A method and circuit for measuring input offset voltage

Abstract

The present invention discloses a circuit for measuring input offset voltage, comprising: a first resistor R1, a first end of which is connected to a first voltage input end of an operational amplifier, and a second end of which is connected to a first end of a second switch; a second end of the second switch, a second end of which is connected to a voltage output end of the operational amplifier and to a first end of a third switch; a second end of the third switch, a second end of which is connected to the first end of the first switch and to an input end of an analog-to-digital converter ADC; and a second end of the first switch, a second end of which is connected to an output end of a DC voltage source.

Description

Technical Field

[0001] The present invention relates to the field of integrated operational amplifiers, and in particular to a circuit and method for measuring input offset voltage. Background Art

[0002] An integrated operational amplifier (IOA), or ICOPAM for short, is an integrated circuit with a high amplification factor. It consists of three parts: an input stage, an intermediate stage, and an output stage. The input stage typically uses a differential amplifier circuit. Ideally, when the input voltage is 0V, the output voltage should also be 0V. However, in practice, since the differential amplifier circuit in the input stage is difficult to achieve complete symmetry, a certain output voltage typically exists when the input voltage is 0V. In this case, to ensure that the output voltage is 0V, a compensation voltage, namely the input offset voltage, is added to the input stage.

[0003] At present, the input offset voltage is mainly measured in the form of an external amplifier circuit during the finished product test (FT) or wafer test (CP test) stage, such as Figure 1 As shown, it is mainly through the on-chip operational amplifier AMP and the off-chip resistor R p and R n Together they form a proportional amplifier, which adjusts the input offset voltage V os Amplify the scale v After multiplying, use a high-performance multimeter to measure the output voltage V out , and then calculate V os =V out / A v This method places high demands on the accuracy of the input voltage source and the test machine and requires off-chip equipment to participate in the test, which increases the complexity and cost of the test method. Summary of the Invention

[0004] To address some or all of the problems in the prior art, the present invention provides a circuit and method for measuring input offset voltage, wherein the input offset voltage measurement circuit is an on-chip circuit, comprising:

[0005] A first resistor R1, a first end of which is connected to the first voltage input terminal of the operational amplifier AMP, and a second end of which is connected to the first end of the second switch;

[0006] a second switch having a second terminal connected to the voltage output terminal of the operational amplifier and to the first terminal of the third switch;

[0007] a third switch having a second terminal connected to the first terminal of the first switch and connected to the input terminal of the analog-to-digital converter ADC; and

[0008] The first switch has a second end connected to the output end of the off-chip DC voltage source.

[0009] Furthermore, the measurement circuit further includes:

[0010] a second resistor R2, a first end of which is connected to the output end of the off-chip DC voltage source, and a second end of which is connected to the first voltage input end of the operational amplifier; and

[0011] The third resistor R3 has a first end connected to the output end of the off-chip DC voltage source, and a second end connected to the second voltage input end of the operational amplifier.

[0012] Furthermore, the measurement circuit further includes a fourth switch connected between the first voltage input terminal of the operational amplifier and the first resistor R1.

[0013] Furthermore, the first switch and / or the second switch and / or the third switch and / or the fourth switch are CMOS transmission gates.

[0014] Furthermore, the resistance ratio R1 / R2 of the first resistor R1 to the second resistor R2 ranges from 20 to 200.

[0015] Based on the measurement circuit, the present invention also provides a method for measuring input offset voltage, comprising:

[0016] Turning on the first switch and turning off the third switch;

[0017] The input voltage Vin of the operational amplifier is measured by an analog-to-digital converter;

[0018] Turning on the second switch and the third switch and turning off the first switch;

[0019] measuring the output voltage Vout of the operational amplifier by an analog-to-digital converter; and

[0020] The input offset voltage Vos of the operational amplifier is determined according to the input voltage Vin and the output voltage Vout.

[0021] Furthermore, the input offset voltage Vos is determined according to the following formula:

[0022] Vos=(Vout-Vin) / (1+R1 / R2).

