Multi-channel sensor differential signal AD conversion circuit

Abstract

The present invention relates to the field of sensor signal processing technology, and in particular to a multi-channel sensor differential signal AD conversion circuit, comprising a four-channel instrumentation amplifier, two rail-to-rail amplifiers, an AD converter and a microcontroller, wherein the microcontroller is connected to the AD converter control, and an external sensor outputs two signals, one in phase with the original signal, and the other in phase with the original signal. The differential signal has a strong ability to resist common-mode interference, is suitable for long-distance transmission, realizes high-speed multi-channel stable conversion function, and can be used in application fields requiring high-speed multi-channel differential signal AD conversion.

Description

Technical Field

[0001] The present invention relates to the technical field of sensor signal processing, and in particular to a multi-channel sensor differential signal AD conversion circuit. Background Art

[0002] The types of analog output signals of sensors mainly include single-ended signals, pseudo-differential signals and differential signals. Most applications collect single-ended signals of sensor analog quantities for AD conversion. When one line of the single-ended input changes, the GND does not change, so the voltage difference changes greatly. Single-ended signals rely on two threshold voltages, high and low, and are greatly affected by the process and temperature. For low-amplitude signals, the timing error is large. Summary of the invention

[0003] The purpose of the present invention is to solve the above problems and provide a multi-channel sensor differential signal AD conversion circuit to achieve high-speed multi-channel stable conversion function, which can be used in application fields requiring high-speed multi-channel differential signal AD conversion.

[0004] Because differential is to transform the single-ended signal into a differential signal, output two signals, one is in phase with the original signal, and the other is in phase with the original signal. When differential input is used, the voltage difference between the two signal lines is determined.

[0005] Differential signals have strong resistance to common-mode interference and are suitable for longer distance transmission, while single-ended signals do not have this function.

[0006] When the signal is disturbed, the two differential lines will be affected at the same time, but the voltage difference will not change much. When one line of the single-ended input changes, the GND does not change, so the voltage difference changes greatly.

[0007] The technical solution adopted by the present invention is:

[0008] A multi-channel sensor differential signal AD conversion circuit, characterized in that it includes four instrument amplifiers, two rail-to-rail amplifiers, an AD converter and a microcontroller, wherein the microcontroller is connected to the AD converter control, the input end of the first instrument amplifier is connected to the first sensor differential signal, and the single-ended signal converted by the first instrument amplifier is connected to the reverse input end of the first amplifier channel of the first rail-to-rail amplifier; the input end of the second instrument amplifier is connected to the second sensor differential signal, and the single-ended signal converted by the second instrument amplifier is connected to the reverse input end of the second amplifier channel of the first rail-to-rail amplifier; the input end of the third instrument amplifier is connected to the third sensor differential signal, and the single-ended signal converted by the third instrument amplifier is connected to the reverse input end of the second amplifier channel of the second rail-to-rail amplifier. The first rail-to-rail operational amplifier is connected to the reverse input end of the first operational amplifier channel of the first rail-to-rail operational amplifier; the input end of the fourth instrument operational amplifier is connected to the fourth sensor differential signal; the single-ended signal converted by the fourth instrument operational amplifier is connected to the reverse input end of the second operational amplifier channel of the second rail-to-rail operational amplifier; the REF pin of the AD converter is respectively connected to the positive input end of the third operational amplifier channel of the first rail-to-rail operational amplifier and the positive input end of the third operational amplifier channel of the second rail-to-rail operational amplifier; the two input ends of the first and second operational amplifier channels of the first rail-to-rail operational amplifier are simultaneously input with voltage, and the output ends are respectively connected to the input channels of the AD converter; the two input ends of the first and second operational amplifier channels of the second rail-to-rail operational amplifier are simultaneously input with voltage, and the output ends are respectively connected to the input channels of the AD converter.

[0009] Furthermore, the four-way sensor differential signals are connected to the input terminals of the corresponding four-way instrument amplifiers through low-pass filters respectively.

[0010] Furthermore, the single-ended signals converted by the four-channel instrumentation amplifier are sent to the inverting input terminals of the corresponding amplifier channels of the rail-to-rail amplifier through resistors.

[0011] Furthermore, the output ends of the first and second operational amplifiers of the two rail-to-rail operational amplifiers are connected through resistors to form a negative feedback circuit.

