In fixed-point multiplication, two numbers from separate registers are multiplied, creating a result that occupies the space of two registers. If values are stored using one register, it is necessary to reduce that result to fit one register. To do this, the least significant portion of the result is truncated or rounded-off, reducing the accuracy of the result. Overflow occurs when the addition of two numbers creates a result 1 bit larger than the register wordlength. These spikes are called overflow noise .
Overflow noise is preventable and is normally identified in system tests.
The goal of digital feedback control is to minimize the error between a desired value and the actual value. Because of round-off and truncation, the controller cannot match the actual value to the desired value. Instead, the actual value oscillates around the desired value. Depending upon the application and the characteristics of the oscillations, this phenomenon may be of concern. These oscillations are minimized by Scaling the input to a level that avoids overflow while maintaining the necessary dynamic range and Implementing algorithms in a manner that minimizes the effects of round-off and truncation.