[0023] The present invention provides a circuit and method for measuring input offset voltage. This circuit utilizes an on-chip operational amplifier, resistors, and switches to form a proportional amplifier. An on-chip analog-to-digital converter is used to measure the operational amplifier's input and output voltages. By controlling the on / off switching of each switch, the input and output voltages of the operational amplifier can be conveniently measured, and the input offset voltage can be calculated. Compared to existing technologies, this circuit significantly increases test speed and reduces the accuracy requirements for the test equipment, thereby reducing testing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] To further illustrate the above and other advantages and features of various embodiments of the present invention, a more detailed description of various embodiments of the present invention will be presented with reference to the accompanying drawings. It will be understood that these drawings depict only typical embodiments of the present invention and are not to be considered as limiting the scope thereof. In the drawings, for clarity, identical or corresponding components will be represented by the same or similar reference numerals.

[0025] Figure 1 A schematic diagram showing a circuit for measuring input offset voltage in the prior art;

[0026] Figure 2 A schematic diagram showing an input offset voltage measurement circuit according to an embodiment of the present invention;

[0027] Figure 3 A schematic diagram showing an input offset voltage measurement circuit according to yet another embodiment of the present invention; and

[0028] Figure 4 A flow chart illustrating a method for measuring input offset voltage according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0029] In the following description, the present invention is described with reference to various embodiments. However, those skilled in the art will recognize that the various embodiments can be implemented without one or more of the specific details or with other alternative and / or additional methods, materials, or components. In other cases, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring the inventive aspects of the present invention. Similarly, for the purpose of explanation, specific quantities, materials, and configurations are described to provide a comprehensive understanding of the embodiments of the present invention. However, the present invention is not limited to these specific details. In addition, it should be understood that the various embodiments shown in the drawings are illustrative representations and are not necessarily drawn to scale.

[0030] In this specification, reference to "one embodiment" or "the embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. The appearances of the phrase "in one embodiment" in various places in this specification are not necessarily all referring to the same embodiment.

[0031] It should be noted that the embodiments of the present invention describe the process steps in a specific order. However, this is only for the purpose of illustrating the specific embodiment and does not limit the order of the steps. On the contrary, in different embodiments of the present invention, the order of the steps can be adjusted according to the process.

[0032] To reduce the accuracy requirements for test equipment when measuring the input offset voltage of an integrated operational amplifier (OPA), thereby lowering testing costs, the present invention provides an input offset voltage measurement circuit and method. These circuits utilize an on-chip circuit and a test process based on this circuit. The present invention is further described below with reference to the accompanying drawings.

[0033] The principle on which the present invention is based is explained below.

[0034] The present invention is based on the following insights: The inventors discovered through research that existing input offset voltage measurement solutions are difficult to integrate on the same chip as an amplifier circuit primarily because: first, the integration cost of high-precision measurement equipment for measuring output voltage, such as a high-precision digital multimeter, is high; second, voltage measurement requires millisecond-level switching and settling times. To address these technical challenges, the inventors have devised the following ingenious solutions: first, an analog-to-digital converter (ADC) is employed as the measurement device, enabling easy on-chip integration and precise measurement accuracy (the ADC can achieve very high conversion accuracy as required); second, a MOS switch is employed to control the switching of the input and output voltages, achieving very short switching and settling times for the measured voltages. Furthermore, the MOS switch can be easily integrated on-chip. Thus, the inventors have integrated a high-precision measurement circuit on the same chip as the amplifier circuit, achieving both high integration and high accuracy. Furthermore, by arranging an additional switch, the amplifier circuit can be easily switched between its normal operating mode and input offset voltage measurement mode without affecting the normal operation of the amplifier circuit or measurement accuracy.

[0035] The present invention is further described below through specific embodiments.

