Search

This work presents a Time-to-Digital Converter implemented using two nested Johnson counters and suitable for time-lapse measurement applications. The proposed structure is composed of two 4-bit nested counters, two digital-logic control networks, two registers and a single decoder. Semi-dynamic logic was used for the decoder to reduce its power consumption. The system has a standard digital output and is powered by a 1.8 V supply with a total power consumption of 32.4 mW. A prototype was fabricated using a TSMC 180 nm CMOS technology. The proposed structure uses a 508 µm x 225 µm area. In addition, this TDC has a standard deviation of 0.78 LSB with a fixed input time interval operating at a frequency of 1 MHz. The proposed structure shows good performance results and repeatability for continuous conversion conditions, these results are attributed to the simplicity of the system and the use of counters with minimum gate delay as the main elements for the TDC.

The paper describes the construction, operation and test results of three most popular interpolators from a viewpoint of time-interval (TI) measurement systems consisting of many tapped-delay lines (TDLs) and registering pulses of a wide-range changeable intensity. The comparison criteria include the maximum intensity of registered time stamps (TSs), the dependency of interpolator characteristic on the registered TSs’ intensity, the need of using either two counters or a mutually-complementing pair counter-register for extending a measurement range, the need of calculating offsets between TDL inputs and the dependency of a resolution increase on the number of used TDL segments. This work also contains conclusions about a range of applications, usefulness and methods of employing each described TI interpolator. The presented experimental results bring new facts that can be used by the designers who implement precise time delays in the field-programmable gate arrays (FPGA).