Positive and negative output weak current source circuit

Abstract

The invention relates to the technical field of precise instruments, in particular to a positive and negative output weak current source circuit, which comprises a digital-to-analog conversion module, a first-order active filtering module, a positive and negative voltage switching module, a proportional amplification module, a range switching module and a following module, and is characterized in that the influence of a load on an output current is eliminated by arranging the weak current source circuit from 10pA to 2uA, and the output current is stable. The defect that an existing current source is small in output range is overcome, the situation that the stability of current output is affected by uncertain impedance of a load in a high-precision environment is avoided, positive and negative current output is achieved through relay switching, the circuit structure is simple, and the current output range can be controlled by selecting the resistance value of a resistor; and the weak current source circuit is more convenient to control during application.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of precision instruments, and particularly relates to a weak current source circuit with positive and negative outputs. BACKGROUND

[0002] The weak current source is an electronic device capable of providing stable output current, which is used for converting a small current signal into a measurable voltage signal, maintaining stable current output, and being not affected by load or voltage changes, and can be used in weak current generated by devices such as photodiodes, mass spectrometers or chemical sensors, and is widely used in various research and product measurement applications, especially in semiconductors, nanotechnology and superconductors.

[0003] The current source is currently mainly capacitive, resistive and ionization type. For the resistive current source, the circuit idea is basically the same, that is, a resistance is used as an intermediate element, a voltage-current conversion is adopted to convert a standard voltage signal into a current signal proportional to the voltage signal, and in the case that the input voltage is constant, the resistance value is changed, and the converted current is also changed. Although it is convenient to realize, since the impedance of the load in the application circuit of the constant current source is uncertain, the load has a great influence on the constant current source, which can cause the output current of the constant current source to be unstable, especially in the environment with high precision, the influence of the uncertain impedance of the load on the constant current source is more obvious. Therefore, a weak current source circuit with positive and negative outputs is provided. SUMMARY

[0004] In order to solve the technical problems existing in the prior art, the present application provides a weak current source circuit with positive and negative outputs.

[0005] In order to solve the above technical problems, the present application provides the following technical scheme: a weak current source circuit with positive and negative outputs, comprising a digital-to-analog conversion module, a first-order active filter module, a positive and negative voltage switching module, a proportional amplification module, a range switching module and a following module, the digital-to-analog conversion module converts discrete digital signals into voltage signals, the digital-to-analog conversion module is connected with the first-order active filter module, the first-order active filter module filters out the frequency components of interference, the first-order active filter module is connected with the positive and negative voltage switching module, the positive and negative voltage switching module realizes the switching and output of positive and negative voltages, the positive and negative voltage switching module is connected with the proportional amplification module, the proportional amplification module amplifies the input voltage signal by a fixed proportion set, the proportional amplification module is connected with the range switching module, the range switching module realizes the output of different currents, the range switching module is connected with the following module, and the following module constitutes a negative feedback to make the output voltage accurately follow the load current change.

[0006] Preferably, the digital-to-analog conversion module comprises a digital-to-analog converter U1, a single-chip microcomputer GPIO output pin 1, a single-chip microcomputer GPIO output pin 2, and a single-chip microcomputer GPIO output pin 3, and three input control pins of the digital-to-analog converter U1 are connected with the single-chip microcomputer GPIO output pin 1, the single-chip microcomputer GPIO output pin 2, and the single-chip microcomputer GPIO output pin 3 respectively.

[0007] Preferably, the first-order active filter module comprises a resistor R1, a capacitor C1, and an operational amplifier U2, an output pin of the digital-to-analog converter U1 is connected with one end of the resistor R1, the other end of the resistor R1 is connected with a non-inverting terminal of the operational amplifier U2 and the capacitor C1, and the other end of the capacitor C1 is grounded.

[0008] Preferably, the positive and negative voltage switching module comprises a resistor R2, a resistor R3, a resistor R4, a digital transistor Q1, a relay RLY1, and an operational amplifier U3, an output terminal of the operational amplifier U2 is connected with one end of the resistor R2 and one end of the resistor R3 respectively, the other end of the resistor R2 is connected with an inverting terminal of the operational amplifier U3, the other end of the resistor R3 is connected with a non-inverting terminal of the operational amplifier U3 and a contact of the relay RLY1 respectively, a coil end of the relay RLY1 is connected with one end of the digital transistor Q1, a control pin of the digital transistor Q1 is connected with a single-chip microcomputer GPIO output pin 4, and the resistor R4 is connected between the output terminal and the inverting terminal of the operational amplifier U3, and the output voltage of the operational amplifier U3 is V2.

