Analog-to-digital converter combined instrument amplifier

Abstract

The invention relates to the technical field of amplifiers, and discloses an analog-to-digital converter combination instrument amplifier which comprises a first-stage amplifier, the first-stage amplifier is in signal connection with a second-stage amplifier, the second-stage amplifier is in signal connection with a front-end low-pass filter (LPF), the front-end low-pass filter (LPF) is in signal connection with an analog-to-digital converter (ADC), and the analog-to-digital converter (ADC) is in signal connection with the analog-to-digital converter. And an unbalanced input-to-balanced differential circuit output module is arranged between the second-stage amplifier signal and a front-end low-pass filter (LPF). From the perspective of signal processing and conversion, a precise signal transition bridge is constructed by adding an unbalanced input-to-balanced differential circuit output module, unbalanced signals output by a second-stage amplifier are converted into double-end balanced differential signals, common-mode noise interference is effectively resisted through a differential transmission mode, the signal purity is guaranteed, and the signal quality is improved. The front-end low-pass filter and the analog-to-digital converter are adaptive to differential signals, so that the signal transmission is stable and anti-interference, and the analog-to-digital conversion is more accurate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of amplifiers, in particular to a combination of an analog-to-digital converter and an instrument amplifier. BACKGROUND

[0002] Among all electronic special-purpose amplifiers, the commonly used one is an instrument amplifier, which mainly functions to amplify weak differential signal electric signals, suppress useless common-mode noise signals, and improve signal quality. This amplifier circuit is commonly used in the high-precision signal acquisition front end of an instrument. Figure 1 The deficiency of the circuit is that the circuit is complex, the resistance is large, the precision is high, and it is difficult to match the same resistance value, which will affect the common-mode rejection ratio, increase the difficulty of production and design, or only high-cost instrument amplifier chips can be used to replace the deficiencies of the discrete circuit.

[0003] According to the search of application No. 202221493518.X, a combination of an analog-to-digital converter and an instrument amplifier is disclosed. In today's digital era, a large part of the demand requires high amplification of analog signals, and then the ADC sampling is performed before digital processing. Therefore, the present application combines a high-performance differential input analog-to-digital converter and an instrument amplifier. The main function of the instrument amplifier is to amplify weak differential signal electric signals, suppress useless common-mode noise signals, and improve signal quality. This amplifier circuit is commonly used in the high-precision signal acquisition front end of an instrument. The signal acquisition device has a weak signal output from a sound (such as a microphone) sensor, a photosensitive sensor, a magnetic induction (such as a radar) sensor, etc.

[0004] However, since the electric signal converted by the sensor is weak, and the power supply and components in the circuit itself have different noise interference sources, how to improve the signal-to-noise ratio and anti-interference of the instrument amplifier, ensure the signal acquisition quality, and reduce the cost and production difficulty of the instrument amplifier is the key research direction of the present application. SUMMARY

[0005] The present application aims to provide a combination of an analog-to-digital converter and an instrument amplifier, which optimizes the common-mode rejection ratio according to the CMR calculation formula, greatly weakens the common-mode interference, accurately amplifies the weak differential signal, and lays a solid foundation for subsequent high-precision conversion of the ADC. From signal acquisition and amplification to conversion and output, the whole link realizes high-quality signal processing, aiming to solve the problems in the prior art.

[0006] The application is implemented as follows: an analog-digital converter combination instrument amplifier, comprising a first-stage amplifier, a second-stage amplifier connected with the first-stage amplifier, a front-end low-pass filter (LPF) connected with the second-stage amplifier, and an analog-digital converter (ADC) connected with the front-end low-pass filter (LPF), wherein a non-balanced input to balanced differential circuit output module is arranged between the second-stage amplifier and the front-end low-pass filter (LPF).

[0007] Further, the first-stage amplifier comprises: Two amplifiers U1-A and U1-B, two resistors R1 and R1', and a fixed resistor RG, wherein the amplifiers U1-A and U1-B are connected in parallel, the input positive terminal of the amplifiers U1-A and U1-B is connected with a signal input source, the output terminals of the amplifiers U1-A and U1-B are respectively connected with the resistors R1 and R1', and the input negative terminals of the amplifiers U1-A and U1-B are connected in series through the fixed resistor RG.

[0008] Further, the second-stage amplifier comprises: One amplifier U2-A, four resistors R2, R2', R3, and R3', wherein the resistor R2 is connected with the output terminal of the amplifier U1-A, the resistor R2' is connected with the output terminal of the amplifier U1-B, the outputs of the resistors R2 and R2' are commonly connected to the input negative terminal of the amplifier U2-A, the input positive terminal of the amplifier U2-A is connected with a VREF signal through the resistor R3', the output terminal of the amplifier U2-A is connected with the resistor R3, the resistor R3 is connected back to the input negative terminal of the amplifier U2-A, and the output terminal of the amplifier U2-A serves as a Uout- signal output terminal.

