printed circuit board design is based on the schematics , circuit designers to achieve the required functionality . Printed circuit board layout design mainly refers to the need to consider the layout of the external connections. Optimize the layout of the internal electronic components. Optimize the layout of metal wires and vias . Electromagnetic protection . Heat dissipation , and other factors . Excellent layout can reduce production costs , to achieve good performance of the circuit and thermal performance . Simple layout can be achieved by hand , complex layout needs the computer-aided design (CAD) implementation.
Introduction to Design
In high-speed design, controlled impedance characteristic impedance circuit board and is one of the most important and widespread problem. First, look at the definition of the transmission line : transmission line consists of two conductors composed of a certain length , a conductor used to send a signal , and the other for receiving signals ( remember " loop " instead of "ground " concept ) . In a multilayer board , the lines are each part of a transmission line , as a reference plane adjacent to the second line or loop. A line a " good" is the key to make the transmission line characteristic impedance is maintained constant throughout the line .
Circuit boards become critical " controlled impedance board" is to make all the characteristic impedance of the line to meet a specified value , usually between 25 ohms and 70 ohms . In the multi-layer circuit boards , the good performance of the transmission line characteristic impedance of the key is that it remains constant in the entire line .
However , what is the characteristic impedance ? Understand the characteristic impedance of the easiest ways is to look at the signal transmission encountered something. When the microwave along a transmission having the same cross-section as shown in a transmission line is moved, which is similar to FIG . Assumed that the distal end of the stepped wave and a voltage V to this transmission line , such as the one volt battery is connected to the transmission line ( which is located between the transmission line and the loop ) , once connected , the signal voltage wave along the line speed of light spread , its speed is usually about 6 inches / nanosecond . Of course, this is really the signal transmission line and the voltage difference between the loops , which can be any point from the adjacent points of the transmission line and the circuit to be measured. Figure 2 is a schematic diagram of the voltage signal transmission .
Zen method is to " generating a signal" , then 6 inches / nanosecond propagation velocity along the transmission lines . The first 0.01 ns 0.06 inches forward , when the transmission line has a positive excess charge and the loop has excess negative charge, the charge difference between the two is maintained at 1 volt difference between the two conductors , and two conductors which form a capacitor .
0.01 in the next nanosecond , but also the period of 0.06 inches voltage transmission line from 0 to 1 volt adjustment , which must be added a number of positive charges to the transmission line , and add some negative charge to the receiving line . Every move 0.06 inches , must put more charge moves to the transmission line , and the more negative charge added to the circuit . Every 0.01 nanoseconds , the transmission line must be charged another paragraph , and then propagate the signal to start along this section . Charge from the front end of the battery cable , when moving along this line , give a continuous portion of the transmission line charging , thus forming the loop between the transmission line and the voltage difference of one volt . Advancing 0.01 per nanosecond , you get some of the charges (± Q) from the battery in a constant time interval (± t) flowing from the battery within a constant power (± Q) is a constant current.
Negative current actually flowing into the circuit and a positive current flowing out of the same, but just in front of the wave alternating current signal through the upper and lower lines form a capacitor , the end of the cycle .
Design Software
First, the domestic use of the relatively large number of protel, protel 99se, protel DXP, Altium, which is a development of the company , escalating software ; Altium Designer 9.1 is the current version of relatively simple design is more casual, but do these complex pcb software is not very good .Two , Cadende spb software Cadende spb This is Cadence software , the current version of the Cadence SPB 16.5; ORCAD schematic design which is the international standard ; which PCB design, simulation, very full , with up complex than protel, mainly requirements, set up complex ; but do the requirements for the design , so the design together with less than protel obviously powerful.
Three , Mentor 's BORDSTATIONG and EE, which BOARDSTATION due only applies to UNIX system is not designed for the PC , so people use less ; currently MentorEE version of Mentor EE 7.9 and Cadence spb belong to the same levels of PCB design software, it cadence spb worse in some places than it is to pull strengths , fly line , known as the king of the fly line .