[0009] Preferably, the proportional amplification module comprises an operational amplifier U4, a resistor R5, a resistor R7, and a resistor R8, one end of the resistor R5 is connected with the output terminal of the operational amplifier U3, the other end of the resistor R5 is connected with a non-inverting terminal of the operational amplifier U4, the resistor R8 is connected between the output terminal and an inverting terminal of the operational amplifier U4, the inverting terminal of the operational amplifier U4 is connected with one end of the resistor R7, and the other end of the resistor R7 is grounded.

[0010] Preferably, the range switching module comprises digital transistor Q2, digital transistor Q3, digital transistor Q4, digital transistor Q5, relay RLY2, relay RLY3, relay RLY4, relay RLY5, resistor R9, resistor R10, resistor R11 and resistor R12, the output end of the operational amplifier U4 is connected with one end of the relay RLY2, relay RLY3, relay RLY4 and relay RLY5 contact respectively, the other end of the relay RLY2, relay RLY3, relay RLY4 and relay RLY5 contact is connected with the resistor R9, resistor R10, resistor R11 and resistor R12 respectively, the other end of the resistor R9, resistor R10, resistor R11 and resistor R12 is connected with the same direction end of the operational amplifier U5 and one end of the resistor RL1, the other end of the resistor RL1 is grounded;

[0011] The relay RLY2, relay RLY3, relay RLY4 and relay RLY5 are connected with one end of the digital transistor Q2, digital transistor Q3, digital transistor Q4 and digital transistor Q5 respectively, the control end of the digital transistor Q2, digital transistor Q3, digital transistor Q4 and digital transistor Q5 is connected with the single-chip microcomputer GPIO output pin 5, single-chip microcomputer GPIO output pin 6, single-chip microcomputer GPIO output pin 7 and single-chip microcomputer GPIO output pin 8 respectively, and the other end of the digital transistor Q2, digital transistor Q3, digital transistor Q4 and digital transistor Q5 is grounded.

[0012] Preferably, the following module comprises an operational amplifier U5, the reverse end of the operational amplifier U5 is connected with one end of the resistor R6, and the other end of the resistor R6 is connected with the same direction end of the operational amplifier U4.

[0013] Compared with the prior art, the present application has the following beneficial effects:

[0014] 1. The present application sets a weak current source circuit of 10pA to 2uA, eliminates the influence of the load on the output current, overcomes the small output range of the existing current source, and avoids the influence of the impedance uncertainty of the load on the stability of the current output in a high-precision environment.

[0015] 2. The current source can realize positive and negative output through relay switching.

[0016] 3. The circuit structure in the present application is simple, and the control of the current output range can be realized by selecting the resistance value, so that the weak current source circuit is more convenient to control in application. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 It is a positive and negative output weak current source circuit principle diagram of the present application. DETAILED DESCRIPTION

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments, which illustrate the above and other technical features and advantages of the present invention. However, the following embodiments are merely preferred embodiments of the present invention and are not exhaustive.

[0019] Example:

[0020] like Figure 1 As shown, this invention provides a weak current source circuit with positive and negative outputs, including a digital-to-analog converter module, a first-order active filter module, a positive and negative voltage switching module, a proportional amplifier module, a range switching module, and a follower module. The digital-to-analog converter module converts discrete digital signals into voltage signals. The digital-to-analog converter module is connected to the first-order active filter module, which filters out interference frequency components. The first-order active filter module is connected to the positive and negative voltage switching module, which realizes the switching and output of positive and negative voltages. The positive and negative voltage switching module is connected to the proportional amplifier module, which reduces the input voltage signal by a set fixed ratio. The proportional amplifier module is connected to the range switching module, which realizes the output of different currents. The range switching module is connected to the follower module, which forms negative feedback, causing the output voltage to accurately follow the changes in load current.

[0021] In this embodiment, the digital-to-analog converter module includes a digital-to-analog converter U1, a microcontroller GPIO output pin 1, a microcontroller GPIO output pin 2, and a microcontroller GPIO output pin 3. The three input control pins of the digital-to-analog converter U1 are respectively connected to the microcontroller GPIO output pin 1, the microcontroller GPIO output pin 2, and the microcontroller GPIO output pin 3. The power supply voltage of the digital-to-analog converter U1 is 5V, the reference voltage is 2.048V, the voltage output range is 0-2.048V, and the output voltage of the digital-to-analog converter U1 is V7.

[0022] In this embodiment, the first-order active filter module includes a resistor R1, a capacitor C1, and an operational amplifier U2. The output pin of the digital-to-analog converter U1 is connected to one end of the resistor R1, and the other end of the resistor R1 is connected to the non-inverting input of the operational amplifier U2 and the capacitor C1. The other end of the capacitor C1 is grounded to filter out signal noise. The output voltage of the operational amplifier U2 is V1.

