The hottest high-speed and high-precision integrat

2022-07-23
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DPWM based high-speed and high-precision integrated analog-to-digital converter Abstract: a high-speed, high-precision and integrated analog-to-digital converter is proposed, which is powered by a single division continuous artificial intelligence (AI) burst point power supply and based on the principle of digital pulse width modulation (DPWM). By comparing the pulse width modulated signal with the measured signal after low-pass filtering, the analog-to-digital conversion is realized, which avoids the complexity of analog circuit design of high-precision analog-to-digital converter and achieves high precision. This method can further improve the conversion speed after using the fast search algorithm, and can be easily realized by single chip microcomputer, DSP, FPGA, etc. it can also provide a useful method for chip integration

key words: digital pulse width modulation; Integral A/D converter; Programmable gate array; PWM signal

0 introduction

using digital signal processing can easily realize various advanced adaptive algorithms and complete functions that can not be realized by analog circuits. Therefore, more and more analog signal processing is being digitized. At present, the most widely used a/D converters are integral, successive approximation and delta A/D converters. The principle of integral A/D converter is to convert the input voltage into time (pulse width signal) or frequency (pulse frequency), and then obtain the digital value by timer/counter. The advantage is that high resolution can be obtained with a simple circuit; The disadvantage is that the conversion accuracy depends on the integration time and the conversion rate is low- Delta type A/D converter is composed of integrator, comparator, 1-bit D/a converter and digital filter. Its principle is similar to that of integral type. It converts the input voltage into time (pulse width) signal, and obtains the digital value after being processed by digital filter. The digital part of the circuit is basically easy to chip, so it is easy to achieve high resolution, but the cost is high, and it is difficult to chip the whole circuit. The existing a/D converter has high requirements for the performance and parameters of the relevant analog devices, so it is not easy to integrate. In applications that require a/D conversion, it is generally difficult to integrate high-performance A/D, and corresponding IP cores need to be purchased; The principle of double oblique integration type A/D, etc. generally requires dual power supply or negative voltage reference because it requires negative reference voltage for reverse integration, which brings inconvenience to many applications, affects universality, and the speed is slow. Generally, it does not support the function of communication and display. In order to solve the above problems, DPWM technology is used for analog-to-digital conversion. On the one hand, it provides a convenient solution for MCU, FPGA and other applications that lack a/D resources. On the other hand, this solution has no special requirements for the performance of analog devices, is easy to integrate, can be used for chip manufacturing, and has a low cost. It can be applied to single power supply work. The conversion rate can be improved by adopting a fast search algorithm, At the same time, it has the function of communication and display

1 principle of high-speed and high-precision integral A/D converter

the basic working principle of the converter used here is to generate pulse width signal (DPWM) through dp-wm module. After the signal is filtered by a simple RC low-pass filter, it is compared with the detected signal by the comparator, processed and sent out by the comparator. Finally, the signal sent by the comparator is picked up and analyzed by the logic operation module, and the relevant information of the detected signal is obtained and sent to the communication module and the display module. The specific scheme is shown in Figure 1. The converter is realized by using DPWM principle, and the duty cycle of the transmitted signal has a certain corresponding relationship with the measured value, which avoids the complexity of analog circuit design of high-precision analog-to-digital converter, and the conversion rate can be improved by using fast search algorithm

1.1 design of digital pulse width modulation module

the core control part of the converter can be realized by MCU, DSP, fp-ga, etc. It mainly completes the generation of DPWM, the measurement of analog signals and the display and control of a/D conversion results. The design prototype uses CY clone Ⅱ FPGA as the control chip, and the overall structure of the program is shown in Figure 2

specific working process: get high-speed clock through phase-locked loop to generate high-resolution DPWM signal; The DPWM signal that adjusts the duty cycle according to a certain law is used to control the external capacitor voltage. It is compared with the input analog signal until the comparator turns over. At this time, the duty VREF is the A/D conversion result. In the system, input 50MHz clock, multiply the frequency to 400MHz through PLL, and the A/D conversion accuracy reaches 165 v. the specific design is shown in Figure 3, and its signal functions are shown in Table 1

1.2 DPWM generator design

dpwm generation module sends high-resolution DPWM signal through the duty cycle setting value updated in real time. In this system, the frequency of DPWM signal is 20 kHz, and the accuracy of DPWM is 20000 clock cycles/duty cycle. As shown in Figure 4, its signal function is shown in Table 2

