Patent ID: 8319567

Claim:
A two oscillator system wherein said oscillators can be operated independently or synchronously, comprising: first and second oscillators, each comprising: an integrator having input, output and reset nodes and arranged to provide a signal at said output node which ramps at a rate proportional to a signal applied at said input node, said integrator output signal being resettable by applying a reset signal to said reset node; a comparator which receives said integrator's output signal and a reference signal at respective inputs and is arranged to toggle an output when said integrator's output signal crosses said reference signal; a mode selection switching circuit arranged to receive the outputs of both of said comparators at respective inputs and to provide a selected one of said comparator outputs at its output in response to a select signal; and a one-shot circuit which is arranged to receive the output of said mode selection switching circuit at an input and to generate said reset signal when said received switching circuit output toggles to indicate that the ramping integrator output signal provided to the comparator selected by said mode selecting switching circuit has crossed said reference signal; such that each of said oscillators runs independently when its mode selection switching circuit provides said oscillator's own comparator output to its one-shot circuit, and such that the ramp voltage of each oscillator operates to reset the integrator of the other oscillator such that said oscillators run synchronously when said oscillators' mode selection switching circuits provide the comparator output of said other oscillator to their one-shot circuits; said system arranged such that the reference signals provided to said comparators are at a first value when said oscillators run independently and are at a second value when said oscillators run synchronously.