CN202026301U - Self-calibration closed-loop analog-digital (AD) conversion circuit - Google Patents

Abstract

The utility model belongs to an AD conversion circuit, in particular to a self-calibrating closed-loop AD conversion circuit. The analog input signal of the circuit is connected to the negative input terminal of the operational amplifier in the integrator through the electronic switch and resistor R1; the reference source and ground are connected in series to one end of the resistor R1 through the electronic switch, and the other end of the resistor R1 is connected to the negative input terminal of the operational amplifier. The input terminal is connected, the positive input terminal of the operational amplifier is grounded, the negative input terminal of the operational amplifier is connected to one end of the capacitor C1, the other end of C1 is connected to the output terminal of the operational amplifier, and the output terminal of the operational amplifier is connected to one end of the resistor R2 , the other end of the resistor R2 is connected to the 14-bit A/D converter, the constant current source is connected to the negative input end of the integrator through the electronic switch, the other output end of the electronic switch is grounded, and the other end of the A/D converter is connected to the processing The input end of the processor is connected, one control port of the processor is connected with the constant current source, and the other control port of the processor is connected with the output end of the electronic switch. The utility model has the effects of high precision and small error.

Description

A self-calibrating closed-loop AD conversion circuit

technical field

The utility model belongs to an AD conversion circuit, in particular to a self-calibrating closed-loop AD conversion circuit. the

Background technique

The contradiction that exists in the system application of ordinary charge-balanced V/F conversion circuits is: on the one hand, since the circuit accuracy is inversely related to the maximum output frequency, this limits the maximum operating frequency of the circuit. For a certain range of input, it is The maximum scale coefficient is limited; on the other hand, in order to make the system have sufficient dynamic accuracy and ensure that the sampling value in the navigation cycle is large enough when the input signal is small, the circuit scale coefficient should be as large as possible, so that the inertial navigation system is in a small state for a long time. In the acceleration state, sufficient calculation accuracy can also be guaranteed. It is impossible to completely solve this pair of contradictions by using ordinary solutions, and only a compromise solution can be used to find a balance between accuracy and speed. the

The integral output AD conversion circuit is the same as the traditional V/F converter. It is based on the working principle of charge balance, including integrators, current sources, switches, logic circuits and other basic parts. The switch controls the on-off of the current source to achieve integration. The charge on the device is balanced to obtain a quantized value of the input voltage. However, the integral output AD conversion circuit, as a self-calibrating digital output V/F converter, also includes input switch, multi-bit high-speed AD converter, counter, Nios II soft core, serial communication interface and other parts, so as to realize the circuit Self-calibration, counting, output and other functions. the

Contents of the invention

The purpose of the utility model is to provide a self-calibrating closed-loop AD conversion circuit with high calculation precision aiming at the defects of the prior art. the

The utility model is achieved in this way: a self-calibration closed-loop A/D conversion circuit includes a signal input terminal, and the analog input signal is connected with the negative input terminal of the operational amplifier in the integrator through an electronic switch and a resistor R1; the reference source and the ground The electronic switch is connected in series to one end of the resistor R1, the other end of the resistor R1 is connected to the negative input end of the operational amplifier, the positive input end of the operational amplifier is grounded, the negative input end of the operational amplifier is connected to one end of the capacitor C1, and the other end of C1 One end is connected to the output terminal of the operational amplifier, while the output terminal of the operational amplifier is connected to one end of the resistor R2, and the other end of the resistor R2 is connected to the 14-bit A/D converter, and the resistor R1, the resistor R2, and the capacitor C1 form together with the operational amplifier. In the integrator circuit unit, the constant current source is connected to the negative input terminal of the integrator through an electronic switch, the other output terminal of the electronic switch is grounded, the other terminal of the A/D converter is connected to the input terminal of the processor, and one control of the processor The port is connected with the constant current source, another control port of the processor is connected with the output end of the electronic switch, the clock is connected with the clock port of the processor, and the processor outputs converted digital signals. the

A self-calibrating closed-loop A/D conversion circuit as described above, wherein the processor is an EP2C8T144 chip. the

A self-calibrating closed-loop A/D conversion circuit as described above, wherein the electronic switch is a single-pole double-throw switch. the

A self-calibrating closed-loop A/D conversion circuit as described above, wherein the electronic switch is a single-pole double-throw switch. the

The effect of the utility model is: a larger scale coefficient can be obtained, the measurement accuracy of the accelerometer is improved, the feedback control speed is lower, the circuit accuracy is improved, and the measurement error is reduced by using AD to measure the residual charge. Using the work/calibration mode, the input of each digitizer can be multiplexed among the accelerometer input, precision voltage reference source, and ground, which provides a guarantee for high precision, miniaturization, and low cost of the circuit . There is no need to connect a reversible counter, and the direct digital interface can be output flexibly. the

Description of drawings

FIG. 1 is a schematic diagram of the circuit structure of the calibration closed-loop AD conversion circuit provided by the present invention. the

In the figure: 1. Input signal, 2. Electronic switch, 3. Reference source and ground, 4. Electronic switch, 5. Constant current source, 6. Integrator, 7. A/D converter, 8. Processor, 9 . Clock, 10. Output signal. the

