RU2741075C1 - Tracking sine-cosine angle-to-code converter with built-in digital conversion error correction - Google Patents

Abstract

FIELD: measurement.SUBSTANCE: invention relates to measurement equipment and automatic control equipment. Converter includes two multipliers for multiplication of voltages of input sine-cosine signal with digital codes of cosine and sine values of output code of angle, subtractor of signals of multipliers, counting pulses generator, which generates counting pulses from error signal, reversible counter of the output angle code, the counting direction of which depends on pulses from the generator, unit for generating digital values of sine and cosine, outputs of which are connected to inputs of the first and second multipliers, outputs of unit for generating digital values of sine and cosine are connected to inputs of sine and cosine of correction unit. Correction unit corrects bias voltage, amplitude imbalance and phase shift of sine-cosine signal. Outputs of correction unit are connected to inputs of sine and cosine of CORDIC unit operating in vector mode, output of which is output code of converter angle.EFFECT: technical result consists in improvement of accuracy of conversion of sine-cosine signal to angle code while providing high speed of conversion, characteristic for tracking systems.1 cl, 3 dwg, 1 tbl

Description

The technical solution relates to measuring technology and automatic control technology, in particular, to tracking sine-cosine angle-to-code converters, and can be used in systems where it is required to measure position using a sensor that generates a sine-cosine signal, the phase of which is proportional to the measured angle. The invention is expediently used in the design of specialized integrated circuits for high-speed position sensors based on tracking angle-code converters.

A known method of digital conversion of an angle into a code with a conversion error correction [1] is based on the fact that the values of the output code are formed by summing the output code of the main channel of the amplitude digital conversion of the tracking angle and the output code of the correcting channel, while the corresponding values of the output code of the correcting channel are formed when rotation of the rotor of the angle sensor of the main conversion channel with a constant angular velocity equal to half its maximum operating value, by analog-digital conversion of the tachometric signal of the main conversion channel, integrating the variable component of the converted tachometric signal and registering the integrated signal. The disadvantage of this technical solution is the requirement for an additional channel to correct the angle code.

There is a method of digital conversion of an angle into a code with a conversion error correction [2] based on the fact that two conversion channels (two sensors) with different spectra of spatial error are used to correct the conversion error. Differences of the first and second angle codes are calculated, according to which the amplitudes and phases of the spatial harmonics of the error of the first sensor are determined, the first correction is formed as the sum of the spatial harmonics of the error of the first sensor for the angle corresponding to the first angle code, the output code is generated by adding the first correction to the first angle code. The disadvantage of this solution is that to correct the conversion error, two sensors with different error spectra are required, which, if implemented at the level of an integral position sensor with an integrated sensor system, is technically impossible.

A known method of digital correction of the conversion error for sine-cosine converters angle-code [3] includes two ADCs that convert analog sine and cosine signals into a digital code, from the outputs of the ADC signals are fed to the input of the offset correction unit, amplitude and phase imbalance, from the output of the correction unit the signals go to the detector of displacement imbalance, gain and phase imbalance, signals proportional to the corresponding imbalances are sent from the detector output to the input of the correction unit. The corrected signal after the imbalance correction is fed to the harmonic distortion correction unit and then to the angle-code converter. The disadvantage of the proposed solution is the limited speed of the system due to the use of separate discrete ADCs, which usually have a relatively low speed for angle-code converters.

Known converter angle-code [4] is implemented in the chip for processing signals from sine-cosine position sensors. In the processing path of this microcircuit, a direct algorithm for correcting the sine-cosine signal is implemented, including the correction of the offset (including the temperature sensor), amplitude imbalance and phase shift. The corrected signal is fed to the angle-code converter. The described design is applicable for converters with independent conversion of a sine-cosine signal on discrete ADCs and, like [3], has a limited performance.

Known high-speed tracking converter sine-cosine signal in the position code, selected as a prototype [5]. The converter is built according to a servo circuit and contains two multipliers of input signals, a subtractor, a comparator and a voltage-controlled generator (VCO), which generates signals for incrementing and decrementing a reversing counter based on the difference signal of the subtractor. The upcounter code is the output code of the converter. A feature of the converter is that the sine and cosine values are not selected from the sine and cosine tables according to the counter code, but are calculated by the CORDIC calculator block, which generates the sine and cosine value codes fed to the input of the cosine and sine signal multipliers, respectively, which makes it possible to reduce the amount of ROM, but at the same time reduces the speed of the converter. The disadvantage of this solution is the lack of correction of the conversion error of the sine-cosine signal, which is always present in real systems and leads to an error in measuring the angle.

