A Time-to-Digital converter is an integrated solution that measures time-of-flight. And time-of-flight is when a LASER, for example, sends out a short optical pulse and measures the time until the reflection portion of that pulse is received back. The distance is then calculated using the speed of light. Due to this high velocity, the temporal (time) accuracy must be very high – e.g. 1 ns for a spatial (relating to the distance between objects) accuracy of 15 cm.
There are various ways to measure distance in such applications as range-finders, drones, machine vision and more via light waves (LIDAR), RF waves (RADAR), or sound waves (ultrasonics)
Texas Instruments has an excellent app note regarding Short Time Measurement using their TDC7201 Time-to-Digital converter. This product also has an evaluation board.
ams has also just recently introduced their TDC-GPX2 which measures time intervals at a resolution of up to 10ps for ultra-accurate time-of-flight measurements. Light detection and ranging (LIDAR) as well as laser-ranging devices in positron emission tomography (PET) medical scanners are two big areas of usage. You know how much I value demo boards as a designer’s way of getting to market faster, and ams has a good one here
Autonomous vehicles will be users of Time-to-Digital converters as well. MEMS scanning mirrors will make this possible with LIDAR.
Continental AG has a really advanced design for a LIDAR system that has no moving parts like most scanning LIDAR devices. The design uses a pulsed laser source that bounces off an object and is reflected back to a 2D pixel array, similar to that of a digital camera. The system also measures time-of-flight. This system generates a high-resolution real-time 3D spatial environment of the surrounding area, accurate to within a few centimeters.
Reference 1 is developing a LIDAR system combined with a MEMS scanner and uses an indirect time of flight method for distance measurement. It seems to me that this might be one of the most accurate systems if it can be successfully produced in production after full testing and development. See Figures 1 and 2.
Reference 1 LIDAR system with MEMS (Image courtesy of Reference 1)
Measured distance values using a single laser spot and scanning laser via a MEMS scanner. (Image courtesy of Reference 1)
So it looks like a time-to-digital converter is a marked improvement over discrete designs. What are your experiences in this area? Please register on Planet Analog, if not already registered, and share with our audience in the comments below.
1 LIDAR system using indirect time of flight method and MEMS scanner for distance measurement, Sung-Woo Lee, Haesoo Jeong, Seoung-Ki Lee, Young-Kweon Kim, Jae-Hyoung, 2016 International Conference on Optical Mems and Nanophotonics (OMN)