A novel differential amplifier with feedforward bias correction circuit and apparatus

Abstract

The embodiment of the application provides a novel differential amplifier with a feedforward bias correction circuit and equipment, a common-mode voltage output of the differential amplifier is dynamically adjusted by the bias correction circuit according to an input voltage, and then input voltage errors of the differential amplifier caused by common-mode voltage output offset can be greatly reduced, so that a very small input signal can be detected with high precision, a common-mode adjustment channel is assisted to track the common-mode voltage output, so that the common-mode voltage output offset is reduced, and the precision of the differential amplifier is improved.

Description

Technical Field

[0001] This application relates to the field of differential amplifier technology, specifically to a novel differential amplifier and device with a feedforward bias correction circuit. Background Technology

[0002] A differential amplifier is a circuit that amplifies the difference between two input voltages. It is a direct-coupled amplifier with very small zero-point drift and is often used for DC amplification. It can be balanced (the term "balanced" means differential) input and output or single-ended (unbalanced) input and output. It is often used to realize the mutual conversion between balanced and unbalanced circuits and is a basic unit of various integrated circuits.

[0003] When designing a fully differential amplifier, it was found that the effective bias voltage of the amplifier is related to the common-mode voltage output. For very small input signals, the common-mode voltage output produces an unacceptably large offset, resulting in low accuracy of the differential amplifier. Summary of the Invention

[0004] Therefore, this application provides a novel differential amplifier and device with a feedforward bias correction circuit to solve the technical problem in the prior art where a very small input signal results in an unacceptably large offset in the common-mode voltage output, leading to low accuracy of the differential amplifier.

[0005] To achieve the above objectives, the embodiments of this application provide the following technical solutions:

[0006] According to a first aspect of the embodiments of this application, the embodiments of this application provide a differential amplifier with a feedforward bias correction circuit, characterized in that it includes a differential amplifier and a bias correction circuit;

[0007] The differential amplifier includes an operational amplifier. The input terminal of the bias correction circuit is connected to the high-level input terminal and the low-level input terminal of the differential amplifier, respectively. The output terminal of the bias correction circuit is connected to the operational amplifier. The bias correction circuit dynamically adjusts the common-mode voltage output of the differential amplifier according to the input voltage of the differential amplifier.

[0008] As a preferred embodiment of this application, the differential amplifier further includes a first resistor, a second resistor, a first feedback circuit, and a second feedback circuit;

[0009] The first end of the first resistor is connected to the high-level input terminal of the differential amplifier, the second end of the first resistor is connected to the first input terminal of the operational amplifier, the first end of the second resistor is connected to the low-level input terminal of the differential amplifier, the second end of the second resistor is connected to the second input terminal of the operational amplifier, the first end of the first feedback circuit is connected to the first input terminal of the operational amplifier, the first end of the second feedback circuit is connected to the second input terminal of the operational amplifier, and the second ends of the first feedback circuit and the second feedback circuit are respectively connected to the output terminal of the operational amplifier.

[0010] As a preferred embodiment of this application, the bias correction circuit includes a clamping voltage setting circuit and a common-mode voltage adjustment circuit;

[0011] The first terminal of the clamping voltage setting circuit is connected to the reference voltage setting circuit, the second terminal of the clamping voltage setting circuit is connected to the first input terminal of the common-mode voltage adjustment circuit, the first input terminal of the common-mode voltage adjustment circuit is connected to the high-level input terminal of the differential amplifier, the second input terminal of the common-mode voltage adjustment circuit is connected to the low-level input terminal of the differential amplifier, and the output terminal of the common-mode voltage adjustment circuit is connected to the operational amplifier. The clamping voltage setting circuit is used to set the clamping voltage of the common-mode voltage adjustment circuit.

