A Low Supply Voltage All-Digital Phase-Locked Loop With a Bootstrapped and Forward Interpolation Digitally Controlled Oscillator

An all-digital phase-locked loop (ADPLL) with a multiphase digitally controlled oscillator (DCO) incorporating the bootstrapped and interpolated schemes is proposed in this paper. The bootstrapped ring oscillator can boost the output voltage to a higher level than the supply voltage. Thus, the oscillator can be operated in low-supply-voltage applications. MOS varactor is used in the bootstrapped capacitor to reduce the area cost. Circuit analysis and simulated verification were performed for an optimized design. The interpolated DCO has multiphase outputs and a high operating frequency. The test chip was implemented in a 90-nm CMOS process, and the core area was
$60\times 117\,\,\mu \text{m}^{2}$
. The power consumptions at 1160 MHz and 20 MHz were
$912.6~\mu \text{W}$
(at 0.6 V) and
$2.94~\mu \text{W}$
(at 0.2 V), respectively. In the worst-case jitter performance, the root mean square (RMS) jitters were less than 0.42%.