Time-to-digital converter and method therefor
Time-to-digital converter system including: an event detector configured for detecting an event and generating an event detection signal upon detection of the event; and a time-to-digital converter coupled or connectable to the event detector and including a fine resolution part configured for counting fine time intervals, organized such that the fine resolution part is activated in response to the event detection signal and deactivated in response to a reference clock. 3D imager including an array of pixels, with in each pixel such a time-to-digital converter system, and further including a reference clock generator.
1. A time-to-digital converter system comprising:
an event detector configured for detecting an event and generating an event detection signal upon detection of the event;
a time-to-digital converter coupled to the event detector and comprising a fine resolution part configured for counting fine time intervals, organized such that the fine resolution part only becomes active in response to the event detection signal and is deactivated at a next edge of a reference clock; and
a coarse resolution part configured for counting coarse time intervals determined by a characteristic of the fine resolution part,
wherein the fine resolution part comprises a ring oscillator, and
wherein the characteristic of the fine resolution part is its oscillation cycle period.
2. A time-to-digital converter system according to claim 1 , wherein the time-to-digital converter comprises a controller, configured for passing on the event detection signal to the fine resolution part for its activation and for passing on a reference clock edge of the reference clock to the fine resolution part for its deactivation.
3. A time-to-digital converter system according to claim 2 , further comprising a gating device for gating the reference clock with the event detection signal, such that the reference clock is only seen by fine resolution part following detection of an event.
4. A time-to-digital converter system according to claim 1 , wherein the coarse resolution part comprises a ripple counter which follows the fine resolution part.
5. A time-to-digital converter system according to claim 1 , wherein the coarse time intervals are a multiple of the fine time intervals.
6. A time-to-digital converter system according to claim 1 , wherein the controller comprises an AND-gate and wherein the ring oscillator comprises a delay line of which a first tap has a first input connected to the AND-gate and a second input connected to an output of a last tap of the delay line.
7. A time-to-digital converter system according to claim 6 , wherein the ring oscillator is provided with arbiters for capturing a state of the delay line, the arbiters comprising a switched inverter structure with an enable input.
8. A time-to-digital converter system according to claim 1 , wherein the coarse resolution part comprises a ripple counter following a tap of the ring oscillator.
9. A time-to-digital converter system according to claim 8 , wherein the ripple counter is connected to an arbiter which is in turn connected to a tap of the ring oscillator.