Four , EAGLE Layout which is Europe's most widely used PCB design software. PCB design software mentioned above , with a relatively large number of , Cadence spb inside and MentorEE is worthy of the king . If you are a beginner , I think Cadencespb PCB design better, it can give the designer to develop a good design practice , but also to ensure good quality of design.
PCB Layout design grid setting skills
Design needs to be different at different stages of the points set at the layout stage can be carried out using a large grid device layout ;For IC, connectors and other large non-locating devices , you can use the grid of 50 ~ 100mil precision layout , and for resistors and capacitors and inductors and other passive small devices can be carried 25mil grid layout . Accuracy in favor of large grid alignment and appearance of the device layout .
PCB layout rules :
1 , under normal circumstances , all of the components should be arranged on the same side of the board, only the top-level element too close to some of the highly limited and heat a small device , such as chip resistors, chip capacitors, stickers chip IC , etc. on the lower layers.
2 , under the premise of guaranteed electrical performance , components should be placed on the grid and aligned parallel or perpendicular to each other , in order to clean, beautiful , does not allow overlapping elements in general ; elements are arranged to be compact , components should be on the entire layout distribution , density consistent .
3 , the different components on the circuit board adjacent minimum distance between the pad pattern should 1MM or more.
4 , from the edge of the board is generally not less than 2MM. Optimal rectangular board shape , aspect ratio of 3:2 or 4:3 . Circuit board foot by greater than 200MM 150MM, consider the circuit board can withstand mechanical strength.
PCB layout techniques:
In the PCB layout design to analyze the circuit board unit , according to the layout from the function , when all the components of the circuit layout , to comply with the following principles:
1 , the circuit arrangement in accordance with the position of each process function of the circuit unit , the signal flow so easy layout , and to maintain the same direction as the signal .
2, the core components of each functional unit centered around him for layout. Components should be uniform, overall , compact arrangement on the PCB, minimize and shorten the leads and connections between the various components .
3 , the circuit at high frequency operation , to consider the distribution parameters between components . General circuit should be possible to make components arranged in parallel , so not only beautiful, but also easy to install dry , easy to mass production.
Special components and layout
In the PCB , the special high-frequency components is the key component part of the circuit core components susceptible to interference , components with high pressure , heat large components, as well as some heterosexual components , the location of these particular components requires careful analysis , done in line with the layout of the circuit functional requirements and production needs. Improper placement of their compatibility problems may arise circuit , signal integrity problems , resulting in failure of PCB design.
First consider in the design of PCB size How to place special components . Tesco fast pcb size that is too large, the length of the printing line , the impedance increases, the anti- drying capacity decreased , the cost is increased ; too small , good heat dissipation , and near the lines susceptible to interference . After determining the size of the PCB , in determining the location of specific components of the pendulum side . Finally, the functional units of the circuit layout of all components . Location specific components in the layout generally comply with the following principles:
1 , the shortest possible connection between the high-frequency components , trying to reduce their distribution parameters and electromagnetic interference and mutual . Susceptible to interference from the components can not be too close to each other , the input and output should be kept away .
2 Some components or wires may have a higher potential difference , should increase their distance to avoid accidental discharge caused by a short circuit . High voltage components should be placed out of reach of the hand .
3 , weighing more than 15G components , can stand to be fixed, and then welding. Those heavy and hot components , should not be placed on the board , should be placed on the main chassis of the bottom plate , and considering the heat. Keep away from heat sensitive components components .
4, with the potentiometer , adjustable inductors , variable capacitors , micro-switches , such as adjustable layout of components should be considered piece wrench structural requirements , some of the frequently used switches under construction permit, should place hand easily accessible place . Layout components to a balanced , there are degrees of density , not top-heavy .
A successful product , it is necessary to pay attention to the intrinsic quality . But to take into account the overall appearance , both of which are relatively perfect wrench in order to become successful products.
Placing components in general order:
1 , is placed close cooperation with the structure of components, such as electrical outlets , lights, switches, connectors , etc.
2 , placing special components , such as large components, heavy components, heating components , transformers , IC and so on.
3 , placing small components.
