amplifier PGA; the in-phase input end of the integrated operational amplifier A21 is sequentially connected with a switch S2 and a resistor R25 and then is grounded; the in-phase input end of the integrated operational amplifier A21 is sequentially connected with a switch S2, a programmable resistor R24 and a driver A22; a programmable resistor R21 is connected between the out-phase input end and the out-phase output end of the integrated operational amplifier A21; the out-phase input end of the integrated operational amplifier A21 is sequentially connected with a resistor R22 and a switch S4 and then is grounded; the out-phase input end of the integrated operational amplifier A21 is connected with a resistor R22, a switch S3 and a resistor R23 and then is grounded. According to the invention, the self-correction of the gain error can be realized, and the accurate gain is obtained.

Description

Technical Field

[0001] The present invention relates to a programmable gain operational amplifier (PGA), a self-calibration system and a self-calibration method thereof. Background Art

[0002] Programmable gain operational amplifiers (PGAs) are widely used in industrial control, motors, household appliances, power supplies and other products. Their typical application is to sample and amplify current. In an application system, an analog-to-digital converter (ADC) is used to convert the amplified current, and the converted data is applied to the algorithm of the CPU to achieve control of the entire system.

[0003] Traditional programmable operational amplifiers such as Figure 1 As shown, R11 and R12 are internal resistors of the chip, where R11 is a programmable resistor. During the chip production process, there will actually be a certain deviation in the resistance values of R11 and R12, and the maximum deviation can be ±30%. With the current chip production technology, although there are deviations in the resistance values, the ratio of R11 and R12 is fixed. Since the gain of the PGA is equal to R11 / R12 + 1, the gain of the PGA is fixed.

[0004] In practical applications, a resistor is connected in series at the input port of the operational amplifier to prevent high voltage from damaging the chip. And the selectable gain levels of the programmable PGA are limited. This series resistor is also used to adjust the gain of the PGA. Due to the introduction of this series resistor at the input end, the gain of the PGA becomes uncertain.

[0005] Such as Figure 1 With the introduction of R13, the gain of the PGA becomes R11 / (R12 + R13)+1. The highest accuracy of the resistance value of the series resistor R13 at the input port is only ±1%, while the actual deviation of the resistance values of R12 and R11 is even greater. Although it is required that R12 is much larger than R13 during use, the actual gain error is still greater than 2%, resulting in deviation of the entire system. Summary of the Invention

[0006] The technical problem to be solved by the present invention is: to provide a programmable gain operational amplifier (PGA), a self-calibration system and a self-calibration method thereof, which can achieve self-calibration of gain error and obtain accurate gain.

[0007] To solve the above technical problem, the present invention provides the following technical solution: A programmable gain operational amplifier (PGA) includes an integrated operational amplifier A21, a driver A22, a programmable resistor R21, a resistor R22, a resistor R23, a programmable resistor R24, a resistor R25, a switch S1, a switch S2, a switch S3 and a switch S4; A switch S1 is connected between the non-inverting input terminal of the integrated operational amplifier A21 and the input port VIP2 of the programmable gain amplifier PGA; The non-inverting input terminal of the integrated operational amplifier A21 is grounded after being sequentially connected to a switch S2 and a resistor R25; The non-inverting input terminal of the integrated operational amplifier A21 is sequentially connected to a switch S2, a programmable resistor R24, and a driver A22; A programmable resistor R21 is connected between the inverting input terminal and the output terminal of the integrated operational amplifier A21; The inverting input terminal of the integrated operational amplifier A21 is grounded after being sequentially connected to a resistor R22 and a switch S4; The inverting input terminal of the integrated operational amplifier A21 is grounded after being connected to a resistor R22, a switch S3, and a resistor R23.

[0008] The further limitation of the above technical solution is that the actual gain of the programmable gain amplifier PGA is R21 / (R22 + R23)+1.

[0009] The further limitation of the above technical solution is that the resistor R25, the programmable resistor R24, and the driver A22 are used to provide a bias voltage to the non-inverting input terminal of the integrated operational amplifier A21, where the resistance value R25 = R22 and the resistance value R24 = R21. When programming the gain of the PGA, the change in the resistance values of R24 and R25 completely follows R21 and R22 and always remains equal.

