This page shows the design of my first music synthesizer using a programmable logic device (PLD). The design was originally created for a simple Xilinx PLD that we used at the university around 10 years ago, and was expanded to come close to classic analog music synthesizers. It already partly overcomes the capabilities of my Casio HT 3000.

In a digital circuit like this, the functions are programmed using pure mathematical methods to incorporate the characteristics of well-known analog synthesizers.

The design uses DDS technology with a tuning word derived from the frequency information in the MIDI word, which drives a phase counter. Together with the newly introduced vibrato, this generates a final phase that is available to the waveform generators.

The phase counter is used a a saw tooth directly. The triangle is generated by flipping the bits partially when the phase counter is greater than 50%.
The sine wave then is generated with a trick, in a way known from diode limiters such as the ICL8038: When the amplitude increases, it is clipped. To achieve this, it required a lot of compare function with are too much for the PLD. Therefore another way is used: A wave is subtracted from the actual triangle, in fact the third harmonic. The phase of that harmonic is generated by shift-and-add processing like f-sine = tria(f) * 3 + tria (3f). Together with a clipping this produces a (more) sine-like tone.

A simulation demonstrates the quality that could be achieved if the chip had more resources available to implement additional waves. Due to limited space, modulation via the parameters and the ADSR is also very coarse and has only a few levels. This could be better with a larger PLD.

For the moment it works much better in my TMS320-Music-System