Detailed ways

As shown in accompanying drawing 1, a kind of self-calibration closed-loop A/D conversion circuit comprises a signal input terminal, and an analog input signal 1 is connected with the negative input terminal of the operational amplifier in the integrator 6 through an electronic switch 2 and a resistor R1; and the ground 3 are connected in series to one end of the resistor R1 through the electronic switch 2, the other end of the resistor R1 is connected to the negative input terminal of the operational amplifier, and the positive input terminal of the operational amplifier is grounded. Electronic switch 2 can be considered as a single pole double throw switch. The negative input end of the operational amplifier is connected to one end of the capacitor C1, the other end of C1 is connected to the output end of the operational amplifier, and the output end of the operational amplifier is connected to one end of the resistor R2. The other end of the resistor R2 is connected to the 14-bit A/D converter 7 . Resistor R1, resistor R2, capacitor C1 and the operational amplifier together form an integrator circuit unit. The constant current source 5 is connected to the negative input terminal of the integrator 6 through the electronic switch 4 . The other output end of electronic switch 4 is grounded, and electronic switch 4 can be considered as a single-pole double-throw switch. The other end of the A/D converter 7 is connected to the input end of the processor 8. In this example, the processor 8 selects the EP2C8T144 chip. One control port (FB0) of the processor 8 is connected with the constant current source 5, and the other control port (S0) of the processor 8 is connected with the output end of the electronic switch 2. The clock 9 is connected to the clock port of the processor 8 . Processor 8 outputs the converted digital signal. the

The working principle and working process of this circuit are: the input signal 1 passes through the electronic switch 2, enters the integrator 6 for integration, the output voltage is sent to the A/D converter 7, and the A/D converter 7 performs A/D conversion at regular intervals, processing The converter 8 judges the conversion result. Once the output voltage of the integrator 6 exceeds the set value, the processor 8 starts the electronic switch 4 of the balance circuit to turn on, releasing an equivalent charge, and at the same time, the output accumulator inside the processor 8 increases the rated value , so that the loop is always in a balanced state, and the output accumulator inside the processor is constantly accumulating, and the sum of the accumulated value multiplied by the weight and the current A/D converter value is the digital value of the input signal 1 within the sampling period of the new circuit , that is, the output signal 10. The clock signal enters into the processor 8 to form the sampling time, and the value is taken away regularly to output the signal 10, and the processor 8 clears the output accumulator to be zero at the same time to prepare for the next accumulation. Theoretically, due to the action of the integrator, there is no loss of charge, that is, no cumulative error. If the A/D converter in Figure 1 degenerates into a one-bit converter that is a comparator, and the A/D conversion and digital processing time are negligible, the circuit degenerates into a commonly used V/F conversion circuit at present. the

The circuit has two operating states, one is working mode and the other is calibration mode. the

In working mode, the input signal 1 is connected to the integrator 6 via the electronic switch 2 . The output of the integrator 6 is sampled and converted by the A/D converter 7 . When the output of the integrator 6 reaches the predetermined value, the processor 8 starts to execute rebalancing control with appropriate polarity, and then the software starts to read the remaining quantity of the integrator 6, and integrates the remaining quantity with the number of pulses used for rebalancing , the output digital quantity 10 is proportional to the input signal 1, realizing the function of A/D conversion. the

In the calibration mode, the input terminal of the integrator 6 is grounded through the electronic switch 2, and the A/D converter 7 works outside the specified voltage range to determine the channel error. The input of integrator 6 is then connected to reference source 3 and an additional conversion is performed to determine the ratio of the channels. When the asymmetry calibration is performed, a negative polarity rebalance control process is started, and a positive polarity rebalance control process is immediately performed, followed by AD conversion at the output terminal of the integrator 6 . After a calibration cycle is completed, the processor 8 stores the error constant of the integrator, switches the input terminal of the integrator 6 to the port of the input signal 1 through the electronic switch 2, and after a calibration cycle is completed, the processor 8 stores the error constant of the integrator 6 Constant, switch the input terminal of integrator 6 to the port of input signal 1 through electronic switch 2, and then calibrate the next channel. the

Claims (4)

1. A self-calibration closed-loop A/D conversion circuit is characterized in that: comprise signal input terminal, analog input signal (1) is by the negative input of the operational amplifier in electronic switch (2) and resistance R1 and integrator (6) The reference source and the ground (3) are connected in series to one end of the resistor R1 through the electronic switch (2), the other end of the resistor R1 is connected to the negative input terminal of the operational amplifier, the positive input terminal of the operational amplifier is grounded, and the negative input terminal of the operational amplifier One end of the capacitor C1 is connected to the input end, the other end of C1 is connected to the output end of the operational amplifier, and the output end of the operational amplifier is connected to one end of the resistor R2, and the other end of the resistor R2 is connected to the 14-bit A/D converter ( 7), the resistor R1, the resistor R2, the capacitor C1 and the operational amplifier together constitute an integrator circuit unit, the constant current source (5) is connected to the negative input terminal of the integrator (6) through the electronic switch (4), and the electronic switch (4) The other output end of the A/D converter (7) is connected to the input end of the processor (8), and a control port of the processor (8) is connected to the constant current source (5), and the processor ( The other control port of 8) is connected to the output end of the electronic switch (2), the clock (9) is connected to the clock port of the processor (8), and the processor (8) outputs the converted digital signal. 2. A kind of self-calibration closed-loop A/D conversion circuit as claimed in claim 1, characterized in that: the processor (8) is an EP2C8T144 chip. 3. A self-calibrating closed-loop A/D conversion circuit as claimed in claim 2, characterized in that: the electronic switch (2) is a single-pole double-throw switch. 4. A self-calibrating closed-loop A/D conversion circuit as claimed in claim 3, characterized in that: the electronic switch (4) is a single-pole double-throw switch. the