Cadence OrCAD PCB Designer
Cadence OrCAD PCB Designer Cadence OrCAD PCB Designer
Fixup. The next problem is that only 7 pins are defined on the electrical symbols for the op-amps but the package has 8 pins. You might expect that the software would assume that undefined pins are not connected but it does not: It must be told this formally. This should have been done by Cadence in their libraries but we have to do it ourselves at present. Here’s how. 1. Select one of the op-amps and choose Edit > Part, which brings up the Part Editor. 2. Choose Options > Part Properties. . . , which brings up the list of User Properties. 3. Click the New. . . button. Give the new property the name NC, which stands for No Connect, and the value 8, which is the number of the unconnected pin. (Use a list separated by commas, such as 7,8, if more pins are not connected.) 4. Click OK to get rid of the dialog boxes and close the Part Editor. Choose Update All so that this change is applied to all LF411 parts in your design. Print your schematic when it has been completed correctly and survived the DRC. ☛ Milestone: Have your drawing checked before you go any further. 6.4 Import into PCB Editor and place the components You can now create a netlist and send the design to PCB Editor as before. Check the Session Log: You can ignore any warnings (I got 6) about RVMAX and CMAX but check with a demonstrator if you get any others. We’ll place the components using a different technique this time. Choose Place > Quickplace. . . from the menu bar. The defaults should be suitable (Place all components, Around package keepin, Top). Click Place then OK. Your components are now arranged at the top of the board, ready for you to move them into position. Place the components to resemble the schematic drawing and adjust them to make the ratsnest simple with as few crossings as possible. This is really important. It is easy to route the tracks on a well-placed board; conversely, a poorly-placed board will need long, convoluted tracks or may even be unroutable. Hint for demonstrators. Some students will complain that Quickplace has not placed their components. The usual problem is that the screen has been zoomed to fit the board but the components are above the board and therefore out of sight! ❦ Run a Design Rules Check when the components have all been placed and save your board. 6.5 Preparation for routing It is usual to make power tracks wider than signal tracks as they have to carry more current. Our tracks are already so wide that it’s barely necessary but we’ll do it for future reference. 1. Choose Setup > Constraints > Physical. . . from the menu bar. This brings up the Constraint Manager and a Tip of the Day if you are unlucky (sigh). 2. The left-hand part of the window shows the various properties that can be edited. Click on All Layers under Net. See figure 13 on the next page for guidance. 30
Figure 13. Constraint manager after changing the widths of the three power nets. 3. The main part of the window now shows a list of the nets in your design. Most of them have random-looking numbers, such as N00451, but a few are named. These are the nets that carry power, to which we assigned names in Capture: VCC, VEE and GND or something similar, depending on the symbol that you chose. 4. Change the minimum width for these three nets from 20 to 30 mil. 5. Choose File > Close to return to PCB Editor. 6.6 Autorouting a single-sided board In this more complicated design we are going to use the autorouter to do the routing. You will do this twice: first as a single-sided board as in the one-transistor amplifier, and later as a double-sided board. It should be possible to route all tracks on the single-sided board if you have laid it out well but the double-sided board may have a simpler layout with a smaller total length of track. The Allegro autorouter is called SPECCTRA. Save your board before autorouting in case anything catastrophic goes wrong. There are two ways of routing the board automatically, both shown in figure 4 on page 11: Everything can be done from within PCB Editor or you can run SPECCTRA as a separate application. The first is more convenient when it works but the second offers finer control. Autorouting from within PCB Editor Choose Route > Route Automatic. . . from the menu bar. This brings up the Automatic Router dialogue box. Unfortunately it often causes a fatal error message that SPECCTRA quit unexpectedly, in which case you will have to use the other method. If it does work, select Use smart router for the Strategy. For a single-sided board deselect the box next to the TOP Routing Subclass. You might wish to experiment with the Routing Direction for the bottom layer. Click Route and wait for the results to come back. Click on the 31
- Page 1 and 2: Electronic Design Project 2 Cadence
- Page 3 and 4: The first two should be familiar fr
- Page 5 and 6: 2. The base-emitter junction of a t
- Page 7 and 8: • Select an Analog or Mixed A/D p
- Page 9 and 10: Figure 2. Gain as a function of fre
- Page 11 and 12: Capture Draw schematic PCB Editor S
- Page 13 and 14: 2. Choose Edit > Properties. . . fr
- Page 15 and 16: Figure 6. Completed dialogue box fo
- Page 17 and 18: Figure 7. Completed dialogue box fo
- Page 19 and 20: Figure 8. Screenshot of OrCAD PCB E
- Page 21 and 22: Figure 9. The Placement dialogue bo
- Page 23 and 24: • To rotate a selected component,
- Page 25 and 26: Hint for demonstrators. Some studen
- Page 27 and 28: • Usually the Plot scaling should
- Page 29: Table 2. Footprints for instrumenta
- Page 33 and 34: Figure 15. Screenshot of SPECCTRA,
- Page 35 and 36: Figure 17. My one-sided layout afte
- Page 37 and 38: Figure 18. Printout at actual size
- Page 39 and 40: • The pins of the integrated circ
- Page 41 and 42: in 2007-08, which was an electronic
- Page 43 and 44: Property Editor with Edit > Propert
- Page 45 and 46: 9 Summary: PCB design flow This lis
- Page 47 and 48: A Where to learn more The online he
- Page 49 and 50: B Power-user tips and random jottin
- Page 51 and 52: Figure 24. Padstack editor settings
- Page 53 and 54: Figure 26. Screenshot and photomask
- Page 55 and 56: 3. The list on the right-hand side
- Page 57 and 58: • Our local allegro library doesn
Figure 13. Constraint manager after changing the widths of the three power nets.<br />
3. The main part of the window now shows a list of the nets in your design. Most of them<br />
have random-looking numbers, such as N00451, but a few are named. These are the<br />
nets that carry power, to which we assigned names in Capture: VCC, VEE and GND or<br />
something similar, depending on the symbol that you chose.<br />
4. Change the minimum width for these three nets from 20 to 30 mil.<br />
5. Choose File > Close to return to <strong>PCB</strong> Editor.<br />
6.6 Autorouting a single-sided board<br />
In this more complicated design we are going to use the autorouter to do the routing. You<br />
will do this twice: first as a single-sided board as in the one-transistor amplifier, and later as<br />
a double-sided board. It should be possible to route all tracks on the single-sided board if<br />
you have laid it out well but the double-sided board may have a simpler layout with a smaller<br />
total length of track. The Allegro autorouter is called SPECCTRA. Save your board before<br />
autorouting in case anything catastrophic goes wrong.<br />
There are two ways of routing the board automatically, both shown in figure 4 on page 11:<br />
Everything can be done from within <strong>PCB</strong> Editor or you can run SPECCTRA as a separate<br />
application. The first is more convenient when it works but the second offers finer control.<br />
Autorouting from within <strong>PCB</strong> Editor<br />
Choose Route > Route Automatic. . . from the menu bar. This brings up the Automatic Router<br />
dialogue box. Unfortunately it often causes a fatal error message that SPECCTRA quit unexpectedly,<br />
in which case you will have to use the other method.<br />
If it does work, select Use smart router for the Strategy. For a single-sided board deselect<br />
the box next to the TOP Routing Subclass. You might wish to experiment with the Routing<br />
Direction for the bottom layer. Click Route and wait for the results to come back. Click on the<br />
31
Change language