I / F circuit linearity calibration method and verification method

Abstract

The invention relates to the field of I / F circuit testing, in particular to an I / F circuit linearity calibration method and verification method. The calibration method comprises the following steps: S1, carrying out current scanning on a tested I / F circuit, measuring pulse values Ni of the I / F circuit under different input current values Ii, dividing each pulse value Ni by a scale factor to obtain a pulse proportion value pi, carrying out second-order curve fitting on n pulse proportion values p1, p2,... pn and corresponding input current values I1, I2,... In, and carrying out second-order curve fitting on the n pulse proportion values p1, p2,... pn to obtain a first-order curve; solving a constant term coefficient a0, a monomial coefficient a1 and a quadratic term coefficient a2 of the second-order fitting curve; s2, calculating an I / F circuit pulse proportionality coefficient pj of the I / F circuit working under the current input current Ij through second-order curve fitting coefficients a0, a1 and a2; and S3, the compensated I / F circuit pulse calibration value Nj '= Nj / pj. The verification method comprises the following steps: F1, calculating a pulse value array of the tested I / F circuit after compensation under different excitation current values; f2, calculating the linearity of the compensated I / F circuit; and F3, calculating the calibrated nonlinearity error KD of the I / F circuit.

Description

Technical Field

[0001] The invention relates to the field of I / F circuit testing of an accelerometer in an inertial navigation system, and in particular to an I / F circuit linearity calibration method and a verification method. Background Art

[0002] The linearity of the I / F circuit in the accelerometer is one of the important factors affecting the dynamic performance of the inertial navigation product. Currently, the linearity test of the I / F circuit of the inertial navigation product is mostly based on the constant current provided by the multi-function calibrator.

[0003] The I / F circuit is a charge balance circuit using some separated components. Based on the charge balance, the current / frequency conversion is realized through the current integrator. When the current is input, the output voltage waveform of the integrator is a sawtooth wave. When the amplitude of the sawtooth wave reaches the set threshold voltage, the signal acquisition circuit controls the switch to turn on the integrator, so that the reverse constant current source current and the input current enter the integrator together for discharge. After the discharge is completed, the signal acquisition circuit controls the switch tube to connect to the ground terminal, and the constant current source current is bypassed. This reciprocates to control the integrator to charge and discharge and maintain charge balance.

[0004] The debugging method of the existing charge balance I / F circuit is to use a multi-function calibrator to output a standard constant current excitation to the input current terminal. The current passes through the integrator to the acquisition and processing circuit to obtain a digital pulse result. According to the project requirements, the parameters of the I / F circuit are debugged so that the digital pulse under the standard constant current excitation meets the project requirements. In general, the scale factor of the I / F circuit is 8000. When debugging, the standard constant current excitation is selected as 1mA. Under the action of this constant current excitation, the I / F circuit is debugged. When the debugging is completed, the pulse output corresponding to the I / F circuit is 8000.

[0005] Ideally, the output pulse value of the I / F conversion circuit is linearly related to the excitation current value. However, under high current excitation, important components of the I / F circuit, such as switches and triodes, generate leakage current due to high-speed disconnection. At the same time, the temperature of the precision resistor increases and the resistance value changes, which will also affect the discharge current. Changing currents such as leakage current and discharge current pass through the integrator to the acquisition and processing circuit, affecting the digital pulse results, causing the pulse value under high current excitation to change, and ultimately affecting the linearity results within the full range. Summary of the invention

[0006] Aiming at the problem that the pulse value under large current excitation in an I / F circuit changes and affects the linearity result within the full range, the present invention provides an I / F circuit linearity calibration method and verification method.

