Analog-to-digital converter combination instrumentation amplifier

Abstract

This utility model relates to the technical field of amplifiers and discloses an analog-to-digital converter (ADC) combined instrumentation amplifier, including a first-stage amplifier, a second-stage amplifier connected to the first-stage amplifier, a front-end low-pass filter (LPF) connected to the second-stage amplifier, and an analog-to-digital converter (ADC) connected to the front-end low-pass filter (LPF). An unbalanced input to balanced differential circuit output module is provided between the second-stage amplifier signal and the front-end low-pass filter (LPF). From the perspective of signal processing and conversion, the addition of the unbalanced input to balanced differential circuit output module constructs a precise signal transition bridge. The unbalanced signal output from the second-stage amplifier is converted into a dual-ended balanced differential signal by the module. The differential transmission method effectively resists common-mode noise interference, ensuring signal purity. Due to the differential signal compatibility between the front-end low-pass filter and the ADC, signal transmission is stable and interference-resistant, making the analog-to-digital conversion more accurate.

Description

Technical Field

[0001] This utility model relates to the technical field of amplifiers, and more specifically, to an analog-to-digital converter combined instrumentation amplifier. Background Technology

[0002] Among all electronic amplifiers, the most commonly used is the instrumentation amplifier. The main function of an instrumentation amplifier is to amplify weak differential electrical signals, suppress unwanted common-mode noise, and improve signal quality. This amplifier circuit is commonly used in the high-precision signal acquisition front-end of instruments and meters. A typical instrumentation amplifier generally consists of three operational amplifiers, such as... Figure 1 The shortcomings of discrete circuits are that they are complex, have many resistors, require high precision, and are difficult to match with the same resistance value, which will affect the common-mode rejection ratio, increasing the difficulty of production and design. Alternatively, high-cost instrumentation amplifier chips may be used to replace discrete circuits.

[0003] A search of application number 202221493518.X reveals a combined analog-to-digital converter (ADC) instrument amplifier. In today's digital age, a significant portion of the demand requires analog signals to be amplified to a high degree before being sampled by an ADC and then digitized. Therefore, this invention incorporates a high-performance differential input ADC. The main function of the instrument amplifier is to amplify weak differential electrical signals, suppress unwanted common-mode noise, and improve signal quality. This amplifier circuit is commonly used in the high-precision signal acquisition front-end of instruments and meters. Signal acquisition devices collect weak output signals from sensors such as sound sensors (e.g., microphones), photosensitive sensors, and magnetic induction sensors (e.g., radar).

[0004] However, since the electrical signals converted by the sensors are weak, and the power supply and components in the circuit have different sources of noise interference, how to improve the signal-to-noise ratio and anti-interference ability of the instrumentation amplifier, ensure the quality of signal acquisition, avoid misjudgment, and reduce the cost and manufacturing difficulty of the instrumentation amplifier is the key research direction of this application. Utility Model Content

[0005] The purpose of this invention is to provide an analog-to-digital converter combined instrumentation amplifier that optimizes the common-mode rejection ratio based on the CMR calculation formula, significantly reduces common-mode interference, and enables precise amplification and transmission of weak differential signals, laying a solid foundation for subsequent high-precision ADC conversion. From signal acquisition and amplification to conversion output, it achieves high-quality signal processing across the entire chain, aiming to solve the problems in the existing technology.

[0006] This invention is implemented as follows: an analog-to-digital converter combined instrumentation amplifier includes a first-stage amplifier, a first-stage amplifier signal connected to a second-stage amplifier, a second-stage amplifier signal connected to a front-end low-pass filter (LPF), a front-end low-pass filter (LPF) signal connected to an analog-to-digital converter (ADC), and an unbalanced input to balanced differential circuit output module disposed between the second-stage amplifier signal and the front-end low-pass filter (LPF).

[0007] Furthermore, the first-stage amplifier includes:

[0008] Two amplifiers, U1-A and U1-B, are connected in parallel with two resistors, R1 and R1', and a fixed resistor, RG. The positive input terminals of amplifiers U1-A and U1-B are connected to a signal input source. The output terminals of amplifiers U1-A and U1-B are respectively connected to resistors R1 and R1'. The negative input terminals of amplifiers U1-A and U1-B are connected in series through the fixed resistor RG.

[0009] Furthermore, the second-stage amplifier includes:

[0010] An amplifier U2-A and four resistors R2, R2', R3, and R3' are used. Resistor R2 is connected to the output signal terminal of amplifier U1-A, and resistor R2' is connected to the output signal terminal of amplifier U1-B. The outputs of resistors R2 and R2' are connected together to the negative input terminal of amplifier U2-A. The positive input terminal of amplifier U2-A is connected to the VREF signal through resistor R3'. The output signal terminal of amplifier U2-A is connected to resistor R3, and resistor R3 is connected back to the negative input terminal of amplifier U2-A. The output terminal of amplifier U2-A serves as the Uout- signal output terminal.