[0012] Furthermore, the REF pin of the AD converter is input to the positive input terminal of the third operational amplifier channel of the first and second rail-to-rail operational amplifiers after voltage division by a voltage divider resistor, and the voltage outputted from the output terminal of the third operational amplifier channel is input to the non-inverting input terminal of the first and second operational amplifier channels after voltage division by a resistor.

[0013] Furthermore, the output ends of the first and second operational amplifier channels of the two rail-to-rail operational amplifiers are respectively connected to the filter circuit and then to the input channel of the AD converter.

[0014] Furthermore, the model of the instrument amplifier is AD8421BRZ, the model of the rail-to-rail amplifier is AD8608ARZ, the model of the AD converter is AD7689, and the model of the microcontroller is 10M08SAE144CG.

[0015] The beneficial effects of the present invention are:

[0016] Compared with ordinary single-ended signal routing, the most obvious advantages of differential signals are reflected in the following aspects:

[0017] (1) Strong anti-interference ability, because the coupling between the two differential lines is very good (it is best to wire them adjacently). When there is noise interference from the outside, it is almost coupled to the two lines at the same time, and the receiving end only cares about the difference between the two signals, so the common-mode noise from the outside can be completely offset;

[0018] (2) It can effectively suppress EMI. For the same reason, since the polarities of the two signals are opposite, the electromagnetic fields they radiate can cancel each other out. The tighter the coupling, the less electromagnetic energy is released to the outside world.

[0019] (3) Accurate timing positioning. Since the switching change of the differential signal is located at the intersection of the two signals, unlike the ordinary single-ended signal that relies on high and low threshold voltages for judgment, it is less affected by the process and temperature, which can reduce the timing error. It is also more suitable for circuits with low amplitude signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The first and second AD sampling signal conditioning circuit schematics of the present invention;

[0021] Figure 2 The schematic diagram of the 3rd and 4th AD sampling signal conditioning circuit of the present invention;

[0022] Figure 3 It is a schematic diagram of the four-way AD acquisition and controller communication of the present invention. DETAILED DESCRIPTION

[0023] The specific implementation of the multi-channel sensor differential signal AD conversion circuit of the present invention is described in detail below with reference to the accompanying drawings.

[0024] Referring to the accompanying drawings, the high-speed multi-channel differential signal AD conversion circuit of the present invention includes instrumentation amplifiers U1-U4, rail-to-rail amplifiers U5-U6, AD converter U7, and microcontroller U8.

[0025] The microcontroller U8 is connected to the AD converter U7, that is, the MOSI end of the microcontroller U8 is connected to the DIN pin of the AD converter U7, the SCLK end of the microcontroller U8 is connected to the SCK pin of the AD converter U7, the MISO end of the microcontroller U8 is connected to the SDO pin of the AD converter U7, and the CONV end of the microcontroller U8 is connected to the CNV pin of the AD converter U7.

[0026] The input end of the instrument amplifier U1 is connected to the external sensor differential signal. The first sensor differential signal passes through a first-order RC low-pass filter composed of resistor R1 and capacitor C1, resistor R2 and capacitor C2 to remove unnecessary high-frequency signals. Vout1 is the difference between IN+ and IN-, realizing the differential to single-ended signal function.

[0027] The input end of instrument amplifier U2 is connected to the external sensor differential signal. The second sensor differential signal passes through a first-order RC low-pass filter composed of resistor R3 and capacitor C3, resistor R4 and capacitor C4 to remove unnecessary high-frequency signals. Vout2 is the difference between IN+ and IN-, realizing the differential to single-ended signal function.

[0028] The input end of instrument amplifier U3 is connected to the external sensor differential signal. The third sensor differential signal passes through a first-order RC low-pass filter composed of resistor R5 and capacitor C5, resistor R6 and capacitor C6 to remove unnecessary high-frequency signals. Vout3 is the difference between IN+ and IN-, realizing the differential to single-ended signal function.

[0029] The input end of instrument amplifier U4 is connected to the external sensor differential signal. The fourth sensor differential signal passes through a first-order RC low-pass filter composed of resistor R7 and capacitor C7, resistor R8 and capacitor C8 to remove unnecessary high-frequency signals. Vout4 is the difference between IN+ and IN-, realizing the differential to single-ended signal function.

[0030] The first converted single-ended signal Vout1 is sent to the inverting input terminal of the first operational amplifier channel of the rail-to-rail operational amplifier U5 through the resistor R10.