[0007] A method for calibrating linearity of an I / F circuit, characterized in that it comprises the following steps:

[0008] S1: Calculate the coefficient of the second-order fitting curve of the I / F circuit under test: Perform a current scan on the I / F circuit under test and measure the I / F circuit at different input current values ​​I i The pulse value N i , where I i is the i-th input value of the I / F circuit under test, i=1, 2, ..., n, n≥6, N i For the I / F circuit under test, i Input the pulse measurement value obtained below, and convert each pulse value N i Divide by the scale factor to get the pulse ratio value p i , the input current value I i As the x-coordinate, the pulse ratio value p i As the y coordinate, for n pulse ratio values ​​p 1 , p 2 , ...p n , and the corresponding input current value I 1 , I 2 ,..I n Perform second-order curve fitting and find the constant term coefficient a of the second-order fitting curve 0 , linear coefficient a 1 and the quadratic coefficient a 2 ;

[0009] S2: Calculate the current input current I j The I / F circuit pulse ratio coefficient p under j : Through the second-order curve fitting coefficient a 0 、a 1 、a 2 Calculate the I / F circuit working at the current input current I j The I / F circuit pulse ratio coefficient p under j ;

[0010] S3: Use pulse proportional coefficient p j Compensation: I / F circuit pulse calibration value N after compensation j ′=N j / p j , where N j is the current input current I j Raw measurement value of the I / F circuit pulse under.

[0011] When performing step S1, the second-order curve fitting is used to obtain the following equation (1): 0 , linear coefficient a 1 and the quadratic coefficient a 2 :

[0012] p(x)=a 2 × 2 +a 1 × 1 +a 0 × 0 (1)

[0013] In the above formula (1),

[0014] x——Each input current value I i ,

[0015] p(x)——The pulse proportional value of each pulse obtained by dividing the pulse value corresponding to each input current value by the scale factor.

[0016] When performing step S2, the excitation current value I to be compensated is calculated by formula (2) under ideal conditions. j The pulse proportional coefficient p under j , formula (2) is as follows:

[0017] p j =a 2 ×j 2 +a 1 ×j 1 +a 0 ×j 0 (2)

[0018] In the above formula (2),

[0019] j——excitation current value to be compensated I j ,

[0020] p j ——Pulse proportional coefficient.

[0021] When performing step S3, the pulse proportionality factor p is used. j The measured pulse value N j Compensation is performed, and the calculation is shown in formula (3):

[0022] N j ′=N j / p j (3)

[0023] In the above formula (3),

[0024] N j ′——I / F circuit pulse calibration value after compensation,

[0025] N j ——Current input current I j The raw measured value of the I / F circuit pulse under

[0026] pj ——Pulse proportional coefficient.

[0027] A method for verifying the linearity of an I / F circuit based on the above-mentioned I / F circuit linearity calibration method comprises the following steps:

[0028] F1: Calculate the I / F of the I / F circuit under different excitation current values ​​according to equations (1) to (3). 1 ,I 2 ,...,I n The compensated pulse value is obtained by formula (4) to obtain the compensated pulse value array N(I 1 )′,N(I 2 )′,...,N(I n )′, where N(I n )′ is as follows:

[0029]

[0030] In the above formula (4),

[0031] n——represents the total number of current scanning points within the total range for current scanning of the I / F circuit under test.

[0032] N(I n )——At the excitation current value I n The original pulse value measured below;

[0033] N(I n )'——at the excitation current value I n Get the compensated pulse value;

[0034] F2: Calculate the linearity of the I / F circuit after compensation. First, the current value I under different excitation current values ​​is 1 ,I 2 ,...,I n As x-axis data, the compensated pulse value N(I 1 )′,N(I 2 )′,...,N(I n )′ as the y-axis data, perform linear fitting on it, obtain the slope k and intercept b of the fitting line, and obtain the fitting line pulse value N(I n )″;

[0035]

[0036] In the above formula (5),

[0037] k, b——linear fitting coefficients, slope k and intercept b,

[0038] N(I n )″——at the excitation current value I n The fitted straight line pulse value under .

