System and method for realizing digital-to-analog conversion by using superposition pulse width modulation

Abstract

The invention discloses a system and method for realizing digital-to-analog conversion by using superposition pulse width modulation, and the system comprises a controller which serves as a multi-path PWM generator and is correspondingly connected with a multi-path digital-to-analog conversion circuit; each digital-to-analog conversion circuit comprises a Schmidt inverter, a summing amplifier, a filtering and smoothing circuit and an output follower which are connected in sequence, and the output follower is provided with an analog output port. And the addition amplification circuit is used for carrying out waveform superposition on the multiple paths of PWM waveforms output in a timing manner. On the basis of realizing digital-to-analog conversion by utilizing a PWM (Pulse Width Modulation) technology, frequency multiplication of PWM frequency is realized by superposing multiple paths of waveforms, so that the precision of an analog output signal is further improved. In product design, the precision requirement problem in low-cost application can be solved, and the method is worthy of being popularized in design.

Description

Technical Field

[0001] The invention relates to a digital-to-analog conversion technology, and in particular to a system and method for realizing digital-to-analog conversion by using superimposed pulse width modulation. Background Art

[0002] Today's world is a digital world, and the transmission, calculation, and storage of various information are all realized in digital form. Digital signals have the advantages of strong anti-interference ability, easy calculation and processing, and easy storage. However, when it comes to specific high-speed and high-precision control and measurement, digital signals still have some disadvantages. The main disadvantages of digital signals include quantization error, processing complexity, and slow response speed. Quantization error is one of the main disadvantages of digital signals. That is, during the sampling process, due to the discreteness of digital signals, the signal will introduce errors, which may cause signal distortion. Especially in the case of low resolution, this error has a more serious impact on the signal; moreover, digital signal processing is relatively complex, and the processing of digital signals usually requires the use of digital processors (DSPs). Therefore, compared with analog signals, the processing of digital signals requires more computing resources and programming work, which increases the complexity and cost of the system for some simple applications; in addition, the processing and conversion of digital signals requires a certain amount of time. In applications with high real-time requirements, digital signals may not respond in time, thus affecting the performance of the system. Relatively speaking, analog signals still have many advantages in these aspects and can be widely used in control, measurement, and signal synthesis with high requirements for accuracy and response speed. Due to the respective advantages of digital signals and analog signals, in many applications we need to convert digital signals into analog signals for processing. Therefore, the demand for digital-to-analog converters in circuit design is increasing day by day.

[0003] However, with the increasing demand for analog-to-digital converters in circuits, higher requirements are also placed on the accuracy of analog-to-digital conversion. In order to enable analog-to-digital converters to be used in situations where certain accuracy requirements are required, the usual practice is to increase the number of data bits of the analog-to-digital converter, thereby indirectly improving the output accuracy of the analog-to-digital converter. However, two problems will be encountered in actual design. First, the number of bits of the digital-to-analog converter cannot be increased indefinitely. In addition, even if the number of bits of the digital-to-analog converter can be increased indefinitely, it costs a lot to increase each data bit, which is unacceptable in products. Therefore, studying a high-precision digital-to-analog conversion method that can control costs within a certain range has become an urgent need in product design.

[0004] Since the actual design uses high-bit, low-error digital-to-analog conversion chips to achieve digital-to-analog conversion, additional devices are needed and the cost is relatively high. In consumer products with relatively strict cost control, although this method has superior performance, it is often unacceptable due to cost issues. The use of relatively inexpensive low-error digital-to-analog conversion devices cannot meet the accuracy requirements in the design, and designers are often in a dilemma.