[0031] The second converted single-ended signal Vout2 is sent to the inverting input terminal of the second operational amplifier channel of the rail-to-rail operational amplifier U5 through the resistor R11.

[0032] The third converted single-ended signal Vout3 is sent to the inverting input terminal of the first operational amplifier channel of the rail-to-rail operational amplifier U6 through the resistor R13.

[0033] The fourth converted single-ended signal Vout4 is sent to the inverting input terminal of the second operational amplifier channel of the rail-to-rail operational amplifier U6 through the resistor R14.

[0034] The output end of the first operational amplifier of the rail-to-rail operational amplifier U5 forms a negative feedback circuit through the resistor R15, and the resistors R15 and R10 form an inverse proportional operation relationship.

[0035] The output end of the second operational amplifier of the rail-to-rail operational amplifier U5 forms a negative feedback circuit through the resistor R16, and the resistors R16 and R11 form an inverse proportional operation relationship.

[0036] The output end of the first operational amplifier of the rail-to-rail operational amplifier U6 forms a negative feedback circuit through the resistor R17, and the resistors R17 and R13 form an inverse proportional operation relationship.

[0037] The output end of the second operational amplifier of the rail-to-rail operational amplifier U6 forms a negative feedback circuit through the resistor R18, and the resistor R18 and the resistor R14 form an inverse proportional operation relationship.

[0038] The REF pin of AD converter U7 uses an internal reference source to generate a 4.096V system reference voltage, which is divided by resistors R23 and R21 and then input to the positive input of the third op amp of rail-to-rail op amp U5. The third op amp is a non-inverting follower. The voltage output from the output end is divided by resistors R19 and R9 and then input to the non-inverting input of the first op amp of rail-to-rail op amp U5 and the non-inverting input of the second op amp of U5.

[0039] The REF pin of AD converter U7 uses an internal reference source to generate a 4.096V system reference voltage, which is divided by resistors R24 and R22 and then input to the positive input of the 3rd op amp of rail-to-rail op amp U6. The 3rd op amp is a non-inverting follower. The voltage output from the output end is divided by resistors R20 and R12 and then input to the non-inverting input of the 1st op amp and the non-inverting input of the 2nd op amp of rail-to-rail op amp U6.

[0040] The two input terminals of the first operational amplifier of the rail-to-rail operational amplifier U5 have voltage inputs at the same time, forming a subtractor. The voltage value of the output terminal ADC1 of the first operational amplifier of the rail-to-rail operational amplifier U5 is the difference between the voltage value of the non-inverting input terminal and the voltage value of the inverting input terminal, which is calculated by the reference voltage VREF, resistor R23, resistor R21, resistor R19, resistor R9, instrumentation operational amplifier U1 output voltage Vout1, resistor R10 and resistor R15.

[0041] The two input terminals of the second operational amplifier of the rail-to-rail operational amplifier U5 have voltage inputs at the same time, forming a subtractor. The voltage value of the output terminal ADC2 of the second operational amplifier of the rail-to-rail operational amplifier U5 is the difference between the voltage value of the non-inverting input terminal and the voltage value of the inverting input terminal, which is calculated by the reference voltage VREF, resistor R23, resistor R21, resistor R19, resistor R9, instrumentation operational amplifier U2 output voltage Vout2, resistor R11 and resistor R16.

[0042] The two input terminals of the first operational amplifier of the rail-to-rail operational amplifier U6 have voltage inputs at the same time, forming a subtractor. The voltage value of the output terminal ADC3 of the first operational amplifier of the rail-to-rail operational amplifier U6 is the difference between the voltage value of the non-inverting input terminal and the voltage value of the inverting input terminal, which is calculated by the reference voltage VREF, resistor R24, resistor R22, resistor R20, resistor R12, instrumentation operational amplifier U3 output voltage Vout3, resistor R13 and resistor R17.

[0043] The two input terminals of the second operational amplifier of the rail-to-rail operational amplifier U6 have voltage inputs at the same time, forming a subtractor. The voltage value of the output terminal ADC4 of the second operational amplifier of the rail-to-rail operational amplifier U6 is the difference between the voltage value of the non-inverting input terminal and the voltage value of the inverting input terminal, which is calculated by the reference voltage VREF, resistor R24, resistor R22, resistor R20, resistor R12, instrumentation operational amplifier U4 output voltage Vout4, resistor R14 and resistor R18.