Check the layout
1, the circuit board size and dimension drawings are consistent processing .
2, the layout of the components are balanced, neatly arranged , if they have all finished cloth .
3 , all levels of the presence or absence of conflict . Such as components , frame , India needs the private level is reasonable.
3 , common to the components are easy to use. Such as switches, plug-in boards inserted into the device and require frequent replacement of components and so on.
4 , thermal components and heating components are reasonable distance .
5, the heat dissipation is good.
6 , the line interference is to be considered.
Specific methods
The purpose of the role
1.1 specification design work, increase productivity and improve product quality.
Scope
1.1 XXX development of the company 's Super VCD VCDDVD audio products .
Responsibility attitudes
All electronic engineers , technicians and computer draftsmen 3.1 XXX Development Department .
Qualifications Training
4.1 electronic technology infrastructure ;
4.2 has knowledge of basic computer operation ;
4.3 PCB familiar with using computer graphics software .
Guiding
5.1 Minimum foil width : 0.1MM, 0.2MM edge of the panel to foil the minimum 1.0MM
5.2 copper minimum clearance : 0.1MM, panel : 0.2MM.
5.3 copper plate edge minimum distance 0.55MM, element and a minimum distance of the plate edge 5.0MM, plate and the plate edge distance is minimum 4.0MMSize
5.4 General through-hole mounting element pad ( diameter ) twice the aperture , dual-panel minimum 1.5MM, single panel minimum 2.0MM, Yee (2.5MM) If you can not use a circular pad with a circular welded waist plate , small as shown below ( if any standard cell library , then the standard cell library prevail )
5.5 electrolytic capacitors untouchable heating elements , high power resistors, thermistors , pressure , heat , etc. solution capacitance minimum interval between the radiator 10.0MM, its components to the heat sink minimum spacing 2.0MM.
5.6 Large components ( such as: transformers, electrolytic capacitors diameter 15.0MM above , the high current sockets, etc. ) to increase copper and tin area below ; partially shaded area to be equal to the minimum fat pad area .
5.7 Can not have copper screw holes within a radius of 5.0MM ( required ground outside ) components. ( According to diagram required ) .
5.8 does not have a screen on the tin bit of oil .
5.9 Center distance of less than 2.5MM pad , the pad perimeter adjacent parcels have oil printing , ink width 0.2MM ( recommended 0.5MM).
5.10 jumpers do not put under IC below or motors, potentiometers , and other bulky metal components.
5.11 PCB design in a large area (more than about 500CM2 above ) to prevent excessive bending furnace PCB board , PCB board to stay in the middle of a wide gap of 5 to 10MM hold components ( traces ) , used in the tin stove when coupled with the PCB to prevent bending layering .
5.12 Each grain of the transistor must be labeled e, c, b feet on screen .
5.13 needs after soldering tin stove elements , tin plate to drive away place, and tin to the opposite direction, depending on the size of the hole is 0.5MM to 1.0MM
5.14 double panel design should pay attention to , metal components , plug-in enclosure with PCB contact pad can not open the top , be sure to use green oil or oil screen cover ( eg feet of crystal ) .
5.15 In order to reduce solder short circuit , all the double-sided PCB , vias not open green oil window .
5.16 on every piece of PCB must be marked with a solid arrow over the direction of tin stove :
5.17 The minimum distance between holes is 1.25MM ( double panel invalid )
5.18 layout , IC DIP package placed in the direction of the vertical direction must be over the furnace , non- parallel , as shown below ; If you have difficulty layout that allows horizontal IC (OP package DIP IC placed opposite direction ) .
5.19 horizontal or vertical direction wirings by 45 degrees vertically to go into the horizontal transfer .
5.20 member is placed horizontally or vertically.
5.21 screen character is placed horizontally or turn right 90 degrees .
5.22 If the foil into a round pad width than the diameter of the circle pad hours , you need to add teardrop .
5.23 Number coding and design materials to be placed on board the space .
5.24 where no reasonable connection for ground or power use .
5.25 cabling as short as possible , pay special attention to the clock line , low frequency circuit signal lines and all the wiring to be shorter.
