TIME TO DIGITAL CONVERTER RESOLVES PICOSECONDS IN TIME INTERVAL MEASUREMENTS
Original Publication Date: 1982-Jan-01
Included in the Prior Art Database: 2001-Oct-10
This circuit converts single-shot time intervals to a digital number using a dual vernier interpolation technique that resolves 2.5 plcoseconds while measuring time intervals from -23 seconds to +23 seconds. The circuit operates by starting ramp A when a 'START' signal is received, then ramp A is stop. ped on the next edge of a 200 MHZ STANDARD. Ramp B is started when the 'STOP' signal is received and stopped on the next edge of the 200 MHZ STANDARD. The 200 MHZ STANDARD is also counted between the 'START' and 'STOP' by a 32.bit N counter. The time interval is then equal to the N count times 5 nseconds, plus the A ramp times 2.5 plcoseconds minus the B ramp times 2.5 picosecond% The key to high accuracy is the three coincidence flip-flops that allow the circuit to define a coincidence within 2.5 plcoseconds. The circuit.works well with no special circuits, and the MPU is used to perform the only needed adjustment, adjusting the ramp slopes with an eight-bit D/A to provide exactly 5 nseconds over 2000 counts of the AID.