[0009] Further, the second-stage amplifier suppresses the common-mode voltage of two input signals and calculates the difference of the two signals, and the calculation formula is as follows: CMR (dB) = 20log[(1+R3 / R2) / Kr]; wherein Kr is the total R2 / R3=R2' / R3' matching ratio, R3 / R2=R3' / R2' is a pair of relatively equal resistors; when R2=R3, the matching ratio error of 0.1% is 66dBCMR, and when R2=R3, the error of one resistor is 1% and the CMR is 46dBCMR.

[0010] Further, one end of the resistors R1 and R1' away from the output terminals of the amplifiers U1-A and U1-B is respectively connected with the input negative terminals of the amplifiers U1-A and U1-B.

[0011] Further, the output end of the front-end low-pass filter (LPF) and the analog input end of the analog-to-digital converter (ADC) are connected, and the gain of the front-end low-pass filter (LPF) is 1:1.

[0012] Further, the analog-to-digital converter (ADC) is a high-precision sigma-delta single power analog-to-digital converter (ADC), and the analog-to-digital converter (ADC) is internally provided with a differential amplifier.

[0013] Further, the input end of the unbalanced input to balanced differential circuit output module is connected with the output end of the second-stage amplifier, and receives the unbalanced signal output by the second-stage amplifier.

[0014] Further, 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 in a differential transmission mode.

[0015] Further, the output end of the unbalanced input to balanced differential circuit output module is connected with the input end of the low-pass filter (LPF), provides a required differential signal for the first-stage circuit, and realizes adaptive conversion of the signal form.

[0016] Compared with the prior art, the analog-to-digital converter combined instrument amplifier provided by the application has the following beneficial effects: 1. 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 double-ended balanced differential signal, the differential transmission mode effectively resists common-mode noise interference, guarantees signal purity, the front-end low-pass filter and the analog-to-digital converter are adapted to the differential signal, signal transmission is stable and anti-interference, the analog-to-digital conversion is more accurate, and the various-stage amplifiers are cooperatively matched, the first-stage double operational amplifier is connected in parallel, negative feedback and resistance series connection, a high-input impedance and low-noise front end is built, the second-stage uses an operational amplifier and a resistance network to suppress common-mode voltage and realize differential operation, the common-mode rejection ratio is optimized according to the CMR calculation formula by reasonably setting resistance parameters, common-mode interference is greatly weakened, weak differential signals are accurately amplified and transmitted, a solid foundation is built for subsequent high-precision ADC conversion, and from signal acquisition and amplification to conversion and output, high-quality signal processing is realized in the whole link. 2. High-precision sigma-delta single power supply ADC with internal differential amplifier, perfectly compatible with front-end balanced differential signal output, single power supply for more low-power, portable scenarios, front-end amplifier with flexible resistance parameter configuration, compatible with input signals of different amplitude and impedance characteristics, meeting the needs of diversified industrial, control and other scenarios, non-balanced to balanced module for more flexible signal link interface matching, compatible with different architecture circuits in front and back stages, system integration and compatibility improved, and each part of the circuit design follows clear theoretical basis, easy to accurately debug and optimize according to actual needs, from basic signal amplification to complex scenario application, good scalability and debugging convenience of the system, helping it to run stably and reliably in multiple fields, tapping the potential of signal processing, and improving the upper limit of the overall analog-digital conversion system performance. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The prior art amplifier circuit structure schematic diagram is shown in Figure 1. Figure 2 The improved amplifier circuit structure schematic diagram in the prior art is shown in Figure 2. Figure 3 The circuit structure schematic diagram of the analog-digital converter combination instrument amplifier proposed by the present application is shown in Figure 3. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme and advantages of the present application clearer and more apparent, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0019] The implementation of the present application will be described in detail below in combination with specific examples.