5.26 ground and power supply systems and digital circuits analog circuits to be completely separate.
5.27 If there is a large area of ground and power line area ( area of more than 500 mm2 ) on the PCB should be partially opened window.
5.28 electrical plug PCB positioning holes defined as follows , not put shaded components, except the hand inserted components, the range of L is 50 330mm, range of H is 50 250mm, fruit less than 50X50 will have to be electric plug mold puzzle If it is to hand over 330X250 flapper . The long side of the hole to be positioned .
Basic concept
Fewer vias
Once selected through the hole , be sure to handle it with the gap surrounding entities , especially in the middle layers and easily overlooked through the gap is not connected with the line hole vias , if it is automatic routing , in the " number of vias minimize "(Via Minimiz8tion) sub-menu , select " on " key to automatically resolved. ( 2 ) set the required flow , the greater the size of the desired vias , such as power and ground vias coupled to the other layers should be used in a large number .
Silkscreen
Overlay
To facilitate installation and maintenance of such circuits , printed on both upper and lower surfaces of the printed board and the desired character code, such as flag patterns , and the nominal value of such components numerals , the shape of the contour member and manufacturers logo , production date , etc. . Many beginners when relevant content designed silkscreen only note text symbols positioned neat appearance , ignoring the actual effect of the system out of the PCB . They printed board design , the character is not being blocked elements invaded the area wiped fluxing credit , there 's the element label hit the adjacent elements , so all sorts of designs will bring great for assembly and maintenance inconvenience. Correct silkscreen character layout principle is: " no ambiguity , they must attack , nice ."
SMD package
Particularity
Protel package library has a large number of SMD package, namely the surface welding devices. In addition to the small size of these devices is characterized by one-sided distribution of the maximum per -pin holes. Therefore , the choice of where you want to define these devices face good device to avoid "missing pin (Missing Plns)". In addition, the relevant text of these components can be placed with the label where the surface element .
Fill Area Fill grid area (External Plane) and the filling region (Fill)
As the name implies both , network-shaped region is filled with a large area of the copper foil processed into a mesh , the fill area is only intact foil . Beginners design process on the computer often can not see the difference between the two , in essence , as long as you enlarge the surface after a glance . It is usually not easy to see because the difference between the two , so pay attention to the use of more distinction between the two, to emphasize is that the former have a stronger role in the high-frequency interference suppression circuit characteristics apply to be done large areas populated places, especially in some regions as the shielded area , is particularly appropriate when the partition or large current power cord. The latter are used for the general line end or transition zones that require a small area populated areas.
Pad
Pad is the most contact with the PCB design is the most important concept, but for beginners , but it 's easy to overlook the selection and correction , invariably using a circular pad design. Select the type of element to the pad considering the shape, size , arrangement of the vibration and heat , the driving force of the element and other factors . Protel gives a range of different sizes and shapes of pads in the package repository, such as round , square , octagonal , square and round positioning pads , etc. , but sometimes this is not enough , you need to edit their own . For example, fever and a larger force , the current larger pads can be designed as a " teardrop " in the line output transformer pin pad design familiar TV PCB 's , many manufacturers is using this form. In general, self- editing pad except when talking about above , but also consider the following principles:
( A ) when the length of the shape to be considered inconsistent with the particular width of the connection side of the pad is not too large difference in size ;
( 2 ) selection of the length of the pad is often more effective when the asymmetry between the components need to take the lead angle of the line ;
( 3 ) the size of each component pad according to component pin holes were edited to determine the thickness , the principle is the size of the hole 0.2 - 0.4 mm larger than the pin diameter.
PCB pad placement :
1 . Method of placing the pad
Commands can be executed from the main menu Place / Pad, you can also use component placement Place Pad button in the toolbar .
After entering the place pads (Pad) state , the mouse will turn into a cross shape , move the mouse to click on the appropriate location to complete the pad placement.
2 . Property pads set
Set properties pads have the following two methods :
● When placing the pad with the mouse , the mouse will turn into a cross shape , press the Tab key will pop Pad ( Pad Properties ) Settings dialog box.
