A spread spectrum clock generator includes a plurality of delay cells, wherein each delay cell includes at least one delayer receiving an external clock signal and causing a predetermined propagation delay to the received clock signal, and a controller transmitting a control signal to the delayer to control the propagation delay of the delayer according to a state value of the control signal. Charges accumulated in a first capacitor spill over into a second capacitor when a charge storage capacity of the first capacitor is exceeded. The convection cell is formed by gravitational forces acting on the fluid mixture and is operable to deposit a heavy constituent of the fluid mixture about a lower end of the vessel and a light constituent of the fluid mixture about an upper end of the vessel.