1.3 design of analog quantity monitor

the main function of this module is to monitor the comparison results in real time, further improve the manufacturing technology level and overall strength of NT, continuously adjust the duty, and obtain the final conversion result duty display. The analog switch control signal ASW completes the control of a monitoring process. The process is as follows: capacitance discharge to ground measurement calibration analog measurement (duty cycle change) comparator turnover completes the conversion. The above three steps continue to cycle. The analog measurement module is shown in Figure 5, and its signal functions are shown in Table 3

1.4 design of display controller module

this module mainly completes the task of notifying the main module to display updates. In this design, the update cycle is 100 ms. The display control module is shown in Figure 6, and its signal function is shown in Table 4

2 advantages of high-speed and high-precision integral analog-to-digital converter

2.1 meet the conditions of single power supply

in many applications, single power supply is used for cost or system reliability. The traditional integral A/D converter needs to use positive and negative dual power supply. The integrator integrates the input voltage within a fixed time interval, which usually corresponds to the maximum number of internal counting units. After the time, reset the counter, and connect the integrator input to ensure that the negative power supply voltage is stable when the whole machine is forced to experiment. Under the action of this reverse polarity signal, the integrator is reversely integrated until the output returns to zero, the counter is terminated, and the integrator is reset. The accuracy of the integrated a/D converter can be very high, but their sampling speed and bandwidth are very low

the integrated a/D converter based on DPWM principle proposed here can realize single power supply +5 V power supply. When the polarity of the measured signal DPWM signal is the same, the feasibility of using a single power supply shows that if the polarity of the measured signal is opposite to that of the DPWM signal after the experiment, the polarity conversion can be carried out under the condition of a single power supply by using the method of op amp inverse amplifier. Therefore, the scheme can work under the condition of a single power supply without adding an additional negative power supply. The principle is shown in Figure 7. At this time, vo=-r2vin/R1, because VIN o, VO 0, meets the single power supply condition

2.2 convenient for chip integration

the integrated analog-to-digital converter is implemented based on the principle of DPWM, and there are few analog devices. Its main implementation method is that it only needs to generate DPWM module, and only needs to add a common analog operational amplifier and necessary logic units such as communication and operation; It is easy to implement in fp-ga, and its code can be easily used in IC design. Compared with the traditional A/D converter, it is much easier to manufacture analog cells with high precision and high linearity. The converter is reasonable in design and simple in structure. The duty cycle of the transmitted signal has a certain corresponding relationship with the measured value, which avoids the complexity of the analog circuit design of high-precision analog-to-digital converter. It is convenient for the design of integrated chips, can be used for chip manufacturing, and has a low cost. It is also convenient for the realization of single chip microcomputer and programmable gate array

2.3 fast search algorithm improves a/D conversion speed

the initial search adopts finite step dichotomy, golden section or random search (such as Monte Carlo) to quickly determine the search range, and then perform duty cycle traversal, which can greatly improve a/D conversion speed

2.4 improve the accuracy of DPWM by dithering

since no additional measures are taken, the accuracy of DPWM depends on the switching frequency and FPGA dominant frequency. In order to pursue higher precision, the main frequency can be increased or the switching frequency can be reduced. It is unrealistic to blindly increase the main frequency. Significantly reducing the switching frequency will affect the conversion speed. The accuracy of DPWM can be easily improved by using dithering method. This method can reduce the main frequency and power consumption, thus reducing the cost. In addition, performance can be improved at the same cost

2.5 several problems needing attention

the comparator will oscillate in the critical state, and the methods of hysteresis comparison and logic blocking can be considered. PWM reference needs a stable reference source; The contradiction between accuracy and conversion speed can be coordinated according to specific needs; The influence of digital switching noise needs careful wiring and filtering to suppress; The automatic gain technique can be properly used to improve the low voltage measurement accuracy

3 experimental results

the DPWM output waveform in this paper is shown in Figure 8. The integral test waveform of the low-pass filter is shown in Figure 9. The A/D converter has high integral linearity and a resolution of 165 v

4 conclusion

the high-speed, high-precision and integral A/D converter, which is powered by a single power supply and based on the principle of DPWM, can be conveniently realized by single chip microcomputer, DSP, fp-ga, etc. There is no need for external a/D converter, and it is convenient for integrated chip design, avoiding the complexity of analog circuit design of high-precision A/D converter. It can provide a useful method for integrated and related IC design. After adopting the fast search algorithm, the conversion rate can be improved, and it has the function of both communication and display, which is suitable for a wider range of applications

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