R obust
L ow
P ower
VLSI
Yousef Shakhsheer yousefshak@gmail.com
Robust Low Power VLSI Group
Revision 1.0

Revision History
Revision History Date
1.0
4/30/12
Reviser
Yousef Shakhsheer (yas5b)
Notes
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Overview
This tutorial is intended to get people started with the PADS flow and basic PCB schematic capture.
We use PADS Logic 9.3.1 for schematics and PADS
Layout 9.3.1 for PCB layout for this tutorial.
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Outline
 Schematics
 Creating a library/components
 Create a schematic
 Exporting designs to netlists
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Schematics
 The schematic is a top-level symbolic representation of the circuit you are designing
 It affiliates parts (symbols in the schematic) with nets (connections in the schematic)
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Open a new schematic
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Libraries
 Libraries hold sets of parts (symbols and PCB decal information)
 Libraries are not affiliated with a particular schematic or design so that parts can be reused and shared
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Creating a Library
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Creating a Library
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Creating a Library
Keep on pushing up until tutorial is on the top of the list
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Parts
 Parts reside in libraries, they contain all the information required to place a component onto a PCB
 Affiliate schematic symbols with a PCB footprint
(see Layout tutorial for more)
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Create a part
 Lets create a part
 SMT: LT1167 - Single
Resistor Gain
Programmable,
Precision
Instrumentation
Amplifier
 http://www.linear.co
m/product/LT1167
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Create a part
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Create a part
Add part information. See the pictures for details.
Hit OK.
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Symbol
 Symbols are what show up when we add a part to a schematic
 We can either create this symbol by-hand (from a set of pins and lines) or use a wizard to autogenerate it for us
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Let’s draw a symbol
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Setting a Decal Name
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Lets draw the decal
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CAE Decal Wizard
A simple tool for quick creation of multi-pin symbols.
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Return to the part editor.
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Back to the schematic
File→Exit Parts Editor
You will get two warnings. You can ignore them for the time being
Warning: Duplicate pin name RG for pin number 8 on Gate A.
Warning: Part has no
PCB Decal assigned.
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Let’s add a part to our schematic!
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Add a LT1167 and a 1206 resistor
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Schematic Basics
 F2 to create wires
 Two types of connections
 Physical wire connection
 Off page connectors: click on the wire and then right click, “Add off page connectors”
 Additional you can use the ground symbol by click on the first part of the wire and then right clicking and selecting “Ground”
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Lets put together an example schematic
Part numbers:
 U1- LTC1167
 U2- LDO – Digikey P/N - LP3996SD-3333CT-ND
 U3- MicroUSB – Digikey P/N - A31727CT-ND
 P1- Power Jack – Digikey P/N - CP-037A-ND
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Example (this is not a functional circuit)
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Other schematic entry tips
 Right click on the schematic for the selection menu
 You can make it so you can only click on/select only certain objects
 Always change the background color before exporting/printing any schematics from PADs layout
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Netlists
 The netlist affiliates a group of symbolic pins with a what is referred to as a “net”
 We sometimes label these nets for convenience
(Vcc and GND are common names) but we do not have to name all the nets
 When the netlist is exported all non-named nets have their names auto-generated so the layout tool can correctly affiliate all the pins
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Export an Netlist for Layout
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On Netlist Export
Two files will open up.
1. Whatever you named your netlist.asc – The netlist for your schematic
2. tutorial.err – An error report file (make sure you always check this)
At this stage:
1.
You haven’t assigned PCB decals, so you should see errors for this
2.
You may also see single ended nodes
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Bill of Materials
 Once we have created a PCB we will need to order all the components necessary to populate the board
 The Bill of Materials (BoM) makes this easy and outputs a simple list of items in the schematic
 Any field included in the attributes of a part included in a schematic is allowed to be added to the BoM for that schematic, this means we can have columns like DigiKey Part Number,
Approximate Cost, or even product page URL if these attributes are added to the parts on creation
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Creating a Bill of Materials
 File -> Reports
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BoM Export
 The BoM is a text-based report but a CSV output file can be created (this allows an effected export to Excel)
 The BoM is a useful tool both for ordering parts and also for population as it affiliates part numbers with part reference numbers in the schematic and layout
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See the Layout tutorial for creation of an affiliated PCB design
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