Time To Digital Converters
In measurement range 2 the maximum time interval is extended using a pre-divider. The resolution in LSB remains unchanged by that. In this mode the high-speed unit of the TDC does not measure the whole time interval but only time intervals from START and STOP to the next rising edge of the reference clock (fine-counts). In between the fine-counts the TDC counts the number of periods of the reference clock (coarse-count).
The BIN size (LSB) is typically 65 ps at 3.6 V and 25 °C ambient temperature. The gate propagation delay times strongly depend on temperature and voltage. In measuring range 2 the result is the sum of different fine and coarse-count results. Therefore it is necessary in measuring range 2 to make a calibration. During a calibration the TDC measures 1 and 2 periods of the reference clock.
The measuring unit is actuated by a START signal and stopped by a STOP signal. Based on the position of the ring oscillator and the coarse counter the time interval between START and STOP is calculated with a 26 Bit measurement range.
The measurement range is limited by size of the coarse counter:
tyy = Tref x 16384 ~ 4 ms
|tph||2.5 ns||Minimum pulse width|
|tpl||2.5 ns||Minimum pulse width|
|tss||500 ns min.||Start to Stop|
|trr||ns||Rising edge to rising edge|
|tff||ns||Falling edge to falling edge|
|tva||4.6 µs calibrated||Last hit to data valid|
|tyy||4 ms||Measurement range|