7-24 pads Properties Settings dialog box
● good pad has been placed on the PCB , simply double-click , you can also pop pads Properties Settings dialog box . In the pad properties dialog box has the following in several settings :
● Hole Size: inner diameter of the pad is used to set the size .
● Rotation: Set the rotation angle with a pad placed .
● Location: the center of the pad is used to set the position of the x and y coordinates.
● Designator text box: used to set the number pad .
● Layer drop-down list : You can choose from the wiring layer pads placed in the drop-down list .
● Net drop-down list : This drop-down list is used to set the network pads .
● Electrical Type drop-down list : used to select the pad electrical characteristics. There are three kinds of the drop-down list and select the mode : Load ( node ), Source ( source ) and Terminator ( end ) .
● Testpoint complex options : whether to set the pads as test points, test points can be done only at the top level and the bottom of the pad .
● Locked complex options : Select the check option , which means that the placement of the pads will be stationary.
● Size and Shape Options area : used to set the size and shape of the pad
● X-Size and Y-Size: pads are provided in the x and y dimensions .
● Shape drop-down list : used to set the shape of the pad with Round ( round ), Octagonal ( octagon ) and Rectangle
( Rectangle ) .
● Paste Mask Expansions Options area : used to set the flux layer properties.
● Solder Mask Expansions Options area : used to set the solder layer properties. [1] abc
Various types of film
Mask
These films are not only essential PcB production process , but it is a necessary condition for the welding element .
According to the location and its role "film" , "film" can be divided into the component side ( or solder side ) flux membranes (TOp or Bottom and component side ( or solder side ) solder mask (TOp or BottomPaste Mask) two class name suggests , flux is applied to the membrane pad , improved solderability performance of a film , which is slightly larger than the green board on each colored circle Bambi pads. solder mask opposite situation , in order to so that the board made to adapt the form of wave soldering , such as welding , requires copper pad on the board at the non- stick tin can , so all parts of the pad to be outside coated with paint , used to prevent these parts tin. seen , these two films is a complementary relationship whereby discussion , it is easy to determine the menu Similar settings "solder Mask En1argement" projects such as the .
Fly line
There are two meanings
Automatic network connection wiring for observation with a rubber band like , and after doing a preliminary component and transferred through the network layout table, with "Show commands you can see status of the network connection cross under the layout constantly adjust position elements make this cross least , to get the maximum automatic routing routability this step is very important , can be said to quicken power , more time , value ! addition, automatic routing end , also What network has not yet Bouton , but also to look through this feature. identify cloth after not pass network , available manual compensation , it is not necessary to use compensation " fly line " second layer of meaning, is the future of printing plates these network connectivity on the wire . to explain that if the circuit board is a high-volume automated production line , this can be regarded as 0 Ou fly line resistance , the resistance element having a uniform spacing of the pads to be designed .
PCB (Printed circuit board, PCB) which appear in almost every electronic device. If there is a kind of electronic parts in the device, then they are also set in the sizes of PCB. In addition to fixing a variety of small parts , the main function is to provide top of the PCB components are electrically connected . As electronic devices become more complex , the need for more and more parts , PCB top of the line with the part of the increasingly dense . Standard PCB looks like this. Bare board ( no top parts ) is also often referred to as "PCB Printed Wiring Board (PWB) ."
The board itself is made of an insulating substrate insulation, not easy to bend the material made into . Can be seen on the surface of the fine copper wiring material , the original copper foil covering the entire board , and in the manufacturing process is partially etched disposed , on the left part of the mesh lines becomes small . These lines are called conductors (conductor pattern) , or said wiring and connecting the circuit to provide the parts on the PCB .Parts to be fixed above the PCB, we will take their feet welded directly on the wiring . At the most basic PCB ( single panel ) , the parts are concentrated in one side , the wire is focused on the other side. Suppose we need burrows on the board , so that the pin to pass through to the other side of the board , so the parts are welded pin on the other surface. Because of this , PCB 's are called positive and negative parts surface (Component Side) and the welding surface (Solder Side).