Known tracking sine-cosine angle converter in position code [6] differs from [5] in that as a block for generating digital values of sine and cosine uses a tabular formation method with a shortened table and interpolation of intermediate values by the least significant bits of the counter.

The task of the technical solution is to improve the accuracy of converting a sine-cosine signal into an angle code while ensuring a high conversion speed.

The problem is solved due to the fact that in the structure of the tracking converter containing the first multiplier for multiplying the input voltage of the sine signal by the digital value of the cosine of the output code, the second multiplier for multiplying the input voltage of the cosine signal by the digital value of the sine of the output code, the subtractor-error amplifier, the inputs of which are connected with the outputs of the multipliers, and the output with the counter signal generator, which generates the increment and decrement signals of the reverse counter depending on the sign and magnitude of the mismatch, the outputs of the forward and reverse counting of the generator are connected to the reverse counter of the output angle code, the counter output is connected by the sine and cosine values formation unit , the outputs of which are connected to the digital inputs of the multipliers, the following differences are provided, namely, the outputs of the unit for generating sine and cosine values are connected to the inputs of the sine-cosine signal correction unit, the outputs of which connected to the inputs of the CORDIC digital converter operating in vector mode, the output code of this converter is the output of the angle-code converter.

There is a causal relationship between the set of essential features of the claimed technical solution and the achieved technical result, namely, the block for digital correction of the sine-cosine signal makes it possible to eliminate imperfections of the input sine-cosine signal (offset errors, imbalance of gains, phase, as well as temperature dependence of data errors) by means of a small number of tuning registers while ensuring high performance due to the tracking loop.

The technical essence of the proposed solution is illustrated by drawings, where FIG. 1 contains a block diagram of a converter of a sine-cosine signal into an angle code, FIG. 2 contains a block diagram of a sine-cosine signal correction unit, FIG. 3 contains graphs showing conversion error compensation.

The block diagram of the converter is shown in Fig. one.

Sine-cosine angle-to-code converter contains:

1, 2 - multipliers;

3 - error amplifier-subtractor;

4 - pulse generator for counting;

5 - reverse counter;

6 - block for generating digital values of sine and cosine;

7 - sine-cosine signal correction unit;

8 - CORDIC converter in vector mode;

9 - temperature sensor.

Multipliers 1, 2 are connected to an error subtractor-amplifier 3, the difference voltage from which is fed to a counter pulse generator 4, which generates signals for incrementing and decrementing a reversing counter depending on the sign and magnitude of the error. The counter pulse generator 4 is connected by the signal lines of the forward UP and the reverse DN of the counter with a reverse counter 5, the value of which is the input of the block for generating digital values of the sine-cosine signal 6. This block can be implemented in different ways - in the form of a sine and cosine table of the ROM line selection address which is the counter code (including with the use of interpolation of the least significant bits), in the form of a CORDIC block in the "rotation" mode, in the form of calculating a direct mathematical function in various ways.

The outputs of the sine-cosine signal generating unit are connected to the inputs of the multipliers, thus closing the feedback loop and forming a servo system that minimizes the conversion error Err = Usin (θ-ϕ _T ).

The outputs of the sine-cosine signal generating unit are fed to the inputs of the correction unit 7 performing the correction of the sine and cosine signal, including using data from the temperature sensor 9. The structure of the correction unit is shown in FIG. 2.

The sinusoidal Sin (ϕ _T ) signal is fed to the input of the first adder 10, where it is summed with the digital value of the offset of the sinus channel OFFs, from the output of the first adder, the signal is fed to the input of the second adder 11 where it is summed with the output signal of the temperature dependence correction unit of the sinus channel 12 OFFTs (Tcode ). This block calculates the offset correction value based on the readings of the temperature sensor Tcode and the tuning factors. This block can have different implementations of the dependency function OFFTs = f (Tcode), for example, a 2nd order polynomial, tabular data or tabular data with interpolation of intermediate values, etc. From the output of the second adder 11, the signal is fed to the input of the unit for correcting the amplitude of the sinus channel 13, which multiplies the signal by the value of Gs.