[0011] Furthermore, the second-stage amplifier suppresses the common-mode voltage of the two input signals and calculates the difference between the two signals using the following formula: CMR (dB) = 20log[(1+R3 / R2) / Kr]; where Kr is the total matching ratio fraction of R2 / R3 = R2' / R3', and R3 / R2 = R3' / R2' is a pair of relatively equal resistors; setting R2=R3, the matching ratio error of 0.1% is 66dBCMR, and setting R2=R3, the error of one of the resistors is 46dBCMR.

[0012] Furthermore, the signals at the ends of resistors R1 and R1' furthest from the output terminals of amplifiers U1-A and U1-B are connected to the negative input terminals of amplifiers U1-A and U1-B, respectively.

[0013] Furthermore, the output of the front-end low-pass filter (LPF) is connected to the analog input of the analog-to-digital converter (ADC), and the gain of the front-end low-pass filter (LPF) is 1:1.

[0014] Furthermore, the analog-to-digital converter (ADC) is a high-precision Σ-Δ single-supply digital-to-analog converter (ADC), and the ADC has a differential amplifier internally configured.

[0015] Furthermore, the input terminal of the unbalanced input to balanced differential circuit output module is connected to the output terminal of the second-stage amplifier to receive the unbalanced signal output by the second-stage amplifier.

[0016] Furthermore, the unbalanced input to balanced differential circuit output module converts the input single-ended unbalanced signal into a double-ended balanced differential signal through internal circuit conversion, and outputs it in a differential transmission mode.

[0017] Furthermore, the output terminal of the unbalanced input to balanced differential circuit output module is connected to the input terminal of the low-pass filter (LPF) to provide the required differential signal for the circuit and realize the signal form adaptation conversion.

[0018] Compared with the prior art, the analog-to-digital converter combined instrumentation amplifier provided by this utility model has the following advantages:

[0019] 1. From the perspective of signal processing and conversion, the addition of the unbalanced input to balanced differential output circuit module builds a precise signal transition bridge. The unbalanced signal output from the second-stage amplifier is converted into a dual-ended balanced differential signal. The differential transmission method effectively resists common-mode noise interference and ensures signal purity. The front-end low-pass filter and analog-to-digital converter are adapted to the differential signal, resulting in stable signal transmission and anti-interference, making the analog-to-digital conversion more accurate. At the same time, the amplifiers at each stage work together. The first stage uses parallel dual op-amps, negative feedback, and series resistors to build a high input impedance and low noise front-end. The second stage uses op-amps and resistor networks to suppress common-mode voltage and realize differential operation. By reasonably setting the resistor parameters and optimizing the common-mode rejection ratio according to the CMR calculation formula, the common-mode interference is greatly reduced, allowing the weak differential signal to be accurately amplified and transmitted, laying a solid foundation for the subsequent high-precision ADC conversion. From signal acquisition and amplification to conversion output, high-quality signal processing is achieved throughout the entire chain.

[0020] 2. The high-precision ∑-⊿ single-supply ADC, paired with an internal differential amplifier, is perfectly matched with the front-end balanced differential signal output. The single-supply configuration is suitable for more low-power and portable scenarios. The front-end amplifier can be flexibly configured with resistor parameters to adapt to input signals with different amplitudes and impedance characteristics, meeting the needs of diverse industrial, measurement and control, and other scenarios. The unbalanced to balanced module makes the signal link interface more flexible and compatible with different front-end and rear-end circuit architectures, improving system integration and compatibility. Moreover, the circuit design of each part follows a clear theoretical basis, which facilitates precise debugging and optimization according to actual needs. From basic signal amplification to complex scenario applications, it gives the system good scalability and debugging convenience, helping it to operate stably and reliably in multiple fields, tapping the potential of signal processing, and improving the overall performance limit of the analog-to-digital conversion system. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of an amplifier circuit structure in the prior art;

[0022] Figure 2 This is a schematic diagram of the improved amplifier circuit structure in the prior art;

[0023] Figure 3 This is a schematic diagram of the circuit structure of an analog-to-digital converter combined instrumentation amplifier proposed in this utility model. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present utility model and are not intended to limit the present utility model.

[0025] The implementation of this utility model will be described in detail below with reference to specific embodiments.

