A variable-gain time amplifier with automatic interval detection

This paper presents an all-digital standard cell SR-Latch based time amplifier (TA) with a variable gain of 6X and 12X. In this TA, a two-stage gain selection unit is applied to enable the TA to select either the high gain for short input pulse intervals or the low gain for long input pulse intervals. The time amplification gain is 6 in the input range of -700ps ~700ps, and reaches 12 if the input range is -300~300ps. We present a design that automatically detects the input pulse and switches to the proper TA gain. By applying the proposed TA, a standard cyclic TDC implemented in a UMC CMOS 65-nm process shows the resolution improved from 1.6ps to 0.8 ps.