[0039] F3: Calculate the nonlinearity error K of the I / F circuit after calibration D , as shown in formula (6):

[0040]

[0041] The present invention has the following beneficial effects:

[0042] The I / F circuit linearity calibration method of the present invention calculates the second-order fitting curve coefficient of the I / F circuit under test and calculates the current input current I j The I / F circuit pulse ratio coefficient p under j , use pulse proportional coefficient p j The three steps of compensation are performed to make the input-output relationship of the I / F circuit as close to linear as possible. Even if the semiconductor components have leakage current or the precision resistors change in resistance, etc., which causes the output to deviate from linearity, the compensation method of the present invention can make the compensated input-output relationship return to linearity, thereby achieving the purpose of reducing the I / F circuit linearity test error and improving the test accuracy. The I / F circuit linearity verification method of the present invention has the corresponding technical features of the I / F circuit linearity calibration method, and therefore has the corresponding technical effects, which will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a flow chart of a preferred embodiment of the I / F circuit linearity calibration method of the present invention.

[0044] Figure 2 It is a flow chart of a preferred embodiment of the I / F circuit linearity verification method of the present invention.

[0045] Figure 3 1 is a schematic diagram of the I / F circuit x channel fitting residual before linearity calibration compensation in the experimental verification embodiment.

[0046] Figure 4 It is a schematic diagram of the fitting residual of the y channel of the I / F circuit before linearity calibration compensation in the experimental verification embodiment.

[0047] Figure 5 Schematic diagram of the z-channel fitting residual of the I / F circuit before linearity calibration compensation in the experimental verification embodiment.

[0048] Figure 6 1 is a schematic diagram of the I / F circuit x channel fitting residual after linearity calibration compensation in the experimental verification embodiment.

[0049] Figure 7It is a schematic diagram of the y-channel fitting residual of the I / F circuit after linearity calibration compensation in the experimental verification embodiment.

[0050] Figure 8 Schematic diagram of the z-channel fitting residual of the I / F circuit before linearity calibration compensation in the experimental verification embodiment. DETAILED DESCRIPTION

[0051] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0052] Preferred embodiment of I / F circuit linearity calibration method:

[0053] A method for calibrating linearity of an I / F circuit, characterized in that it comprises the following steps:

[0054] S1: Calculate the coefficient of the second-order fitting curve of the I / F circuit under test: Perform a current scan on the I / F circuit under test and measure the I / F circuit at different input current values ​​I i The pulse value N i , where I i is the i-th input value of the I / F circuit under test, i=1, 2, ..., n, n≥6, N i For the I / F circuit under test, i Input the pulse measurement value obtained below, and convert each pulse value N i Divide by the scale factor to get the pulse ratio value p i , the input current value I i As the x-coordinate, the pulse ratio value p i As the y coordinate, for n pulse ratio values ​​p 1 , p 2 , ...p n , and the corresponding input current value I 1 , I 2 ,..I n Perform second-order curve fitting and find the constant term coefficient a of the second-order fitting curve 0 , linear coefficient a 1 and the quadratic coefficient a 2 ;

[0055] S2: Calculate the current input current I j The I / F circuit pulse ratio coefficient p under j : Through the second-order curve fitting coefficient a 0 、a 1 、a 2 Calculate the I / F circuit working at the current input current I j The I / F circuit pulse ratio coefficient p under j ;

[0056] S3: Use pulse proportional coefficient pj Compensation: I / F circuit pulse calibration value N after compensation j ′=N j / p j , where N j is the current input current I j Raw measurement value of the I / F circuit pulse under.

[0057] When performing step S1, the second-order curve fitting is used to obtain the following equation (1): 0 , linear coefficient a 1 and the quadratic coefficient a 2 :

[0058] p(x)=a 2 × 2 +a 1 × 1 +a 0 × 0 (1)

[0059] In the above formula (1),

[0060] x——Each input current value I i ,

[0061] p(x)——The pulse proportional value of each pulse obtained by dividing the pulse value corresponding to each input current value by the scale factor.