[0012] In a preferred embodiment of this application, the clamping voltage setting circuit includes a buffer amplifier and a third resistor. The first input terminal of the buffer amplifier is connected to the reference voltage setting circuit, the second input terminal of the buffer amplifier is connected to the common terminal between the output terminal of the buffer amplifier and the first terminal of the third resistor, and the second terminal of the third resistor is connected to the high-level input terminal of the common-mode voltage adjustment circuit.

[0013] In a preferred embodiment of this application, the common-mode voltage regulation circuit includes a fourth resistor, a fifth resistor, and a differential amplifier;

[0014] The first end of the fourth resistor is connected to the high-level input terminal of the differential amplifier, the second end of the fourth resistor is connected to the first input terminal of the differential amplifier, the first end of the fifth resistor is connected to the low-level input terminal of the differential amplifier, and the second end of the fifth resistor is connected to the second input terminal of the differential amplifier; the output terminal of the differential amplifier is connected to the operational amplifier so as to input the reference common-mode voltage set by the differential amplifier to the operational amplifier.

[0015] In a preferred embodiment of this application, the differential amplifier is an instrumentation amplifier.

[0016] As a preferred embodiment of this application, the common-mode voltage regulation circuit further includes a third feedback circuit, wherein the first terminal of the third feedback circuit is connected to the common terminal between the second terminal of the fifth resistor and the second input terminal of the differential amplifier.

[0017] Compared with the prior art, the embodiments of this application provide a novel differential amplifier and device with a feedforward bias correction circuit. By dynamically adjusting the common-mode voltage output of the differential amplifier according to the input voltage through the bias correction circuit, the input voltage error of the differential amplifier caused by the common-mode voltage output offset can be greatly reduced. This enables high-precision detection of very small input signals, assists the common-mode adjustment channel to track the common-mode voltage output, thereby reducing the common-mode voltage output offset and improving the accuracy of the differential amplifier.

[0018] Secondly, embodiments of this application also provide an apparatus including the differential amplifier described in the first aspect.

[0019] Compared with the prior art, the beneficial effects of the device provided in this application embodiment are the same as those of the differential amplifier provided in the first aspect, and will not be repeated here. Attached Figure Description

[0020] To more clearly illustrate the embodiments of this application or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0021] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which this application can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and purposes that this application can produce, should still fall within the scope of the technical content disclosed in this application.

[0022] Figure 1 A schematic diagram of a differential amplifier structure provided for the prior art;

[0023] Figure 2 A schematic diagram of a differential amplifier structure with a feedforward bias correction circuit is provided for an embodiment of this application;

[0024] Figure 3 A schematic diagram of the differential amplifier used in a battery charger according to an embodiment of this application;

[0025] Figure 4 This is a schematic diagram of the structure of a differential amplifier used in a battery charger, as provided in an embodiment of this application. Detailed Implementation

[0026] The following specific embodiments illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] like Figure 1 As shown, Figure 1 The circuit diagram of the differential amplifier provided in the prior art includes an operational amplifier 105, a first resistor (R1) 101, a second resistor (R1) 102, a first feedback circuit (R2) 103, and a second feedback circuit (R2) 104.

[0028] The first terminal of the first resistor 101 is connected to the high level V of the differential amplifier. in+ The input terminals are connected as follows: the second terminal of the first resistor 101 is connected to the first input terminal a1 of the operational amplifier 105; the first terminal of the second resistor 102 is connected to the low-level voltage V of the differential amplifier. in- The input terminals are connected, the second terminal of the second resistor 102 is connected to the second input terminal a2 of the operational amplifier 105, the first terminal of the first feedback circuit 103 is connected to the first input terminal a1 of the operational amplifier 105, the first terminal of the second feedback circuit 104 is connected to the second input terminal a2 of the operational amplifier 105, and the second terminals of the first feedback circuit 103 and the second terminals of the second feedback circuit 104 are respectively connected to the output terminal b of the operational amplifier 105.

