Measuring circuit for common-mode rejection ratio of operational amplifier

Abstract

The utility model provides an operational amplifier common mode rejection ratio measuring circuit which comprises an operational amplifier DUT to be measured and an auxiliary measuring operational amplifier AMP, a pin 2 of the operational amplifier DUT to be measured is grounded through a resistor R2, a pin 3 of the operational amplifier DUT to be measured is grounded through a resistor R1 and is connected with an output end of the auxiliary measuring operational amplifier AMP through a resistor R6, a pin 4 of the operational amplifier DUT to be measured is connected with a power supply VEE1 and a power supply VEE2 through a switch S2, and the pin 4 is further connected with a pin 7 through a resistor R4 and a resistor R3. The pin 7 is connected with the power supply VAA1 and the power supply VAA2 through the switch S1, the pin 6 is connected with the negative input end of the auxiliary measurement operational amplifier AMP through the resistor R5, the common end of the resistor R3 and the resistor R4 is connected with the positive input end of the AMP, and the negative input end of the AMP is connected with the output end of the auxiliary measurement operational amplifier AMP through the capacitor C1. According to the utility model, the resistor and the capacitor are not required to be high in precision, and accurate measurement of the common-mode rejection ratio of the operational amplifier can be realized.

Description

Technical Field

[0001] The utility model relates to the technical field of electronic circuits, and more specifically, to a measuring circuit for the common-mode rejection ratio of an operational amplifier. Background Art

[0002] The structural diagram of a conventional measuring circuit for the common-mode rejection ratio of an operational amplifier is as Figure 1 shown, and mainly includes a device under test (DUT) operational amplifier. The positive input terminal of the DUT operational amplifier is respectively connected to the positive pole of the power supply through resistors R3 and R1. The positive input terminal of the DUT operational amplifier is also grounded through R4. The negative input terminal of the DUT operational amplifier is connected to the output terminal of the DUT operational amplifier through resistor R2.

[0003] The working principle of measuring the common-mode rejection ratio of the operational amplifier is the matching resistor method. Without considering the resistance value error, it is assumed that R1 = R3 = RA and R2 = R4 = RB.

[0004] Set the resistance error to δ (δ is much less than 1), R1 = RA*(1 - δ), R2 = RB*(1 + δ), RA = R*(1 + δ), RB = R*(1 - δ).

[0005] Under this circuit, the output generated by the common-mode voltage at the DUT is:

[0006]

[0007] Therefore, the common-mode gain of the circuit is:

[0008]

[0009] According to the common-mode rejection ratio formula:

[0010]

[0011] For an operational amplifier, it is desirable that the CMRR is as large as possible. From the above formula, it can be seen that the CMRR is directly related to the resistance error. Measuring the common-mode rejection ratio of the operational amplifier through this circuit requires a relatively high precision of the resistor. Summary of the Utility Model

[0012] The present utility model aims at the technical problems existing in the prior art and provides a measuring circuit for the common-mode rejection ratio of an operational amplifier, which includes a device under test (DUT) operational amplifier and an auxiliary measuring operational amplifier AMP. Pin 2 of the DUT operational amplifier is grounded through a resistor R2, pin 3 is grounded through a resistor R1, and pin 3 is also connected to the output terminal of the auxiliary measuring operational amplifier AMP through a resistor R6. Pin 4 of the DUT operational amplifier is connected to power supplies VEE1 and VEE2 through a two-way switch S2, pin 4 is also connected to pin 7 of the DUT operational amplifier through a resistor R4 and a resistor R3, pin 7 is also connected to power supplies VAA1 and VAA2 through a two-way switch S1, pin 6 is connected to the negative input terminal of the auxiliary measuring operational amplifier AMP through a resistor R5, the common terminal of the resistors R3 and R4 is connected to the positive input terminal of the auxiliary measuring operational amplifier AMP, and the negative input terminal of the auxiliary measuring operational amplifier AMP is also connected to the output terminal of the auxiliary measuring operational amplifier AMP through a capacitor C1.

[0013] Based on the above technical solution, the present utility model can also make the following improvements.

[0014] Optionally, the resistance value of the resistor R1 is equal to that of the resistor R2, and the resistance value of the resistor R3 is equal to that of the resistor R4.

[0015] Optionally, VAA1 - VEE1 = VAA2 - VEE2.

[0016] The measuring circuit for the common-mode rejection ratio of an operational amplifier provided by the present utility model designs a circuit for measuring the common-mode rejection ratio of an operational amplifier. The resistors and capacitors used do not require high precision to accurately measure the common-mode rejection ratio of the operational amplifier. Description of the Drawings

[0017] Figure 1 It is a schematic structural diagram of a conventional measuring circuit for the common-mode rejection ratio;

[0018] Figure 2 It is a schematic structural diagram of a measuring circuit for the common-mode rejection ratio of an operational amplifier provided by the present utility model. Detailed Embodiment

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present utility model clearer, the technical solutions in the embodiments of the present utility model will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present utility model. Apparently, the described embodiments are some, but not all, of the embodiments of the present utility model. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present utility model without creative efforts shall fall within the protection scope of the present utility model. In addition, the technical features in each embodiment or single embodiment provided by the present utility model can be combined with each other arbitrarily to form a feasible technical solution. Such combination is not restricted by the order of steps and / or the pattern of structural composition, but must be based on the fact that those of ordinary skill in the art can implement it. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the protection scope required by the present utility model.