[0062] When performing step S2, the excitation current value I to be compensated is calculated by formula (2) under ideal conditions. j The pulse proportional coefficient p under j , formula (2) is as follows:

[0063] p j =a 2 ×j 2 +a 1 ×j 1 +a 0 ×j 0 (2)

[0064] In the above formula (2),

[0065] j——excitation current value to be compensated I j ,

[0066] p j ——Pulse proportional coefficient.

[0067] When performing step S3, the pulse proportionality factor p is used. j The measured pulse value N j Compensation is performed, and the calculation is shown in formula (3):

[0068] N j ′=N j / p j (3)

[0069] In the above formula (3),

[0070] N j ′——I / F circuit pulse calibration value after compensation,

[0071] N j ——Current input current I j The raw measured value of the I / F circuit pulse under

[0072] p j ——Pulse proportional coefficient.

[0073] The I / F circuit linearity calibration method of the present invention is used to calculate the second-order fitting curve coefficient of the I / F circuit under test and calculate the current input current I j The I / F circuit pulse ratio coefficient p under j , use pulse proportional coefficient p j The three steps of compensation are performed to make the input-output relationship of the I / F circuit as close to linear as possible. Even if the semiconductor components have leakage current or the precision resistors change in resistance, causing the output to deviate from linearity, the compensation method of the present invention can make the compensated input-output relationship return to linearity, thereby achieving the purpose of reducing the I / F circuit linearity test error and improving the test accuracy.

[0074] Preferred embodiment of I / F circuit linearity verification method:

[0075] A method for verifying the linearity of an I / F circuit based on the above-mentioned I / F circuit linearity calibration method comprises the following steps:

[0076] F1: Calculate the I / F of the I / F circuit under different excitation current values ​​according to equations (1) to (3). 1 ,I 2 ,...,I n The compensated pulse value is obtained by formula (4) to obtain the compensated pulse value array N(I 1 )′,N(I 2 )′,...,N(I n )′, where N(I n )′ is as follows:

[0077]

[0078] In the above formula (4),

[0079] n——represents the total number of current scanning points within the total range for current scanning of the I / F circuit under test.

[0080] N(I n )——At the excitation current value I n The original pulse value measured below;

[0081] N(I n )'——at the excitation current value I n Get the compensated pulse value;

[0082] F2: Calculate the linearity of the I / F circuit after compensation. First, the current value I under different excitation current values ​​is 1 ,I 2 ,...,I n As x-axis data, the compensated pulse value N(I 1 )′,N(I 2 )′,...,N(I n )′ as the y-axis data, perform linear fitting on it, obtain the slope k and intercept b of the fitting line, and obtain the fitting line pulse value N(I n )″;

[0083]

[0084] In the above formula (5),

[0085] k, b——linear fitting coefficients, slope k and intercept b,

[0086] N(I nn )″——at the excitation current value I j The fitted straight line pulse value under .

[0087] F3: Calculate the nonlinearity error K of the I / F circuit after calibration D , as shown in formula (6):

[0088]

[0089] Experimental verification example:

[0090] An I / F circuit in a random laboratory is experimentally verified according to the I / F circuit linearity calibration method and verification method of the present invention:

[0091] The fitting residuals of the I / F circuit x, y, and z channels before linearity calibration compensation are as follows: Figures 3 to 5 As shown;

[0092] After linearity calibration compensation, the fitting residuals of the I / F circuit x, y, and z channels are as follows: Figures 6 to 8 As shown;

[0093] The comparison of linearity results within the measuring range before and after linearity calibration compensation is shown in the following table:

[0094] I / F circuit test channel x y z Linearity before compensation 4.21763105132944e-06 6.11038906476238e-06 -4.74334894483124e-06 Linearity after compensation 1.91450782158195e-06 1.84692922403505e-06 -1.30729319191105e-06