[0023] In this embodiment, the positive and negative voltage switching module includes resistors R2, R3, R4, digital transistor Q1, relay RLY1 and operational amplifier U3, realizing flexible switching and output of positive voltage and negative voltage, the output end of operational amplifier U2 is connected with one end of resistors R2 and R3 respectively, the other end of resistor R2 is connected with the reverse end of operational amplifier U3, the other end of resistor R3 is connected with the same direction end of operational amplifier U3 and the contact of relay RLY1 respectively, the coil end of relay RLY1 is connected with one end of digital transistor Q1, the control pin of digital transistor Q1 is connected with the GPIO output pin 4 of single-chip microcomputer, resistor R4 is connected between the output end and the reverse end of operational amplifier U3, the output end voltage of operational amplifier U3 is V2;

[0024] When the GPIO output pin 4 of single-chip microcomputer is high level, the relay RLY1 is attracted, and the operational amplifier U3 outputs negative voltage.

[0025] When the GPIO output pin 4 of single-chip microcomputer is low level, the relay RLY1 is disconnected, and the operational amplifier U3 outputs positive voltage.

[0026] In this embodiment, the proportional amplification module includes operational amplifier U4, resistors R5, R7 and R8, which amplifies the input voltage signal by a fixed proportion, one end of resistor R5 is connected with the output end of operational amplifier U3, the other end of resistor R5 is connected with the same direction end of operational amplifier U4, resistor R8 is connected between the output end and the reverse end of operational amplifier U4, the reverse end of operational amplifier U4 is connected with one end of resistor R7, and the other end of resistor R7 is grounded.

[0027] In this embodiment, the range switching module includes digital transistors Q2, Q3, Q4, Q5, relays RLY2, RLY3, RLY4, RLY5, resistors R9, R10, R11 and R12, which flexibly switches the measurement range of the instrument according to the size of the measurement signal, so as to adapt to input signals of different amplitudes and ensure measurement accuracy, the output end of operational amplifier U4 is connected with one end of the contacts of relays RLY2, RLY3, RLY4 and RLY5 respectively, the other end of the contacts of relays RLY2, RLY3, RLY4 and RLY5 is connected with resistors R9, R10, R11 and R12 respectively, the other end of resistors R9, R10, R11 and R12 is connected with the same direction end of operational amplifier U5 and one end of resistor R11 respectively, and the other end of resistor R11 is grounded;

[0028] The relay RLY2, the relay RLY3, the relay RLY4 and the relay RLY5 are connected with the digital transistor Q2, the digital transistor Q3, the digital transistor Q4 and the digital transistor Q5 respectively, the control end of the digital transistor Q2, the digital transistor Q3, the digital transistor Q4 and the digital transistor Q5 are connected with the single-chip microcomputer GPIO output pin 5, the single-chip microcomputer GPIO output pin 6, the single-chip microcomputer GPIO output pin 7 and the single-chip microcomputer GPIO output pin 8 respectively, and the other end of the digital transistor Q2, the digital transistor Q3, the digital transistor Q4 and the digital transistor Q5 is grounded.

[0029] The output voltage of the operational amplifier U4 is V5, and the same-phase input voltage of the operational amplifier U5 is V6.

[0030] In the embodiment, the following module includes the operational amplifier U5, the following module constitutes a negative feedback, and the output voltage is accurately followed to change the load current, the reverse end of the operational amplifier U5 is connected with one end of the resistor R6, the other end of the resistor R6 is connected with the same direction end of the operational amplifier U4, the output voltage of the operational amplifier U5 is V4, and the same-phase input voltage of the operational amplifier U5 is V6.

[0031] In the embodiment, the operational amplifier U2 and the operational amplifier U3 are low offset voltage types, the operational amplifier U4 and the operational amplifier U5 are low bias current types, and the voltage relationship of each node is as follows:

[0032] ;

[0033] ;

[0034] ;

[0035] ;

[0036] ;

[0037] ;

[0038] Because:

[0039] , ;

[0040] Therefore:

[0041] ;

[0042] Wherein, R is the resistance value selected when the range is switched; the value of R can be R9 (1GΩ), R10 (100MΩ), R11 (10MΩ), R12 (1MΩ); according to the above calculation formula, the setting voltage and the resistance value when the range is switched are determined according to the required output current size;

[0043] When the single-chip microcomputer GPIO output pin 4 is high, the relay RLY1 is attracted, , At this time, the output current direction is negative; the output of negative current can be used for the calibration of part of the measuring equipment, such as FPD detector;

[0044] When the single-chip microcomputer GPIO output pin 4 is low, the relay RLY1 is disconnected, , At this time, the output current direction is positive; the output of positive current can be used for the calibration of part of the measuring equipment, such as FID detector;

[0045] When the required output current is +10pA, V7=10mV, R=1GΩ, the single-chip microcomputer GPIO output pin 5 is high, the relay RLY2 is attracted, and the output current is +10pA.