[0020] The same or similar reference numerals in the drawings of the present embodiment correspond to the same or similar parts; in the description of the present application, it should be understood that the orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right" and the like is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the terms describing the positional relationship in the drawings are only used for example, and cannot be understood as a limitation of the present application, for those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0021] Reference Figure 3As shown, a kind of analog-digital converter combination instrument amplifier, including first stage amplifier (① stage circuit), first stage amplifier signal is connected second stage amplifier (② stage circuit), second stage amplifier signal is connected with front-end low-pass filter (LPF) (④ stage circuit), front-end low-pass filter (LPF) signal is connected with analog-digital converter (ADC) (⑤ stage circuit), non-balanced input is converted balanced differential circuit output module (③ stage circuit) is set between second stage amplifier signal and front-end low-pass filter (LPF), from the angle of signal processing and conversion, the addition of non-balanced input is converted balanced differential circuit output module constructs accurate signal transition bridge, the non-balanced signal of second stage amplifier output is converted into double-end balanced differential signal, and differential transmission mode effectively resists common-mode noise interference, guarantees signal purity.

[0022] In the embodiment, the first stage amplifier of the ① stage circuit includes: two amplifiers U1-A and U1-B and two resistors R1 and R1' and a fixed resistor RG, the amplifier U1-A and the amplifier U1-B are connected in parallel, the input positive terminal signal of the amplifier U1-A and the amplifier U1-B is connected with a signal input source, the output of the amplifier U1-A and the amplifier U1-B is respectively connected with the resistor R1 and the resistor R1', and the input negative terminal of the amplifier U1-A and the amplifier U1-B is connected in series through the fixed resistor RG.

[0023] In the embodiment, the second stage amplifier of the ② stage circuit includes: one amplifier U2-A, four resistors R2, R2', R3 and R3', the resistor R2 is connected with the output of the amplifier U1-A, the resistor R2' is connected with the output of the amplifier U1-B, the output of the resistor R2 and the resistor R2' is commonly connected to the input negative terminal of the amplifier U2-A, the input positive terminal of the amplifier U2-A is connected with the VREF signal through the resistor R3', the output of the amplifier U2-A is connected with the resistor R3, and the resistor R3 is connected back to the input negative terminal of the amplifier U2-A, and the output of the amplifier U2-A is used as the Uout- signal output terminal.

[0024] In the embodiment, the second stage amplifier is to suppress the common-mode voltage of the two input signals, and the difference of the two signals is calculated, and the calculation formula is as follows: CMR (dB)=20log [(1+R3 / R2) / Kr]; wherein, Kr is the total R2 / R3=R2' / R3' matching ratio fraction, R3 / R2=R3' / R2' is a pair of relatively equal resistors; when R2=R3, the matching ratio error of 0.1% is 66dBCMR, and when R2=R3, the error of one of the resistors is 46dBCMR.

[0025] In the embodiment, the resistors R1 and R1' are connected to the input negative terminals of the amplifiers U1-A and U1-B respectively, and the output terminals of the front-end low-pass filter (LPF) and the analog input terminals of the analog-to-digital converter (ADC) are connected to the signal signals, the gain of the front-end low-pass filter (LPF) is 1:1, the analog-to-digital converter (ADC) is a high-precision sigma-delta single power supply digital-to-analog converter (ADC), the internal differential amplifier of the analog-to-digital converter (ADC) is provided, the front-end low-pass filter and the analog-to-digital converter are adapted to the differential signal, the signal transmission is stable and anti-interference, the analog-to-digital conversion is more accurate, and the amplifiers at each stage are cooperated, the first-stage double operational amplifier is connected in parallel, the negative feedback and the resistor are connected in series, the high-input impedance and low-noise front-end are constructed, the second-stage operational amplifier and the resistor network are used to suppress the common-mode voltage and realize differential operation, and the resistor parameters are reasonably set.

[0026] In the 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, receives the unbalanced signal output by the second-stage amplifier, converts the input single-ended unbalanced signal into double-ended balanced differential signal through the internal circuit, outputs in the differential transmission mode, the output terminal is connected to the input terminal of the low-pass filter (LPF), provides the differential signal meeting the requirements for the first-stage circuit, realizes the adaptive conversion of the signal form, optimizes the common-mode rejection ratio according to the CMR calculation formula, greatly weakens the common-mode interference, accurately amplifies the weak differential signal, and lays a solid foundation for subsequent high-precision conversion of the ADC, realizes the high-quality signal processing of the whole link from signal acquisition and amplification to conversion and output.

[0027] The high-precision sigma-delta single power supply ADC of the technical solution is perfectly adapted to the front-end balanced differential signal output, is adapted to more low-power and portable scenes by single power supply, the front-end amplifier can be flexibly configured through the resistor parameters, can be adapted to input signals with different amplitude and impedance characteristics, meets the needs of diversified industrial and measurement and control scenes, the unbalanced to balanced module makes the signal link interface matching more flexible, is compatible with different architecture circuits of front and rear stages, the system integration and compatibility are improved, the circuit design of each part follows clear theoretical basis, is convenient for accurate debugging and optimization according to actual needs, has good scalability and debugging convenience from basic signal amplification to complex scene application, helps stable and reliable operation in multiple fields, excavates the signal processing potential, and improves the upper limit of the overall analog-to-digital conversion system performance.