[0005] Prior art 1, a technical solution for digital-to-analog conversion using a digital-to-analog converter chip:

[0006] This technical solution is the most common one, which is to use a digital-to-analog converter integrated circuit chip and add a follower or other type of amplifier at the back end to convert the digital signal into an analog voltage signal. The technical solution is as follows:

[0007] First, the control chip transmits the digital signal to the digital-to-analog converter integrated circuit chip through a parallel or serial communication interface;

[0008] Afterwards, the digital-to-analog converter integrated circuit chip uses a resistor network, analog switches, and operational amplifiers to convert the digital signal into an analog voltage or current signal that is proportional to the reference source voltage;

[0009] Then, the analog signal output by the digital-to-analog converter integrated circuit chip is processed by the back-end follower or amplifier for impedance matching, voltage conversion, filtering, etc., and then output, thereby realizing the conversion of digital signals to analog signals.

[0010] Disadvantages of using DAC chips for DAC conversion:

[0011] 1) The solution of using a digital-to-analog converter chip for digital-to-analog conversion can meet the requirements of high precision, but if the conversion accuracy is improved, the number of data bits of the digital-to-analog converter chip needs to be increased, which greatly increases the cost. If the low cost requirement is to be achieved, it is often impossible to obtain the conversion accuracy that meets the design requirements, and it is impossible to achieve both accuracy and cost.

[0012] 2) Data transmission between the DAC and the controller is completed through parallel or parallel communication interfaces, but in microcontrollers, especially low-cost controllers, communication interfaces are often limited and scarce resources. If multi-channel DAC is required, more interface resources are needed, which invisibly increases the design cost.

[0013] In view of this, the present invention is proposed. Summary of the invention

[0014] The purpose of the present invention is to provide a system and method for realizing digital-to-analog conversion by using superimposed pulse width modulation, so as to solve the above-mentioned technical problems existing in the prior art.

[0015] The objective of the present invention is achieved through the following technical solutions:

[0016] The system for realizing digital-to-analog conversion by superimposed pulse width modulation of the present invention comprises a controller, which serves as a multi-channel PWM generator and is correspondingly connected to a multi-channel digital-to-analog conversion circuit;

[0017] Each digital-to-analog conversion circuit comprises a Schmidt inverter, an adding amplifier, a filtering and smoothing circuit and an output follower connected in sequence, wherein the output follower is provided with an analog output port.

[0018] The method for implementing digital-to-analog conversion by the system using superimposed pulse width modulation to implement digital-to-analog conversion comprises the following steps:

[0019] Use the controller as a PWM generator to generate PWM waveforms of different frequencies, and change the duty cycle of the PWM wave through the controller, thereby achieving the purpose of output voltage adjustment by changing its duty cycle;

[0020] The edge of the PWM wave output by the controller is made steeper through the Schmitt inverter to ensure the consistency and stability of the PWM wave duty cycle, thereby improving the accuracy of digital-to-analog conversion;

[0021] The filter smoothing circuit smoothes the PWM square wave into a continuous analog output waveform by configuring appropriate RC parameters;

[0022] The follower further filters the smoothed analog output signal to eliminate the influence of high-frequency signals on the output, while reducing the output impedance and improving the driving ability of the analog output signal.

[0023] Compared with the prior art, the system and method for realizing digital-to-analog conversion using superimposed pulse width modulation provided by the present invention, based on realizing digital-to-analog conversion using PWM pulse width modulation technology, realizes PWM frequency doubling by superimposing multiple waveforms, thereby further improving the accuracy of the analog output signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A structural block diagram of a system and method for implementing digital-to-analog conversion using superimposed pulse width modulation provided in an embodiment of the present invention.

[0025] Figure 2 Schematic diagram of the principle of an embodiment of the present invention.

[0026] Figure 3 This is a schematic diagram of an embodiment of the present invention for effectively controlling the waveform phases of several PWM outputs. DETAILED DESCRIPTION

[0027] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention; it is obvious that the described embodiments are only part of the embodiments of the present invention, not all of the embodiments, which does not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of the present invention.

[0028] First, the terms that may be used in this article are explained as follows:

[0029] The term “and / or” means that either or both of them can be realized at the same time. For example, X and / or Y means both “X” or “Y” and “X and Y”.