[0010] To solve the above technical problems, the present invention proposes the following technical solution: A programmable gain amplifier PGA self-calibration system, including a programmable gain amplifier PGA, an analog-to-digital converter ADC, and a control module CTRL that are sequentially electrically connected, and the control module CTRL is electrically connected to the programmable gain amplifier PGA; The programmable gain amplifier PGA includes an integrated operational amplifier A21, a driver A22, a programmable resistor R21, a resistor R22, a resistor R23, a programmable resistor R24, a resistor R25, a switch S1, a switch S2, a switch S3, and a switch S4; A switch S1 is connected between the non-inverting input terminal of the integrated operational amplifier A21 and the input port VIP2 of the programmable gain amplifier PGA; The non-inverting input terminal of the integrated operational amplifier A21 is grounded after being sequentially connected to a switch S2 and a resistor R25; The non-inverting input terminal of the integrated operational amplifier A21 is sequentially connected to a switch S2, a programmable resistor R24, and a driver A22; A programmable resistor R21 is connected between the inverting input terminal and the output terminal of the integrated operational amplifier A21; The non-inverting input terminal of the integrated operational amplifier A21 is connected to the ground after being connected to the resistor R22 and the switch S4 in sequence; The non-inverting input terminal of the integrated operational amplifier A21 is connected to the ground after being connected to the resistor R22, the switch S3 and the resistor R23; The control module CTRL is composed of a CPU and a logic circuit inside the chip; The driver A22 is enabled by the control module CTRL, and the switches S1, S2, S3 and S4 are controlled to be turned on and off by the control module CTRL. The on-resistances of the switches S3 and S4 are less than 1‰ of the value of R21 + R22; The analog-to-digital converter ADC is used to detect the values of the bias voltage VREF output by the driver A22 and the output VOUT of the integrated operational amplifier A21, and give the converted values to the control module CTRL.

[0011] A further limitation of the above technical solution is that the actual gain of the programmable gain amplifier PGA is R21 / (R22 + R23)+1.

[0012] A further limitation of the above technical solution is that the resistors R25, the programmable resistor R24 and the driver A22 are used to provide a bias voltage to the non-inverting input terminal of the integrated operational amplifier A21, where the value of R25 = R22 and the value of R24 = R21. When programming the gain of the PGA, the changes in the values of R24 and R25 completely follow R21 and R22 and always remain equal.

[0013] A further limitation of the above technical solution is that the effective conversion accuracy of the analog-to-digital converter ADC is greater than or equal to 10 bits.

[0014] In order to solve the above technical problems, the present invention proposes the following technical solution: A self-calibration method for applying a programmable gain amplifier PGA self-calibration system, including the following steps: Step 1: The control module CTRL enables the driver A22 in the PGA, the switches S1 and S3 are disconnected, and the switches S2 and S4 are closed; the analog-to-digital converter ADC respectively converts the output VOUT1 voltage of the integrated operational amplifier A21 at this time to obtain the conversion data Dvout1, and gives it to the control module CTRL; Since the resistor R25 = R22 and the value of R24 = R21, theoretically the output of VOUT should be equal to VREF; actually, due to the offset voltage existing in the integrated operational amplifier A21, there will be a deviation between the VOUT1 voltage and VREF; the gain of the PGA is Av = R21 / R22 + 1, and the offset voltage Vos equivalent to the input terminal of the integrated operational amplifier A21: Equation 1: Vos=(VOUT1 - VREF) / Av; Step 2: Keep the enable of driver A22, keep switch S1 open and switch S2 closed; the control module CTRL controls switch S3 to close and switch S4 to open; at this time, the externally series resistor R23 is connected to the internal resistor R22, and the analog-to-digital converter ADC converts the output VOUT2 voltage at this time to obtain the conversion data Dvout2, and gives it to the control module CTRL; Assume the actual gain is Av´, and the voltage of the positive input terminal INP of the operational amplifier is VREF / Av. Therefore, the operational amplifier output voltage VOUT2 at this time is: Equation 2: VOUT2 = (VREF / Av + Vos) * Av´; Step 3: The control module CTRL turns off driver A22, switches S1 and S3 are closed, switches S2 and S4 are open, and the circuit of the PGA returns to the normal working mode; the control module CTRL calculates the true gain value according to the results of the two conversions, which is the self-calibration of the gain; According to Equation 1 and Equation 2, substitute VREF, VOUT1, and VOUT2 with the conversion data Dvref, Dvout1, and Dvout2, and the actual Av´ = Dvout2 / Dvout1 * Av is obtained.

