I / F conversion module scale compensation method

Abstract

The invention discloses an I / F conversion module scale compensation method, which is based on a table look-up method, and comprises the following steps of: adjusting the duty ratio of a feedback pulse (namely a feedback pulse fed back to an analog switch by a quantization module in an I / F conversion module) output by an I / F conversion module, and controlling the feedback pulses with different duty ratios to perform feedback at a set pulse interval; according to the method, the change of the minimum scale of 1ppm is realized, so that accurate compensation of the scale temperature coefficient and the scale symmetry is realized, full-temperature compensation can be realized, the compensation precision is high, any scale temperature change curve can be compensated theoretically, few logic resources are occupied, and the method is easy to realize by an FPGA (Field Programmable Gate Array).

Description

Technical Field

[0001] The invention relates to the technical field of current-frequency conversion of an inertial navigation system, and in particular to a scaling compensation method for an I / F conversion module. Background Art

[0002] Current-to-frequency conversion, commonly referred to as I / F conversion, is a high-precision current detection module that converts current into a frequency signal. It is currently mainly used in the acquisition of quartz flexible accelerometers in inertial navigation systems.

[0003] The core principle of I / F conversion is to use charge balance to achieve detection, such as Figure 1 As shown, the external input current charges and discharges the integration capacitor through the integration circuit. When the charge level reaches a certain threshold, the comparison circuit output is triggered to flip. The analog switch is controlled through the quantization circuit, and the fixed constant current source is controlled to input a fixed charge amount to achieve closed-loop feedback, thereby achieving charge balance in the integration circuit and converting the input current into a pulse number.

[0004] The I / F conversion circuit has the following characteristics:

[0005] 1) The zero bias is small over the entire temperature range and can be ignored in actual measurements;

[0006] 2) High nonlinear index;

[0007] 3) High repeatability of temperature characteristics.

[0008] Based on the above characteristics, the I / F module has good compensability. At present, the I / F modules in the industry will be scaled temperature compensated and scaled symmetry compensated before leaving the factory. There are two commonly used solutions:

[0009] 1) Use LM134H for temperature compensation;

[0010] LM134H is an adjustable current source. The output current is linearly related to the temperature, satisfying formula (1)

[0011] I SET =(227uV / K) / R … (1)

[0012] By adjusting the resistance value of R, the gain between the LM134H output current and temperature can be adjusted, and the LM134H output current can be incorporated into Figure 1 In the positive and negative constant current sources, the relationship between the positive and negative constant current sources and the temperature can be adjusted to achieve compensation for the scale.

[0013] This compensation method is hardware compensation, which has the following advantages and disadvantages:

[0014] Advantages: Directly compensate the constant current source without affecting the signal-to-noise ratio of the output pulse;

[0015] Disadvantages: First, only rough linear compensation can be performed, and the compensation accuracy is low; second, each circuit requires additional components, which increases costs; third, LM134H will bring additional error sources.

[0016] 2) Methods of post-event compensation

[0017] First, test the original pulse and temperature corresponding data, perform quadratic fitting on the test data, and obtain the functional relationship between temperature and pulse. When outputting positive and negative pulses, add pulses to the positive and negative pulse output channels according to the current test temperature to adjust the output data and achieve the purpose of temperature compensation and scale compensation.

[0018] This compensation method is software compensation, which has the following advantages and disadvantages:

[0019] Advantages: First, the compensation cost is low and the compensation range is large, which can achieve the unification of the scale of all modules (for example, unified to 10000); second, the compensation accuracy is high, and the full temperature data can be fitted to achieve higher-precision compensation;

[0020] Disadvantages: Post-compensation will increase the signal-to-noise ratio of the output pulse. The output pulse of the normal IF conversion has a 2-value change in the accumulated value of 1 second, and the pulse fluctuation range is 1 pulse. After compensation using this method, the pulse fluctuation range will be expanded to 3 pulses, and the noise band will be expanded by 3 times. Summary of the invention

[0021] In view of this, the present invention provides an I / F conversion module scale compensation method, which adjusts the duty cycle of the feedback pulse output by the I / F conversion module, controls the feedback pulses with different duty cycles to set the pulse interval for feedback, and achieves a minimum scale adjustment of 1ppm, thereby achieving precise compensation for the scale temperature coefficient and scale symmetry, effectively solving the problems existing in the above-mentioned background technology.