[0020] Figure 2 A measurement circuit for the common-mode rejection ratio of an operational amplifier provided by the present utility model includes a device under test (DUT) operational amplifier and an auxiliary measurement operational amplifier (AMP). Pin 2 of the DUT is grounded through a resistor R2, pin 3 is grounded through a resistor R1, and pin 3 is also connected to the output terminal of the auxiliary measurement operational amplifier AMP through a resistor R6. Pin 4 of the DUT is connected to power supplies VEE1 and VEE2 through a one-select-two switch S2. Pin 4 is also connected to pin 7 of the DUT through a resistor R4 and a resistor R3. Pin 7 is also connected to power supplies VAA1 and VAA2 through a one-select-two switch S1. Pin 6 is connected to the negative input terminal of the auxiliary measurement operational amplifier AMP through a resistor R5. The common terminal of resistors R3 and R4 is connected to the positive input terminal of the auxiliary measurement operational amplifier AMP. The negative input terminal of the auxiliary measurement operational amplifier AMP is also connected to the output terminal of the auxiliary measurement operational amplifier AMP through a capacitor C1.

[0021] Among them, the constraint conditions of the circuit are: the resistance value of resistor R1 is equal to the resistance value of resistor R2, the resistance value of resistor R3 is equal to the resistance value of resistor R4, and VAA1 - VEE1 = VAA2 - VEE2.

[0022] Use Figure 2 The working principle of measuring the common-mode rejection ratio of an operational amplifier using the circuit in

[0023] The DUT is the operational amplifier under test, the AMP is an operational amplifier for auxiliary measurement, the resistor accuracy is 1%, R1 = R2, R3 = R4, and VAA1 - VEE1 = VAA2 - VEE2. S1 and S2 are one-select-two switches, and the circuit gain

[0024] When measuring for the first time, S1 is connected to VAA1 and S2 is connected to VEE1. At this time, the common-mode voltage of the DUT is Recorded as Vout1.

[0025] During the second measurement, S1 is connected to VAA2 and S2 is connected to VEE2. At this time, the common-mode voltage of the DUT is Record Vout2.

[0026] With the two measurement data, the common-mode rejection ratio (CMRR) of the operational amplifier under test (DUT) can be calculated:

[0027]

[0028] According to the calculation formula of the common-mode rejection ratio of the operational amplifier under test (DUT), there is no relationship between the common-mode rejection ratio of the operational amplifier under test (DUT) and the size and accuracy of the resistor. Therefore, the accuracy requirement for the resistor is not high.

[0029] For the measurement circuit of the common-mode rejection ratio of an operational amplifier provided by an embodiment of the present invention, the resistors and capacitors used do not require high precision to accurately measure the common-mode rejection ratio of the operational amplifier.

[0030] It should be noted that in the above embodiments, the descriptions of each embodiment have their own emphases. For the parts not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0031] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications once they know the basic inventive concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0032] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A circuit for measuring common mode rejection ratio of an operational amplifier, characterized in that: The invention comprises an operational amplifier DUT to be tested and an auxiliary measuring operational amplifier AMP. Pin 2 of the operational amplifier DUT to be tested is grounded through a resistor R2, pin 3 is grounded through a resistor R1, pin 3 is also connected to the output end of the auxiliary measuring operational amplifier AMP through a resistor R6, pin 4 of the operational amplifier DUT to be tested is connected to power supplies VEE1 and VEE2 through a one-to-two switch S2, pin 4 is also connected to pin 7 of the operational amplifier DUT to be tested through a resistor R4 and a resistor R3, pin 7 is also connected to power supplies VAA1 and VAA2 through a one-to-two switch S1, pin 6 is connected to the negative input end of the auxiliary measuring operational amplifier AMP through a resistor R5, a common end of the resistor R3 and the resistor R4 is connected to the positive input end of the auxiliary measuring operational amplifier AMP, and the negative input end of the auxiliary measuring operational amplifier AMP is also connected to the output end of the auxiliary measuring operational amplifier AMP through a capacitor C1.

2. The measurement circuit of the common mode rejection ratio of an operational amplifier according to claim 1, characterized in that: The resistance value of the resistor R1 is equal to the resistance value of the resistor R2 , and the resistance value of the resistor R3 is equal to the resistance value of the resistor R4 .

3. The measurement circuit of the common mode rejection ratio of an operational amplifier according to claim 1, characterized in that: VAA1-VEE1=VAA2-VEE2.

Images