2.56 GHz sub-harmonically injection-locked PLL with cascaded DLL for multi-phase injection

A 2.56 GHz injection-locked phase-locked loop (ILPLL) cascaded with a delay-locked loop (DLL) for minimising phase noise is presented. Generally, an ILPLL includes an injection-locked voltage-controlled oscillator (ILVCO), which is directly injected with the reference clock phase. However, the proposed scheme connects the output multiphased clocks of the DLL to the injection node and they can be selected with turn on/off switches. This can shorten the realignment time of the VCO phases and thus the in-band phase noise is decreased. The proposed circuit is implemented in a 65 nm CMOS technology, and reduces the phase noise by 10.86 dBc/Hz at a 1 MHz offset with 16 multi-phased injections, compared with a conventional PLL.