If there are certain parts PCB top , you need to complete post-production can also be removed or put back , it will be used when the part is installed socket (Socket). Because the socket is soldered directly to the board , the parts can be any disassembly. Below see a ZIF (Zero Insertion Force, Zero Insertion Force dial type ) socket, which allows parts ( here refers to the CPU) can be easily inserted into the socket, it can be removed . Fixed pole socket beside parts can be inserted after your fixed .
If you want two interconnected PCB, generally we will edge connector commonly used in " Goldfinger " in (edge connector). Goldfinger contains many bare copper pad , in fact, is part of the copper wiring PCB pads . Typically connections, which we will insert a finger on the PCB appropriate slot on another piece of PCB ( commonly called slot Slot). In the computer, such as graphics card , sound card or other similar interface cards are connected to the motherboard through the finger .
Green or brown on the PCB is solder mask (solder mask) color. This layer is an insulating protective layer can protect the wire can be prevented from being welded to the part not the right place . In addition will be printed on the solder layer on the surface layer of screen printing (silk screen). Usually in it will be printed on text and symbols ( mostly white ) to mark the location of the parts on the board . Also referred to silkscreen icon plane (legend).
PCB proofing
The Chinese name of PCB printed circuit board known as printed circuit boards , printed circuit boards is an important electronic component is the support of electronic components ? Electronic components are provided by the electrical connection . Because it is produced by the use of electronic printing are called " printed " circuit board.
PCB proofing refers to the plant after the trial production of printed circuit boards in front of the main applications for the production of electronic engineers design better circuits ? PCB Layout and completed trial production of small quantities of PCB proofing process is . PCB proofing and production quantities are generally no specific boundaries are generally engineers in product design is not completed before the confirmation and completion of the test are known as PCB proofing.
PCB design analog / digital converter is amazing
High-speed analog / digital converter (High speed ADC) is usually an analog front-end circuitry PCB assembly consisting of the basic system . As the overall performance analog / digital converter performance element determines the system, so the system manufacturers tend to analog / digital converter as the most important component. This article will detail the operation of the principle of front-end ultrasound systems , and in particular on the role of an analog / digital converter in which the play .
When the front-end PCB design PCB circuit ultrasound systems , manufacturers must consider several important factors , so that appropriate trade-offs. Medical personnel can make the correct diagnosis is dependent on PCB circuit simulation key role in this process .
PCB circuit simulation performance depends on many different parameters , including crosstalk between channels , spurious signal dynamic range (SFDR) and total harmonic distortion. Therefore, the decision makers in the selection of the simulation before PCB circuit , these parameters must be carefully considered .
Analog / digital converter as an example , if the additional advanced serial LVDS driver PCB circuit board PCB can be reduced , and electromagnetic interference suppression of noise , etc., contribute to further improvement of the system PCB design . Miniaturization , high performance and full-featured ultrasound system manufactured products , resulting in continued production of low-power requirements of the market simulation IC, it has the amplifier , analog / digital converter and a small package of better integration.
System Overview
Ultrasound imaging system is the most commonly used and most sophisticated signal processing instrument that can help medical staff to make the correct diagnosis. The distal end of the ultrasound system , using extreme precision PCB analog signal processing circuit such as an analog / digital converter , low noise amplifier (LNA) , etc., and the performance of these circuits is an analog PCB determine the key factors in system performance .
Ultrasonic devices are very close to the radar or sonar system, but operating at a different frequency band ( range ) of the . Radar operating in GHz ( gigahertz ) range , the sonar in kHz ( kilohertz ) range , while the ultrasound system is operating in MHz ( megahertz ) range. The principle of these devices is almost the commercial and military aircraft used - array antenna radar system with the same mode of operation. PCB designers radar system is operated using a phased array beamformer as principles that was later adopted by the ultrasound system and improved PCB designers .
In all ultrasound system instruments , there is a multi- conversion at the end of a relatively long cable ( about 2 meters) . Cables containing up to 256 micro- coaxial cables , is one of the most expensive components of the ultrasound system . Ultrasound systems typically equipped with multiple probes of different converters allow medical personnel responsible for operating the site in accordance with the needs of the scanned image can be used to select the appropriate converter.