[0015] The present invention has the following beneficial effects: The present invention proposes a self-calibration system and method for a programmable gain operational amplifier, which can realize self-calibration of gain errors. The present invention makes full use of the internal ADC and CPU modules of the chip, changes the PGA module, and constructs the self-calibration system. By using the self-calibration method proposed by the present invention, accurate measurement of the internal resistor is realized. In applications such as industrial control, motors, household appliances, and power supplies, in the case of an externally series resistor, the influence brought by the production process deviation of the internal resistor is effectively solved, and accurate gain is obtained. Brief Description of the Drawings

[0016] Figure 1 It is the circuit diagram of a programmable gain operational amplifier (PGA) in the prior art.

[0017] Figure 2 It is the circuit diagram of the programmable gain operational amplifier PGA of the present invention.

[0018] Figure 3 It is the schematic diagram of the self-calibration system of the programmable gain operational amplifier PGA of the present invention. Detailed Embodiment

[0019] Such as Figure 2As shown in the figure, the present invention proposes a programmable gain operational amplifier PGA (Programmable Gain Amplifier), which includes an integrated operational amplifier A21, a driver A22, a programmable resistor R21, a resistor R22, a resistor R23, a programmable resistor R24, a resistor R25, a switch S1, a switch S2, a switch S3, and a switch S4.

[0020] A switch S1 is connected between the non-inverting input terminal of the integrated operational amplifier A21 and the input port VIP2 of the programmable gain operational amplifier PGA.

[0021] The non-inverting input terminal of the integrated operational amplifier A21 is connected to the ground after sequentially connecting a switch S2 and a resistor R25.

[0022] The non-inverting input terminal of the integrated operational amplifier A21 is sequentially connected to a switch S2, a programmable resistor R24, and a driver A22.

[0023] A programmable resistor R21 is connected between the inverting input terminal and the output terminal of the integrated operational amplifier A21.

[0024] The inverting input terminal of the integrated operational amplifier A21 is connected to the ground after sequentially connecting a resistor R22 and a switch S4.

[0025] The inverting input terminal of the integrated operational amplifier A21 is connected to the ground after connecting a resistor R22, a switch S3, and a resistor R23.

[0026] The gain of the above programmable gain operational amplifier PGA is determined by the internal resistor R22, the internal programmable resistor R21, and the externally series-connected resistor R23, and the actual gain is R21 / (R22 + R23)+1.

[0027] The resistor R25, the programmable resistor R24, and the driver A22 are used to provide a bias voltage to the non-inverting input terminal (positive terminal) of the integrated operational amplifier A21, where the resistance value R25 = R22 and the resistance value R24 = R21. When programming the gain of the PGA, the changes in the resistance values of R24 and R25 completely follow those of R21 and R22 and always remain equal.

[0028] In the actual layout implementation of the circuit, the programmable resistor R21, the resistor R22, the programmable resistor R24, and the resistor R25 need to be well matched, and it is easy to achieve a relative error less than 1‰.

[0029] As Figure 3 shown, the present invention proposes a programmable gain operational amplifier PGA self-calibration system, which includes the programmable gain operational amplifier PGA as Figure 2 shown, and further includes a control module CTRL and an analog-to-digital converter ADC.

[0030] A programmable gain operational amplifier PGA, an analog-to-digital converter ADC, and a control module CTRL are electrically connected in sequence, and the control module CTRL is electrically connected to the programmable gain operational amplifier PGA.

[0031] The control module CTRL can be composed of a CPU and logic circuits inside the chip to achieve control during the self-calibration process.

[0032] The driver A22 is enabled by the control module CTRL, and the switches S1, S2, S3, and S4 are also controlled by the control module CTRL to be turned on and off. The on-resistances of switches S3 and S4 should be less than 1‰ of the value of R21 + R22.

[0033] The analog-to-digital converter ADC is used to detect the values of the bias voltage VREF output by the driver A22 and the output VOUT of the integrated operational amplifier A21, and give the converted values to the control module CTRL. To ensure the accuracy of calibration, the effective conversion accuracy of the analog-to-digital converter ADC should be greater than or equal to 10 bits, and this accuracy is also easy to achieve for the ADC inside the chip.

[0034] The present invention proposes a self-calibration method applying the above self-calibration system of the programmable gain operational amplifier PGA, including the following steps: Step 1 (first conversion): The control module CTRL enables the driver A22 in the PGA, switches S1 and S3 are turned off, and switches S2 and S4 are turned on. The analog-to-digital converter ADC respectively converts the output VOUT1 voltage of the integrated operational amplifier A21 at this time to obtain the conversion data Dvout1, and gives it to the control module CTRL.

