Design Interface Ltd

Circuit schematics are the starting point for board level design. A rigorous checking procedure ensures that the electrical, physical and ordering information associated with the devices in our component libraries is complete and correct. Completed schematics are then subjected to internal review and if appropriate a client review prior to PCB layout.

The power and portability of hardware description languages such as VHDL and Verilog has made them the design methodology of choice for ASIC, FPGA and large CPLD designs. A library of tested functions described by HDL source code can be integrated into new designs to reduce design time. Our CAD tools also provide support for test bench development, source code simulation and post synthesis (gate level) simulation.

Whilst the design capture programs can detect some connectivity errors, design verification really starts with the simulator. Functional simulation confirms that the HDL source is logically correct before synthesis. Whilst it is possible to re-simulate using the signal delay information that is generated during compilation in order to determine whether the design will operate at the chosen frequencies; most designs are large enough to make this a very slow operation. The normal approach now is to set timing constraints and to use the compiler tools to check for timing closure. Debugging of the compiled design can then be achieved using the FPGA manufacturer's signal tapping tools which use spare logic and RAM inside the FPGA to implement an on-chip logic analyser. A Spice based analogue circuit simulator can be used standalone or coupled to the digital simulator to support mixed mode system development.

PCB layout is critical to achieving signal integrity, high operating frequencies and reducing emitted radiation. Minimising track lengths reduces signal cross talk and reflection. For this reason PCB component placement is guided or often actually done by the same person who did the electronic design, only this way can optimal placement be achieved. The particular requirements of sensitive analogue circuits, DC-DC converters or split power planes also receive due care such as hand routing or current steering. A choice of two state of the art autorouters is available to route boards, configurable design rules allow suitable routing strategies to be applied to each board, or area within a board. Post route information can be passed to a signal integrity and EMC analysis package which can help in the selection of appropriate termination and highlight where routing or screening should be improved.