Generated image
The first step of the scanning process , each of the converter is responsible for generating a pulse signal , and the signal sent out . Sent out in the form of pulse signals of high frequency sound waves through the body tissue , the transmission speed of the sound wave is generally between 1 and 20MHz. The start pulse signals in the human body detection timing and scaling . When the signal through the body's tissues , some of which sound waves are reflected back to the converter module , by the converter is responsible for detecting potential of these echoes ( after conversion will send out the signal will be switched immediately switch to receive mode ) . Depending on the intensity of the echo signal in the body position of the echo signal reflection point . Back reflection signals directly from the subcutaneous tissue is generally strong , and from deep parts of the human body reflected signal is very weak .
Due to health and safety laws on the maximum amount of radiation required by the human body can withstand , so engineers designed electronic PCB receiving system must be extremely sensitive. Area close to the human skin disorder , called near-field (near field), the energy is reflected back is high .
However, if the conditions deep in the body region portion , is called the far field (far field), the received echo is very weak, and therefore must be amplified 1000 times or more.
In the far-field imaging mode , the performance limitations from all the noise present in the receive chain . Converter / Cable Assemblies and low noise amplifier receiving system are the two largest sources of external noise . The near- field imaging mode, the performance limit is from the size of the input signal. The ratio between the two determines the ultrasound signal dynamic range of the instrument .
When the receiver through a series of phase transition , the amplitude of the echo cumulative adjustment and intelligent energy and other processes , both high-resolution images can be obtained . When using the converter array shift and adjust the amplitude of the received signal allows the principle of scanning devices with fixed-point observation site functionality. After a sequence of observations in different parts of the positioning , you can create a combination of ultrasound images .
Poly wave can complete portfolio of digital signal processing . In the digital wave together , back in the body via a point reflection echo pulse signals are first stored in each channel within it , and then arranged according to their priorities together and fixed to become coherent signals , and then come together . Such a plurality of analog / digital converter with the output of the aggregation treatment can increase the gain in the channel since the noise is uncorrelated .
The basic analog poly wave technology has become outdated methods , mostly used in modern digital poly wave ) . The image formation is in the layer closest to the converter system simulation sampling , storing them , and then digitized them together from.
DBF system requires accurate channel to channel matching . Require a two -channel VGA ( video graphics array ) , this situation will continue until the analog / digital converter device sufficient to meet the large dynamic range , and can provide a reasonable cost , and low power consumption.
Ultrasound imaging mode
1 grayscale images - black and white images to produce basic
Analysis of the images will be so small as one millimeter units , showing images are those returned by the energy emitted from the energy and detection ( as previously described ) .
Two Doppler imaging (Doppler) -. Doppler mode (Doppler mode) by tracking the echo frequency offset to detect the speed of movement of objects in various environments . These principles are applied in the case of checking the blood flow in the body , or other liquids . This technique is a series of sound waves into the body through the emitter , and the reflected wave of the fast Fourier transform (Fourier Transform, FFT) processing . This calculation method to determine the frequency of the signal processing components from the human body, as well as their relationship with the fluid velocity .
3 veins and arteries modes - Such approach is combined with Doppler imaging and grayscale modes. Rate and rhythm can be obtained by processing the audio signal generated by the Doppler shift .
Design steps
Schematic design is the foundation of the entire circuit design , it is designed to have a direct effect of PCB design decisions behind . In general , the design of the circuit diagram below.
The specific design of the steps of:
First, start ProtelDXP Schematic Editor
The second step, to set the size of the circuit schematic and layout
The third step is necessary to remove from the library components are placed in the working plane
A fourth step according to the design needs of the connection part
The fifth step of wiring the components to be adjusted
The sixth step, save the document has been drawn schematic good
The seventh step , the printout drawings
The main flow
In PCB design, in fact, before the official wiring , even after a very long step , the following is the main PCB design process:
System Specifications
First you have to plan out the system specifications of the electronic device . The system includes a function of limiting the cost , size, operation situation and so forth.