[0036] Figure 2 FIG1 is a schematic diagram showing a circuit for measuring input offset voltage according to an embodiment of the present invention. Figure 2 As shown, a circuit for measuring input offset voltage uses an on-chip resistor and an operational amplifier AMP to form a proportional amplification circuit, and uses an on-chip analog-to-digital converter ADC to measure the output voltage of the operational amplifier to obtain the input offset voltage. The two voltage input terminals of the operational amplifier are connected to the same off-chip common-mode DC voltage source, and the measurement circuit includes the following components (the symbol "·" indicates the corresponding component):

[0037] A first resistor R1 , having a first end connected to a first voltage input terminal of the operational amplifier AMP and a second end connected to a first end of a second switch S2 ; the first resistor R1 , the operational amplifier AMP and the second switch S2 are all on-chip components.

[0038] A second switch S2 , a second end of which is connected to the voltage output end of the operational amplifier AMP and to the first end of the third switch S3 ; in one embodiment of the present invention, the second switch S2 is, for example, a CMOS transmission gate.

[0039] A third switch S3 , whose second end is connected to the first end of the first switch S1 and to the input end of the analog-to-digital converter ADC; wherein the analog-to-digital converter ADC is an on-chip component. In one embodiment of the present invention, the third switch S3 is, for example, a CMOS transmission gate.

[0040] A first switch S1 , whose second end is connected to the output end of the DC voltage source. In one embodiment of the present invention, the first switch S1 is, for example, a CMOS transmission gate.

[0041] In this embodiment, the measurement circuit optionally further includes the following components:

[0042] A second resistor R2, having a first end connected to the output of the DC voltage source and a second end connected to the first voltage input of the operational amplifier. Taking into account the operating voltage of the operational amplifier and the accuracy of the ADC, in one embodiment of the present invention, the resistance ratio R1 / R2 between the first resistor R1 and the second resistor R2 is in the range of 20-200.

[0043] A third resistor R3, a first end of which is connected to the output end of the DC voltage source, and a second end of which is connected to the second voltage input end of the operational amplifier.

[0044] Figure 3 A schematic diagram showing a circuit for measuring input offset voltage according to yet another embodiment of the present invention is shown.

[0045] Figure 3 Examples and Figure 2 The main difference between the embodiments is that Figure 3 In the embodiment, a fourth switch S4 is further provided between the first voltage input terminal of the operational amplifier and the first resistor R1. Figure 3 As shown, the fourth switch S4 is, for example, a CMOS transmission gate.

[0046] When the operational amplifier is in normal working state, the first switch S1 and the third switch S3 are turned on, and the second switch S2 is turned off. In order to further avoid the influence of the parasitic capacitance generated by the first resistor R1 on the operational amplifier, Figure 3 In the embodiment shown, in the normal working state, the fourth switch S4 also remains in the off state, so that the first resistor R1 is completely disconnected from the operational amplifier circuit;

[0047] When measuring the input offset voltage, the input voltage Vin and the output voltage Vout of the operational amplifier are measured by switching the states of the switches as described above, and then the input offset voltage Vos is obtained according to the following formula:

[0048] Vos=(Vout-Vin) / (1+R1 / R2),

[0049] When measuring the input voltage Vin, the first switch S1 is turned on, the third switch S3 is turned off, and the second switch S2 and the fourth switch S4 (if any) are in any state, but are preferably turned off. In this state, the operational amplifier does not operate. Therefore, the ADC measures the output voltage of the DC voltage source, i.e., the input voltage Vin of the operational amplifier.

[0050] When measuring the output voltage Vout, the first switch S1 is turned off, and the second switch S2, the third switch S3, and the fourth switch S4 (if provided) are turned on. In this state, the resistors and the operational amplifier form a proportional amplification circuit. Due to the presence of an input offset voltage, the output voltage value Vout measured by the ADC is the proportionally amplified sum of the output voltage Vin of the DC voltage source and the input offset voltage Vos, that is:

[0051] Vout = Vos (1 + R1 / R2) + Vin.

[0052] In one embodiment of the present invention, the measurement circuit further includes a non-volatile memory, and the non-volatile memory is used to store the measured input voltage, output voltage, and calculated input offset voltage.

[0053] Figure 4 A flow chart illustrating a method for measuring input offset voltage according to an embodiment of the present invention is shown.

[0054] First, in step 401, test preparation is performed. The chip is powered on and the analog-to-digital converter and operational amplifier are configured to operate normally.