[0095] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for calibrating the linearity of an I / F circuit, characterized in that: The following steps are involved: S1: Calculate the coefficient of the second-order fitting curve of the I / F circuit under test: Perform a current scan on the I / F circuit under test and measure the I / F circuit at different input current values ​​I i The pulse value N i , where I i is the i-th input value of the I / F circuit under test, i=1, 2, ..., n, n≥6, N i For the I / F circuit under test, i Input the pulse measurement value obtained below, and convert each pulse value N i Divide by the scale factor to get the pulse ratio value p i , the input current value I i As the x-coordinate, the pulse ratio value p i As the y coordinate, for n pulse ratio values ​​p1, p2, ... p n , and the corresponding input current values ​​I1, I2, ..I n Perform second-order curve fitting to obtain the constant term coefficient a0, the first-order term coefficient a1 and the second-order term coefficient a2 of the second-order fitting curve; S2: Calculate the current input current I j The I / F circuit pulse ratio coefficient p under j :The I / F circuit works at the current input current I calculated by the second-order curve fitting coefficients a0, a1, and a2. j The I / F circuit pulse ratio coefficient p under j ; S3: Use pulse proportional coefficient p j Compensation: I / F circuit pulse calibration value N after compensation j ′=N j / p j , where N j is the current input current I j Raw measurement value of the I / F circuit pulse under.

2. The I / F circuit linearity calibration method according to claim 1, characterized in that: When performing step S1, the second-order curve fitting is performed to obtain the following formula (1), and the constant term coefficient a0, the first-order term coefficient a1 and the second-order term coefficient a2 of the second-order fitting curve are obtained: p(x)=a2×x 2 +a1×x 1 +a0×x 0 (1) In the above formula (1), X——Each input current value I i , p(x)——The pulse proportional value of each pulse obtained by dividing the pulse value corresponding to each input current value by the scale factor.

3. The I / F circuit linearity calibration method according to claim 2, characterized in that: When performing step S2, the excitation current value I to be compensated is calculated by formula (2) under ideal conditions. j The pulse proportional coefficient p under j , formula (2) is as follows: p i =a2×j 2 +a1×j 1 +a0×j 0 (2) In the above formula (2), j——excitation current value to be compensated I j , p j ——Pulse proportional coefficient.

4. The I / F circuit linearity calibration method according to claim 3, characterized in that: When performing step S3, the pulse proportionality factor p is used. j The measured pulse value N is compensated, and the calculation is shown in formula (3): N j ′=N j / p j (3) In the above formula (3), N j ′——I / F circuit pulse calibration value after compensation, N j ——Current input current I j The raw measured value of the I / F circuit pulse under p j ——Pulse proportional coefficient.

5. A method for verifying the linearity of an I / F circuit based on the method for calibrating the linearity of an I / F circuit according to any one of claims 1 to 4, characterized in that: The following steps are involved: F1: Calculate I1, I2, ..., I2 of the I / F circuit under test at different excitation current values ​​according to equations (1) to (3). n The compensated pulse value is obtained by formula (4) to obtain the compensated pulse value array N(I1)′, N(I2)′, ..., N(I n )′, where N(I n )′ is as follows: In the above formula (4), n——represents the total number of current scanning points within the total range for current scanning of the I / F circuit under test. N(I n )——At the excitation current value I n The original pulse value measured below; N(I n )′——at the excitation current value I n Get the compensated pulse value; F2: Calculate the linearity of the I / F circuit after compensation. First, the current values ​​I1, I2, ..., I n As x-axis data, the compensated pulse values ​​N(I1)′, N(I2)′, ..., N(I n )′ as the y-axis data, perform linear fitting on it, obtain the slope k and intercept b of the fitting line, and obtain the fitting line pulse value N(I n )″; In the above formula (5), k, b——linear fitting coefficients, slope k and intercept b; N(I n )″——at the excitation current value I n The fitted straight line pulse value under F3: Calculate the nonlinearity error K of the I / F circuit after calibration D , as shown in formula (6):

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