[0028] The non-balanced input to balanced differential circuit output module of the technical solution constructs a precise signal transition bridge, the non-balanced signal output by the second amplifier is converted into a double-ended balanced differential signal, the differential transmission mode effectively resists common-mode noise interference, guarantees signal purity, and optimizes the common-mode rejection ratio according to the CMR calculation formula, greatly weakens the common-mode interference, accurately amplifies and transmits the weak differential signal, and lays a solid foundation for subsequent ADC high-precision conversion, from signal acquisition and amplification to conversion and output, realizing high-quality signal processing of the whole link.

[0029] In the embodiment, the whole operation process can be controlled by a computer, and in each operation link, signal feedback can be realized through electrical signals, and the steps are sequentially performed. These are all conventional knowledge of automatic control, and will not be described one by one in the embodiment.

[0030] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An analog-to-digital converter combination instrumentation amplifier, comprising a first stage amplifier, said first stage amplifier signal connected to a second stage amplifier, said second stage amplifier signal connected to a front end low pass filter (LPF), said front end low pass filter (LPF) signal connected to an analog-to-digital converter (ADC), characterized by, A non-balanced input to balanced differential circuit output module is arranged between the second-stage amplifier signal and a front-end low-pass filter (LPF); The input end of the non-balanced input to balanced differential circuit output module is connected with the output end of the second-stage amplifier, and receives the non-balanced signal output by the second-stage amplifier.

2. An analog-to-digital converter combination meter amplifier as defined in claim 1, wherein, The first-stage amplifier comprises: The two amplifiers U1-A and U1-B are connected in parallel with the two resistors R1 and R1' and a fixed resistor RG. The input positive end of the amplifier U1-A and the input positive end of the amplifier U1-B are connected with a signal input source. The output end of the amplifier U1-A is connected with the resistor R1, and the output end of the amplifier U1-B is connected with the resistor R1'. The input negative end of the amplifier U1-A and the input negative end of the amplifier 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 comprises: The second-stage amplifier comprises one amplifier U2-A and four resistors R2, R2', R3 and R3'. The resistor R2 is connected with the output end of the amplifier U1-A, and the resistor R2' is connected with the output end of the amplifier U1-B. The output of the resistor R2 and the output of the resistor R2' are connected to the input negative end of the amplifier U2-A. The input positive end of the amplifier U2-A is connected with a VREF signal through the resistor R3'. The output end of the amplifier U2-A is connected with the resistor R3, and the resistor R3 is connected to the input negative end of the amplifier U2-A. The output end of the amplifier U2-A is used as a Uout- signal output end.

4. An analog-to-digital converter combination meter amplifier as defined in claim 3, wherein, The second-stage amplifier is used to suppress the common-mode voltage of the two input signals and calculate the difference between the two signals. The calculation formula is as follows: CMR (dB) = 20log[(1+R3 / R2) / Kr]. Wherein, Kr is the total R2 / R3=R2' / R3' matching ratio, and R3 / R2=R3' / R2' is a pair of relatively equal resistors. When R2=R3, the matching ratio error of 0.1% is 66dBCMR, and when R2=R3, the error of one of the resistors is 46dBCMR.

5. An analog-to-digital converter combination meter amplifier as defined in claim 4, wherein, The one end of the resistor R1 and the one end of the resistor R1' far away from the output end of the amplifier U1-A and the output end of the amplifier U1-B are connected with the input negative end of the amplifier U1-A and the input negative end of the amplifier U1-B respectively.

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

1.

7. An analog-to-digital converter combination instrument amplifier as claimed in any one of claims 1-6, characterized in that, The input end of the non-balanced input to balanced differential circuit output module is connected with the output end of the second-stage amplifier, and receives the non-balanced signal output by the second-stage amplifier.

8. An analog-to-digital converter combination meter amplifier as defined in claim 7, wherein, The non-balanced input to balanced differential circuit output module converts the input single-ended non-balanced signal into a double-ended balanced differential signal through internal circuit conversion, and outputs in a differential transmission mode.

9. An analog-to-digital converter combination meter amplifier as defined in claim 8, wherein, The output end of the non-balanced input to balanced differential circuit output module is connected with the input end of a low-pass filter (LPF), so as to provide a differential signal meeting the requirements for the first-stage circuit and realize the adaptive conversion of the signal form.

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