Good circuit designers knows through their experiences how to create design specification, convert the specification to circuit design and create a good printed circuit board with minimal errors. For beginners however this process is a dark road, difficult and time consuming.
So here we outline the major steps with tips of how circuit design works from specification to actual design. Planning of the circuit and circuit board before actual PCB manufacturing reduces error, mistakes and the cost associated with design.
Following are steps which one can use for circuit design:
1. Collect Requirement for the design
Writing initial specification is the most important part of the circuit design so the first step is to focus on design requirement. This requires lot of experiences and you should have knowledge with todays technology, protocol standards, frequency spectrum, industry standards, components and ICs that are available etc. The optimum design has many different aspects such as cost, power consumption, size and weight, functional and reliability etc. At this state it is useful to draw the whole design as a system and its components as subsystem. That is divide the design into system and subsystem and write the functional/ operational description of the design.
At this stage you dont know which components and IC to choose but you know in the broadest sense what the design is to achieve. This might be look easy but is difficult. This might not look important but is the most important design step.
Thus this step of collecting information about the design requirements and to plan how to fit them on the circuit board is most difficult step. It comes primarily through experiences.
Some hints on collecting requirements and forming the initial design plan are:
2. Initial conversion of the requirement into circuit design
Once you know the requirements you should make an initial conversion of requirement into the design. That is what components, ICs, technology to use, seperation of analog blocks and digital blocks, consideration of PCB point of view etc. This is an initial guess and requires searching and researching through manufacturer datasheets about compacitbilities issues, voltage and power supply issues, aviability of different technologies(FPGA, microprocessors for example).
Again experience is the key. Use the block diagrams that was suggested in the first step to guide through the conversion. Start thinking about what devices you could use for most essential functional components/IC and critical components in your design. Then move on to other subsystem more in details in terms of operational concern, availability of the components, rules and regulation. Keep in mind the power supply.
This step is important because if for example, you have set out a plan but suppose that later during the printed circuit board design requirement changes- component is/ are simply not available or you come to know that you are not allowed to operate the device in the frequency spectrum that your design operates. Then the whole process of circuit design has to be repeated, replacing components is one thing the other is searching the new part and then there is change to be made in teh PCB board. This will spoil your design besides your time and effort.
The frequency spectrum gives some design gives information such as if the design is on audio frequency(KHz) then discrete component may be more suitable, if the design is on MHz radio frequency(RF) then transmission line effects should be focused in the PCB design stage, if the design is to work in the microwave. So this is important both in terms of circuit operation and from the circuit board design point of view.
With the frequency, throughput required and major functional requirement knowledge, you should try to convert the design requirement by choosing the best technology that fits your design. If your design is for commercial application then time to market, performance vs cost are important factor to consider.
Circuit design software should be used design the circuit. There are many free circuit design software and printed circuit board design software out there. Most of these software have both circuit design facility and PCB design facility. For example Eagle is a free circuit design and PCB design software. There are other software which are expensive but provides other useful feature such as Altium designer. It supports multiple PCB layers, 3D views, good routing algorithms etc.
3. Final Circuit Design
After you have done your initial circuit design according to specification, convert it a final circuit design. Here make replacements the components that would not work as planned in the initial circuit design. Make final checks on the ICs and components, their interconnection. Use circuit design software for this. At this stage you also may require simulation of your circuit to analyze expected output and compare with your desired ones.
4. Create Circuit Layout
Creating circuit layout means converting the circuit schematic into printed circuit board. Most of the software provides means of creating PCB for the circuit. That means the interconnection of the circuit component is not lost while you work on PCB. The circuit component with their actual size are placed on the printed circuit board manually one by one. There are also PCB software that does the component placement automatically. However the placement might not be best suitable for your requirement. In the manual mode, you start by placing the most critical such as processor or microcontroller on the printed circuit board, then you place power supply and external connector on the suitable edges of the PCB. Following this you would place the discrete components near to the bigger components according to the connection to the component in order to reduce the trace length. After placing and arranging all the components you would starting working on routing the traces. After routing, the trace width, vias, silk outlines etc are checked. They must comply to the PCB manufacturer capability to whom you will send the PCB files for manufacturing. PCB software like altium designer makes it easy for circuit designers to enter the desired trace width, via hole size, the separation of traces, the separation of traces with components etc.
So here we outline the major steps with tips of how circuit design works from specification to actual design. Planning of the circuit and circuit board before actual PCB manufacturing reduces error, mistakes and the cost associated with design.
