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Principles of Top-Down Mixed-Signal Design

Design Drivers

FIGURE 1

The expected investment and return for the same product developed using three different approaches.

$

time

Incremental Investment and Return

$

Accumulated Investment and Return

time

Efficient and Timely

Inefficient and Untimely

Inefficient but Timely

the market leadership position is largely determined and the need to develop the product in a timely manner is balanced by the need to control development costs.

To get a product to market in a timely manner one must have a design methodology that reduces the number of design and silicon iterations, maximizes the effectiveness of each designer, and makes it possible to effectively use more designers to speed the design by avoiding the “baby creation” problem. With the existing baby creation process, it takes nine months to create a new human baby. Adding more women to the process does not get the baby out any faster. To a large extent, the same is true with the current analog design process. Putting more designers on an analog design might get the design out somewhat sooner, but there are limits. Existing design methodology has limited oppor- tunities for parallelism. In other words, there are several inherently serial tasks in the current design methodology that limit the reduction in time-to-market that results when adding more engineers to the product development team. A new design methodology is needed that is intrinsically more parallelizable.

2.2 Complexity

Moore’s observation that the number of transistors available on an integrated circuit doubles every 18 to 24 months continues to hold. Competitive pressures compel design- ers to use these transistors to provide additional functionality and to increase the integra- tion level and thereby decreasing the size, weight, power and cost of the product. As a result, designers are confronted with larger and more complex designs. The increasing size and complexity of these designs combines with the shrinking time available to develop and get them to market; making the job of the circuit designer today much more difficult than in the past.

Circuits are getting more complex in two different ways at the same time. First, circuits are becoming larger. Consider wireless products. 40 years ago a typical receiver con- tained between 5 and 10 transistors whereas it is common for a modern cell phone to contain 10 million transistors, an average growth rate of 30× per decade. Second, the operation of the circuits are becoming more complex. 30 years ago integrated circuits generally consisted of simple functional blocks such as op-amps and gates. Verification typically required simulating the block for two or three cycles. Today, mixed-signal chips implement complex algorithms that require designers to examine their operation

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The Designer’s Guide Community

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