Time of Flight Measurement TDC
The history of time to digital converters began with experimental high energy physics needing to measure time of flight. Time of flight or TOF is the process of measuring the time a particle, object, signal or stream takes to travel over a known distance. This time of flight time measurement process is accomplished using a detector and TDC.

Using time of flight to study the inner structure of atoms, particles are accelerated by an accelerator to enormous energies and beamed to collide with each other or still targets. Upon collision particles burst into many smaller parts. Detectors observe and record the results of these collisions to calculate their time of flight. The properties of the particle parts can be derived from their path in a magnetic field. This path is detected by drift chambers. Drift chambers are used in big colliders like the Large Hadron Collider at CERN. Using TDCs in drift chambers is an effective way to measure time of flight.

In drift chambers the detectors are arranged circular around the collision point. These consist of gas filled tubes in which a live wire is strung. If a reaction particle hits a gas molecule in one of these tubes, a cloud current is generated which drifts along the wire due to the electrical field (that's why it is called drift chamber). If the cloud current reaches the wire, an electrical pulse is triggered. The time from the particle collision to hitting the wire by the current cloud is measured by time to digital converters and used to calculate the time of flight.

Since some of these time of flight experiments require several hundred thousand of these gas filled tubes, reliable, precise, energy efficient and low cost time to digital converters are very important. The required resolution is around 500 pico seconds - 1 nano second and can be reached with todays multi-channel single chip time to digital converters easily. There are many advantages to using this method to calculate time of flight and a range of time of flight applications that benefit from this digital technology.