I use a 4MHz crystal oscillator.I have tried a 10 MHz crystal as well but the results are about the same. The reason i want to to do it with this way is because the power supply is going to be provided by a 12V battery which is going to be charged by a photovoltaic system.And therefore i want to keep the power consumption as minimum as possible.On the other hand the circuit i have thought of is i believe very simple and the one that needs very little energy to work, compared to others that produce sawtooth waveforms.
Thanks for your interest!!