[0029] Existing differential amplifiers have a common-mode voltage input V cmi Common-mode voltage output V cmo High level V in+ Input terminal, low level V in- Input terminal, high level V out+ Output terminal and low level V out- At the output, if the open-loop gain of the differential amplifier approaches infinity, then the output voltage of the differential amplifier ( Calculated using the following formula:

[0030]

[0031] Formula (Ⅰ)

[0032] Wherein, R1 is the resistance value of the first resistor 101 and the second resistor 102, and the resistance values ​​of the first resistor 101 and the second resistor 102 are the same. R2 is the resistance value of the first feedback circuit 103 and the second feedback circuit 104, and the resistance values ​​of the first feedback circuit 103 and the second feedback circuit 104 are the same. In the differential amplifier circuit, the first resistor (R1) 101, the second resistor (R1) 102, the first feedback circuit (R2) 103 and the second feedback circuit (R2) 104 are used to set the gain of the differential amplifier. The value of R2 / R1 is used to set the gain ratio of the closed-loop differential amplifier. The gain ratio can be from 20 times to 100 times, and the gain can also be greater. This application embodiment does not limit this.

[0033] Assuming the open-loop gain of the differential amplifier approaches infinity, and the common-mode voltage output offset is negligible, the output error of the differential amplifier is caused by the mismatch between individual resistors R2. Calculated using the following formula:

[0034]

[0035] Formula (II)

[0036] in, For common-mode voltage output, R1 represents the resistance of the first resistor 101 and the second resistor 102, and the resistance values ​​of the first resistor 101 and the second resistor 102 are the same. R2 represents the resistance of the first feedback circuit 103 and the second feedback circuit 104, and the resistance values ​​of the first feedback circuit 103 and the second feedback circuit 104 are the same. In practical applications of integrated circuits, due to slight variations in the manufacturing process, the two devices are not exactly the same. Therefore, the two resistors R2 are connected through the sum of the values ​​of R2 and (1 + ... The value of R² is expressed as ) × R², where This refers to the error variation between the two R2s. A similar analysis can be performed on R1, but the results are very similar, including the common-mode voltage output. The output error of the differential amplifier is obtained by multiplying it by the gain of the differential amplifier. .

[0037] The output error of the differential amplifier can be obtained from the above formula (II). It mainly consists of a first resistor (R1) 101, a second resistor (R1) 102, a first feedback circuit (R2) 103, a second feedback circuit (R2) 104, and a common-mode voltage output V. cmo Decide.

[0038] As is known from existing technology, in order to reduce the output error of a differential amplifier To improve the accuracy of a differential amplifier, it is necessary to reduce the common-mode output voltage V. cmo To achieve this, the embodiments of this application provide the following technical solutions.

[0039] like Figure 2 As shown, this application provides a novel differential amplifier with a feedforward bias correction circuit, including a differential amplifier 21 and a bias correction circuit 22.

[0040] The differential amplifier 21 includes an operational amplifier 205;

[0041] The input terminals c and d of the bias correction circuit 22 are respectively connected to the high-level input terminal V of the differential amplifier. in+ and low-level input terminal V in- The bias correction circuit 22 is connected to the operational amplifier 205 at its output terminal m. The bias correction circuit 22 dynamically adjusts the common-mode voltage output of the differential amplifier 21 according to the input voltage of the differential amplifier 21.

[0042] The differential amplifier 21 also includes a first resistor (R1) 201, a second resistor (R1) 202, a first feedback circuit (R2) 203, and a second feedback circuit (R2) 204;

[0043] The first terminal of the first resistor (R1) 201 is connected to the high-level input terminal V of the differential amplifier. in+ The first resistor (R1) 201 is connected to its second terminal, which is connected to the first input terminal e of the operational amplifier 205. The second resistor (R1) 202 is connected to its first terminal, which is connected to the low-level input terminal V of the differential amplifier. in- The second resistor (R1) 202 is connected to the second input terminal f of the operational amplifier 205. The first terminal of the first feedback circuit (R2) 203 is connected to the first input terminal e of the operational amplifier 205. The first terminal of the second feedback circuit (R2) 204 is connected to the second input terminal f of the operational amplifier 205. The second terminals of the first feedback circuit (R2) 203 and the second terminals of the second feedback circuit (R2) 204 are respectively connected to the output terminal n of the operational amplifier 205.

