A direct digital frequency synthesizer using an IIR filter implemented with a DSP microprocessor

Direct digital frequency synthesizers (DDFSss) are generally implemented by successively scanning trough a lookup table stored in a read-only memory (ROM) and converting the recalled sine samples to an analog waveform via a digital to analog converter (DAC). This paper describes a new implementation of a DDFS using a second order IIR resonator, whose impulse response is a sine wave; as this impulse response can be expressed in a second order recursive form, sample generation only requires few multiplications and additions. Therefore, the idea is to use a fast DSP microprocessor that can implement the recursive equation in “real-time”. This technique guarantees a larger set of output frequencies, a high spectral purity and a very simple, compact, and reliable hardware design