[0035] Since the resistance R25 = R22 and the resistance value R24 = R21, theoretically the output of VOUT should be equal to VREF. Actually, due to the offset voltage existing in the integrated operational amplifier A21, there will be a deviation between the VOUT1 voltage and VREF. The gain of the PGA is Av = R21 / R22 + 1, and the offset voltage Vos of the integrated operational amplifier A21 equivalent to the input end is: Equation 1: Vos = (VOUT1 - VREF) / Av.

[0036] Step 2 (second conversion): Keep the driver A22 enabled, keep switch S1 off and switch S2 on. The control module CTRL controls switch S3 to turn on and switch S4 to turn off. At this time, the externally series-connected resistor R23 is connected to the internal resistor R22, and the analog-to-digital converter ADC converts the output VOUT2 voltage at this time to obtain the conversion data Dvout2, and gives it to the control module CTRL.

[0037] Assume the actual gain is Av´, and the voltage of the positive input terminal INP of the operational amplifier is VREF / Av. Therefore, the output voltage VOUT2 of the operational amplifier at this time is: Equation 2: VOUT2 = (VREF / Av + Vos) * Av´.

[0038] Step 3 (self - calibration calculation): The control module CTRL turns off the driver A22. The switch S1 and switch S3 are closed, and the switch S2 and switch S4 are opened. The circuit of the PGA returns to the normal working mode. The control module CTRL calculates the true gain value according to the results of the two conversions, which is the self - calibration of the gain.

[0039] According to Equation 1 and Equation 2, substituting VREF, VOUT1, and VOUT2 with the conversion data Dvref, Dvout1, and Dvout2, the actual Av´ = Dvout2 / Dvout1 * Av is obtained.

[0040] The present invention has the following beneficial effects: The self - calibration system and the self - calibration method of the programmable gain operational amplifier PGA of the present invention can realize the self - calibration of the gain error. The present invention makes full use of the internal ADC and CPU modules of the chip, modifies the PGA module, and constructs the self - calibration system. By adopting the self - calibration method proposed by the present invention, the accurate measurement of the internal resistance is realized, and finally the accurate gain value error can be less than one thousandth. In applications such as industrial control, motors, household appliances, and power supplies, in the case of an external series resistor, the influence brought by the production process deviation of the internal resistance is effectively solved, and an accurate gain is obtained.

Claims

1. A programmable gain operational amplifier PGA, characterized in that: It includes an integrated operational amplifier A21, a driver A22, a programmable resistor R21, a resistor R22, a resistor R23, a programmable resistor R24, a resistor R25, a switch S1, a switch S2, a switch S3, and a switch S4; A switch S1 is connected between the non-inverting input terminal of the integrated operational amplifier A21 and the input port VIP2 of the programmable gain operational amplifier PGA; The non-inverting input terminal of the integrated operational amplifier A21 is sequentially connected to the switch S2 and the resistor R25 and then grounded; The non-inverting input terminal of the integrated operational amplifier A21 is sequentially connected to the switch S2, the programmable resistor R24, and the driver A22; A programmable resistor R21 is connected between the inverting input terminal and the output terminal of the integrated operational amplifier A21; The inverting input terminal of the integrated operational amplifier A21 is sequentially connected to the resistor R22 and the switch S4 and then grounded; The inverting input terminal of the integrated operational amplifier A21 is connected to the resistor R22, the switch S3, and the resistor R23 and then grounded; 2. The programmable gain operational amplifier PGA according to claim 1, wherein: The actual gain of the programmable gain operational amplifier PGA is R21 / (R22 + R23)+1.

3. The programmable gain operational amplifier PGA according to claim 1, wherein: The resistor R25, the programmable resistor R24, and the driver A22 are used to provide a bias voltage to the non-inverting input terminal of the integrated operational amplifier A21, where the resistance value R25 = R22 and the resistance value R24 = R21. When programming the gain of the PGA, the changes in the resistance values of R24 and R25 completely follow R21 and R22 and always remain equal.

