1. INTRODUCTION
Sinusoidal signals are used in many signal processing
applications. As a result, systems that are able to generate
high quality sine and cosine waveforms in digital form
are needed. The traditional method for producing sine
waves is to store the samples in a lookup table and then
read these samples at constant time intervals. Another
possibility is to use a second order recursive structure
whose characteristic roots are located on the unit circle.
Even though this method is more flexible and requires
less hardware, the stability problems that appear when
finite precision arithmetic is used have limited its usage.
For a simple recursive digital oscillator, the finite wordlength
effects create amplitude and frequency fluctuation.
Moreover, even if the desired frequency is a rational
number, the sequence of samples produced by a recursive
oscillator is not always periodic. To reduce these negative
effects, a control method that reduces the roundoff error
and makes the generated sequence periodic is used. The
coupled form structure was chosen, because it has better
frequency resolution than the direct form [1].