On-Chip System for Fast, High-Range, High-Precision Measurements of Delays

Precision delay measurements are useful for many integrated circuits, especially time-to-digital converters. A new, fully integrated delay measurement circuit using the standard field-programmable gate array (FPGA) or application-specific integrated circuit (ASIC) blocks is presented. This circuit comprises a variable frequency generator built from phase-locked loops, an arbiter, and a control system. The performance of the circuit is evaluated in an FPGA, both as a function of time and over a range of delays. The implementation has demonstrated a delay measurement precision of 2 ps, over a range of 4-14 ns. The circuit incorporates a novel control scheme for continuous calibration of delays, in the presence of variations in the chip due to process, voltage, temperature, or radiation effects. Variations in a single delay setting are measured for 1600 s. The associated power spectral density of the variations reveal 1/f noise below 1 Hz and white noise above at the level of 0.02 ps(2) Hz(-1). Collections of many delays are measured combined to show that measurement biases in this method are below 2 ps.