Warren Craddock and Tamara Schmitz, Intersil Corp
EETimes (1/15/2011 12:41 PM EST)
Mixed-signal designs combine the most powerful features and advantages of both analog and digital circuitry. One common mixed-signal architecture is a chain of analog signal blocks, each controlled by digital logic. These designs take advantage of the stability and algorithmic capabilities of digital logic to control traditional analog circuitry.
Because digital logic can be easily modified throughout a design cycle, it is often preferable to keep most of the “intelligence” of a control loop in the digital logic. The analog circuitry should be as simple and direct as possible. Decoders, delays, and other functions should be implemented digitally whenever possible.
Digital logic does not suffer from drift or process variation in the same sense as analog circuitry. Phenomena such as oscillation are much easier to control or prevent entirely. Certain functions – such as control loops that can hold a specific value indefinitely – become very easy to implement in logic. Such circuits are small in area, resistant to noise, and easy to implement.
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