Following are steps which one can use for circuit design:
1. Collect Requirement for the design
Writing initial specification is the most important part of the circuit design so the first step is to focus on design requirement. This requires lot of experiences and you should have knowledge with todays technology, protocol standards, frequency spectrum, industry standards, components and ICs that are available etc. The optimum design has many different aspects such as cost, power consumption, size and weight, functional and reliability etc. At this state it is useful to draw the whole design as a system and its components as subsystem. That is divide the design into system and subsystem and write the functional/ operational description of the design.
At this stage you dont know which components and IC to choose but you know in the broadest sense what the design is to achieve. This might be look easy but is difficult. This might not look important but is the most important design step.
Thus this step of collecting information about the design requirements and to plan how to fit them on the circuit board is most difficult step. It comes primarily through experiences.
Some hints on collecting requirements and forming the initial design plan are:
- Frequency Spectrum in which the design will operate(KHz, MHz, GHz)
- The environment in which the design will operate
- Microcontroller/ Microprocessor based/ software or hardware processors
- Separation of Digital and Analog
- Specific protocols and standards, rules and regulation to be followed
- Required data rate and throughput
- Sensors, transducers, actuators and their interfacing to the circuit in case of processing plant design environment or robotic applications
2. Initial conversion of the requirement into circuit design
Once you know the requirements you should make an initial conversion of requirement into the design. That is what components, ICs, technology to use, seperation of analog blocks and digital blocks, consideration of PCB point of view etc. This is an initial guess and requires searching and researching through manufacturer datasheets about compacitbilities issues, voltage and power supply issues, aviability of different technologies(FPGA, microprocessors for example).
Again experience is the key. Use the block diagrams that was suggested in the first step to guide through the conversion. Start thinking about what devices you could use for most essential functional components/IC and critical components in your design. Then move on to other subsystem more in details in terms of operational concern, availability of the components, rules and regulation. Keep in mind the power supply.
This step is important because if for example, you have set out a plan but suppose that later during the printed circuit board design requirement changes- component is/ are simply not available or you come to know that you are not allowed to operate the device in the frequency spectrum that your design operates. Then the whole process of circuit design has to be repeated, replacing components is one thing the other is searching the new part and then there is change to be made in teh PCB board. This will spoil your design besides your time and effort.
The frequency spectrum gives some design gives information such as if the design is on audio frequency(KHz) then discrete component may be more suitable, if the design is on MHz radio frequency(RF) then transmission line effects should be focused in the PCB design stage, if the design is to work in the microwave. So this is important both in terms of circuit operation and from the circuit board design point of view.
With the frequency, throughput required and major functional requirement knowledge, you should try to convert the design requirement by choosing the best technology that fits your design. If your design is for commercial application then time to market, performance vs cost are important factor to consider.
Circuit design software should be used design the circuit. There are many free circuit design software and printed circuit board design software out there. Most of these software have both circuit design facility and PCB design facility. For example Eagle is a free circuit design and PCB design software. There are other software which are expensive but provides other useful feature such as Altium designer. It supports multiple PCB layers, 3D views, good routing algorithms etc.
3. Final Circuit Design
After you have done your initial circuit design according to specification, convert it a final circuit design. Here make replacements the components that would not work as planned in the initial circuit design. Make final checks on the ICs and components, their interconnection. Use circuit design software for this. At this stage you also may require simulation of your circuit to analyze expected output and compare with your desired ones.
4. Create Circuit Layout
Creating circuit layout means converting the circuit schematic into printed circuit board. Most of the software provides means of creating PCB for the circuit. That means the interconnection of the circuit component is not lost while you work on PCB. The circuit component with their actual size are placed on the printed circuit board manually one by one. There are also PCB software that does the component placement automatically. However the placement might not be best suitable for your requirement. In the manual mode, you start by placing the most critical such as processor or microcontroller on the printed circuit board, then you place power supply and external connector on the suitable edges of the PCB. Following this you would place the discrete components near to the bigger components according to the connection to the component in order to reduce the trace length. After placing and arranging all the components you would starting working on routing the traces. After routing, the trace width, vias, silk outlines etc are checked. They must comply to the PCB manufacturer capability to whom you will send the PCB files for manufacturing. PCB software like altium designer makes it easy for circuit designers to enter the desired trace width, via hole size, the separation of traces, the separation of traces with components etc.
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