Time To Digital Converter

A TDC identifies two event boundaries and determines the interval separating them rather than relying only on the nearest sampled clock edge. It then quantizes that interval into a digital code. Coarse timing may come from clock cycles or counters, while delay lines or interpolation can refine the residual interval and reduce timing uncertainty.

These elements provide different ways to resolve elapsed time. A reference clock establishes a timing framework, and counters measure longer intervals in clock-cycle units. Delay lines subdivide a clock period into smaller segments, while fine-resolution interpolation estimates the remaining fraction. Combining coarse and fine measurements can extend measurable range while improving temporal precision.

Resolution, linearity, measurement range, and conversion speed are central performance characteristics. Resolution determines the smallest timing difference that can be represented, while range limits the interval that can be measured. Linearity affects how consistently physical intervals map to digital values, and conversion speed determines how rapidly timing results can be produced.

Conventional clock sampling associates events with discrete clock instances, so timing differences within one clock interval may remain unresolved. A TDC can refine that interval using delay-based measurement or interpolation in addition to clock counting. This provides more detailed event timing when the relevant information occurs between ordinary sampling points.

A typical workflow establishes the reference timing, receives a start event, receives the corresponding stop event, and determines their separation. The converter represents the interval through clock counts, fine timing elements, or both. Engineers then examine the resulting digital value in relation to the required resolution, range, linearity, and conversion speed.

Engineers choose this approach when the timing of an event carries useful measurement information, particularly in time-of-flight measurement, event timing, phase analysis, or frequency analysis. It can support sensor instrumentation when small differences in arrival time must be represented digitally, including systems associated with radar, lidar, and particle detection.

In radar and lidar, measured timing intervals support time-of-flight information. Particle-detection systems use event timing to characterize detected occurrences, while digital communication systems can use precise timing for signal-related analysis. The same timing-conversion principle also supports phase and frequency analysis, making TDCs useful across sensing, detection, and communication instrumentation.