A low power oscillator based TDC with in-system non-linearity correction

A time to digital converter for positron emission tomography readout circuits is presented. The converter is based on a ring oscillator and is optimized for low power consumption down to 36 µW at low event rates. Non-linearities caused by the oscillator startup are corrected in the digital domain. The proposed correction scheme is able to estimate the non-linearities of the converter without additional analog circuitry. A resolution of 15.08 ENOB using a 10 MHz reference clock is achieved. The circuit is implemented in a 180 nm CMOS technology occupying only 0.0077 mm².