[0022] A method for compensating an I / F conversion module scale, comprising the following steps:

[0023] S1, testing the correspondence between the positive and negative scales corresponding to 80% of the original feedback pulses of the I / F conversion module and the temperature;

[0024] S2, the positive / negative scale corresponding to the test calibration pulse;

[0025] The duty cycle of the calibration pulse is set to 75%;

[0026] S3, obtaining a temperature and compensation coefficient lookup table based on a corresponding curve between the positive / negative scale corresponding to the original feedback pulse and the temperature, and adding the positive / negative scale corresponding to the calibration pulse;

[0027] S4, collecting the current operating temperature of the I / F conversion module, using the temperature and compensation coefficient query table to query the compensation coefficient corresponding to the current operating temperature, and judging whether the number of pulses of the feedback pulse output by the I / F conversion module is equal to the compensation coefficient. If so, the calibration pulse is fed back to its analog switch as the next feedback pulse, and the pulse count is cleared; otherwise, the feedback pulse output by the I / F conversion module continues to count until the number of pulses is equal to the compensation coefficient.

[0028] Preferably, the forward scale of the I / F conversion module refers to the accumulated value of the number of forward feedback pulses corresponding to each 1 mA forward input current within 1 second;

[0029] The negative scale of the I / F conversion module refers to the cumulative value of the number of negative feedback pulses corresponding to each 1mA negative input current within 1 second.

[0030] Preferably, the specific steps of testing the correspondence between the positive / negative scale of the I / F conversion module and the temperature in step S1 are:

[0031] Place the I / F conversion module in an incubator, set the incubator to a temperature cycle program of -40 to 70 degrees, input a positive 1mA standard current, record the 1-second cumulative count value of the positive pulse output by the IF module and the module temperature, and obtain the positive original scale and temperature corresponding data; similarly, change the input to a negative 1mA standard current to obtain the negative original scale and temperature corresponding data.

[0032] Preferably, the specific steps of obtaining the temperature and compensation coefficient lookup table according to the positive / negative scale of the feedback pulse and the positive / negative scale of the calibration pulse in step S3 are:

[0033] When the quantization module of the I / F conversion module feeds back a pulse signal to the analog switch, a calibration pulse is inserted at a set time interval to adjust and compensate the positive / negative scale of the feedback pulse at a certain operating temperature to a desired scale, and a compensation coefficient at the current temperature is calculated based on the positive / negative scale of the feedback pulse and the positive / negative scale of the calibration pulse;

[0034] Traverse the working temperature and repeat the above steps to obtain the compensation coefficient at different temperatures;

[0035] All data are converted into a temperature and compensation coefficient lookup table and stored in the quantization module.

[0036] Preferably, the calculation formula of the compensation coefficient is:

[0037]

[0038] Among them, K 80 The positive / negative scale of the feedback pulse corresponding to an 80% duty cycle pulse, K75 is the positive / negative scale of the calibration pulse corresponding to the 75% duty cycle pulse, K0 is the expected scale after feedback pulse compensation; and n is the compensation coefficient.

[0039] Preferably, the temperature and compensation coefficient lookup table is solidified into the code through the ROM core in the FPGA chip of the quantization module.

[0040] The beneficial effects of the present invention are:

[0041] 1. The present invention is based on a table lookup method. By adjusting the duty cycle of the feedback pulse output by the I / F conversion module (i.e., the feedback pulse fed back by the quantization module in the I / F conversion module to the analog switch), the feedback pulses with different duty cycles are controlled to be fed back at a set time interval, and the scale adjustment of a minimum of 1ppm is achieved, thereby achieving accurate compensation for the scale temperature coefficient and scale symmetry, and can achieve full temperature compensation with high compensation accuracy. In theory, any scale temperature change curve can be compensated, and less logic resources are occupied, which is easy to implement in FPGA.

[0042] 2. The present invention combines the advantages of LM134H and the post-compensation method, while avoiding the disadvantages of the two compensation methods. It is significantly better than the two compensation schemes, does not add additional components, has low cost, and because it adjusts the feedback pulse, it will not affect the output pulse noise band, so the output noise band is small. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0044] Figure 1 This is the circuit principle block diagram of the I / F conversion module.

[0045] Figure 2 Flowchart for FPGA scaling compensation. DETAILED DESCRIPTION

[0046] In order to better understand the technical solution of the present invention, the embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0047] It should be clear that the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] The present application is further described in detail below through specific embodiments and in conjunction with the accompanying drawings.