[0026] In the accompanying drawings of this embodiment, the same or similar reference numerals correspond to the same or similar components. In the description of this utility model, it should be understood that if terms such as "upper," "lower," "left," and "right" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting this utility model. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0027] Reference Figure 3As shown, an analog-to-digital converter (ADC) combined instrumentation amplifier includes a first-stage amplifier (stage ① circuit), a second-stage amplifier (stage ② circuit) whose signal is connected to the first-stage amplifier, a front-end low-pass filter (LPF) (stage ④ circuit) whose signal is connected to the front-end low-pass filter (LPF) whose signal is connected to the analog-to-digital converter (ADC) (stage ⑤ circuit), and an unbalanced input to balanced differential circuit output module (stage ③ circuit) between the second-stage amplifier signal and the front-end low-pass filter (LPF). From the perspective of signal processing and conversion, the addition of the unbalanced input to balanced differential circuit output module builds a precise signal transition bridge. The unbalanced signal output by the second-stage amplifier is converted into a dual-ended balanced differential signal by the module. The differential transmission mode effectively resists common-mode noise interference and ensures signal purity.

[0028] In this embodiment, the first-stage amplifier of the ① stage circuit includes: two amplifiers U1-A and U1-B, two resistors R1 and R1', and a fixed resistor RG. Amplifiers U1-A and U1-B are connected in parallel. The positive input terminals of amplifiers U1-A and U1-B are connected to signal input sources. The output terminals of amplifiers U1-A and U1-B are respectively connected to resistors R1 and R1'. The negative input terminals of amplifiers U1-A and U1-B are connected in series through the fixed resistor RG.

[0029] In this embodiment, the second-stage amplifier of the ② stage circuit includes: an amplifier U2-A and four resistors R2, R2', R3, and R3'. Resistor R2 is connected to the output terminal of amplifier U1-A, and resistor R2' is connected to the output terminal of amplifier U1-B. The outputs of resistors R2 and R2' are connected to the negative input terminal of amplifier U2-A. The positive input terminal of amplifier U2-A is connected to the VREF signal through resistor R3'. The output terminal of amplifier U2-A is connected to resistor R3, and resistor R3 is connected back to the negative input terminal of amplifier U2-A. The output terminal of amplifier U2-A serves as the Uout- signal output terminal.

[0030] In this embodiment, the second-stage amplifier suppresses the common-mode voltage of the two input signals and calculates the difference between the two signals using the following formula: CMR (dB) = 20log[(1+R3 / R2) / Kr]; where Kr is the total matching ratio fraction of R2 / R3 = R2' / R3', and R3 / R2 = R3' / R2' is a pair of relatively equal resistors; with R2=R3, a matching ratio error of 0.1% is 66dB CMR, and with R2=R3, a 1% error of one of the resistors is 46dB CMR.

[0031] In this embodiment, the signals at the ends of resistors R1 and R1' furthest from the output terminals of amplifiers U1-A and U1-B are connected to the negative input terminals of amplifiers U1-A and U1-B, respectively. The output terminal of the front-end low-pass filter (LPF) is connected to the analog input terminal of the analog-to-digital converter (ADC). The LPF gain is 1:1. The ADC is a high-precision Σ-Δ single-supply digital-to-analog converter (ADC). The ADC has a differential amplifier internally. Due to the differential signal matching between the front-end low-pass filter and the ADC, the signal transmission is stable and anti-interference, making the analog-to-digital conversion more accurate. At the same time, the amplifiers at each stage work together. The first stage uses two operational amplifiers in parallel, negative feedback, and resistors in series to build a high input impedance and low noise front-end. The second stage uses operational amplifiers and resistor networks to suppress common-mode voltage and realize differential operation by reasonably setting the resistor parameters.

[0032] In this embodiment, the input terminal of the unbalanced input to balanced differential circuit output module is connected to the output terminal of the second-stage amplifier, receiving the unbalanced signal output by the second-stage amplifier. Through internal circuit conversion, it converts the input single-ended unbalanced signal into a double-ended balanced differential signal and outputs it in differential transmission mode. Its output terminal is connected to the input terminal of the low-pass filter (LPF), providing the required differential signal for the second-stage circuit, realizing the adaptation and conversion of signal form. Based on the CMR calculation formula, the common-mode rejection ratio is optimized, which greatly reduces common-mode interference and allows the weak differential signal to be accurately amplified and transmitted, laying a solid foundation for the subsequent high-precision conversion of the ADC. From signal acquisition and amplification to conversion and output, high-quality signal processing is achieved throughout the entire chain.