[0046] When the required output current is -2uA, V7=2V, R=1MΩ, the single-chip microcomputer GPIO output pin 1 is high, the relay RLY1 is attracted, the single-chip microcomputer GPIO pin 8 is high, the relay RLY5 is attracted, and the output current is -2uA.

[0047] The above only describes the preferred embodiments of the present application, which are only illustrative but not restrictive. Those skilled in the art understand that many changes, modifications and even equivalents can be made to the present application within the spirit and scope defined by the claims of the present application, and all shall fall within the protection scope of the present application.

Claims

1. A weak current source circuit with positive and negative outputs, characterized in that, The system includes a digital-to-analog converter (DAC), a first-order active filter, a positive / negative voltage switching module, a proportional amplifier, a range switching module, and a follower module. The DAC converts discrete digital signals into voltage signals. The DAC is connected to the first-order active filter, which filters out interference frequency components. The positive / negative voltage switching module switches between positive and negative voltages and outputs them. The positive / negative voltage switching module is connected to the proportional amplifier, which amplifies the input voltage signal by a set fixed ratio. The proportional amplifier is connected to the range switching module, which outputs different currents. The range switching module is connected to the follower module, which provides negative feedback to ensure that the output voltage accurately follows changes in the load current.

2. The weak current source circuit with positive and negative outputs as described in claim 1, characterized in that, The digital-to-analog converter module includes a digital-to-analog converter U1, a microcontroller GPIO output pin 1, a microcontroller GPIO output pin 2, and a microcontroller GPIO output pin 3. The three input control pins of the digital-to-analog converter U1 are respectively connected to the microcontroller GPIO output pin 1, the microcontroller GPIO output pin 2, and the microcontroller GPIO output pin 3.

3. The weak current source circuit with positive and negative outputs as described in claim 1, characterized in that, The first-order active filter module includes a resistor R1, a capacitor C1, and an operational amplifier U2. The output pin of the digital-to-analog converter U1 is connected to one end of the resistor R1, and the other end of the resistor R1 is connected to the non-inverting input of the operational amplifier U2 and the capacitor C1. The other end of the capacitor C1 is grounded.

4. The weak current source circuit with positive and negative outputs as described in claim 1, characterized in that, The positive and negative voltage switching module includes resistors R2, R3, and R4, a digital transistor Q1, a relay RLY1, and an operational amplifier U3. The output terminal of the operational amplifier U2 is connected to one end of resistors R2 and R3, respectively. The other end of resistor R2 is connected to the inverting terminal of the operational amplifier U3. The other end of resistor R3 is connected to the non-inverting terminal of the operational amplifier U3 and the contact of the relay RLY1, respectively. The coil terminal of the relay RLY1 is connected to one end of the digital transistor Q1. The control pin of the digital transistor Q1 is connected to the GPIO output pin 4 of the microcontroller. Resistor R4 is connected between the output terminal and the inverting terminal of the operational amplifier U3. The output voltage of the operational amplifier U3 is V2.

5. A weak current source circuit with positive and negative outputs as described in claim 1, characterized in that, The proportional amplifier module includes an operational amplifier U4, resistors R5, R7, and R8. One end of resistor R5 is connected to the output terminal of operational amplifier U3, and the other end of resistor R5 is connected to the non-inverting terminal of operational amplifier U4. Resistor R8 is connected between the output terminal and the inverting terminal of operational amplifier U4. The inverting terminal of operational amplifier U4 is connected to one end of resistor R7, and the other end of resistor R7 is grounded.

6. The weak current source circuit with positive and negative outputs as described in claim 5, characterized in that, The range switching module includes digital transistors Q2, Q3, Q4, and Q5, relays RLY2, RLY3, RLY4, and RLY5, resistors R9, R10, R11, and R12. The output terminal of the operational amplifier U4 is connected to one end of the contacts of relays RLY2, RLY3, RLY4, and RLY5, respectively. The other end of the contacts of relays RLY2, RLY3, RLY4, and RLY5 is connected to resistors R9, R10, R11, and R12, respectively. The other end of resistors R9, R10, R11, and R12 is connected to the non-inverting terminal of operational amplifier U5 and one end of resistor RL1. The other end of resistor RL1 is grounded. The relays RLY2, RLY3, RLY4, and RLY5 are connected to one end of digital transistors Q2, Q3, Q4, and Q5 respectively. The control terminals of digital transistors Q2, Q3, Q4, and Q5 are connected to the GPIO output pins 5, 6, 7, and 8 of the microcontroller respectively. The other end of each digital transistor is grounded.

7. A weak current source circuit with positive and negative outputs as described in claim 1, characterized in that, The follower module includes an operational amplifier U5, the inverting terminal of which is connected to one end of a resistor R6, and the other end of the resistor R6 is connected to the non-inverting terminal of an operational amplifier U4.

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