[0030] The terms "include", "comprises", "contains", "has" or other descriptions with similar semantics should be interpreted as non-exclusive inclusion. For example, including certain technical feature elements (such as raw materials, components, ingredients, carriers, dosage forms, materials, dimensions, parts, components, mechanisms, devices, steps, procedures, methods, reaction conditions, processing conditions, parameters, algorithms, signals, data, products or products, etc.) should be interpreted as including not only certain technical feature elements explicitly listed, but also other technical feature elements known in the art that are not explicitly listed.

[0031] The term "consisting of..." means excluding any technical feature elements not explicitly listed. If this term is used in a claim, it will make the claim closed, so that it does not contain technical feature elements other than the technical feature elements explicitly listed, except for the conventional impurities related to them. If this term only appears in a clause of a claim, it only limits the elements explicitly listed in the clause, and the elements recorded in other clauses are not excluded from the overall claim.

[0032] The contents not described in detail in the examples of the present invention belong to the prior art known to professionals in the field. If no specific conditions are specified in the examples of the present invention, the conditions are carried out according to the conventional conditions in the field or the conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used in the examples of the present invention, they are all conventional products that can be purchased commercially.

[0033] The system for realizing digital-to-analog conversion by superimposed pulse width modulation of the present invention comprises a controller, which serves as a multi-channel PWM generator and is correspondingly connected to a multi-channel digital-to-analog conversion circuit;

[0034] Each digital-to-analog conversion circuit comprises a Schmidt inverter, an adding amplifier, a filtering and smoothing circuit and an output follower connected in sequence, wherein the output follower is provided with an analog output port.

[0035] The adding amplifier is used as a waveform superposition circuit for the PWM waveforms of the multi-channel timing outputs.

[0036] Use SN74LVC14 as Schmitt inverter; use TL074 as follower and summing amplifier; use ceramic capacitors as smoothing and filtering capacitors.

[0037] The method for implementing digital-to-analog conversion by the system using superimposed pulse width modulation to implement digital-to-analog conversion comprises the following steps:

[0038] Use the controller as a PWM generator to generate PWM waveforms of different frequencies, and change the duty cycle of the PWM wave through the controller, thereby achieving the purpose of output voltage adjustment by changing its duty cycle;

[0039] The edge of the PWM wave output by the controller is made steeper through the Schmitt inverter to ensure the consistency and stability of the PWM wave duty cycle, thereby improving the accuracy of digital-to-analog conversion;

[0040] The filter smoothing circuit smoothes the PWM square wave into a continuous analog output waveform by configuring appropriate RC parameters;

[0041] The follower further filters the smoothed analog output signal to eliminate the influence of high-frequency signals on the output, while reducing the output impedance and improving the driving ability of the analog output signal.

[0042] By increasing the PWM output frequency, the waveform quality and accuracy of the analog output can be improved;

[0043] The PWM waveforms output by multiple timers are superimposed using an adder. As long as the phases of the waveforms of several PWM outputs are effectively controlled, the frequency doubling of the output waveform can be achieved.

[0044] Using SN74LVC14 as a Schmitt inverter can make the edge of the PWM waveform steep and neat, eliminating the waveform edge distortion caused by parasitic parameters on the wire, and further eliminating the duty cycle error caused by the inconsistency between the rising edge and the falling edge;

[0045] Using TL074 as the follower and summing amplifier has the characteristics of high precision and can improve the driving ability of signal output and adapt to the driving of different back-end circuits;

[0046] Ceramic capacitors are used as smoothing and filtering capacitors to eliminate the accuracy impact caused by high-frequency noise and improve output quality.

[0047] In summary, the system and method for realizing digital-to-analog conversion by superimposing pulse width modulation in the embodiment of the present invention is a method for realizing digital signal and analog signal conversion based on PWM pulse width modulation technology and RC filter; on the basis of realizing digital-to-analog conversion by using PWM pulse width modulation technology, the multiplication of PWM frequency is realized by superimposing multiple waveforms, thereby further improving the accuracy of analog output signal. Therefore, this technology can solve the accuracy requirement problem in low-cost applications in product design, and is worthy of promotion in design.

