This paper presents a referenceless digital clock and data recovery (CDR) with an unlimited frequency detection capability that is extended from a multi-phase oversampling scheme. The CDR achieves a capture range from 4Gb/s to 20Gb/s, which is limited only by the operating frequency of the oscillator. Frequency acquisition is possible at any initial frequency and the worst-case acquisition time is 25μs with a PRBS31 pattern. The CDR fabricated in 65nm CMOS consumes 37.3mW at 20Gb/s and occupies 0.045mm².