Similarly, the cosine Cos (ϕ _T ) signal is fed to the input of the first adder 16, where it is summed with the digital value of the offset of the cosine channel OFFc, from the output of the first adder, the signal goes to the input of the second adder 17, where it is summed with the output signal of the temperature dependence correction unit of the cosine channel 18 OFFTc (Tcode). From the output of the second adder 17, the signal is fed to the input of the amplitude correction unit of the cosine channel 19, which multiplies the signal by the value of Gc.

Thus, at the output of the amplitude correction blocks 13 and 19, the received signal will have the form:

Usa = Gs⋅ [Sin (ϕ _T ) + OFFs + OFFTs (Tcode))]

Uca = Gc⋅ [Cos (ϕ _T ) + OFFc + OFFTc (Tcode))]

Next, the phase shift between the sine and cosine channels is corrected by mutual summation of the signal of each channel with a certain weighting factor.

А⋅sin (ϕ _K ) = Usa + Gp⋅Uca

A⋅cos (ϕ _K ) = Uca + Gp⋅Usa

Where Gp is a signed correction factor.

The introduced phase shift is determined in accordance with the expression:

Δϕ = 2⋅arctg (Gp)

In this case, the input signal is changed to a scaling factor equal to:

The sine-cosine signal correction unit 7 may contain both full correction described above, and partially, for example, only offset correction.

The corrected sine and cosine signals are fed to the angle-code 8 converter block, which can be executed as a CORDIC converter in vector mode.

The proposed design makes it possible to correct the basic imperfections of the sine-cosine signal caused by the imperfection of the sensor system and the analog processing path.

FIG. 3 is a graph showing the result of the proposed system when compensating for the conversion error caused by the appearance of a DC bias voltage in the channels of the sine and cosine signals. The transformation resolution for the simulation was 13 bits. The results are also shown in Table 1.

The data in Table 1 show that the proposed design makes it possible to reduce the conversion error to the minimum value for a given resolution.

The conversion delay of the proposed system is defined as:

Td = Tt + Tk + Tc

where Tt is the servo system conversion delay, Tk is the correction block conversion delay, Tc is the CORDIC block conversion delay.

The servo system conversion delay Tt for clocked systems is:

Tt = 2⋅Tclk

where Tclk is the clock period.

The delay in the transformation of the correction block depends on its implementation and the number of correcting units. When using the pipelined architecture of this block without intermediate registers, the latency can be reduced to two clock cycles. Similarly, the latency of the CORDIC block in the case of its pipelined implementation without intermediate registers between stages can be reduced to two clock cycles. Thus, the minimum conversion delay of the proposed angle-code converter is 6 clock cycles. For a 16 MHz system clock, the conversion delay is 750 ns and the sample rate is 2.6 MHz.

The technical and economic effect of the proposed technical solution is to improve the accuracy of converting a sine-cosine signal into an angle code while ensuring a high conversion speed characteristic of tracking systems.

Information sources

1. RF patent 2488958

2. RF patent 2235422

3. US patent 7250881

4. Article "Integrated position processor for precision motion control systems of movable units and mechanisms". Journal "Components and Technologies", No. 7, 2016, pp. 81-85.

5. RF patent 167428 - prototype

6. RF patent 2659468

Claims (1)

Tracking sine-cosine angle-to-code converter containing the first multiplier for multiplying the input voltage of the sine signal by the digital value of the cosine of the output code, the second multiplier for multiplying the input voltage of the cosine signal by the digital value of the sine of the output code, a subtractor whose inputs are connected to the outputs of the multipliers, and output - with a counter pulse generator, which generates signals for incrementing and decrementing a reversing counter depending on the sign and magnitude of the mismatch, the outputs of the forward and backward counting of the generator are connected to the reversing counter of the output angle code, the counter output is connected to the unit for generating digital values of the sine and cosine, outputs which are connected to the inputs of the first and second multipliers, characterized in that the outputs of the unit for generating digital values of the sine and cosine are connected to the inputs of the sine and cosine of the correction unit, which corrects the bias voltage, amplitude imbalance beats and phase shift of the sine-cosine signal, the sine and cosine outputs of the correction block are connected to the sine and cosine inputs of the CORDIC block in the vector mode, the output of which is the output code of the converter angle.

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