4. A programmable gain operational amplifier (PGA) self - calibration system, characterized in that, It includes a programmable gain operational amplifier PGA, an analog-to-digital converter ADC, and a control module CTRL that are electrically connected in sequence, and the control module CTRL is electrically connected to the programmable gain operational amplifier PGA; The programmable gain operational amplifier PGA includes an integrated operational amplifier A21, a driver A22, a programmable resistor R21, a resistor R22, a resistor R23, a programmable resistor R24, a resistor R25, a switch S1, a switch S2, a switch S3, and a switch S4; A switch S1 is connected between the non-inverting input terminal of the integrated operational amplifier A21 and the input port VIP2 of the programmable gain operational amplifier PGA; The non-inverting input terminal of the integrated operational amplifier A21 is sequentially connected to the switch S2 and the resistor R25 and then grounded; The non-inverting input terminal of the integrated operational amplifier A21 is sequentially connected to the switch S2, the programmable resistor R24, and the driver A22; A programmable resistor R21 is connected between the inverting input terminal and the output terminal of the integrated operational amplifier A21; The inverting input terminal of the integrated operational amplifier A21 is sequentially connected to the resistor R22 and the switch S4 and then grounded; The inverting input terminal of the integrated operational amplifier A21 is connected to the resistor R22, the switch S3, and the resistor R23 and then grounded; The control module CTRL is composed of a CPU and a logic circuit inside the chip; The driver A22 is enabled by the control module CTRL, and the switches S1, S2, S3, and S4 are turned on and off by the control module CTRL. The on-resistances of the switches S3 and S4 are less than 1‰ of the resistance value of R21 + R22; The analog-to-digital converter ADC is used to detect the values of the bias voltage VREF output by the driver A22 and the output VOUT of the integrated operational amplifier A21, and send the converted values to the control module CTRL.

5. The programmable gain operational amplifier PGA self-calibration system according to claim 4, characterized in that, The actual gain of the programmable gain operational amplifier PGA is R21 / (R22+R23)+1.

6. The programmable gain operational amplifier PGA self-calibration system according to claim 4, wherein: The resistor R25, the programmable resistor R24 and the driver A22 are used to provide a bias voltage to the non-inverting input terminal of the integrated operational amplifier A21, where the resistance value R25 = R22 and the resistance value R24 = R21. When programming the gain of the PGA, the changes in the resistance values of R24 and R25 completely follow R21 and R22 and always remain equal.

7. The programmable gain operational amplifier PGA self-calibration system according to claim 4, characterized in that: The effective conversion accuracy of the analog-to-digital converter ADC is greater than or equal to 10 bits.

8. A self-calibration method for a programmable gain operational amplifier (PGA) self-calibration system applying one of claims 4-7, characterized in that It includes the following steps: Step 1: The control module CTRL enables the driver A22 in the PGA, the switch S1 and the switch S3 are disconnected, and the switch S2 and the switch S4 are closed; the analog-to-digital converter ADC converts the output VOUT1 voltage of the integrated operational amplifier A21 at this time respectively, obtains the conversion data Dvout1, and sends it to the control module CTRL; Because the resistor R25 = R22 and the resistance value R24 = R21, theoretically the output of VOUT should be equal to VREF; actually, due to the offset voltage existing in the integrated operational amplifier A21, there will be a deviation between the VOUT1 voltage and VREF; the gain of the PGA is Av = R21 / R22+1, and the offset voltage Vos equivalent to the input terminal of the integrated operational amplifier A21: Equation 1: Vos=(VOUT1-VREF) / Av; Step 2: Keep the driver A22 enabled, keep the switch S1 disconnected and the switch S2 closed; the control module CTRL controls the switch S3 to be closed and the switch S4 to be disconnected; at this time, the externally connected resistor R23 and the internal resistor R22 are connected, and the analog-to-digital converter ADC converts the output VOUT2 voltage at this time, obtains the conversion data Dvout2, and sends it to the control module CTRL; Assume that the actual gain is Av´, and the voltage of the positive input terminal INP of the operational amplifier is VREF / Av, so the output voltage VOUT2 of the operational amplifier at this time is: Equation 2: VOUT2=(VREF / Av+Vos)* Av´; Step 3: The control module CTRL turns off the driver A22, the switch S1 and the switch S3 are closed, the switch S2 and the switch S4 are disconnected, and the circuit of the PGA returns to the normal working mode; the control module CTRL calculates the true gain value according to the results of the two conversions, which is the self-calibration of the gain; According to Equation 1 and Equation 2, substitute VREF, VOUT1 and VOUT2 with the conversion data Dvref, Dvout1 and Dvout2 respectively, and obtain the actual Av´ = Dvout2 / Dvout1*Av.

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