[0044] The bias correction circuit 22 includes a clamping voltage setting circuit 22-1 and a common-mode voltage adjustment circuit 22-2; the first terminal of the clamping voltage setting circuit 22-1 is connected to the reference voltage setting circuit 212, and the second terminal of the clamping voltage setting circuit 22-1 is connected to the first input terminal k of the common-mode voltage adjustment circuit 22-2; the first input terminal k of the common-mode voltage adjustment circuit 22-2 is connected to the high-level input terminal V of the differential amplifier. in+ The common-mode voltage regulation circuit 22-2's second input terminal l is connected to the low-level input terminal V of the differential amplifier. in-The common-mode voltage regulation circuit 22-2 is connected to the operational amplifier 205, and the clamping voltage setting circuit 22-1 is used to set the clamping voltage of the common-mode voltage regulation circuit 22-2.

[0045] The clamping voltage setting circuit 22-1 includes a buffer amplifier 206 and a third resistor (r2) 207. The first input terminal h of the buffer amplifier 206 is connected to the reference voltage setting circuit 212. The second input terminal i of the buffer amplifier 206 and the output terminal j of the buffer amplifier 206 are connected to a common terminal between the first terminal of the third resistor (r2) 207. The second terminal of the third resistor (r2) 207 and the second terminal of the fourth resistor (r1) 208 are connected to a common terminal between the first input terminal k of the differential amplifier 210.

[0046] The buffer amplifier 206 is used to prevent the reference voltage setting circuit 212 from overloading. Overload of the reference voltage setting circuit 212 usually occurs in bandgap circuits. The reference voltage setting circuit 212 also has high impedance when overloaded. Any overload will affect the reference voltage (VREF) of the reference voltage setting circuit 212. By using the buffer amplifier 206, the accuracy of the reference voltage (VREF) of the reference voltage setting circuit 212 can be maintained. The third resistor (r2) 207 can reduce the clamping voltage of the bias correction circuit 22.

[0047] The common-mode voltage regulation circuit 22-2 includes a fourth resistor (r1) 208, a fifth resistor (r1) 209, and a differential amplifier 210; the first terminal of the fourth resistor (r1) 208 is connected to the high-level input terminal V of the differential amplifier. in+ The fourth resistor (r1) 208 is connected to its second terminal, which is connected to the first input terminal k of the differential amplifier 210; the fifth resistor (r1) 209 is connected to its first terminal, which is connected to the low-level input terminal V of the differential amplifier. in- The fifth resistor (r1) 209 is connected to its second input terminal i of the differential amplifier 210; the output terminal m of the differential amplifier 210 is connected to the operational amplifier 205. The differential amplifier 210 is an instrumentation amplifier, and it outputs the high-level input terminal V of the differential amplifier. in+ and low-level input terminal V in- The difference is summed with the reference voltage (VREF) of the reference voltage setting circuit 212 to obtain the reference common-mode voltage output by the differential amplifier 210. Calculate according to the following formula (Ⅲ):

[0048]

[0049] Formula (III)

[0050] The reference common-mode voltage VREF_VCM is set by the instrumentation amplifier 210. The common-mode reference voltage VREF_VCM set by the common-mode voltage setting circuit is used to adjust the common-mode voltage output of the differential amplifier. The reference common-mode voltage VREF_VCM is also another input terminal of the differential amplifier, so as to adjust the common-mode voltage output of the differential amplifier. In order to reduce the influence of the common-mode voltage output on the differential amplifier, the instrumentation amplifier 210 adjusts the input voltage V... in (V in + -V in - Set the reference common-mode voltage VREF_VCM.