[0048] The present invention realizes high-precision, low-cost digital-to-analog conversion; realizes further improvement of accuracy compared with a single PWM output solution; and realizes saving and releasing of controller communication interfaces in system design.

[0049] In order to more clearly demonstrate the technical solution and technical effects provided by the present invention, the embodiments of the present invention are described in detail with specific embodiments below.

[0050] Example 1

[0051] like Figure 1 Shown is the technical block diagram of this technical solution.

[0052] This technical solution uses a controller as a PWM generator to generate PWM waveforms of different frequencies. In practical applications, the output PWM wave does not need to change frequency in real time, and only needs to select a fixed output frequency according to the accuracy requirements. On the other hand, the use of a controller can easily change the duty cycle of the PWM wave, and then achieve the purpose of output voltage adjustment by changing its duty cycle.

[0053] In addition to the controller, the main functional components involved in this technical solution include Schmitt inverter, summing amplifier, filter smoothing circuit and output follower. The Schmitt inverter can make the edge of the PWM wave output by the controller steeper, which is done to ensure the consistency and stability of the PWM wave duty cycle, thereby improving the accuracy of digital-to-analog conversion; the filter smoothing circuit smoothes the PWM square wave into a continuous analog output waveform by configuring appropriate RC parameters; the follower further filters the smoothed analog output signal to eliminate the impact of high-frequency signals on the output, while reducing the output impedance and improving the driving ability of the analog output signal. Its schematic diagram is shown below. Figure 2 shown.

[0054] Example 2

[0055] In addition to the above-mentioned PWM pulse width modulation voltage regulation scheme, another unique optimization scheme of the present technical scheme is to improve the waveform quality and accuracy of the analog output by increasing the PWM output frequency. As is well known, the higher the PWM output frequency, the lower the ripple of the analog output waveform after PWM modulation and smoothing, and its accuracy is also improved. The analog signal after digital-to-analog conversion is often used as a reference source, voltage reference, output given reference, etc., which have high requirements for accuracy and ripple. In order to cope with such application occasions, analog-to-digital conversion must obtain a high-quality output signal, so increasing the output frequency of the PWM wave becomes the simplest and most effective solution. In practical applications, a problem is usually encountered. Since the number of bits of the counter is fixed, if the output frequency of the PWM wave is to be increased, the adjustment resolution of the PWM duty cycle will inevitably be sacrificed, thereby affecting the output resolution of the entire digital-to-analog converter. If the output resolution of the digital-to-analog converter is to be retained, the output frequency will be affected. If a method is found to multiply the frequency while ensuring the output resolution, thereby effectively improving the output waveform quality of the digital-to-analog converter, the waveform quality of the PWM modulated digital-to-analog converter output can be further improved.

[0056] like Figure 1 As shown in the figure, we propose to use the adder circuit to superimpose the PWM waveforms output by multiple timers. As long as the phases of the waveforms of several PWM outputs are effectively controlled, the frequency doubling of the output waveform can be achieved. The schematic diagram is shown in Figure 3 .

[0057] In practical applications, using SN74LVC14 as a Schmitt inverter can make the edge of the PWM waveform steeper and neater, eliminating the waveform edge distortion caused by parasitic parameters on the wire, and further eliminating the duty cycle error caused by the inconsistency between the rising and falling edges; using TL074 as a follower and summing amplifier has the characteristics of high precision, and can also improve the driving capability of the signal output and adapt to the driving of different back-end circuits; using ceramic capacitors as smoothing and filtering capacitors can eliminate the accuracy impact caused by high-frequency noise and improve the output quality.

