Design method of FPGA digital electronic system
Ora pubblicata: 2020-06-26 12:12:21
1. Hardware unit circuit design
When designing the hardware unit circuit, the specific requirements for each unit circuit must be clearly defined, the performance index of the unit circuit must be drawn up in detail, the interrelationship between each unit circuit should be carefully considered, and the signal transmission method and signal between the front and rear unit circuits Matching, as few interface circuits as possible or without level shifting, and considering that the power supply of each unit circuit is as uniform as possible in order to make the entire electronic system simple and reliable. In addition, try to choose existing, mature circuits to achieve the function of the unit circuit; sometimes you can't find a ready-made circuit that fully meets the requirements. You can appropriately improve on the basis of the circuit that is closer to the design requirements, or you can creatively design yourself. In order to make the electronic system small in size and high in reliability, the unit circuit is composed of integrated circuits as much as possible, such as integrated operational amplifiers, integrated voltage stabilizing devices, analog switches, and frequency-voltage conversion.
When calculating the design parameters of the hardware unit circuit, the parameters of the unit circuit components should be determined according to the performance requirements of the unit circuit. For example, according to the magnitude of the voltage amplification factor, the value of the feedback resistance can be determined; according to the oscillation frequency required by the oscillator, using the formula, the resistance and capacitance values that determine the oscillation frequency can be calculated. However, the theoretical parameter values that generally meet the requirements of circuit performance indicators are not unique, and designers should flexibly choose based on component performance, price, volume, versatility, and supply. Pay attention to the following points when calculating unit circuit parameters:
(1) When calculating the working current, voltage and power parameters of components, the most unfavorable working conditions should be considered, and an appropriate margin should be left.
(2) There must be sufficient margin for the limit parameters of the components, generally 1.5 to 2 times the rated value.
(3) For the values of resistance and capacitance parameters, the nominal value near the calculated value should be selected. The resistance value is generally selected within 1MΩ; non-electrolytic capacitors are generally selected from 100pF to 0.47F; electrolytic capacitors are generally selected within the range of 1 to 2000μF.
(4) On the premise of ensuring that the circuit meets the requirements of functional indicators, try to reduce the variety, price, and volume of components.
2. Software design
In order to meet the requirements of system functions and technical indicators of electronic systems, software design must first complete the design of functional modules, such as keyboard, digital display, A/D, D/A conversion and other functional modules. After the functional module is designed, it can be used repeatedly to make the design more fast and convenient. Write functional modules in VHDL language, connect each functional module with graphic input method, download it to FPGA chip, and then connect FPGA chip and hardware circuit to form the entire FPGA electronic system with certain functions and technical indicators .
3. Selection of components
The design of the electronic system is to select the most suitable components and combine them organically. When determining the electronic components, the frequency range of the signal processed by the circuit, the ambient temperature, the size of the space, the cost, and other factors should be fully considered. The specific performance is:
(1) The integrated circuit is generally preferred. Due to the small size and strong function of the integrated circuit, the reliability of the electronic system can be enhanced, the installation and debugging is convenient, and the design of the electronic system is greatly simplified. With the continuous development of analog integration technology, integrated operational amplifiers suitable for various occasions emerge in endlessly, as long as a very small number of components are added, the operational amplifier can form an amplifier with good performance. Similarly, when designing a DC stabilized power supply, discrete components are rarely used for design. Instead, an integrated voltage regulator with more stable performance, more reliable operation, and lower cost is used.
(2) Resistors and capacitors are the two most common components. There are many types of them, and their performances are very different. The application occasions are also different. Therefore, for designers, they should be familiar with the main performance indicators and characteristics of various resistors and capacitors in order to make the correct choice of components according to the circuit requirements.
(3) Selection of discrete semiconductor components. First of all, you must be familiar with their performance and master their scope of application; according to the functional requirements of the circuit and the working conditions of the components in the circuit, such as the maximum current passed, the maximum reverse operating voltage, the maximum operating frequency, the maximum power consumption, etc., Determine the component model.
4. Computer simulation
With the rapid development of computer technology, the design methods of electronic systems have changed a lot. At present, EDA (Electronic Design Automation) technology has become a necessary means of modern electronic system design. On the computer platform, the use of EDA software can debug, measure, and modify various electronic circuits, which greatly improves the effect and accuracy of electronic design, while saving design costs.
5. Experimental debugging
There are many factors and problems to be considered in the design of electronic systems. Because the parameters and models of components used in the simulation of the circuit on the computer are different from the actual devices, actual experiments must be carried out on the circuit simulated by the computer. You can find and solve problems through experiments. If the performance index fails to meet the requirements, it should be analyzed in-depth on which unit circuit or software designed module, and then redesigned and selected them until the performance index is completely reached.
6. Draw the overall circuit diagram
The overall circuit diagram is drawn on the basis of the general block diagram, unit circuit design, software design, parameter calculation, and component selection. It is the basis for assembly, debugging, printed circuit board design, and maintenance. At present, drawing circuit diagrams is generally done on a computer using drawing software. When drawing the circuit diagram, pay attention to the following points:
(1) The overall circuit diagram is drawn on the same picture as much as possible; pay attention to the flow of the signal, generally drawn from the input terminal, drawing each unit circuit in sequence from the left to the right or from top to bottom according to the flow of the signal; the circuit diagram is more complicated If necessary, the main circuit drawing should be on one or several drawings, and the two ends of all ports of each drawing should be marked with labels to explain the connection relationship between the drawings in order.
(2) Pay attention to the compactness and coordination of the overall circuit diagram, requiring a reasonable layout and even arrangement. The symbols of the components in the figure should be standardized, and the model and parameters should be marked next to the symbol of the component. An integrated circuit is usually represented by a box, and its model number is marked in the box, and the function and pin number of each wire are marked on both sides of the box.
(3) The connection lines are generally drawn as horizontal lines or vertical lines, and crossings and bends are reduced as much as possible. Lines that cross each other should be marked with dots at the intersection. For the connection to the negative pole of the power supply, it is generally indicated by the ground symbol; for the connection to the positive pole of the power supply, only the voltage value needs to be marked.
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