Function Block
Next, the system must produce a functional block diagram . Relations between the box must also be marked.
The system is split several PCB PCB system partition number , then , not only in size can be reduced , but also allows the system has the ability to upgrade and exchange parts . System function block diagram provides a basis for our division . Like a computer can be divided into motherboards, graphics cards, sound cards , floppy drives , and power , and so on .
Decided to use the encapsulation method , and the size of each PCB circuit when the quantity of each PCB technology and have decided to use the good, the next step is to determine the size of the board . If the PCB design is too large, the packaging technology will change , or for re- segmentation operation . When selecting technology , but also the quality and speed of the circuit diagram are considered inside.
High-speed process
The traditional PCB design flow , increasing the signal rate , and even high-speed PCB design GHZ above no longer applies . High-speed PCB design and simulation, and verification must be perfect together. The simulation is not in the traditional sense of a simple design for verification , but before embedding simulation throughout the design process has been the rule , rule -driven design , to final post- simulation.
Precautions
( 1 ) avoid the edge of the PCB important signal line arrangement , such as a clock and reset signals.
( 2 ) chassis ground and signal line spacing of at least 4 mm ; chassis ground to keep the aspect ratio of less than 5:1 to minimize inductance effects.
( 3 ) has been determined by the position of the device and the line LOCK function to lock it , so that in the future is not malfunction.
( 4 ) The minimum wire width of not less than 0.2mm (8mil), precision in high-density printed circuit, conductor width and spacing is generally preferable to 12mil.
( 5 ) between the alignment pin DIP IC package , 10-10 and 12-12 can be applied to the principle that when both-feet by two lines, the diameter of the pad can be set 50mil, the line width and pitch are 10mil, between his legs when only through a line , pad diameter can be set to 64mil, line width and line spacing are 12mil.
( 6 ) When the pad diameter of 1.5mm, to increase the peel strength of the pad , can be not less than the length of 1.5mm, 1.5mm and a width of oblong pads.
(7 ) Design encountered traces connecting smaller pads , pads and traces the connection between To design a teardrop-shaped , so that the pad is not easy to peel, easy alignment with the pads off .
(8 ) large copper design should open a window on copper , plus vents and open windows are designed to mesh .
( 9 ) the shortest possible connection between the high-frequency components to reduce electromagnetic interference parameters and their distribution between each other . Susceptible to interference components can not endure too close to each other , the input and output components should be kept away .
Special components
1 , high-frequency components: a connection between the high-frequency components as short as possible , try to reduce electromagnetic interference distribution parameters and the connection between them , is not susceptible to interference components too close . Inputs and components from affiliated affiliated output should be as large as possible between .
2 , has a high potential difference components: the distance should increase with a high potential difference between the components and connections, to avoid damage to the components when accidental short circuit . In order to avoid the occurrence of creepage , the general requirements of the copper film line distance between the potential difference 2000V should be greater than 2mm, if a higher potential difference for the distance should also increase . Devices with high voltage , you should try is arranged in the hands of the reach of debugging .
3 , much of the weight of components: such elements should have the bracket , and for large and heavy , heat and more components , not mounted on the circuit board.
4 , heating and thermal components : attention away from the heating element should be sensitive components.
PCB design rules and assembly considerations
In the design, PCB board from the assembly point of view , to consider the following parameters:
1 ) The maximum diameter of the hole according to the material conditions (MMC) and with minimal material conditions (LMC) to decide. A non-porous support such components should be selected diameter , subtracting from the MMC MMC pin holes, resulting in a difference 0.15 -0. 5mm between . And the pin strip , the diagonal and non- nominal inner diameter difference between the pin supporting hole will not exceed 0.5mm, and less than 0.15mm.
2 ) a reasonable place smaller components , so that it will not be covered larger components .
3 ) the thickness of the solder should not exceed 0.05mm.
4 ) screen printing logo can not intersect any pads .
5 ) Upper half and the lower half of the board should be the same, in order to achieve structural symmetry. Because asymmetric circuit board may become bent.
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