[0049] The I / F conversion module is a current detection method based on the charge balance principle. In order to accurately measure the input charge in conventional applications, it is necessary to ensure that the positive and negative feedback pulses are of equal width, that is, the duty cycle is fixed. Since the constant current source can ensure that the current I is a fixed value and the on-time T of the feedback pulse is fixed, the amount of charge represented by each pulse is fixed. At this time, the scale is fixed, and when the on-time T of the feedback pulse changes, the scale will also change accordingly. However, the frequency of the feedback pulse is usually 128K~256K, and the resolution of the duty cycle adjustment of the feedback pulse is low. Taking the FPGA master clock 50M as an example, the resolution of the duty cycle adjustment of the 256K feedback pulse is about 0.005. For each minimum resolution change of the feedback pulse, the corresponding scale change is about 5000ppm. This resolution cannot meet the scale adjustment requirements of the I / F conversion module.

[0050] The present invention provides an I / F conversion module scale compensation method, which is mainly based on a table lookup method. By adjusting the duty cycle of a feedback pulse output by the I / F conversion module (i.e., a feedback pulse fed back by a quantization module in the I / F conversion module to an analog switch), feedback pulses with different duty cycles are controlled to be fed back at a set time interval, thereby achieving a minimum scale adjustment of 1ppm, thereby achieving accurate compensation for the scale temperature coefficient and scale symmetry.

[0051] The I / F conversion module described above is a current-frequency conversion circuit in the invention patent with application number 202210665371.1 and invention name as a high-precision low-power current-frequency conversion circuit and conversion method, such as Figure 1 As shown, its constant current source conversion module generates two reference voltages of equal magnitude and opposite polarity, and uses the two reference voltages as a positive reference constant current source and a negative reference constant current source;

[0052] When the input current is a forward current, the integral current polarity of the integrator is positive. When the integral voltage output by the integrator reaches or exceeds the forward preset voltage, the level of the comparator output is triggered to flip. The quantization module quantizes the level signal output by the comparator and feeds back a forward pulse signal to the analog switch. The analog switch controls the negative reference constant current source output by the constant current source conversion module to discharge the integrator, so that the integral voltage output by the integrator is reduced to below the forward preset voltage.

[0053] When the input current is negative, the integral current polarity of its integrator is negative. When the integral voltage output by the integrator reaches or is lower than the negative preset voltage, the level of the comparator output is triggered to flip. The quantization module quantizes the level signal output by the comparator and feeds back a negative pulse signal to the analog switch. The analog switch controls the positive reference constant current source output by the constant current source conversion module to charge the integrator, so that the integral voltage output by the integrator is reduced to below the negative preset voltage.

[0054] The present invention provides an I / F conversion module scale compensation method, which specifically comprises the following steps:

[0055] S1, testing the correspondence between the positive and negative scales corresponding to 80% of the original feedback pulses of the I / F conversion module and the temperature;

[0056] The forward scale of the I / F conversion module refers to the cumulative value of the number of forward feedback pulses corresponding to each 1mA forward input current within 1 second;

[0057] The negative scale of the I / F conversion module refers to the cumulative value of the number of negative feedback pulses corresponding to each 1mA negative input current within 1 second.

[0058] Specifically, the steps for testing the correspondence between the positive / negative scale of the I / F conversion module and the temperature are as follows:

[0059] Place the I / F conversion module in an incubator, set the incubator to a temperature cycle program of -40 to 70 degrees, input a positive 1mA standard current, record the 1-second cumulative count value of the positive pulse output by the IF module and the module temperature, and obtain the positive original scale and temperature corresponding data; similarly, change the input to a negative 1mA standard current to obtain the negative original scale and temperature corresponding data.

[0060] S2, test the positive / negative scale of the calibration pulse.

[0061] The duty cycle of the calibration pulse is set to 75%.

[0062] S3, obtaining a temperature and compensation coefficient lookup table according to the positive / negative scale of the feedback pulse and the positive / negative scale of the calibration pulse.

[0063] Specifically, the specific steps for obtaining the temperature and compensation coefficient query table are:

[0064] First, when the quantization module of the I / F conversion module feeds back a pulse signal to the analog switch, a calibration pulse is inserted according to a set pulse interval to adjust and compensate the positive / negative scale of the feedback pulse at a certain working temperature to the expected scale, and the compensation coefficient at the current temperature is calculated according to the positive / negative scale of the feedback pulse and the positive / negative scale of the calibration pulse;

[0065] The calculation formula of the compensation coefficient is:

[0066]

[0067] Among them, K 80 The positive / negative scale of the feedback pulse corresponding to an 80% duty cycle pulse, K 75 is the positive / negative scale of the calibration pulse corresponding to the 75% duty cycle pulse, K0 is the expected scale after feedback pulse compensation; n is the compensation coefficient;

[0068] Then, the working temperature is changed and the above steps are repeated to obtain the compensation coefficients at different temperatures;

[0069] Finally, all data are converted into a temperature and compensation coefficient query table and stored in the quantization module. In this embodiment, the Matlab processing program is used to convert the data file containing the temperature and compensation coefficient into a query table recognizable by the FPGA, and then solidified into the code through the ROM core in the FPGA chip of the quantization module.