[0051] The common-mode voltage regulation circuit 22-2 further includes a third feedback circuit (r2) 211, the first terminal of which is connected to the common terminal between the second terminal of the fourth resistor (r1) 209 and the second input terminal i of the differential amplifier 210.

[0052] Differential amplifiers have a common-mode voltage input and output. When the first feedback circuit (R2) 203 and the second feedback circuit (R2) 204 are mismatched, the common-mode voltage output will cause the differential amplifier to deteriorate in accuracy. In the embodiment of this application, the bias correction circuit 22 in the differential amplifier adjusts the common-mode voltage output according to the input voltage to reduce common-mode error.

[0053] like Figure 3 As shown, Figure 3 The differential amplifier provided in this application embodiment is applied to a battery charger with very low inductive resistance. Through this application embodiment, the current can be detected and adjusted with high precision, thereby extending battery life, charging with higher precision, preventing battery damage and reducing the risk of fire.

[0054] In a specific battery charger, the negative terminal of battery 215 is connected to a fixed voltage node via a sensing resistor RSNS, enabling more accurate measurement of the battery current. The output terminal n of operational amplifier 205 is connected to an analog-to-digital converter (ADC) 212, which is a device used to convert continuous analog signals into discrete digital signals. The ADC 212 is connected to a digital controller 213, which typically has a program to convert input signals into output signals. The ADC 213 uses computer software programming to implement specific control algorithms. The ADC 213 is connected to the positive terminal of battery 215 via a DC-DC converter 214, which converts the input voltage into an effective fixed output voltage. The battery charger uses the differential amplifier provided in this embodiment to regulate the battery current and prevent damage to the battery.

[0055] In battery charging applications, because the sensing resistor RSNS is directly connected in the current path, it generates a voltage drop to maintain low impedance and reduce power loss. Therefore, a high-fidelity amplifier is needed to detect the low voltage across the sensing resistor RSNS and amplify it to ensure correct readings from the analog-to-digital converter ADC 212. The gain of the differential amplifier 21 can range from 20x to 100x, depending on the battery current requirements, the input requirements of the ADC 212, and the selection of the sensing resistor RSNS. The instrumentation amplifier 210 is configured to improve the accuracy of the differential amplifier by sampling the input voltage and simultaneously adjusting the common-mode voltage output of the differential amplifier 21.

[0056] like Figure 4 As shown, the differential amplifier provided in this application embodiment is used in a battery charger. The battery average current mode charger can have multiple high-precision differential amplifiers, each with its own bias correction circuit. Figure 3 In one embodiment, the same structure can be used to accurately measure the battery voltage at the precise current measurement point. Figure 4 In this embodiment, a novel differential amplifier 2 is used to detect the battery current, and another novel differential amplifier 1 is used to detect the inductor current. The negative terminal of the battery 215 is connected to the fixed voltage node, and the positive terminal is connected to one of the novel differential amplifiers 1 in this application. The differential amplifier 1 includes a differential amplifier 21 and a bias correction circuit 22. The novel differential amplifier 1 and the periodic current detection module 3 detect the battery current. The output terminal of the periodic current detection module 3 is connected to the current error amplifier 5. The output terminal of the current error amplifier 5 is connected to the input terminal of the pulse width modulator 217 to modulate the pulse width. The output terminal of the pulse width modulator 217 is connected to the buck conversion logic module 6. The buck conversion logic module 6 is connected to the inductor 218 and the resistor 219 in sequence. The novel differential amplifier 1 is connected to the resistor 219 to detect the current across the resistor 219.

[0057] In this embodiment, both differential amplifier 1 and differential amplifier 22 have bias correction circuits 22 to enhance the regulation and control of the DC-DC converter loop. By more accurately detecting the inductor current, the regulation accuracy of the average current mode loop can be improved. This embodiment allows for high-precision detection and regulation of the current, thereby extending battery life, enabling more precise charging, preventing battery damage, and reducing the risk of fire.

[0058] Secondly, embodiments of this application also provide an apparatus including the differential amplifier described in the first aspect.