[0033] This technical solution features a high-precision ∑-⊿ single-supply ADC paired with an internal differential amplifier, perfectly matched with the front-end balanced differential signal output. The single-supply configuration is suitable for a wider range of low-power and portable applications. The front-end amplifier, with its flexible resistor parameters, can adapt to input signals of different amplitudes and impedance characteristics, meeting diverse industrial and measurement / control requirements. The unbalanced-to-balanced module allows for more flexible signal link interface matching, compatible with different front-end and rear-end circuit architectures, improving system integration and compatibility. Furthermore, the circuit design follows clear theoretical principles, facilitating precise debugging and optimization based on actual needs. From basic signal amplification to complex application scenarios, the system offers excellent scalability and debugging convenience, enabling stable and reliable operation in multiple fields, unlocking signal processing potential, and raising the overall performance ceiling of the analog-to-digital conversion system.

[0034] The addition of the unbalanced input to balanced differential circuit output module in this technical solution constructs a precise signal transition bridge. The unbalanced signal output from the second-stage amplifier is converted into a dual-ended balanced differential signal. The differential transmission method effectively resists common-mode noise interference, ensuring signal purity. Furthermore, the common-mode rejection ratio is optimized based on the CMR calculation formula, significantly reducing common-mode interference and enabling precise amplification and transmission of weak differential signals. This lays a solid foundation for subsequent high-precision ADC conversion, achieving high-quality signal processing across the entire chain from signal acquisition and amplification to conversion output.

[0035] In this embodiment, the entire operation process can be controlled by a computer, and in each operation stage, signal feedback can be carried out through electrical signals to realize the sequential execution of steps. These are all conventional knowledge of current automatic control, and will not be elaborated on in this embodiment.

[0036] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. An analog-to-digital converter (ADC) combined instrumentation amplifier, comprising a first-stage amplifier, a second-stage amplifier connected to the first-stage amplifier, a front-end low-pass filter (LPF) connected to the second-stage amplifier, and an analog-to-digital converter (ADC) connected to the front-end low-pass filter (LPF), characterized in that, An unbalanced input to balanced differential circuit output module is provided between the second-stage amplifier signal and the front-end low-pass filter (LPF).

2. An analog-to-digital converter combination meter amplifier as defined in claim 1, wherein, The first stage amplifier includes: Two amplifiers, U1-A and U1-B, are connected in parallel with two resistors, R1 and R1', and a fixed resistor, RG. The positive input terminals of amplifiers U1-A and U1-B are connected to a signal input source. The output terminals of amplifiers U1-A and U1-B are respectively connected to resistors R1 and R1'. The negative input terminals of amplifiers U1-A and U1-B are connected in series through the fixed resistor RG.

3. An analog-to-digital converter combination meter amplifier as defined in claim 2, wherein, The second-stage amplifier includes: An amplifier U2-A and four resistors R2, R2', R3, and R3' are used. Resistor R2 is connected to the output signal terminal of amplifier U1-A, and resistor R2' is connected to the output signal terminal of amplifier U1-B. The outputs of resistors R2 and R2' are connected together to the negative input terminal of amplifier U2-A. The positive input terminal of amplifier U2-A is connected to the VREF signal through resistor R3'. The output signal terminal of amplifier U2-A is connected to resistor R3, and resistor R3 is connected back to the negative input terminal of amplifier U2-A. The output terminal of amplifier U2-A serves as the Uout- signal output terminal.

4. An analog-to-digital converter combination meter amplifier as defined in claim 3, wherein, The second-stage amplifier suppresses the common-mode voltage of the two input signals and calculates the difference between them using the following formula: CMR (dB) = 20log[(1 + R3 / R2) / Kr]; where Kr is the total matching ratio fraction of R2 / R3 = R2' / R3', and R3 / R2 = R3' / R2' is a pair of relatively equal resistors; With R2=R3, the matching ratio is 0.1% and the error is 66 dBCMR. With R2=R3, the error of one of the resistors is 1% and the error is 46 dBCMR.

5. An analog-to-digital converter combination meter amplifier as defined in claim 4, wherein, The signals at the ends of resistors R1 and R1' furthest from the output terminals of amplifiers U1-A and U1-B are respectively connected to the negative input terminals of amplifiers U1-A and U1-B.

6. An analog-to-digital converter combination meter amplifier as defined in claim 5, wherein, The output of the front-end low-pass filter (LPF) is connected to the analog input of the analog-to-digital converter (ADC), and the gain of the front-end low-pass filter (LPF) is 1:

1.

7. An analog-to-digital converter combination meter amplifier as defined in claim 6, wherein, The analog-to-digital converter (ADC) is a high-precision Σ-Δ single-supply digital-to-analog converter (ADC), and the ADC has a differential amplifier installed inside.

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