[0044] Through the reference voltage and the above-mentioned conditioning circuit, the voltage accuracy and voltage range of the voltages ADC1, ADC2, ADC3, ADC4 at the output terminals of the rail-to-rail op amps U5 and U6 input to the input channel of the AD converter U7 are guaranteed.

[0045] ADC1 passes through the RC filter formed by resistors R25 and C13 and is input to channel IN2 of the AD converter.

[0046] ADC2 passes through the RC filter formed by resistors R27 and C15 and is input to channel IN3 of the AD converter.

[0047] ADC3 passes through the RC filter formed by resistors R26 and C14 and is input to channel IN6 of the AD converter.

[0048] ADC4 is input to channel IN7 of the AD converter after passing through the RC filter formed by resistors R28 and C16.

[0049] After conversion by AD converter U7, microcontroller U8 communicates with U7 through SPI communication protocol to achieve fast communication of sensor data.

[0050] The model of instrumentation amplifier U1-U4 is AD8421BRZ, the model of rail-to-rail amplifier U5-U6 is AD8608ARZ, the model of AD converter U7 is AD7689, and the model of microcontroller U8 is 10M08SAE144CG.

[0051] The above are only preferred embodiments of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and modifications without departing from the principles of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A multi-channel sensor differential signal AD conversion circuit, characterized in that: include Four instrumentation amplifiers, two rail-to-rail amplifiers, an AD converter and a microcontroller, the microcontroller is connected to the AD converter control, The input end of the first instrument amplifier is connected to the first sensor differential signal, and the single-ended signal converted by the first instrument amplifier is connected to the reverse input end of the first amplifier channel of the first rail-to-rail amplifier; The input end of the second instrument amplifier is connected to the second sensor differential signal, and the single-ended signal converted by the second instrument amplifier is connected to the reverse input end of the second amplifier channel of the first rail-to-rail amplifier; The input end of the third instrument amplifier is connected to the differential signal of the third sensor, and the single-ended signal converted by the third instrument amplifier is connected to the reverse input end of the first amplifier channel of the second rail-to-rail amplifier; The input end of the 4th instrument amplifier is connected to the 4th sensor differential signal; The single-ended signal converted by the 4th instrumentation amplifier is connected to the inverting input terminal of the 2nd amplifier channel of the 2nd rail-to-rail amplifier; The REF pin of the AD converter is respectively connected to the positive input terminal of the third operational amplifier channel of the first rail-to-rail operational amplifier and the positive input terminal of the third operational amplifier channel of the second rail-to-rail operational amplifier; Voltages are input to two input ends of the first and second operational amplifier channels of the first rail-to-rail operational amplifier at the same time, and the output ends are respectively connected to input channels of an AD converter; The two input ends of the first and second operational amplifier channels of the second rail-to-rail operational amplifier input voltages simultaneously, and the output ends are respectively connected to the input channels of the AD converter. The REF pin of the AD converter is input to the positive input terminal of the third operational amplifier channel of the first and second rail-to-rail operational amplifiers after voltage division by a voltage divider resistor. The voltage outputted from the output terminal of the third operational amplifier channel is input to the non-inverting input terminal of the first and second operational amplifier channels after voltage division by a resistor. The output ends of the first and second operational amplifier channels of the two rail-to-rail operational amplifiers are respectively connected to the filter circuit and then to the input channel of the AD converter.

2. The multi-channel sensor differential signal AD conversion circuit according to claim 1, characterized in that: The four-way sensor differential signals are connected to the input terminals of the corresponding four-way instrument amplifiers through low-pass filters respectively.

3. The multi-channel sensor differential signal AD conversion circuit according to claim 2, characterized in that: The single-ended signals converted by the four-channel instrumentation amplifier are sent to the inverting input terminal of the corresponding rail-to-rail amplifier channel through resistors.

4. The multi-channel sensor differential signal AD conversion circuit according to claim 3, characterized in that: The output ends of the first and second operational amplifiers of the two rail-to-rail operational amplifiers are connected through resistors to form a negative feedback circuit.

5. The multi-channel sensor differential signal AD conversion circuit according to any one of claims 1 to 4, characterized in that: The model of the instrument amplifier is AD8421BRZ, the model of the rail-to-rail amplifier is AD8608ARZ, the model of the AD converter is AD7689, and the model of the microcontroller is 10M08SAE144CG.

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