mixed signal design methodology- Top-down design approach

To address the above issues of bottom-up design, many design teams are looking at the top-down design methodology. In a basic top-down approach, the architecture of the chip is defined as a block diagram and simulated and optimized using either an MS-HDL (Mixed-Signal Hardware Descriptive Language) simulator or a system simulator. From the high-level simulation, requirements for the individual circuit blocks are derived. Circuits are then designed individually to meet these specifications. Finally, the entire chip is laid out and verified against the original requirements
A well-designed top-down design process methodically proceeds from architecture to
transistor-level design. Each level is fully designed before proceeding to the next and
each is fully leveraged in design of the next. It acts to partition the design into smaller,
well-defined blocks and so allows more designers to work together productively. This
tends to reduce the total time required to complete the design. A top-down process also
formalizes and improves communication among designers. The formal nature of the
communication also allows designers to be at different sites and still be effective.
Following a top-down methodology also reduces the impact of changes that come late in
the design cycle. If the circuit has to be partially redesigned, the infrastructure put in
place as part of the methodology allows the change to be made quickly. The models can
be updated and the impact on the rest of system can be quickly evaluated. The simulation
plan and the infrastructure for mixed-level simulations are available and can be quickly
applied to verify changes.