Cadence OrCAD PCB Designer

Figure 3. Gain as a function of frequency for different bypass capacitors.
Hint for demonstrators. My results are in figure 3. Increasing the bypass capacitor improves
the gain until it is limited at low frequency by C 1
instead. There isn’t much difference between
the results for 100 µF and 1000 µF so I would use 100 µF. ❦
4 Preparation for PCB layout
Once the design of the circuit has been finalised, it should be laid out on the printed circuit
board (PCB). This takes a few steps before you leave Capture. The overall design flow for
making a PCB is shown in figure 4 on the next page and there is a summary in section 9.
4.1 Edit the circuit
First, the ‘virtual components’ in the schematic must be replaced by real components. Here
this means the voltage sources and param block. There is no way that you can build a real
circuit with a param block for instance! (Well, you could use a pair of sockets and unplug the
component to change it.) The real circuit has connectors for input, output and power, which
must be placed instead. This is shown in figure 5. The types of connector are HEADER 2 and
the like. They are in the connector library, which is in the directory one level above pspice.
The connectors are oriented so that pin 1 is connected to ground in both cases. It is shown by a
square marker on the PCB. I have changed the names to make them more descriptive than the
defaults, such as HEADER 2; do not edit the references J1 and J2. Add text to label the pins
of each connector and put your name on the circuit, or you won’t be able to identify it when it
comes out of the printer.
Hint for demonstrators. Some students change the Reference (J1 or J2) of the connectors
to Input or Output instead of changing the Value (HEADER 2 or HEADER 3). This causes
trouble with the netlister later on. ❦
10