[0055] Next, at step 402, the input voltage is measured. The first switch S1 is turned on and the third switch S3 is turned off. The input voltage Vin of the operational amplifier is then measured using an analog-to-digital converter. At this point, the second switch S2 and / or the fourth switch S4 are preferably in the off state.

[0056] Next, in step 403, the output voltage is measured. The second switch S2, the third switch S3, and the fourth switch S4 are turned on and the first switch S1 is turned off; the output voltage Vout of the operational amplifier is then measured by the analog-to-digital converter; and

[0057] Finally, in step 404, the input offset voltage is calculated. The input offset voltage Vos of the operational amplifier is determined based on the input voltage Vin and the output voltage Vout. In one embodiment of the present invention, the amplified input offset voltage Vos is determined according to the following formula:

[0058] Vos (放大) =Vout-Vin=Vos(1+R1 / R2)+Vin-Vin=Vos(1+R1 / R2),

[0059] Then, we can get:

[0060] Vos=Vos (放大) / (1+R1 / R2)=(Vout-Vin) / (1+R1 / R2).

[0061] If the measurement circuit includes a non-volatile memory, the values ​​of the input voltage Vin, the output voltage Vout, and the input offset voltage Vos can be written into the non-volatile memory. After the measurement is completed, the second switch S2 and the fourth switch S4 are turned off, so that the operational amplifier is in a normal working state.

[0062] Although various embodiments of the present invention have been described above, it should be understood that they are presented by way of example only and not limitation. It will be apparent to those skilled in the relevant art that various combinations, modifications, and variations may be made thereto without departing from the spirit and scope of the present invention. Therefore, the breadth and scope of the present invention disclosed herein should not be limited by the exemplary embodiments disclosed above, but should be defined solely in accordance with the appended claims and their equivalents.

Claims

1. A circuit for measuring input offset voltage, characterized in that: The measurement circuit is an on-chip circuit, comprising: an on-chip analog-to-digital converter connected to the output of the operational amplifier and configured to measure the output voltage of the operational amplifier; a first resistor R1, a first end of which is connected to the first voltage input terminal of the operational amplifier, and a second end of which is connected to the first end of the second switch; a second switch having a second terminal connected to the voltage output terminal of the operational amplifier and connected to a first terminal of the third switch; a third switch having a second terminal connected to the first terminal of the first switch and to the input terminal of the on-chip analog-to-digital converter; and The first switch has a second end connected to the output end of a DC voltage source, wherein the DC voltage source is an off-chip voltage source, and the first voltage input end and the second voltage input end of the operational amplifier are both connected to the DC voltage source.

2. The measuring circuit according to claim 1, wherein: Also includes: a second resistor R2, a first end of which is connected to the output end of the DC voltage source, and a second end of which is connected to the first voltage input end of the operational amplifier; as well as The third resistor R3 has a first end connected to the output end of the DC voltage source, and a second end connected to the second voltage input end of the operational amplifier.

3. The measuring circuit according to claim 2, wherein: The measurement circuit further includes a fourth switch connected between the second end of the second resistor R2 and the first end of the first resistor R1 .

4. The measuring circuit according to claim 3, wherein: The first switch and / or the second switch and / or the third switch and / or the fourth switch are CMOS transmission gates.

5. The measuring circuit according to claim 2, wherein: The resistance ratio R1 / R2 of the first resistor R1 to the second resistor R2 ranges from 20 to 200.

6. A method for measuring input offset voltage, characterized in that: The measuring circuit according to any one of claims 1 to 5 is used, and comprises the steps of: Turning on the first switch and turning off the third switch; The input voltage Vin of the operational amplifier is measured by an analog-to-digital converter; Turning on the second switch and the third switch and turning off the first switch; The output voltage Vout of the operational amplifier is measured by an analog-to-digital converter; as well as The input offset voltage Vos of the operational amplifier is determined according to the input voltage Vin and the output voltage Vout.

7. The measuring method according to claim 6, wherein: The input offset voltage Vos is determined according to the following formula: Vos=(Vout-Vin) / (1+R1 / R2).

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