[0070] S4, collecting the current operating temperature of the I / F conversion module, using the temperature and compensation coefficient query table to query the compensation coefficient corresponding to the current operating temperature, and judging whether the number of pulses of the feedback pulse output by the I / F conversion module is equal to the compensation coefficient. If so, the calibration pulse is fed back to its analog switch as the next feedback pulse, and the pulse count is cleared; otherwise, the feedback pulse output by the I / F conversion module continues to count until the number of pulses is equal to the compensation coefficient.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for compensating an I / F conversion module scale, characterized in that: The specific steps include: S1, testing the correspondence between the positive and negative scales corresponding to 80% of the original feedback pulses of the I / F conversion module and the temperature; The positive and negative scale of the I / F conversion module is the 1-second cumulative value of the corresponding positive and negative feedback pulses when the input is positive or negative 1mA; S2, the positive / negative scale corresponding to the test calibration pulse; The duty cycle of the calibration pulse is set to 75%; S3, obtaining a temperature and compensation coefficient lookup table based on a corresponding curve between the positive / negative scale corresponding to the original feedback pulse and the temperature, and adding the positive / negative scale corresponding to the calibration pulse; S4, collecting the current operating temperature of the I / F conversion module, using the temperature and compensation coefficient query table to query the compensation coefficient corresponding to the current operating temperature, and judging whether the number of pulses of the feedback pulse output by the I / F conversion module is equal to the compensation coefficient, if so, feeding back the calibration pulse as the next feedback pulse to its analog switch, and clearing the pulse count; Otherwise, the feedback pulses output by the I / F conversion module continue to be counted until the number of pulses is equal to the compensation coefficient.

2. The I / F conversion module scale compensation method according to claim 1, characterized in that: The positive scale of the feedback pulse output by the I / F conversion module refers to the cumulative value of the number of positive feedback pulses corresponding to each 1mA positive input current within 1 second; The negative scale of the feedback pulse output by the I / F conversion module refers to the accumulated value of the number of negative feedback pulses corresponding to each 1mA negative input current within 1 second.

3. The I / F conversion module scale compensation method according to claim 2, characterized in that: The specific steps of testing the correspondence between the positive / negative scale of the I / F conversion module and the temperature in step S1 are: Place the I / F conversion module in a temperature box, set the temperature cycle program of -40 to 70 degrees, input a positive 1mA standard current, record the 1-second cumulative count value of the positive pulse output by the I / F conversion module and the module temperature, and obtain the positive original scale and temperature corresponding data; Similarly, the input is modified to a negative 1mA standard current to obtain negative original scale and temperature corresponding data.

4. The I / F conversion module scale compensation method according to claim 1, characterized in that: In step S3, the specific steps of obtaining the temperature and compensation coefficient query table according to the corresponding data of the positive / negative original scale of the feedback pulse and the temperature and the positive / negative scale of the calibration pulse are: When the quantization module of the I / F conversion module feeds back a pulse signal to the analog switch, a calibration pulse is inserted according to a set pulse interval to adjust and compensate the positive / negative scale of the feedback pulse at a certain working temperature to an expected scale, and a compensation coefficient at the current temperature is calculated according to the positive / negative scale of the feedback pulse and the positive / negative scale of the calibration pulse; Traverse the working temperature and repeat the above steps to obtain the compensation coefficient at different temperatures; All data are converted into a temperature and compensation coefficient lookup table and stored in the quantization module.

5. The I / F conversion module scale compensation method according to claim 4, characterized in that: The calculation formula of the compensation coefficient is: Among them, K 80 The positive / negative scale of the feedback pulse corresponding to an 80% duty cycle pulse, K 75 is the positive / negative scale of the calibration pulse corresponding to the 75% duty cycle pulse, K0 is the expected scale after feedback pulse compensation; and n is the compensation coefficient.

6. The I / F conversion module scale compensation method according to claim 4, characterized in that: The temperature and compensation coefficient lookup table is solidified into the code through the ROM core in the FPGA chip of the quantization module.

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