[0058] Beneficial effects of the present invention:

[0059] 1) The digital-to-analog converter built using the PWM generator in the controller and low-cost components such as Schmitt inverters, operational amplifiers, resistors and capacitors can achieve lower costs than the integrated analog-to-digital converter chip with the same accuracy and resolution;

[0060] 2) Based on the traditional PWM voltage regulation scheme, the output accuracy and waveform quality are improved by adjusting the PWM output waveform frequency and duty cycle in a coordinated manner;

[0061] 3) By using the method of superimposing multiple PWM output waveforms, the output frequency is doubled without affecting the resolution of digital-to-analog conversion through output waveform phase control, thereby further improving the output accuracy and waveform quality.

[0062] In specific applications, a PWM generation circuit can be used to replace the controller in this solution to achieve PWM output, or an inverter or a Schmitt trigger can be used to replace the Schmitt inverter in this solution. In practical applications, PWM digital-to-analog conversion can be achieved, but the fundamental principle is basically the same as that of this solution.

[0063] Key technical points of the present invention:

[0064] The frequency and duty cycle linkage control method is adopted to achieve high-precision and high-quality analog-to-digital conversion output.

[0065] The digital-to-analog conversion accuracy is improved without losing the digital-to-analog conversion resolution by superimposing multiple PWM output waveforms and controlling the output waveform phase.

[0066] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed in the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims. The information disclosed in the background technology section of this article is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as an admission or in any form that the information constitutes prior art known to those skilled in the art.

Claims

1. A system for realizing digital-to-analog conversion by superimposed pulse width modulation, characterized in that: It includes a controller, which serves as a multi-channel PWM generator and is correspondingly connected to a multi-channel digital-to-analog conversion circuit; Each digital-to-analog conversion circuit comprises a Schmidt inverter, an adding amplifier, a filtering and smoothing circuit and an output follower connected in sequence, wherein the output follower is provided with an analog output port.

2. The system for realizing digital-to-analog conversion by superimposed pulse width modulation according to claim 1, characterized in that: The adding amplifier is used as a waveform superposition circuit for the PWM waveforms of the multi-channel timing outputs.

3. The system for realizing digital-to-analog conversion by superimposed pulse width modulation according to claim 2, characterized in that: Use SN74LVC14 as Schmitt inverter; use TL074 as follower and summing amplifier; use ceramic capacitors as smoothing and filtering capacitors.

4. A method for implementing digital-to-analog conversion in a system for implementing digital-to-analog conversion using superimposed pulse width modulation as claimed in claim 1, 2 or 3, characterized in that: Includes steps: Use the controller as a PWM generator to generate PWM waveforms of different frequencies, and change the duty cycle of the PWM wave through the controller, thereby achieving the purpose of output voltage adjustment by changing its duty cycle; The edge of the PWM wave output by the controller is made steeper through the Schmitt inverter to ensure the consistency and stability of the PWM wave duty cycle, thereby improving the accuracy of digital-to-analog conversion; The filter smoothing circuit smoothes the PWM square wave into a continuous analog output waveform by configuring appropriate RC parameters; The follower further filters the smoothed analog output signal to eliminate the influence of high-frequency signals on the output, while reducing the output impedance and improving the driving ability of the analog output signal.

5. The method for realizing digital-to-analog conversion by superimposed pulse width modulation according to claim 4, characterized in that: By increasing the PWM output frequency, the waveform quality and accuracy of the analog output can be improved; The PWM waveforms output by multiple timers are superimposed using an adder. As long as the phases of the waveforms of several PWM outputs are effectively controlled, the frequency doubling of the output waveform can be achieved.

6. The method for realizing digital-to-analog conversion by superimposed pulse width modulation according to claim 5, characterized in that: Using SN74LVC14 as a Schmitt inverter can make the edge of the PWM waveform steep and neat, eliminating the waveform edge distortion caused by parasitic parameters on the wire, and further eliminating the duty cycle error caused by the inconsistency between the rising edge and the falling edge; Using TL074 as the follower and summing amplifier has the characteristics of high precision and can improve the driving ability of signal output and adapt to the driving of different back-end circuits; Ceramic capacitors are used as smoothing and filtering capacitors to eliminate the accuracy impact caused by high-frequency noise and improve output quality.

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