[0059] Compared with the prior art, the beneficial effects of the device provided in this application embodiment are the same as those of the differential amplifier provided in the first aspect, and will not be repeated here.

[0060] Although this application has been described in detail above with general descriptions and specific embodiments, some modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of this application fall within the scope of protection claimed in this application.

Claims

1. A novel differential amplifier with a feedforward bias correction circuit, characterized in that, Includes a differential amplifier and a bias correction circuit; The differential amplifier includes an operational amplifier. The input terminal of the bias correction circuit is connected to the high-level input terminal and the low-level input terminal of the differential amplifier, respectively. The output terminal of the bias correction circuit is connected to the operational amplifier. The bias correction circuit dynamically adjusts the common-mode voltage output of the differential amplifier according to the input voltage of the differential amplifier. The bias correction circuit includes a clamping voltage setting circuit and a common-mode voltage adjustment circuit; The first terminal of the clamping voltage setting circuit is connected to the reference voltage setting circuit, the second terminal of the clamping voltage setting circuit is connected to the first input terminal of the common-mode voltage adjustment circuit, the first input terminal of the common-mode voltage adjustment circuit is also connected to the high-level input terminal of the differential amplifier, the second input terminal of the common-mode voltage adjustment circuit is connected to the low-level input terminal of the differential amplifier, and the output terminal of the common-mode voltage adjustment circuit is connected to the operational amplifier. The clamping voltage setting circuit is used to set the clamping voltage of the common-mode voltage adjustment circuit.

2. A novel differential amplifier with a feedforward bias correction circuit as described in claim 1, characterized in that, The differential amplifier also includes a first resistor, a second resistor, a first feedback circuit, and a second feedback circuit. The first end of the first resistor is connected to the high-level input terminal of the differential amplifier, the second end of the first resistor is connected to the first input terminal of the operational amplifier, the first end of the second resistor is connected to the low-level input terminal of the differential amplifier, the second end of the second resistor is connected to the second input terminal of the operational amplifier, the first end of the first feedback circuit is connected to the first input terminal of the operational amplifier, the first end of the second feedback circuit is connected to the second input terminal of the operational amplifier, and the second ends of the first feedback circuit and the second feedback circuit are respectively connected to the output terminal of the operational amplifier.

3. A novel differential amplifier with a feedforward bias correction circuit as described in claim 1, characterized in that, The clamping voltage setting circuit includes a buffer amplifier and a third resistor. The first input terminal of the buffer amplifier is connected to the reference voltage setting circuit. The second input terminal of the buffer amplifier is connected to the common terminal between the output terminal of the buffer amplifier and the first terminal of the third resistor. The second terminal of the third resistor is connected to the high-level input terminal of the common-mode voltage adjustment circuit.

4. A novel differential amplifier with a feedforward bias correction circuit as described in claim 1, characterized in that, The common-mode voltage regulation circuit includes a fourth resistor, a fifth resistor, and a differential amplifier; The first end of the fourth resistor is connected to the high-level input terminal of the differential amplifier, the second end of the fourth resistor is connected to the first input terminal of the differential amplifier, the first end of the fifth resistor is connected to the low-level input terminal of the differential amplifier, and the second end of the fifth resistor is connected to the second input terminal of the differential amplifier; the output terminal of the differential amplifier is connected to the operational amplifier so as to input the reference common-mode voltage set by the differential amplifier to the operational amplifier.

5. A novel differential amplifier with a feedforward bias correction circuit as described in claim 4, characterized in that, The differential amplifier is an instrumentation amplifier.

6. A novel differential amplifier with a feedforward bias correction circuit as described in any one of claims 3 to 5, characterized in that, The common-mode voltage regulation circuit also includes a third feedback circuit, wherein the first terminal of the third feedback circuit is connected to the common terminal between the second terminal of the fifth resistor and the second input terminal of the differential amplifier.

7. A device, characterized in that, Includes the differential amplifier as described in any one of claims 1 to 6.

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