A Time to Digital converter (TDC) may have a Vernier architecture of multiple successive modules arranged in series. Each of the modules may output an indication of a differential in phase between two received signals. Each module may include two signal lines for the received signals, and it may be desirable to calibrate the two signal lines. To this end, a signal output from a proceeding module may be provided to both signal lines of a succeeding module and used as a reference or calibration signal to calibrate the two signal lines of the module.