Digitally controlled analogue signal synthesizer: improvement of the waveform

Realisation of a periodic analogue signal v(t) from digital data, by means of a digital to analogue converter is feasible from a stream of digital data if this stream supplies the DAC by at least two samples per period of the desired signal. The analogue signal is recovered from the stream of samples with the aid of a low pass filter. However, when generating very low frequency signals, this low pass filter, due to a too long response time, can no longer be employed and the number of samples per period must be increased to generate a curve which is almost smooth. Even if numerous samples are used for its approximation, the obtained signal is not a smooth signal because it is made up of a series of constant amplitudes. To remove its sharp corners, a set-up is proposed which can be added onto an existing digital to analogue converter card and which generates the required correcting voltage between two samples. This modification makes it possible to create a smooth digitally controlled analogue wave using only few segments per period